Puercosuchus

Puercosuchus was a mid-sized quadrupedal reptile that broadly resembled other large azendohsaurids in general shape. It was robustly built–albeit less bulky than Azendohsaurus or Shringasaurus–with deep shoulders, sprawling limbs and the characteristically long and raised neck of azendohsaurids. Unlike other large azendohsaurids, its skull was more like those of earlier predatory archosauromorphs, with a proportionally longer and lower snout as well as recurved teeth with fine serrations. The tail of Puercosuchus is also longer and more tapering compared to the shortened tails of other large azendohsaurids. Puercosuchus is known by almost its entire skeleton, but because its bones have only been found disarticulated and mixed together in bonebeds with few associated remains its overall limb and body proportions cannot be determined. It is not known whether these claws come from the fore or hind feet, but strongly curved claws are present on both in other azendohsaurids. The scapula (shoulder blade) of Puercosuchus is similar to other azendohsaurids, being tall and relatively broad, although it is not constricted anywhere along its length unlike those of Azendohsaurus or Shringasaurus. Like them, though, the glenoid (shoulder joint) faces not only out to the side but back as well. The interclavicle, a bone that connects each side of the shoulder girdle down the middle of the chest, is T-shaped with two sharply projecting lateral processes that articulate with the clavicles. It sports a pair of short anterior processes at the front with a notch in between, typical of various other archosauromorphs (such as Prolacerta) but differing from both the single pointed anterior process of Azendohsaurus and Shringasaurus and the smooth anterior margin of Malerisaurus. The hips (pelvic girdle) are overall similar to that of Azendohsaurus, including a pointed and tapering posterior process on the ilium. However, the anterior process in front of the hip socket is much shorter in Puercosuchus. Its femur is long and somewhat S-shaped, as in Azendohsaurus, but like the humerus is comparatively more gracile. Similarly, the tibia is not as robust, including a smaller cnemial crest for muscle attachment. The fibula is twisted into an S-shape and compressed from side-to-side, with a ridge on its front and rear surfaces. Uniquely, Puercosuchus also has a rounded ridge and associated groove on the lower half of its inner surface. In some regards, the bones of the ankle such as the astragalus bone are more similarly shaped to those of Trilophosaurus, but still bear azendohsaurid features (such as a longer attachment for the fibula). Similar to the forelimb, the only definitively known parts of the feet are the metatarsals, of which the hooked fifth metatarsal has a unique tubercle on its top surface. ==History of discovery==

Fossils of Puercosuchus are known primarily from two bonebeds in Arizona: the type locality PFV 217 (informally known as "Dinosaur Wash") in the Petrified Forest National Park (PEFO) where Puercosuchus was first recognised, and NMMNH L-3764 (or the "Krzyzanowski bonebed") near the city of St. Johns. Although Dinosaur Wash was discovered in 1998, The bonebed was then subsequently mapped and excavated during the summers of 2014 and 2015, with large blocks of material jacketed and collected along with individually collected isolated bones. The majority of the bones in the Dinosaur Wash are disarticulated and only very rarely in association with each other, even in the same jacket. Over 900 bones were collected from the quarry in all, with 492 of the prepared bones belonging to Puercosuchus and hundreds more that remain in field jackets . Over 90% of the fossils excavated at Dinosaur Wash belong to Puercosuchus, with the remaining belonging to various fish, temnospondyl amphibians, and other archosauromorphs, making it a monodominant but multitaxic bonebed. At least eight individuals of Puercosuchus are represented at Dinosaur Wash based upon duplicated elements (including eight right fibulae, seven left fibulae and six right quadrates) and belong to animals of varying size and presumably also maturity. Although Puercosuchus was not recognised until the discovery of the bonebed in 2014, additional isolated remains of Puercosuchus had been collected at Dinosaur Wash decades prior, including a large cervical misidentified as belonging to a long-necked plateosaurid dinosaur in 1999. At the Krzyzanowski Bonebed, fossils of Puercosuchus had been discovered from the early 1990s to 2013. However, they had been incorrectly identified as the bones and teeth of various other disparate reptiles, including theropod, sauropodomorph and ornithischian dinosaurs, phytosaurs, "sphenosuchian" crocodylomorphs, and the related allokotosaur Trilophosaurus. Some isolated bones were even mistakenly referred to actinopterygian fish. The discovery of the Dinosaur Wash bonebed was described by the palaeontologists as like a "Rosetta Stone" for Puercosuchus, allowing for all the previously disparate remains at the Krzyzanowski Bonebed (and elsewhere in the southwestern US) to be referred to a single taxon. Material from the Krzyzanowski Bonebed is found in association more often than at Dinosaur Wash, including parts of the jaws, limbs and backbones. Dinosaur Wash more precisely correlates to the upper Blue Mesa Member, and so has been roughly estimated to be between 220 and 218 million years old. This corresponds to the Adamanian teilzone, a local biostratigraphic unit in the southwestern United States that precedes a faunal turnover between it and the succeeding Revueltian that saw the extinction of almost all allokotosaurs in North America. ==Classification and taxonomy==

