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A new megaraptoran theropod dinosaur from the Upper Cretaceous Bajo de la Carpa Formation of northwestern Patagonia
Abstract
We describe Tratayenia rosalesi gen. et sp. nov., a new megaraptoran theropod dinosaur from the Upper Cretaceous of Patagonia, Argentina. The holotype consists of a well-preserved, mostly articulated series of dorsal and sacral vertebrae, two partial dorsal ribs, much of the right ilium, and pubis and ischium fragments. It was found in a horizon of the Upper Cretaceous (Santonian) Bajo de la Carpa Formation of the Neuquén Group in the Neuquén Basin exposed near the town of Añelo in Neuquén Province of northwestern Patagonia. Phylogenetic analysis recovers Tratayenia within the Gondwanan megaraptoran subclade Megaraptoridae. The new taxon exhibits similarities to other megaraptorids such as Aerosteon riocoloradensis, Megaraptor namunhuaiquii, and Murusraptor barrosaensis, but also presents differences in the architecture of the dorsal and sacral vertebrae and the morphology of the ilium. Tratayenia is the first megaraptoran that unequivocally preserves the complete sequence of sacral vertebrae, thereby increasing knowledge of the osteology of the clade. Moreover, depending on the chronostratigraphic ages of the stratigraphically controversial megaraptorids Aerosteon and Orkoraptor burkei, as well as the phylogenetic affinities of several fragmentary specimens, the new theropod may be the geologically youngest megaraptorid or megaraptoran yet discovered. Tratayenia is also the largest-bodied carnivorous tetrapod named from the Bajo de la Carpa Formation, reinforcing the hypothesis that megaraptorids were apex predators in southern South America from the Turonian through the Santonian or early Campanian, following the extinction of carcharodontosaurids.
... The Bajo de la Carpa Formation (Santonian, Upper Cretaceous) is a continental unit belonging to the Neuqu en Group of the Neuqu en Basin, which presents a wide distribution throughout northwestern Patagonia (Garrido, 2010(Garrido, , 2011. This geological unit has yielded a large diversity of terrestrial tetrapods, mainly dominated by dinosaurs (e.g., Woodward, 1896;Bonaparte, 1991;Caldwell and Albino, 2001;Apesteguía, 2004;Gianechini et al., 2011;Filippi et al., 2016;Porfiri et al., 2018;Cruzado-Caballero et al., 2019;Gianechini et al., 2020). Particularly, the theropod fauna from these deposits has a major role in our understanding of the evolution as a whole of the theropod lineage history in South America (see Novas et al., 2013;Holtz, 2021). ...
... Particularly, the theropod fauna from these deposits has a major role in our understanding of the evolution as a whole of the theropod lineage history in South America (see Novas et al., 2013;Holtz, 2021). The non-avian theropod record includes at least three clades, i.e., Abelisauroidea, Megaraptoridae, and Alvarezsauridae (Bonaparte, 1991;Martinelli and Vera, 2007;Ezcurra and M endez, 2009;Filippi et al., 2016;Porfiri et al., 2018;Gianechini et al., 2020). The first one is represented by the small abelisauroid Velocisaurus unicus (Bonaparte, 1991), an indeterminate form (Ezcurra and M endez, 2009), and two new taxa recently published, Viavenator exxoni and Llukalkan aliocranianus (Filippi et al., 2016;Gianechini et al., 2020). ...
... The first one is represented by the small abelisauroid Velocisaurus unicus (Bonaparte, 1991), an indeterminate form (Ezcurra and M endez, 2009), and two new taxa recently published, Viavenator exxoni and Llukalkan aliocranianus (Filippi et al., 2016;Gianechini et al., 2020). Concerning megaraptorids, there are two records from the Neuqu en province to date, one of them is Tratayenia rosalesi, based on an associated but partial postcranial skeleton (Porfiri et al., 2018), and the other consists of fragmentary postcranial remains (M endez et al., 2021). Regarding the Alvarezsauria, they are known to date from two taxa provenant from the Neuqu en and Río Negro provinces, Alvarezsaurus calvoi and Achillesaurus manazzonei, respectively (Bonaparte, 1991;Martinelli and Vera, 2007). ...
The abundant record of theropods from Bajo de La Carpa Formation (Neuquén Group, Santonian), known from the end of the nineteenth century, come from numerous locations within the Neuquén Basin. During the excavation of the titanosaur Bonitasaura salgadoi at the La Bonita fossiliferous site, northwest of Río Negro province Argentina, were recovered three isolated teeth assignable to non-avian theropod dinosaurs. Previous studies of these dental materials suggested that MPCA-Pv-247 corresponds to an indeterminate tetanure possibly related to Orkoraptor, a taxon of uncertain phylogenetic position at that moment, and MPCA-Pv-249 and 251 as possible abelisauroids. Three methods were carried out, namely, a cladistic analysis performed on a dentition-based data matrix, and a discriminant and cluster analyses performed in a large dataset including measurements of non-avian theropod teeth. The results assign for the first time a confidently phylogenetic position to the described dental material. The analysis shows that MPCA-Pv 247 belongs to Megaraptoridae, whereas MPCA-Pv 249 and 251 were recovered as belonging to Abelisauridae, supporting in a reliable way the previous assignments. The results show the presence of Megaraptoridae at La Bonita and, additionally, they represent an evidence of the first direct association of megaraptorids and abelisaurids at the same locality of the Bajo de La Carpa Formation, according to similar associations from other units of the Neuquén Group.
... however, theropod remains are scarce from the Río Neuquén Subgroup (Portezuelo, Los Bastos, Sierra Barrosa and Plottier formations; middle Turonian-lower Santonian), except for the Portezuelo Formation (Novas, 1997(Novas, , 1998Novas & Puerta, 1997;Calvo et al., 2004a;Novas & Pol, 2005). This paucity of theropods mainly affects the allosauroid record, since only two specimens have been recorded from the middle Late Cretaceous (Coria & Currie, 2016;Porfiri et al., 2018). however, when we take into account the global allosauroid record (excepting Argentina), this paucity is even worse, since no middle Late Cretaceous (Coniacian-Santonian) specimens have been discovered anywhere else up to now. ...
... The allosauroid record is globally scarce after the Turonian age, since it only includes megaraptoran taxa and several post-Cenomanian carcharodontosaurid teeth that have been reevaluated as belonging to Abelisauridae (see Canale et al., 2009 and references therein). From Argentina proceed the Cenomanian-Turonian Aoniraptor and two unnamed specimens (Motta et al., 2016;Lamanna et al., 2020), the late Turonian-early Coniacian Megaraptor namunhuaiquii (Novas, 1998;Porfiri et al., 2014), the middle Coniacian Murusraptor barrosaensis (Coria & Currie, 2016), and the Santonian Tratayenia rosalesi (Porfiri et al., 2018). From the Campanian of Argentina, Aerosteon riocoloradensis (Sereno et al., 2008), ...
... lower Campanian). Moreover, the allosauroid fossil record from the Coniacian to the Santonian is globally scarce, with some exceptions in South America (e.g., Coria & Currie, 2016;Porfiri et al., 2018). Therefore, we consider MAU-PV-CM-653 important to fill the paucity of this clade in the middle Late Cretaceous. ...
The Late Cretaceous theropod fauna of South America is composed of Abelisauridae, Noasauridae, Spinosauridae, Carcharodontosauridae, Megaraptora, and Coelurosauria. These groups include mostly small (Noasauridae and Coelurosauria) and medium- tolarge-sized taxa (Carcharodontosauridae, Abelisauridae, and Megaraptora). Some of these lineages are predominantly Gondwanic (Abelisauridae, Noasauridae, Carcharodontosauridae, Megaraptora) and poorly represented in Laurasian landmasses. Particularly, several theropods have been reported from Patagonia, known either due to distinct anatomical features or due to their high degree of preservation, such as Carnotaurus, Skorpiovenator, Giganotosaurus, Megaraptor, Alvarezsaurus, and Unenlagia. Here we describe a new incomplete tibia (MAU-PV-CM-653) from the Sierra Barrosa Formation (middle Coniacian, Upper Cretaceous), Patagonia, Argentina. MAU-PV-CM-653 shows an anteroposteriorly reduced cnemial crest that is strongly curved laterally. Finally, the tibia lacks a proximal extension of the fibular crest. These traits are reminiscent of tetanuran morphology and, together with the stratigraphic provenance of MAU-PV-CM-653, they allow us to assign it to an allosauroid theropod, thus improving the Allosauroidea global record for the middle Late Cretaceous.
... Megaraptorids are medium to large-sized theropods that lived in the Cretaceous of Gondwana. These theropods were specialised predators with long skulls, serrated and curved teeth, highly pneumatized skeletons, gracile hindlimbs, robust pectoral girdles and stout forearms with enlarged trenchant manual claws (Calvo et al. 2004;Hocknull et al. 2009;Novas et al. 2013Novas et al. , 2016Porfiri et al. 2014Porfiri et al. , 2018Coria and Currie 2016;Aranciaga-Rolando and Novas 2019;Lamanna et al. 2020). The pectoral girdle and forelimbs show several modifications that make them very efficient and powerful tools for prey capture (White et al. 2015;Novas et al. 2016). ...
... The pectoral girdle and forelimbs show several modifications that make them very efficient and powerful tools for prey capture (White et al. 2015;Novas et al. 2016). Although several megaraptorid taxa has been discovered, the phylogenetic relationships of this clade are still being questioned (Benson et al. 2010;Novas et al. 2013;Porfiri et al. 2014Porfiri et al. , 2018Coria and Currie 2016;Aranciaga-Rolando and Novas 2019). Probably this is caused by the poor anatomical overlap between different specimens. ...
... A third Argentinian megaraptoran is Murusraptor which is represented by most parts of the skull, column and limbs (Coria and Currie 2016; Aranciaga-Rolando and Novas 2019) that comes from Sierra Barrosa Formation. From the Bajo de la Carpa Formation (Santonian age) comes Tratayenia rosalesi (Porfiri et al. 2018) composed of an articulated series of dorsals and sacrals and some fragmentary bones of the girdles and limbs. Also, in Argentina but from the Anacleto Formation (Campanian age) is Aerosteon . ...
Aerosteon riocoloradensis represents one of the most complete megaraptorans yet discovered. This theropod comes from Anacleto Formation (Campanian) of Mendoza Province, Argentina. The aims of this contribution are: to present a detailed, bone by bone description of this specimen with figures of each bone; provide comparisons to other closely related theropods; revise the original assignation and diagnosis of such taxa. Three bones were re-assigned and almost all the autapomorphies of Aerosteon were modified. Features in the vertebral columns, which are shared with other megaraptorans, show that these theropods shared features with basal coelurosaurs.
Anatomical Abbreviations
ACDL: Anterior centrodiapophyseal lamina; CDF: Centrodiapophyseal fossa; CPAL: Centroparapophyseal lamina; CPRL: Centroprezygapophyseal lamina; CPRF: Centroprezygapophyseal fossa; CPR-CDF: Centroprezygapophyseal-centrodiapophyseal fossa; Hye: Hyposphene; Hym: Hypantrum; ILT: Intervertebral ligament tuberosity; IPOL: Infrapostzygapophysela lamina; IZL: Intrazygapophyseal lamina; PADL: Paradiapophyseal lamina; PAD-CDF: Paradiapophyseal-centrodiapophsyeal fossa; PCDL: Posterior centrodiapophyseal lamina; POEL: Postzygaepipophysela lamina; PODL: Postzygadiapophyseal lamina; POSF: Postspinal fossa; POCDF: Postzygapophsyeal-centrodiapophyseal fossa; Poz: Postzygapophysis; PRDL: Prezygadiapophyseal lamina; PRPAF: Prezygaparapophyseal fossa; PRPAL: Prezygaparapophyseal lamina; PRSF: Prespinal fossa; PRSL: Prespinal lamina; PRD-CDF: Prezygadiapophyseal-centrodiapophyseal fossa; PRD-PADF: Prezygadiapophyseal-paradiapophyseal fossa; PRD-PODF: Prezygadiapophyseal-postzygadiapophyseal fossa; PRCDF: Prezygapophyseal-centrodiapophyseal fossa; Prz: Prezygapophyses; SDF: Supradiapophsyeal fossa; SDL: Supradiapophyseal lamina; SPOF: Spinopostzygapophyseal fossa; SPOL: Spinopostzygapophyseal lamina; SPRF: Spinoprezygapophyseal fossa; SPRL: Spinoprezygapophyseal lamina; SR(number): Sacral rib; STP(number): Sacral transverse process
... Fossil discoveries within the past three decades have revealed an unexpected diversity of tetanuran theropod dinosaurs from Cretaceous localities in the Southern Hemisphere landmasses, especially South America (e.g., Bonaparte 1991;Coria and Salgado 1995;Kellner and Campos 1996;Martill et al. 1996;Novas 1997Novas , 1998Novas and Puerta 1997;Kellner 1999;Naish et al. 2004;Makovicky et al. 2005Makovicky et al. , 2012Novas and Pol 2005;Novas et al. 2005Novas et al. , 2008aNovas et al. , 2008bNovas et al. , 2012Coria andCurrie 2006, 2016;Martínez and Novas 2006;Martinelli and Vera 2007;Sereno et al. 2008;Kellner et al. 2011;Porfiri et al. 2011aPorfiri et al. , 2018Agnolín et al. 2012;Apesteguía et al. 2016;Motta et al. 2016Motta et al. , 2020Coria et al. 2020; see reviews in Novas et al. 2013;Ezcurra and Novas 2016). Among the most enigmatic of these predominantly Gondwanan tetanuran clades is Megaraptora, definitively represented in South America by the Argentinean Late Cretaceous species Aerosteon riocoloradensis (Sereno et al. 2008), Megaraptor namunhuaiquii (Novas 1998;Calvo et al. 2004;Porfiri et al. 2007aPorfiri et al. , 2007bPorfiri et al. , 2008Porfiri et al. , 2014Paulina-Carabajal and Porfiri 2018), Murusraptor barrosaensis (Coria and Currie 2016;Paulina-Carabajal and Currie 2017;Aranciaga Rolando et al. 2019), Orkoraptor burkei (Novas et al. 2008a), and Tratayenia rosalesi , as well as multiple taxonomically indeterminate (e.g., Aranciaga Rolando et al. 2015Novas et al. 2019;Ibiricu et al. 2020) or as-yet undescribed (e.g., Porfiri et al. 2011b;Casal et al. 2019;Méndez et al. 2019) specimens. ...
... Subsequently, Novas et al. (2013) proposed yet another position for Megaraptora within Tetanuraeas a lineage within the basal coelurosaurian clade Tyrannosauroidea-and erected the subclade Megaraptoridae to encompass Australovenator and the Argentinean megaraptoran species known at the time. Most recently, some authors (e.g., Apesteguía et al. 2016;Aranciaga Rolando et al. 2018;Porfiri et al. 2018) have (in at least some of their respective phylogenetic analyses) recovered Megaraptora as an early branching radiation of non-tyrannosauroid coelurosaurs, whereas others (e.g., Porfiri et al. 2014;Aranciaga Rolando et al. 2019) have continued to find support for proposed tyrannosauroid affinities of the clade. Still others (e.g., Novas et al. 2016) have identified conflicting morphological characters within Megaraptora, some of which support a position with Coelurosauria and others that are more consistent with allosauroid affinities. ...
... That matrix was expanded from one of the two datasets analyzed by Apesteguía et al. (2016) in their description of the bahariasaurid Gualicho shinyae, which was in turn based on those of Porfiri et al. (2014) and ultimately Novas et al. (2013) and sources therein. We further modified the matrix of Aranciaga Rolando et al. (2019) by adding two additional OTUs: another recently described northern Patagonian megaraptorid, Tratayenia rosalesi (based on the description of this species provided by Porfiri et al. [2018] and personal observations of the holotype [MUCPv 1162] by MCL) and the unnamed Australian megaraptorid LRF 100-106 (based on the description provided by Bell et al. [2016]). We also contend that six of the characters treated as additive (= ordered) by Aranciaga Rolando et al. (2019) (characters 15, 27, 317, 323, 324, and 338) are more appropriately regarded as non-additive (2, 4, 6, 13, 17, 69, 106, 148, 155, 158, 160, 167, 169, 171, 179, 181, 194, 195, 205, 208, 217, 233, 241, 258, 266, 270, 309, 314, 315, and 322) (2019); that is, the matrix was analyzed using the traditional search function (tree bisection-reconnection [TBR] swapping algorithm, random seed 1, 1,000 replications, ten trees saved per replication) of TNT (Tree analysis using New Technology) version 1.5 (Goloboff and Catalano 2016). ...
