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Fossil Vertebrates From The Cerro Fortaleza Formation (Upper Cretaceous), Santa Cruz Province, Argentina
... Hydromedusinae and two pan-chelids; Agnolin et al., 2024), and the Maastrichtian Chorrillo (two species: Hydromedusinae and Meiolaniformes indet.; Moyano-Paz et al., 2022) and Dorotea (cf. ...
... For the analysis of occurrences, we downloaded the data from the PaleoBiology DataBase (PBDB) in two formats: the occurrences from the Tithonian to the Santonian (only considering accepted names) (Supplementary Online Information, SOI) and the number of occurrences in each stage over Location Map. 1, map of southern Patagonia showing Cretaceous findings; 2, a geologic map showing the outcrops of the Piedra Clavada Formation and the location of the turtle specimen described herein; 3, geologic profile of the Piedra Clavada Formation with the location of the turtle finding. Abbreviations: 1, turtles from the Mata Amarilla Formation; 2, turtles from the Cerro Fortaleza Formation(Agnolin et al., 2024); 3, Chorrillo Formation(Moyano-Paz et al., 2022); Dorotea Formation(Alarcón-Muñoz et al., 2020). ...
Thescelosaurines are a group of early diverging, ornithischian dinosaurs notable for their conservative bauplans and mosaic of primitive features. Although abundant within the latest Cretaceous ecosystems of North America, their record is poor to absent in earlier assemblages, leaving a large gap in our understanding of their evolution, origins, and ecological roles. Here we report a new small bodied thescelosaurine—Fona herzogae gen. et sp. nov.—from the Mussentuchit Member of the Cedar Mountain Formation, Utah, USA. Fona herzogae is represented by multiple individuals, representing one of the most comprehensive skeletal assemblages of a small bodied, early diverging ornithischian described from North America to date. Phylogenetic analysis recovers Fona as the earliest member of Thescelosaurinae, minimally containing Oryctodromeus, and all three species of Thescelosaurus, revealing the clade was well‐established in North America by as early as the Cenomanian, and distinct from, yet continental cohabitants with, their sister clade, Orodrominae. To date, orodromines and thescelosaurines have not been found together within a single North American ecosystem, suggesting different habitat preferences or competitive exclusion. Osteological observations reveal extensive intraspecific variation across cranial and postcranial elements, and a number of anatomical similarities with Oryctodromeus, suggesting a shared semi‐fossorial lifestyle.
Atlantoceratodus iheringi (Ameghino, 1898) from Argentine territory is restudied based on its known tooth plates and newly discovered material, which includes previously unknown skull roof bones and vomerine tooth plates. The latter represent the first records of such elements from the Mesozoic era in South America. The comparative morphological analysis reveals its distinctiveness from other dipnoans, and offers valuable data for future systematic and phylogenetic research. The pterygopalatine tooth plates display narrow-based first denticulations and lack anterior wear facets, with the inner angle positioned at the level of the second denticulation. Similarly, the pre-articular tooth plates feature straight mediolingual edges, and a wide-based first denticulation without sinuosities at the tip. Histological sections are performed and analyzed in detail for the first time. A. iheringi presents in this aspect distinctive features such as: large-lumen denteons tending to cluster together, circumdenteonal dentine arranged in a double band (an inner birefringent and an outer monorefringent), and a disordered interdenteonal dentine, with birefringence surrounding denteons and areas with monorefringence. A. iheringi exhibits histological structure closer to Mesozoic and Cenozoic dipnoans than Paleozoic, especially resembling the disposition observed in the Upper Cretaceous Patagonian species Metaceratodus baibianorum. The wide distribution of features designated as diagnostic for Atlantoceratodus is discussed.
In the dusk of the Mesozoic, advanced duck-billed dinosaurs (Hadrosauridae) were so successful that they likely outcompeted other herbivores, contributing to declines in dinosaur diversity. From Laurasia, hadrosaurids dispersed widely, colonizing Africa, South America, and, allegedly, Antarctica. Here, we present the first species of a duck-billed dinosaur from a subantarctic region, Gonkoken nanoi, of early Maastrichtian age in Magallanes, Chile. Unlike duckbills further north in Patagonia, Gonkoken descends from North American forms diverging shortly before the origin of Hadrosauridae. However, at the time, non-hadrosaurids in North America had become replaced by hadrosaurids. We propose that the ancestors of Gonkoken arrived earlier in South America and reached further south, into regions where hadrosaurids never arrived: All alleged subantarctic and Antarctic remains of hadrosaurids could belong to non-hadrosaurid duckbills like Gonkoken. Dinosaur faunas of the world underwent qualitatively different changes before the Cretaceous-Paleogene asteroid impact, which should be considered when discussing their possible vulnerability.
Titanosaurian sauropod dinosaurs were diverse and abundant throughout the Cretaceous, with a global distribution. However, few titanosaurian taxa are represented by multiple skeletons, let alone skulls. Diamantinasaurus matildae, from the lower Upper Cretaceous Winton Formation of Queensland, Australia, was heretofore represented by three specimens, including one that preserves a braincase and several other cranial elements. Herein, we describe a fourth specimen of Diamantinasaurus matildae that preserves a more complete skull—including numerous cranial elements not previously known for this taxon—as well as a partial postcranial skeleton. The skull of Diamantinasaurus matildae shows many similarities to that of the coeval Sarmientosaurus musacchioi from Argentina (e.g. quadratojugal with posterior tongue-like process; braincase with more than one ossified exit for cranial nerve V; compressed-cone–chisel-like teeth), providing further support for the inclusion of both taxa within the clade Diamantinasauria. The replacement teeth within the premaxilla of the new specimen are morphologically congruent with teeth previously attributed to Diamantinasaurus matildae, and Diamantinasauria more broadly, corroborating those referrals. Plesiomorphic characters of the new specimen include a sacrum comprising five vertebrae (also newly demonstrated in the holotype of Diamantinasaurus matildae), rather than the six or more that typify other titanosaurs. However, we demonstrate that there have been a number of independent acquisitions of a six-vertebrae sacrum among Somphospondyli and/or that there have been numerous reversals to a five-vertebrae sacrum, suggesting that sacral count is relatively plastic. Other newly identified plesiomorphic features include: the overall skull shape, which is more similar to brachiosaurids than ‘derived' titanosaurs; anterior caudal centra that are amphicoelous, rather than procoelous; and a pedal phalangeal formula estimated as 2-2-3-2-0. These features are consistent with either an early-branching position within Titanosauria, or a position just outside the titanosaurian radiation, for Diamantinasauria, as indicated by alternative character weighting approaches applied in our phylogenetic analyses, and help to shed light on the early assembly of titanosaurian anatomy that has until now been obscured by a poor fossil record.
