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21 December 2019 A New Large Late Cretaceous Lamniform Shark from North America, with Comments on the Taxonomy, Paleoecology, and Evolution of the Genus Cretodus
Kenshu Shimada, Michael J. Everhart
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Abstract

We describe a partial skeleton of the Late Cretaceous shark, Cretodus, collected from the Blue Hill Shale (middle Turonian) in north-central Kansas, U.S.A. It consists of 134 disarticulated teeth, 61 vertebrae, 23 placoid scales, and fragments of calcified cartilage. The scale morphology suggests that Cretodus was a rather sluggish shark, and the vertebral morphology affirms its placement into Lamniformes. With a strong tendency towards monognathic heterodonty, the dental morphology indicates that the specimen belongs to a new species, C. houghtonorum, sp. nov., increasing the total known species of Cretodus to five. The five species can be divided into three distinct groups: the longiplicatus/semiplicatus-grade, gigantea/houghtonorum-grade, and crassidens-grade. Cretodus, that successively evolved by broadening the tooth crown. The individual of C. houghtonorum, sp. nov., is estimated to be about 515 cm in total length (TL). Our vertebra-based growth analysis suggests that the shark was about 118 cm TL at birth and that the species had an estimated maximum growth length of 684 cm TL. The large size at birth indicates that the intrauterine cannibalism behavior of embryos seen in extant lamniforms had already evolved by the Late Cretaceous. Where C. houghtonorum, sp. nov., preferred nearshore environments, the specimen co-occurred with isolated teeth of Squalicorax and fragments of two dorsal fin spines of a hybodont shark, circumstantially indicating that the individual of Cretodus fed on the much smaller hybodont and was scavenged by Squalicorax.

© by the Society of Vertebrate Paleontology
Kenshu Shimada and Michael J. Everhart "A New Large Late Cretaceous Lamniform Shark from North America, with Comments on the Taxonomy, Paleoecology, and Evolution of the Genus Cretodus," Journal of Vertebrate Paleontology 39(4), (21 December 2019). https://doi.org/10.1080/02724634.2019.1673399
Received: 30 November 2018; Accepted: 9 September 2019; Published: 21 December 2019
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