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Elemgasem nubilus: a new brachyrostran abelisaurid (Theropoda, Ceratosauria) from the Portezuelo Formation (Upper Cretaceous) of Patagonia, Argentina

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Abstract

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.

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... In particular, the stratigraphic record of abelisaurids encompasses all Patagonian Upper Cretaceous basins in which continental rocks are preserved (e.g., Neuquén Basin, Somuncura-Cañadón Asfalto Basin, Golfo San Jorge Basin, and Austral Basin). The knowledge of this family of theropods concerning their anatomy, evolutionary history, and phylogenetic relationships has increased notably in recent decades, with the Patagonian records providing the most novel information due to the abundance and diversity of the group to date (e.g., Bonaparte, 1985;Bonaparte & Novas, 1985;Bonaparte et al., 1990;Coria & Salgado, 1998;Coria et al., 2002;Calvo et al., 2004;Canale et al., 2009;Novas et al., 2013;Gianechini et al., 2015Gianechini et al., , 2021Filippi et al., 2016Filippi et al., , 2018bMéndez et al., 2018Méndez et al., , 2022Cerroni & Paulina-Carabajal, 2019;Cerroni et al., 2020;Aranciaga-Rolando et al., 2021;Baiano et al., , 2022. ...
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Apart from marsupials and edentates, there is no order of mammals, living or fossil, which displays a greater diversity of locomotor and postural adaptations than extant primates. With body weight varying from about 100 grams to 200 kilograms, the Order Primates includes leapers, climbers, brachiators, knuckle-walkers and a variety of arboreal and terrestrial quadrupeds. Despite the interest which primate positional behaviour has engendered in anatomists, anthropologists and zoologists throughout this century, we still understand very little about the relationships between locomotor and postural behaviour on the one hand, and basic aspects of these animals’ biology, such as gross diet and use of forest structure on the other.
Article
Although osteohistology has proven to be useful to discern several palaeobiological traits and systematics in non-avian dinosaurs, the bone microstructure of several groups (e.g., abelisaurid theropods) is still poorly documented. Here, we provide a microstructural description of different bones (a cervical epipophysis, three dorsal ribs, three grastralia, and the left femur) of the type specimen of the abelisaurid Aucasaurus garridoi, its ontogenetic stage and compare its growth with other theropods, especially abelisauroid taxa. The cortical bone is mostly composed by fibrolamellar bone tissue composed of a woven-fibred matrix. Secondary remodelling varies among the different elements. The compacta of the rib shows eleven growth marks (with an additional seven in the external fundamental system), implying that the specimen was at least eleven years old and had reached somatic maturity when it died. The presence of lines of arrested growth/annuli supports a cyclical growth strategy, as in Niebla, Quilmesaurus, and Abelisauridae indet. MMCh-PV 69. All these abelisaurids indicate that the maturity based on cyclical growth marks spacing is not reliable, due to considerable variability of this parameter within a single element. This study represents the first intensive osteohistological investigation for an Abelisauridae member, providing new information on palaeobiological traits of this clade.
Preprint
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.
Article
The record of unenlagiines in Brazil, except for one dorsal vertebra, is still under debate based on isolated teeth. Here, we describe Ypupiara lopai gen. et sp. nov., the first dromaeosaurid species from Brazil, from the Maastrichtian of the Bauru Group, Paraná Basin. The specimen consists of a partial right maxilla (with three teeth in loci) and a right dentary. Ypupiara is characterized by a restricted number of neurovascular foramina on the lateral surface of the maxilla, a rectangular and anteroposteriorly expanded interdental plate, and a labiolingual compression of the teeth, which have a labiolingual diameter more than 3/5 of the rostrocaudal diameter. Our phylogenetic analysis recovers Ypupiara as an unenlagiine based on the fluted teeth and places it as the sister taxon of Austroraptor due to the ratio of the labiolingual and mesiodistal diameters of the teeth being more than 3/5. We also erect the new group Unenlagiinia, which includes Unenlagiinae and Halszkaraptorinae. Ypupiara nests within Unenlagiinia based on the widely spaced teeth and the lack of mesial and distal carinae in the maxillary teeth. The morphology of the teeth is similar to Buitreraptor, although the proportions are markedly distinct. The teeth and comparisons with other Unenlagiinia also support fish being part of the diet for Ypupiara. We also performed a parsimony analysis of endemicity, which suggested that the presence of unenlagiines in Brazilian Upper Cretaceous outcrops is explained by dispersion or extinction events. The new species provides new information on the evolution of Gondwanan dromaeosaurids, and its preserved teeth provide new data to enable the assignment of isolated dromaeosaurid teeth from the Bauru Group.