Monotremata is a clade of egg-lying mammals, represented by the living platypus and echidnas, which is endemic to Australia, and adjacent islands. Occurrence of basal monotremes in the Early Cretaceous of Australia has led to the consensus that this clade originated on that continent, arriving later to South America. Here we report on the discovery of a Late Cretaceous monotreme from southern Argentina, demonstrating that monotremes were present in circumpolar regions by the end of the Mesozoic, and that their distinctive anatomical features were probably present in these ancient forms as well.
A new extinct sclerorhynchoid sawfish, Ptychotrygon ameghinorum sp. nov., is presented here based on abundant isolated teeth and some dermal denticles, which were recovered from the Mata Amarilla Formation, belonging to the lower Upper Cretaceous of the Santa Cruz Province in the Austral Basin of Patagonia, Argentina. This new species is the first Ptychotrygon occurrence in the southern hemisphere, which so far only has been reported from northern hemisphere deposits (Europe, North Africa, and North America). The presence of P. ameghinorum sp. nov. in these southern high-latitude deposits of Patagonia, Argentina, extends the geographic range of Ptychotrygon considerably southwards. This distribution pattern in the “middle” Cretaceous seems to correlate with the South Atlantic opening at the end of the Albian. The presence of lateral cephalic dermal denticles and the simultaneous absence of rostral denticles in the abundant fossil material support the view that Ptychotrygon did not develop such rostral structures. A reinvestigation of all known species assigned to Ptychotrygon reveals that P. ellae is a junior synonym of P. boothi, P. benningensis belongs to Texatrygon, P. rugosum belongs to Asflapristis, and P. clementsi represents an unidentifiable species (Ptychotrygon? sp.). The stratigraphic distribution demonstrates that Ptychotrygon might have originated in the Albian in south-western Europe and subsequently dispersed to obtain its widest distribution during the Cenomanian. In the Coniacian, a steep diversity decline is recognizable with a subsequent distribution shift from Europe to North America.
Los mosasaurios son un clado especializado de Squamata marinos de amplia distribución global durante el Cretácico superior y su presencia es relativamente frecuente en depósitos marinos del Maastrichtiano de Chile Central y Antártica, sin embargo, hasta ahora, el grupo estaba ausente del registro fósil en el extremo sur de Chile. Aquí documentamos, por primera vez, la presencia del clado en niveles del Cretácico Superior de la Formación Dorotea, en la Región de Magallanes. El material consiste en un bloque con vértebras caudales recuperado en la localidad de Sierra Dorotea, en las cercanías de Puerto Natales. A pesar de la naturaleza fragmentaria del espécimen, el material permite confirmar la presencia de mosasaurios en la Formación Dorotea, junto con la previamente conocida diversidad local de reptiles marinos hasta ahora representada por plesiosaurios elasmosáuridos. Este nuevo registro permite establecer conexiones con existencias previas de mosasaurios de la Cuenca de James Ross en Antártica, agregando nuevos datos para la herpetofauna compartida en la Provincia Biogeográfica Wedelliana.
The Upper Cretaceous Winton Formation of Queensland, Australia, has produced several partial sauropod skeletons, but cranial remains—including teeth—remain rare. Herein, we present the first description of sauropod teeth from this formation, based on specimens from three separate sites. An isolated tooth and a dentary fragment from the Diamantinasaurus matildae type locality are considered to be referable to that titanosaurian taxon. A single tooth from the D. matildae referred specimen site is similarly regarded as being part of that individual. Seventeen teeth from a new site that are morphologically uniform, and similar to the teeth from the two Diamantinasaurus sites, are assigned to Diamantinasauria. All sauropod teeth recovered from the Winton Formation to date are compressed-cone-chisel-shaped, have low slenderness index values (2.00–2.88), are lingually curved at their apices, mesiodistally convex on their lingual surfaces, and lack prominent carinae and denticles. They are markedly different from the chisel-like teeth of derived titanosaurs, more closely resembling the teeth of early branching members of the titanosauriform radiation. This provides further support for a ‘basal’ titanosaurian position for Diamantinasauria. Scanning electron microscope microwear analysis of the wear facets of several teeth reveals more scratches than pits, implying that diamantinasaurians were mid-height (1–10 m) feeders. With a view to assessing the spatio-temporal distribution of sauropod tooth morphotypes before and after deposition of the Winton Formation, we provide a comprehensive continent-by-continent review of the early titanosauriform global record (Early to early Late Cretaceous). This indicates that throughout the Early–early Late Cretaceous, sauropod faunas transitioned from being quite diverse at higher phylogenetic levels and encompassing a range of tooth morphologies at the start of the Berriasian, to faunas comprising solely titanosaurs with limited dental variability by the end-Turonian. Furthermore, this review highlights the different ways in which this transition unfolded on each continent, including the earliest records of titanosaurs with narrow-crowned teeth on each continent.
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 aim of the present contribution is to review the fossil record of chimaeroids in Argentina. We review previous records from Argentina, including the presence of Cretaceous chimaeroids reported by Ameghino in the 19th century from the Cretaceous of Santa Cruz province. We re-analyse the species Callorhynchus crassus described from the Miocene of Patagonia by Smith Woodward and Withe in the early 20th century. It is here considered as a valid taxon within the genus Ischyodus as I. crassus nov. comb. Ichyodus dolloi is reported for the first time for the Palaeocene of Patagonia, Argentina. We report for the first time in Argentina fossils belonging to Callorhinchus from Holocene deposits in Buenos Aires province. The long temporal range of Holocephali in Argentina (from Late Cretaceous to Holocene) contrasts with the paucity of their fossil record. This indicates that the history of the clade in southern South America is far from well known.
