Stenopterygius quadriscissus (Quenstedt, 1856)

Partial synonymy.

Stenopterygius eos von Huene, 1931: Fraas 1891 pl. 4, fig. 1 (lectotype sensu Maisch (2008)).

Stenopterygius incessus von Huene, 1931: pl. 1, fig. 1.

Stenopterygius promegacephalus von Huene, 1949: Maisch (2008) pl. 8, fig. 1.

Stenopterygius macrophasma McGowan, 1979: pl. 3, fig. 2.

Magnipterygius huenei Maisch & Matzke, 2022: p. 170, figs 2–12.

Lectotype.

GPIT -PV-30028; for a list of paralectotypes, see Hungerbühler (1994).

Diagnosis.

Modified from Maxwell (2012); characters indicated by an asterisk are new. Moderately large form, maximum length approximately 3.5 m, antorbital segment moderately long, approximately two-thirds the length of the lower jaw; tooth reduction in individuals greater than 2 m total length; forelimb shorter than in Stenopterygius longipes, longer than in S. triscissus; ulnar facet of intermedium usually shorter than radial facet * (ratio usually <1 and never> 1.07; radial facet longer in S. triscissus (1.20–1.75) and S. longipes (1.03–1.18)); premaxilla and lower jaw shorter relative to length of humerus, femur, scapula and ischiopubis than in S. longipes or S. triscissus. In osteologically mature individuals, distal tarsal II strongly notched with smaller surface area than the astragalus or calcaneum, unlike in S. longipes; body deeper than S. longipes and S. triscissus; tailstock vertebral count 34–40 in adults and large juveniles * (mean = 35.6; higher in S. triscissus: 34–44, mean = 39.8); postflexural length 0.35–0.44 total caudal length in adults * (reduced in S. triscissus: 0.31–0.36).

Remarks.

Juvenile S. quadriscissus (specimens with lower jaw lengths between 200 and 400 mm) can have a relative postflexural length either longer or shorter than adult individuals (ratio to total caudal length = 0.34–0.47). If the length of the ulnar facet of the intermedium is longer than the radial facet (Uf / Rf = 1.0–1.07), comparisons with S. longipes are necessary to correctly refer a specimen to species.

Description of SMNS 55110, the Ravenscar Stenopterygius.

SMNS 55110 is a nearly complete articulated skeleton exposed on its right lateral side for most of the body length (Fig. 6 A). The skull is exposed ventro-laterally, revealing the mandible, but not the majority of skull roof. The fore-limbs and the pectoral girdle have become detached from the axial skeleton, as have the majority of the ribs. Nevertheless, the fore-limbs and the pectoral girdle remain completely articulated as an anatomical unit. The hind-limbs and the pelvic girdle are missing. Some parts of the posterodorsal skull are also disarticulated, including both scleral rings, supratemporals and postorbitals and the left postfrontal, quadrate and squamosal. The total length of the specimen is 145.8 cm (Table 1). It is worth noting that the excellent preservation of the specimen is only highlighted due to the excellent preparation of the skeleton, something that most historical specimens lack. More recently collected material from the Whitby area residing in private collections is similarly well-prepared and displays similar levels of preservation (DRL pers. obs.).