Article
In the Neuquén Basin, the Portezuelo Formation (Turonian-Coniacian, Upper Cretaceous) is represented by extended fluvial outcrops that are well-known for yielding an abundant and diversified vertebrate fossil record. However, most of the sauropod fossil record is represented by incomplete specimens, and only two taxa are formally described for the upper Turonian–lower Santonian of the Neuquén Basin: Malarguesaurus and Futalognkosaurus. In this contribution we report new sauropod specimens composed of partially associated axial and appendicular elements coming from the upper section of the Portezuelo Formation of the Los Bastos locality, in the southern Neuquén Basin. The bones show a set of morphological features that allow us to refer them to a titanosaur sauropod: a “cone-chisel-like” tooth, procoelic caudal vertebrae, a dorsally expanded ulna olecranon, and a femur with a prominent lateral bulge and an elliptical diaphysis in cross-section. The phylogenetic analysis recovers the sauropod remains as an unstable colossosaurian within Titanosauria, an effect likely attributable to the incomplete condition of the specimens. Nevertheless, osteological and phylogenetic analyses, together with morphological comparisons with the sauropod fossil record of the Portezuelo Formation, suggest that the new specimens represent a titanosaur different to previously known taxa. Pending better preserved and more complete remains from Los Bastos, the new evidence allows us to improve our knowledge of sauropod diversity during the upper Turonian–lower Santonian, at least in the southern Neuquén Basin.
Article
Abelisauridae is a theropod clade with a wide distribution in the Late Cretaceous of Gondwana. Some of the best preserved abelisaurid specimens were recovered from Patagonia (Argentina) such as Skorpiovenator, Ilokelesia, Carnotaurus and Aucasaurus. Here we describe a dorsal part of a neural spine; a middle caudal vertebra; a distal part of a left metatarsal IV; a complete right phalanx IV-1; left phalanges IV-1, 2 and 3; and a pedal ungual phalanx. These materials were recovered from the same quarry of a recently published indeterminate abelisaurid specimen (MPCN-PV-69). The most distinctive characters are a triangular shape of the distal end of metatarsal IV (present in other abelisauroids); phalanx IV-1 with the proximal surface dorsoventrally tall and the ventral surface wider than the dorsal one causing a medial tilting of bone (set of features considered autapomorphic in Velocisaurus, although is also present in different abelisaurids); phalanx IV-1 and 2 with a ridge which spans from the proximodorsal projection, splits in two branch and surrounds a laterally displaced and obliquely oriented oval hyperextensor pit; a pedal ungual phalanx with two medial and lateral vascular grooves, and lacking a flexor tubercle (abelisauroids synapomorphies). The mentioned feature of phalanges IV-1 and 2 is only found among abelisaurids and is here considered as a possible new synapomorphy of Abelisauridae. Thus, besides they constitute new abelisaurid remains from Patagonia, the new materials provide valuable morphological data that could expand the diagnosis of Abelisauridae.
Article
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.
Article
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.
Article
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.