We describe two partial postcranial skeletons belonging to the enigmatic theropod dinosaur clade Megaraptoridae from the Upper Cretaceous (lower Cenomanian-upper Turonian) Bajo Barreal Formation of southern Chubut Province, central Patagonia, Argentina. The specimens are assigned to Megaraptoridae due to their possession of multiple anatomical features that are considered synapomorphies of that predatory dinosaur group, such as a greatly enlarged, laterally compressed ungual of manual digit I that possesses asymmetrical lateral and medial vascular grooves. Overlapping elements of the two skeletons are nearly identical in morphology, suggesting that they probably represent the same taxon, a large-bodied theropod that was previously unknown from the early Late Cretaceous of southern South America. The Bajo Barreal specimens constitute the most ancient unquestionable records of Megaraptoridae from that continent, and exhibit particularly strong osteological resemblances to penecontemporaneous megaraptorids from the Winton Formation of Australia. Phylogenetic analysis recovers the unnamed Bajo Barreal taxon as the earliest-diverging South American megaraptorid and the oldest-known representative of this clade that likely attained a body length of at least seven meters and a mass of at least one metric ton. Overall, the balance of the evidence suggests that megaraptorids originated in eastern Gondwana (Australia) during the Early Cretaceous, then subsequently dispersed to western Gondwana (South America) during the mid-Cretaceous, where they attained substantially larger body sizes, ultimately coming to occupy the apex predator niches in their respective habitats.
... In recent years, some incomplete sacral elements have been described for megaraporans (e.g. SMNS 58023, CPPLIP 1324, Phuwiangvenator, Murusraptor, Megaraptor and Tratayenia;Martinelli et al., 2013;Coria and Currie, 2016;Porfiri et al., 2014;Porfiri et al., 2018, Aranciaga-Rolando et al., 2019Samathi et al., 2019). The internal pneumatic structure of all these sacral elements is camellate. ...
... Aoniraptor, Murusraptor, Megaraptor and Tratayenia). This is comprised of deep fossae located at the ventral side of the transverse process (Porfiri et al., 2018). Further, Aoniraptor and Tratayenia exhibit pneumatic cdf and prcdf (Porfiri et al., 2018) and an apomorphic accessory fossa is observed in ...
... This is comprised of deep fossae located at the ventral side of the transverse process (Porfiri et al., 2018). Further, Aoniraptor and Tratayenia exhibit pneumatic cdf and prcdf (Porfiri et al., 2018) and an apomorphic accessory fossa is observed in ...
Aoniraptor libertatem is a mid‐sized megaraptoran that comes from the Late Cretaceous (Turonian) Huincul Formation at Río Negro province, Patagonia, Argentina. In this study, we conducted a detailed analysis of pneumaticity of the sacrum and tail of Aoniraptor . This shows a complex structure within these vertebrae, being composed by small diverticulae surrounding large pneumatic canals and a central chamber that opens outside through pleurocoels or pneumatic canals. Further, we carried out a histologic analysis which confirms the pneumatic nature of these anatomical features. Both analyses found that chevrons in Aoniraptor were invaded by pneumaticity, a feature that appears to be unique to this taxon. In addition, a comparative analysis between Aoniraptor and other theropods (e.g. Gualicho and other megaraptorans) was carried out. This resulted in the modification of previous schemes about the evolution of pneumaticity through Theropoda, the finding of some evolutionary pneumatic traits through Megaraptora, and the usefulness of pneumatic traits as a taxonomic tool.
... In these datasets, subtly different combinations of taxa and/or character coding schemes tended to produce radically different trees where compsognathids were resolved as an immediate outgroup to maniraptorans, or where 'basal' coelurosaur taxa found different associations with larger, better-recognized clades such as alvarezsaurs, ornithomimids, and tyrannosauroids. These preliminary results are consistent with the findings of the previous analyses (Apesteguía et al., 2016;Azuma et al., 2016;Bell et al., 2016;Brusatte et al., 2014;Cau et al., 2017;Choiniere et al., 2010aChoiniere et al., , b, 2012Choiniere et al., , 2014Dal Sasso and Maganuco, 2011;Godefroit et al., 2013;Loewen et al., 2013;Porfiri et al., 2018Porfiri et al., , 2014Rauhut et al., 2012;Rolando et al., 2019;Samathi et al., 2019). A full exploration of these results is beyond the scope of this paper, but this instability among coelurosaur lineages implies that sampling efforts, along with further insights into allometric and ontogenetic variations of characters, will shake up the current coelurosaur tree. ...
... Our choice of the dataset illustrates the current challenges of basal coelurosaurian systematics. The dataset from Choiniere et al. (2014) does not extensively sample megaraptorids d a Southern Hemispheric clade that potentially falls among coelurosaurs or even onto tyrannosauroids (Porfiri et al., 2014(Porfiri et al., , 2018Rolando et al., 2019). This is relevant to compsognathid relationships, as one megaraptorid (Orkoraptor) is compared extensively with compsognathids (Novas et al., 2008). ...
... Many small theropod taxa have been assigned to Compsognathidae, or are considered closely related to this clade, without consensus. Among 'basal' coelurosaurs, the following genera consistently sit outside compsognathids in recent analyses: Aniksosaurus, Aorun, Bicentenaria, Fukuivenator, Ornitholestes, Santanaraptor, and Zuolong (typically in their own branches outside Maniraptora); Coelurus and Tanycolagreus (sometimes considered tyrannosauroids); Nqwebasaurus (associated with alvarezsaurids or ornithomimosaurs); Orkoraptor (considered as megaraptorid, but compared with compsognathids; megaraptorids as a whole may fall within Coelurosauria); Sciurumimus (generally considered a megalosauroid, but recovered as a coelurosaur in some analyses) (Apesteguía et al., 2016;Azuma et al., 2016;Bell et al., 2016;Brusatte et al., 2014;Cau et al., 2017;Choiniere et al., 2010aChoiniere et al., , b, 2012Choiniere et al., , 2014Dal Sasso and Maganuco, 2011;Godefroit et al., 2013;Loewen et al., 2013;Porfiri et al., 2018Porfiri et al., , 2014Rauhut et al., 2012;Rolando et al., 2019;Samathi et al., 2019). Several taxa, however, may belong to compsognathids and expand the geographic and chronological distributions of the clade substantially: Aristosuchus, Mirischia, and Scipionyx. ...
... Megaraptorans are medium to large-sized theropods with elongate and slender hind limb bones, highly pneumatic cranial and vertebral elements, and large and trenchant manual claws. Their remains have been found in Argentina (e.g., Novas et al., 2013;Coria and Currie, 2016;Motta et al., 2016;Porfiri et al., 2018), Brazil (e.g., M endez et al., 2012;Martinelli et al., 2013;Porfiri et al., 2018), Australia (Smith et al., 2007;Hocknull et al., 2009;Agnolín et al., 2010;Benson et al., 2010;White et al., 2013a,b;Bell et al., 2015) and Japan (Azuma and Currie, 2000). The temporal range of megaraptorans includes taxa from different Cretaceous stages: AptianeAlbian (Fukuiraptor kitadaniensis; Azuma and Currie, 2000), Cenomanian (Australovenator wintonensis; Hocknull et al., 2009), Cenomanianelower Coniacian (Orkoraptor burkei; Novas et al., 2008), Turonian (Megaraptor namunhuaiquii; Novas, 1998), Coniacian (Murusraptor barrosaensis; Coria and Currie, 2016), Santonian (Tratayenia rosalesi; Porfiri et al., 2018) and Campanian (Aerosteon riocoloradensis; . ...
... Megaraptorans are medium to large-sized theropods with elongate and slender hind limb bones, highly pneumatic cranial and vertebral elements, and large and trenchant manual claws. Their remains have been found in Argentina (e.g., Novas et al., 2013;Coria and Currie, 2016;Motta et al., 2016;Porfiri et al., 2018), Brazil (e.g., M endez et al., 2012;Martinelli et al., 2013;Porfiri et al., 2018), Australia (Smith et al., 2007;Hocknull et al., 2009;Agnolín et al., 2010;Benson et al., 2010;White et al., 2013a,b;Bell et al., 2015) and Japan (Azuma and Currie, 2000). The temporal range of megaraptorans includes taxa from different Cretaceous stages: AptianeAlbian (Fukuiraptor kitadaniensis; Azuma and Currie, 2000), Cenomanian (Australovenator wintonensis; Hocknull et al., 2009), Cenomanianelower Coniacian (Orkoraptor burkei; Novas et al., 2008), Turonian (Megaraptor namunhuaiquii; Novas, 1998), Coniacian (Murusraptor barrosaensis; Coria and Currie, 2016), Santonian (Tratayenia rosalesi; Porfiri et al., 2018) and Campanian (Aerosteon riocoloradensis; . ...
... Their remains have been found in Argentina (e.g., Novas et al., 2013;Coria and Currie, 2016;Motta et al., 2016;Porfiri et al., 2018), Brazil (e.g., M endez et al., 2012;Martinelli et al., 2013;Porfiri et al., 2018), Australia (Smith et al., 2007;Hocknull et al., 2009;Agnolín et al., 2010;Benson et al., 2010;White et al., 2013a,b;Bell et al., 2015) and Japan (Azuma and Currie, 2000). The temporal range of megaraptorans includes taxa from different Cretaceous stages: AptianeAlbian (Fukuiraptor kitadaniensis; Azuma and Currie, 2000), Cenomanian (Australovenator wintonensis; Hocknull et al., 2009), Cenomanianelower Coniacian (Orkoraptor burkei; Novas et al., 2008), Turonian (Megaraptor namunhuaiquii; Novas, 1998), Coniacian (Murusraptor barrosaensis; Coria and Currie, 2016), Santonian (Tratayenia rosalesi; Porfiri et al., 2018) and Campanian (Aerosteon riocoloradensis; . In spite of their wide geographical and temporal distribution, megaraptorans were known until recently by incomplete specimens; thus, the phylogenetic affinities of the clade remain uncertain (e.g., Novas, 1998;Calvo et al., 2004;Smith et al., 2007;Hocknull et al., 2009). ...
Phylogenetic relationships of megaraptorid theropods are under intense debate. Some authors interpret them as archaic allosauroids that survived up to Late Cretaceous, whereas others consider megaraptorids as basal tyrannosauroids. The recently described Patagonian taxon Murusraptor barrosaensis offers novel information on skull, axial and hind limb anatomy, all of which may help in elucidating the phylogenetic affinities of megaraptorids as a whole. Murusraptor is particularly similar to juvenile specimens of tyrannosaurids; both share: 1) lacrimal with a long anterior process; 2) corneal process and; 3) lateral pneumatic fenestra; 4) square and dorsoventrally low frontals; 5) parietals with well-developed sagittal and nuchal crests, among other features. The current study lends further support to the hypothesis that megaraptorans are basal members of Coelurosauria (supported by 20 synapomophies), with strongest affiliation with Tyrannosauroidea (supported by >20 synapomorphies).
... Despite some shared manual features, Novas et al. (2016) questioned whether megaraptorids should be nested within Tyrannosauroidea. Indeed, a new phylogenetic analysis that accompanied the description of a new Megaraptoridae, Tratayenia rosalesi, positioned the megaraptoran theropods as non-tyrannosauroid Coelurosauria (Porfiri et al., 2018) Currently, the phylogenetic placement of Santanaraptor and the Australian specimens remains unresolved (Apesteguía et al., 2016;Coria and Currie, 2016;Novas et al., 2013;Porfiri et al., 2018Porfiri et al., , 2014, and it is uncertain whether megaraptorids should be included within Coelurosauria. To address this important biogeographical question, we investigated the phylogenetic positions of Santanaraptor and the two Australian specimens among theropods, megaraptorids, and tyrannosauroids using three different phylogenetic datasets (i.e., Carr et al., 2017;Choiniere et al., 2012;Porfiri et al., 2018). ...
... Despite some shared manual features, Novas et al. (2016) questioned whether megaraptorids should be nested within Tyrannosauroidea. Indeed, a new phylogenetic analysis that accompanied the description of a new Megaraptoridae, Tratayenia rosalesi, positioned the megaraptoran theropods as non-tyrannosauroid Coelurosauria (Porfiri et al., 2018) Currently, the phylogenetic placement of Santanaraptor and the Australian specimens remains unresolved (Apesteguía et al., 2016;Coria and Currie, 2016;Novas et al., 2013;Porfiri et al., 2018Porfiri et al., , 2014, and it is uncertain whether megaraptorids should be included within Coelurosauria. To address this important biogeographical question, we investigated the phylogenetic positions of Santanaraptor and the two Australian specimens among theropods, megaraptorids, and tyrannosauroids using three different phylogenetic datasets (i.e., Carr et al., 2017;Choiniere et al., 2012;Porfiri et al., 2018). ...
... Indeed, a new phylogenetic analysis that accompanied the description of a new Megaraptoridae, Tratayenia rosalesi, positioned the megaraptoran theropods as non-tyrannosauroid Coelurosauria (Porfiri et al., 2018) Currently, the phylogenetic placement of Santanaraptor and the Australian specimens remains unresolved (Apesteguía et al., 2016;Coria and Currie, 2016;Novas et al., 2013;Porfiri et al., 2018Porfiri et al., , 2014, and it is uncertain whether megaraptorids should be included within Coelurosauria. To address this important biogeographical question, we investigated the phylogenetic positions of Santanaraptor and the two Australian specimens among theropods, megaraptorids, and tyrannosauroids using three different phylogenetic datasets (i.e., Carr et al., 2017;Choiniere et al., 2012;Porfiri et al., 2018). Our findings strongly suggest that Santanaraptor and Timimus should be included in Tyrannosauroidea, whereas NMV P186046 could have a relationship within coelurosaurian Tyrannosauroidea. ...
Tyrannosauroidea is a well-studied group of carnivorous dinosaurs known mainly from the Late Cretaceous of the Northern Hemisphere. Specimens from Australia (Timimus hermani and the articulated pubes NMV P186046) and Brazil (Santanaraptor placidus) have been referred to this clade, but their phylogenetic placement is unresolved. Here, we investigated the phylogenetic positions of these Southern Hemisphere specimens within the theropods and among tyrannosauroids using three different phylogenetic datasets: the first covered all major theropod clades, the second was focused on non-Maniraptoriformes Tetanurae, and the third was focused on Tyrannosauroidea. It was found that Santanaraptor and Timimus were tyrannosauroids of a type that was more derived than Dilong paradoxus and more basal than Xiongguanlong baimoensis. However, the pubes NMV P186046 may have phylogenetic relationships among Coelurosauria, probably within Tyrannosauroidea. The resultant topologies, which were associated with temporal and geographical distributions of basal non-proceratosaurid tyrannosauroids, suggest a worldwide cosmopolitan distribution for this clade (named Pantyrannosauria), at least from the Bajocian-Callovian. Our analyses also support a Late Cretaceous monophyletic clade of gigantic animals that occurred exclusively in the Northern Hemisphere (named Eutyrannosauria).
... Both of our phylogenetic analyses supported a position of Megaraptora within Tyrannosauroidea (Novas et al., 2013;Aranciaga Rolando et al., 2019, in contrast to previous analyses that exclude this clade from Tyrannosauroidea (Delcourt and Grillo, 2018;Porfiri et al., 2018). Of particular interest was the position of Compsognathidae within Megaraptora in our Bayesian analysis, although this is not supported by our parsimony analysis. ...
... Although several recent studies have supported the idea that Megaraptora occupies an early-branching position within Coelurosauria, often as sister to Tyrannosauroidea (Delcourt and Grillo, 2018;Porfiri et al., 2018), megaraptorans have alternatively been resolved within Tyrannosauroidea, basal to Tyrannosauridae (Novas et al., 2013;Porfiri et al., 2014;Aranciaga Rolando et al., 2019Ding et al., 2020;Naish and Cau, 2022). Considering that the width: length ratio of NMV P229038 is higher than in Coelurosauria and Tyrannosauroidea (excluding Tyrannosauridae), within the range of juvenile to adult Tyrannosauridae, and less so than in Megaraptoridae, widening of the frontal might have both ontogenetic and phylogenetic significance within Megaraptora. ...
