A new Pliensbachian elasmobranch (Vertebrata, Chondrichthyes) assemblage from Europe, and its contribution to the understanding of late Early Jurassic elasmobranch diversity and distributional patterns

Sebastian Stumpf,Jürgen Kriwet

doi:10.1007/s12542-019-00451-4

Abstract

Here we describe a new, previously unrecognized elasmobranch microfossil assemblage consisting of isolated dental material from late Pliensbachian marginal marine, near-shore deposits of Grimmen in north-eastern Germany. The faunal composition indicates close affinities to other European pre-Toarcian elasmobranch-bearing localities, as it is predominantly composed of Hybodontiformes (Hybodus reticulatus?, H. hauffianus?, Lissodus sp.), Synechodontiformes (Palidiplospinax enniskilleni, P. occultidens, Paraorthacodus sp., Sphenodus sp.), and Hexanchiformes (Notidanoides sp.), as well as teeth attributable of the enigmatic Early Jurassic galeomorph shark Agaleus dorsetensis. In addition, the here reported elasmobranch tooth assemblage includes the oldest undisputable fossil records of Orectolobiformes and Batomorphii, each being represented by a single complete tooth only. The orectolobiform specimen is reminiscent of hemiscyllids but left in open nomenclature due to its very generalized morphology preventing any taxonomic identification. The batomorph tooth, conversely, is characterized by a unique combination of morphological features, which allows the introduction of new genus and species, Antiquaobatis grimmenensis gen. et sp. nov. The fossil assemblage presented here contributes to our current knowledge of late Early Jurassic chondrichthyan diversity and distributional patterns, providing some support for the hypothesis that most modern neoselachian lineages were initially linked to marginal marine, near-shore environments, before moving into open marine, offshore habitats by the Toarcian.

Highlights

Neoselachii form a highly diversified monophyletic group of marine vertebrates encompassing more than 1,100 extant species of sharks, rays, and skates (Compagno et al 2005; Weigmann 2016)
The high and labio-lingually narrow tooth crown morphology, combined with the presence of simple, nonbifurcating enameloid folds covering the lower part of the cusp, and the absence of nodes along the base of the labial side of the crown are dental characters that are consistent with teeth of Hybodus reticulatus Agassiz, 1837, the type species of Hybodus, separating the above-described teeth from those of all other Hybodus species reported from the Early Jurassic
Jurassic fossil records traditionally referred to the genus Hybodus are known from several European localities, with H. reticulatus being previously known from both isolated teeth and disarticulated skeletal material ranging from the middle Hettangian to the early Pliensbachian (Woodward 1889; Maisey 1987; Delsate and Duffin 1993; Duffin 1993; Rees 1998; Delsate et al 2002)

Summary

Introduction

Neoselachii form a highly diversified monophyletic group of marine vertebrates encompassing more than 1,100 extant species of sharks, rays, and skates (Compagno et al 2005; Weigmann 2016). The late Early Jurassic is considered to mark a key time interval in the evolutionary history of neoselachian elasmobranchs, because the Toarcian witnessed a first major radiation event resulting in a significant taxonomic and ecological diversity increase (Underwood 2006; Kriwet et al 2009; Guinot et al 2012; Guinot and Cavin 2016). The Early Jurassic elasmobranch fossil record is strongly biased towards isolated material such as teeth and placoid scales from open marine, offshore environments; material from marginal marine, near-shore facies remains extremely rare due to the scarcity of productive localities (Rees 1998) This renders recognition of Early Jurassic elasmobranch macroevolutionary patterns and processes difficult (Underwood 2004, 2006). In north-eastern Germany, outcrops of Mesozoic strata are rare (see Katzung 2004; Petzka et al 2004), and Early Jurassic strata crop out only in the abandoned open-cast clay pits of Grimmen and Dobbertin (Fig. 1a), both giving access to parautochthonous successions of late Pliensbachian to early Toarcian marine sediments that were glacially a Germany c

Polish Basin tenuicostatum semicelatum

Materials and methods

Discussion

Conclusion