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

Abstract

The fossil-Lagerst€ atte of Bolca (Italy) is well known for the diversity and exquisite preservation of its bony and cartilaginous fishes documenting tropical shallow-water marine environments associated with coral reefs in the western Tethys during the early Eocene. In this study, the taxonomic, systematic and phylogenetic position of two batoid species traditionally assigned to the living thornback ray genus Platyrhina is re-evaluated. †Platyrhina bolcensis Heckel, 1851 is recognized as a separate species of the Platyrhinidae because of its plate-like antorbital cartilage with an irregular outline and a small horn on the nasal capsules. Also, the rostral cartilage does not reach the anterior border of the disc. Support for the placement of this species within the new genus †Eoplatyrhina gen. nov. is based on a combination of morphological and meristic features (e.g. nasal capsules at right angles to the rostrum; large space between the hyomandibulae and mandibular arch; approximately 132 vertebral centra; 15-16 rib pairs; 81-87 pectoral radials; 18-21 pelvic radials; short, straight and stout claspers; 40-50 caudal-fin radials; thorns absent). A second species, †Platyrhina egertoni (De Zigno, 1876), is more closely related to the living panray Zanobatus than Platyrhina and is assigned here to †Plesiozanobatus gen. nov. because of a combination of characters that support its placement within the family Zanobatidae (tail stout and short, distinctly demarcated from disc; two dorsal fins and complete caudal fin; small dermal denticles and scattered thorns covering disc and tail; rostral cartilage absent; nasal capsules without horn-like processes; mesopterygium absent). The systematic position of a third taxon, †Platyrhina gigantea (Blainville, 1818), is currently impossible to establish due to the poor preservation of the only known specimen, and therefore we propose to consider it a nomen dubium. Palaeoecological and biogeographic features of the Eocene platyrhinids and zanobatids from Bolca are also discussed.

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 2020b). Monte Postale has been tentatively referred to the extinct callorhynchid chimaeriform Ischyodus (see Marramà et al 2018a), whose fossil record spreads from middle Jurassic to Pliocene according to Stahl (1999).…”

“…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.…”

A new synapomorphy in the pelvic girdle reinforces a close relationship of Zanobatus and Myliobatiformes (Chondrichthyes: Batoidea)

“…Accordingly, the phylogenetic position of some taxa is still debatable, as is the case of the genus Zanobatus Garman 1913, which has been considered as more closely related to Myliobatiformes (Aschliman, Claeson et al, 2012; Aschliman, Nishida et al, 2012; McEachran & Aschliman, 2004; McEachran et al, 1996) or as a member of the order Rhinopristiformes (Naylor et al, 2012). The order Rhinobatiformes was never recovered as a monophyletic group under a cladistic analysis (e.g., Aschliman, Claeson et al, 2012; Aschliman, Nishida et al, 2012; McEachran & Aschliman, 2004; Naylor et al, 2012; Nishida, 1990), and recent molecular and morphological hypotheses (Brito et al, 2019; Last et al, 2016; Marramà et al, 2020; Villalobos‐Segura et al, 2019) failed to recover the original arrangement, and therefore, the monophyly of Rhinopristiformes ( sensu Naylor et al, 2012). Consequently, the interrelationships and classification of the batoids are not consensual or yet established.…”

“…The order Rhinobatiformes was never recovered as a monophyletic group under a cladistic analysis (e.g., Aschliman, Claeson et al, 2012;Aschliman, Nishida et al, 2012;McEachran & Aschliman, 2004;Naylor et al, 2012;Nishida, 1990), and recent molecular and morphological hypotheses (Brito et al, 2019;Last et al, 2016;Marramà et al, 2020;Villalobos-Segura et al, 2019) failed to recover the original arrangement, and therefore, the monophyly of Rhinopristiformes (sensu Naylor et al, 2012). Consequently, the interrelationships and classification of the batoids are not consensual or yet established.…”