Torvoneustes undetermined

Young, Mark T., Andrade, Marco Brandalise De, Etches, Steve & Beatty, Brian L., 2013, A new metriorhynchid crocodylomorph from the Lower Kimmeridge Clay Formation (Late Jurassic) of England, with implications for the evolution of dermatocranium ornamentation in Geosaurini, Zoological Journal of the Linnean Society 169 (4), pp. 820-848 : 823-824

TORVONEUSTES CORYPHAEUS SP. NOV.

ZooBank Life Science Identifier (LSID) for new species: urn:lsid:zoobank.org:act:475C6196-571A-4D19-918F-4C55634D88AF

Holotype

MJML K1863 , three-dimensionally preserved skull (lacking most of the rostrum), the posterior half of the left mandibular ramus, and seven isolated teeth found in close association with the skull.

Etymology

The savage swimmer Leader. Coryphaeus, Latinized form of the Greek term koryphaîos (κορυφαι´ος) meaning the leader of a movement or a chorus. So named as the specimen is beautifully (and threedimensionally) preserved, helping to elucidate metriorhynchid cranial form. Koryphaîos is derived from koryphe (κορυφη´), meaning the top of the head; appropriate as the external surface of the dermatocranium in this specimen has intriguing evolutionary implications. Coryphaeus is used as a noun in apposition.

Type locality

Studley Grange landfill, Lydiard Tregoze, Wiltshire, England, UK.

Type horizon

Pictonia baylei sub-Boreal ammonite zone, Lower Kimmeridge Clay Formation (lowermost Kimmeridgian in age).

Differential diagnosis

Torvoneustes coryphaeus sp. nov. differs from the type species T. carpenteri in the nine following ways.

1. The ornamentation of the distal border of the prefrontals. In T. coryphaeus sp. nov. the ornamentation of this border is similar to other metriorhynchids in having irregular ‘notches’ along this border, although it does not have as many as Metriorhynchus superciliosus (Blainville, 1853) (see Andrews, 1913: 148, fig. 57). The distal border of the prefrontals of T. coryphaeus sp. nov. are very similar to those of cf. Torvoneustes . Torvoneustes carpenteri , however, has a distinct morphology: there are four large ‘finger-like’ projections rather than irregular notches ( Fig. 3 ).

2. In dorsal view, the frontal anteromedial process of T. coryphaeus sp. nov. reaches the same relative position as the anterior margin of the prefrontals; however, in T. carpenteri the frontal anteromedial process is shorter, and although the prefrontals are incomplete in the type species holotype, the frontal would not have reached the same relative position as the prefrontal anterior margin. In cf. Torvoneustes (Young, 2013) the prefrontals are longer than the anteromedial process of the frontal.

3. The ornamentation on the external surface of the cranial bones is more pronounced in T. coryphaeus sp. nov., especially on the nasals and frontal, which are unornamented in T. carpenteri . The ornamentation patterns and extent is very similar between T. coryphaeus sp. nov. and cf. Torvoneustes ( Table 1; Young, 2013).

4. The supraorbital notch forms an acute angle (less than 45°) in T. coryphaeus sp. nov., whereas in T. carpenteri the supraorbital notch is an open continuous curve, with an angle close to 90°.

5. The prefrontal posterolateral margin in dorsal view forms an acute angle in T. coryphaeus sp. nov., whereas in T. carpenteri this margin is rounder, forming an angle close to 90°.

6. The tooth crowns of T. coryphaeus sp. nov. are more strongly mediolaterally compressed and lingually recurved than those of T. carpenteri , which when partially and fully erupted are more circular in cross section, and can lack any lingual curvature. It must be noted, however, that the newly erupting tooth crowns of T. carpenteri have a similar mediolateral compression to the crowns of T. coryphaeus sp. nov.

7. Torvoneustes coryphaeus sp. nov. has longer maxillae, reaching posteriorly to the same relative position as the anterior border of the orbit, whereas in T. carpenteri the maxillae end anteriorly to the orbit. Although the maxillae are incomplete in cf. Torvoneustes (Young, 2013) , the maxillae would have been at least as long as those of T. coryphaeus sp. nov.

8. The maxillary tooth row of T. coryphaeus sp. nov. terminates immediately posterior to the anterior margin of the orbit, whereas in T. carpenteri the

Figures

Figure 3. Dorsal view photographs of the prefrontals of: (A) Torvoneustes carpenteri holotype BRSMG Ce17365; and (B) Torvoneustes coryphaeus sp. nov. holotype MJML K1863. Scale bars: 10 cm.