Proterochampsids were small to medium size carnivorous quadrupedal archosauriforms from the Middle–Upper Triassic of America. In Argentina, they are distributed in the Ischigualasto-Villa Unión Basin. Here, we describe the bone histology of Argentinean proterochampsids Proterochampsa barrionuevoi PVSJ 606 (humerus), Tropidosuchus romeri PVL 4602 (femur), Gualosuchus reigi PVL 4576 (humerus, femur and tibia) and Chanaresuchus bonapartei PVL 4575 (humerus and tibia) and PVL 6244 (humerus, femur, dorsal rib) to infer growth dynamics (using qualitative and quantitative approaches), inter and intraspecific variation and lifestyle (using statistical models). Proterochampsa and Tropidosuchus reached a moderate–fast growth, based in woven-fibred bone tissue and radial-longitudinal vascularisation, although Proterochampsa exhibits an external fundamental system, indicating growth cessation. Gualosuchus displays fibrolamellar complex highly vascularised during early stages of its ontogeny, indicative of rapid growth. Individuals of Chanaresuchus show disparate growth strategies, characterized by parallel-fibred bone tissue alone or in association with patches of woven-fibred bone, together with moderate to high levels of vascularization. Therefore, proterochampsids present a notable diversification in their growth strategies, which is reflected between species and within the individuals (specially marked in Chanaresuchus). Quantitative analyses indicate irregular growth rates, similar to those of extant crocodiles. Analyses of the lifestyle suggest a differentiation in the divergence of Proterochampsidae subfamilies, with Proterochampsinae (Proterochampsa) as amphibious/aquatic and Rhadinosuchinae (Chanaresuchus, Gualosuchus and Tropidosuchus) as terrestrial. These findings provide new insights into the palaeobiology and ecological diversification of Proterochampsidae, shedding light on the evolutionary pathways that preceded the emergence of crown-group Archosauria.
Abelisaurids are a group of mostly Gondwanan theropod dinosaurs, whose anatomy and phylogenetic relationships are well known. However, this is not the case for some paleobiological aspects such as postcranial pneumaticity. In this work, the pneumaticity of the fifth cervical vertebra of Viavenator exxoni was analyzed. This was done using CT scans and comparing their results with other abelisauroids. Furthermore, in order to obtain a more precise result regarding pneumaticity, an analysis was performed of air space proportion (ASP) of the fifth cervical vertebra of Viavenator exxoni. Viavenator has a polycamerate internal structure, similar to that of some noasaurids from Brazil and Majungasaurus crenatissimus. However, in Viavenator, unlike other analyzed taxa, a ventral pneumatic foramen was found, a unique characteristic among abelisaurids and even theropods. Regarding the ASP, it was found that the vertebra is more pneumatized in the anterior portion than in the posterior portion. This is the first ASP study on an abelisaurid vertebra, making it extremely important to expand this type of analysis in the future across this fascinating group of theropods.
This study reports the first occurrence of Faveoloolithidae eggshells from “the upper section” (late Maastrichtian) of the Lago Colhué Huapi Formation, Chubut Group, in the Golfo San Jorge Basin, Argentina. A total of 161 eggshell fragments were examined using a binocular microscope, petrographic microscope, and scanning electron microscope. The specimens show morphological features consistent with the oofamily Faveoloolithidae, including a dinosauroid-spherulitic basic organization, a filispherulitic structural morphotype and a multicanaliculate pore system. However, as evidenced in others South American record, their well-developed external ornamentation and greater thickness distinguish them from other ootaxa within the oofamily; therefore, they are assigned to Faveoloolithidae indet. These eggshell fragments were recovered within deposits interpreted as low energy, shallow water bodies, developed in floodplain environments near the coastline. These levels are characterized by a remarkable abundance of hadrosaurid remains and, to date, the absence of sauropod fossils. Although an association with hadrosaurids might be suggested, a titanosaurian affinity cannot be excluded, as these sauropods are traditionally linked to Faveoloolithidae eggshells. This uncertainty reflects the complexity of taxonomic assignments in fragmentary oological records.
