Agustin Guillermo Martinelli

Sauropodomorph dinosaurs show how appendicular skeletal architecture accommodated extreme increases in body mass. Although sauropod gigantism has been linked to columnar limbs, wide-gauge posture, thick articular cartilage and tubular long-bone organization, the biomechanical interaction among these components is poorly understood. Here, we examine how femo ral shape, internal bone architecture and articular soft tissues influenced mechanical scaling across Sauropodomorpha. We generated three-dimensional femoral models spanning early sauropodomorphs, narrow-gauge diplodocoids, intermediate-gauge titanosauriforms, wide-gauge titanosaurs and an African elephant control. Finite element analyses compared theoretical solid models with taxon-specific native configurations, incorporating medullary cavities and articular cartilage caps. Mechanical performance was assessed using 95th-percentile von Mises stress, strain energy density and structural stiffness. Femoral performance did not scale uniformly with body mass. The two sampled narrow-gauge taxa, Diplodocus and Amargasaurus, defined steeper scaling trajectories for stress and strain energy density, whereas wide-gauge titanosaurs generally displayed flatter trajectories, comparatively lower stress and strain energy density, and elevated stiffness in several large-bodied forms. Targeted sensitivity analyses further showed that the mechanical effects of medullary architecture and cartilage depended on their interaction with taxon-specific femoral geometry. These findings suggest that sauropod gigantism was sustained by lineage-specific combinations of femoral geometry, internal architecture and articular soft tissues.

The sauropod dinosaurs were the largest terrestrial animals to have inhabited the Earth (Carballido et al., 2017; Upchurch et al., 2004; Wilson, 2002), with an adult body mass exceeding 50 metric t...

We describe a new large‐sized paracrocodylomorph pseudosuchian, Shakajlura riojanensis gen. et sp. nov., from the Tarjadia Assemblage Zone (AZ) levels (upper Ladinian to lower Carnian) of the Chañares Formation, La Rioja Province, northwestern Argentina. The specimen consists of several disarticulated cranial, and a few postcranial, bones and was collected from stratigraphic levels seemingly coeval with those where Luperosuchus fractus , a loricatan of similar size, was found. The general morphology and stratigraphic occurrence of Shakajlura riojanensis suggests the possibility of close affinities with Luperosuchus fractus , but considerable differences in key features between the two holotypes (e.g. Shakajlura riojanensis lacks the following: ornamentation on the lateral side of the maxilla, a prominent curvature of the dorsal portion of the nasals, and a knob‐like structure on the postorbital) and a unique combination of character states among pseudosuchians enabled us to erect a new genus and species. Shakajlura riojanensis can be distinguished by the presence of a prominent shelf on the medial surface of the jugal, an incision on the ventral portion of the ascending process of the quadrate, and an enlarged prearticular compared with the preserved jaw elements. Shakajlura riojanensis is recovered as an early‐diverging paracrocodylomorph, but the possibility that it represents an early‐diverging member of Loricata cannot be discarded. This new species expands the current knowledge of the paracrocodylomorphs of the Tarjadia AZ and introduces a new component to the top predators of the Chañares Formation.

Arhinolemur scalabrinii † Ameghino, 1898 was originally described as a strepsirrhine primate (Mammalia) but has been recognized as an anostomid fish since 2012. It remains the only extinct anostomid species known from complete cranial material. The holotype and only known specimen come from the Ituzaingó Formation, Entre Ríos province, Argentina, dated to the Late Miocene. This study provides a comprehensive redescription of its cranial anatomy using micro‐CT data and comparative osteology. Phylogenetic analyses combining morphological, cytogenetic, and molecular data place Arhinolemur scalabrinii within a clade that includes species previously assigned to Megaleporinus , supporting the treatment of Megaleporinus as a junior synonym of Arhinolemur . The species exhibits a unique combination of features—such as a rhomboidal‐shaped mesethmoid, a distinct fontanelle, and specialized dentition—that justify the revalidation of the genus. Arhinolemur scalabrinii represents a key morphological reference for understanding Miocene diversification within Anostomidae and illustrates the paleontological value of micro‐CT analysis of exceptional, articulated fossil fishes in reconstructing the evolutionary history of Neotropical freshwater ichthyofaunas.

