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Postosuchus was a basal archosaur which lived in what is now North America during the middle through to the late Triassic period (228-202 million years ago). It was a rauisuchian, a cousin of crocodiles and came from the same ancestry as dinosaurs. Its name means "crocodile from Post", named after the Post Quarry in Texas, where many fossils of the species were found. It was one of the top 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 dicynodonts and many other creatures smaller than itself.

Postosuchus was a quadrupedal reptile with a wide skull and a long tail. This carnivore attacked with its large curved claws.[1] It was about 4-5 meters long (12-15 feet),[1] and was held up by columnar legs (a quite uncommon feature in reptiles). A crocodile-like snout, filled with many large-sized dagger-like teeth, was used to kill its prey. Rows of protective plates covering its back formed a defensive shield.

General Description[]

Postosuchus kirkpatricki

P. kirkpatricki compared to a human

Postosuchus was one of the largest carnivorous reptile species of the Triassic, reaching 5-7 meters (16-23 ft) long 2 to 3.5 meters tall and weighed 300–600 kg (550-660 lbs). It had a massively built skull, bearing powerful jaws and dagger like teeth that can easily kill its quarry by cutting through its flesh and ripping off pieces. Rows of protective osteoderms covering its back formed a defensive shield, protecting it from other predators and dangerous prey.

Skull[]

2560px-Postosuchus profile

Skull cast

Postosuchus tooth from Arizona

A tooth belonging to Postosuchus from the Upper Triassic Chinle Formation.

The skull of Postosuchus was constructed narrow in front and extended wide and deep behind. It 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 had very good long distant sight, due to large orbits, supporting large and sharp eyes, and strong olfaction provided by elongated nostrils. Inside the skull, under the nostrils, there was a hollowing that probably was for the Jacobson's organ, an olfactory sensory organ sometimes referred as the "sixth sense".[8] The jaws held large and sharp serrated teeth and in some points were developed even larger to operate as hooked sabers. A complete tooth found among Postosuchus remains in North Carolina measured about 7.2 cm in height.[10] Postosuchus possessed heterodonty dentition, which means each tooth was different in size and shape from the others. The upper jaw composed of seventeen teeth, with each premaxilla bore only four teeth and each maxilla thirteen teeth.[9] In the lower jaw were counted over thirty teeth. Replacement activity in Postosuchus was different from that of crocodiles, since the replacement tooth didn't fit directly in the pulp cavity of the old tooth, but grew until resorption of the old tooth was complete.

Limbs and posture[]

Postosuchus BW

Restoration showing quadrupedal pose

Postosuchus's forelimbs were over half the size of its hind legs, this characteristic of short forelimbs can usually be seen in bipedal reptiles. Chatterjee suggested that Postosuchus could walk in an erect stance, since the short forelimbs were used probably only during slow moving locomotion. However, in 1995, Robert Long and Phillip A. Murry claimed that Postosuchus was a stocky quadruped. There is a debate over whether Postosuchus was either a biped or a quadruped as scientists aren't sure yet. However, some paleontologists suggested that Postosuchus was probably a facultative biped, meaning that it altered between bipedally and quadrupedally. Some early depictions show the Postosuchus stalking around on its hind legs, with its front legs hanging irregularly from their joints as it walked.

Postcranial anatomy[]

The neck of Postosuchus consists of at least eight cervical vertebrae followed by sixteen dorsals, while four co-ossified sacral vertebrae supported the hips. It is thought to be over thirty vertebrae in the tail decreasing in size to the end. The pelvis with the hooked pubis and the rod-like ischium looked like those of carnosaur dinosaurs. Along with remains of the skeleton, paleontologists also identify osteoderms, which were thick plates forming scales. These were on its back, neck, and possibly above or under the tail. The ribcage of Postosuchus had typical archosaur structure, composed of large and slender, curved ribs. In some discoveries ribs were found associated with gastralia, dermal bones which located in the ventral region of the body.[15] The limbs were located underneath the body giving Postosuchus an upright stance.[5] With the forelimbs being approximately 64% of the hindlimbs, Postosuchus had small hands bearing five toes. Only the first toe bore a large claw, which was used as an offensive weapon, and the forelimbs were robust, probably to hold the prey. Peyer et al. 2008, argued that the thick pectoral girdle served for locomotion of the forelimbs.[16] However, this doesn't detract from the theory that Postosuchus could walk bipedally. The feet were much larger than the hands, with the fifth metatarsal forming a hook shape. The halluxes were more slender than the other toes and the marginal ones couldn't touch the ground. As crurotarsan, the heel and ankle of Postosuchus resemble those of modern crocodiles.