X-ray computed microtomography was used to segment and re-describe the braincase of the juvenile specimen of Megaraptor namunhuaiquii, providing novel anatomical endocranial information. The reconstructed soft tissues include the brain, cranial nerves, blood vessels, inner ear, and pneumatic sinuses. Some structures of the braincase anatomy were re-interpreted, and the endocranial anatomy was compared with that of Murusraptor barrosaensis (the only other megaraptoran with studied endocranial anatomy) and more derived theropods. The braincase and the brain exhibit a mosaic of primitive and derived characters that support the previously proposed close relation of Megaraptor with basal coelurosaurian theropods (including basal Tyrannosauroidea). A high degree of braincase pneumaticity, a high mean range of hearing, and a relatively large floccular lobe of the cerebellum are features that suggest that Megaraptor was an agile bipedal predator compared to non-coelurosaur coeval theropods, such as abelisaurids. Its cognitive and sensorial abilities may have allowed Megaraptor to compete with coelurosaurs (unenlagiines?) or at least reach many of their hunting capabilities.
The Late Miocene Ituzaing & oacute; Formation (northeastern Argentina) has the most diverse caviomorph rodent assemblage of South America. The family Dinomyidae, with a single extant species (Dinomys branickii), also has its highest taxonomic diversity in this unit: 18 genera and 27 species, many of doubtful status. A reexamination of the holotypes of several species and other published and unpublished material leads to the following conclusions: "Tetrastylomys castellanosi" should be considered Tetrastylussp.; the type series of "Eumegamys contortus" pertains to Carlesiapendolaiand Rusconia crassidens; "Pentastylomysseriei" is ajunior synonym Gyriabrusholmbergi; "Protomegamys" coligatusshould be included in the genus Gyriabrus; "Doellomys parcus" is ajunior synonym of Gyriabrus coligatus (new combination); "Diaphoromys compressidens" and "Eumegamys dubius" are ajunior synonyms of Diaphoromys gamayensis; "Briaromys trouessartianus" is a nomen dubium; "Megamys racedi" and "Megamys depressidens" are nomina vana; and Pseudosigmomys paranensis, Telodontomys compressidens, Diaphoromys mesopotamicus, Eumegamysscalabrinianus, and Rusconia crassidens are valid. In addition, Arazamys castiglionii is recognized for the first time in Argentina. With this revision, the taxonomic diversity of Dinomyidae from the Ituzaing & oacute; Formation is reduced to 13 genera and 19 species. Nevertheless, it remains higher than other coeval units of South America, like the Urumaco Formation in Venezuela (five genera), Solim & otilde;es Formation in Brazil (nine genera), Camacho Formation in Uruguay (four genera), and Cerro Azul Formation in Central Argentina (four genera).
Scolecodonts were particularly abundant during the Ordovician, with low extinction rates that experienced a slight increase in the Late Ordovician. In this work, we describe for the first time a Late Ordovician scolecodont fauna from La Pola creek, in the Villicum Range of the Eastern Precordillera. This fauna was collected from the upper part of the La Pola Formation and the lower members of the Don Braulio Formation. The recovery methodology included modifications to standard techniques to obtain complete forms without mechanical and/or chemical damage. Two distinctive scolecodont assemblages have been identified. The oldest assemblage, named Assemblage A, located in the La Pola Formation, is characterized by Xanioprion sp. 1, Xanioprion sp. 2, Oenonites aff. O. eichwaldi, and Oenonites sp. The youngest assemblage, Assemblage B, located in the Fossiliferous Mudstones and Sandstones Member, includes Andiprion paxtonae, Xanioprion cf. X. borealis, Kettneritessp., and forms of the Ramphoprionidae family. Both assemblages span the Sandbian, Katian, and Hirnantian sequences. A significant difference in polychaete diversity has been observed between the two assemblages. This difference relates to geological events during the Katian-Hirnantian interval, including tectonic activity, sea level changes, glaciation, and the potential for massive extinction.
