Ichthyosaura sp.

Delfino, Massimo, Bailon, Salvador & Pitruzzella, Gaetano, 2011, The Late Pliocene amphibians and reptiles from “ Capo Mannu D 1 Local Fauna ” (Mandriola, Sardinia, Italy), Geodiversitas 33 (2), pp. 357-382 : 363-364

cf. Ichthyosaura sp. ( Fig. 2J, K )

MATERIAL EXAMINED. — Trunk vertebra: 3.

DESCRIPTION

These three opistocoelous vertebrae are much larger in size than the vertebrae referred to the genus Salamandrina . The best preserved remain, an anterior trunk vertebra (DSTC 6030), has a centrum length of 1.8 mm, whereas the length of the other vertebrae can be assumed to slightly exceed 2 mm. DSTC 6030 is a nearly complete vertebra (damaged in the left anterior and right posterior areas). The condyle and cotyle are nearly circular. The condyle is well defined and there is a modest precondylar constriction (without the development of marked neck as in Salamandrina ). The neural canal is particularly wide. The neural arch has a V-shaped anterior margin. The prezygapohyseal facets are anterolaterally elongated and are faintly tilted dorsally.The posterior edge of the neural arch is nearly straight; it does not surpass the postzygapophyses even if it is prolonged in a small point which extends the neural crest. The neural crest is partly broken but is clearly moderately tall, undivided (not forked) and not thickened. The rib-bearers are relatively thick and subequal in size (the ventral one is slightly thicker); they are connected to each other by a bony lamina. The bony laminae connecting the rib-bearers with the centrum are, both dorsally and ventrally, underdeveloped in the anterior sector of the vertebra but evident in the posterior one where they have a lateral deeply concave profile. The surface of the ventral laminae hosts elongated and relatively large foramina.

The two other vertebrae have a similar morphology but are a little larger in size, with a comparatively narrower neural canal and thinner, more posteriorly directed, rib-bearers. The anteroventral edge of the ventral rib-bearers develops in both vertebrae an evident ridge. Small foramina are present on the bony laminae connecting the rib-bearers with the posterior sector of the centrum. There is no precondylar constriction in the only vertebra that preserves the anterior end of the centrum. The posterior area of the neural arch is broken off in both cases.

DISCUSSION

The width of the neural canal and the orientation of the rib-bearers indicate that DSTC 6030 is an anterior trunk vertebra, whereas the other two vertebrae come from a posterior sector of the column. The described morphology of the vertebrae is congruent with that of a newt of the genus Ichthyosaura , but the laminae developed anterior to the rib-bearers and the precondylar constriction are less developed in the fossils than in extant Ichthyosaura . Even the presence of the genus Euproctus Gené, 1838 (which still inhabits the island but has no fossil record yet) cannot be ruled out: a direct analysis of limited skeletal material of E. platycephalus (Gravenhorst, 1829) (MNCN 15981), E.montanus (Savi, 1838) (MNCN 15966, 15967), and Calotriton asper (Dugès, 1852) (MNCN 16130, 16131) revealed that these species, once grouped in a single genus, possess a vertebral morphology that is well characterized and rather variable. The region hosting the best characterizing features is the posterior area of the neural arch (the lamina developing from the dorsal rib-bearers to the postzygapophyses, and the shape of the posterior edge of the neural arch), area that is broken in the two fossil posterior trunk vertebrae.

Taking into consideration their poor preservation, the fossil remains from the Capo Mannu D1 LF are tentatively referred to cf. Ichthyosaura sp. Further fossil material or a detailed analysis of a larger sample of Euproctus vertebrae could possibly allow deepening such provisional identification.

Order ANURA Fischer von Waldheim, 1813

Figures

FIG. 2. — Fossil remains of amphibians from Capo Mannu D1 Local Fauna (Sardinia): A-I, Salamandrina sp.; A, B, right occipito-otic unit (DSTC 6000), dorsal and ventral views; C-E, middle trunk vertebra (DSTC 6001), dorsal, ventral, and left lateral views; F, trunk vertebra (DSTC 6002), anterior view; G-I, anterior trunk vertebra (DSTC 6003), dorsal, ventral, and left lateral views; J, K, cf. Ichthyosaura sp., trunk vertebra (DSTC 6004), dorsal and ventral views. Scale bars: 2 mm.