P. alisonae[]

A partial skeleton of Postosuchus from Durham County, North Carolina was discovered in 1994 and named in 2008 as new species P. alisonae. The specific name is in reference to Alison L. Chambers, who worked to popularize paleontology in North Carolina. The skeleton of P. alisonae consists of a few cranial bones, seven neck, one back, and four tail vertebrae, ribs, gastralia ("belly ribs"), chevrons, bony scutes, much of the shoulder girdles, most of the forelimbs except the left wrist and hand, most of the hindlimbs except for the thigh bones, and pieces from the hip. This specimen is unusual in preserving gut contents: bones from at least four other animals, including a partial skeleton of an aetosaurid, a snout, coracoid, and humerus of the traversodontid cynodont Plinthogomphodon, two phalanges from a dicynodont, and a possible temnospondyl bone. Furthermore, the Postosuchus was positioned on top of a skeleton of the sphenosuchian Dromicosuchus, which included tooth marks on the skull and neck.[2]

History[]

Postosuchus Map Discoveries

Postosuchus have been discovered only in the United States within the states of Arizona, New Mexico, North Carolina and Texas.

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. In the following years further excavation in the Post Quarry, in Cooper Canyon Formation (Dockum Group), unearthed many remains of late Triassic terrestrial fauna. The holotype of P. kirkpatricki (TTUP 9000), representing a well-preserved skull and a partial postcranial skeleton, was described along with other findings of this new genus by paleontologist Sankar Chatterjee in 1985. A paratype, TTU-P 9002, representing a well-preserved skull and a complete skeleton was also assigned to this species. Chatterjee named the species after Mr. and Mrs. Jack Kirkpatrick who helped during his fieldwork. 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 skeleton of P. alisonae consists of a few cranial bones, seven neck, one back, and four tail vertebrae, ribs, gastralia ("belly ribs"), chevrons, bony scutes, much of the shoulder girdles, most of the forelimbs except the left wrist and hand, most of the hindlimbs except for the thigh bones, and pieces from the hip. Moreover, the well-preserved remains of P. alisonae shed new light on parts of Postosuchus anatomy, which were previously not well known. Specifically, the differences between the manus bones of P. kirkpatricki and P. alisonae confirm the chimera theory (associated fossils belonging to different animals) suggested by Long and Murry. The holotype specimen of P. alisonae (UNC 15575) is also unusual in its preservation of gut contents: bones from at least four other animals, including a partial skeleton of an aetosaur, a snout, coracoid, and humerus of the traversodontid cynodont Plinthogomphodon, two phalanges from a dicynodont, and a possible temnospondyl bone. Furthermore, the Postosuchus was positioned on top of a skeleton of the sphenosuchian Dromicosuchus, which included tooth marks on the skull and neck. P. alisonae represents the largest suchian reptile recovered from the quarry and the first articulated specimen of 'rauisuchian' archosaur found in eastern North America.

Paleoecology[]

HMNS Postosuchus and Desmatosuchus

Postosuchus and Desmatosuchus

Postosuchus lived in a tropical environment. The moist and warm region consisted of ferns, such as Cynepteris, Phelopteris and Clathropteris, gymnosperms, represented by Pelourdea, Araucarioxylon, Woodworthia, Otozamites and Dinophyton, and cycads like Sanmiguelia. Plants of the Dockum Group are not well known since the oxidizing of the environment has destroyed most of the plant fossils. Some of them may, however, provide information about the climate in Dockum Group during the late Triassic period. For example, the discovery of large specimens belonging to Araucarioxylon determine that the region was well watered.

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.

Appearance in other media[]

Jurassic Park[]

  • Postosuchus is a super rare amphibian that can be created in Jurassic World: The Game, even though in real life it was a terrestrial reptile. It was added as part of the March 16th, 2016 update and can be acquired in a Super Rare pack, or by completing Battle Stage 70. When Postosuchus is in its pen, its tail rests on the ground. While other crocodiles did this, it is unlikely Postosuchus did this. With the legs under its hips like a dinosaur and unlike a semi aquatic crocodile, Postosuchus' tail had to be above the ground for balance. Also, Postosuchus is shown to walk on four legs, whereas recent research suggests it likely walked on two, but this is still being debated.
  • Postosuchus does appear in Jurassic World: Alive. Postosuchus is shown to walk on four legs, whereas recent research suggests it likely walked on two. It is a Rare dinosaur and can be achieved by darting 100 Postosuchus DNA.


Links[]

https://web.archive.org/web/20050307005256fw_/http://www.jpinstitute.com/dinolab/dino_academy/art_gallery_class_gallery.jsp?CLASSID=5

References[]

https://en.wikipedia.org/wiki/Postosuchus

  1. 1.0 1.1 Template:Cite book
  2. Template:Cite journal
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