Cretaceous (non-avian) theropod dinosaurs from Australia are poorly understood, primarily because almost all specimens described thus far comprise isolated postcranial elements. In Australia, only three non-dental cranial elements pertaining to Theropoda have been reported: the left and right dentaries of Australovenator wintonensis from the Winton Formation (Cenomanian–lowermost Turonian) of Queensland, and an isolated surangular from the Eumeralla Formation (lower Albian) of Victoria. Herein, we report the first evidence of non-mandibular cranial material of a non-avian theropod from Australia: a left frontal and fused parietal fragment from the Lower Cretaceous (lower Aptian) upper Strzelecki Group of Victoria. The specimen shares several synapomorphies with the frontals assigned to Megaraptoridae, including an anteroposteriorly elongate postorbital articulation and a truncated nasal articular surface. Accordingly, we regard this frontal as Megaraptoridae gen. et sp. indet. We performed both parsimony-based and Bayesian-based phylogenetic analyses to support our assignment, and both analyses support a placement within Megaraptoridae. However, this specimen appears to possess plesiomorphic characters relative to other megaraptorid frontals, lacking dorsoventrally high walls of bone that emarginate the nasal and prefrontal articular surfaces. The plesiomorphies of this specimen have implications for the evolution of the megaraptoran skull roof, suggesting the acquisition of specialised adaptations for longirostry over time. This specimen improves the limited record of Cretaceous Australian theropod cranial remains, and provides limited support for the hypothesis that Megaraptoridae might have originated in Australia.
... With the aim of testing the taxonomic validity of Maip as well as its phylogenetic relationships with other theropods, two different phylogenetic analyses were performed (see Supplementary Information I). The analyses with and without fragmentary taxa show a topology similar to those of previous analyses 12, 19 , with megaraptorans nested within Coelurosauria, and forming the sister group of Tyrannosauroidea (Fig. 15A). ...
... The tree topology is very similar with the first analysis but shows a higher resolution within Megaraptora. As in previous works, the more basal forms of this clade are the Asian Phuwiangvenator, Vayuraptor, and Fukuiraptor; which constitute successive sister taxa to Megaraptoridae 2,7,10,12,19 . Among megaraptorids, the Australian LRF 100-106 and Australovenator represent the earliest-branching members of the clade and are more closely related to each other than to South American megaraptorids (See Supplementary Information I). ...
Megaraptora is a theropod clade known from former Gondwana landmasses and Asia. Most members of the clade are known from the Early to Late Cretaceous (Barremian–Santonian), with Maastrichtian megaraptorans known only from isolated and poorly informative remains. The aim of the present contribution is to describe a partial skeleton of a megaraptorid from Maastrichtian beds in Santa Cruz Province, Argentina. This new specimen is the most informative megaraptoran known from Maastrichtian age, and is herein described as a new taxon. Phylogenetic analysis nested the new taxon together with other South American megaraptorans in a monophyletic clade, whereas Australian and Asian members constitute successive stem groups. South American forms differ from more basal megaraptorans in several anatomical features and in being much larger and more robustly built.
... The outcrops of the Bajo de la Carpa Formation are scattered throughout different areas of northern Patagonia. This geological unit presents an important paleontological record, including rich and diverse vertebrate fossils recovered in the areas of Neuquén city, Sierra Barrosa, Tratayén, Cerro Overo-La Invernada, and Rincón de los Sauces in Neuquén province; and Rancho de Ávila-La Bonita and Paso Córdoba in Río Negro province (e.g., Woodward, 1896;Bonaparte, 1991;Caldwell and Albino, 2002;Apesteguía, 2004;Coria et al., 2013Coria et al., , 2019Filippi et al., 2016;Porfiri et al., 2018). ...
... Regarding dinosaurs, the record from this unit is profuse. In its deposits, many taxa were found: the titanosaurian sauropods Bonitasaura salgadoi, Traukutitan eocaudata, Overosaurus paradasorum, and Rinconsaurus caudamirus (Apesteguía, 2004;Juárez Valieri and Calvo, 2011;Coria et al., 2013;Filippi, 2015); ornithopods, such as the elasmarian Mahuidacursor lipanglef and indeterminate forms (Cruzado-Caballero et al., 2018; and theropods, such as the noasaurids Velocisaurus unicus (Bonaparte, 1991), abelisaurids (Ezcurra and Méndez, 2009), the megaraptorid tetanuran Tratayenia rosalesi (Porfiri et al., 2018), the alvarezsaurids Alvarezsaurus calvoi and Achillesaurus manazonnei (Bonaparte, 1991;Martinelli and Vera, 2007), and the avialans Patagopteryx deferrariisi and Neuquenornis volans (Alvarenga and Bonaparte, 1992;Chiappe and Calvo, 1994). It should be noted that all these taxa come from different localities and different levels in the Bajo de la Carpa Formation. ...
Abelisaurids are among the most abundant and diverse Patagonian Late Cretaceous theropods. Here, we present a new furileusaurian abelisaurid, Llukalkan aliocranianus gen. et sp. nov., represented by cranial remains from the Bajo de la Carpa Formation (Santonian) at La Invernada fossil area, northwestern Patagonia. Features characterizing this taxon include a possible caudal tympanic recess posterior to the columellar recess, a T-shaped lacrimal with jugal ramus lacking a suborbital process, and large foramina for caudal middle cerebral veins widely separated from the median supraoccipital crest. In addition to this, a bulge on the anteromedial border of the supratemporal fossa, tall and posteriorly projected paroccipital processes, basal tubera interconnected distally, a triangular basisphenoid recess, and a single foramen for the sphenoidal artery on the basisphenoid, differentiate Llukalkan from Viavenator exxoni. The latter is the other furileusaurian taxon from the same area and stratigraphic unit. Although the holotype of Llukalkan probably corresponds to a sub-adult—as the lacrimal morphology suggests— the possibility that it represents a juvenile of V. exxoni is discarded based mainly on the presence of a caudal tympanic recess (which is absent in V. exxoni). The probable coexistence of two abelisaurid taxa demonstrates that the abelisaurids were one of the most important—and likely the main—predator component of the ecosystems, not only in this area, but also in all of Patagonia, during the Late Cretaceous.
... Older phylogenetic studies placed Australovenator Hocknull et al., 2009 as the sister taxon of Fukuiraptor (Azuma & Currie, 2000) from Japan (Benson et al., 2010). However, more recently there has been support for a monophyletic Gondwanan Megaraptoridae that includes Megaraptor Novas, 1998 from Argentina and Australovenator, with Fukuiraptor as sister taxon to this clade (Novas et al., 2013;Bell et al., 2016;Porfiri et al., 2018). Bell et al. (2016) Rich & Vickers-Rich, 1994, a result that is more consistent with an early Pangaean radiation of this clade in the Jurassic, followed by regional extinction (Delcourt & Grillo, 2018). ...
... Bell et al. (2016) Rich & Vickers-Rich, 1994, a result that is more consistent with an early Pangaean radiation of this clade in the Jurassic, followed by regional extinction (Delcourt & Grillo, 2018). However, given that only one tyrannosauroid specimen from South America and two from Australia are currently known [assuming that megaraptorans are not tyrannosauroids Porfiri et al., 2018)], sampling failure could easily have obscured trans-Antarctic relationships. ...
The titanosaurian sauropod dinosaur Diamantinasaurus matildae is represented by two individuals from the Cenomanian-lower Turonian 'upper' Winton Formation of central Queensland, northeastern Australia. The type specimen has been described in detail, whereas the referred specimen, which includes several elements not present in the type series (partial skull, atlas, axis and postaxial cervical vertebrae), has only been described briefly. Herein, we provide a comprehensive description of this referred specimen, including a thorough assessment of the external and internal anatomy of the braincase, and identify several new autapomorphies of D. matildae. Via an expanded data matrix consisting of 125 taxa scored for 552 characters, we recover a close, well-supported relationship between Diamantinasaurus and its contemporary, Savannasaurus elliottorum. Unlike previous iterations of this data matrix, under a parsimony framework we consistently recover Diamantinasaurus and Savannasaurus as early-diverging members of Titanosauria using both equal weighting and extended implied weighting, with the overall topology largely consistent between analyses. We erect a new clade, named Diamantinasauria herein, that also includes the contemporaneous Sarmientosaurus musacchioi from southern Argentina, which shares several cranial features with the referred Diamantinasaurus specimen. Thus, Diamantinasauria is represented in the mid-Cretaceous of both South America and Australia, supporting the hypothesis that some titanosaurians, in addition to megaraptoran theropods and possibly some ornithopods, were able to disperse between these two continents via Antarctica. Conversely, there is no evidence for rebbachisaurids in Australia, which might indicate that they were unable to expand into high latitudes before their extinction in the Cenomanian-Turonian. Likewise, there is no evidence for titanosaurs with procoelous caudal vertebrae in the mid-Cretaceous Australian record, despite scarce but compelling evidence for their presence in both Antarctica and New Zealand during the Campanian-Maastrichtian. These later titanosaurs presumably dispersed into these landmasses from South America before the Campanian (~85 Mya), when seafloor spreading between Zealandia and Australia commenced. Although Australian mid-Cretaceous dinosaur faunas appear to be cosmopolitan at higher taxonomic levels, closer affinities with South America at finer scales are becoming better supported for sauropods, theropods and ornithopods.
... These macroscopic traces are usually attributed to the bite marks of the most likely predators of sauropod carcasses in Mesozoic ecosystems, such as theropod dinosaurs and crocodiles (Botfalvai et al., 2014;Boyd et al., 2013;Carpenter, 1998;Forrest 2003;Hasiotis, 2004;Jacobsen, 1998;Karl and Tichy, 2004;Schwimmer, 2010). Different taxa within these potential candidates are recorded for the Bajo de la Carpa Formation, such as abelisaurid theropods and notosuchid and peirosaurid crocodiles (Smith-Woodward, 1896;Bonaparte, 1991;Gasparini et al., 1991;Turner and Calvo, 2005;Fiorelli and Calvo, 2007;Porfiri et al., 2018). Although it is difficult to attribute bite marks to specific tracemakers and vice versa , the analysis of the feeding traces on MAU-PveCOe651 provides information about potential authors. ...
... In the Neuqu en Basin, the Bajo de la Carpa Formation has contributed a diverse and abundant vertebrate fauna from different localities. Among predators, possible generators of bite marks include like: megaraptorid theropods, such as Tratayenia rosalesi (Porfiri et al., 2018), and several crocodile taxa, such as Notosuchus terrestris (Smith-Woodward, 1896), Cynodontosuchus rothi (Smith-Woodward, 1896), Comahuesuchus brachybuccalis (Bonaparte, 1991), Peirosaurus tormini (Gasparini et al., 1991), Pehuenchesuchus enderi (Turnes and Calvo, 2005), Neuquensuchus universitas (Fiorelli and Calvo, 2007), and Wargosuchus australis (Martinelli and Pais, 2008). Taking into account the localities of Cerro Overo and La Invernada, additional possible generators of bite marks referred to the Bajo de la Carpa Formation are the abelisaurid Viavenator exxoni (Filippi et al., 2016(Filippi et al., y 2018, the peirosaurid crocodile Kinesuchus overoi (Filippi et al., 2018), and a recently recovered megaraptorid indeterminate specimen MAU-PveCOe659 (L.S.F., personal communication). ...
Bite marks in non-avian dinosaur fossil records can constitute the best evidence of predator-prey interactions even if they are uncommon, ambiguous, or of uncertain origin. In this contribution, we present new evidence of feeding traces on an isolated sauropod element from Bajo de la Carpa Formation outcrops (Upper Cretaceous, Santonian), northern Neuquén province, Patagonia, Argentina. The specimen is composed of a partial dorsal vertebral centrum (MAU-Pv-CO-651; deposited at the Museo Municipal Argentino Urquiza, Rincón de los Sauces, Neuquén, Argentina).We tentatively refer it to an indeterminate titanosaur sauropod due to the presence of an opisthocoelic articulation and an internal pneumatic camellate condition. Three kinds of marks are preserved on the lateroventral face of the centrum: large and deep parallel marks, small and shallow longitudinal marks, and deep oval holes that we tentatively consider as punctures. These fossil marks can be considered to be feeding traces produced by a large-bodied carnivore to deflesh the bone and/or to obtain bone nutrients, probably during a single scavenging event. The marks and the punctures on the vertebral centrum can be referred to a theropod dinosaur due to their pattern and distribution. Viavenator exxoni (Filippi et al., 2016) represents the most likely trace-maker candidate among the several theropod and crocodile taxa present in the Bajo de la Carpa Formation fossil record. The fossil feeding traces reported here improve our knowledge about the feeding behaviour of large scavengers in the north of the Neuquén Basin, at least during the Santonian.
... Palaeogeography, Palaeoclimatology, Palaeoecology 556 (2020) 109870 different faunal composition at the end of the Cretaceous. Considering the absence of megaraptorans in post-middle Campanian beds (Porfiri et al., 2018), the taxonomy of the Brazilian specimens remains dubious; these materials must be carefully considered, as suggested by Motta et al. (2016) and Porfiri et al. (2018). ...
... Palaeogeography, Palaeoclimatology, Palaeoecology 556 (2020) 109870 different faunal composition at the end of the Cretaceous. Considering the absence of megaraptorans in post-middle Campanian beds (Porfiri et al., 2018), the taxonomy of the Brazilian specimens remains dubious; these materials must be carefully considered, as suggested by Motta et al. (2016) and Porfiri et al. (2018). ...
Theropod tooth crowns are abundant in the Upper Cretaceous (post-Coniacian) continental deposits of the Bauru Group, Brazil. The distribution of anatomical crown features indicates that a variety of carnivorous dinosaurs inhabited the area at that time, which is consistent with fossil records from other parts of Gondwana. More specifically, some authors have attributed several isolated specimens to the Carcharodontosauridae; while this has important implications for palaeobiogeography and paleoecology, other scholars have argued that the clade became extinct during the Turonian. In this study, we conducted discriminant and phylogenetic analyses for 18 crowns putatively assigned to the Carcharodontosauridae. In short, the discriminant analysis suggested that the specimens should be tentatively assigned to the following groups: non-abelisauroid Ceratosauria, Abelisauridae, Neovenatoridae, Dromaeosauridae, and Pantyrannosauria. By contrast, the phylogenetic analysis indicated that all should be assigned to abelisaurid theropods, which is consistent with the theropod osteological records in both Brazil and Argentina. We recommend using a combined approach involving morphometric and phylogenetic tools when identifying isolated teeth, as this may yield more reliable identifications. We also suggest that all previous reports on the presence of post-Turonian carcharodontosaurids in the Bauru Group are invalid, which also corroborates previous work. Our results indicate that abelisaurids from the Bauru Basin were diverse in morphology and activity; that is, many were quite large and/or played important ecological roles. Findings also support the hypothesis that this taxon had a preference for semi-arid environments.
... The spatio-temporal range of Megaraptora (and Megaraptoridae) is becoming ever better understood as a result of numerous discoveries made within the last 2 decades. The South American record is the most extensive, diverse and abundant, with six taxa named to date: Aoniraptor libertatem [37], Orkoraptor burkei [33], Megaraptor namunhuaiquii [32,38,39], Murusraptor barrosaensis [30,40,41], Aerosteon riocoloradensis [28], and Tratayenia rosalesi [42]. Numerous fragmentary specimens have also been reported from South America (see supplementary table 7 in [1]), which include the oldest (Albian [43]) and the youngest (Campanian [44]). ...
... The 'Marilyn' Site (AODL 261), Elderslie Station, approximately 60 km NW of Winton, Queensland, Australia. The likely positions of AODF 967 and AODF 968 within the vertebral series were estimated by comparisons with other megaraptorids [29,32,33,37,40,42]. Although incomplete, AODF 968 would likely have been longer than it is wide or tall (based in part on the presumed mid-centrum position of the pleurocoel; see below) with a nearly flat (anterior) endplate and no indication of paraphophyses. ...
