Anatomy, taxonomy and phylogeny of the Eocene guitarfishes from the Bolca Lagerstätten, Italy, provide new insights into the relationships of the Rhinopristiformes (Elasmobranchii: Batomorphii)

Abstract

We here re-evaluate the skeletal anatomy and the systematic position of the two Eocene guitarfish species represented by almost complete and articulated material from the Konservat-Lagerstätten of Bolca in Italy. The analyses of morphometric, skeletal and dental features of ‘Rhinobatos’ dezignii and ‘R.’ primaevus allow them to be excluded from the living guitarfish genus Rhinobatos and assigned to the new genera †Pseudorhinobatos gen. nov. and †Eorhinobatos gen. nov., respectively. The placement of these new genera within the rhinopristiform family Rhinobatidae is based on the possession of a series of morphological features (e.g. pectoral fins fused to head forming a wedge-shaped pectoral disc; rostral cartilage extending to the tip of the snout; nuchal cartilages and horn-like processes of nasal capsules absent; teeth with Rhinobatos-like morphology displaying smooth enameloid, central uvula and two lateral uvulae) that unambiguously exclude their assignment to any other rhinopristiform family. A new morphology-based phylogenetic analysis that includes the two new fossil genera, described herein, provides novel insights into the relationships of the Batoidea and recovers the Rhinopristiformes as a paraphyletic group. This indicates that the monophyly of extant taxa could be the result of the extinction of crucial taxa.

Diversity, palaeoecology and palaeoenvironmental significance of the Eocene chondrichthyan assemblages of the Bolca Lagerstätte, Italy

“…Rhinopristiforms are represented by a single specimen of an extinct rhinobatid, Eorhinobatos primaevus (Marramà et al . 2020c ). Finally, Plesiozanobatus egertoni is the first known panray (family Zanobatidae) in the fossil record (Marramà et al .…”

“…The morphological analysis of three previously undescribed specimens from the Pesciara deposit revealed the existence of a peculiar stingray, Lessiniabatis aenigmatica, which is unique among the myliobatiforms in its body plan making its referral to a known stingray family difficult (Marramà et al 2019d). Rhinopristiforms are represented by a single specimen of an extinct rhinobatid, Eorhinobatos primaevus (Marramà et al 2020c). Finally, Plesiozanobatus egertoni is the first known panray (family Zanobatidae) in the fossil record (Marramà et al 2020b).…”

“…3 Low taxonomic overlap between Bolca and coeval Boreal and Tethyan assemblages. The revision of the Bolca species traditionally referred to Dasyatis, Urolophus, Rhinobatos and Platyrhina revealed the existence of considerable differences between extinct and extant species, resulting in separate generic placements (Marramà et al 2019b(Marramà et al , 2020a(Marramà et al , 2020b(Marramà et al , 2020c. The cosmopolitan B. lerichei is the only species shared with other assemblages, whereas at genus level, Ischyodus, Galeorhinus and Arechia, are present in a few other assemblages.…”

“…The last comprehensive account focussing on these fishes was provided at the end of 19th century by Jaekel (1894). Except for revisions of selected taxa by Cappetta (1975), Carvalho (2010) and Fanti et al (2016), a number of detailed re-evaluations of the taxonomy, systematics and palaeobiology of the Bolca Lagerstätten chondrichthyans have been carried out by the authors of this paper in the last years (Marramà et al 2018a(Marramà et al -c, 2019a(Marramà et al -d, 2020a(Marramà et al , 2020b(Marramà et al , 2020c.…”

“…( 2016 ), a number of detailed re‐evaluations of the taxonomy, systematics and palaeobiology of the Bolca Lagerstätten chondrichthyans have been carried out by the authors of this paper in the last years (Marramà et al . 2018a–c , 2019a–d , 2020a , 2020b , 2020c ).…”