The dawn of an Era: New contributions on comparative and functional anatomy of Triassic tetrapods.

The Triassic period stands as a crucial moment for understanding tetrapod evolution, marking the emergence and early diversification of numerous lineages that persist in today's ecosystems. Birds, crocodiles, testudines, lizards, and mammals can all trace their origins to the Triassic, which is distinguished by several adaptive radiation events that fostered unparalleled diversity in body plans and lifestyles. Beyond this macroevolutionary significance, the Triassic period serves as fertile ground for scientific inquiry, especially in tetrapod studies. The aim of this Special Issue is to assemble a diverse array of new contributions focused on continental Triassic tetrapods globally, encouraging collaboration among researchers across generations, pooling their efforts to comprehend this pivotal moment in tetrapod evolutionary history. This issue encompasses almost 40 varied contributions, spanning topics from comparative and functional anatomy, including descriptions of novel taxa, comprehensive anatomical reviews, systematic investigations, phylogenetic analyses, paleoneurological studies, biomechanical assessments, and detailed examinations of histology and ontogeny. Collectively, this Special Issue offers an extensive exploration of Triassic tetrapods from anatomical, ecological, and evolutionary perspectives, unveiling fresh insights into this intriguing moment in vertebrate evolutionary history.

A new archosauriform species from the Panchet Formation of India and the diversification of Proterosuchidae after the end-Permian mass extinction.

Proterosuchidae represents the oldest substantial diversification of Archosauromorpha and plays a key role in understanding the biotic recovery after the end-Permian mass extinction. Proterosuchidae was long treated as a wastebasket taxon, but recent revisions have reduced its taxonomic content to five valid species from the latest Permian of Russia and the earliest Triassic (Induan) of South Africa and China. In addition to these occurrences, several isolated proterosuchid bones have been reported from the Induan Panchet Formation of India for over 150 years. Following the re-study of historical specimens and newly collected material from this unit, we erect the new proterosuchid species Samsarasuchus pamelae, which is represented by most of the presacral vertebral column. We also describe cf. proterosuchid and proterosuchid cranial, girdle and limb bones that are not referred to Samsarasuchus pamelae. Phylogenetic analyses recovered Samsarasuchus pamelae within the new proterosuchid clade Chasmatosuchinae. The taxonomic diversity of Proterosuchidae is substantially expanded here, with at least 11 nominal species and several currently unnamed specimens, and a biogeographical range encompassing present-day South Africa, China, Russia, India, Brazil, Uruguay and Australia. This indicates a broader taxonomic, phylogenetic and biogeographic diversification of Proterosuchidae than previously thought in the aftermath of the end-Permian mass extinction.

Earliest teredid beetle from mid-Cretaceous amber of northern Myanmar (Coleoptera: Coccinelloidea: Teredidae): new genus and species

The earliest fossil member of Teredidae, Delteredolaemus hei Li & Cai gen. et sp. nov., is reported from mid-Cretaceous Burmese amber. Delteredolaemus is assigned to the extant tribe Teredini, and shares a generally similar morphology with the extant genus Teredolaemus Sharp, 1885, although it can be distinguished from all other members in the tribe by the shape of the pronotum and mesoventral process, as well as the anteromedially tumid metaventrite.(AU)

Anomocephalobus, a new genus of minute marsh-loving beetles from mid-Cretaceous Burmese amber (Coleoptera: Limnichidae)

Limnichidae are currently a moderately diverse beetle family with a sparse fossil record. Here we describe a new limnichid genus and species, Anomocephalobus liuhaoi Li, Jäch & Cai gen. et sp. nov., from the mid-Cretaceous amber from northern Myanmar. Anomocephalobus gen. nov. is tentatively assigned to the extant subfamily Cephalobyrrhinae, based on its transverse metacoxae, 5-segmented protarsi, and absence of grooves on the ventral surface for reception of legs, though its oval body shape is somewhat deviating from extant Cephalobyrrhinae. The generic placement of the recently described Erichia cretacea Yu, Ślipiński, Ren & Pang, 2018 is also discussed.(AU)

A paraphyletic 'Silesauridae' as an alternative hypothesis for the initial radiation of ornithischian dinosaurs.

