Abstract
BackgroundEnd-Cretaceous niche-filling by benthic Mesozoic survivors resulted in a prominent increase of durophagous fish families, resulting in the appearance of the earliest representatives of several extant fish lineages, including the pelagic durophagous stingrays, a monophyletic clade of myliobatiform batoids that is characterized by a derived swimming mode and feeding habits. Although the earliest members appeared in the Late Cretaceous, most of the crown genera date back to the Eocene.ResultsIn this study, we re-examine the anatomy of the Eocene eagle ray Promyliobatis gazolai (de Zigno), represented by two nearly complete and articulated specimens from the world-famous Ypresian Konservat-Lagerstätte of Bolca, in detail. This taxon exhibits a mosaic of plesiomorphic and derived characters (e.g. tail sting displaced posteriorly on the tail, at about 50–60% of tail length; pectoral fins joining in front of the head; anterior and posterior pectoral fin margins nearly straight; compagibus laminam absent; single, unfragmented mesopterygium) that clearly define a new body plan within the pelagic durophagous stingrays.ConclusionsThe significant morphological differences between Promyliobatis and extant representatives of Myliobatidae, Aetobatidae, Rhinopteridae, and Mobulidae, support its placement as separate stem group member. The phylogenetic placement of Promyliobatis, based on skeletal and dental characters, strongly supports its basal position within pelagic stingrays. However, its position within the Myliobatiformes becomes unstable when stingray taxa known by fossil teeth only are included. A comparative analysis of the skeletal and tooth morphologies, as well as of the evolutionary trends of pelagic stingrays is also discussed.
Highlights
End-Cretaceous niche-filling by benthic Mesozoic survivors resulted in a prominent increase of durophagous fish families, resulting in the appearance of the earliest representatives of several extant fish lineages, including the pelagic durophagous stingrays, a monophyletic clade of myliobatiform batoids that is characterized by a derived swimming mode and feeding habits
Pelagic stingrays are a group batoid fishes of the order Myliobatiformes characterized by a set of derived morphological characters
The aim of this paper is to re-describe the anatomy of the sole pelagic stingray taxon recovered from Bolca, Promyliobatis gazolai, in detail, based on new material recently discovered in historical collections, and to discuss its relationships within the Myliobatiformes
Summary
End-Cretaceous niche-filling by benthic Mesozoic survivors resulted in a prominent increase of durophagous fish families, resulting in the appearance of the earliest representatives of several extant fish lineages, including the pelagic durophagous stingrays, a monophyletic clade of myliobatiform batoids that is characterized by a derived swimming mode and feeding habits. According to the most recent classifications based on both molecular and morphological data, these taxa should be arranged in four families: the Myliobatidae (including seven species of the eagle ray Aetomylaeus Garman, 1908 [11], and 11 species of Myliobatis Cuvier, 1816 [12]), the Aetobatidae (five species of the pelagic eagle ray Aetobatus Blainville, 1816 [13]), the Rhinopteridae (eight species of the cownose ray Rhinoptera Cuvier, 1829 [14]), and the Mobulidae (eight species of the devil ray Mobula Rafinesque, 1810 [15]) [7]. Two taxa represented by nearly complete and articulated skeletal remains of pelagic stingrays have been recovered so far: Weissobatis micklichi Hovestadt and Hovestadt-Euler, 1999 [22] from the Oligocene Grube Unterfeld in Germany, and Promyliobatis gazolai (de Zigno, 1882) [23] from the Eocene Lagerstätte of Bolca in Italy [24, 25]
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