Paleontologist Prof. Kenshu Shimada of DePaul University and his colleagues have discovered a new genus of extinct planktivorous (plankton-eating) sharks.
Pseudomegachasma sharks had a large mouth with many small teeth. Image credit: Kenshu Shimada.
The new lineage, named Pseudomegachasma, is represented by two extinct species – Pseudomegachasma casei (formerly known as Eorhincodon casei) from RF’s Belgorod and Volgograd provinces and P. comanchensis (formerly Megachasma comanchensis) from the U.S.
These sharks were 16-20 feet (5-6 m) long and had small teeth very similar to the modern-day megamouth shark (Megachasma pelagios).
“Pseudomegachasma means ‘false megamouth shark’ due to its dental features superficially nearly identical to the modern-day, plankton-eating megamouth shark,” explained Prof. Shimada, who is the lead author of a paper published in the Journal of Vertebrate Paleontology.
“E. casei and M. comanchensis are two Cretaceous taxa initially described as putative planktivorous elasmobranchs, but the type specimens of these two taxa were subsequently reinterpreted to represent taphonomically abraded teeth of an odontaspidid, Johnlongia,” Prof. Shimada and co-authors wrote in the paper.
“We redescribe the type materials of E. casei and M. comanchensis and describe additional specimens of these species from other Late Cretaceous localities.”
“These specimens demonstrate that: (i) the two fossil taxa are valid species; (ii) they warrant the establishment of a new genus of presumed planktivorous sharks, Pseudomegachasma.”
Tiny, hook-shaped tooth of Pseudomegachasma shark. Image credit: Kenshu Shimada.
They added: “the new genus is sister to Johnlongia and together constitute a new subfamily Johnlonginae, tentatively placed in the family Odontaspididae.”
Pseudomegachasma sharks lived in warm oceans during the age of the dinosaurs about 100 million years ago.
“Pseudomegachasma would represent the oldest known plankton-feeding shark in the fossil record,” Prof. Shimada said.
“These sharks would have evolved independent of the four known lineages of modern-day planktivorous cartilaginous fishes: the megamouth sharks, basking sharks, whale sharks, and manta rays.”
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Kenshu Shimada et al. 2015. A new clade of putative plankton-feeding sharks from the Upper Cretaceous of Russia and the United States. Journal of Vertebrate Paleontology, vol. 35, no. 5; doi: 10.1080/02724634.2015.981335
