Intraspecific dental variations in the deep-sea shark Etmopterus spinax and their significance in the fossil record
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ORIGINAL PAPER
Intraspecific dental variations in the deep‑sea shark Etmopterus spinax and their significance in the fossil record Nicolas Straube1 · Jürgen Pollerspöck2 Received: 10 August 2020 / Revised: 28 September 2020 / Accepted: 3 October 2020 © The Author(s) 2020
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. Keywords Dentition · Fossil · Shark · Squaliform · Sexual dimorphism · Ontogenetic dimorphism
Introduction The fossil record of modern sharks (Neoselachii) dates back to the Triassic (Maisey 2012) and the majority of fossil evidence comprises teeth only. While articulated fossils are scarce, numerous dental fossils form a rather detailed fossil record partially documenting the evolutionary history of taxa quite detailed (Maisey 2012). The reason for this lies in the sharks’ ability to replace teeth continuously throughout their lifetime (Luer et al. 1990; Overstrom 1991; Reif et al. 1978), depositing numerous organic matter in the environment, Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00435-020-00503-3) contains supplementary material, which is available to authorized users. * Nicolas Straube [email protected] 1
Department of Natural History, University Museum of Bergen, Realfagbygget, Allégaten 41, 5020 Bergen, Norway
Benediktinerring 34, 94569 Stephansposching, Germany
2
which is ideal for fossilization due to its composition. Contrasting, the cartilage skeleton is less suited for fossilization and is only fragmentary or not at all preserved. The tooth morphologies of living species are the basis for identifyin
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