Article
Abelisaurid theropods are well known in Cretaceous beds along South America, particularly Patagonia. However, the record of latest Cretaceous abelisauroids is still far from satisfactory. Until recently, few taxa were described from Maastrichtian beds: Carnotaurus sastrei and Quilmesaurus curriei, but also perhaps Abelisaurus comahuensis. In this contribution, we describe a new genus and species (Niebla antiqua gen. et sp. nov.), of medium-sized abelisaurid coming from Late Cretaceous (Maastrichtian) beds from Río Negro province, northern Patagonia, Argentina. The paleohistological analysis shows that this individual has reached the somatical maturity and that it represents an adult of a mid-sized abelisaurid. The specimen is represented by a nearly complete braincase, fragmentary jaw and teeth, relatively complete scapulocoracoid, dorsal ribs and incomplete vertebrae. The new taxon is relatively small, much smaller than other coeval abelisaurids such as Carnotaurus and Abelisaurus. The braincase shows autapomorphic features such a dorsoventrally tall basal tuber and postemporal foramen enclosed by parietal and exoccipitals. The scapulocoracoid is notably similar to that of Carnotaurus in having a posterodorsally oriented glenoid, a dorsoventrally expanded and wide coraco-scapular plate, and a very narrow and straight scapular blade. These features are very different from those of other abelisaurids, which may indicate a unique conformation of the pectoral girdle among these South American theropods.
Article
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.
Article
A new ceratosaurian theropod dinosaur, Huinculsaurus montesi gen. et sp. nov., is described here. This taxon is based on the last three dorsal vertebrae and the first and second sacral vertebrae found in association at Aguada Grande, Neuquén Province, Argentina. Although fragmentary, Huinculsaurus shows a unique mix of features which differentiates it from all other theropods, including the sympatric abelisaurid Ilokelesia, and is diagnosed by prezygapophyseal articular facets twice longer than wide, anterior centroparapophyseal lamina strongly developed as an extensive lateral lamina in the posterior dorsal vertebrae, pneumatic foramina located ventrally to the postzygodiapophyseal lamina in the posterior dorsal vertebrae, posteriorly tapering postzygapophysis pointed posteriorly, and an accessory lamina bisecting the parapophyseal centrodiapophyseal fossa in the posterior dorsal neural arches. Phylogenetic analyses recovered Huinculsaurus as most closely related to the Late Jurassic Elaphrosaurus than to other Cretaceous abelisauroids, suggesting the persistence of the elaphrosaurine lineage in South America up to the early Late Cretaceous.
Article
A new carcharodontosaurid taxon, Lajasvenator ascheriae gen. et sp. nov. is described. The new taxon is based on two specimens: MLL-PV-Pv-005 is a partial skeleton represented by a portion of the snout, partially articulated presacral vertebral series, four articulated caudal vertebra and fragments of the pelvic girdle; MLL-PV-Pv-007 includes the anterior ends of both dentaries, a quadratojugal, and fragments of cervical vertebrae, ribs and a possible tarsal bone. Lajasvenator is unique in having anterior projections on cervical prezygapophyses, lip-like crests on the lateral surfaces of cervical postzygapophyses, and bilobed anterior processes on cervical ribs. Lajasvenator material was collected from the terrestrial sandstones of the Valanginian Mulichinco Formation. It is the oldest carcharodontosaurid record from South America. This medium sized theropod was found associated with remains of the dicraeosaurid sauropod Pilmatueia, indeterminate diplodocid remains, and a yet unidentified iguanodontian-like ornithopod.
Article
The Cretaceous Cerro Barcino Formation (Chubut Group) of Central Patagonia, Argentina has yielded a remarkable fossil vertebrate fauna, which form important components of the South American “mid-Cretaceous” fauna, including titanosauriform sauropod dinosaurs, theropod dinosaurs, crocodyliforms, turtles, and lepidosauromorphs. However, a lack of robust chronostratigraphic framework for its fossil occurrences has so far hampered a full realization of their paleobiologic significance. This contribution presents new stratigraphic, sedimentologic, and U-Pb isotopic age data from 11 localities throughout the Patagonian Somuncurá-Canadón Asfalto Basin and analyzes the evolutionary characteristics of the Cerro Barcino fauna within the biostratigraphic context of the Cretaceous of Gondwana. Four new high-precision ²⁰⁶Pb/²³⁸U zircon dates by the CA-ID-TIMS method range from 118.497 ± 0.063 Ma to 98.466 ± 0.048 Ma (2σ internal errors) and limits the Puesto La Paloma, Cerro Castaño and Las Plumas members of the Cerro Barcino Formation largely to the Aptian, Albian and Cenomanian stages of the Cretaceous, respectively. Accordingly, the majority of the Cerro Barcino vertebrates fall within a ~118–110 Ma time interval in the latest Early Cretaceous, which makes them the oldest documented component of the “mid-Cretaceous” faunal assemblage of Gondwana. Paleobiologic analyses of the latter assemblage suggests a ~10 m.y. period of faunistic stability characterized by only minor evolutionary novelties or faunal turnovers.
