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To provide context for the diversification of archosaurs—the group that includes crocodilians, dinosaurs, and birds—we generated draft genomes of three crocodilians: Alligator mississippiensis (the American alligator), Crocodylus porosus (the saltwater crocodile), and Gavialis gangeticus (the Indian gharial). We observed an exceptionally slow rate of genome evolution within crocodilians at all levels, including nucleotide substitutions, indels, transposable element content and movement, gene family evolution, and chromosomal synteny. When placed within the context of related taxa including birds and turtles, this suggests that the common ancestor of all of these taxa also exhibited slow genome evolution and that the comparatively rapid evolution is derived in birds. The data also provided the opportunity to analyze heterozygosity in crocodilians, which indicates a likely reduction in population size for all three taxa through the Pleistocene. Finally, these data combined with newly published bird genomes allowed us to reconstruct the partial genome of the common ancestor of archosaurs, thereby providing a tool to investigate the genetic starting material of crocodilians, birds, and dinosaurs.

The archosaur species Teleocrater rhadinus , part of the new clade Aphanosauria, is an example of the earliest divergence of the avian stem lineage (Avemetatarsalia), the lineage that contains dinosaurs (including birds). Earliest avian archosaur The early history of the bird-line archosaurs, a group including dinosaurs, birds and pterosaurs, but excluding crocodilians, is not well defined. This is due in part to a fragmentary fossil record, but the distinctive morphology of pterosaurs has also obscured their ancestry. Sterling Nesbitt and colleagues describe a new species, Teleocraterrhadinus , from the Middle Triassic of Tanzania, that represents the most primitive known member of the bird-line archosaurs. Teleocrater provides the best guide so far to the ancestral bird-line condition. It was a lightly built, quadrupedal carnivore, so more like a crocodile than the small bipeds often depicted at this point in archosaur evolution. These are long-awaited findings on Teleocrater , which was undergoing study by the late Alan Charig of the Natural History Museum in London, and remained unpublished on his death in 1997. The relationship between dinosaurs and other reptiles is well established 1 , 2 , 3 , 4 , but the sequence of acquisition of dinosaurian features has been obscured by the scarcity of fossils with transitional morphologies. The closest extinct relatives of dinosaurs either have highly derived morphologies 5 , 6 , 7 or are known from poorly preserved 8 , 9 or incomplete material 10 , 11 . Here we describe one of the stratigraphically lowest and phylogenetically earliest members of the avian stem lineage (Avemetatarsalia), Teleocrater rhadinus gen. et sp. nov., from the Middle Triassic epoch. The anatomy of T. rhadinus provides key information that unites several enigmatic taxa from across Pangaea into a previously unrecognized clade, Aphanosauria. This clade is the sister taxon of Ornithodira (pterosaurs and birds) and shortens the ghost lineage inferred at the base of Avemetatarsalia. We demonstrate that several anatomical features long thought to characterize Dinosauria and dinosauriforms evolved much earlier, soon after the bird–crocodylian split, and that the earliest avemetatarsalians retained the crocodylian-like ankle morphology and hindlimb proportions of stem archosaurs and early pseudosuchians. Early avemetatarsalians were substantially more species-rich, widely geographically distributed and morphologically diverse than previously recognized. Moreover, several early dinosauromorphs that were previously used as models to understand dinosaur origins may represent specialized forms rather than the ancestral avemetatarsalian morphology.

Simultaneously analysing morphological, molecular and stratigraphic data suggests a potential resolution to a major remaining inconsistency in crocodylian evolution. The ancient, long-snouted thoracosaurs have always been placed near the Indian gharial Gavialis , but their antiquity ( ca 72 Ma) is highly incongruous with genomic evidence for the young age of the Gavialis lineage ( ca 40 Ma). We reconcile this contradiction with an updated morphological dataset and novel analysis, and demonstrate that thoracosaurs are an ancient iteration of long-snouted stem crocodylians unrelated to modern gharials. The extensive similarities between thoracosaurs and Gavialis are shown to be an almost ‘perfect storm’ of homoplasy, combining convergent adaptions to fish-eating, as well resemblances between genuinely primitive traits (thoracosaurs) and atavisms ( Gavialis ). Phylogenetic methods that ignore stratigraphy (parsimony and undated Bayesian methods) are unable to tease apart these similarities and invariably unite thoracosaurs and Gavialis. However, tip-dated Bayesian approaches additionally consider the large temporal gap separating ancient (thoracosaurs) and modern ( Gavialis ) iterations of similar long-snouted crocodyliforms. These analyses robustly favour a phylogeny which places thoracosaurs basal to crocodylians, far removed from modern gharials, which accordingly are a very young radiation. This phylogenetic uncoupling of ancient and modern gharial-like crocs is more consistent with molecular clock divergence estimates, and also the bulk of the crocodylian fossil record (e.g. all unequivocal gharial fossils are very young). Provided that the priors and models attribute appropriate relative weights to the morphological and stratigraphic signals—an issue that requires investigation—tip-dating approaches are potentially better able to detect homoplasy and improve inferences about phylogenetic relationships, character evolution and divergence dates.

