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Phytosaurs are a group of Upper Triassic semi‐aquatic archosauriform reptiles. Their variable skull morphology forms the foundation of our understanding of their relationships and paleoecology, while only a few studies have focused on demonstrating the existence of postcranial variation. The numbers of vertebrae in the sacrum are thought to vary from two, the plesiomorphic condition for archosauriforms, to three, with the addition of a sacralized dorsal (i.e., dorsosacral) vertebra. In this study, we demonstrate the presence of a sacralized first caudal (i.e., caudosacral) vertebra in a sacrum belonging to Machaeroprosopus mccauleyi. We rule out taphonomic distortion or pathology as explanations for the inclusion of this element in the sacrum, suggesting instead that it occurred through modifications of the same developmental processes that likely produced dorsosacral vertebrae in phytosaurs. Additionally, we show that a dorsosacral vertebra is common in phytosaur specimens from the Chinle Formation and Dockum Group of the southwestern United States and suggest that it may be widespread among phytosaurs. The addition of sacral vertebrae potentially aided adaptation to larger body sizes or more terrestrial lifestyles in certain taxa. [ABSTRACT FROM AUTHOR]

A new Mystriosuchinae phytosaur, Colossosuchus techniensis, is described from the Upper Triassic Tiki Formation of India. Colossosuchus is diagnosed by multiple apomorphies, including a strongly downturned terminal rosette (c. 70°), closely spaced mediolateral band‐like ornamentation on dorsal surface of the nasal, dorsolaterally oriented supratemporal fenestra, ventrolaterally inclined postorbital–squamosal bars depressed below the skull table, dorsally convex parietal–squamosal bar that descends ventrolaterally below the skull roof, dome‐shaped skull in lateral view, prominent neural arch laminae and fossae, three sacral vertebrae, robust proximal end of the tibia, and fibula with high anteroposterior flaring of the distal end. The total body length of the largest individual recovered from the bonebed is estimated to be more than 8 m, suggesting that Colossosuchus is one of the largest phytosaurs known. Phylogenetic analysis nests Colossosuchus and other undescribed specimens from India within Mystriosuchinae. These form a distinct clade and represent the earliest record of endemism among Gondwanan phytosaurs. This clade is recovered as sister taxa to ((Volcanosuchus + Rutiodon) + Leptosuchomorpha), where the depressed supratemporal fenestra first appeared in the phytosaur lineage, a feature previously used to diagnose the derived leptosuchomorphs. Early‐diverging phytosaur diversification may have coincided with the final stages of the Carnian Pluvial Event with their possible migratory routes along the circum‐Tethyan coastline. The lineage continued to evolve mostly through endemic radiations and experienced an extinction event during early Norian, which marked the disappearance of most of the non‐leptosuchomorph taxa. This is attributed to post‐CPE aridification, although more study is required. [ABSTRACT FROM AUTHOR]

Detailed description and phylogenetic assessment of a phytosaur skull collected from the Tiki Formation of the Rewa Gondwana Basin of India and earlier diagnosed as Parasuchus hislopi, show that it pertains to a new genus and species, Volcanosuchus statisticae. The new taxon is characterized by marginal overlapping of the nostrils by the antorbital fenestrae, external nares situated on a bulbous and raised dome, the lateral surface of the jugal ornamented by a prominent ridge defined by multiple tubercles and radiating thread‐like structures, and distinct ornamentation patterns on the rostrum and skull table. Phylogenetic analysis nests Volcanosuchus within Mystriosuchinae, where it forms a sister taxon to (Rutiodon + Leptosuchomorpha) and marks the transition between the basal Parasuchidae and more derived Mystriosuchinae phytosaurs. Evolution of the phytosaur skulls resulted in changes from non‐overlapping nostril and antorbital fenestra to an overlapping state, anteroposterior elongation of the exoccipital–supraoccipital shelf, appearance of a median ridge on the basioccipital, and reduction of the supratemporal fenestra. Considerable faunal overlap of the Tiki Formation is evident with the lower Maleri Formation, which is late Carnian based on the occurrence of Hyperodapedon, Parasuchus and Exaeretodon. The Tiki Formation correlates with the Ischigualasto Formation of Argentina, the upper part of the Santa Maria Formation, and the overlying lower Caturrita Formation of Brazil, the Isalo II Beds of Madagascar, Lossiemouth Sandstone of Scotland, and the lower Tecovas Formation of the Chinle Group of North America, and ranges from late Carnian to early/middle Norian. [ABSTRACT FROM AUTHOR]