www.zoobank.org/urn:lsid:zoobank.org:pub:2D6C9E8D-6A32-40E8-89A3-98E7D06ED6D3
Armoured dinosaurs are well known for their evolution of specialized tail weapons—paired tail spikes in stegosaurs and heavy tail clubs in advanced ankylosaurs1. Armoured dinosaurs from southern Gondwana are rare and enigmatic, but probably include the earliest branches of Ankylosauria2–4. Here we describe a mostly complete, semi-articulated skeleton of a small (approximately 2 m) armoured dinosaur from the late Cretaceous period of Magallanes in southernmost Chile, a region that is biogeographically related to West Antarctica5. Stegouros elengassen gen. et sp. nov. evolved a large tail weapon unlike any dinosaur: a flat, frond-like structure formed by seven pairs of laterally projecting osteoderms encasing the distal half of the tail. Stegouros shows ankylosaurian cranial characters, but a largely ancestral postcranial skeleton, with some stegosaur-like characters. Phylogenetic analyses placed Stegouros in Ankylosauria; specifically, it is related to Kunbarrasaurus from Australia6 and Antarctopelta from Antarctica7, forming a clade of Gondwanan ankylosaurs that split earliest from all other ankylosaurs. The large osteoderms and specialized tail vertebrae in Antarctopelta suggest that it had a tail weapon similar to Stegouros. We propose a new clade, the Parankylosauria, to include the first ancestor of Stegouros—but not Ankylosaurus—and all descendants of that ancestor. Stegouros elengassen, an ankylosaur from the late Cretaceous of Chile, has a large tail weapon, named a macuahuitl after the Aztec club, with a frond-like structure formed by seven pairs of laterally projecting osteoderms encasing the distal half of the tail.
Mosasaur researchers have used varieties of tooth crown ornamentation as diagnostic and phylogenetic characters for decades. Such tooth crown features include facets, flutes, striations, serrated carinae, and coarse anastomosing texture. is study investigates the relative contributions of dentine and enamel to the development of these dental characters and assesses homology statements between these structures. Histological analysis of isolated mosasaur teeth reveals that flutes and facets develop initially from the dentine, and the external enamel morphology we observe macroscopically mirrors the shape of the underlying dentine. Striations combine underlying contributions from the dentine with additional and irregular enamel deposition resulting strictly from amelogenesis. In both serrated carinae and anastomosing texture the Dentine-Enamel Junction is smooth, and these external ornamentations form exclusively through variations in enamel development. Based on these observations, we infer that flutes and facets form a morphological spectrum and should not be treated as separate phylogenetic characters. Conversely, striations develop differently than flutes and facets, and should therefore be treated as a distinct character. We recommend referring to serrations on mosasaur carinae as false denticulations to differentiate these enamel-only structures from true denticles possessing a dentine core. Anastomosing texture can also coincide with significant apical enamel thickening, both of which could be adaptations for processing harder prey, as they are in modern reptiles. Care must be taken when using tooth crown features as diagnostic or phylogenetic characters because seemingly different morphologies can have similar developmental origins, and tooth morphology can be more closely tied to diet than common ancestry.
The Late Cretaceous dinosaur record in southern South America has been improved recently; particularly with findings from Chorrillo and Cerro Fortaleza formations, both bearing ankylosaur remains, a clade that was not previously recorded in the Austral Basin. The dinosaur fauna of the type locality of Cerro Fortaleza Formation is known from -and biased to- large-sized sauropod remains and a single described taxon, the titanosaur Dreadnoughtus schrani. Here, we report the taxonomic composition of a site preserving thirteen isolated teeth and several osteoderms belonging to three dinosaur clades (Abelisauridae, Titanosauria, and Nodosauridae), and at least one clade of notosuchian crocodyliforms (Peirosauridae). They come from sediments positioned at the mid-section of the Cerro Fortaleza Formation, which is Campanian-Maastrichtian in age, adding valuable information to the abundance and biodiversity of this Cretaceous ecosystem. Since non-titanosaur dinosaur bones are almost absent in the locality, the teeth presented here provide a window onto the archosaur biodiversity of the Late Cretaceous in southern Patagonia. The nodosaurid tooth and small armor ossicles represent the first record of ankylosaurs for this stratigraphic unit. The peirosaurid material also represents the most austral record of the clade in South America.
A key event in the paleogeographic evolution of the Austral-Magallanes foreland basin was the Santonian-Maastrichtian continentalization, marked by the appearence of deltaic, fluvial and wetland sequences stacked on top of deep marine deposits. The expanding ecological niche was exploited by theropods and influenced the evolutionary history of dinosaurs. We present new detrital zircon U-Pb geochronological data across this littoral to continetnal depocenter, in order to provide insights of its age, geographical extension, source regions and geodynamic setting. Littoral sandstones from La Anita Formation yield Maximum Depositional Ages (MDA) between ~86-80 Ma (weighted mean ages), and ~79-78 Ma youngest zircons. Our results are in accordance with Santonian-Campanian depositional age. The sequence continues with badlands and fluvial systems (Cerro Fortaleza and La Irene Formations), followed by meandering fluvial and lacustrine deposits (Chorrillo Formation). Transgressive marine facies topping the sequence (Calafate Formation) yield a preferred Maastrichtian 69 ± 2 Ma MDA from the youngest zirzon. The provenance and tectonic analyses indicate that basin shallowing during Santonian-Campanian times was driven by advance of the orogenic front, which produced the shift from foredeep setting to a wedge-top depozone. The unroofing of progressively deeper structural levels is registered in the basin fill, which suggests exhumation in the Basement domain during the Santonian-Maastrichtian.
In the last decades, several discoveries have uncovered the complexity of mammalian evolution during the Mesozoic Era, including important Gondwanan lineages: the australosphenidans, gondwanatherians, and meridiolestidans (Dryolestoidea). Most often, their presence and diversity is documented by isolated teeth and jaws. Here, we describe a new meridiolestidan mammal, Orretherium tzen gen. et sp. nov., from the Late Cretaceous of southern Chile, based on a partial jaw with five cheek teeth in locis and an isolated upper premolar. Phylogenetic analysis places Orretherium as the earliest divergence within Mesungulatidae, before other forms such as the Late Cretaceous Mesungulatum and Coloniatherium , and the early Paleocene Peligrotherium . The in loco tooth sequence (last two premolars and three molars) is the first recovered for a Cretaceous taxon in this family and suggests that reconstructed tooth sequences for other Mesozoic mesungulatids may include more than one species. Tooth eruption and replacement show that molar eruption in mesungulatids is heterochronically delayed with regard to basal dryolestoids, with therian-like simultaneous eruption of the last premolar and last molar. Meridiolestidans seem endemic to Patagonia, but given their diversity and abundance, and the similarity of vertebrate faunas in other regions of Gondwana, they may yet be discovered in other continents.
