Pseudomegachasma comanchensis

(Shimada, 2007)


Classification: Elasmobranchii Lamniformes Odontaspididae

Reference of the original description
Shimada, K. (2007)
Mesozoic origin for megamouth shark (Lamniformes: Megachasmidae). Journal of Vertebrate Paleontology, 27(2), 512–516

Synonyms / new combinations and misspellings
Megachasma comanchensis

Types
Pseudomegachasma comanchensis

Megachasma comanchensis
Holotype: FHSM: VP-15095; Paratype: FHSM: VP-15176;


Description:


Citation: Pseudomegachasma comanchensis (Shimada, 2007): In: Database of fossil elasmobranch teeth www.shark-references.com, World Wide Web electronic publication, Version 01/2023

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Description
Original diagnose after Shimada (2007) p. 513 [2178]: Small lamnoid teeth (holotype as the largest specimen measuring 6 mm in total tooth height) consisting of tall crown (variably inclined distally), well-marked tooth neck, and massive root, with the following combination of characters: osteodont tooth histology (note absence of pulp cavity in Figure 1F); crown triangular in labial and lingual views, with pointed tip and sprawling base (except along the labial side); crown tip strongly directed lingually, giving hook-like appearance; mesial and distal cutting edges weak and blunt towards to apex and base of crown, and absent at mid-portion of crown outlining nearly perfect circle in transverse cross-section; crown surfaces smooth; lingual crown face strongly convex and labial face moderately convex; basal margin of crown gently convex or concave on labial face and broadly and deeply concave on lingual face (particularly noticeable in mesial and distal views); labiolingual length and mesiodistal length at crown base about equal; root massive and short apicobasally, with deep nutritive groove that bisects pronounced lingual protuberance and may possess prominent nutritive pore near center of the groove; apical face of lingual protuberance flat or weakly convex; basal face of each root lobe flat or weakly convex; and labiomesial corner of root labially pointing and labiodistal corner blunt and rounded. Mesiodistally oriented, low heel may occur at mesial and distal extremities of crown base along labial margin. Differing from teeth of Megachasma pelagios in possessing prominent nutritive groove that deeply bisects root longitudinally from the top of the lingual root protuberance.

Remarks
valid after Shimada et al. (2015) [22941];


References
Condamine, F.L. & Romieu, J. & Guinot, G. (2019)
Climate cooling and clade competition likely drove the decline of lamniform sharks. Proceedings of the National Academy of Sciences of the United States of America, 116(41), 20584–20590
DOI: 10.1073/pnas.1902693116
Shimada, K. & Popov, E.V. & Siversson, M. & Welton, B.J. & Long, D.J. (2015)
A new clade of putative plankton-feeding sharks from the Upper Cretaceous of Russia and the United States. Journal of Vertebrate Paleontology, 35(5), Article e981335
DOI: 10.1080/02724634.2015.981335
Shimada, K. & Popov, E.V. & Siversson, M. & Welton, B.J. & Long, D.J. (2015)
A new clade of putative plankton-feeding sharks from the Upper Cretaceous of Russia and the United States. Journal of Vertebrate Paleontology, 35(5), Article e981335
DOI: 10.1080/02724634.2015.981335
Gallardo, C. & Shimada, K. & Schumacher, B.A. (2013)
A New Late Cretaceous Marine Vertebrate Assemblage from the Lincoln Limestone Member of the Greenhorn Limestone in Southeastern Colorado. Transactions of the Kansas Academy of Science, 115(3–4), 107–116
DOI: 10.1660/062.115.0303
Cumbaa, S.L. & Shimada, K. & Cook, T.D. (2010)
Mid-Cenomanian vertebrate faunas of the WesternInterior Seaway of North America and their evolutionary, paleobiogeographical, and paleoecological implications. Palaeogeography, Palaeoclimatology, Palaeoecology, 295(1–2), 199–214
DOI: 10.1016/j.palaeo.2010.05.038
Shimada, K. (2007)
Mesozoic origin for megamouth shark (Lamniformes: Megachasmidae). Journal of Vertebrate Paleontology, 27(2), 512–516
DOI: 10.1671/0272-4634(2007)27[512:MOFMSL]2.0.CO;2