Caimanines are crocodylians currently restricted to South and Central America and the oldest members are from lower Palaeocene localities of the Salamanca Formation (Chubut Province, Argentina). We report here a new caimanine from this same unit represented by a skull roof and partial braincase. Its phylogenetic relationships were explored in a cladistic analysis using standard characters and a morphogeometric two-dimensional configuration of the skull roof. The phylogenetic results were used for an event-based supermodel quantitative palaeobiogeographic analysis. The new species is recovered as the most basal member of the South American caimanines, and the Cretaceous North American lineage ‘ Brachychampsa and related forms' as the most basal Caimaninae. The biogeographic results estimated north-central North America as the ancestral area of Caimaninae, showing that the Cretaceous and Palaeocene species of the group were more widespread than thought and became regionally extinct in North America around the Cretaceous–Palaeocene boundary. A dispersal event from north-central North America during the middle Late Cretaceous explains the arrival of the group to South America. The Palaeogene assemblage of Patagonian crocodylians is composed of three lineages of caimanines as a consequence of independent dispersal events that occurred between North and South America and within South America around the Cretaceous–Palaeogene boundary.

Amazonia contains one of the world's richest biotas, but origins of this diversity remain obscure. Onset of the Amazon River drainage at approximately 10.5 Ma represented a major shift in Neotropical ecosystems, and proto-Amazonian biotas just prior to this pivotal episode are integral to understanding origins of Amazonian biodiversity, yet vertebrate fossil evidence is extraordinarily rare. Two new species-rich bonebeds from late Middle Miocene proto-Amazonian deposits of northeastern Peru document the same hyperdiverse assemblage of seven co-occurring crocodylian species. Besides the large-bodied Purussaurus and Mourasuchus, all other crocodylians are new taxa, including a stem caiman—Gnatusuchus pebasensis—bearing a massive shovel-shaped mandible, procumbent anterior and globular posterior teeth, and a mammal-like diastema. This unusual species is an extreme exemplar of a radiation of small caimans with crushing dentitions recording peculiar feeding strategies correlated with a peak in proto-Amazonian molluscan diversity and abundance. These faunas evolved within dysoxic marshes and swamps of the long-lived Pebas Mega-Wetland System and declined with inception of the transcontinental Amazon drainage, favouring diversification of longirostrine crocodylians and more modern generalist-feeding caimans. The rise and demise of distinctive, highly productive aquatic ecosystems substantially influenced evolution of Amazonian biodiversity hotspots of crocodylians and other organisms throughout the Neogene.

Skulls are a critical part of the crocodile through which we can distinguish between the different genera and species. Most of the crocodiles which previously studied from the Eocene–Oligocene to the Miocene times in Egypt were concerned with the identification of the genus and sometimes on the species without a detailed focusing on the evolution, comparing between them and trying to determine the ancestor or the closest species of them to the living crocodile in Egypt. The only known living species of Crocodylus in Egypt is Crocodylus niloticus which inhabits Lake Nasser in Aswan, southern of Egypt. From the Cenozoic era, broad snouted crocodiles diversity had been reported in Egypt. About 35 million years ago, through the Eocene epoch, the crocodilian fossils from Fayum provided evidence of the diversity of crocodile species including Crocodylus articeps and Crocodylus megarhinus . In addition to that, throughout the Early Miocene epoch, from about 18 million years ago, in Wadi Moghra Egypt crocodilian fossils demonstrate another diversity, extended to the first appearance of Rimasuchus lloydi which placed inside the Osteolaeminae later. By various measurements and carefully morphological examination of the different species recorded from Egypt, it was found that there are high levels of variation in morphology of the skulls including their dimensions, and the sutures shapes especially between premaxilla and maxilla ventrally and also between maxilla and palatine, as well as the extension of the maxillary ramus of the ectopterygoid. Using cluster analysis, it is proven that Eocene Crocodylus is the ancestor to all known broad snouted species recorded from Egypt since the Eocene time. The closest species to the Eocene specimen is the living Crocodylus niloticus . That in fact make that most of the broad snouted crocodiles in Egypt are endemic.

The first crocodyliform specimen from the Maastrichtian Chorrillo Formation (Austral Basin, Patagonia) is here described. The discovery was made about 30 km to the SW of the town of El Calafate (Province of Santa Cruz, Argentina) and consists of a beautifully preserved and articulated skull and jaws, and part of the postcranial skeleton that were preserved encased in a large concretion. This new taxon belongs to the notosuchian clade Peirosauridae, representing the latest and southernmost record for this group of crocodyliforms. The new taxon is recovered as closely related to other robust and broad-snouted peirosaurids that lived by the end of the Cretaceous Period, such as Colhuehuapisuchus from the Maastrichtian of Central Patagonia and Miadanasuchus oblita from the Maastrichtian of Madagascar. The completeness of the new specimen reveals, for the first time, the anatomy and body plan of a large and broad snouted peirosaurid. The new taxon bears large ziphodont teeth, a broad oreinirostral snout that is only slightly longer than 50% the skull length, and a deep adductor chamber in the temporal region and posterior mandibular ramus. The anterior region of its postcranial skeleton is preserved and shows broad scapula and a robust humerus features previously known in large predatorial notosuchians. The new crocodyliform adds to the predatorial component of terrestrial ecosystems at high paleolatitudes by the end of the Cretaceous Period.

