Squaloraja Riley 1833 (Holocephala: Squalorajidae) from the Lower Jurassic of Osteno Konservat-Lagerstätte (Como, NW Italy)

Abstract

A remarkable, complete specimen of a squalorajid holocephalian is described for the first time from the Lower Jurassic (lower Sinemurian) rocks of Osteno (Como, NW Italy). It is the only such specimen known from the locality and belongs to a (possibly juvenile) female. The Italian specimen is assigned to Squaloraja sp., and has a large dorsoventrally flattened head, long rostrum, a single mandibular tooth plate on each lower jaw, a well-developed synarcual, thick notochordal sheath calcifications, and only slightly reduced squamation comprising distinctive placoid scales with stellate bases. There is no ethmoid canal, dorsal fin or fin spine. The Lower Jurassic succession (‘Lower Lias’) of Lyme Regis (Dorset, UK) has yielded only two incomplete purported female specimens of the type species of the genus, Squaloraja polyspondyla, thus restricting potential comparison with the Italian specimen. This new record of the genus expands the known palaeogeographical distribution of this rare holocephalian.