Over the last 25 years, researchers, mostly paleontologists, have developed a system of rank-free, phylogenetically defined names for the primary clades of turtles. As these names are not considered established by the PhyloCode, the newly created nomenclatural system that governs the naming of clades, we take the opportunity to convert the vast majority of previously defined clade names for extinct and extant turtles into this new nomenclatural framework. Some previously defined names are converted with minor adjustments. We also define a number of new clade names to close apparent nomenclatural gaps. In total, we establish 113 clade names, of which 79 had already received phylogenetic definitions and 34 are new.
ZooBank LSID: urn:lsid:zoobank.org:pub:43B418C2-BE9A-4BD5-91B7-8A9E0C8CB79D.
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.
Gondwanatheria is an enigmatic mammaliaform clade distributed in the Cretaceous and Paleogene of South America, Africa, Madagascar, India and Antarctica. The Mesozoic record in South America is restricted to the Latest Cretaceous of Río Negro and Chubut provinces, Argentina and Magallanes Region of southern Chile. The aim of the present contribution is to describe a new specimen of gondwanatherian mammaliaforms from beds belonging to the Maastrichtian Chorrillo Formation, cropping out 30 km SW of El Calafate, Santa Cruz Province, Argentina. It is represented by a single molariform referable to the species Magallanodon baikashkenke with which it shares a unique combination of characters. Analysis of the unique combination of characters exhibited by Magallanodon shed doubts on the monophyly of Ferugliotheriidae and suggest that South American taxa may be closely related to each other. The wide geographical distribution and occurrence of gondwanatherians on geological units of diverse origins suggest that they were capable of facing disparate environmental conditions.
We describe Magallanodon baikashkenke gen. et. sp. nov., a new gondwanatherian mammal from the Late Cretaceous of the Magallanes Region in southern Chile (Río de Las Chinas Valley, Estancia Cerro Guido, north of Puerto Natales city, Última Esperanza Province). The mammal-bearing layer is placed within the Late Campanian-Early Maastrichtian levels of the Dorotea Formation (Magallanes/Austral Basin). The new remains constitute the southernmost record of a Mesozoic gondwanatherian mammal, as well as the frst Mesozoic mammal from Chile. This taxon is comparable in size to the hypsodont-toothed Gondwanatherium (Late Cretaceous) and Sudamerica (Early Paleocene) but with noticeably brachyodont molariforms supported by four to fve roots. As in other gondwanatherians, it has at least one hypertrophied, rodent-like incisor in the upper jaw. The new taxon is here diagnosed and described, and is regarded as a possible ferugliotheriid (?Ferugliotheriidae). If confrmed, it would represent the largest known taxon for this family. Its molariform occlusal crown pattern, after wear, resembles that of other gondwanatherians, particularly ferugliotheriids and that of the sudamericid Gondwanatherium. This adds new evidence on the phylogenetic proximity of ferugliotheriid and sudamericid gondwanatherians. An analysis of the enamel microstructure of the upper incisor of Magallanodon was performed demonstrating several crucial similarities with the pattern shown by Gondwanatherium (Sudamericidae). We discuss the signifcance of Magallanodon for understanding the acquisition, within gondwanatherians, of a lophed molariform pattern. Finally, we discuss the signifcance of the new fnding in the context of southern biotas, including those of Patagonia and Antarctica.
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.
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.
The sedimentary infill of the Austral-Magallanes Basin since the onset of its foreland stage in the Lago Argentino region is dominated by deep-marine and coastal deposits. However, during the Late Cretaceous the basin accumulated a thick and poorly known continental sedimentary succession, which has received different lithostratigraphic names. The aim of this work is to characterize the here defined Uppermost Cretaceous Continental Deposits (UCCD) from a detailed facies and architectural analysis, as well as the resulting stacking pattern. Seven Facies Associations (FAs) were discriminated in order to define the sedimentary paleoenvironments: FA1, gravelly sheet bodies; FA2, tabular bodies of conglomerates with mud rip-up clasts; FA3, complex tabular sandy bodies; FA4, simple tabular sandy bodies; FA5, tabular bodies of structureless sandstones; FA6, heterolithic deposits; and FA7, fine-grained deposits. Three different fluvial styles were recognized: meandering systems dominated by avulsion and meander abandonment processes (fluvial style a), braided systems (fluvial style b), and meandering systems dominated by overbank flood processes (fluvial style c). The stacking pattern of the FAs allowed to divide the UCCD into two major depositional stages related to the accommodation space vs sediment supply (A/S) ratio. Stage I is characterized by the alternation of fluvial styles a and b, while the Stage II is represented by the alternation of fluvial styles c and b, and the Stage III is characterized entirely by fluvial style c deposits. Although the UCCD are considered as a whole within a framework of low A/S ratio, several high frequency variations were recognized. The Stage I records seven high frequency intervals of which four are characterized by high A/S ratio interrupted by three events of low A/S. While the stage II is represented by six high frequency periods of low A/S ratio and other five high frequency events of high A/S ratio. The Stage II is considered as deposited in a relative higher A/S context in comparison with the Stage I, based on the behavior of the moderate to high sinuosity meander fluvial systems. Finally, the Stage III is represented entirely by a high frequency low A/S ratio event.
In the last two decades, the number of phylogenetically informative anatomical characters recognized in the appendicular skeleton of titanosaurian sauropod dinosaurs has increased dramatically with the discovery of new and comparatively complete specimens. here we provide an overview of the appendicular skeletal morphology of South American titanosaurs and discuss its significance for phylogenetic reconstruction. the appendicular skeletal diversity of South American titanosaurs is substantially greater than was initially appreciated. Moreover, some regions of the appendicular skeleton, such as the pes, exhibit remarkable variability in form. Multiple synapomorphies of titanosauria and the less inclusive clades Lithostrotia and Saltasauridae consist of characters of the girdles and limbs. Although the phylogenetic definitions of titanosaurian clades such as Saltasaurinae and Lognkosauria are stable, the taxonomic content of these clades has varied in recent analyses depending on the phylogenetic topology recovered. Within titanosauria, the results of four recent, largely independent analyses support the existence of a derived titanosaurian lineage distinct from the 'Saltasaurinae line,' which is herein termed Colossosauria. At present, this clade is mainly comprised by taxa within Lognkosauria and rinconsauria, and is useful in discussions of titanosaurian lower-level relationships.