Challenges in freshwater organism conservation in West Africa are worsened by significant knowledge gaps, even for charismatic species like crocodiles. This study addresses these gaps by assessing crocodile diversity, distribution, and conservation threats in Guinea-Bissau, where existing data is outdated. We used visual surveys, inquiries, molecular barcoding, camera trapping, and bibliographic reviews to investigate crocodile populations. Notably, we found evidence suggesting the Nile crocodile ( Crocodylus niloticus ), previously thought extinct in West Africa since about 200 years, may persist in Guinea-Bissau’s Cacheu region. We also confirmed the presence of the West African crocodile ( Crocodylus suchus ) in major river basins and coastal lagoons, including the Bijagós Archipelago, and the West African dwarf crocodile ( Osteolaemus cf. tetraspis ) in the southern mainland and the Bijagós Archipelago. Habitat loss and deliberate killings were identified as major threats. Standardized surveys and genetic sampling are essential to assess population size, connectivity, and genetic diversity, informing evolutionary studies and conservation planning. Conservation efforts should prioritize habitat protection through community-managed reserves and restoration initiatives. Additionally, engaging local communities to raise awareness and develop conflict mitigation strategies is crucial, particularly in areas with human-crocodile interactions.

Crocodilians have dominated predatory niches at the water-land interface for over 85 million years. Like their ancestors, living species show substantial variation in their jaw proportions, dental form and body size. These differences are often assumed to reflect anatomical specialization related to feeding and niche occupation, but quantified data are scant. How these factors relate to biomechanical performance during feeding and their relevance to crocodilian evolutionary success are not known. We measured adult bite forces and tooth pressures in all 23 extant crocodilian species and analyzed the results in ecological and phylogenetic contexts. We demonstrate that these reptiles generate the highest bite forces and tooth pressures known for any living animals. Bite forces strongly correlate with body size, and size changes are a major mechanism of feeding evolution in this group. Jaw shape demonstrates surprisingly little correlation to bite force and pressures. Bite forces can now be predicted in fossil crocodilians using the regression equations generated in this research. Critical to crocodilian long-term success was the evolution of a high bite-force generating musculo-skeletal architecture. Once achieved, the relative force capacities of this system went essentially unmodified throughout subsequent diversification. Rampant changes in body size and concurrent changes in bite force served as a mechanism to allow access to differing prey types and sizes. Further access to the diversity of near-shore prey was gained primarily through changes in tooth pressure via the evolution of dental form and distributions of the teeth within the jaws. Rostral proportions changed substantially throughout crocodilian evolution, but not in correspondence with bite forces. The biomechanical and ecological ramifications of such changes need further examination.

A new notosuchian crocodyliform from the Late Cretaceous Bauru Group found in the southeastern State of São Paulo (Brazil) is described here. The new taxon, Caipirasuchus stenognathus, is referred as a new species of the recently erected genus Caipirasuchus within the clade Sphagesauridae based on a phylogenetic analysis of basal mesoeucrocodylians. Caipirasuchus stenognathus is represented by an almost complete skull and lower jaw that has autapomorphic characters that distinguish it from other species of Sphagesauridae. These autapomorphies include: maxilla forming part of the orbital margin (absence of lacrimal-jugal contact), nasal with smooth depressions on the posterior region close to the contact with the maxilla and lacrimal, postorbital with posterior palpebral facet that extends posteriorly underneath the ear-flap groove, and a distinct anterior process of the medial flange of the retroarticular process. Additionally, the new taxon lacks autapomorphic features described in other sphagesaurids. The phylogenetic analysis results in a monophyletic genus Caipirasuchus, that is the sister group of a clade fomed by Sphagesaurus huenei, Caryonosuchus pricei, and Armadillosuchus arrudai. Sphagesaurids also include a basal clade formed by Adamantinasuchus navae and Yacarerani boliviensis. Other notosuchian taxa, such as Mariliasuchus amarali, Labidiosuchus amicum, Notosuchus terrestris, and Morrinhosuchus luziae are successive sister taxa of Sphagesauridae, forming a clade of advanced notosuchians that are restricted to the Late Cretaceous of South America. These results contrast with most previous phylogenetic hypotheses of the group that depicted some members of Sphagesauridae as more closely related to baurusuchids, or found Asian (e.g., Chimaerasuchus) or African (Malawisuchus, Pakasuchus) forms nested within advanced notosuchians that are, according to our analysis, endemic of the Late Cretaceous of South America.