'' Puercosuchus is a member of Azendohsauridae, one of the major subclades of the unusual archosauromorph clade Allokotosauria that was established from the herbivorous and stockily built Azendohsaurus. Puercosuchus further forms the azendohsaurid subclade Malerisaurinae with the closely related but smaller Malerisaurus, which unlike other azendohsaurids and indeed other allokotosaurs were carnivorous. The same relationship between Puercosuchus and Malerisaurus spp. were recovered in an updated analysis following the redescription of Malerisaurus robinsonae by Saradee Sengupta and colleagues, irrespective of variations elsewhere within Allokotosauria. The cladograms below depicts the simplified consensus result of Nesbitt et al. (2021)—where the uncertain relationships of Puercosuchus (as "Malerisaurus-like taxon PEFO") to other malerisaurines are presented as a polytomy—and the results of Sengupta et al. (2024). Relationships in bolded terminal clades are not reproduced for simplicity. Based only on the holotype specimen PEFO 43914, Puercosuchus is diagnosed from other azendohsaurids by its procumbent first premaxillary tooth and its heterodont maxillary teeth—although the state of the former feature is unknown in both species of Malerisaurus and the latter unknown for M. langstoni. However, additional diagnostic autapomorphies have been identified from the referred hypodigm, and include the keeled frontals, a quadrate with a hooked and pointed head and a foramen penetrating its body, the cultriform tooth, a foramen on the ventral ramus of the opisthotic, posterior caudal vertebrae with a high anterior process taller than their neural spines, a hooked anteromedial process of the ulna, a ridge on the inner surface of the distal, and a tubercle on the dorsal surface of the fifth metatarsal. Although Puercosuchus and other malerisaurines are interpreted as retaining the ancestral carnivorous biology of azendohsaurids, it is simultaneously one of the youngest known members of the clade, with most other azendohsaurids only being known from the Middle Triassic and the older Carnian stage of the Late Triassic—only indeterminate malerisaurines from another bonebed in Petrified Forest National Park are slightly younger. Puercosuchus then appears to represent a late-surviving member of a relatively early-diverging lineage of azendohsaurid, having survived later than its more specialised, herbivorous relatives. Its appearance in the fossil record coincides with a faunal turnover in North America between the Adamanian and Revueltian teilzones, which appears to represent the extinction of most allokotosaurs in at least North American ecosystems. As one of the youngest azendohsaurids known, the extinction of Puercosuchus would have coincided with the extinction of azendohsaurids globally. However, in 2024 fossils of malerisaurines distinct from Puercosuchus were discovered in the slightly younger Kaye Quarry of Petrified Forest National Park, dated to the earliest Revueltian (roughly 215-213 million years ago). Puercosuchus thus pre-dates the final extinction of azendohsaurids. ==Palaeobiology and palaeoecology==

The serrated, recurved teeth of Puercosuchus closely resemble those of theropod dinosaurs (indeed, they are indistinguishable in isolation), and like them Puercosuchus would have had a carnivorous diet (as would other malerisaurines). Growth and pathology The long bones of the limbs of Puercosuchus appear to have grown isometrically, meaning that the proportions of the limb bones (both individually and to each other) stayed approximately the same as it grew (except possibly for the humerus). However, it is not known for sure whether the relative size of each limb bone is indicative of their growth stage, although the smallest and the largest femurs at least do show changes in the size and number of muscle scars associated with ontogenetic growth. Histological analysis of the largest humerus shows signs of skeletal maturity, including more lines of arrested growth and an external fundamental system (a microstructure in the outer layer of the cortical bone in mature bones). One specimen of Puercosuchus, a small femur, is notably pathological. The distal third of its shaft is noticeably warped and twisted, artificially shortening the length of the femur, and its surface is scarred and shows excessive bone growth (hyperossification). However, it is unclear if this pathology is due to a bone fracture, a cancerous growth, infection (e.g. osteomyelitis), a metabolic bone disease (e.g. osteomalacia) or a developmental disease (e.g. osteogenesis imperfecta) without further investigation. Palaeoecology Although dominating the bonebeds they are known from, Puercosuchus was found alongside a variety of other Late Triassic vertebrates. Metoposaurid temnospondyls and phytosaurs are found at both quarries, while a more diverse fauna of fish and reptiles is known from Dinosaur Wash. This includes coelacanths, hybodont sharks, lungfish, actinopterygian (ray-finned) fishes, a tanystropheid archosauromorph, the semi-aquatic archosauriform Vancleavea, the armoured aetosauriforms Acaenasuchus and a non-desmatosuchin aetosaur, a predatory paracrocodylomorph, and an indeterminate dinosauromorph. ==References==