Redescription of Dapedium pholidotum (Agassiz, 1832) (Actinopterygii, Neopterygii) from the Lower Jurassic Posidonia Shale, with comments on the phylogenetic position of Dapedium Leach, 1822

Abstract

Dapedium pholidotum (Agassiz, 1832) (Actinopterygii, Neopterygii) is redescribed based on new material from the Posidonia Shale (Early Jurassic: Early Toarcian) of Germany. Dapediiformes ord. nov. is introduced for Dapedium Leach, 1822 and other deep-bodied Mesozoic neopterygians. The species diagnosis of D. pholidotum is amended. Comparison with D. stollorum Thies & Hauff, 2011 and D. caelatum Quenstedt, 1858, also from the Lower Jurassic Posidonia Shale, shows that D. pholidotum is unique in having: (1) a length/height ratio of the operculum of c. 0.73, whereas in D. stollorum and D. caelatum this value reaches only c. 0.58; (2) a length/width ratio of the gular plate of c. 1.6, whereas in D. stollorum and D. caelatum this value is 1.3; (3) 27 or more caudal fin lepidotrichia, whereas in D. stollorum and D. caelatum there are 24 and 25 lepidotrichia, respectively; (4) at least 26 dorsal fin lepidotrichia, whereas D. stollorum and D. caelatum possess only 24 dorsal fin lepidotrichia each; and (5) a length/height ratio of the flank scales immediately behind the operculum of 0.37, whereas in D. stollorum and D. caelatum this ratio ranges around 0.31 and 0.5, respectively. A cladistic analysis based on modification of a previously published taxon–character matrix shows that Dapedium is the sister group of the ginglymodian fishes [Semionotiformes + Lepisosteiformes]. The generic diagnosis of Dapedium Leach, 1822 is amended.