The holotype specimen of the megaraptorid Australovenator wintonensis, from the Upper Cretaceous Winton Formation (Rolling Downs Group, Eromanga Basin) of central Queensland, is the most complete non-avian theropod found in Australia to date. In fact, the holotype of A. wintonensis and isolated megaraptorid teeth (possibly referable to Australovenator) constitute the only theropod body fossils reported from the Winton Formation. Herein, we describe a new fragmentary megaraptorid specimen from the Winton Formation, found near the type locality of A. wintonensis. The new specimen comprises parts of two vertebrae, two metatarsals, a pedal phalanx and multiple unidentifiable bone fragments. Although the new megaraptorid specimen is poorly preserved, it includes the only megaraptorid vertebrae known from Queensland. The presence of pleurocoels and highly pneumatic caudal centra with camerate and camellate internal structures permit the assignment of these remains to Megaraptora gen. et sp. indet. A morphological comparison revealed that the distal end of metatarsal II and the partial pedal phalanx II-1 of the new specimen are morphologically divergent from Australovenator. This might indicate the presence of a second megaraptorid taxon in the Winton Formation, or possibly intraspecific variation.
... Novas et al. (2013) later erected Megaraptoridae to include A. wintonensis and other Gondwanan megaraptorans. Megaraptora has been nested amongst allosauroids with Carcharodontosauridae, or amongst coelurosaurians either within (see Delcourt & Grillo 2018, Lamanna et al. 2020, Naish and Cau 2022, or outside of Tyrannosauroidea (Porfiri et al. 2018, Lamanna et al. 2020. Australovenator wintonensis might indicate an Australian origin for Megaraptoridae (Bell et al. 2016. ...
In 2020, the Australasian palaeontological association Australasian Palaeontologists (AAP) joined the Australian government-supported Australian National Species List (auNSL) initiative to compile the first Australian Fossil National Species List (auFNSL) for the region. The goal is to assemble comprehensive systematic data on all vertebrate, invertebrate and plant fossil taxa described to date, and to present the information both within a continuously updated open-access online framework, and as a series of primary reference articles in AAP’s flagship journal Alcheringa. This paper spearheads these auFNSL Alcheringa publications with an annotated checklist of Australian Mesozoic tetrapods. Complete synonymy, type material, source locality, geological age and bibliographical information are provided for 111 species formally named as of 2022. In addition, chronostratigraphically arranged inventories of all documented Australian Mesozoic tetrapod fossil occurrences are presented with illustrations of significant, exceptionally preserved and/or diagnostic specimens. The most diverse order-level clades include temnospondyl amphibians (34 species), saurischian (13 species) and ornithischian (12 species) dinosaurs (excluding ichnotaxa), and plesiosaurian marine reptiles (11 species). However, numerous other groups collectively span the earliest Triassic (earliest Induan) to Late Cretaceous (late Maastrichtian) and incorporate antecedents of modern Australian lineages, such as chelonioid and chelid turtles and monotreme mammals. Although scarce in comparison to records from other continents, Australia’s Mesozoic tetrapod assemblages are globally important because they constitute higher-palaeolatitude faunas that evince terrestrial and marine ecosystem evolution near the ancient South Pole. The pace of research on these assemblages has also accelerated substantially over the last 20 years, and serves to promote fossil geoheritage as an asset for scientific, cultural and economic development. The auFNSL augments the accessibility and utility of these palaeontological resources and provides a foundation for ongoing exploration into Australia’s unique natural history.
... They have narrow teeth of variable labial-lingual compression and oval crosssection, with well-developed mesial and distal serrated carinae (Smith 2007;Delcourt et al. 2020). Megaraptora, on the other hand, have considerably smaller representativeness in the Bauru Basin, and its identification is still questioned by some authors (Motta et al. 2016;Delcourt and Iori 2018;Porfiri et al. 2018). The only records would be a caudal vertebra found in the SJRP Formation and another from the Uberaba Formation, identified as Megaraptora mainly due to its pneumaticity (Méndez et al. 2012;Martinelli et al. 2013). ...
By studying fossil bite traces, we can reconstruct the behaviour of extinct organisms and better understand past communities, environments, and ecosystems. In this paper, we analyse bite traces on a fragmented sauropod rib from the Upper Cretaceous of the Bauru Basin, southeastern Brazil. The fossil was collected in the Ibirá municipality, São Paulo State, in the strata of the São José do Rio Preto Formation (Santonian-?Maastrichtian). The analysed specimen displays nine tooth drag traces on its external surface, produced by
six or seven biting events. The traces consist of shallow linear grooves, with tapered ends and a serrated or smooth edge morphology. They can be classified as Linichnus serratus, Linichnus bromleyi, and Knethichnus parallelum and were produced by an organism with ziphodont dentition, probably an Abelisauridae. This work adds to the knowledge of the Bauru Basin palaeoecology and palaeobiology and expands the record of Mordichnia of Gondwana.
... Los estratos de esta unidad han aportado números ejemplares fósiles, la mayoría provenientes de la zona de las bardas de la ciudad de Neuquén. Entre los dinosaurios terópodos se encuentran representados los alvarezsáuridos, abelisáuridos y megaraptores, como Achillesaurus manazzonei , Alvarezsaurus calvoi , Velocisaurus unicus Brisson Egli et al., 2016), Viavenator exxonei (Filippi et al., 2016) y Tratayenia rosalesi (Porfiri et al., 2018). En cuanto a los dinosaurios saurópodos, sólo se encuentran representados por los ejemplares holotípicos de Bonitasaura salgadoi (Apesteguía, 2004) y Traukutitan eocaudata (Juárez Valieri y Calvo, 2011). ...
This Doctoral Thesis presents an exhaustive review of the Patagonian alvarezsaurids (Dinosauria, Theropoda). It includes a detailed osteological description of specimens of Patagonykus puertai (Holotype, MCF-PVPH-37), cf. Patagonykus puertai (MCF-PVPH-38), Patagonykinae indet. (MCF-PVPH-102), Alvarezsaurus calvoi (Holotype, MUCPv-54), Achillesaurus manazzonei (Holotype, MACN-PV-RN 1116), Bonapartenykus ultimus (Holotype, MPCA 1290), and cf. Bonapartenykus ultimus (MPCN-PV 738). A phylogenetic analysis and a discussion about the taxonomic validity of the recognized species and the taxonomic assignment of the materials MCF-PVPH-38, MCF-PVPH-102 and MPCN-PV 738 are presented. Different evolutionary and paleobiological studies were carried out in order to elucidate functional and behavioral aspects.
Alvarezsaurus calvoi (MUCPv-54), Achillesaurus manazzonei (MACN-PV-RN 1116), Patagonykus puertai (MCF-PVPH-37) and Bonapartenykus ultimus (MPCA 1290) are valid species due to the presence of many autapomorphies. In this sense, the hypothesis proposed by P. Makovicky and collaborators that Achillesaurus manazzonei is a junior synonym of Alvarezsaurus calvoi is rejected. Likewise, certain morphological evidence allows hypothesizing that Alvarezsaurus calvoi represents a growth stage earlier than skeletal maturity. Specimen MCF-PVPH-38 is referable as cf. Patagonykus puertai, while MCF-PVPH-102 is considered an indeterminate Patagonykinae. In turn, MPCN-PV 738 is assigned as cf. Bonapartenykus ultimus based on the little overlapping material with the Bonapartenykus ultimus holotype.
The results obtained from the mineralogical characterization through the X-ray diffraction method of specimens MPCN-PV 738 and the holotype of Bonapartenykus ultimus (MPCA 1290), allow to suggest that both specimens come from the same geographical area and stratigraphic level.
The phylogenetic analysis, which is based upon the matrix of Gianechini and collaborators of 2018 with the inclusion of proper characters, and the database of Xu and collaborators of 2018, recovered the South American members of Alvarezsauria, such as Alnashetri cerropoliciensis (Candeleros Formation; Cenomanian), Patagonykus puertai (Portezuelo Formation, Turonian-Coniacian), Alvarezsaurus calvoi and Achillesaurus manazzonei (Bajo de La Carpa Formation, Coniacian-Santonian), and Bonapartenykus ultimus (Allen Formation, Campanian-Maastrichtian), nesting within the family Alvarezsauridae. In this sense, the forms that come from the Bajo de La Carpa Formation (Coniacian-Santonian) are recovered at the base of the Alvarezsauridae clade, while Alnashetri cerropoliciensis nests as a non-Patagonykinae alvarezsaurid. Regarding the type specimens of Patagonykus puertai and Bonapartenykus ultimus, they are recovered as members of the Patagonykinae subclade, a group that is recovered as a sister taxon of Parvicursorinae, both nested within the Alvarezsauridae. In addition, the topology obtained allows discerning the pattern, rhythm and time of evolution of the highly strange and derived alvarezsaurian skeleton, concluding in a gradual evolution. The Bremer and Bootstrap supports of the nodes (Haplocheirus + Aorun), [Bannykus + (Tugulusaurus + Xiyunykus)], and Patagonykinae, show indices that represent very robust values for these nodes. Likewise, these values suggest that two endemic clades originated early in Asia, while one endemic clade is observed in Patagonia, i.e., Patagonykinae.
The analysis of the directional trends of the Alvarezsauria clade, tested by means of a own database on body masses based on the Christiansen and Fariña method, subsequently calibrated with the group's phylogeny using the R software, shows two independent miniaturization events in the alvarezsaurid evolution, namely the former originating from the base of the Alvarezsauridae (sustained by Alvarezsaurus), and the latter within the Parvicursorinae. Analysis of the Alvarezsauria dentition reveals possible dental synapomorphies for the Alvarezsauria clade that should be tested in an integrative phylogenetic analysis. The general characterization of the forelimb and a partial reconstruction of the myology of alvarezsaurs demonstrate different configurations for Patagonykinae and Parvicursorinae. The multivariate analyzes carried out from the databases of Elissamburu and Vizcaíno, plus that of Cau and collaborators, show that the Patagonykinae would have had ranges of movements greater than those observed in Parvicursorinae, although the latter would have had a greater capacity to carry out more strenuous jobs. The morphometric analysis of the hindlimb and the use of the Snively and collaborators equations, show that the configuration of this element in Alvarezsauria is indicative of a highly cursorial lifestyle, as well as possible particular strategies for more efficient locomotion. The topology obtained in the phylogenetic analysis that was carried out in this Doctoral Thesis, allowed clarifying the ontogenetic changes observed in the ontogenetic series of the manual ungueal element II-2 within the clade Alvarezsauridae. In addition, the multivariate analysis carried out from the manual phalanx II-2 allows us to infer that alvarezsaurs could have performed functions such as hook-and-pull and piercing, where the arm would function as a single unit. The anatomy and myology of the alvarezsaurian tail show that the caudal vertebrae of alvarezsaurians exhibit a combination of derived osteological features that suggests functions unique among theropods, such as considerable dorsal and lateral movements, as well as exceptional abilities to support distal loading of their long tail without compromising stability and/or mobility.
... With the aim of testing the validity of Maip as well as its phylogenetic relationships with other theropods, two different phylogenetic analyses were performed (see Supplementary Information I). The analyses with and without fragmentary taxa show a topology similar to those of previous analyses 19,12 being megaraptorans nested within Coelurosauria, and forming the sister group of Tyrannosauroidea (Fig. 15A). Aoniraptor results as a megaraptoran of uncertain a nities (Fig. 15A), like has been observed in other works 13,31 . ...
Megaraptorans are a theropod clade distributed in former Gondwana landmasses and Asia. Most members of the clade are known from early Cretaceous to Turonian times whereas Maastrichtian megaraptorans are known just from isolated and poorly informative remains. The aim of present contribution is to describe a partial skeleton of a megaraptorid coming from Maastrichtian beds at Santa Cruz province, Argentina. This new taxon constitutes the most informative megaraptoran from post-Turonian beds. Phylogenetic analysis nested the new taxon together with South American megaraptorans in a monophyletic clade, whereas Australian and Asian members constitute successive stem groups. South American forms differ from more basal megaraptorans in several anatomical features and in being much larger and more robustly built. It is possible that the Cenomanian-Turonian extinction of carcharodontosaurids was allowed to megaraptorans to occupy the niche of top predators in South America.
... Finally, the Bajo de la Carpa Formation in Argentina (e.g. [118][119][120][121][122][123][124][125][126]) preserves an excellent record of Santonian dinosaurs, but these include groups like abelisaurids and elasmarians which are entirely unknown in North America and Asia. ...
During the Cretaceous, diversifications and turnovers affected terrestrial vertebrates experiencing the effects of global geographical change. However, the poor fossil record from the early Late Cretaceous has concealed how dinosaurs and other terrestrial vertebrates responded to these events. I describe two dinosaurs from the Santonian to Early Campanian of the obscure North American paleolandmass Appalachia. A revised look at a large, potentially novel theropod shows that it likely belongs to a new clade of tyrannosauroids solely from Appalachia. Another partial skeleton belongs to an early member of the Hadrosauridae, a highly successful clade of herbivorous dinosaurs. This skeleton is associated with the first small juvenile dinosaur specimens from the Atlantic Coastal Plain. The tyrannosauroid and hadrosaurid substantiate one of the only Late Santonian dinosaur faunas and help pinpoint the timing of important anatomical innovations in two widespread dinosaur lineages. The phylogenetic positions of the tyrannosauroid and hadrosaurid show Santonian Appalachian dinosaur faunas are comparable to coeval Eurasian ones, and the presence of clades formed only by Appalachian dinosaur taxa establishes a degree of endemism in Appalachian dinosaur assemblages attributable to episodes of vicariance.
... In Buitreraptor, also is observed asymmetry regarding the lateral fossa of the neural arch, because in some middle dorsal vertebrae a different number of foramina is present within the pacdf on both sides. Indeed, bilateral variability in pneumatic structures is not a rare feature in non-avian theropods (Motta et al., 2016;Porfiri et al., 2018). Unfortunately, the presence of foramina within the pacdf of Austroraptor cannot be confirmed. ...
Postcranial skeletal pneumaticity (PSP) characterizes extant birds. This feature is related to a series of air sacs connected to the lungs and prolonged in diverticula that invade bones internally. Previous works revealed that PSP was present along the line to birds, being distinctive of pterosaurs and saurischian dinosaurs. PSP is profuse in the vertebral column of sauropods and theropods and was very studied in sauropods, although scarcely in non-avian theropods. Here we analyze the vertebral pneumaticity of the unenlagiine theropod Unenlagia comahuensis, including the observation through CT scans. Unenlagiinae is a clade of southern dromaeosaurid theropods that is closely related to birds. The vertebral centra have lateral pneumatic foramina (lpf) within fossae (commonly termed ‘pleurocoels’) in middle and posterior dorsals, an unusual feature among extant birds and many non-avian theropods. Another possibly pneumatic fossa stands out at both sides of the neural spine base, which is not present in dorsals of other non-avian theropods, except the unenlagiine Unenlagia paynemili. CT scans revealed camellate tissue in the centra, consisting of small chambers separated by thin trabeculae. Camellae are also observed in the unenlagiines U. paynemili and Austroraptor cabazai, other dromaeosaurids, other coelurosaurs, and some non-coelurosaurian tetanurans. Instead, more primitive groups generally have camerae (larger chambers separated by scarce thick septa). Thus, a possible trend of the vertebral inner pneumaticity types is observed throughout non-avian theropod evolution, as indicated by previous authors. This study provides valuable information that helps to clarify this trend, not only in dromaeosaurids but also throughout theropod evolution.
... Other tetanuran theropod fossils from the Bajo Barreal Formation pertain to the predominantly Gondwanan clade Megaraptora Ibiricu et al., 2020;Lamanna et al., 2020). This group of large-clawed avetheropods is particularly abundant in the Late Cretaceous of the Neuqu en Basin (in, e.g., the Portezuelo, Sierra Barrosa, and Bajo de la Carpa formations; Novas, 1998;Coria and Currie, 2016;Porfiri et al., 2018). To date, however, remains of Abelisauridae are the most common theropod fossils from the Bajo Barreal Formation. ...
