Salamandrina 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 : 360-363

Salamandrina sp. ( Fig. 2 A-I)

MATERIAL EXAMINED. — Occipito-otic unit: 3; precaudal vertebra: 16; caudal vertebra: 4.

DESCRIPTION

Two of the three occipito-otic units are relatively well preserved and allow identifying the following characters: the overall size is small and the shape is elongated (maximum length and width of about 2.1 and 1.5 mm respectively; but part of the width is due to the long tectum synoticum); the well-marked convexities of the dorsal surface surround an evident median concavity (in which a foramen opens in two of the three units); the medial convexity hosts, in the posterior sector, a dorsally directed small tubercle; the tectum synoticum narrows apically where it is naturally truncated; the axis of the tectum synoticum and the main axis of the capsule form an angle of approximately 60°. In medial view, the area of suture contact with the other occipito-otic unit is reduced; the endolymphatic and the perilymphatic foramina, as well as the large cavity that hosts the three acoustic nerves are visible; the latter cavity is deep and well defined; the oval fenestra is large, slightly oval in shape and with funnel-shaped rims; the lateral margin of the oval fenestra is markedly raised from the surface of the capsule; the condylar articular surface is concave; two foramina are placed laterally and lateroventrally to the occipital condyle. In lateral view, the contact area for the squamosal is small and oval-shaped.

The precaudal vertebrae are rather small (maximum centrum length estimated at about 1.8 mm, but most of the vertebrae are much smaller). The centrum is opistocoelous; condyle and cotyle are roundish or slightly oval in shape; an evident constriction is placed at the base of the condyle. In dorsal view, the anterior edge the prezygapophyses does not significantly surpass the neural arch. The prezygapophyseal facets are vaguely drop-shaped, longer than wide, and proportionally rather large in most of the cases (each prezygapophysis is as wide as the anterior edge of the neural arch). The lateral edge of the neural arch is distinctly constricted just anteriorly to the rib-bearers.The dorsal rib-bearer has invariably a laminar anterior edge. The rib-bearers are posterolaterally directed. A shallow groove is developed along the posterior contact between the dorsal rib-bearer and the neural arch. A deep notch is developed at the posterior edge of the neural arch; the latter does not extend beyond the posterior edge of the postzygapophyses. The neural crest has a variable length: it does not reach the anterior edge of the neural arch but it extends up to its posterior edge. It regularly bifurcates in the posterior area of the vertebra where it is apically thickened and develops laterally directed “lips”. The thickening of the crest can be present also anteriorly to the bifurcation in the most anterior vertebrae. One or few foramina can be present in the depression between the two rami just posterior to the bifurcation. In ventral view, the centrum is nearly cylinder-shaped (with a weak median constriction). The surface of the centrum is well delimited laterally, but it is covered by a bony lamina (anterior ventral crest) that extends slightly anteriorly of the rib-bearers and up to the basis of the condyle neck where it has an irregularly concave profile. The ventral rib-bearer has laminar edges both anteriorly (the above mentioned anterior ventral crest) and posteriorly (posterior ventral crest). The posterolateral edges of the lamina are variably concave. The lamina can host, posteriorly to the root of the rib-bearers, few wide depressions with foramina opening at their bottom (in some cases there are no depressions and the foramina open directly at the surface of the lamina). In lateral view, the neural crest is moderately tall in the posterior two thirds of its length. The rib-bearers are moderately divergent but always linked by a bony lamina for their entire length. A foramen pierces the base of the lateral wall of the neural arch behind each couple of rib-bearer processes. In anterior and posterior views, the pre- and postzygapophyses are nearly horizontal. The neural canal varies in shape and size: in the vertebrae that are proportionally short and wide (therefore more anteriorly placed) it is much larger than the condyle, in the vertebrae that are relatively more elongated it is proportionally not so large. The neural arch usually shows at least a hint of zygosphene and zygantrum.

One vertebra (DSTC 6027) referred to the precaudal section of the vertebral column could represent a sacral vertebra because of the slightly enlarged tips of the rib-bearers, and at least another one (DSTC 6028) could come from the caudo-sacral region because of the possible presence of the remnants of haemal processes.

The caudal vertebrae are smaller than the precaudal ones (the maximum length of the opistocoelous centra is of about 1.0 mm). At least in the two better preserved vertebrae, the incomplete neural arches show the hint of zygosphene and zygantrum and the neural crests are thickened and bifurcated. Haemal arches are regularly present and at least in one case (DSTC 6029) they develop a posteriorly bifurcated crest, hosting a foramen. At least three of the four caudal vertebrae are characterized by lateral processes forming a laid down “M” (with the base oriented towards the posterior sector of the vertebra).

DISCUSSION

The occipito-otic units can be referred to genus Salamandrina because of the combination of the following characters (see Pitruzzella 2008): elongated general morphology, development of the convexities and of the median depression on the dorsal surface; presence of a tubercle on the medial convexity; morphology of the bone encircling the oval fenestra.

The vertebrae can be referred to this genus on the basis of several characters (see Sanchiz1988; Pitruzzella 2008; Pitruzzella et al. 2008), among which the most relevant are:the presence of zygosphene and zygantrum; thickened and posteriorly bifurcated neural crest developing lateral “lips”; development of a ventral bony lamina covering the centrum and reaching the basis of the condyle (in precaudal vertebrae); “M”-shaped lateral process (in caudal vertebrae).

As for the specific identification, the absence of skeletal diagnostic characters distinguishing the two extant species of this genus(Pitruzzella 2008) does not support the specific identification of the fossil remains from the Capo Mannu D1 LF. However, it is worth noting that all the remains here described are distinctly smaller than the corresponding skeletal elements of extant Salamandrina perspicillata (Savi, 1821) and S. terdigitata (Lacépède, 1788) , as well as of fossil Salamandrina sp. from Oschiri (Pitruzzella 2008).

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.