Whereas ornithischian dinosaurs are well known from Jurassic and Cretaceous deposits, deciphering the origin and early evolution of the group remains one of the hardest challenges for palaeontologists. So far, there are no unequivocal records of ornithischians from Triassic beds. Here, we present an alternative evolutionary hypothesis that suggests consideration of traditional 'silesaurids' as a group of low-diversity clades representing a stem group leading to core ornithischians (i.e. unambiguous ornithischians, such as Heterodontosaurus tucki). This is particularly interesting because it fills most of the ghost lineages that emerge from the Triassic. Following the present hypothesis, the lineage that encompasses the Jurassic ornithischians evolved from 'silesaurids' during the Middle to early Late Triassic, while typical 'silesaurids' shared the land ecosystems with their relatives until the Late Triassic, when the group completely vanished. Therefore, Ornithischia changes from an obscure to a well-documented clade in the Triassic and is represented by records from Gondwana and Laurasia. Furthermore, according to the present hypothesis, Ornithischia was the first group of dinosaurs to adopt an omnivorous/herbivorous diet. However, this behaviour was achieved as a secondary step instead of an ancestral condition for ornithischians, as the earliest member of the clade is a faunivorous taxon. This pattern was subsequently followed by sauropodomorph dinosaurs. Indeed, the present scenario favours the independent acquisition of an herbivorous diet for ornithischians and sauropodomorphs during the Triassic, whereas the previous hypotheses suggested the independent acquisition for sauropodomorphs, ornithischians, and 'silesaurids'.

Exceptional preservation of comma shrimp from a mid-Cretaceous Lagerstätte of Colombia, and the origins of crown Cumacea.

Mesozoic rocks with exceptional preservation of marine arthropods are known worldwide but largely restricted to mid-high latitudes. The scarcity of assemblages with exceptional preservation in low, tropical latitudes greatly limits our understanding of the origins of several modern groups and the evolution of tropical biotas through time. Here, we report the oldest crown Cumacea, or 'comma' shrimp (Arthropoda: Eumalacostraca: Peracarida) with modern familial affinities, from a new mid-Cretaceous (95-90 Ma) Lagerstätte in tropical South America. Cumaceans have one of the poorest fossil records among marine arthropods, despite today being abundant and speciose benthic organisms associated with fine-grained sediments with high fossilization potential. Eobodotria muisca gen. et sp. nov., found in mass accumulation surfaces, preserves with detail the gut, mouth parts, thoracic legs/pereopods, pleopods, uropods bearing setae, antennal flagella and even small eyes bearing ommatidia. These features, rarely preserved in fossil crustaceans, plus the large sample size (greater than 200 individuals, 6-8 mm long), allow us to discuss phylogenetic/systematic aspects and explore possible mechanisms behind their unusual accumulation. Eobodotria bridges an approximately 165 Myr gap in the cumacean fossil record, provides a reliable calibration point for phylogenetic studies and expands our understanding of exceptional preservation in past and present tropical settings.

A geometric morphometric approach to the analysis of skull shape in Triassic dicynodonts (Therapsida, Anomodontia) from South America.

Dicynodont therapsids were a major component of the Permo-Triassic terrestrial ecosystems across Pangea and have been regarded as specialized herbivores. In South America, the group was represented by several taxa of the clade Kannemeyeriiformes spanning from the Middle to the Late Triassic. In order to evaluate if cranial differences among taxa are potentially related to differences in feeding function, we performed a geometric morphometric analysis on 28 South American dicynodont crania. We digitized 19 cranial landmarks and conducted generalized Procrustes analysis, principal component analysis (PCA), principal component analysis between groups (bg-PCA), and a branch weighted squared-change parsimony approach. Phylogenetic inertia was not a significant driver of cranial shape evolution in the group, whereas PCA and bg-PCA support that major morphological shape differences are concentrated in the preorbital region (relative length of the snout and width of the caniniform process), in the position of quadrate condyle in relation to the caniniform process, and in the increase in the intertemporal surface area. In this context, tusked Dinodontosaurus, "Kannemeyeria," and Vinceria have relatively smaller adductor attachment areas and input moment arm than younger taxa lacking tusks, such as Ischigualastia, Stahleckeria, and Jachaleria. Differences in cranial morphology in later dicynodonts reflect modifications in feeding mechanics, probably due to changes in food resources (vegetation) in their habitats toward the end of the Triassic.

Braincase and endocranial anatomy of two thalattosuchian crocodylomorphs and their relevance in understanding their adaptations to the marine environment.

