Eomakhaira molossus, A New Saber-Toothed Sparassodont (Metatheria: Thylacosmilinae) from the Early Oligocene (? Tinguirirican) Cachapoal Locality, Andean Main Range, Chile Author Engelman, Russell K. Author Flynn, John J. Author Wyss, André R. Author Croft, Darin A. text American Museum Novitates 2020 2020-07-17 2020 3957 1 76 https://bioone.org/journals/american-museum-novitates/volume-2020/issue-3957/3957.1/Eomakhaira-molossus-A-New-Saber-Toothed-Sparassodont-Metatheria--Thylacosmilinae/10.1206/3957.1.full journal article 10.1206/3957.1 0003-0082 5370642 Eomakhaira molossus , gen. et sp. nov. Figures 3–4 , 6–16 ; tables 1–2 HOLOTYPE : SGOPV 3490 , a partial rostrum of a senescent individual preserving the right maxilla with C-P3, alveoli and partial roots of M1–2, and part of M3; left maxilla with C-P3, anterior root of M1, and M3–4; left and right horizontal rami of the mandible, including both lower canines and most of the postcanine dentition, as well as parts of the coronoid processes; the entire left and parts of the right nasal; parts of the palatine; and the orbital process of the left lacrimal. DIAGNOSIS: A member of Borhyaenoidea based on its short, robust rostrum, presence of lingual median canine sulci, extremely small protocone, small and unicuspid talonid on m4. Differs from all other borhyaenoid sparassodonts in the following combination of features: small size (smaller than most other borhyaenoids; length of m1–4 = 37.3 mm , comparable to Fredszalaya hunteri or the extant dasyuromorphian Sarcophilus harrisii ); maxilla very deep and maxillary “cheeks” absent; mandibular symphysis unfused and anteroposteriorly narrow; two mental foramina present; length/width ratio of palate>1.5; palate extending to level of M4; presence of postpalatine tori (shared only with Arminiheringia and possibly Callistoe among borhyaenoids); absence of postpalatine torus foramen; sphenorbital foramen opening dorsal to M4; large canines; absence of longitudinal striations on the canine roots (shared only with other thylacosmilines and possibly Lycopsis viverensis ); median keel on the labial face of upper canines; medial sulcus on lingual face of upper and lower canines; short lower canine roots; presence of three premolars with no diastemata between them; premolars large and robust but not globular; asymmetric protoconid of P1 (shared only with Arminiheringia and Callistoe ); P3 significantly longer than p3 (possibly autapomorphic for this taxon); bulbous roots only on p3; preparacingulum absent; M3 with narrow stylar shelf and prominent ectoflexus; M4 extremely narrow anteroposteriorly (only comparable to Patagosmilus among borhyaenoids), subequal or greater in width to M3, and with three roots; protocone vestigial (at least on M4); absence of an anteriorly projecting ventral keel of paraconid (which only occurs in proborhyaenids among sparassodonts); protoconid of m4 posteriorly salient; metaconid absent on m4 and probably m2–3; posterolabial cingulid present; talonid of m4 almost absent; and p1–3 short relative to m1–4 (shared with Paraborhyaena among borhyaenoids with three premolars). Canines more mediolaterally compressed than in borhyaenoids other than Patagosmilus , Thylacosmilus , and possibly Proborhyaena . P/p3 labiolingually narrower than in Fredszalaya , Plesiofelis , Acrocyon , Arctodictis , Australohyaena , Borhyaena , and Callistoe , but wider than in Prothylacynus and some individuals of Pharsophorus , comparable in relative proportions to Arminiheringia , Paraborhyaena , and Proborhyaena . TYPE LOCALITY : Cachapoal locality, west side of Estero Los Llanos of the upper Río Cachapoal drainage, Libertador General Bernardo O’Higgins Region , central Chile (fig. 2). STRATIGRAPHIC OCCURRENCE: Abanico Formation. Most specimens from Estero Los Llanos were recovered from talus cones at the SE nose of a roughly N-S running ridge of ~ 1,500 m relief. This ridge roughly parallels the strike of the steeply west-dipping beds. The thickness of the Abanico Formation in the Cachapoal region has not been measured in detail but is on the order of 2000–4000 m . Within this thick succession, the exact horizon that produced SGOPV 3490 is not known, as the specimen was collected from talus. For additional geological context of the Cachpaoal locality see Flynn and Wyss (2004), Hitz et al. (2006), and West et al. (2014) . AGE: Probably early Oligocene,?Tinguirirican SALMA. Fossils from the Cachapoal locality are likely at least 29.3 ± 0.1 million years old (at least in part), based on an unpublished date for a volcanic tuff that is thought to either correlate with or overlie the fossil-producing horizons at Los Llanos (Charrier et al., 1997; Flynn and Wyss, 2004). It must be cautioned, however, that this date is from ~ 5 km to the south, in the neighboring Las Leñas drainage, and that the units involved have not been traced directly between the two locations due to precipitous intervening topography. The only radioisotopic date for the Cachapoal Valley itself is an 40 Ar/ 39 Ar date of 11.1 ± 1.8 Ma reported by West (2017) from levels far above the fossil-producing strata, which does little to precisely constrain the age of the fossils. The presence of the polydolopid Kramadolops ( Polydolops in Flynn and Wyss, 2004) and the archaeohyracid Archaeotypotherium (Croft et al., 2008a) suggest a pre-Deseadan age, and the presence of the interathere Johnbell hatcheri , otherwise known only from the Tinguirirican type locality (Hitz et al., 2006), suggests that fossils from the Cachapoal locality are probably similar in age to those of the Tinguiririca Fauna (~33–32 Ma; Flynn et al., 2003). ETYMOLOGY: The name of the genus derives from the Greek root Eo s, meaning “dawn,” and makhaira , a type of short sword or large knife (often translated as “carving knife”), in reference to the bladelike canines of thylacosmilines. The specific epithet comes from the Greek molossus , a term used to refer to short-snouted, robust-skulled dog breeds such as mastiffs and bulldogs and refers to the short, robust snout of this species. Gender is masculine.