Xenotarsosaurus bonapartei was the third abelisaurid theropod dinosaur to be named from Argentina. The holotype comprises two partial anterior dorsal vertebrae and a complete right hind limb from the Upper Cretaceous (lower Cenomanian–upper Turonian) Bajo Barreal Formation, central Patagonia, Argentina. The materials display morphological features that undoubtedly position Xenotarsosaurus within Abelisauroidea. Moreover, detailed comparisons with members of that theropod group confirm the close relationship of this taxon to abelisaurids. Here we provide an emended diagnosis of Xenotarsosaurus bonapartei that includes five newly recognized autapomorphies: (1) anterior dorsal vertebrae with large, strongly dorsoventrally developed parapophyses; (2) anterior dorsal vertebrae with well-developed centroprezygapophyseal fossae that are taller dorsoventrally than wide mediolaterally; (3) fibular condyle of femur triangular in shape and projecting posteriorly; (4) well-marked groove on the anterolateral corner of the proximal fibula; and (5) iliofibularis tubercle of fibula distally interrupted by a hook-like shaped concavity. To determine its systematic position within Abelisauroidea, we incorporated Xenotarsosaurus into a phylogenetic analysis, recovering this theropod as a non-carnotaurine abelisaurid more derived than Eoabelisaurus mefi. Xenotarsosaurus displays several plesiomorphic traits when compared with penecontemporaneous abelisaurids from the Neuquén Group. Similarly, other non-avian dinosaur taxa from the Bajo Barreal Formation are frequently postulated as more phylogenetically basal than coeval forms from northern Patagonia. This scenario suggests the potential existence of provincialism in early Late Cretaceous continental vertebrate faunas of southern South America. The present study increases knowledge of abelisaurid systematics, evolution, and paleobiogeography and augments our understanding of the Late Cretaceous dinosaur assemblage of central Patagonia.
... The Australian occurrence of a possible tyrannosauroid is inferred based on a late Early Cretaceous pubis described in 2010 (Benson et al.), although the material's affinity to megaraptorids was proposed later (Novas et al., 2013). Some authors (Novas et al., 2013;Porfiri et al., 2014Porfiri et al., , 2018 put megaraptorids within Tyrannosauroidea, which may imply a wider distribution of the clade within Gondwanan landmasses. ...
The Coelurosauria are a group of mostly feathered theropods that gave rise to birds, the only dinosaurians that survived the Cretaceous-Paleogene extinction event and are still found today. Between their first appearance in the Middle Jurassic up to the end Cretaceous, coelurosaurians were party to dramatic geographic changes on the Earth’s surface, including the breakup of the supercontinent Pangaea, and the formation of the Atlantic Ocean. These plate tectonic events are thought to have caused vicariance or dispersal of coelurosaurian faunas, influencing their evolution. Unfortunately, few coelurosaurian biogeographic hypotheses have been supported by quantitative evidence. Here, we report the first, broadly sampled quantitative analysis of coelurosaurian biogeography using the likelihood-based package BioGeoBEARS. Mesozoic geographic configurations and changes are reconstructed and employed as constraints in this analysis, including their associated uncertainties. We use a comprehensive time-calibrated coelurosaurian evolutionary tree produced from the Theropod Working Group phylogenetic data matrix. Six biogeographic models in the BioGeoBEARS package with different assumptions about the evolution of spatial distributions are tested against geographic constraints. Our results statistically favor the DIVALIKE+J and DEC+J models, which allow vicariance and founder events, supporting continental vicariance as an important factor in coelurosaurian evolution. Ancestral range estimation indicates frequent dispersal events via the Apulian route (connecting Europe and Africa during the Early Cretaceous) and the Bering land bridge (connecting North America and Asia during the Late Cretaceous). These quantitative results are consistent with commonly inferred Mesozoic dinosaurian dispersals and continental-fragmentationinduced vicariance events. In addition, we recognize the importance of Europe as a dispersal center and gateway in the Early Cretaceous, as well as other vicariance events such as those triggered by the disappearance of land bridges.
... The Australian occurrence of a possible tyrannosauroid is inferred based on a late Early Cretaceous pubis described in 2010 (Benson et al.), although the material's affinity to megaraptorids was proposed later (Novas et al., 2013). Some authors (Novas et al., 2013;Porfiri et al., 2014Porfiri et al., , 2018 put megaraptorids within Tyrannosauroidea, which may imply a wider distribution of the clade within Gondwanan landmasses. ...
The Coelurosauria are a group of mostly feathered theropods that gave rise to birds, the only dinosaurians that survived the Cretaceous-Paleogene extinction event and are still found today. Between their first appearance in the Middle Jurassic up to the end Cretaceous, coelurosaurians were party to dramatic geographic changes on the Earth's surface, including the breakup of the supercontinent Pangaea, and the formation of the Atlantic Ocean. These plate tectonic events are thought to have caused vicariance or dispersal of coelurosaurian faunas, influencing their evolution. Unfortunately , few coelurosaurian biogeographic hypotheses have been supported by quantitative evidence. Here, we report the first, broadly sampled quantitative analysis of coelurosaurian biogeography using the likelihood-based package BioGeoBEARS. Mesozoic geographic configurations and changes are reconstructed and employed as constraints in this analysis, including their associated uncertainties. We use a comprehensive time-calibrated coelurosaurian evolutionary tree produced from the The-ropod Working Group phylogenetic data matrix. Six biogeographic models in the BioGeoBEARS package with different assumptions about the evolution of spatial distributions are tested against geographic constraints. Our results statistically favor the DIVALIKE+J and DEC+J models, which allow vicariance and founder events, supporting continental vicariance as an important factor in coelurosaurian evolution. Ancestral range estimation indicates frequent dispersal events via the Apulian route (connecting Europe and Africa during the Early Cretaceous) and the Bering land bridge (connecting North America and Asia during the Late Cretaceous). These quantitative results are consistent with commonly inferred Mesozoic dinosaurian dispersals and continental-fragmentation-induced vicariance events. In addition, we recognize the importance of Europe as a dispersal center and gateway in the Early Cretaceous, as well as other vicariance events such as those triggered by the disappearance of land bridges.
... The metatarsal III of Aratasaurus museunacionali is similar to Aarun zhaoi by lacking a flange on the anterolateral surface of the distal articulation, which is present in Zuolong sallei. Aratasaurus museunacionali differs from megaraptorans, with the last exhibiting wide metatarsal III with a deeply excavated crescent-shaped extensor fossa and the metatarsal III narrower than metatarsal II and IV in anterior view 51 . The width of the metatarsals II, III and IV are about the same in Aratasaurus museunacionali, while Zuolong sallei shows a metatarsal III twice the width of the metatarsals II and IV. ...
The Romualdo Formation (Araripe Basin) is worldwide known for the large number of well-preserved fossils but the dinosaur record is rather scarce. Here we describe a new coelurosaur, which is the first tetrapod recovered from the basal layers of this stratigraphic unit that consist of dark shales. Aratasaurus museunacionali gen. et sp. nov. is known by an incomplete but articulated right hind limb with the distal portion of the femur, proximal half of tibia and incomplete pes. The new species differs from other coelurosaurs by a medial fossa in the tibia and digits II, III and IV being symmetric. The phylogenetic analysis recovered Aratasaurus museunacionali closely related to Zuolong salleei, forming a basal coelurosaur lineage. The paleohistology indicate that the specimen is a juvenile, with an estimated body length around 3.12 m. The new taxon represents the first occurrence of basal coelurosaurians in the Araripe Basin and suggests a widespread distribution of this group during the Lower Cretaceous.
... Among them, Aerosteon riocoloradensis is particularly interesting because it represents an early Campanian (Garrido, 2010) basal avetheropod with extreme cranial and postcranial pneumatization . The phylogenetic relationships of Aerosteon and closely related taxa (i.e., other members of the clade Megaraptora: Megaraptor, Orkoraptor, Australovenator, Fukuiraptor, Murusraptor, Tratayenia) are highly debated, and the clade has recently been referred to neovenatorid allosauroids (Benson et al., 2010;Carrano et al., 2012;Zanno and Makovicky, 2013), basal tyrannosauroids (Aranciaga Rolando et al., 2019;Novas et al., 2013;Porfiri et al., 2014) or the earliest branching coelurosaurians (Aranciaga Rolando et al., 2018;Porfiri et al., 2018;Samathi et al., 2019). Aerosteon is known from cranial and postcranial material, and a single shed tooth crown constitutes the only element that provides information on the dentition of this theropod. ...
... This condition is observed in isolated dorsal centra of the megaraptorids Aerosteon and Murusraptor Coria & Currie, 2016), while the caudal centra of these theropods have a neural canal constricted around mid-length. In lateral view, the centrum is squared-shaped in outline, contrasting with other megaraptorids, in which the centrum is shorter and taller (e.g., Megaraptor Aerosteon, Murusraptor, Tratayenia; Coria & Currie, 2016;Porfiri et al., 2014Porfiri et al., , 2018. However, Wilson et al. (2016) noted that this feature seems size-dependant, and may be related with the fact that all of the above mentioned megaraptorids are 8-10 meters long. ...
The first fossil remains of vertebrates, invertebrates, plants and palynomorphs of the Chorrillo Formation (Austral Basin), about 30km to the SW of the town of El Calafate (Province of Santa Cruz), are described. Fossils include the elasmarian (basal Iguanodontia) Isasicursor santacrucensis gen. et sp. nov., the large titanosaur Nullotitan glaciaris gen. et sp. nov., both large and small Megaraptoridae indet., and fragments of sauropod and theropod eggshells. The list of vertebrates is also composed by the Neognathae Kookne yeutensis gen. et sp. nov., two isolated caudal vertebrae of Mammalia indet., and isolated teeth of a large mosasaur. Remains of fishes, anurans, turtles, and snakes are represented by fragmentary material of low taxonomical value, with the exception of remains belonging to Calyptocephalellidae. On the other hand, a remarkable diversity of terrestrial and freshwater gastropods has been documented, as well as fossil woods and palinological assemblages. The Chorrillo Formation continues south, in the Las Chinas River valley, southern Chile, where it is called Dorotea Formation. Both units share in their lower two thirds abundant materials of titanosaurs, whose remains cease to appear in the upper third, registering only elasmarians (Chorrillo Formation) and hadrosaurs (Dorotea Formation). Above both units there are levels with remains of invertebrates and marine reptiles. It is striking that the dinosaurs of the lower two thirds of the Chorrillo and Dorotea formations are represented by large basal titanosaurs and Megaraptoridae coelurosaurs, being the Saltasaurinae and Aeolosaurinae sauropods and Abelisauridae theropods totally absent. In contrast, these taxa are dominant components in sedimentary units of central and northern Patagonia (e.g., Allen, Los Alamitos, La Colonia formations). Such differences could reflect, in part, a greater antiquity (i.e., late Campanian-early Maastrichtian) for the Chorrillo fossils, or, more probably, different environmental conditions. Thus, knowledge of the biota of the southern tip of Patagonia is expanded, particularly those temporarily close to the K-Pg boundary.
... This group is particularly abundant in the Cretaceous of Argentina but is also known from Brazil, Australia, the United States, Thailand, and Japan (Samathi et al., 2019;Poropat et al., in press). The temporal range includes forms from the Early Cretaceous (Barremian) to the Late Cretaceous (Campanian) (Porfiri et al., 2018;Samathi et al., 2019;Poropat et al., in press). Megaraptoran remains are also known from the Campanian Lago Colhué Huapi Formation, specifically they were found on an ephemeral island near the southeastern shore of Colhué Huapi Lake (but see discussion). ...
In this paper, we present an updated revision of fossil vertebrates from the Chubut Group, Golfo San Jorge Basin, while also describing some new remains. Extensive exposures of both Lower and Upper Cretaceous sedimentary sequences are present in central Patagonia. These outcrops have, over the past several decades, yielded a varied vertebrate fauna, including fishes, turtles, crocodyliforms, pterosaurs, and dinosaurs, currently herein characterized and described. Although vertebrate diversity in the Chubut Group in central Patagonia is remarkable, the most abundant vertebrates recovered are dinosaurs. The Matasiete Formation (Hauterivian?–Albian) is markedly less prolific in terms of fossils discoveries than either the Bajo Barreal Formation (Cenomanian–early Turonian) or the recently recognized Lago Colhué Huapi Formation (Coniacian–Maastrichtian). The Bajo Barreal fauna is, at a high level, typical of coeval Gondwanan faunas. However, interestingly, several taxa occupy a basal position within their respective groups. The Lago Colhué Huapi Formation has produced a more derived vertebrate fauna, again similar to those from other Gondwanan regions. Finally, in a broad context, the new materials described augment our understanding of Cretaceous terrestrial vertebrate assemblage of central Patagonia and add to the generally meager record of vertebrate in the Cretaceous of the Southern Hemisphere.
... Fossils of the former include an isolated tooth, vertebrae, and pedal phalanges from the recently-discovered Playa Paraíso locality on the northeastern shore of Lago Colhué Huapi . Megaraptoran specimens-some of the stratigraphically youngest yet reported (see Porfiri et al. 2018)-include two large, well-preserved manual unguals (UNPSJB-PV 1028 and 1046; probably those of digit I) and an incomplete but associated skeleton consisting of a tooth, a manual ungual I, and a hind limb element, either a tibia or a metatarsal III (UNPSJB-PV 1066; Casal et al. 2016Casal et al. , 2018GAC pers. obs. ...
Peirosaurid crocodyliforms were diverse and abundant in the Cretaceous of the Gondwanan landmasses, especially South America. Here, we describe Colhuehuapisuchus lunai, gen. et sp. nov., a new peirosaurid taxon from the Upper Cretaceous (Campanian-?lower Maastrichtian) Lago Colhué Huapi Formation of southern Chubut Province in central Patagonia, Argentina. Although represented by only the anterior ~one-third of the mandible with several complete, in situ teeth, the new taxon exhibits a combination of distinctive morphologies that does not occur in other peiro-saurids, including several mandibular and dental autapomorphies. The symphyseal region of the Colhuehuapisuchus mandible is transversely wider than that of any other representative of Peirosauridae, and as such the new form may be most closely related to other broad-snouted peirosaurids such as Barrosasuchus neuquenianus, Gasparinisuchus peirosauroides, and Patagosuchus anielensis. The exceptional diversity of snout and tooth shapes among definitive and probable members of Peirosauridae suggests the existence of a variety of ecological and dietary preferences within the clade. Colhuehuapisuchus constitutes the southernmost peirosaurid occurrence worldwide and arguably the youngest record from Patagonia, thereby expanding the paleobiogeographic range of these distinctive mesoeucrocodylians to nearly the end of the Mesozoic and the southern tip of South America. RESUMEN Los crocodiliformes peirosáuridos fueron diversos y abundantes en las masas continentales del Cretácico de Gondwana, especialmente en América del Sur. Aquí describimos a Colhuehuapisuchus lunai gen. et sp. nov., un nuevo peirosáurido del Cretácico Superior (Campaniano-Maastrichtiano inferior?) de la Formación Lago Colhué Huapi, del sur de la provincia de Chubut en la Patagonia central, Argentina. Aunque representado solamente por el tercio anterior de la mandíbula con varios dientes in situ y completos, el nuevo taxón exhibe una combinación de morfologías distintivas no registradas en otros peirosáuridos, incluidas varias autapomorfías mandibulares y dentales. La región sinfisiaria de la mandíbula de Colhuehuapisuchus es más ancha transversalmente que la de cualquier otro representante de Peirosauridae, y por lo tanto, este nuevo taxón podría estar más estrechamente relacionado con otros peirosáuridos de hocico ancho como Barrosasuchus neuquenianus, Gasparinisuchus peirosauroi-des, y Patagosuchus anielensis. La excepcional diversidad de morfologías de hocico y dientes entre los miembros confirmados y probables de Peirosauridae sugiere la existencia de una variedad de preferencias ecológicas y tróficas dentro del clado. Colhuehuapisuchus constituye el registro más austral de peirosáurido del mundo y posiblemente el más reciente de la Patagonia, expandiendo así el rango paleobiogeográfico de estos car-acterísticos mesoeucrocodilos hasta casi el final del Mesozoico y el extremo sur de América del Sur.
... A more derived clade, the Megaraptoridae (sensu Novas et al. 2013), is known from the Cenomanian to Santonian rocks of Gondwana (Porfiri et al. 2014;Novas et al. 2016). The clade consists of the South American taxa Megaraptor (Novas 1998), Aerosteon , Murusraptor (Coria and Currie 2016), Orkoraptor (Novas et al. 2008), and Tratayenia (Porfiri et al. 2018) as well as Australovenator from Australia (Hocknull et al. 2009). ...