Thalattosuchians are a group of Mesozoic crocodylomorphs known from aquatic deposits of the Early Jurassic-Early Cretaceous that comprises two main lineages of almost exclusively marine forms, Teleosauridae and Metriorhynchoidea. Teleosaurids were found in shallow marine, brackish and freshwater deposits, and have been characterized as semiaquatic near-shore forms, whereas metriorhynchids are a lineage of fully pelagic forms, supported by a large set of morphological characters of the skull and postcranial anatomy. Recent contributions on Thalattosuchia have been focused on the study of the endocranial anatomy. This newly available information provides novel evidence to suggest adaptations on the neuroanatomy, senses organs, vasculature, and behavioral evolution of these crocodylomorphs. However, is still not clear if the major morphological differences between teleosaurids and metriorhynchids were also mirrored by changes in the braincase and endocranial anatomy. Based on X-ray CT scanning and digital endocast reconstructions we describe the braincase and endocranial anatomy of two well-preserved specimens of Thalattosuchia, the semiaquatic teleosaurid Steneosaurus bollensis and the pelagic metriorhynchid Cricosaurus araucanensis. We propose that some morphological traits, such as: an enlarged foramen for the internal carotid artery, a carotid foramen ventral to the occipital condyle, a single CN XII foramen, absence of brain flexures, well-developed cephalic vascular system, lack of subtympanic foramina and the reduction of the paratympanic sinus system, are distinctive features of Thalattosuchia. It has been previously suggested that the enlarged foramen for the internal carotid artery, the absence of brain flexures, and the hypertrophied cephalic vascular system were synapomorphies of Metriorhynchidae; however, new information revealed that all of these features were already established at the base of Thalattosuchia and might have been exapted later on their evolutionary history. Also, we recognized some differences within Thalattosuchia that previously have not been received attention or even were overlooked (e.g., circular/bilobate trigeminal foramen, single/double CN XII foramen, separation of the cranioquadrate canal from the external otic aperture, absence/presence of lateral pharyngeal foramen). The functional significances of these traits are still unclear. Extending the sampling to other Thalattosuchia will help to test the timing of acquisition and distribution of these morphological modifications among the whole lineage. Also comparison with extant marine tetrapods (including physiological information) will be crucial to understand if some (and/or which) of the morphological peculiarities of thalattosuchian braincases are products of directional natural selection resulting in a fully adaptation to a nektonic life style.

Spondyloarthropathy in vertebrae of the aquatic Cretaceous snake Lunaophis aquaticus, and its first recognition in modern snakes.

Inflammatory arthritis is documented for the first time in snakes. Ossification of the intervertebral capsule and zygapophyseal joints resulting in segmental vertebral fusion was observed in the aquatic Cretaceous snake Lunaophis aquaticus. Such pathologic alterations are pathognomonic for the spondyloarthropathy form of inflammatory arthritis. A survey of 2144 snakes in recent collections, performed to identify Holocene prevalence, revealed only two occurrences in extant snakes. The findings in Bitis gabonica and Elaphe taeniura were indistinguishable from those noted in Lunaophis aquaticus and identical to those previously recognized in modern varanids. The pathology likely represents a form of reactive arthritis related to enteropathic infection. While the disease probably did not affect general locomotion, its vertebral column position may have compromised mating.

A Late Cretaceous mammal from Brazil and the first radioisotopic age for the Bauru Group.

In the last three decades, records of tribosphenidan mammals from India, continental Africa, Madagascar and South America have challenged the notion of a strictly Laurasian distribution of the group during the Cretaceous. Here, we describe a lower premolar from the Late Cretaceous Adamantina Formation, São Paulo State, Brazil. It differs from all known fossil mammals, except for a putative eutherian from the same geologic unity and Deccanolestes hislopi, from the Maastrichtian of India. The incompleteness of the material precludes narrowing down its taxonomic attribution further than Tribosphenida, but it is larger than most coeval mammals and shows a thin layer of parallel crystallite enamel. The new taxon helps filling two major gaps in the fossil record: the paucity of Mesozoic mammals in more northern parts of South America and of tribosphenidans in the Cretaceous of that continent. In addition, high-precision U-Pb geochronology provided a post-Turonian maximal age (≤87.8 Ma) for the type stratum, which is overlain by the dinosaur-bearing Marília Formation, constraining the age of the Adamantina Formation at the site to late Coniacian-late Maastrichtian. This represents the first radioisotopic age for the Bauru Group, a key stratigraphic unit for the study of Cretaceous tetrapods in Gondwana.

Molecular development of fibular reduction in birds and its evolution from dinosaurs.