Article
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.
Article
Neotheropoda includes the vast majority of the predatory dinosaurs and their oldest members are Late Triassic in age. The Triassic neotheropod record is restricted to North America and Europe with the exception of a few specimens from South America, which includes Zupaysaurus rougieri and Lucianovenator bonoi. Here, the South American record of the group is enriched with the description of the new genus and species Powellvenator podocitus from the middle Norian Los Colorados Formation (Ischigualasto-Villa Unión Basin) of northwestern Argentina. The new taxa are represented by previously undescribed partial hindlimbs collected by J. F. Bonaparte and associated to the hypodigm of the pseudosuchian Riojasuchus tenuisceps. In addition, a specimen originally interpreted by Bonaparte in 1972 as an indeterminate coelurosaur is here referred to the new species. Powellvenator podocitus differs from other basal dinosaurs in character-states that include an astragalus with a distinctly sigmoid posterodorsal margin and a rounded dorsal expansion on the anteromedial portion of the astragalar body in anterior view, calcaneum with a laterally projected flange, and strongly reduced shaft of metatarsal II. The phylogenetic relationships of the new species were tested in a comprehensive analyses focused on early neotheropods, which recovered Powellvenator podocitus within Coelophysoidea and as the sister-taxon of Procompsognathus triassicus and Coelophysinae. Powellvenator podocitus represents the first coelophysoid from South America together with Lucianovenator bonoi from the Marayes-El Carrizal Basin. © 2017 Asociacion Paleontologica Argentina. All Rights Reserved.
Article
Several remains of an abelisaurid theropod including a nearly complete sacral complex articulated with both ilia, the distal boot of the pubes, the furcula, teeth, and fragments of transverse processes of caudal vertebrae was discovered in the La Invernada fossil site, northern Patagonia from the Bajo de la Carpa Formation (Santonian). The sacrum exhibit features typical of abelisauroids as narrowing of the middle sacral centra, fused neural spines forming a continuous sheet and ventral bow of the sacrum, in lateral view. The furcula represents de first mention of this bone for a South American abelisaurid. The morphology observed in the transverse processes with distal end projected forward and sagittal ridge on the ventral surface allows its taxonomic assignment to the clade Brachyrostra.
Article
Carcharodontosauridae and Abelisauridae are two coexisting clades of theropod dinosaurs from the Cretaceous of Africa, South America and possibly Europe. The oldest and most recent carcharodontosaurid remains are from the Kimmeridgian-Tithonian of Africa and Turonian of South America, respectively. Recently, a fragmented maxilla bearing a single in-situ tooth (UFRJ-DG409-R) from the Maastrichtian of Brazil has been interpreted as belonging to a carcharodontosaurid. We here reassessed the phylogenetic distribution of these material using morphological, morphometric and phylogenetic analyses. If the morphology of the tooth is shared with carcharodontosaurids and abelisaurids, the morphometric analyses found the crown in the same morphospace as abelisaurids, and the phylogenetic analysis performed on a dentition-based datamatrix retrieved it among Abelisauridae. The maxilla also shares features with both groups, yet the horizontal striations on the paradental plates of UFRJ-DG409-R support abelisaurid affinities. Our data strongly suggest that these specimens belong to abelisaurid theropods, supporting the fact that carcharodontosaurids were likely extinct from Coniacian.
