A new species of the deep-bodied actinopterygian Dapedium from the Middle Jurassic (Aalenian) of southwestern Germany.

Erin E. Maxwell,Adriana López-Arbarello

doi:10.7717/peerj.5033

Erin E. Maxwell, Adriana López-Arbarello

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https://doi.org/10.7717/peerj.5033

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Abstract

Dapedium is one of the most abundant and diverse genera of ganoid fishes from the Early Jurassic fossil lagerstätte of Europe. In spite of its abundance, however, its timing of extinction is poorly constrained, with the youngest described material being Early Jurassic in age. We describe new diagnostic and relatively complete material of a large species of Dapedium (standard length estimated at 50 cm) from the Middle Jurassic (earliest Aalenian) Opalinuston Formation of Baden-Württemberg, Germany. The Aalenian material represents a distinct species, D. ballei sp. nov., differing from Early Jurassic species in a unique combination of characters pertaining to the shape of the dermal skull elements, pectoral fin position, and scale shape and ornamentation. However, although D. ballei sp. nov. exhibits a unique combination of characters, there are no autapomorphies with which to distinguish it from the Toarcian species of Dapedium. Dapedium ballei represents the geologically youngest species of Dapedium, extending the range of this genus into the Middle Jurassic. The Opalinuston Formation fills an important gap in the marine vertebrate fossil record, and finds from this horizon have the potential to greatly improve our understanding of evolutionary dynamics over this period of faunal transition.

Highlights

Dapedium Leach, 1822 is a speciose genus of deep-bodied ganoid fish, first appearing in the Late Triassic but reaching its acme in the Early Jurassic, where it is one of the most abundant genera in the Hettangian–Sinemurian Blue Lias and Toarcian-aged Posidonia Shale fossil lagerstätte of England and Germany, respectively (Hauff & Hauff, 1981; Forey, Longbottom & Mulley, 2010)
Fourteen species are provisionally recognised (Table 1), species named from the Early Jurassic of the UK require re-evaluation and as-yet undescribed species may be present in the Posidonienschiefer Formation
We formally describe the actinopterygian remains from the Opalinuston Formation attributed to Dapedium, and discuss their significance for faunal change and survivorship of the genus

Summary

Introduction

Dapedium Leach, 1822 is a speciose genus of deep-bodied ganoid fish, first appearing in the Late Triassic (late Norian: Tintori, 1983) but reaching its acme in the Early Jurassic, where it is one of the most abundant genera in the Hettangian–Sinemurian Blue Lias and Toarcian-aged Posidonia Shale fossil lagerstätte of England and Germany, respectively (Hauff & Hauff, 1981; Forey, Longbottom & Mulley, 2010). How to cite this article Maxwell and López-Arbarello (2018), A new species of the deep-bodied actinopterygian Dapedium from the Middle Jurassic (Aalenian) of southwestern Germany. Thies & Waschkewitz (2016) proposed additional characters for differentiating species from the Toarcian of southwestern Germany, including axial fineness, width of the skull roof, fragmentation or fusion of elements in the orbital series, presence or absence of a presupracleithrum, and gular, opercle, and scale shape Recently cusp number has been suggested to be relatively variable, tooth size may represent a useful character for species differentiation (Smithwick, 2015). Thies & Waschkewitz (2016) proposed additional characters for differentiating species from the Toarcian of southwestern Germany, including axial fineness, width of the skull roof, fragmentation or fusion of elements in the orbital series, presence or absence of a presupracleithrum, and gular, opercle, and scale shape

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