Birds have a distally reduced, splinter-like fibula that is shorter than the tibia. In embryonic development, both skeletal elements start out with similar lengths. We examined molecular markers of cartilage differentiation in chicken embryos. We found that the distal end of the fibula expresses Indian hedgehog (IHH), undergoing terminal cartilage differentiation, and almost no Parathyroid-related protein (PTHrP), which is required to develop a proliferative growth plate (epiphysis). Reduction of the distal fibula may be influenced earlier by its close contact with the nearby fibulare, which strongly expresses PTHrP. The epiphysis-like fibulare however then separates from the fibula, which fails to maintain a distal growth plate, and fibular reduction ensues. Experimental downregulation of IHH signaling at a postmorphogenetic stage led to a tibia and fibula of equal length: The fibula is longer than in controls and fused to the fibulare, whereas the tibia is shorter and bent. We propose that the presence of a distal fibular epiphysis may constrain greater growth in the tibia. Accordingly, many Mesozoic birds show a fibula that has lost its distal epiphysis, but remains almost as long as the tibia, suggesting that loss of the fibulare preceded and allowed subsequent evolution of great fibulo-tibial disparity.

An overview of the South American fossil squamates.

The evolution of squamates in South America is the result of the complex geological and paleoclimatic history of this part of the world. The incomplete and episodic fossil record allows us to know only a small part of this evolution. Most Mesozoic squamate remains come from the Patagonian region, but remarkable specimens have also been recovered from Brazil. Both major squamate clades (Iguania and Scleroglossa) are present in the South American Mesozoic. Remains of Mesozoic snakes are common and diverse in Cretaceous deposits, including some of the most primitive terrestrial forms. Paleogene and Neogene squamate remains have been recognized from Argentina, Bolivia, Brazil, Colombia, Ecuador, Peru, and Venezuela. Paleogene lizard record appears to be scarce in comparison to that of the Mesozoic, whereas snakes show an important Paleogene diversity. At least two extant boid snakes appeared during this epoch (Boa and Corallus). The South American Miocene included some extant genera of Iguania, Teiidae, and Boidae but extinct genera were also present. "Colubrids" appeared at the early Miocene, whereas the first viperid is known from the late Miocene. Most of the Paleogene and early Neogene squamate families and genera have been recognized outside their current range of distribution following favorable climatic conditions for ectothermic vertebrates. During the latest Miocene and Pliocene few extant squamate taxa are found to occur outside their present distribution. The earliest amphisbaenian of South America is known from the Pliocene. Most Pleistocene and Holocene squamate remains are assigned to living genera, and some extant species were recognized.

A new fossil subfamily of Bethylidae (Hymenoptera) from the Early Cretaceous Lebanese amber and its phylogenetic position

A new subfamily, a new genus and a new species of Bethylidae are described and illustrated from a single individual in Early Cretaceous amber from central Lebanon. Lancepyrinae subfam. nov. represented by Lancepyris opertus gen. and sp. nov. present a mosaic of features common among several bethylid subfamilies. The new taxon is easily distinguished from related taxa mainly by the forewing venation, which has an unusual combination of closed lanceolate marginal cell, Rs+M tubular and well pigmented and M+RS angled. Phylogenetic analysis including indicates that Lancepyris opertus gen. and sp. nov. is a sister group of all subfamilies that have Coleoptera as hosts. A checklist of the 45 known fossil bethylid species is provided.

A new fossil subfamily of Bethylidae (Hymenoptera) from the Early Cretaceous Lebanese amber and its phylogenetic position

A new subfamily, a new genus and a new species of Bethylidae are described and illustrated from a single individual in Early Cretaceous amber from central Lebanon. Lancepyrinae subfam. nov. represented by Lancepyris opertus gen. and sp. nov. present a mosaic of features common among several bethylid subfamilies. The new taxon is easily distinguished from related taxa mainly by the forewing venation, which has an unusual combination of closed lanceolate marginal cell, Rs+M tubular and well pigmented and M+RS angled. Phylogenetic analysis including indicates that Lancepyris opertus gen. and sp. nov. is a sister group of all subfamilies that have Coleoptera as hosts. A checklist of the 45 known fossil bethylid species is provided.

A new fossil subfamily of Bethylidae (Hymenoptera) from the Early Cretaceous Lebanese amber and its phylogenetic position

A new subfamily, a new genus and a new species of Bethylidae are described and illustrated from a single individual in Early Cretaceous amber from central Lebanon. Lancepyrinae subfam. nov. represented by Lancepyris opertus gen. and sp. nov. present a mosaic of features common among several bethylid subfamilies. The new taxon is easily distinguished from related taxa mainly by the forewing venation, which has an unusual combination of closed lanceolate marginal cell, Rs+M tubular and well pigmented and M+RS angled. Phylogenetic analysis including indicates that Lancepyris opertus gen. and sp. nov. is a sister group of all subfamilies that have Coleoptera as hosts. A checklist of the 45 known fossil bethylid species is provided.