Talenkauen santacrucensis represents one of the most complete South American ornithopods yet discovered. This dinosaur comes from the Mata Amarilla Formation (Turonian) of Santa Cruz Province, Argentina. The aim of this contribution is to present a detailed description of Talenkauen santacrucensis. Features of the cervical series of Talenkauen, which are shared with other elasmarians, indicate that these dinosaurs have a proportionally longer neck than other ornithopods. These traits were convergently acquired by several saurischian clades. Additionally, some features, including an ornamented labial surface of the mandibular teeth and a sigmoidal greater trochanter of femur, are traits shared by most elasmarians, and may prove to be synapomorphies of this clade. A phylogenetic analysis recovers most Cretaceous Gondwanan ornithopods in the clade Elasmaria. This analysis indicates that Elasmaria was distributed more widely geographically and temporally than previously thought.
Coastal depositional systems are commonly classified in terms of the relative interaction of wave, tide and fluvial processes. The La Anita Formation represents the opportunity to study and better understand coastal sedimentary systems. It is a poorly studied prograding siliciclastic deltaic-coastal wedge accumulated in the Campanian during the foreland stage of the Austral-Magallanes Basin. A detailed depositional process-based facies analysis have allowed the definition of 13 sedimentary facies and 9 facies associations for the La Anita Formation, ranging from prodelta to interdistributary delta-channel deposits. According to the spatial distribution of these facies associations, the La Anita Formation was divided into two informal units bounded by a regional erosion surface. The lower unit shows abundant hummocky cross-bedded and bioturbated sandstones, coarsening-upward trends and mainly aggradational to progradational vertical stacking pattern, and it was interpreted as a wave-dominated fluvial-influenced delta. The upper unit is characterized by unidirectional dune cross-bedding, coarsening-upward trend and a progradational vertical stacking pattern, and was interpreted as a fluvio-dominated delta with no evidence of tide or wave influence. These two units represent two genetically unrelated depositional sequences bounded by a regional erosion surface, which is interpreted as a sequence boundary triggered by a relative sea-level fall. The lower unit is part of a progradational highstand systems tract which involves the underlying deep-marine Alta Vista Formation. The upper unit contain deposits that reflect a complete relative sea-level cycle which includes an undifferentiated lowstand and transgressive systems tracts deposits and, toward the top, highstand systems tract deposits.
The limited fossil record of Australian Cretaceous theropods is dominated by megaraptorids, reported from associated and isolated material from the Early Cretaceous of Victoria and the ‘Mid’-Cretaceous of central-north New South Wales and central Queensland. Here, we report on new postcranial theropod material from the early Late Cretaceous Griman Creek Formation at Lightning Ridge. Among this new material is an associated set consisting of two anterior caudal vertebrae and a pubic peduncle of the ilium, to which a morphologically similar partial vertebral centra from a separate locality is tentatively referred. These elements display a combination of characteristics that are present in megaraptorid and carcharodontosaurid theropods, including camellate internal organization of the vertebral centra, ventrally keeled anterior caudal centra and a pubic peduncle of the ilium with a ventral surface approximately twice as long anteroposteriorly as mediolaterally wide. Unfortunately, a lack of unambiguous synapomorphies precludes accurate taxonomic placement; however, avetheropodan affinities are inferred. This new material represents the second instance of a medium-sized theropod from this interval, and only the third known example of associated preservation in an Australian theropod. Additional isolated theropod material is also described, including an avetheropodan femoral head that shows similarities to Allosaurus and Australovenator, and a mid-caudal vertebral centrum bearing pneumatic foraminae and extensive camellae that is referrable to Megaraptora and represents the first axial skeletal element of a megaraptorid described from Lightning Ridge.
The Spinosauridae is a specialised clade of theropod dinosaurs known from the Berriasian to the Cenomanian of Africa, South America, Europe and Asia. Spinosaurs were unusual among non-avian dinosaurs in exploiting a piscivorous niche within riverine and estuarine habitats, and they include the largest known theropod. Although fossils of giant spinosaurs are increasingly well-represented in the fossil record, little juvenile material has been described. Here, we describe new examples of juvenile spinosaurines from the middle Cretaceous (Cenomanian) Kem Kem beds of Morocco. The fossils include material from a range of sizes and are relatively common within the Kem Kem deposits, suggesting that juveniles exploited the same semiaquatic niche as the adults throughout ontogeny. This implies that the Cenomanian delta habitats supported an age-inclusive population of spinosaurs that was neither geographically or environmentally separated, though some ecological separation between juveniles and adults is likely based on the large variation in size. Bones or teeth of very small (<2 m) spinosaurs have not been found, however. This could represent a taphonomic bias, or potentially an ecological signal that the earliest ontogenetic stages inhabited distinct environments. Skeletal remains include individuals referable to Sigilmassasaurus brevicollis and a second spinosaurine taxon. Consistent with this, we also identify two distinct cranial morphs of Spinosauridae present within the Kem Kem, supporting previous recognition of distinct taxa in the assemblage.
The end Cretaceous mass extinction was marked by a dramatic change in biodiversity, and the extinction of all non-avian dinosaurs. To understand the diversity of dinosaur clades prior to this event, as well as recovery by avian dinosaurs (birds), we need a better understanding of the global fossil record. However, the fossil record from southern localities, particularly southernmost (>60°S) South America, has only recently begun to be described. Discoveries from Patagonia are important to accurately assess global trends in dinosaur diversity, particularly during the latest Cretaceous before the Cretaceous/Paleogene (K/Pg) mass extinction event. Here we describe new theropod dinosaur specimens, representing both associated material and isolated elements, from Upper Cretaceous (Campanian-Maastrichtian) deposits of the Río de las Chinas Valley, Magallanes-Austral Basin, Chile. These discoveries include the southern-most known occurrences of several theropod clades outside of Antarctica, including megaraptorids, unenlagiines, enantiornithines and ornithurines. Notably, these remains provide much needed time-constrained records of smaller theropods, including birds, which are less often recovered from Upper Cretaceous deposits. While fragmentary, these fossils are the first records of theropods from Chilean Patagonia, and provide insight into the distribution of avian and non-avian theropods in southern high latitude ecosystems prior to the K/Pg mass extinction event. Sampling from this region is still sparse, and more fossils from age-controlled sections are needed to accurately assess global extinction dynamics through the end Cretaceous.
Enantiornithes were the dominant avialan clade in the Mesozoic. However, their record for the Upper Cretaceous is scarce. In this study, we present and describe Yatenavis ieujensis gen. et sp. nov., one of the youngest occurrence of an enantiornithine bird. The specimen, the distal half of a right humerus, was found in Chorrillo Formation, southern Santa Cruz Province of Argentina, making it also the australmost enantiornithine specimen recorded to date. Yatenavis is unique among enantiornithines for its combination of characters, including a crest on the medial side of the shaft which bears a muscular scar cranially; the presence of a dorsal supracondylar process proximal to the dorsal epicondyle; equally distally projected dorsal and ventral condyles; and a rod-like caudal extension of the ventral condyle bearing a distal sulcus scapulotricipitalis. Several of these features are shared with an unnamed enantiornithine recovered from Upper Cretaceous beds in another fossil site in Patagonia.
