Plesiozanobatus egertoni ( De Zigno, 1876 ) Marram̀ & Carneval & Claeso & Naylo & Kriwe, 2020

Marram ̀, Giuseppe, Carneval, Giorgio, Claeso, Kerin M., Naylo, Gavin J. P. & Kriwe, Jurgen, 2020, Revision of the Eocene ‘ Platyrhina’ species from the Bolca Lagerst atte (Italy) reveals the first panray (Batomorphii: Zanobatidae) in the fossil record, Journal of Systematic Palaeontology 18 (18), pp. 1519-1542 : 1529

† Plesiozanobatus egertoni ( De Zigno, 1876) comb. nov.

Figs 8–10

1876 Torpedo egertoni De Zigno : 452, pl. 17, figs 1, 2 (original occurrence of name, description and figures).

1878 Torpedo egertoni, De Zigno : 10, pl. 3, figs 1–2.

1894 Platyrhina egertoni De Zigno sp.; Jaekel: 100, pl. 2.

1904 Platyrhina egertoni Zigno ; Eastman: 27.

1905 Platyrhina egertoni Zigno ; Eastman: 351.

1922 Platyrhina egertoni (De Zigno) ; D’ Erasmo: 12.

1980 Platyrhina egertoni (De Zigno) ; Blot: 344.

1987 Platyrhina egertoni ( Zigno, 1876) ; Cappetta: 139, fig. 118A.

1991 Platyrhina egertoni De Zigno ; Frickhinger: 204, unnumbered fig.

1991 Torpedo spec.?; Frickhinger: 210, unnumbered fig.

2004 Platyrhina egertoni ; Carvalho: 78, fig. 12B.

2012 Platyrhina egertoni ( Zigno, 1876) ; Cappetta: 346, fig. 335A.

2014 Platyrhina egertoni De Zigno, 1878 ; Carnevale, Bannikov, Marram̀a, Tyler & Zorzin: 41.

2018c ‘ Platyrhina ’ egertoni ; Marram̀a, Carnevale, Engelbrecht, Claeson, Zorzin, Fornasiero & Kriwet: 287, fig. 13A, B.

Holotype. MGP-PD 154 Z, incomplete, poorly preserved articulated skeleton, 306.4 mm DW, 481.2 mm TL ( Fig. 8A, B ).

Referred material. MCSNV IG.43347, incomplete and poorly preserved articulated skeleton, 281 mm DW, 479.8 mm TL ( Fig. 8C ); MB.f 1608.1/2, nearly complete articulated skeleton in part and counterpart, 291.6 mm DW, 426.2 mm TL ( Fig. 8D ); MCSNV IG.142530, poorly preserved articulated skeleton, 336.3 mm DW, 524.5 mm TL ( Fig. 8E ); MCSNV VII.B.80/81, nearly complete articulated skeleton in part and counterpart, 749.2 mm DW, 1149.3 mm TL ( Fig. 8F ); MCSNV VII.B.88/89, partially complete articulated skeleton in part and counterpart, 311.7 mm DW, 506.3 mm TL.

Type locality and horizon. Pesciara site, Bolca Konservat-Lagerst¨atte, Italy; early Eocene, late Ypresian, middle Cuisian, SBZ 11, † Alveolina dainelli Zone (see Papazzoni et al. 2014).

Diagnosis. As for the genus.

Description

† Plesiozanobatus egertoni comb. nov. is represented by six specimens showing different ontogenetic stages, with the largest individual measuring more than 1 m in length ( Fig. 8 ). Counts and measurements are shown in the Supplemental material (File 1, Table S 2). The pectoral disc is large and nearly round, representing 56–70% TL. The tail is stout and short, distinctly demarcated from the disc and measuring about 40–50% TL ( Fig. 9A–B ). The most complete specimens show two nearly triangular dorsal fins of similar size, located well behind the pelvics; a nearly complete caudal fin is visible exclusively in MCSNV IG.43347.

Although the general body shape is still detectable, a detailed analysis of all the skeletal structures is very difficult due to the generally poor preservation of the available specimens. The rostral cartilage is clearly absent in all the specimens, and a large empty space can always be recognized between the anterior propterygial radials ( Fig. 9C, D ). The nasal capsules are laterally expanded and do not show evidence of the horn-like processes typical of platyrhinids. The antorbital cartilages are difficult to detect but they probably articulated with the mesial margin of the propterygia. The propterygia are long, extending close to the anterior margin of the disc, well beyond the nasal capsules. The mesopterygium appears absent, as in Zanobatus , Gymnura and some pelagic stingrays, suggesting that the mesocondyle (not visible) might have been replaced by a ridge. There are about 65–75 highly calcified pectoral radials (= ‘crustal pattern’ of Schaefer & Summers 2005). Most of them articulate with the pterygia and some others articulate directly with the scapulocoracoid. The puboischiadic bar is scarcely visible in all the specimens and appears as a narrow and moderately arched bar at least in MB.f 1608.1/2. About 20 pelvic-fin rays can be recognized in the pelvic fins of † P. egertoni comb. nov. The most complete specimens exhibit 80–90 vertebrae and around 10 pairs of ribs. Small, imbricated and densely set dermal denticles form a continuous pavement throughout the body ( Fig. 10A ); their crowns are roughly rhomboid or polygonal in shape, with a flat and smooth surface. Large rounded thorns are more widely spaced, sparse and cover the whole pectoral disc and tail ( Fig. 10B ), whereas some scattered star-shaped thorns cover the scapular region ( Fig. 10C ). However, parallel anteroposteriorly directed rows of thorns are clearly absent. There are no teeth preserved in the available specimens.

Figures

Figure 8. †Plesiozanobatus egertoni (De Zigno, 1876) comb. nov. from the Pesciara site. A, the holotype MGP-PD 154Z; B, original historical plate of the holotype illustrated and labelled as Torpedo egertoni by Achille de Zigno (1813–1892). Photo: courtesy of Universit̀a degli Studi di Padova; C, MCSNV IG.43347; D, MB.f 1608.1; E, MCSNV IG.142530; F, MCSNV VII.B.81. Scale bars = 100 mm.

Figure 9. †Plesiozanobatus egertoni (De Zigno, 1876) comb. nov. from the Pesciara site. A, MB.f 1608.1; B, reconstruction of the body outline and main skeletal structures (denticles and radials omitted); C, close-up of the head and pectoral girdle of MCSNV VII.B.81; D, reconstruction. Abbreviations: af, anterior fontanel; cb, ceratobranchials; cf, caudal fin; df, dorsal fins; hyo, hyomandibula; mc, Meckel’s cartilage; met, metapterygium; nc, nasal capsules; pf, pelvic fins; pq, palatoquadrate; pro, propterygium; pub, puboischiadic bar; rad, pectoral radials; sca, scapulocoracoid; sy, synarcual; ss, suprascapula; vc, vertebral centra. Scale bars = 50mm.

Figure 10. †Plesiozanobatus egertoni (De Zigno, 1876) comb. nov. from the Pesciara site. A, dermal denticles from the tail of MCSNV IG.43347; B, thorns from the tail of MCSNV IG.43347; C, thorns from the scapular region of MCSNV VII.B.80. Scale bars: A = 400 µm; B, C = 1 mm.