Intraspecific dental variations in the deep-sea shark Etmopterus spinax and their significance in the fossil record

Abstract

An important character on several taxonomic levels for shark identification is the tooth morphology. Sharks show a variety of highly specialized dentitions reflecting adaptations to their feeding habits. Intraspecific variation of tooth morphology such as sexual or ontogenetic dimorphism is poorly known in many species, even though tooth morphology plays a decisive role in the characterization of the fossil record of sharks, which comprises mostly fossil teeth. Here we analyzed the dentition of 40 jaws of the Velvet Belly Lantern Shark Etmopterus spinax and identified ontogenetic and sexual dimorphic characters such as total number of teeth, number of upper teeth, cusplet numbers in upper jaw teeth and width of lower jaw teeth. Dimorphic characters may reduce intraspecific competition for food, as E. spinax segregates by sex and size and may allow for identifying the male sex. The lower jaw tooth height, a sexually non-dimorphic character, was used to re-calculate the total length of specimens, which represents the first such approach for a squaliform shark. Results derived from the extant E. spinax are subsequently applied to fossil Etmopterus sp. teeth (Miocene) to gain individual information such as sex or size, but also characterize the extinct population from the excavation site by a size distribution profile in comparison to data from extant populations. This approach indicates the presence of multiple ontogenetic stages in the extinct population.

Are shark teeth proxies for functional traits? A framework to infer ecology from the fossil record

“…Nonetheless, whereas monognathic and dignathic heterodonty are known in many shark species, gynandric and ontogenetic heterodonty are more poorly studied in sharks and better studied in rays (Cappetta, 2012). Of the studies that have been conducted, gynandric and ontogenetic heterodonty have been described in only a few species ( e.g ., C. carcharias , Carcharhinus leucas , Scyliorhinus stellaris , Etmopterus spinax and G. cuvier ; Berio et al ., 2020; Cullen & Marshall, 2019; French et al ., 2017; Straube & Pollerspöck, 2020; Turtscher et al ., 2022). Nonetheless, because the aim of this research was to apply resulting dental character–functional trait relationships to isolated fossil teeth (from which life stage and sex are often unknown), the authors contend that the absence of gynandric and ontogenetic heterodonty from their analyses should not distort the interpretation and application of the resulting framework to fossils.…”

Trophic relationships in the Early Miocene Upper Marine Molasse of Baden-Württemberg, Southwest Germany, with special emphasis on the elasmobranch fauna

“…Tooth morphology provides clues to the diet of extinct taxa, as tooth shape strongly correlates with diet in extant shark species (Moss, 1977;Cappetta, 1986Cappetta, , 2012Powter et al, 2010;Pollerspöck and Straube, 2019;Straube and Pollerspöck, 2020;Bazzi et al, 2021;Goodman et al, 2022). In the works of Cappetta (1986Cappetta ( , 2012, elasmobranch teeth were classified into eight dental types according to their morphology, each corresponding to a type of trophic adaptation: 1) clutching; 2) tearing; 3) cutting (with the subtypes "sensu stricto cutting" and "cutting-clutching"); 4) crushing; 5) grinding; 6) clutching-grinding; 7) cutting-grinding; 8) crushinggrinding.…”

First genetically confirmed records of the little gulper shark Centrophorus uyato (Squaliformes: Centrophoridae) from Cypriot waters

“…Photographs of individual teeth and of a closer view of the scales are framed in white. Individual teeth were removed and photographed following the method by Straube and Pollerspöck (2020) .…”