The most representative ankylosaurian remains from Argentina have been found in sediments of the Allen Formation (Campanian–Maastrichtian) in Salitral Moreno, Río Negro Province. Several authors have discussed the identity and history of these remains. In this study, we review all published material along with some new remains in order to summarize all the knowledge about these ankylosaurs. Previously published material includes a tooth, dorsal and anterior caudal vertebrae, a femur and several osteoderms. The new remains include synsacral and caudal elements, a partial femur and osteoderms. The anatomy of the tooth, the synsacrum, the mid-caudal vertebra, the femur and the osteoderms, and the histology of the post-cervical osteoderms, support a nodosaurid identification, as proposed in previous descriptions of the Salitral Moreno material. Patagopelta cristata gen. et sp. nov. is a new nodosaurid ankylosaur characterized by the presence of unique cervical half-ring and femoral anatomies, including high-crested lateral osteoderms in the half rings and a strongly developed muscular crest in the anterior surface of the femur. The ∼2 m body length estimated for Patagopelta is very small for an ankylosaur, comparable with the dwarf nodosaurid Struthiosaurus. We recovered Patagopelta within Nodosaurinae, related to nodosaurids from the ‘mid’-Cretaceous of North America, contrasting the previous topologies that related this material with Panoplosaurini (Late Cretaceous North American nodosaurids). These results support a palaeobiogeographical context in which the nodosaurids from Salitral Moreno, Argentina, are part of the allochthonous fauna that migrated into South America during the late Campanian as part of the First American Biotic Interchange.
https://zoobank.org/urn:lsid:zoobank.org:pub:FBA24443-F365-49FD-A959-10D2848C2400
Giant carnivorous dinosaurs such as Tyrannosaurus rex and abelisaurids are characterized by highly reduced forelimbs that stand in contrast to their huge dimensions, massive skulls, and obligate bipedalism.¹,² Another group that follows this pattern, yet is still poorly known, is the Carcharodontosauridae: dominant predators that inhabited most continents during the Early Cretaceous3, 4, 5 and reached their largest sizes in Aptian-Cenomanian times.6, 7, 8, 9, 10 Despite many discoveries over the last three decades, aspects of their anatomy, especially with regard to the skull, forearm, and feet, remain poorly known. Here we report a new carcharodontosaurid, Meraxes gigas, gen. et sp. nov., based on a specimen recovered from the Upper Cretaceous Huincul Formation of northern Patagonia, Argentina. Phylogenetic analysis places Meraxes among derived Carcharodontosauridae, in a clade with other massive South American species. Meraxes preserves novel anatomical information for derived carcharodontosaurids, including an almost complete forelimb that provides evidence for convergent allometric trends in forelimb reduction among three lineages of large-bodied, megapredatory non-avian theropods, including a remarkable degree of parallelism between the latest-diverging tyrannosaurids and carcharodontosaurids. This trend, coupled with a likely lower bound on forelimb reduction, hypothesized to be about 0.4 forelimb/femur length, combined to produce this short-armed pattern in theropods. The almost complete cranium of Meraxes permits new estimates of skull length in Giganotosaurus, which is among the longest for theropods. Meraxes also provides further evidence that carchardontosaurids reached peak diversity shortly before their extinction with high rates of trait evolution in facial ornamentation possibly linked to a social signaling role.
Few latest Cretaceous fossil floras are known for South America, and in particular for the Austral-Magallanes Basin. Recent studies carried out in the Chorrillo Formation (Maastrichtian) revealed a diverse array of fossil elements, including continental invertebrates, vertebrates, palynomorphs, fossil woods and leaf impressions. In this work, we describe the megafloristic elements identified in the unit from two fossiliferous levels, along with a palynological sample obtained from one such level. The first Mesozoic Nymphaeaceae (water lilies) remains for Argentina are reported, consisting of fragmentary leaves and seeds of a minute Nuphar-grade plant. Several leaf impressions referred to dicotiledonean and monocotiledonean morphotypes are also described. Additionally, microscopic remains reveal a diverse palynological assemblage containing terrestrial and aquatic ferns, conifers and angiosperms. A community that inhabited low energy, probably paludal, freshwater environments was identified, based on the sedimentology of the bearing strata such as the presence of hydromorphic paleosols and poorly decomposed organic matter suggesting poor drainage and eventual reducing and anoxic conditions, as well as the presence of Salviniaceae (water ferns), Marsileaceae (water-clovers), Nymphaeaceae and Zygnemataceae (freshwater conjugate algaes). Palynological elements suggest similarities with Campanian to Paleocene Patagonian units, mostly located in the Austral-Magallanes, Cañadón Asfalto and Golfo the San Jorge basins. Finally, aquatic communities from other Maastrichtian units (e.g. La Colonia and Lago Colhué Huapi formations) are compared with the Chorrillo Formation presented herein, suggesting similarities in functional groups even though taxa involved differ partially
Aggradational deltaic successions are uncommon in the stratigraphic record since deltas are progradational by nature. However, deltaic coastlines fed by multiple small distributaries rather than by a well-defined trunk fluvial distributary system might result in aggradational successions if the sediment is effectively redistributed from river mouths by active basinal processes (e.g., tides, fairweather waves, and/or storm waves). The wave-dominated deltaic succession in the lower part of the La Anita Formation accumulated during the foreland stage of the Austral-Magallanes Basin (Argentina). Through a sedimentological and ichnological study of the interval, we evaluate and discuss the potential controls on the evolution of aggradational wave-dominated deltaic successions.
The studied stratigraphic interval is up to 150 m thick and includes facies deposited in wave-dominated prodelta, wave-dominated distal delta-front, wave-influenced mouth bar, terminal channel, and distributary channel settings. These facies associations stack vertically, forming clear thick aggradational sets. Fairweather wave processes largely dominate the delta-front and prodelta deposits, although discrete beds point to the periodic importance of linked storm-wave and river-flood processes. Owing to the alternation of beds generated during fairweather shoaling waves with those of coupled storm-wave and river-flood cycles, it is proposed that the overall aggradational stacking pattern of the delta is the response to the sediment balance. Clastic material supplied by the distributary channels of the delta was easily transported alongshore during fairweather conditions by longshore currents and basinward via storm-generated waves, and/or hyperpycnal currents and hypopycnal plumes generated by river floods.
