Postosuchus

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Postosuchus
Temporal range: Late Triassic (Norian)
Skeleton at the Museum of Texas Tech University, near Post, Texas
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Archosauria
Clade: Pseudosuchia
Family: †Rauisuchidae
Genus: †Postosuchus
Chatterjee, 1985
Type species
†Postosuchus kirkpatricki
Chatterjee, 1985
Species
  • †P. kirkpatricki Chatterjee, 1985
  • †P. alisonae Peyer et al., 2008

Postosuchus, meaning "Crocodile from

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).[1]

The skeleton of Postosuchus is large and robust with a deep skull and a long tail. It was a large animal up to 5–6 m (16–20 ft) long or even more.

bipedal locomotion.[3]

Description

P. kirkpatricki compared to a human

Postosuchus was one of the largest carnivorous reptiles during the late Triassic. The length of the paratype is estimated up to 3.5–4 m (11–13 ft) long,[3] and an individual of such length would have measured 2 metres (6.6 ft) tall at the head when stood upright and weighed around 250–300 kilograms (550–660 lb).[4] The holotype is estimated up to 5–6 m (16–20 ft) long, and the largest known individual may measure up to 5–7 m (16–23 ft) long or more based on a complete cervical series specimen (TTU-P 9235).[3][5]

The neck of Postosuchus consists of at least eight

carnosaurs. The ribcage of Postosuchus had typical archosaur structure, composed of large and slender, curved ribs.[4] In some discoveries ribs were found associated with gastralia, dermal bones located in the ventral region of the body.[6]

Skull

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

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

dentary with other jaw bones (surangular and angular).[4]

Postosuchus likely had very good long distant sight, due to large

Jacobson's organ, an olfactory sensory organ sometimes referred as the "sixth sense". The jaws held large and sharp serrated teeth, of which some were developed even larger to operate as hooked sabers.[4]

A complete tooth found among Postosuchus remains in

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.[4] In the lower jaw were 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.[4]

Limbs and posture

With the forelimbs being approximately 64% the size of the hindlimbs, Postosuchus had small hands bearing five toes, of which only the first digit bore a claw. Due to the diminutive size of the hands, it is uncertain this claw was especially predominant in predation, but it may have helped in grappling prey.

crurotarsan
, the heel and ankle of Postosuchus resemble those of modern crocodiles.

Restoration showing quadrupedal pose

The limbs were located underneath the body giving Postosuchus an upright stance.

theropod dinosaurs, nearly all of which are thought to have been strictly bipedal.[3] However a 2015 study noted several load-bearing adaptations present in the manus of Postosuchus, substantiating the view that its manus was used for support.[10] 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.[11]

History

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

During an expedition in

junior synonym of Shuvosaurus.[15]

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

temnospondyl bone.[17] Furthermore, the Postosuchus was positioned on top of a skeleton of the sphenosuchian Dromicosuchus, which included tooth marks on the skull and neck.[17] P. alisonae represents the largest suchian reptile recovered from the quarry and the first articulated specimen of 'rauisuchian' archosaur found in eastern North America.[17]

Putative occurrences

Specimens similar to Postosuchus were discovered in

UMMP 13670) in Rotten Hill, Texas, and a complete pelvis (UCMP V72183/113314) near Kalgary, Texas.[18] 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).[18] Later, more remains came to light. In 1943, Case again described a pelvis along with a pubis (UM 23127) from the Dockum Group of Texas, which dates from the Carnian through the early Norian stages of Late Triassic period.[23] These early findings, from 1932 to 1943, were initially referred to as a new phytosaur reptile, but assigned forty years later to Postosuchus.[4]

The first articulated skeleton referred to P. kirkpatricki (

crocodylomorph, thus referable neither to P. kirkpatricki nor to Rauisuchidae.[27]

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.[28]

Paleoecology

Postosuchus and Desmatosuchus

Postosuchus lived in a tropical environment.

cycads like Sanmiguelia.[4][30] Plants of the Dockum Group are not well known since the oxidizing of the environment has destroyed most of the plant fossils.[4] 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.[4][31]

Postosuchus was one of the largest animals in that ecosystem and preyed on herbivores in the uplands like the dicynodont

labyrinthodonts (Latiscopus) and reptiles such as Malerisaurus and Trilophosaurus, and even the archosaurs Coelophysis, Desmatosuchus, Typothorax, Leptosuchus, Nicrosaurus and Rutiodon.[4]

Notes

  1. ISBN 9780789471673
    .
  2. ISBN 1-57765-488-9
    .
  3. ^
    S2CID 129092753
    .
  4. ^
    ISSN 0080-4622
    .
  5. ISBN 9781862393615. Retrieved 14 September 2022.{{cite book}}: CS1 maint: multiple names: authors list (link
    )
  6. ^ Peyer et al. (2008), p. 370.
  7. ^ Peyer et al. (2008), p. 368.
  8. ^ a b c Peyer et al. (2008), p. 380.
  9. ^ Long and Murry (1995), p. 139.
  10. doi:10.1111/jzo.12232
    . Retrieved March 30, 2023.
  11. ISSN 1424-2818
    .
  12. ^ Chatterjee (1985), p. 398–399.
  13. ^ a b Long and Murry (1995), pp. 148–162.
  14. ^ Long and Murry (1995), pp. 154–162.
  15. ^ Nesbitt and Norrell (2006), pp. 1045–1048.
  16. ^ a b c Peyer et al. (2008), p. 365.
  17. ^ a b c d Peyer et al. (2008), p. 363.
  18. ^ a b c d e Peyer et al. (2008), pp. 363–364.
  19. ^ Case (1922), pp. 78–80.
  20. ^ Case (1922), pp. 70–74.
  21. ^ Case (1932), pp. 81–82.
  22. ^ Gower (2002), p. 66.
  23. ^ Case (1943), pp. 201–203.
  24. ^ Long and Murry (1995), pp. 120–141.
  25. ^ a b Weinbaum (2002), 78 pp.
  26. ^ a b Novak (2004), 78 pp.
  27. S2CID 83493714
    .
  28. PMID 27651983
    .
  29. ^ Dunay (1972), 370 pp.
  30. ^ Ash (1976), pp. 799–804.
  31. ^ Ash (1972), pp. 124–128.

References

External links
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