Article
Abelisaurid theropods were most abundant in the Gondwana during the Cretaceous Period. Pycnonemosaurus nevesi was the first abelisaurid dinosaur described from the Bauru Group (Brazil, Upper Cretaceous). Nevertheless, its initial description was based on the comparison of a restricted number of remains with other abelisaurids. In this paper, I present a new description of the morphology of Pycnonemosaurus nevesi, including three new caudal transverse processes and a discussion of several new characteristics based on perspectives derived from recently described abelisauroids. Pycnonemosaurus nevesi differs from other abelisaurids based on the following features: a pubis with a small rounded foot and a ventrally-bowed anterior distal end; posterior caudal vertebrae with a hook-shaped transverse process that has an anterodistal expansion that is short and bowed; a strong and massive tibia with a well-developed lateral malleolus that is ventrally expanded. The unfused sutures represent signs of skeletal immaturity, but the specific ontogenetic stage is still uncertain. The current phylogenetic analysis suggests strongly relationship within Pycnonemosaurus and the most-derived abelisaurids (e.g Carnotaurus and Aucasaurus).
Article
Ontogenetic variation is documented within many dinosaur species, but extreme ontogenetic changes are rare among dinosaurs, particularly among theropods. Here, we analyze 19 specimens of the Jurassic ceratosaurian theropod Limusaurus inextricabilis, representing six ontogenetic stages based on body size and histological data. Among 78 ontogenetic changes we identify in these specimens, the most unexpected one is the change from fully toothed jaws in the hatchling and juvenile individuals to a completely toothless beaked jaw in the more mature individuals, representing the first fossil record of ontogenetic edentulism among the jawed vertebrates. Jaw morphological data, including those derived from Mi-CT and SR-μCT scanning of Limusaurus specimens, reveal dental alveolar vestiges and indicate that ontogenetic tooth loss in Limusaurus is a gradual, complex process. Our discovery has significant implications for understanding the evolution of the beak, an important feeding structure present in several tetrapod clades, including modern birds. This radical morphological change suggests a dietary shift, probably from omnivory for juvenile Limusaurus to herbivory for adult Limusaurus, which is also supported by additional evidence from gastroliths and stable isotopes. Incorporating new ontogenetic information from Limusaurus into phylogenetic analyses demonstrates surprisingly little effect on its placement when data from different stages are used exclusively, in contrast to previous analyses of tyrannosaurids, but produces subtle differences extending beyond the placement of Limusaurus.
Article
Here, we describe new theropod materials (several isolated teeth, an axis, two caudal centra and a proximal left tibia) from the type locality of the Bajada Colorada Formation (Lower Cretaceous, Berriasian–Valanginian). Although fragmentary, the recovered material shows a diverse association of meat-eating dinosaurs for this poorly understood period of time. Three techniques were used to assess the phylogenetic position of the isolated teeth: multivariate (PCA), discriminant and phylogenetic analyses. The morphotypes 1, 2 and 3 (small non-recurved isolated crowns) were regarded as Theropoda indet., as our analyses failed to support a more precise classification. Two large almost complete ziphodont crowns, considered morphotype 4, were identified as belonging to megalosaurid tetanurans by phylogenetic, discriminant and multivariate analyses, thus likely representing the first record of this ancient family in South America, and the youngest worldwide. We refer the axis to a small abelisauroid ceratosaurian based on the following suite of characters; long and pointed epipophyses, a pneumatic foramen in the centrum, the invaginated spinopostzygapophyseal lamina, and the anteroposteriorly long, dorsally convex, and dorsally/posteriorly unexpanded neural spine. The caudal centra can be referred to a theropod, and tentatively to Abelisauroidea, suggesting that they may belong to the same taxon than that represented by the axis. The tibia lacks the incisura tibialis, presents a low, sharp and proximally positioned fibular crest, and has a deep lateral fossa, which is limited dorsally by a coarse, rounded in section and anteriorly directed crest. This combination of features allows to refer it to a large abelisaurid. The Bajada Colorada dinosaur record includes so far a small abelisauroid, a large abelisaurid, a probably medium to large megalosaurid tetanuran, diplodocid and dicraeosaurid sauropods. It shows some similarities with Middle and Upper Jurassic units in central Patagonia, Africa and Portugal, suggesting that no significant dinosaur faunal turnover took place through the Jurassic-Cretaceous event in the southern part of South America.
