Gaimanlestes pascuali, Abello & Martin & Cardoso, 2021

Abello, María Alejandra, Martin, Gabriel M. & Cardoso, Yamila, 2021, Review of the extinct ‘ shrew-opossums’ (Marsupialia: Caenolestidae), with descriptions of two new genera and three new species from the Early Miocene of southern South America, Zoological Journal of the Linnean Society 193 : -

GAIMANLESTES PASCUALI SP. NOV.

( FIG. 10A–E)

Zoobank registration: lsid: urn:lsid:zoobank.org:act:EB85070B-345B-4E2B-AF2A-D2F51B5092D9

Etymology: This species is named for the late Dr. Rosendo Pascual, in recognition of his major contribution to the understanding of South American mammal evolution and his outstanding work as professor of the Facultad de Ciencias Naturales y Museo, Universidad de La Plata, Argentina.

Holotype: MPEF-PV 4849 , left mandibular fragment with m1-3 and alveolus for m4 ( Fig. 10A–C).

Referred material: MPEF-PV 5735, right mandibular fragment with p3-m1 and alveoli of m2-4 ( Fig. 10D, E).

Temporal distribution: Early Miocene, Colhuehuapian SALMA.

Stratigraphic and geographic distribution: Sarmiento Formation, Trelew Member. Gaiman(Bryn Gwyn locality, see: Goin et al., 2007), Chubut province, Argentina.

Measurements: Supporting Information, File S6, Table 1a.

Diagnosis: Gaimanlestes pascuali differs from the remaining caenolestids by its (1) basally compressed molars, (2) short anterobasal cinguli on m1-3, (3) metaconid and protoconid of m1 transversely aligned, (4) metaconid of m2-3 anteriorly positioned with respect to the protoconid, (5) distal end of the entocristid lower than that of the cristid obliqua in m1 and (6) distal ends of the entocristid and cristid obliqua of equal height in m2-3.

Description: The mandibular body of the type specimen, MPEF-PV 4849, is relatively deep and of uniform height along the molar row. Labially, it has two small mental foramina close to each other, that open bellow the posterior root of m1. A large retromolar foramen is present in the retromolar space, where the mandible is broken. The preserved molars are scarcely worn and all have short and narrow anterobasal cinguli that do not extend beyond posterior wall of the protoconid. The trigonids are labiolingually narrower than talonids and show a morphological gradient, similar to that described for Pliolestes and Stilotherium , in which relative trigonid/ talonid width decreases from m1 to m3. In m1, the protoconid is the largest trigonid cusp, joined to the paraconid by a short and straight paracristid. The metaconid is transversely aligned with the protoconid and is larger than the reduced paraconid. The talonid basin is labiolingually narrow, labially delimited by a tall cristid obliqua, and lingually by a straight and anterolabially to posterolingually oriented entocristid. The entoconid is slender, labiolingually compressed and transversely aligned to the hypoconid. The hypoconid is labially salient and joined to the hypoconulid by an oblique postcristid. In contrast to m1, the metaconid of m2-3 is positioned anteriorly in relation to the protoconid and closer to the paraconid in m2 than in m3 ( Fig. 3F). On both molars, the paraconid is smaller and more labially positioned than the metaconid. The postparacristid is transverse on both molars. Different than in m1, entocristids in m2-3 are lingually curved. The hypoconid is more salient in m2 than in m3. As in m1, both molars have entoconids transversely aligned to the hypoconids, and oblique postcristids. Judging by its alveolus, half the size of the posterior alveolus of m3, the m4 was uniradiculate and reduced.

MPEF-PV 5735 shows the same dimensions of the mandibular body of the type specimen. Like the type specimen, it has a large retromolar foramen. In labial view, it has two mental foramina:an anterior and large foramen between the anterior root of m1 and the posterior root of p3, and a small posterior foramen below the posterior root of m1. Despite the mandible being broken anterior to p3, a relatively deep, forwardly developed groove can be distinguished anterior to the mental foramen. The p3 is a relatively large tooth; it is longer than the trigonid of m1 and its main cusp is as tall as the protoconid of m1. The p3 lacks an anterobasal cusp and its talonid is poorly developed. The m1 is the only preserved molar, which has a similar morphology to that of the type specimen, but is somewhat shorter. The alveoli for m2-4 show the same size differences observed in the type.

Remarks: Gaimanlestes pascuali is the only caenolestid recovered from sediments of the Sarmiento Formation at Gaiman locality.The m1 morphology of Gaimanlestes is primitive in the context of Caenolestidae , with the exception of the entocristid being lower than the cristid obliqua, and similar to that of Stilotherium . Contrary to this, the morphology of the m 2-3 in Gaimanlestes presents a mosaic of primitive and derived characters within Caenolestidae . Derived characters are related to m2-3 morphology, where the metaconid is anterior to protoconid and the anterobasal cinguli are short; both characters are shared with Pliolestes tripotamicus . Plesiomorphic characters include m2-3 talonid morphology, where entocristid and cristid obliqua are of the same height, entoconid and hypoconid are in the same line, transversely, and a shelf lingual to the entocristid in m1-2 is absent.