Caudata Scopoli, 1777

Skutschas, Pavel P., 2016, A relict stem salamander: evidence from the Early Cretaceous of Siberia, Acta Palaeontologica Polonica 61 (1), pp. 119-123 : 119-120

Caudata Scopoli, 1777 (sensu Milner, 1988)

Genus et species indet.

Material.— LMCCE 1/4, fragmentary trunk vertebra ( Fig. 1 ). Shestakovo locality (Shestakovo 1 local site), bluff on right (i.e., east) side of Kiya River, 1.5 km downstream from Shestakovo village, Kemerovo Region, Western Siberia, Russia. Coarsegrained sand and sandstone of the Ilek Formation. Early Cretaceous or Aptian–Albian in age. For more details on the Shestakovo locality and its vertebrate assemblage, see Averianov et al. (2006: 361, fig. 1); Skutschas (2014: 89, fig. 1).

Description. — LMCCE 1/4 is an incomplete trunk vertebral centrum that lacks the anterodorsal portion of the anterior cotyle ( Fig. 1 ). It is large (relative to trunk vertebrae of the possible cryptobranchoid Kiyatriton leshchinskiyi from the same locality, see Skutschas 2014: fig. 4), with a ventral midline length of about 5.5 mm. LMCCE 1/4 is heavily ossified vertebra (= heavily built) that appears to have an endochondral component. The lateral and ventral surfaces of the centrum Fig. 1A–C ) are roughened and indented by scattered, small, rounded and oval pits (= pitted texture). These numerous pits are not densely situated and do not form a net-like texture. In lateral view, the centrum is relatively short anteroposteriorly and deep (ratio of ventral midline length vs. maximum height is about 1.3) and its ventral surface is broadly concave dorsally. The centrum is amphicoelous and both cotyles are deeply concave. The posterior cotyle is intact and nearly circular in posterior outline, with the ventral portion slightly narrower than the dorsal ( Fig. 1D ); the anterior cotyle is missing its dorsal portion, but it probably had a similar outline ( Fig. 1E, F ). Both cotyles retain a modest-sized notochordal pit. That pit is located slightly above the dorsoventral midpoint of posterior cotyle and it likely was in about the same location in the anterior cotyle. The inner walls of both cotyles are lined with a thin layer of calcified cartilage. The ventral surface lacks a subcentral keel. Instead, the ventral surface is moderately broad, shallowly convex from side-to-side and bracketed on either side by a shallow subcentral depression. Those depressions are perforated by small and nearly equal-sized subcentral foramina (not visible in figure); there are three foramina in the right subcentral depression and two in the left. Anteroventral to each subcentral depression, there is an anteroposteriorly elongate patch having a weakly rugose surface and bearing along its posterior portion a low, but distinct tubercle (=?anterior basapophysis). Bases of transverse processes (= rib-bearers) are present higher up and midway along the lateral sides of the centrum, but those bases are too damaged to determine whether the transverse processes were bicipital or unicipital. As best shown on the left side, the anterior and posterior bases of the transverse process are perforated by a small canal. Best preserved on the right side, the posterior alar process is an anteroposteriorly short flange that extends posteriorly from the base of the lower part of the transverse process.

Figures

Fig.1. Fragmentary trunk vertebral centrum (LMCCE 1/4) of stem salamander Caudata, gen.et sp. indet. from the Shestakovo locality, Lower Cretaceous Aptian–Albian), Ilek Formation, Western Siberia, Russia; in right lateral (A), left lateral (B), ventral (C, anterior towards top), posterior (D), anterior (E), and dorsal (F, anterior towards top) views. Photographs (A1–C1, D–F) and interpretive drawings (A2–C2).