Megaraptora is a clade of mid to large-sized theropods that are long-snouted, large-clawed, highly pneumatized, and have long and gracile metatarsals. The basal member was reported from the Barremian of Japan. A more derived clade, the Megaraptoridae, is known from the Cenomanian to Santonian of Gondwana. Here two new basal coelurosaurs from the Lower Cretaceous Sao Khua Formation of Thailand are described and named as Phuwiangvenator yaemniyomi gen. et sp. nov. and Vayuraptor nongbualamphuensis gen. et sp. nov. Phuwiangvenator is a megaraptoran coelurosaur and diagnosed by the ventrally flat sacral vertebrae with sulci in the anterior and posterior region of the centra and the anterior rim of metatarsal IV sloping proximolaterally to distomedially and being much lower than that of metatarsal III anteriorly. Vayuraptor is a basal coelurosaur and diagnosed by its astragalus which has two horizontal grooves, two fossae at the base of the ascending process, the ascending process being straight laterally and straight and parallel medially with the medial rim sloping to the tip laterally, and a long and slender astragalar ascending process. Although the position of the basal coelurosaur Vayuraptor remains unclear and must await further discovery, megaraptoran affinities are likely. The Early Cretaceous megaraptoran fossil record has been recovered from the Barremian to Aptian of Asia. All Asian megaraptorans might be a monophyletic clade or a paraphyletic series relative to the Megaraptoridae. Several specimens have been reported from the Aptian to mid-Cretaceous of Australia, and one report from the Albian of South America. These fossils show a high diversity of the Early Cretaceous megaraptorans and a wide distribution during that time. The clade then became more provincial in the Late Cretaceous.
... c Stratigraphic distribution of Allosauria in North America (incl. Megaraptora but see ref. 70 for alternative hypotheses regarding this clade) documents overlap with M. intrepidus in early Late Cretaceous ecosystems leading to (d) refined calibration on the origin of late diverging tyrannosauroids and clade-level faunal turnover within apex predator roles throughout the Late Jurassic-Late Cretaceous of North America. Colored polygons are stylized call-outs and are not intended to reflect twodimensional data. ...
To date, eco-evolutionary dynamics in the ascent of tyrannosauroids to top predator roles have been obscured by a 70-million-year gap in the North American (NA) record. Here we report discovery of the oldest Cretaceous NA tyrannosauroid, extending the lineage by ~15 million years. The new taxon—Moros intrepidus gen. et sp. nov.—is represented by a hind limb from an individual nearing skeletal maturity at 6–7 years. With a ~1.2-m limb length and 78-kg mass, M. intrepidus ranks among the smallest Cretaceous tyrannosauroids, restricting the window for rapid mass increases preceding the appearance of colossal eutyrannosaurs. Phylogenetic affinity with Asian taxa supports transcontinental interchange as the means by which iconic biotas of the terminal Cretaceous were established in NA. The unexpectedly diminutive and highly cursorial bauplan of NA’s earliest Cretaceous tyrannosauroids reveals an evolutionary strategy reliant on speed and small size during their prolonged stint as marginal predators.
... Given that all known theropod specimens from Victoria constitute isolated elements, there is little doubt that debates over the palaeobiogeographic implications of the assemblage as a whole, and of each faunal component, will continue. However, one thing does seem quite clear: megaraptorans (be they neovenatorid allosauroids or tyrannosauroid coelurosaurs) were present in Victoria during the late Early Cretaceous , Benson et al. 2012, New South Wales during the late Early Cretaceous (Bell et al. 2016), Queensland during the early Late Cretaceous , White et al. 2012, White, Falkingham et al. 2013, White et al. 2015 and South America from at least the Albian to the Santonian (Novas 1998, Calvo et al. 2004, Porfiri et al. 2007, Novas et al. 2008, Sereno et al. 2008, Méndez et al. 2012, Porfiri et al. 2014, Coria & Currie 2016, Aranciaga Rolando et al. 2018, Porfiri et al. 2018. Megaraptorans remain unknown from Africa, India and Madagascar. ...
Although Cretaceous fossils (coal excluded) from Victoria, Australia, were first reported in the 1850s, it was not until the 1950s that detailed studies
of these fossils were undertaken. Numerous fossil localities have been identified in Victoria since the 1960s, including the Koonwarra Fossil
Bed (Strzelecki Group) near Leongatha, the Dinosaur Cove and Eric the Red West sites (Otway Group) at Cape Otway, and the Flat Rocks site
(Strzelecki Group) near Cape Paterson. Systematic exploration over the past five decades has resulted in the collection of thousands of fossils representing
various plants, invertebrates and vertebrates. Some of the best-preserved and most diverse Hauterivian–Barremian floral assemblages in
Australia derive from outcrops of the lower Strzelecki Group in the Gippsland Basin. The slightly younger Koonwarra Fossil Bed (Aptian) is a
Konservat-Lagerstätte that also preserves abundant plants, including one of the oldest known flowers. In addition, insects, crustaceans (including
the only syncaridans known from Australia between the Triassic and the present), arachnids (including Australia’s only known opilione), the stratigraphically
youngest xiphosurans from Australia, bryozoans, unionoid molluscs and a rich assemblage of actinopterygian fish are known from the
Koonwarra Fossil Bed. The oldest known—and only Mesozoic—fossil feathers from the Australian continent constitute the only evidence for tetrapods
at Koonwarra. By contrast, the Barremian–Aptian-aged deposits at the Flat Rocks site, and the Aptian–Albian-aged strata at the Dinosaur
Cove and Eric the Red West sites, are all dominated by tetrapod fossils, with actinopterygians and dipnoans relatively rare. Small ornithopod
(=basal neornithischian) dinosaurs are numerically common, known from four partial skeletons and a multitude of isolated bones. Aquatic meiolaniform
turtles constitute another prominent faunal element, represented by numerous isolated bones and articulated carapaces and plastrons. More
than 50 specimens—mostly lower jaws—evince a high diversity of mammals, including monotremes, a multituberculate and several enigmatic
ausktribosphenids. Relatively minor components of these fossil assemblages are diverse theropods (including birds), rare ankylosaurs and ceratopsians,
pterosaurs, non-marine plesiosaurs and a lepidosaur. In the older strata of the upper Strzelecki Group, temnospondyl amphibians—the youngest
known worldwide—are a conspicuous component of the fauna, whereas crocodylomorphs appear to be present only in up-sequence deposits of
the Otway Group. Invertebrates are uncommon, although decapod crustaceans and unionoid bivalves have been described. Collectively, the Early
Cretaceous biota of Victoria provides insights into a unique Mesozoic high-latitude palaeoenvironment and elucidates both palaeoclimatic and
palaeobiogeographic changes throughout more than 25 million years of geological time.
Megaraptora is a group of enigmatic, carnivorous non‐avian theropod dinosaurs from the Cretaceous of Asia, Australia, and especially South America. Perhaps the most striking aspect of megaraptoran morphology is the large, robustly constructed forelimb that, in derived members of the clade, terminates in a greatly enlarged manus with hypertrophied, raptorial unguals on the medialmost two digits and a substantially smaller ungual on digit III. The unique forelimb anatomy of megaraptorans was presumably associated with distinctive functional specializations; nevertheless, its paleobiological significance has not been extensively explored. Here we draw from observations of the pectoral girdle and forelimb skeletons of Megaraptora and myological assessments of other archosaurian taxa to provide a comprehensive reconstruction of the musculature of this anatomical region in these singular theropods. Many muscle attachment sites on megaraptoran forelimb bones are remarkably well developed, which in turn suggests that the muscles themselves were functionally significant and important to the paleobiology of these theropods. Furthermore, many of these attachments became increasingly pronounced through megaraptoran evolutionary history, being substantially better developed in derived taxa such as Australovenator wintonensis and especially Megaraptor namunhuaiquii than in early branching forms such as Fukuiraptor kitadaniensis. When considered alongside previous range of motion hypotheses for Australovenator, our results indicate that megaraptorans possessed a morphologically and functionally specialized forelimb that was capable of complex movements. Notable among these were extensive extension and flexion, particularly in the highly derived manus, as well as enhanced humeral protraction, attributes that very probably aided in prey capture.
Abelisaurids are medium–large-sized theropod dinosaurs that were predominant in the carnivorous fauna during the Late Cretaceous of Gondwana. These predators are abundant in the Cretaceous fossil strata of Patagonia, which yield the best record for this group. In the Late Cretaceous, abelisaurids appear in almost all regions of Gondwana and in all stages, except for the Coniacian, in which they are globally unknown. Here we describe a new abelisaurid, Elemgasem nubilus gen. et sp. nov., from the Portezuelo Formation (Turonian–Coniacian), Patagonia, Argentina. The palaeohistology of the appendicular bones of Elemgasem shows that the holotype was a subadult individual, but had achieved sexual maturity. This taxon is based on several axial and appendicular elements, and is diagnosed by the presence of a marked pattern of rugosity on the lateral surface of the fibula and a dorsoventrally deep lateral wall of the calcaneum. Moreover, the posterior caudal vertebrae have a morphology slightly different from any other abelisaurid. Elemgasem nubilus is recovered as an unstable taxon within Brachyrostra, given that it was recovered as sister taxon of Furileusauria or in several positions within this clade. Despite the problematic phylogenetic relationships of Elemgasem nubilus, it is important because it is the first abelisaurid from the Turonian–Coniacian interval and it increases the diversity of this theropod family at a time of marked turnover in the tetrapod fauna of South America, global climate change, and mass extinction events recorded worldwide in the marine realm.
Phuwiangvenator yaemniyomi is a mid-sized, early branching megaraptoran theropod from the Lower Cretaceous Sao Khua Formation of Phu Wiang Mountain, Khon Kaen Province, northeastern Thailand. The holotype includes dorsal and sacral vertebrae, lower legs, hand and foot elements. Here we describe new skeletal material pertaining to the same individual representing the holotype of Phuwiangvenator based on size, shape, and shared phylogenetic affinities. This material was recovered at the same quarry as the holotype and consists of an incomplete fibula, left and right metatarsals. A new autapomorphy observed from the new material is the presence of a long, deep fossa between the lateral and medial distal condyles of the metatarsal II that extends to the distal articular facet is visible in anterior view. The metatarsal III of Phuwiangvenator is relatively short, more similar to the proportion present in basal carcharodontosaur Concavenator than in the derived megaraptorans, but more gracile than other basal allosauroids. Its hindlimb proportions are similar to the basal carcharodontosaur Neovenator than other more derived megaraptorans and coelurosaurs. Phuwiangvenator shows a combination of features shared with allosauroids and basal coelurosaurs and appears to be “intermediate” between non-megaraptorid and megaraptorid theropods. The present work adds anatomical data on this theropod and provides information on the early evolution of the Megaraptora.
Two new specimens of abelisaurid theropods from La Invernada fossil area (Bajo de la Carpa Formation; Santonian) are described. They correspond to an incomplete skull and several postcranial remains. MAU-Pv-LI-582 (skull) shares some morphological traits with other furileusaurs (Viavenator exxoni and Llukalkan aliocranianus) from the same area, as: presence of a rounded knob on the anteromedial border of the supratemporal fossa, large foramina for the caudal middle cerebral veins, and a triangular basisphenoid recess with Llukalkan, and a basituberal web ventrally concave, a large common foramen for the exit of CNs III and IV, and particularly the absence of a caudal tympanic recess with Viavenator. MAU-Pv-LI-665 (vertebrae and ribs) shares some features with Viavenator, such as the presence of a single pneumatic foramen in the mid cervical centrum, and the shape and orientation of the neural spine of the mid dorsal vertebra. These findings, added to the previous ones, not only reveal the abundance of abelisaurids in this geographical area, but also the variety of morphotypes that coexisted during the middle of the Upper Cretaceous, at least in the north of Argentine Patagonia.
Well-sampled dinosaur communities from the Jurassic through the early Late Cretaceous show greater taxonomic diversity among larger (>50 kg) theropod taxa than communities of the Campano-Maastrichtian, particularly to those of eastern/central Asia and Laramidia. The large carnivore guilds in Asiamerican assemblages are monopolized by tyrannosaurids, with adult medium-sized (50–500 kg) predators rare or absent. In contrast, various clades of theropods are found to occupy these body sizes in earlier faunas, including early tyrannosauroids. Assemblages with “missing middle-sized” predators are not found to have correspondingly sparser diversity of potential prey species recorded in these same faunas. The “missing middle-sized” niches in the theropod guilds of Late Cretaceous Laramidia and Asia may have been assimilated by juvenile and subadults of tyrannosaurid species, functionally distinct from their adult ecomorphologies. It is speculated that if tyrannosaurids assimilated the niches previously occupied by mid-sized theropod predators, we would expect the evolution of distinct transitions in morphology and possibly the delay of the achievement of somatic maturity in species of this taxon.
The deposits corresponding to the Upper Cretaceous Neuquén and San Jorge Gulf basins from northern and central Patagonia have provided two of the most complete sequences of terrestrial vertebrate faunas of all Gondwanan landmasses. Among the carnivorous components, the carcharodontosaurid theropods appeared as common elements during the Early Cretaceous and the earliest Late Cretaceous in northern and central Patagonia. Although recorded mostly in the lower Turonian, isolated teeth suggest their presence in younger strata in northern and central Patagonia, reaching the clade in the region as late as the early Maastrichtian. Here, we verify the assignment of such isolated teeth previously identified as belonging to Carcharodontosauridae from the Upper Cretaceous strata of northern and central Patagonia. Using three different methods, namely a cladistic analysis performed on a dentition-based data matrix, and discriminant and cluster analyses conducted on a large dataset of theropod crown measurements, we assign a tooth from Candeleros Formation to carcharodontosaurid theropods and teeth from Cerro Lisandro, Bajo Barreal, Portezuelo, Plottier and Allen formations to abelisaurid theropods. These new reappraisals provide additional evidence about the extinction of Carcharodontosauridae in South America at about the late Turonian–earliest Coniacian as part of a general faunistic turnover event, with the last clear evidence of this lineage in Patagonia coming from the early–middle Turonian.
Not enough room
Modern carnivore communities include species that span a range of body sizes. For example, on the African savannah, there are small species (mongooses), medium species (wild dogs), and large species (lions). This variation reflects available prey sources that best suit each group. Carnivorous dinosaur communities, however, were missing species that fall into the middle, or mesocarnivore, group as adults. Schroeder et al. looked across communities, space, and time and found that this absence appears to have been driven by the distinctive biology of dinosaurs, in which giant adults start out as tiny hatchlings. Growing juvenile dinosaurs thus filled the other niches and limited trophic species diversity.
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A series of axial elements from the Aptian Ferrug-inous Sands Formation of the Lower Greensand Group, discovered on the foreshore near Knock Cliff on the Isle of Wight, UK are (bar some isolated teeth and fragmentary post-cranial material from the Cenomanian Cambridge Greensand) the youngest non-avian theropod remains reported from the British Mesozoic. These specimens have the potential to shed light on a poorly known section of the European dinosaur record. Consistency in size, appearance and adhering matrix indicates that the vertebrae belong to the same individual. This was a mid-sized tetanuran, the presence of several diagnostic characters indicating that it should be recognized as a new taxon, herein named Vectaerovenator inopinatus. The cervical and dorsal vertebrae are camerate and highly pneumatic. Tetanuran features include opisthocoelous cervicals and pneumatic foramina located within fossae; however, assigning this specimen to a specific clade is problematic. Within Tetanurae, Vectaerovenator possesses axial structures and homoplastic features seen in megalosauroids, carcharodontosaurians and certain coelurosaurs. Not only is Vectaerovenator one of the UK's youngest non-bird dinosaurs, and one of few valid British Greensand taxa, it is also the first diagnosable theropod taxon to be named from Aptian deposits of Europe.
Evolutionary teratology recognises certain anatomical modifications as developmental anomalies. Within non avian-theropod dinosaurs, the strong forelimb shortening of Tyrannosauridae, Carnotaurinae and Limusaurus – associated with a reduction or loss of autonomy – have been previously diagnosed as evolutionary anterior micromelias. The feature is here examined with Acrocanthosaurus atokensis (Carcharodontosauridae) and Gualicho shinyae (Neovenatoridae). The micromelic diagnosis is confirmed for Acrocanthosaurus, without supplementary malformations. Gualicho is considered as a borderline case, outside of the micromelic spectrum, but shows a total phalangeal loss on digit III. The reduction in the biomechanical range of Acrocanthosaurus’ forelimbs was compensated by the skull and jaws as main predatory organs. The same is assumed for Gualicho, but its robust first digit and raptorial claw are to be underlined. Other gigantic-sized and derived representatives of Carcharodontosauridae probably shared the anterior micromelia condition, potentially due to developmental modifications involving differential forelimbs/hindlimbs embryological growth rates, secondarily associated with post-natal growth rates leading to large and gigantic sizes; a converging state with Tyrannosauridae. Nevertheless, whereas developmental growth rates are also considered in the shortened condition of Gualicho, there is no association with post-natal gigantism. Finally, the digit III reduction likely followed the same evolutionary pathways as Tyrannosauridae, potentially involving BMPs, Fgfs and Shh signalling.
