Neochoristodera

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Neochoristodera
Temporal range:
Ma
Skeletal mount of Champsosaurus
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Choristodera
Suborder: Neochoristodera
Evans & Hecht, 1993
Genera
Synonyms

Champsosauriformes Hay 1930

Neochoristodera is a lineage of specialised

choristodere reptiles. Noted for their long jaws and large size, these animals were predominant across the Northern Hemisphere, occurring in freshwater and coastal environments across the Cretaceous and early Cenozoic
.

Systematics

Neochoristoderes form a monophyletic group, however there is no consensus about the relationships of the genera, which have been recovered as a polytomy in recent studies. Neochoristodera contains the named genera Champsosaurus, Ikechosaurus, Kosmodraco, Liaoxisaurus, Mengshanosaurus, Simoedosaurus and Tchoiria. Various taxa of uncertain affinities within this group are known, including a partial femur of a choristodere, possibly of a neochoristodere from the Cedar Mountain Formation of the United States and an indeterminate partial skeleton from the Kuwajima Formation of Japan.[2]

Evolution

Skeleton of Tchoiria

Neochoristoderes first appear in the

crocodilians, possibly due to colder temperatures, seems to have opened the ecological niche for these choristoderes to occupy a similar ecological niche.[3][4] The oldest known neochoristodere is Mengshanosaurus, from the Berriasian-Valanginian aged Mengyin Formation of China.[5]

Other than a possible specimen from the Cedar Mountain Formation, a large gap occurs between these Early Cretaceous faunas and the Late Cretaceous ones. There are no fossils of neochoristoderes in the Asian Late Cretaceous, but the subsequent distribution of Simoedosaurus in the Paleocene and Eocene implies that there were Asian taxa around this time, seeing as Simoedosauridae is predominantly Asian and Simoedosaurus only propagated widely after the KT event.[6]

Fossils of Simoedosaurus

Choristoderes reappear in the fossil record in the Campanian of North America under the genus Champsosaurus. This genus survives the KT event unscathed and diversifies in the aftermath, being soon after joined by Simoedosaurus. Both taxa remain at high latitudes in North America and Europe until the Eocene, when they mysteriously disappear.[7]

In 2021, fossil remains of indetermine neochoristoderes were described from several sites from the Navesink Formation of New Jersey, marking the first known occurrence of neochoristoderes from the former landmass Appalachia. Niche modeling based on the presumed niche of Champsosaurus indicates that neochoristoderes may have had a widespread distribution in Appalachia, but the majority of this habitat was not located in areas conducive for Cretaceous fossilization, leading to only a small margin of optimal habitat in New Jersey that preserved choristodere remains.[8]

Competition from

alligatorids and Borealosuchus.[9][10]

Biology

Lateral and dorsal views of a Champsosaurus skeletal mount

Neochoristoderes are thought to be fully aquatic. They possess laterally flattened, muscular tails and paddle-like limbs, their torsos are dorsoventrally flattened with short but massive ribs and their

viviparous, it is likely that at least some neochoristoderes were too.[13]

Champsosaurus skull

Most neochoristoderes have exceptionally large temporal fenestrae, suggesting powerful bite forces; Champsosaurus is estimated to have a bite force around 1194 to 1910 N, as opposed to the modern gharial's 310-497 N.[14] In spite of this, most are thought to have had a diet similar to that of modern gharials due to the long and slender jaws, though Simoedosaurus has a more robust and shorter snout and could have fed on larger prey.[15]

Compared with other choristoderes, which have rather simple teeth, neochoristoderes have teeth completely enveloped in striated enamel with an enamel infolding at the base, labiolingually compressed and hooked, the exception being Ikechosaurus which has still rather simple teeth aside from the start of an enamel infolding. There is some tooth differentiation, with the anterior teeth being larger than the posterior ones. As with most choristoderes, neochoristoderes have palatal teeth, indicating food manipulation in the mouth.[16]

Nearly all neochoristodere remains occur at high latitudes, suggesting a preference for temperate climates.[17] Champsosaurus fossils are known in the Canadian Arctic and Greenland.[18]

References

  1. PMID 35313822
    .
  2. ^ The first record of a long-snouted choristodere (Reptilia, Diapsida) from the Early Cretaceous of Ishikawa Prefecture, Japan Article in Historical Biology 27(5):1-12 · December 2014
  3. ^ R. Matsumoto and S. E. Evans. 2010. Choristoderes and the freshwater assemblages of Laurasia. Journal of Iberian Geology 36(2):253-274
  4. ISSN 2096-9899
    .
  5. ^ R. Matsumoto and S. E. Evans. 2010. Choristoderes and the freshwater assemblages of Laurasia. Journal of Iberian Geology 36(2):253-274
  6. ^ R. Matsumoto and S. E. Evans. 2010. Choristoderes and the freshwater assemblages of Laurasia. Journal of Iberian Geology 36(2):253-274
  7. S2CID 237761128
    .
  8. ^ R. Matsumoto and S. E. Evans. 2010. Choristoderes and the freshwater assemblages of Laurasia. Journal of Iberian Geology 36(2):253-274
  9. ^ The first record of a long-snouted choristodere (Reptilia, Diapsida) from the Early Cretaceous of Ishikawa Prefecture, Japan Article in Historical Biology 27(5):1-12 · December 2014
  10. ^ R. Matsumoto and S. E. Evans. 2010. Choristoderes and the freshwater assemblages of Laurasia. Journal of Iberian Geology 36(2):253-274
  11. ^ R. Matsumoto and S. E. Evans. 2010. Choristoderes and the freshwater assemblages of Laurasia. Journal of Iberian Geology 36(2):253-274
  12. ^ omateus.googlepages.com/Jacobsetal2009CretaceousSkeletoncoas.pdf
  13. ^ R. Matsumoto and S. E. Evans. 2010. Choristoderes and the freshwater assemblages of Laurasia. Journal of Iberian Geology 36(2):253-274
  14. ^ The first record of a long-snouted choristodere (Reptilia, Diapsida) from the Early Cretaceous of Ishikawa Prefecture, Japan Article in Historical Biology 27(5):1-12 · December 2014
  15. ^ R. Matsumoto and S. E. Evans. 2010. Choristoderes and the freshwater assemblages of Laurasia. Journal of Iberian Geology 36(2):253-274