Көне кескелдер: Postosuchus туралы

Genus of reptiles

Postosuchus, meaning "Crocodile from Post", is an extinct genus of rauisuchid reptiles comprising two species, P. kirkpatricki and P. alisonae, that lived in what is now North America during the Late Triassic. Postosuchus is a member of the clade Pseudosuchia, the lineage of archosaurs that includes modern crocodilians (the other main group of archosaurs is Avemetatarsalia, the lineage that includes all archosaurs more closely related to birds than to crocodilians). Its name refers to Post Quarry, a place in Texas where many fossils of the type species, P. kirkpatricki, were found. It was one of the apex predators of its area during the Triassic, larger than the small dinosaur predators of its time (such as Coelophysis). It was a hunter which probably preyed on large bulky herbivores like dicynodonts and many other creatures smaller than itself (such as early dinosaurs). The skeleton of Postosuchus is large and robust with a deep skull and a long tail. It was a large animal up to long or even more.

Postosuchus was one of the largest carnivorous reptiles during the late Triassic. The length of the paratype is estimated up to long, The holotype is estimated up to long, and the largest known individual may measure up to long or more based on a complete cervical series specimen (TTU P 9235). The neck of Postosuchus consists of at least eight cervical vertebrae followed by sixteen dorsals, while four co ossified sacral vertebrae supported the hips. The neck was elongated, expanding to a short torso and long tail. Along with remains of the skeleton, paleontologists also identify osteoderms, which were thick plates forming scales on its back, neck, and possibly above or under the tail.

Postosuchus had a massively built skull, bearing dagger like teeth, which was constructed narrow in front, and extended wide and deep behind. The holotype skull was 55 cm in length and 21 cm broad and deep. There are many fenestrae (openings) present in the bones that lighten the skull, providing space for the muscles. Like more derived archosaurs, the lower jaw had mandibular fenestrae (openings at the lower jaw), formed by the junction of the dentary with other jaw bones (surangular and angular). Postosuchus possessed heterodonty dentition, which means each tooth was different in size and shape from the others. The upper jaw contained seventeen teeth, with each premaxilla bearing only four teeth and each maxilla thirteen teeth. The feet were much larger than the hands, with the fifth metatarsal forming a hook shape. The innermost two digits were less robust than the other toes, and likely could not touch the ground. Peyer et al. 2008, argued that the thick pectoral girdle served for locomotion of the forelimbs. In a 2022 article Postosuchus was considered predominantly bipedal, but probably still capable of supporting its weight on the forelimbs at low speeds, and an ontogenetic shift was noted, with the shortening of the arms as individuals aged, suggesting that at least hatchlings and juveniles were facultatively quadrupedal.

During an expedition in 1980, paleontologists of the Texas Tech University discovered a new geological site rich in fossils near Post, Garza County, Texas, US, where a dozen well preserved specimens belonging to a new rauisuchid were found. Subsequently, some specimens (such manus and toe bones) were re assigned to Chatterjeea and Lythrosuchus; Long and Murry pointed out that many of the juvenile skeletons (TTUP 9003 9011), which Chatterjee assigned to P. kirkpatricki, belong to a distinct genus, named Chatterjeea elegans. Furthermore, in 2006 Nesbitt and Norell argued that Chatterjeea is a junior synonym of Shuvosaurus. In 2008, Peyer et al., described a new species of Postosuchus, P. alisonae that was discovered by two UNC undergrad students, Brian Coffey and Marco Brewer in 1992 in Triangle Brick Co. Quarry, Durham County, North Carolina. The remains were prepared and reconstructed between 1994 and 1998 by the Department of Geological Sciences at the University of North Carolina. The specific name is in reference to Alison L. Chambers, who worked to popularize paleontology in North Carolina. The fossils were composed only of an isolated braincase (UM 7473) and fragments of pelvic bones (UM 7244). Case then mistakenly assigned these specimens to the dinosaur genus Coelophysis. In the case of the braincase later assigned to Postosuchus, in 2002 paleontologist David J. Gower argued that the specimen is not complete and may belong to an ornithodire. Between 1932 and 1934, Case discovered other fossils of caudal vertebrae (UMMP 13670) in Rotten Hill, Texas, and a complete pelvis (UCMP V72183/113314) near Kalgary, Texas. Within the same period, paleontologist Charles Lewis Camp collected over a hundred "rauisuchian" bones, from what is now the Petrified Forest National Park of Arizona, which belong to at least seven individuals (UCMP A296, MNA 207C). These early findings, from 1932 to 1943, were initially referred to as a new phytosaur reptile, but assigned forty years later to Postosuchus. The specimen represents a skeletally immature individual because none of the neural sutures are closed. It was referred to P. kirkpatricki by Long and Murry (1995) without specific justification, and more recent studies accepted this referral. In their description of Vivaron, Lessner et al. (2016) questioned the random referral of all rauisuchid material from the southwestern US to Postosuchus, saying that the discovery of Vivaron stresses the need for a re appraisal of all material from localities younger or older than unequivocal remains of Postosuchus and Vivaron.

Postosuchus lived in a tropical environment. Plants of the Dockum Group are not well known since the oxidizing of the environment has destroyed most of the plant fossils. Postosuchus was one of the largest animals in that ecosystem and preyed on herbivores in the uplands like the dicynodont Placerias. The fauna found in Dockum Group confirm that there were lakes and/or rivers containing fish such as the cartilaginous Xenacanthus, the lobe finned Chinlea and the dipnoan Ceratodus. On the margins of these rivers and in the uplands lived labyrinthodonts (Latiscopus) and reptiles such as Malerisaurus and Trilophosaurus, and even the archosaurs Coelophysis, Desmatosuchus, Typothorax, Leptosuchus, Nicrosaurus and Rutiodon.