Article
The chelonian fauna of the Portezuelo Formation (Turonian-Coniacian), outcropping at Sierra del Portezuelo (Neuquén province, Argentina), is reported. Two new taxa of pleurodiran turtles are described. One of them is Prochelidella portezuelae new species, a short-necked chelid closely related to extinct species of the Lohan Cura (Albian), Candeleros (Cenomanian), and Bajo Barreal (Turonian) formations from northwestern and central Patagonia, and to the extant species of the genus Acanthochelys . The other is Portezueloemys patagonica new genus and species, a member of the epifamily Podocnemidoidea, and is considered the sister group of the family Podocnemididae. This discovery confirms the coexistence in northwestern Patagonia of a north gondwanan component (Pelomedusoides) and a south gondwanan element (Chelidae) during the Turonian-Coniacian.
Article
Version 1.5 of the computer program TNT completely integrates landmark data into phylogenetic analysis. Landmark data consist of coordinates (in two or three dimensions) for the terminal taxa; TNT reconstructs shapes for the internal nodes such that the difference between ancestor and descendant shapes for all tree branches sums up to a minimum; this sum is used as tree score. Landmark data can be analysed alone or in combination with standard characters; all the applicable commands and options in TNT can be used transparently after reading a landmark data set. The program continues implementing all the types of analyses in former versions, including discrete and continuous characters (which can now be read at any scale, and automatically rescaled by TNT). Using algorithms described in this paper, searches for landmark data can be made tens to hundreds of times faster than it was possible before (from T to 3T times faster, where T is the number of taxa), thus making phylogenetic analysis of landmarks feasible even on standard personal computers.
Article
Theropod dinosaurs from the Late Jurassic of Gondwana are still poorly known, with Elaphrosaurus bambergi Janensch, 1920, from the late Kimmeridgian of Tendaguru, Tanzania, being the only taxon represented by more than isolated remains from Africa. Having long been considered a coelurosaurian, more specifically an ornithomimosaur, Elaphrosaurus is currently regarded as a basal ceratosaur. Here, we revise the osteology and phylogenetic position of this important taxon. Elaphrosaurus shows many unusual osteological characters, including extremely elongated and constricted cervical vertebrae, an expansive shoulder girdle with strongly modified forelimbs, a relatively small ilium, and elongate hindlimbs with a very small ascending process of the astragalus that is fused to the tibia. We found this taxon to share many derived characters with noasaurids, such as: strongly elongate cervical and dorsal vertebrae; low, rectangular neural spines in the mid-caudal vertebrae; presence of only an anterior centrodiapophyseal lamina in anterior caudal vertebrae; presence of a wide, U-shaped notch between the glenoid and the anteroventral hook in the coracoid; a laterally flared postacetabular blade of the ilium; a flat anterior side of the distal tibia; and a reduced shaft of metatarsal II. Our analysis placed Elaphrosaurus within a dichotomous Noasauridae as part of a Jurassic subclade, here termed Elaphrosaurinae, that otherwise includes taxa from eastern Asia. These results underscore the long and complex evolutionary history of abelisauroids, which is still only beginning to be understood.
Article
After the two-step extinction event that eliminated all the complex larger benthic foraminifera in the latest Cenomanian, the early Turonian benthic foraminiferal assemblages consisted of small, morphologically simple taxa; these were found in the few carbonate platforms that survived drowning during the Cenomanian-Turonian boundary interval. In this paper, we provide detailed morphologic descriptions of the most typical species of the Turonian benthic foraminiferal assemblages from the Apennine carbonate platform of southern Italy, along with some remarks on their suprageneric systematic position. Their chronostratigraphic range is firmly constrained by integrating carbon- and strontium-isotope stratigraphy.