Sairadelphys, Oliveira, Édison Vicente, Nova, Patricia Villa, Goin, Francisco J. & Avilla, Leonardo Dos Santos, 2011

Oliveira, Édison Vicente, Nova, Patricia Villa, Goin, Francisco J. & Avilla, Leonardo Dos Santos, 2011, A new hyladelphine marsupial (Didelphimorphia, Didelphidae) from cave deposits of northern Brazil, Zootaxa 3041, pp. 51-62 : 54-55

Sairadelphys gen. nov.

Etymology. saíra is a word from Tupi language meaning tiny or slender + delphys, a Greek suffix used for New World marsupials.

Type species. Sairadelphys tocantinensis sp. nov.

Diagnosis. Very small didelphid, with slightly larger size than Hyladelphys . Relatively low crowned molars. M3 with similarly sized paracone and metacone. Stylar cusps are reduced in number and size. Paracone and metacone have convex labial faces. Upper molars not strongly carnassialized (i.e. postmetacristae are only slightly longer than postprotocristae) and postprotocrista are without a carnassial notch. M2 subequal to slightly larger than M3. First lower molar with well-developed prefossid. Differs from Hyladelphys in having a slightly larger size, more inflate and sharpless teeth, deeper ectoflexus in M2, no size difference between paracone and metacone in M2-3, protocone eccentric and very low, absence of anterior cingulum, stronger reduction in number and size of stylar cusps and smaller M4.

Description. M2 is the largest known molar tooth (M1 is unknown); M2>M3>M4. The ectoflexus is very deep and symmetrical so that the parastylar and metastylar areas are very conspicuous. The trigon cusps are low and bunodont. The stylar shelf is much higher than the trigon basin and is transversely wider at both paracone and metacone in relation to the talon. There are no traces of stylar cusps StA, STB, StC and StE; only a hint of StD is present in M2. In general, the stylar shelf surface is smooth, with a rounded labial edge. The preparacrista is poorly developed, low and ends at the anterolabial corner of the tooth. The postmetacrista is slightly longer than the preparacrista, and extends relatively transversely to the dental axis. The paracone and metacone are subequal in height, and their labial faces are convex. The lingual edges of the paracone and the metacone are not vertical but instead gently slope medially. In occlusal view, the paracone is slightly larger than the metacone. A distinct ovate wear facet is observed at the apices of the paracone and metacone. The centrocrista is low, poorly developed and linear. Smooth lingual crests descend from the apex to the base of the paracone and the metacone. There are no traces of anterior or posterior cingulum; para- and metaconules are absent. The protocone is reduced and anteriorly displaced (eccentric). The protocone is round, low and the trigon basin is small.

M3 differs from M 2 in having a more developed metastylar area, the postmetacrista extends slightly less transversely to the dental axis. Furthermore, the anterolingual face of the paracone is mostly rectilinear and the protocone is slightly more eccentric. M4 is very reduced in relation to M2–3 and bears only two cusps, the protocone and a large parastyle. The labial-most cusp is rounded and anterolabially displaced.

The only lower molar available is an isolated m1 ( Fig. 3 ). It presents low and slightly inflated cusps. The trigonid is equivalent in length to the talonid. The protoconid is the tallest trigonid cusp. The metaconid is compressed labio-lingually and placed aligned transversally to protoconid. The paraconid is wide in its basis, with the apex not lingual but displaced labially. The trigonid presents a well-developed prefossid. The prefossid is anteriorly delimited by two short crests running from the apex of the paracone to the basis of the protoconid and of the metaconid. The talonid is wider than the trigonid. The entoconid is the tallest and largest cusp of the talonid, occupying much of the lingual margin of the talonid. The hypoconulid is small, twinned to the entoconid and slightly displaced labially in relation to it. The hypoconid is labially expanded and its basis is displaced posteriorly relative to the entoconid. The cristid obliqua ends anteriorly at a point labial to the posprotocristid notch. The anterior cingulid is narrow, and a short labial cingulid occurs in the postero-labial face of the protoconid.

Figures

FIGURE 3. Lower molar of Sairadelphys tocantinensis gen. et sp. nov., DGEO-UFPE 6746. A, mesial view, B, posterior view. Scale bar = 1 mm.