The biogeography of Cretaceous Australian dinosaur fauna has been characterized variously as endemic, cosmopolitan or closely related to other Gondwanan faunas. Over the past decade, a large number of new Australian dinosaur taxa have been described and included in phylogenetic analyses, allowing for new insights into their biogeographical affinities to be obtained. Here, I combine the latest phylogenies of Australian dinosaurs into a supertree that includes as many Australian taxa as possible and apply it to the construction of biogeographical networks of Cretaceous dinosaurs. The results show that the Cretaceous dinosaurs of Australia have a strong connection with South American dinosaurs and to those of other Gondwanan continents via South America. Community detection algorithms indicate that the Gondwanan continents form a community within Cretaceous dinosaur biogeographical networks. The biogeographical affinities between Australia and Laurasia detected in previous studies were largely due to the scarce dinosaur fossil record of Gondwana at that time and to the unstable phylogenetic position of Australian dinosaurs because of the fragmentary nature of their fossils. Continuing discoveries of new Australian taxa and refinement of resulting phylogenetic analyses can further deepen our understanding of the biogeographical history of Australia.
Megaraptorid theropods thrived in South America and Australia during the mid-Cretaceous. Their Australian record is currently limited to the upper Barremian–lower Aptian upper Strzelecki Group and the upper Aptian–lower Albian Eumeralla Formation of Victoria, the Cenomanian Griman Creek Formation of New South Wales, and the Cenomanian–lowermost Turonian Winton Formation of Queensland. The latter has produced Australovenator wintonensis, the stratigraphically youngest and most complete Australian megaraptorid. The Eric the Red West (ETRW) site on Cape Otway, Victoria (Eumeralla Formation; lower Albian), has yielded two teeth, two manual unguals, and a right astragalus that are almost identical to the corresponding elements in Australovenator. Herein, we classify these as Megaraptoridae cf. Australovenator wintonensis. We also reappraise the ‘spinosaurid’ cervical vertebra from ETRW and suggest that it pertains to Megaraptoridae. Three other theropod elements from ETRW—a cervical rib (preserving a bite mark), a caudal vertebra, and a non-ungual manual phalanx—are also described, although it is not possible to determine their phylogenetic position more precisely than Tetanurae (non-Maniraptoriformes). All elements were found in a fluvial deposit, associated with isolated bones of other theropods, ornithopods, and turtles, amongst others; consequently, no two can be unequivocally assigned to the same theropod individual. The new specimens from ETRW demonstrate that a megaraptorid theropod morphologically similar to Australovenator lived during the late Early Cretaceous in Victoria, at a higher paleolatitude than its northern counterpart. Moreover, they attest to the success of megaraptorids in late Barremian–early Turonian faunas throughout eastern Australia.
Although the fossil record of non-avian dinosaurs from the Cretaceous of Antarctica is the poorest of any continent, fossils representing at least five major taxonomic groups (Ankylosauria, early-diverging Ornithopoda, Hadrosauridae, Titanosauria, and Theropoda) have been recovered. All come from Upper Cretaceous (Coniacian–Maastrichtian) marine and nearshore deposits belonging to the Gustav and Marambio groups of the James Ross Basin at the northern tip of the Antarctic Peninsula. The majority of these finds have come from the Campanian–Maastrichtian Snow Hill Island and López de Bertodano formations of James Ross and Vega islands. Given the rarity of Antarctic Cretaceous non-avian dinosaurs, discoveries of any fossils of these archosaurs, no matter how meager, are of significance. Here we describe fragmentary new ornithischian (ankylosaur and ornithopod) material from the upper Campanian–lower Maastrichtian Cape Lamb Member of the Snow Hill Island Formation and the Maastrichtian Sandwich Bluff Member of the López de Bertodano Formation. One of these specimens is considered to probably pertain to the holotypic individual of the early-diverging ornithopod Morrosaurus antarcticus. We also provide an up-to-date synthesis of the Late Cretaceous non-avian dinosaur record of the James Ross Basin and analyze the biostratigraphic occurrences of the various finds, demonstrating that most (including all named taxa and all reasonably complete skeletons discovered to date) occur within a relatively condensed temporal interval of the late Campanian to early Maastrichtian. Most or all James Ross Basin dinosaurs share close affinities with penecontemporaneous taxa from Patagonia, indicating that at least some continental vertebrates could disperse between southern South America and Antarctica during the final stages of the Mesozoic.
Non‐avian theropods were a highly successful clade of bipedal, predominantly carnivorous, dinosaurs. Their diversity and macroevolutionary patterns have been the subject of many studies. Changes in fossil specimen completeness through time and space can bias our understanding of macroevolution. Here, we quantify the completeness of 455 non‐avian theropod species using the skeletal completeness metric (SCM), which calculates the proportion of a complete skeleton preserved for a specimen. Temporal patterns of theropod skeletal completeness show peaks in the Carnian, Oxfordian–Kimmeridgian and Barremian–Aptian, and lows in the Berriasian and Hauterivian. Lagerstätten primarily drive the peaks in completeness and observed taxonomic diversity in the Oxfordian–Kimmeridgian and the Barremian–Aptian. Theropods have a significantly lower distribution of completeness scores than contemporary sauropodomorph dinosaurs but change in completeness through time for the two groups shows a significant correlation when conservation Lagerstätten are excluded, possibly indicating that both records are primarily driven by geology and sampling availability. Our results reveal relatively weak temporal sampling biases acting on the theropod record but relatively strong spatial and environmental biases. Asia has a significantly more complete record than any other continent, the mid northern latitudes have the highest abundance of finds, and most complete theropod skeletons come from lacustrine and aeolian environments. We suggest that these patterns result from historical research focus, modern climate dynamics, and depositional transportation energy plus association with conservation Lagerstätten, respectively. Furthermore, we find possible ecological biases acting on different theropod subgroups, but body size does not influence theropod completeness on a global scale.
Abelisaurid theropods are well-know from the Cretaceous of several parts of the Southern
Hemisphere, including South America, Madagascar, and Africa, but also in India and Europe. Abelisaurids are high-diverse among other theropods with several cervicocephalic specializations reaching medium/large sizes. In the present contribution, we describe a new abelisaurid (Thanos simonattoi, gen. et sp. nov.) from the São José do Rio Preto Formation, Bauru Group, Brazil (Upper Cretaceous). Thanos differs from other theropods by having a well-developed keel becoming wider and deeper posteriorly on the ventral surface; two lateral small foramina separated by a relative wide wall on each lateral surface of the centrum, and well-developed and deep prezygapophyseal pinodiapophyseal fossae. The closed sutures between the axis and odontoid suggest that Thanos had reached a subadult/adult stage before death. Thanos is phylogenetically related to Brachyrostra abelisaurid. The keel on the ventral axial centrum in abelisauroids is here interpreted as a homoplastic condition that became more pronounced towards the phylogeny. The presence of well-developed keel in Thanos suggests that this taxon could be more derived than other abelisaurids. Finally, even though abelisaurids could reach large sizes, Thanos shared the environment with a larger theropod that was probably close to Megaraptora.
Mato Grosso State is the main area of paleontological investigations in central Brazil, especially regarding Upper Cretaceous beds. Fossil collection in the surroundings of the Morro do Cambambe started as early as late nineteenth century, but prospections and studies are still ongoing. This contribution presents new dinosaur specimens recovered from Upper Cretaceous outcrops of the southeastern portion of Mato Grosso State. These remains enabled the first report of a megaraptoran theropod based on a vertebral centrum and the description of abelisaurid (a fragmentary tooth) and titanosaur remains (a tooth and a fragment of a dorsal vertebra). Based on the amount of compiled reports of tetrapod remains from Mato Grosso, mainly from meeting abstracts and technical reports, the evidence at hand indicates a diverse Upper Cretaceous tetrapod assemblage still poorly explored in comparison to other Upper Cretaceous units of Brazil and Gondwana, in general.
A detailed description of the neuroanatomy of Murusraptor barrosaensis –a mid-sized non-maniraptoran theropod from the Late Cretaceous of north Patagonia – is based on the exceptionally preserved type braincase. CT scans provide new information on the braincase, brain, cranial nerves, encephalic vasculature, and inner ear of this taxon. Worldwide, relatively few non-maniraptoran theropod braincases have been described in detail and the new information reported here is important to better understand the variability of braincase characters within the clade. This study suggests that megaraptorids have a particular brain pattern that is different from those of other non-coelurosaur theropods, such as allosauroids and ceratosaurs, and different from that of some coelurosaurs, such as tyrannosaurids, although sharing more similarities with the latter. The Reptile Encephalization Quotient (REQ) of Murusraptor is within a range between those of Allosaurus and Tyrannosaurus; the Olfactory Ratio (OR) is, however, smaller than the observed in tyrannosaurids and allosauroids. The paleobiological implications on gaze stabilization, hearing, and olfaction in the Argentinean taxon are still poorly understand.
The pedal range of motion in Australovenator wintonensis is investigated to determine what influence soft tissue had on range of motion in the foot. Fortunately, the theropod pes shares a close morphology with extant large cursorial birds. Therefore, to better understand the pedal range of motion of Australovenator, the pedal range of motion of Dromaius novaehollandiae (commonly known as the emu) was analysed with and without soft tissue. We used a variety of innovative digital techniques to analyse the range of motion and biologically restore the Australovenator pes. Computed tomography scans of Dromaius pes in fully flexed and fully extended positions provided the soft tissue range of motion limits. The bone on bone range of motion of the same specimen was replicated following the removal of soft tissue. It was identified that there was an increase in range of motion potential with the removal of soft tissue. This variation provided a guide to develop the potential range of motion of a fully fleshed Australovenator pes. Additionally, the dissection of the Dromaius pes provided a guide enabling the replication of the corresponding soft tissue and keratin sheaths of the Australovenator pes. Subjects Evolutionary Studies, Paleontology
Novas, F.E., Aranciaga Rolando, A.M. and Agnolín, F.L. 2016. Phylogenetic relationships of the Cretaceous Gondwanan theropods Megaraptor and Australovenator: the evidence afforded by their manual anatomy. Memoirs of Museum Victoria 74: 49–61. General comparisons of the manual elements of megaraptorid theropods are conducted with the aim to enlarge the morphological dataset of phylogenetically useful features within Tetanurae. Distinctive features of Megaraptor are concentrated along the medial side of the manus, with metacarpal I and its corresponding digit being considerably elongated. Manual ungual of digit I is characteristically enlarged in megaraptorids, but it is also transversely compressed resulting in a sharp ventral edge. We recognize two derived characters shared by megaraptorans and coelurosaurs (i.e., proximal end of metacarpal I without a deep and wide groove continuous with the semilunar carpal, and metacarpals I and II long and slender), and one derived trait similar to derived tyrannosauroids (i.e., metacarpal III length <0.75 length of metacarpal II). However, after comparing carpal, metacarpal and phalangeal morphologies, it becomes evident that megaraptorids retained most of the manual features present in Allosaurus. Moreover, Megaraptor and Australovenator are devoid of several manual features that the basal tyrannosauroid Guanlong shares with more derived coelurosaurs (e.g., Deinonychus), thus countering our own previous hypothesis that Megaraptora is well nested within Tyrannosauroidea.
A skeleton discovered in the Upper Cretaceous Sierra Barrosa Formation (Turonian-Coniacian) of Neuquén Province, Argentina represents a new species of theropod dinosaur related to the long snouted, highly pneumatized Megaraptoridae. The holotype specimen of Murusraptor barrosaensis n.gen et n.sp. (MCF-PVPH-411) includes much of the skull, axial skeleton, pelvis and tibia. Murusraptor is unique in having several diagnostic features that include anterodorsal process of lacrimal longer than height of preorbital process, and a thick, shelf-like thickening on the lateral surface of surangular ventral to the groove between the anterior surangular foramen and the insert for the uppermost intramandibular process of the dentary. Other characteristic features of Murusraptor barrosaensis n.gen. et n. sp.include a large mandibular fenestra, distal ends of caudal neural spines laterally thickened into lateral knob-like processes, short ischia distally flattened and slightly expanded dorsoventrally. Murusraptor belongs to a Patagonian radiation of megaraptorids together with Aerosteon, Megaraptor and Orkoraptor. In spite being immature, it is a larger but more gracile animal than existing specimens of Megaraptor, and is comparable in size with Aerosteon and Orkoraptor. The controversial phylogeny of the Megaraptoridae as members of the Allosauroidea or a clade of Coelurosauria is considered analyzing two alternative data sets.
Background
Late Cretaceous terrestrial strata of the Neuquén Basin, northern Patagonia, Argentina have yielded a rich fauna of dinosaurs and other vertebrates. The diversity of saurischian dinosaurs is particularly high, especially in the late Cenomanian-early Turonian Huincul Formation, which has yielded specimens of rebacchisaurid and titanosaurian sauropods, and abelisaurid and carcharodontosaurid theropods. Continued sampling is adding to the known vertebrate diversity of this unit.
Methodology/ Principal Findings
A new, partially articulated mid-sized theropod was found in rocks from the Huincul Formation. It exhibits a unique combination of traits that distinguish it from other known theropods justifying erection of a new taxon, Gualicho shinyae gen. et sp. nov. Gualicho possesses a didactyl manus with the third digit reduced to a metacarpal splint reminiscent of tyrannosaurids, but both phylogenetic and multivariate analyses indicate that didactyly is convergent in these groups. Derived characters of the scapula, femur, and fibula supports the new theropod as the sister taxon of the nearly coeval African theropod Deltadromeus and as a neovenatorid carcharodontosaurian. A number of these features are independently present in ceratosaurs, and Gualicho exhibits an unusual mosaic of ceratosaurian and tetanuran synapomorphies distributed throughout the skeleton.
Conclusions/ Significance
Gualicho shinyae gen. et sp. nov. increases the known theropod diversity of the Huincul Formation and also represents the first likely neovenatorid from this unit. It is the most basal tetatanuran to exhibit common patterns of digit III reduction that evolved independently in a number of other tetanuran lineages. A close relationship with Deltadromaeus from the Kem Kem beds of Niger adds to the already considerable biogeographic similarity between the Huincul Formation and coeval rock units in North Africa.
Theropoda includes all the dinosaurs more closely related to birds than to sauropodomorphs (long-necked dinosaurs) and ornithischians (bird-hipped dinosaurs). The oldest members of the group are early Late Triassic in age, and non-avian theropods flourished during the rest of the Mesozoic until they vanished in the Cretaceous-Palaeogene mass extinction. Theropods radiated into two main lineages, Ceratosauria and Tetanurae, which are well represented in Cretaceous rocks from Argentina. Ceratosaurians are the most taxonomically diverse South American non-avian theropods, including small to large-sized species, such as the iconic horned dinosaur Carnotaurus. Argentinean tetanurans are represented by multiple lineages that include some of the largest carnivorous dinosaurs known worldwide (carcharodontosaurids), the enigmatic large-clawed megaraptorans, and small to medium-sized species very closely related to avialans (e.g. unenlagiids). The Argentinean non-avian theropod record has been and is crucial to understand the evolutionary and palaeobiogeographical history of the group in the southern continents during the Mesozoic. Resumen. Theropoda incluye a todos los dinosaurios más cercanamente relacionados a las aves que a los sauropodomorfos (dinosaurios de cuello largo) y ornithisquios (dinosaurios con cadera de ave). Los miembros más antiguos del grupo son del Triásico Tardío temprano, y los terópodos no-avianos florecieron durante el resto del Mesozoico hasta su desaparición en la extinción masiva del Cretácico-Paleógeno. Los terópodos radiaron en dos linajes principales, Ceratosauria y Tetanurae, los cuales están bien representados en las rocas cretácicas de Argentina. Los ceratosaurios son los terópodos no-avianos taxonómicamente más diversos de América del Sur, incluyendo especies de pequeño a gran tamaño, tales como el icónico dinosaurio con cuernos Carnotaurus. Los tetanuros argentinos están representados por múltiples linajes que incluyen a algunos de los dinosaurios carnívoros más grandes conocidos a nivel mundial (carcharodontosáuridos), los enigmáticos megaraptores y especies de pequeño a mediano tamaño muy cercanamente relacionadas a las aves (e.g. unenlágiidos). El registro de terópodos no-avianos argentinos ha sido y es crucial para entender la historia evolutiva y paleobiogeográfica del grupo en los continentes del sur durante el Mesozoico.