The alternation of these depositional processes strongly affected the benthic faunal communities, which is well expressed by the resulting ichnological suites. Storm-wave and river-flood events led to the widespread defaunation of tracemaking organisms, leading to generation of unburrowed beds. Between these events, short-lived colonization windows appeared locally, allowing sparse, facies-crossing dwelling and detritus-feeding burrows to be constructed by the recovering benthic communities. By contrast, during prolonged periods of fairweather shoaling, river-induced physico-chemical stresses were greatly reduced, and the resulting beds display elevated bioturbation intensities with greater numbers of burrows that record a wide range of behaviors.
Wave-, tidal-, and fluvial-dominated deltas are important hydrocarbon reservoirs worldwide, and it is well known that depositional facies types, detrital composition and diagenetic products are key aspects when evaluating potential reservoir properties. Moreover, detrital composition and diagenetic products are controlled by external forces such as tectonism, climate, and depositional conditions. The Upper Cretaceous La Anita Formation (Austral-Magallanes Basin, Argentina) is a deltaic succession that shows a clear vertical variation in the relative role of wave, tidal and fluvial processes. The formation was accumulated during the foreland stage of the basin under relatively warm climate conditions. A detailed compositional and diagenetic analysis for these deposits is provided to evaluate the role of the controlling factors on the detrital and authigenic composition, and the impact on reservoir properties. Samples were analyzed by conventional petrography, X-ray diffraction and scanning electron microscopy to obtain a full spectrum of its detrital, authigenic and diagenetic composition. The analyzed sandstones were classified as lithic arenites which come from the fold-thrust belt region and from the magmatic arc located toward the westward. The clay mineral composition is characterized by variable proportions of illite, smectite, kaolinite and mixed-layer illite-smectite with the sporadic presence of chlorite. Stratigraphic variations in the abundance of authigenic kaolinite and smectite indicate a change in the climatic conditions during the de-positions of the unit evolving from tropical to more temperate conditions. Diagenetic processes affecting the porosity are considered as controlled mainly by the lithological nature of the deposits and depositional facies type. Sandstone porosity is mainly primary in origin, moderate to good in abundance and show micropore to mesopore as the main pore-sizes. This work enhances that the diagenetic products are heavily controlled by the dominant depositional process. The presence of diagenetic products as quartz overgrowth and calcite and hematite cement reduces pore spaces and affects the reservoir properties. The development of these types of cement is conditioned by the relative dominance of wave and river processes. Under wave-dominated conditions, quartz tends to develop thick overgrowths. Conversely, under river-dominated conditions quartz overgrowths are thinner and calcite and hematite cementation patches are developed.
Lungfish remains are a frequent component of the Upper Cretaceous deposits of Patagonia; they are mainly represented by tooth plates fused or not to the jaw bones. Here, we describe the histology of the tooth plates of Metaceratodus baibianorum from the La Colonia Formation, Patagonia. The present study is the first of its kind to be carried out in Argentinian dipnoans. Under the petrographic microscope, the tooth plates show two distinct arrangements of calcium hydroxyapatite crystals in the interdenteonal dentine (cross birefringent pattern and monorefringent pattern), which differ from the one present in the circumdenteonal dentine (lamellar birefringent pattern). The tissue arrangement of M. baibianorum tooth plates is more similar to that of other Mesozoic and Cenozoic species (such as neoceratodontids) than it is to that present in Paleozoic species (such as Dipterus valenciennesi). At the same time, incremental lines in vertical sections are observed. The nature of incremental lines in the interdenteonal dentine and their use in estimating the minimum age of the specimen are discussed.
The Upper Cretaceous (Cenomanian) Mata Amarilla Formation in western Central Santa Cruz Province of Argentina has yielded fragmentary teeth of a large ?docodontan, an australosphenidan, a meridiolestidan (Amarillodon meridionalis gen. et sp. nov.), and a stem dryolestid (Treslagosodon shehuensis gen. et sp. nov.). These represent the first possible records for docodontans, Cretaceous australosphenidans, and stem dryolestids in South America. Both ?docodontan tooth fragments are unusually large and exhibit potential durophagous adaptation. The Amarillodon gen. nov. lower (?deciduous) posterior premolar has a trigonid angulation of 100° and is autapomorphic by a large and exoedaenodont distolabial accessory cusp on the distal cingulid. Both the mesial and distal cingulid are shelf-like. The mesiolabial upper molar fragment of the ausktribosphenid australosphenidan is similar to an upper M1 of aff. ?Bishops from the lower Albian (Lower Cretaceous) of Australia by its large stylar cusp ?C and breached paracone. The lower molar of the new stem dryolestid is characterized by a large talonid cusp d and a mesio-distally strongly compressed mesial root that is weaker than the distal one. The australosphenidan, if corroborated, suggests faunal interrelationships between Australia and South America by the late Early/early Late Cretaceous.
Frogs (Anura) are nowadays common and abundant constituents of terrestrial and freshwater ecosystems near globally and their fossil record shows that they were already important during Cretaceous times. However, their fossils are often very incomplete, challenging their identification, which, coupled to historical reasons, has led to their marginalization in studies of Cretaceous tetrapod assemblages. We here report on the identities of frogs from three upper Campanian–lower Maastrichtian assemblages from Chilean (Dorotea Formation) and Argentinean (Allen and Los Alamitos formations) Patagonia, with focus on humeral morphology. Records from the Dorotea Formation represent the first described Mesozoic frogs from Chile and include the southernmost record of pipids worldwide. In the three assemblages we have identified humeri of the pipid Kuruleufenia and of calyptocephalellid frogs, proving humeral morphology valuable in diagnosing and identifying Cretaceous frogs from Patagonia. These frogs are diagnostic components of the South American Allenian tetrapod assemblage that was widespread across Patagonia near the end of the Cretaceous.
