Shuotherium Explained

Shuotherium is a fossil mammaliaform known from Middle-Late Jurassic of the Forest Marble Formation of England,[1] and the Shaximiao Formation of Sichuan, China.[2] [3]

The original holotype is composed of a partial dentary and seven teeth (two which are incomplete).[2] The holotypes for other species of this genus are solely represented by isolated molars. Shuotherium, along with Pseudotribos has been placed in the family Shuotheriidae as a sister taxon of the Australosphenida (see, Yinotheria),[4] making it a relative of modern monotremes. However, some studies place it and other shuothereres as closer to therian mammals,[5] [6] and another outside of Mammalia altogether.[7]

Description

In the lower molars, the talonid is situated in front of the trigonid, such a unique dental form is distinct from the typical tribosphenic pattern. In this "pseudotribosphenic" trait, the mesial cingulid is expanded to form a pseudotalonid, and its distal talonid is underdeveloped. It shares with Australosphenida a thin, slender lower jaw but differs from the non-monotreme Ausktribosphenida by having more developed postdentary trough. Its dental formula has been reconstructed as: p4, m3 (four premolars, three molars).

had this to say regarding the fossil:

References

Notes and References

  1. Sigogneau−Russell, D. 1998. Discovery of a Late Jurassic Chinese mammalin the upper Bathonian of England. Comptes Rendus de l’Académie des Sciences, Paris 327: 571–576
  2. M. Chow and T. H. V. Rich. 1982. Shuotherium dongi, n. gen. and sp., a therian with pseudo-tribosphenic molars from the Jurassic of Sichuan, China. Australian Mammalogy 54:127-142
  3. Kielan−Jaworowska, Z.; Cifelli, R.L.; Luo, Z.−X. (2002). "Dentition and relationships of the Jurassic mammal Shuotherium" (PDF). Acta Palaeontologica Polonica. 47 (3): 479–86
  4. Kielan-Jaworowska, Zofia; Cifelli, Richard L.; Luo, Zhe-Xi 2004. Mammals from the Age of Dinosaurs: Origins, Evolution, and Structure. New York: Columbia University Press.
  5. Rougier, Guillermo W.; Martinelli, Agustín G.; Forasiepi, Analía M.; Novacek, Michael J., New Jurassic mammals from Patagonia, Argentina : a reappraisal of australosphenidan morphology and interrelationships ; American Museum Novitates, no. 3566, 2007
  6. Tom Rich, Patricia Vickers Rich, Palaeobiogeography of Mesozoic Mammals – Revisited, Article · January 2012DOI: 10.1007/978-90-481-3428-1_32
  7. Mao, Fangyuan; Li, Zhiyu; Wang, Zhili; Zhang, Chi; Rich, Thomas; Vickers-Rich, Patricia; Meng, Jin (2024-04-03). "Jurassic shuotheriids show earliest dental diversification of mammaliaforms". Nature. doi:10.1038/s41586-024-07258-7. ISSN 0028-0836.

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