Abelisauridae were medium to large-bodied carnivorous dinosaurs with short, ornamented skulls, poorly recurved ziphodont teeth, and reduced forelimbs. They were the dominant terrestrial carnivores in many Gondwanan ecosystems during the Cretaceous. Their Jurassic origin, primarily based on the putative abelisaurid Eoabelisaurus from the Early Jurassic of Patagonia, remains debated, with many authors considering Abelisauridae as a strictly Cretaceous theropod radiation. Here, we describe several historically and stratigraphically important isolated theropod teeth from Gondwana, identified as belonging to abelisaurids using new cladistic and machine learning methods. Dental evolution in Abelisauridae was additionally explored using an updated version of a dentition-based data matrix focused on ceratosaurs. Results of this study show that the evolution of the dentition in abelisaurids was marked by a decrease in size of the mesialmost dentary teeth and the displacement of the tallest crowns towards the middle part of the maxilla. Two isolated abelisaurid teeth from the Late Cretaceous of India and Patagonia were also identified as the earliest published record of a non-avian theropod in Asia and an abelisaurid in Argentina, respectively. More importantly, isolated theropod teeth confidently referred to Abelisauridae from the Middle Jurassic of Madagascar provide additional support for the emergence of this clade in Gondwana before the Late Jurassic and reveal that the acquisition of abelisaurid dental traits occurred early in the evolutionary history of one of the most successful radiations of non-avian theropods from Europe and the Southern Hemisphere.
The Colotepec Formation crops out along the southern Pacific coast of Oaxaca, Mexico. This unit harbors a notable diversity of mollusks from the Pleistocene, mainly taxa of Bivalvia and Gastropoda. The malacological assemblage of both localities consists of 53 taxa of Bivalvia and 71 of Gastropoda; all of them are currently distributed in the southern part of Mexico. Also, specimens of rhodoliths, echinoids, and crustaceans were identified. All the identified taxa inhabit shallow and warm tropical waters, and some are from coastal lagoons. Both localities share 16 taxa of Bivalvia and 11 of Gastropoda. The assemblages are considered para-autochthonous. Most taxa inhabit subtidal environments, on both hard and soft substrates. Bivalves with thick shells display a variety of associated sclerobionts, including bivalves, gastropods, sponges, serpulids, and bryozoans. The ichnodiversity comprises Thalassinoides, Psilolichnus, and Ophiomorpha nodosa. According to the rate of subsidence, the maximal age of the Pleistocene sequences may range from 248,000 to 112,000 years BP (Marine Isotope Stage 8 to Marine Isotope Stage 5). The information on the Pleistocene assemblages provides valuable evidence for conservation strategies for modern taxa. Despite their paleontological value, the localities are at risk of natural hazards and anthropogenic pressures.
Several unpublished remains of indeterminate Late Cretaceous dinosaurs -collected by Rodolfo Casamiquela during the late 1950s- are housed in the paleontological collections of the Museo Hist & oacute;rico Jorge Gerhold (Ingeniero Jacobacci, Rio Negro, Argentina) under the acronym MHJG 189 Pa. Among them, one basicranium and two fragments of the ornamented skull roof of a mid-to-large abelisaurid stand out, representing the first record of Theropoda for the Angostura Colorada Formation. A recent prospection of the same locality produced an isolated abelisaurid tooth, representing the first undoubtedly theropod record for the Coli Toro Formation, a unit overlying the Angostura Colorada Fm. Despite their fragmentary nature, these abelisaurid remains represent the first evidence of theropod dinosaurs not only for the Ingeniero Jacobacci area, but for both Angostura Colorada and Coli Toro formations.