During the Late Triassic epoch (237–201 million years ago), the terrestrial ecosystems of Pangaea underwent drastic changes^1,2 that led to the rise and diversification of mammaliaforms³, crocodylomorphs⁴ and dinosaurs⁵. Although the Carnian sedimentary rocks of South America provided much of the available evidence for understanding the early evolution of these clades, key discoveries have remained restricted to the Ischigualasto-Villa Unión^6,7 and Paraná basins⁸ in Argentina and Brazil, respectively. Here we report a Carnian tetrapod assemblage from the previously unrecognized Northern Precordillera Basin in northwestern Argentina. Discoveries at this basin, in the Quebrada Santo Domingo site, include a nearly complete skeleton of the early sauropodomorph Huayracursor jaguensis gen. et sp. nov., and typical components of Late Carnian faunas, such as hyperodapedontine rhynchosaurs, gomphodontosuchine traversodontid cynodonts, and aetosaurs. Compared to its generally small and short-necked Carnian counterparts^9,10, Huayracursor is larger and exhibits an incipient elongation of its cervical vertebrae, representing an intermediate condition for size and cervical elongation between known Carnian and Norian sauropodomorphs¹¹. This discovery provides one of the oldest pieces of evidence of increased body mass and neck elongation in early Sauropodomorpha.

The Upper Triassic Santa Maria Supersequence in Brazil has yielded numerous cynodont species, including derived probainognathians, which are relevant for understanding the cynodont–mammal transition. One of these cynodonts is Brasilodon quadrangularis , considered to be the sister taxon to Mammaliaformes due to a suite of apomorphic features in the skull, dentition and postcranium. Specimens referred to this species have been described in detail, representing different ontogenetic stages. However, we know little of the functional performance and skull mechanics of this species and how this relates to recent studies of cynodont–mammaliaform skull mechanics. Here we use beam analysis and finite element analysis (FEA) to assess the function of the skulls of Brasilodon and compare their functional performance to the early mammaliaforms Morganucodon and Kuehneotherium . The ontogenetic series of Brasilodon shows a trend of increasing overall jaw strength and resistance, potentially indicating a change in diet and feeding behaviour through ontogeny. Beam analysis suggests that this taxon is more similar in bite performance to Morganucodon than to Kuehneotherium , regarding jaw strength and torsion resistance. Additionally, one of the studied skulls (UFRGS‐PV‐1043‐T) was chosen for digital restoration and muscular reconstruction to increase understanding of the jaw muscle modifications in the cynodont–mammal transition. The muscular reconstruction revealed that the relative force contributions of the temporalis and masseter muscles of the Brasilodon ontogenetic series are more similar to non‐mammaliaform cynodonts, such as Chiniquodon , than to mammaliaforms. Our results provide further insight into cranial musculoskeletal anatomy and biomechanics in derived non‐mammaliaform cynodonts.

Dinosaurs evolved a unique respiratory system with air sacs that contributed to their evolutionary success. Postcranial skeletal pneumaticity (PSP) has been used to infer the presence of air sac systems in some fossil archosaurs. While unambiguous evidence of PSP is well documented in pterosaurs and post‐Carnian saurischians, it remains absent within Ornithischia, challenging phylogenetic predictions. We used computed tomography to examine the internal vertebral microanatomy of three Huallasaurus australis specimens, a saurolophine hadrosaur from the Late Cretaceous of Patagonia, Argentina. The internal structure reveals a relatively dense trabecular architecture lacking evidence of invasive pneumaticity across the centra, neural arches, and neural spines, contrasting with the condition in post‐Carnian saurischians. The internal vertebral pattern of Huallasaurus resembles that of silesaurs more than other apneumatic archosauriforms. These observations are consistent with the hypothesis that invasive air sac diverticula did not evolve in Ornithischia and align with the previously proposed “pelvic bellows” ventilation model for the group. The internal vertebral architecture in this hadrosaur shows superficial similarities to the trabecular structure seen in some large mammals, although functional equivalence remains speculative. The absence of invasive air sacs in Huallasaurus , combined with dense trabecular matrix and thin cortical walls, may have supported large body sizes or accommodated intraosseous fat reserves, though this requires further testing. This stock of fatty tissues could have provided energy for these hadrosaurs during regional migration, as observed in modern migratory mammals.