The deposits of the Chorrillo Formation (Maastrichtian) were accumulated during a ‘continental window’ that occurred during the Late Cretaceous in the Austral-Magallanes foreland basin, southern Patagonia, Argentina. The aim of the present contribution is to describe the depositional conditions as well as new vertebrate and plant fossils from this unit. The analysis of these deposits resulted in the definition of five architectural elements: Complex sandy narrow sheets channels (SS), Complex gravelly narrow sheets channels (GS), Sandstone lobes (SL), Thick fine-grained deposits (GF) and Thin dark fine-grained deposits (DF). These were separated into channelized and non-channelized units and represent the accumulation in a fine-grained dominated, fossil rich fluvial depositional system. Vertebrates fossil records include two species of frogs of the genus Calypteocephalella (representing the southernmost record of Pipoidea), snakes belonging to Madtsoiidae and Anilioidea (the latter ones being the first records for the basin), chelid turtles similar to Yaminuechelys-Hydromedusa, meiolaniiform turtles, titanosaur sauropods, megaraptoran theropods, new remains of the elasmarian Isasicursor santacrucensis (including the first cranial remains available for this species), hadrosaur ornithischians, enantiornithine birds. Sharks and elasmosaurs are also recorded and may possibly derive from the overlying marine Calafate Formation. These new taxa, together with previous findings from the Chorrillo Formation, are included into a stratigraphic column, thus providing valuable information that sheds new light on faunistic composition and paleobiogeography of high-latitude biotas of Gondwana.
The fossil record of gondwanatherian mammaliaforms from Patagonia is represented by several species known on the basis of isolated teeth, with the single exception of a partial dentary with two molariforms of the Paleocene species Sudamerica ameghinoi. The aim of the present contribution is to describe both a fragmentary dentary (with the base of the lower incisive) and a partial upper incisor coming from the Campanian–Maastrichtian Chorrillo Formation, at the La Anita Farm, SW Santa Cruz province, Argentina. The specimens are referred to Magallanodon baikashkenke, a species previously known by isolated teeth from the Dorotea (Chile) and Chorrillo (Argentina) beds. The present discovery expands our knowledge of this mammaliaform clade.
The fossil record of ornithischians in South America is sparse, and they are clearly underrepresented when compared with sauropod dinosaurs. However, recent discoveries indicate that ornithischians were more diversified than thought. The aim of the present contribution is to describe isolated remains belonging to ankylosaurs, and ornithopods, including basal euiguanodontians and hadrosaurs coming from the Chorrillo Formation (upper Campanian–lower Maastrichtian), Santa Cruz province, southern Argentina. The fossil remains of ankylosaurs reported here are the southernmost recorded for the continent. They show a unique combination of plesiomorphic features, indicating that they may belong to a basal ankylosaur. Ankylosaurs and hadrosaurids are thought to have arrived in South America during the latest Cretaceous through Central America. However, a detailed overview of the fossil record of Gondwana indicates that both clades were present and probably diversified along southern continents. This indicates that their presence in South America may be alternatively interpreted as the result of migration from other landmasses, including Africa and Europe, or may even be the result of Jurassic–Early Cretaceous vicariance from their northern counterparts.
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.
We describe remains of freshwater turtles from the Upper Cretaceous of Chilean Patagonia. The fossils, which comprise isolated shell fragments and incomplete appendicular bones, were recovered from meandering fluvial deposits of the Dorotea Formation (upper Campanian–Danian), in the Río de Las Chinas Valley, Magallanes region. These remains represent the first records of Upper Cretaceous pan-chelid pleurodiran turtles in the Magallanes-Austral Basin. The shell fragments show a strong ornamentation of irregular polygons distributed over their entire dorsal surface, and one of the peripheral plates is narrow and elongated. These features are consistent with traits described in Yaminuechelys, a chelid genus from the Upper Cretaceous and Paleogene of Argentinian Patagonia. In addition, the suprapygal plate presents sulci that mark the limits of the vertebral scute 5 and the marginal scutes 12 as in Yaminuechelys sulcipeculiaris. This finding represents the southernmost record of a species conferred to Yaminuechelys, extending the distribution of this genus to the Magallanes-Austral basin during the Campanian–Maastrichtian.
The holotype of the elasmosaurid Aphrosaurus furlongi from the Maastrichtian levels of the Moreno Formation is redescribed and considered a valid species based on one autapomorphy, a deep trough in the ventral surface of vertebral centra of the posterior cervicals, and the following combination of features: wide and short clavicle-interclavicle complex with concave anterior border and without posterior medial process or medial ventral keel, humerus with anterior depression, and posterior limb with accessory element on the posterior margin. The phylogenetic analysis recovered A. furlongi as an elasmosaurid within Weddellonectia. The phylogenetic analysis generated a new topology of Elasmosauridae. A new clade, Euelasmosaurida, is recovered, including all post-Cenomanian elasmosaurids other than Zarafasaura oceanis. Euelasmosaurida is composed of two main clades: Elasmosaurinae and Weddellonectia. The latter includes mostly Weddellian elasmosaurids, including Aristonectinae. Based on the new phylogenetic results, the evolution of key cranial and postcranial characters is discussed. Two key intervals of elasmosaurid evolutionary history are recognized: the Cenomanian, with the appearance of Euelasmosaurida, and the Santonian, with the differentiation of Weddellonectia and Elasmosaurinae.
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.
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.
During the Antarctic summer campaigns and as a result of paleontological fieldworks 2013–2015 several mosasaur remains have been collected from the upper Maastrichtian López de Bertodano Formation exposed at Marambio (=Seymour) Island, of the Antarctic Peninsula. One of these specimens preserves part of the skull and dentition, which represent one of the few known skulls from Antarctica. The new specimen (MLP 15-I-24-41) is similar to member of the mosasaur tribe Plotosaurini, sharing the same fronto-parietal suture pattern, and a similar dental morphology as some of the species assigned to the genus. As the specimen is not complete enough to propose a new name it is referred to Mosasaurus sp. The presence of these remains on the southern hemisphere represents one of the most complete records of a Mosasaurus mosasaur.
A new ornithopod dinosaur, the medium-sized Sektensaurus sanjuanboscoi gen. et sp nov. from the Coniacian–Maastricthian strata of the Lago Colhué Huapi Formation, Golfo San Jorge Basin, Patagonia, is here described. The specimen consists of disarticulated postcranial bones belonging to a single individual. It is diagnosed by an unique association of five autapomorphies on the dorsal and sacral vertebrae and the humerus. A cladistics analysis indicates that Sektensaurus was an iguanodontian ornithopod which inhabited Patagonia during the Late Cretaceous. Likewise, Sektensaurus is the first non-hadrosaurid, probably elasmarian, ornithopod recorded from the uppermost Cretaceous of central Patagonia. In a broad context, this discovery increases the anatomical knowledge of ornithopods and adds new data on the composition of dinosaur faunas that lived in Patagonia close to the Antarctica, at the end of the Cretaceous.