Phytosaurs are a group of large, semi‐aquatic archosaurian reptiles from the Middle–Late Triassic. They have often been interpreted as carnivorous or piscivorous due to their large size, morphological similarity to extant crocodilians and preservation in fluvial, lacustrine and coastal deposits. However, these dietary hypotheses are difficult to test, meaning that phytosaur ecologies and their roles in Triassic food webs remain incompletely constrained. Here, we apply dental microwear textural analysis to the three‐dimensional sub‐micrometre scale tooth surface textures that form during food consumption to provide the first quantitative dietary constraints for five species of phytosaur. We furthermore explore the impacts of tooth position and cranial robustness on phytosaur microwear textures. We find subtle systematic texture differences between teeth from different positions along phytosaur tooth rows, which we interpret to be the result of different loading pressures experienced during food consumption, rather than functional partitioning of food processing along tooth rows. We find rougher microwear textures in morphologically robust taxa. This may be the result of seizing and processing larger prey items compared to those captured by gracile taxa, rather than dietary differences per se. We reveal relatively low dietary diversity between our study phytosaurs and that individual species show a lack of dietary specialization. Species are predominantly carnivorous and/or piscivorous, with two taxa exhibiting slight preferences for 'harder' invertebrates. Our results provide strong evidence for higher degrees of ecological convergence between phytosaurs and extant crocodilians than previously appreciated, furthering our understanding of the functioning and evolution of Triassic ecosystems. [ABSTRACT FROM AUTHOR]

The sacrum - consisting of those vertebrae that articulate with the ilia - is the exclusive skeletal connection between the hindlimbs and axial skeleton in tetrapods. Therefore, the morphology of this portion of the vertebral column plays a major role in the evolution of terrestrial locomotion. Whereas most extant reptiles only possess the two plesiomorphic sacral vertebrae, additional vertebrae have been incorporated into the sacrum multiple times independently among early-diverging archosaurian (crocodylians + birds) clades. Phytosauria was a diverse, abundant, and cosmopolitan clade of archosauriforms throughout the Late Triassic, but postcrania of this clade are rarely described and few species-level taxonomic placements of phytosaurian postcranial material are available, potentially hampering knowledge of morphological disparity in the postcranial skeleton among phytosaurs. Here, we describe the sacrum of Smilosuchus adamanensis, a phytosaur recovered from the Upper Triassic Chinle Formation of Arizona. This sacrum consists of the two primordial sacral vertebrae, but has a vertebra incorporated from the trunk into the sacrum (= a dorsosacral) and is therefore the first Late Triassic phytosaur and one of the first non-archosaurian archosauromorphs to be described with more than two sacral vertebrae. Our interpretation of this element as a dorsosacral is justified by the lateral extent of the dorsosacral ribs, clear surfaces of articulation between the distal ends of the dorsosacral ribs and the first primordial sacral ribs, and the scar on the medial surface of each ilium for articulation with each dorsosacral rib. Additionally, we provide the first detailed description of the vertebral junction formed by two anteriorly projecting flanges on the first primordial sacral ribs and their corresponding facets on the centrum of the dorsosacral. Computed tomographic ( CT) imaging reveals that the two primordial sacrals are not co-ossified and that the dorsosacral morphology of this specimen is not the result of obvious pathology. We place this incorporation of a trunk vertebra into the phytosaurian sacrum in a broader evolutionary context, with this shift in vertebral identity occurring at least seven times independently among Triassic archosauriforms, including at least three times in early crocodylian-line archosaurs and at least four times among bird-line archosaurs. Additionally, anteriorly projecting flanges of sacral ribs which articulate with the anterior-adjacent centrum have evolved several times in archosauriforms, and we interpret 'shared' sacral ribs (= a sacral rib that articulates with two adjacent sacral centra more or less equally) present in some archosaurian clades as a more extreme example of this morphology. In extant taxa the highly conserved Hox gene family plays a central role in the patterning of the axial skeleton, especially vertebral identity; therefore, the independent incorporation of a trunk vertebra into the sacrum across multiple archosauriform lineages may suggest a homologous underlying developmental mechanism for this evolutionary trend. [ABSTRACT FROM AUTHOR]