Squalorajidae Woodward 1886

Duffin, Christopher J., Garassino, Alessandro & Pasini, Giovanni, 2023, Squaloraja Riley 1833 (Holocephala: Squalorajidae) from the Lower Jurassic of Osteno Konservat-Lagerstätte (Como, NW Italy), Natural History Sciences 10 (1), pp. 57-74 : 62

Family Squalorajidae Woodward 1886

Remarks: The family includes the single genus Squaloraja Riley 1833, with two nominal species, both from the Lower Lias (bucklandi zone to basal semicostatum zone in the lower Sinemurian; Paul Davis pers. comm., 2021) of Lyme Regis, Dorset (UK): the type species S. polyspondyla (Agassiz 1836) (for full discussion on authorship assignment see Patterson, 1965: 117) and S. tenuispina Woodward 1886. The latter species is known from a single isolated frontal clasper only (NHMUK PV P.2081, Egerton Coll.; Woodward, 1886: 529, pl. 55, fig. 6) ( Fig. 5A ). However, Smith & Patterson (1988: 182) have pointed out that “two species of Squaloraja have been named but they cannot be distinguished”, considering S. tenuispina apparently conspecific with the other Lyme Regis specimens. A comprehensive review of the squalorajid frontal claspers, both isolated and on articulated specimens at the NHMUK leads us to support Smith & Patterson’s statement. The two characters used by Woodward (1886) to define S. tenuispina and distinguish it from the claspers of S. polyspondyla were the slender nature of the trunk of the clasper and the presence of an acuminate, pointed distal tip. The first thing to note is that the holotype of S. tenuispina is complete and measures 105 mm from the base to the distal tip. This makes it one of the shortest frontal claspers in the NHMUK collection. NHMUK PV OR 47402 is an articulated skull with an 82 mm long frontal clasper preserved in life position ( Fig. 5B ). Like the 112 mm long, virtually complete clasper in NHMUK PV OR 43307 ( Fig. 5C ), the structure is slender and although the tip is not sharply pointed, neither is it blunt or rounded. We conclude that the isolated clasper represented by S. tenuispina falls within an accepted range of morphological variation for S. polyspondyla and that S. tenuispina should therefore be considered its junior synonym.

Figures

Fig. 5 - Frontal claspers of male specimens of Squaloraja. A) NHMUK PV P.2081, holotype and only known specimen of Squaloraja tenuispina Woodward, 1886 from the Lower Lias of Lyme Regis (x 1.4). B) NHMUK PV 47402, detail of the skull of S. polyspondyla (x 1.06). C) NHMUK PV 43307, detail of the skull of S. polyspondyla (x 1.02). / Clasper cefalici di esemplari maschili di Squaloraja. A) NHMUK PV P.2081, olotipo e unico esemplare noto di Squaloraja tenuispina Woodward 1886 del Lias inferiore di Lyme Regis (x 1,4). B) NHMUK PV OR 47402, particolare del cranio di S. polyspondyla (x 1,06). C) NHMUK PV OR 43307, particolare del cranio di S. polyspondyla. (x 1,02). (Photo by: / Foto di: C.J. Duffin).