Pseudomegachasma casei
(Nessov, 1999)
Classification: Elasmobranchii Lamniformes Odontaspididae
Reference of the original description
Whale shark Eorhincodon gen. nov. (Rhincodontidae). Oldest and very large rhincodontid from the Cenomanian (Late Cretaceous) of Belgorod and Volgograd provinces. In Materials on the History of Fauna of Eurasia. (Darevskii, I. S. & Averianov, A. O., editors.), Trudy Zoologicheskogo Instituta RAN, 277, 95–103,1 fig.
Whale shark Eorhincodon gen. nov. (Rhincodontidae). Oldest and very large rhincodontid from the Cenomanian (Late Cretaceous) of Belgorod and Volgograd provinces. In Materials on the History of Fauna of Eurasia. (Darevskii, I. S. & Averianov, A. O., editors.), Trudy Zoologicheskogo Instituta RAN, 277, 95–103,1 fig.
Synonyms / new combinations and misspellings
Eorhincodon* casei
Eorhincodon* casei
Description:
Citation: Pseudomegachasma casei (Nessov, 1999): In: Database of fossil elasmobranch teeth www.shark-references.com, World Wide Web electronic publication, Version 12/2024
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Pseudomegachasma casei (Nessov, 1999), Cenomanian of the Volgograd region © Ilya Archakov
Pseudomegachasma casei (Nessov, 1999), Cenomanian of the Volgograd region © Ilya Archakov
Description
Diagnose after Shimada et al. (2015) [22941]:
genus Pseudomegachasma: Small lamnoid teeth (known specimens no more than 9 mm in total tooth height) consisting of tall crown (erect or inclined), well-marked tooth neck on lingual side, and massive root, along with the following combination of characters; crown with sharply pointed apex and sprawling base; crown apex strongly directed lingually, giving hook-like appearance, but crown apex may be flexed occlusally; mesial and distal cutting edges on crown weak and blunt, and may be absent from crown base to mid-portion of crown; 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; labiolingual length and mesiodistal length at crown base about equal; short sharp or blunt lateral cusplet, or mesiodistally oriented low heel, may be present at mesial and distal extremities, or on one side, of crown base; root massive and apicobasally short, with deep nutritive groove that bisects pronounced lingual protuberance and may possess one or more prominent nutritive pores near center of groove; apical face of lingual protuberance flat or weakly convex; one or more lateral root foramina immediately lingual to mesial and distal extremities of tooth neck; and labiomesial corner of root labially pointing and labiodistal corner less pointy than labiomesial corner
As for the genus Pseudomegachasma, gen. nov., with following combination of characters, including distinguishing characters from P. comanchensis, comb. nov. (see below): weak mesial and distal cutting edges on crown more prominent than in P. comanchensis, comb. nov.; smooth labial crown face at crown base more convex than in P. comanchensis, comb. nov., and shows low, blunt longitudinal rise at center of crown base; and lateral cusplets generally present and sharply pointed.
Diagnose after Shimada et al. (2015) [22941]:
genus Pseudomegachasma: Small lamnoid teeth (known specimens no more than 9 mm in total tooth height) consisting of tall crown (erect or inclined), well-marked tooth neck on lingual side, and massive root, along with the following combination of characters; crown with sharply pointed apex and sprawling base; crown apex strongly directed lingually, giving hook-like appearance, but crown apex may be flexed occlusally; mesial and distal cutting edges on crown weak and blunt, and may be absent from crown base to mid-portion of crown; 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; labiolingual length and mesiodistal length at crown base about equal; short sharp or blunt lateral cusplet, or mesiodistally oriented low heel, may be present at mesial and distal extremities, or on one side, of crown base; root massive and apicobasally short, with deep nutritive groove that bisects pronounced lingual protuberance and may possess one or more prominent nutritive pores near center of groove; apical face of lingual protuberance flat or weakly convex; one or more lateral root foramina immediately lingual to mesial and distal extremities of tooth neck; and labiomesial corner of root labially pointing and labiodistal corner less pointy than labiomesial corner
As for the genus Pseudomegachasma, gen. nov., with following combination of characters, including distinguishing characters from P. comanchensis, comb. nov. (see below): weak mesial and distal cutting edges on crown more prominent than in P. comanchensis, comb. nov.; smooth labial crown face at crown base more convex than in P. comanchensis, comb. nov., and shows low, blunt longitudinal rise at center of crown base; and lateral cusplets generally present and sharply pointed.
References
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
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
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
Whale shark Eorhincodon gen. nov. (Rhincodontidae). Oldest and very large rhincodontid from the Cenomanian (Late Cretaceous) of Belgorod and Volgograd provinces. In Materials on the History of Fauna of Eurasia. (Darevskii, I. S. & Averianov, A. O., editors.), Trudy Zoologicheskogo Instituta RAN, 277, 95–103,1 fig.
Cretaceous Non-marine Vertebrates of Northern Eurasia. Edited by L.B. Golovneva & A.O. Averianov. University of St. Petersburg, Instifute of Earth Crust. 218 pp.,60 plates. Price
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
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
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
Whale shark Eorhincodon gen. nov. (Rhincodontidae). Oldest and very large rhincodontid from the Cenomanian (Late Cretaceous) of Belgorod and Volgograd provinces. In Materials on the History of Fauna of Eurasia. (Darevskii, I. S. & Averianov, A. O., editors.), Trudy Zoologicheskogo Instituta RAN, 277, 95–103,1 fig.
Cretaceous Non-marine Vertebrates of Northern Eurasia. Edited by L.B. Golovneva & A.O. Averianov. University of St. Petersburg, Instifute of Earth Crust. 218 pp.,60 plates. Price