The present contribution describes theropod remains coming from the Huincul Formation (Neuquén Group; Cenomanian-Turonian; Upper Cretaceous) at a single locality located in northwestern Río Negro province, Patagonia, Argentina. This theropod association is composed of abelisauroids, two different-sized carcharodontosaurid allosauroids, a coelurosaur of uncertain relationships, a megaraptoran tyrannosauroid, and a possible unenlagiid paravian. Two new theropod genera and species are here described. The new carcharodontosaurid is based on an isolated postorbital bone bearing a unique prominence above the orbital brow. The new megaraptoran of uncertain affinities is described on the basis of a partially articulated tail and sacral vertebra. A new taxon is characterized by having notably elongate and highly pneumatic sacral and caudal vertebrae. It shows a large number of similarities with the African taxa Deltadromeus and Baharisaurus. These genera probably constitute a still poorly known clade of megaraptoran tyrannosauroids different from the Megaraptoridae. These findings support that Patagonia is a key place for understanding theropod evolution in Gondwana.
The Chubut Group, central Patagonia, Argentina, is characterized by a lacustrine and fluvial-lacustrine system with variable participation of volcanic ash. This group includes the Bajo Barreal Formation (Cenomanian-Turonian) and a recently nested new lithostratigraphic unit, the Lago Colhue Huapi Formation (Coniacian-Maastrichtian). The Lago Colhue Huapi Formation overlies the Bajo Barreal Formation. These sedimentary units preserve a rich and diverse vertebrate fossil record including, among others, representatives of Crocodylomorpha, Testudines, Pterosauria and abundant Dinosauria. Nevertheless, the stratigraphic position of several of its taxa has been historically controversial. The unclear stratigraphic provenance of these taxa difficults the correct interpretation of the relationships with other Patagonian and South American basins. In this context, we present a detailed stratigraphic study to clarify the position of the vertebrate fossils of both Late Cretaceous formations. We also discuss the implications of this faunistic arrangement in terms of vertebrate evolution and paleobiogeography. Finally, this study broadens our knowledge on the fossil fauna of these units and therefore the vertebrate assemblages of central Patagonia.
Megaraptorid theropods were an enigmatic group of medium-sized predatory dinosaurs, infamous for the hypertrophied claw on the first manual digit. Megaraptorid dentition is largely restricted to isolated teeth found in association with skeletal parts; however, the
in situ
maxillary dentition of
Megaraptor
was recently described. A newly discovered right dentary pertaining to the
Australovenator
holotype preserves
in situ
dentition, permitting unambiguous characterisation of the dentary tooth morphology. The new jaw is virtually complete, with an overall elongate, shallow profile, and fifteen visible
in situ
teeth at varying stages of eruption.
In situ
teeth confirm
Australovenator
exhibited modest pseudoheterodonty, recurved lateral teeth with a serrate distal carina and reduced mesial carina, similar to other megaraptorids.
Australovenator
also combines of figure-of-eight basal cross-section with a lanceolate shape due to the presence of labial and lingual depressions and the lingual twist of the distal carina. Computed tomography and three-dimensional imagery provided superior characterisation of the dentary morphology and enabled an accurate reconstruction to a pre-fossilised state. The newly established dental morphology also afforded re-evaluation of isolated theropod teeth discovered at the
Australovenator
holotype locality and from several additional Winton Formation localities. The isolated Winton teeth are qualitatively and quantitatively similar to the
in situ
dentary teeth of
Australovenator
, but are also morphometrically similar to Abelisauridae, Allosauridae, Coelophysoidea, Megalosauridae and basal Tyrannosauroidea. Qualitative characters, however, clearly distinguish the teeth of
Australovenator
and the isolated Winton teeth from all other theropods. Evidence from teeth suggests megaraptorids were the dominant predators in the Winton Formation, which contrasts with other penecontemporaneous Gondwanan ecosystems.
The hypertrophied manual claws and modified manus of megaraptoran theropods represent an unusual morphological adaptation among carnivorous dinosaurs. The skeleton of Australovenator wintonensis from the Cenomanian of Australia is among the most complete of any megaraptorid. It presents the opportunity to examine the range of motion of its forearm and the function of its highly modified manus. This provides the basis for behavioural inferences, and comparison with other Gondwanan theropod groups. Digital models created from computed tomography scans of the holotype reveal a humerus range of motion that is much greater than Allosaurus, Acrocanthosaurus, Tyrannosaurus but similar to that of the dromaeosaurid Bambiraptor. During flexion, the radius was forced distally by the radial condyle of the humerus. This movement is here suggested as a mechanism that forced a medial movement of the wrist. The antebrachium possessed a range of motion that was close to dromaeosaurids; however, the unguals were capable of hyper-extension, in particular manual phalanx I-2, which is a primitive range of motion characteristic seen in allosaurids and Dilophosaurus. During flexion, digits I and II slightly converge and diverge when extended which is accentuated by hyperextension of the digits in particular the unguals. We envision that prey was dispatched by its hands and feet with manual phalanx I-2 playing a dominant role. The range of motion analysis neither confirms nor refutes current phylogenetic hypotheses with regards to the placement of Megaraptoridae; however, we note Australovenator possessed, not only a similar forearm range of motion to some maniraptorans and basal coelurosaurs, but also similarities with Tetanurans (Allosauroids and Dilophosaurus).
Megaraptoridae comprises a clade of enigmatic Gondwanan theropods with characteristic hypertrophied claws on the first and second manual digits. The majority of megaraptorids are known from South America, although a single genus (Australovenator) plus additional indeterminate material is also known from Australia. This clade has a controversial placement among theropods, and recently has been interpreted alternatively as a carcharodontosaurian or a tyrannosauroid lineage. We describe new fragmentary but associated postcranial remains from the opal fields of Lightning Ridge (middle-Albian, Griman Creek Formation) in north-central New South Wales. The new unnamed taxon exhibits a number of unusual features that suggest the presence of a hitherto unrecognized Australian megaraptorid. From an Australian perspective, the Lightning Ridge taxon predates Australovenator by c.10Ma and is minimally coeval with megaraptoran material reported from the Eumeralla Formation of Victoria (but potentially 6.1–9.5 Ma younger). It is also notable as the largest predatory dinosaur yet identified from Australia and is only the second theropod known from more than a single element. A Bayesian phylogenetic approach integrating morphological, stratigraphic and palaeogeographic information tested both the carcharodontosaurian and tyrannosauroid placements for Megaraptora. Regardless of the preferred placement among Tetanurae, rigorous palaeobiogeographic analyses support an Asian origin of Megaraptora in the latest Jurassic (about 150-135 Ma), an Early Cretaceous (about 130-121 Ma) divergence of the Gondwanan lineage leading to Megaraptoridae, and an Australian root for megaraptorid radiation. These results indicate that Australia’s Cretaceous dinosaur fauna did not comprise simply of immigrant taxa but was a source for complex two-way interchange between Australia-Antarctica-South America leading to the evolution of at least one group of apex predatory dinosaurs in Gondwana.
The theropod clade Carcharodontosauridae is a broadly distributed group of large allosauroid theropods. The carcharodontosaurids recorded in the Albian– Cenomanian of Gondwana are the youngest and most derived members of this clade. Tyrannotitan chubutensis, from the Cerro Castaño Member of Cerro Barcino Formation (Albian; Chubut Group), Central Patagonia, Argentina, is of prime interest among Gondwanan carcharodontosaurids as it represents the oldest record of the group. Here we offer a detailed osteological comparative description of the holotype and paratype of Tyrannotitan chubutensis together with a new diagnosis of the species. The new information results in a better understanding of this taxon and Carcharodontosauridae. Furthermore, a comparative study of the anatomy of the pectoral girdle of Giganotosaurus is reinterpreted as very similar to that of Tyrannotitan and Mapusaurus. We also present a phylogenetic analysis of Carcharodontosauridae that recovers Tyrannotitan as a derived carcharodontosaurid, being the sister group of the clade formed by Giganotosaurus and Mapusaurus, all nested in the clade Giganotosaurini.
Non-avian theropod dinosaurs attained large body sizes, monopolising terrestrial apex predator niches in the Jurassic-Cretaceous. From the Middle Jurassic onwards, Allosauroidea and Megalosauroidea comprised almost all large-bodied predators for 85 million years. Despite their enormous success, however, they are usually considered absent from terminal Cretaceous ecosystems, replaced by tyrannosaurids and abelisaurids. We demonstrate that the problematic allosauroids Aerosteon, Australovenator, Fukuiraptor and Neovenator form a previously unrecognised but ecologically diverse and globally distributed clade (Neovenatoridae, new clade) with the hitherto enigmatic theropods Chilantaisaurus, Megaraptor and the Maastrichtian Orkoraptor. This refutes the notion that allosauroid extinction pre-dated the end of the Mesozoic. Neovenatoridae includes a derived group (Megaraptora, new clade) that developed long, raptorial forelimbs, cursorial hind limbs, appendicular pneumaticity and small size, features acquired convergently in bird-line theropods. Neovenatorids thus occupied a 14-fold adult size range from 175 kg (Fukuiraptor) to approximately 2,500 kg (Chilantaisaurus). Recognition of this major allosauroid radiation has implications for Gondwanan paleobiogeography: The distribution of early Cretaceous allosauroids does not strongly support the vicariant hypothesis of southern dinosaur evolution or any particular continental breakup sequence or dispersal scenario. Instead, clades were nearly cosmopolitan in their early history, and later distributions are explained by sampling failure or local extinction.
Living birds possess a unique heterogeneous pulmonary system composed of a rigid, dorsally-anchored lung and several compliant air sacs that operate as bellows, driving inspired air through the lung. Evidence from the fossil record for the origin and evolution of this system is extremely limited, because lungs do not fossilize and because the bellow-like air sacs in living birds only rarely penetrate (pneumatize) skeletal bone and thus leave a record of their presence.
We describe a new predatory dinosaur from Upper Cretaceous rocks in Argentina, Aerosteon riocoloradensis gen. et sp. nov., that exhibits extreme pneumatization of skeletal bone, including pneumatic hollowing of the furcula and ilium. In living birds, these two bones are pneumatized by diverticulae of air sacs (clavicular, abdominal) that are involved in pulmonary ventilation. We also describe several pneumatized gastralia ("stomach ribs"), which suggest that diverticulae of the air sac system were present in surface tissues of the thorax.
We present a four-phase model for the evolution of avian air sacs and costosternal-driven lung ventilation based on the known fossil record of theropod dinosaurs and osteological correlates in extant birds: (1) Phase I-Elaboration of paraxial cervical air sacs in basal theropods no later than the earliest Late Triassic. (2) Phase II-Differentiation of avian ventilatory air sacs, including both cranial (clavicular air sac) and caudal (abdominal air sac) divisions, in basal tetanurans during the Jurassic. A heterogeneous respiratory tract with compliant air sacs, in turn, suggests the presence of rigid, dorsally attached lungs with flow-through ventilation. (3) Phase III-Evolution of a primitive costosternal pump in maniraptoriform theropods before the close of the Jurassic. (4) Phase IV-Evolution of an advanced costosternal pump in maniraptoran theropods before the close of the Jurassic. In addition, we conclude: (5) The advent of avian unidirectional lung ventilation is not possible to pinpoint, as osteological correlates have yet to be identified for uni- or bidirectional lung ventilation. (6) The origin and evolution of avian air sacs may have been driven by one or more of the following three factors: flow-through lung ventilation, locomotory balance, and/or thermal regulation.
We describe adaptations for a semiaquatic lifestyle in the dinosaur Spinosaurus aegyptiacus. These adaptations include retraction of the fleshy nostrils to a position near the mid-region of the skull and an elongate
neck and trunk that shift the center of body mass anterior to the knee joint. Unlike terrestrial theropods, the pelvic girdle
is downsized, the hindlimbs are short, and all of the limb bones are solid without an open medullary cavity, for buoyancy
control in water. The short, robust femur with hypertrophied flexor attachment and the low, flat-bottomed pedal claws are
consistent with aquatic foot-propelled locomotion. Surface striations and bone microstructure suggest that the dorsal “sail”
may have been enveloped in skin that functioned primarily for display on land and in water.
Patagonia has yielded the most comprehensive fossil record of Cretaceous theropods from Gondwana, consisting of 31 nominal species belonging to singleton taxa and six families: Abelisauridae, Noasauridae, Carcharodontosauridae, Megaraptoridae nov. fam., Alvarezsauridae, and Unenlagiidae. They provide anatomical information that allows improved interpretation of theropods discovered in other regions of Gondwana. Abelisauroids are the best represented theropods in Patagonia. They underwent an evolutionary radiation documented from the Early Cretaceous through to the latest Cretaceous, and are represented by the clades Abelisauridae and Noasauridae. Patagonian carcharodontosaurids are known from three taxa (Tyrannotitan, Giganotosaurus and Mapusaurus), as well as from isolated teeth, collected from Aptian to Cenomanian beds. These allosauroids constituted the top predators during the mid-Cretaceous, during which gigantic titanosaur sauropods were the largest herbivores. Megaraptorans have become better documented in recent years with the discovery of more complete remains. Megaraptor, Aerosteon and Orkoraptor have been described from Cretaceous beds from Argentina, and these taxa exhibit close relationships with the Aptian genera Australovenator, from Australia, and Fukuiraptor, from Japan. The Gondwanan megaraptorans are gathered into the new family Megaraptoridae, and the Asiatic Fukuiraptor is recovered as the immediate sister taxon of this clade. Although megaraptorans have been recently interpreted as members of Allosauroidea, we present evidence that they are deeply nested within Coelurosauria. Moreover, anatomical information supports Megaraptora as more closely related to the Asiamerican Tyrannosauridae than thought. Megaraptorans improve our knowledge about the scarcely documented basal radiation of Gondwanan coelurosaurs and tyrannosauroids as a whole. Information at hand indicates that South America was a cradle for the evolutionary radiation for different coelurosaurian lineages, including some basal forms (e.g., Bicentenaria, Aniksosaurus), megaraptorans, alvarezsaurids less derived than those of Laurasia, and unenlagiids, revealing that Gondwanan coelurosaurs played sharply differing ecological roles, and that they were taxonomically as diverse as in the northern continents. The unenlagiids represent an endemic South American clade that has been recently found to be more closely related to birds than to dromaeosaurid theropods. Analysis of the theropod fossil record from Gondwana shows the highest peak of origination index occurred during the Aptian–Albian and a less intense one in the Campanian time spans. Additionally, peaks of extinction index are recognized for the Cenomanian and Turonian–Coniacian time spans. In comparison, the Laurasian pattern differs from that of Gondwana in the presence of an older extinction event during the Aptian–Albian time-span and a high origination rate during the Cenomanian time-bin. Both Laurasian and Gondwanan theropod records show a peak of origination rates during the Campanian.
Allosauroid theropods were a diverse and widespread radiation of Jurassic-Cretaceous megapredators. Achieving some of the largest body sizes among theropod dinosaurs, these colossal hunters dominated terrestrial ecosystems until a faunal turnover redefined apex predator guild occupancy during the final 20 million years of the Cretaceous. Here we describe a giant new species of allosauroid - Siats meekerorum gen. et sp. nov. - providing the first evidence for the cosmopolitan clade Neovenatoridae in North America. Siats is the youngest allosauroid yet discovered from the continent and demonstrates that the clade endured there into the Late Cretaceous. The discovery provides new evidence for ecologic sympatry of large allosauroids and small-bodied tyrannosauroids. These data support the hypothesis that extinction of Allosauroidea in terrestrial ecosystems of North America permitted ecological release of tyrannosauroids, which went on to dominate end-Cretaceous food webs.
The Cretaceous terrestrial strata of the Neuquén Basin (northern Patagonia, Argentina) are described together with their tetrapod records. Six local tetrapod assemblages are identified: Amargan (Barremian–Early Aptian), Lohancuran (Late Aptian–Albian), Limayan (Cenomanian–Early Turonian), Neuquenian (Late Turonian–Coniacian), Coloradoan (Santonian–Early Campanian) and Allenian [Late Campanian–Early Maastrichtian (= Alamitense = Alamitian SALMA)]. The last of these includes records from north-eastern Patagonia.