Saurorhynchus brevirostris ( Woodward, 1895 )

Maxwell, Erin E. & Stumpf, Sebastian, 2017, Revision of Saurorhynchus (Actinopterygii: Saurichthyidae) from the Early Jurassic of England and Germany, European Journal of Taxonomy 321 (321), pp. 1-29 : 9

Saurorhynchus brevirostris ( Woodward, 1895)

Figs 1B , 2A , 4 B–E, 6A

Belonorhynchus brevirostris Woodward, 1895 , partim: 17–18, pl. II, fig. 2.

Saurorhynchus brevirostris – Forey et al. 2010: 352, pl. 65, fig. 6.

Revised differential diagnosis

The diagnosis is constructed based on the holotype and referred material housed at the NHMUK. This species can be differentiated from all other Saurorhynchus species by the following combination of characters:short, deep skull, overbite consistently present (overbite slight or absent in S. acutus ); posterior dorsal skull roof deflected dorsally relative to the long axis of the skull (parallel in S. acutus ); postorbital segment approximately equal in length to the depth of the lower jaw; anterior narial opening large and triangular in outline with the apex directed toward the mandible (narrow and elongate in S. acutus ); foramen for the internal carotid and efferent pseudobranchial arteries positioned posterolaterally within the basisphenoid, exposing the large foramen of the ophthalmica magna artery on the anterolateral surface of the basisphenoid; posterior edge of the mandible weakly sinusoidal (strongly sinusoidal in S. acutus ); angle between the posterior and ventral edges of the mandible less than 80 degrees; subnarial laniaries well-developed with acrodin caps directed lingually (subnarial laniaries absent and all acrodin caps straight in S. acutus ); mandibular sensory canal closer to the dorsal than ventral edge of the posterior mandible. Opercle strongly wedge-shaped; lateral supracleithrum bearing prominent anterior process pierced by a foramen; pectoral radials well-ossified.

Material studied

Holotype

UNITED KINGDOM: Lyme Regis ( NHMUK PV OR 40726) ( Fig. 1B ). A skull with partial pectoral girdle preserved in lateral view. This specimen is probably from the Charmouth Mudstone Formation, Black Ven Mudstone Member, latest early Sinemurian to late Sinemurian ( Forey et al. 2010).

Remarks

Here we restrict usage of S. brevirostris to material from the Lower Lias. The anterior tip of the holotype skull is missing, but in the largest referred specimen skull length (tip of rostrum to jaw joint) is 86 mm (Suppl. Table 1). Assuming similar proportions to S. hauffi sp. nov., fork length is estimated at up to 30 cm for S. brevirostris .

Figures

Fig. 1. Holotype specimens of Early Jurassic saurichthyids. A. Saurorhynchus acutus (Agassiz, 1844) (NHMUK PV P 4268). B. Saurorhynchus brevirostris (Woodward, 1895) (NHMUK PV OR 40726). C. Saurorhynchus anningae sp. nov. (NHMUK PV P 3791). D–E. Saurorhynchus hauffi sp. nov. (SMNS 55057). Scale bars: A, C = 20 mm; E = 50 mm. Photos A–C © The Trustees of the Natural History Museum, London.

Fig. 2. Reconstruction of the dermal skull in Early Jurassic saurichthyids. A. Saurorhynchus brevirostris (Woodward, 1895). B. Saurorhynchus anningae sp. nov. C. Saurorhynchus hauffi sp. nov. D. Saurorhynchus acutus (Agassiz, 1844). Not to scale. Dashed lines indicate sensory canals, grey lines indicate bones that were present but where the exact location of the sutural contact is unclear, and question marks indicate areas of uncertainty. Abbreviations: ang = angular; bs = basisphenoid; cl = cleithrum; d = dentary; dh = dermohyal; dpt = dermopterotic; dsp = dermophenotic; f = frontal; io = infraorbital; io.c = infraorbital sensory canal; l = lacrimal; l.ex = lateral extrascapular; m = maxilla; md.c = mandibular sensory canal; mio.c = medial branch of the infraorbital sensory canal; n = neomorph; na-ao = nasaloantorbital; op = opercle; p = parietal; pm = rostropremaxilla; pop = preopercle; ps = parasphenoid; sa = supraangular; scl = supracleithrum; so = supraorbital; so.c = supraorbital sensory canal.

Fig. 4. Orbitotemporal region, illustrating variation in the braincase of Early Jurassic saurichthyids. A. Saurorhynchus anningae sp. nov. (based on NHMUK PV P 36227). B, E. Saurorhynchus brevirostris (Woodward, 1895) (photo pertains to NHMUK PV P 4878, mirrored). C, F. Saurorhynchus hauffi sp. nov. (photo is of SMNS 51888, mirrored). D. Saurorhynchus acutus (Agassiz, 1844) (based on SMNS 87737). Abbreviations: asc = ascending process of the parasphenoid; bs = basisphenoid; dpt = dermopterotic; dsp = dermosphenotic; f.ic+ep = foramen for the internal carotid artery and efferent pseudobranchial artery; f.oma = f.om = foramen for the great ophthalmic artery; my = posterior myodome; n = neomorph; nc = neurocranium; orb = orbit; psr = parasphenoid rostrum; rot = foramen for the lateral otic ramus; spi = ventral opening of the spiracular canal; tf.c = trigeminofacial chamber. Scale bars: E–F = 2 mm. E. Photo © The Trustees of the Natural History Museum, London.