Mosaic of plesiomorphic and derived characters in an Eocene myliobatiform batomorph (Chondrichthyes, Elasmobranchii) from Italy defines a new, basal body plan in pelagic stingrays

Abstract

Background 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. Although the earliest members appeared in the Late Cretaceous, most of the crown genera date back to the Eocene. Results In 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. Conclusions The 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. Electronic supplementary material The online version of this article (10.1186/s40851-019-0128-0) contains supplementary material, which is available to authorized users.

A bizarre Eocene dasyatoid batomorph (Elasmobranchii, Myliobatiformes) from the Bolca Lagerstätte (Italy) reveals a new, extinct body plan for stingrays

“…8a). The tree is consistent with those depicted in recent studies on Bolca stingrays 6,13 . The monophyly of the Myliobatiformes, as recognized by several authors 3,4,49,50 , is confirmed and supported herein (Bremer value 4) by ten characters: basihyal as a single element, but separated from the first hypobranchials (ch.…”

“…Like in many other studies primarily based on morphological data 3,4,6,13,45 , the sixgill stingray Hexatrygon is inferred to be the sister to all other stingrays, although this contrasts with recent molecular phylogenies, where Hexatrygon is recovered as sister to Gymnura 16 or to urolophids 51,52 . The present study detected again a dichotomy of the remaining Myliobatiformes, in which the nature of the two main clades (Myliobatoidea and Dasyatoidea) can be possibly linked to the different calcifications of radial cartilages, body shape, swimming mode and life style 48 .…”

“…The phylogenetic analysis is based on the morphological data set assembled by Marramà et al . 13 , which in turn is mainly based on morphology-based phylogenies of stingrays 3,45 (see Supplementary Information). Character 98 of Marramà et al .…”

“…Examples include stem flatfishes (Pleuronectiformes) showing gradual evolution of asymmetry 28,29 , curious ribbon-like morphology of † Bajaichthys , very different from the deep bodies of modern zeiforms 30 , basal members of the hyperdiverse benthic gobioids 31 , a variety of bizarre anglerfishes 32–35 and plectognaths 36 , or the peculiar paralepidid aulopiform † Holosteus whose body plan mimics that of pike-like ambush predators 23 . In this study, another one in a series of papers highlighting the palaeobiodiversity of the Eocene batoids from the Bolca Lagerstätte 6,13,15,24 , we describe in detail the anatomy and the phylogenetic relationships of a new stingray genus whose unique body plan, unknown in other extinct or living myliobatiform taxa, supports the idea that evolutionary novelties and innovations also occurred in cartilaginous fishes in the aftermath of the end-Cretaceous extinction, leading to the exploitation of new ecological strategies.…”

Revision of the Eocene ‘Platyrhina’ species from the Bolca Lagerstätte (Italy) reveals the first panray (Batomorphii: Zanobatidae) in the fossil record

“… 2016 , 2019 ; Marramà et al . 2018a , b , c , 2019a , b , c, d ;). These batoids are represented by electric rays (Torpediniformes), guitarfishes (Rhinopristiformes), stingrays (Myliobatiformes) and three batoid species that were historically assigned to the thornback ray genus Platyrhina Müller & Henle, 1838 : † P. bolcensis Heckel, 1851 , † P. egertoni (De Zigno, 1876 ) and † P. gigantea (Blainville, 1818).…”