Andemys termasi, Bertrand & Flynn & Croft & Wyss, 2012

Bertrand, Ornella C., Flynn, John J., Croft, Darin A. & Wyss, Andre R., 2012, Two New Taxa (Caviomorpha, Rodentia) from the Early Oligocene Tinguiririca Fauna (Chile), American Museum Novitates 2012 (3750), pp. 1-36 : 8-12

Andemys termasi , gen. et sp. nov.

Figures 3 , 4 ; table 3

HOLOTYPE: SGOPV 2933, right mandibular fragment preserving p4–m3 and the incisor root.

REFERRED SPECIMENS: Known only from the holotype.

ETYMOLOGY: Ande, in reference to the cordillera in which this taxon was found. The derivation of Andes is uncertain, but for linguistic purposes the root is treated as “Ande-” ( Andes representing a Spanish language pluralization of an unknown root, although often argued to be related to the Quechua “andi” referring to mountains; C. Kammerer, personal commun.). The suffix mys, Greek for “mouse,” is commonly applied to names of rodents; the species name termasi derives from Termas del Flaco , the town near which the holotype was recovered and the long-term base of operations for field research in the area.

TYPE LOCALITY: Tinguiririca River valley , Termas del Flaco (34°57´S, 70°27´W), east central Chile ( Wyss et al., 1993); Locality Set 3 ( Flynn et al., 2003; “ Locality C ” of Charrier et al., 1996), ~ 1–2 km north of the Río Tinguiririca (i.e., ~ 5 km north of the two other Tinguiririca Fauna producing localities in the region, locality sets 1 and 2 of Flynn et al., 2003); see also Wyss et al. (1994: fig. 2 ), and Charrier et al. (1996) .

STRATIGRAPHIC OCCURRENCE: Purplish volcaniclastic sediments representing locally basal levels of the Abanico (= Coya-Machalí) Formation ( Wyss et al., 1993, 1994; Flynn et al., 2003).

AGE:?Late Eocene–early Oligocene, Tinguirirican SALMA. Several whole-rock 40K/40Ar dates ranging in mean age from 31.4 to 35.6 Ma ( Wyss et al., 1990; Flynn et al., 2003) have been obtained from south of the Tinguiririca River. Dates from the older end of the spectrum are from units underlying the fossiliferous unit stratigraphically. In addition, two high-precision 40Ar/39Ar dates, both with means near 31.5 Ma, have been obtained for localities south of the Tinguiririca River ( Flynn et al., 2003). Although the most productive localities in the region occur south of the Tinguiririca River, near Paso El Fierro, both rodents described here were collected north of the river. Collecting areas on opposites sides of the river are not directly traceable through a continuous outcrop because of the intervening river valley and alluvial cover, but lithostratigraphic, mapping, and biostratigraphic evidence indicate that all fossiliferous localities in the vicinity of Termas del Flaco fall within the same restricted stratigraphic interval. Perhaps the most convincing basis for regarding the northern and southern collecting areas as contemporaneous is the distinctive taxa they share, including the notoungulates Protarchaeohyrax gracilis and Johnbell hatcheri (both of which are restricted to the Tinguirirican). Moreover, no obviously Deseadan or younger fossils have been recovered from anywhere in the upper Tinguiririca River valley, all other fossils from this region being Eocene in age. That these two rodents and the associated fauna from north of the Tinguiririca River pertain to anything other than the Tinguiririca Fauna is thus exceedingly unlikely.

DIAGNOSIS (figs. 3, 4; table 4): Tetralophodont lower cheek teeth; m1 rounded to slightly squared as in Incamys and Australoprocta ; m1 fossettids round and centrally positioned; m1 posterolophid roughly half as wide mesiodistally as the anterolophid; metafossettid present on m1–2 as in Branisamys , Eobranisamys , Neoreomys , and Australoprocta ; metafossettid/hypoflexid confluent and “stepped” lingually on m3 as in Incamys , Eoincamys , Branisamys , Eobranisamys , Dasyprocta , Neoreomys , Australoprocta ; mesofossettid smaller than anterofossettid on m3 as, e.g., in Incamys , Australoprocta , and Neoreomys ; m2 hypoflexid well developed but narrow, reaching the tooth’s midline as in Incamys , Eoincamys , and Neoreomys ; brachydont to slightly hypsodont. The combined length of the lower cheektooth row (~12.5 mm) is roughly the same as that of Australoprocta , the taxon with which Andemys might most easily be confused. In late wear stages (see Kramarz, 1998: fig. 4e and h, for Australoprocta ), both taxa are characterized by tetralophodont, squared lower molars bearing fossettids that are narrow mesiodistally compared to the lophids. In Andemys , however, the lophids and fossettids are transverse, rather than oblique—as in Australoprocta . In addition, the labial cusps of Andemys are more rounded than in Australoprocta (where they are more angular), and the hypoflexid is more anteroposteriorly compressed at its labial end than in Australoprocta (wherein the hypoflexid is broadly open).

Figures

FIG. 3. The holotype of Andemys termasi, SGOPV 2933. Photographs (opposite page) in (A) lateral, and (B) occlusal views, with shaded drawings in (C) lateral, and (D) occlusal views. Line drawings (above) in (E) lateral and (F) occlusal views illustrating dental terminology used in text (following in part the nomenclature of Frailey and Campbell, 2004; Marivaux et al., 2004; Jenkins et al. 2005; Pérez, 2010); scale bar applies to A–D. Abbreviations: Atfd, anterofossettid; Atld, anterolophid; E, entoconid; Etlp, ectolophid; Hd, hypoconid; Hfxd, hypoflexid; Hlpd, hypolophid; Hpfd, hypofossettid; Ic, incisor; M, metaconid; Mc, masseter crest; Mf, mental foramen; Msfd, mesofossettid; Mtfd, metafossettid; Mtld, metalophid; nMpi, notch for the insertion of the tendon of the pars maxillomandibularis; Prd, protoconid; Psld, posterolophid; Rt, root; tMpi, tubercle for the insertion of the tendon of the pars maxillomandibularis. The angled arrow indicates anterior and lingual directions for occlusal views. Mandibular nomenclature follows Pérez (2010).

FIG. 4. (A) Scanning electron micrograph and (B) drawing of the holotype of Andemys termasi, SGOPV 2933 in lateral view illustrating the level of hypsodonty. Labial views of the lower dentitions of (C) Branisamys luribayensis PU 21944; (D) Incamys bolivianus PU 2093; and (E) Neoreomys australis AMNH 9542.

FIG. 2. Location map; Tinguiririca River valley, Termas del Flaco, Chile (mod- ified from Wyss et al., 1994).