Abelisauridae is a group of ceratosaurian theropods that thrived mainly in Gondwana during the Cretaceous. Their fossil record is currently represented by more than 25 species, and their most complete and abundant records are from the Argentinean Patagonia. Outside Patagonia, the record of named Argentinean ceratosaurians has been limited to the Cretaceous of the Salta Province, with the noasaurid Noasaurus-represented by a fragmentary skeleton-and the brachyrostran abelisaurid Guemesia-represented by a nearly complete braincase and partial skull roof-. Here, we report a new abelisaurid theropod specimen (CRILAR-Pv 506) from the Late Cretaceous of La Rioja Province, northwestern Argentina. It was found at the Tama locality, in outcrops of the Campanian Los Llanos Formation, and associated with titanosaurian sauropod remains. The new abelisaurid specimen is represented by a first dorsal centrum, a second dorsal vertebra, a partial sacrum, left ilium, pubis and ischium, and other indeterminate elements. A unique combination of character states led us to propose the new genus and species Vitosaura colozacani. Phylogenetic analyses found Vitosaura either as a non-brachyrostran abelisaurid, closely related to Indo-Malagasy species in some trees, or a non-carnotaurinin furileusaurian. However, the interrelationships among abelisaurids are poorly supported. Our comparisons confirm the presence of abelisaurids in the Los Llanos Formation and this is the first named theropod taxon in the Cretaceous of La Rioja Province.
Litopterna is an order of South American Native Ungulates, known for their cursorial adaptations. However, these features are only well documented in specimens from the late Oligocene (Deseadan Age) and Neogene. Here, we report a partial skeleton of a small litoptern from Gran Hondonada (middle-late Eocene). It consists of elements from both hind limbs of the same individual. Preliminary cladistic analyses (113 dental, cranial, and postcranial characters scored across 50 taxa) recovered the specimen (MLP-PV 67-II-27-375) as a branch of Lopholipterna that diverged before Macraucheniidae and Proterotheriidae, a position supported by two dental and four postcranial synapomorphies. It shares the following plesiomorphic traits with Protolipternidae: absence of the patellar groove on the tibia, a crest-like peroneal process, and the presence of a plantar process on the ectocuneiform bone. Like other lopholipterns, its tibia shows an anterior facet for the astragalus, a reduced medial malleolus, and more complex facets in the tarsal sinus. Various regression models were applied to associate MLP-PV 67-II-27-375 with a known taxon based on tooth size. An indeterminate Adianthidae was the only compatible match. However, MLP-PV 67-II-27-375 could also belong to a taxon not represented by dental remains. Regardless of its taxonomic identity, MLP-PV 67-II-27-375 suggests that many postcranial specializations characteristic of Macraucheniidae and Proterotheriidae were present in their shared ancestors since at least the late Eocene. Anisolambdidae and Adianthidae were recovered as a polyphyletic group of branches that diverged early. Future discoveries, especially of postcranial material, would help to better understand the evolution of Litopterna.
This work presents the first palynological and palynofacies analysis of the Rio Tarde Formation (Aptian-Albian) from the Parque Nacional Perito Moreno, Santa Cruz Province, Argentina. Four samples from the lower member of the unit were analyzed, revealing a palynological assemblage composed of thirteen species. Nine of these correspond to ferns from the families Anemiaceae, Cyatheaceae, Gleicheniaceae, Lygodiaceae, and Schizaeaceae; three are gymnosperms assigned to the families Araucariaceae, Hirmeriellaceae, and Podocarpaceae; and one species represents a freshwater alga of the genus Botryococcus. The recovered association of palynomorphs allows us to infer temperate to warm and relatively humid paleoclimatic conditions. The palynological organic matter, dominated by dark brown to black translucent phytoclasts, suggests a significant contribution of continental material from macrophyte remains, consistent with a fluvial depositional environment.
The Cerro Overo-La Invernada area (Bajo de la Carpa Formation, Upper Cretaceous, Santonian) in northern Patagonia has yielded abundant fossils of abelisaurid theropods, including cranial, vertebral, pectoral, and pelvic remains. However, forelimb bones were unknown. Here, we describe a humerus that exhibits distinctive features that allow its assignment to Abelisauridae, for example, flattened distal condyles, a greater tubercle distally located, and a humeral head subspherical in proximal view. It also exhibits a noticeable torsion of the distal end. Morphofunctional analysis indicates a substantial capacity for protraction along with a limited capacity for lateromedial movement. In a general aspect, MAU-PV-LI-737 is morphologically intermediate between the more gracile humerus of noasaurids and the robust shape observed in Campanian-Maastrichtian abelisaurid forms.
