CERVOIDEA Batsch, 1788

Gasparini, Germán M., Dutra, Rodrigo Parisi, Perini, Fernando A., Croft, Darin A., Cozzuol, Mario A., Missagia, Rafaela V. & Lucas, Spencer G., 2021, On the Supposed Presence of Miocene Tayassuidae and Dromomerycinae (Mammalia, Cetartiodactyla) in South America, American Museum Novitates 2021 (3968), pp. 1-28 : 12-17

CERVOIDEA Batsch, 1788

REFERRED MATERIAL: LACM 5159 /155113, left ramus with p3–m3, broken at the symphysis just in front of mental foramen (holotype of Surameryx acrensis Prothero et al., 2014 ) (figs. 5–7) .

IDENTITY OF Surameryx acrensis : Dromomerycinae is a group of deerlike ruminants that share some affinities with true deer, as both groups are part of the superfamily Cervoidea . They are usually included in the family Palaeomerycidae ( Janis and Manning, 1998; Prothero and Liter, 2008) but are sometimes considered to constitute a distinct family ( Dromomerycidae ) that is not particularly closely related to the former ( Sánchez et al., 2015). Dromomerycines are restricted to the Miocene and early Pliocene of North America, and were moderately diverse during the middle Miocene, especially in the early Barstovian NALMA ( Janis and Manning, 1998; Prothero and Liter, 2008). They are characterized by the presence of unbranched, nondeciduous cranial appendages on the frontal bone and some dental features, including large and nonmolariform premolars, no permanent first premolar, and the “ Palaeomeryx fold,” a short enamel ridge that extends posteromedially from the protoconid on the labial face of the lower molars. Many species also possess a double posterior lobe on m3 that is closed posteriorly ( Janis and Manning, 1998; Prothero and Liter, 2008).

Prothero et al. (2014) compared Surameryx acrensis to an extensive list of ruminants, including Antilocapridae , Blastomerycinae (Moschidae) , Hypertragulidae , Gelocidae , Leptomerycidae , Protoceratidae , and Camelidae , but we will restrict our discussion to the Palaeomerycidae (Dromomerycinae) and Cervidae because: (1) we agree with the features noted by Prothero et al. (2014) that preclude referral of LACM 5159/155113 to these other families; and (2) these groups are unlikely candidates for referral of the specimen. We will, therefore, address the reasons given for identifying Su. acrensis as a member of the Dromomerycinae and why a cervid identity was discarded. Only dental characters were used to assign the specimen to Dromomerycinae and, although dental characters in cervoid artiodactyls are highly homoplastic, some are in fact diagnostic. However, this is not the case for the characters used by Prothero et al. (2014).

The “ Palaeomeryx fold” occurs in primitive Palaeomerycidae and other groups of noncetacean cetartiodactyls such as some Moschidae , some ruminants like Eumeryx ( Prothero et al., 2014) , and in some Miocene Cervidae ( Janis and Scott, 1987) . This structure, common in primitive Palaeomerycinae, is absent in most later Dromomerycinae ( Solounias, 2007). The “ Palaeomeryx fold” is not present on molars of the holotype of Surameryx acrensis , despite the authors ( Prothero et al., 2014) describing it as the worn shape of a flange of exposed dentine connected to the postprotocristid of the protoconid, which is simply not visible on the specimen (fig. 5). The teeth of the specimen are very worn and, as befits an old individual, the heavy wear has played a part in confounding and obscuring some of the dental features. The protoconid and hypoconid region is broken in m2, which may have been mistaken for a “ Palaeomeryx fold,” but the assertion that it is present in m3 is puzzling. Prothero et al. (2014) also state that the molars “have the classic configuration of palaeomerycids,” although most of the features described subsequently also agree with the molars of a cervid.

Another character mentioned is a vertical groove on the posterolingual face of p4 that divides the trigonid from the talonid. It divides the tooth into a posterior third separated from the anterior two-thirds by a lingual waist and is known to occur in giraffids, the palaeomerycid Amphitragulus , the bovid Eotragus , the ruminant Prolibytherium , dromomerycids, and blastomerycids ( Janis and Scott 1987). The authors ( Prothero et al., 2014) consider it typical of “nearly all palaeomerycids,” but it is also present in large South American cervids (e.g., Odocoileus , Ozotoceros ; fig. 7). They consider the “detailed pattern of pm3 and pm4 are almost identical to those seen in most primitive New World Palaeomerycidae ” ( Prothero et al., 2014: 436).

The holotype of Surameryx acrensis presents a significantly worn premolar series and a nonmolariform p4, interpreted by Prothero et al. (2014) as a dromomerycine-like feature. Barbourumeryx trigonocorneus, a dromomerycine used for comparison, shows a nonmolariform p4, but it is developed in a different way ( Prothero et al., 2014). Prothero et al. (2014) also consider a closed fossette in the p4 trigonid as “a derived feature of dromomerycines,” but it also occurs in cervids ( Heckeberg, 2020). In addition, with wear the premolars lose the cusps and expose the dentine, and the fossettes may be entirely enclosed by wear. The shape of the p4 is highly variable in cervids, ranging from relatively simple to molariform ( Heckeberg, 2020). In Su. acrensis , the p4 is similar to the worn corresponding tooth of South American cervids (fig. 7), being particularly similar to a highly worn p4 of Odocoileus virginianus ( Severinghau, 1949; Cooper et al., 2013).

It is also noteworthy that no records of Dromomerycinae are known from Central America, including the rich early Miocene deposits of Panama ( MacFadden, 2006; Kirby et al., 2008). Despite a great diversity of both browsing and grazing ungulates, including extinct cetartiodactyls such as Protoceratidae , Oreodontidae , and Anthracotheriidae , as well as camels ( Floridatragulinae ), musk deer ( Moschidae ), horses ( Equidae ), and rhinoceros ( Rhinocerotidae ) ( MacFadden, 2006, 2009; Rincon et al., 2015), to date, not a single fossil from Central America can be attributed to Dromomerycinae. At present, the southernmost record of this group is the southern United States ( Janis and Manning, 1998; Prothero and Liter, 2008). If LACM 5159/155113 is indeed a Dromomerycinae, it would imply a huge geographic gap in dromomerycine distribution that cannot reasonably be attributed to a lack of sampling.

We believe that the interpretation of the holotype specimen of Surameryx acrensis as a dromomerycine Palaeomerycidae was heavily influenced by its supposed late Miocene age; at that time, cervids are unknown in North America ( Webb, 1998; Prothero et al., 2014: 437). If the preserved morphology is the only information considered, the identity of the material becomes clearer, and we attribute LACM 5159/155113 to Cervidae , likely an old individual with a dental age greater than seven years ( Cooper et al., 2013). Given the uniformity usually found in the teeth of cervids, a specific identity may be difficult to reach. The size of the specimen agrees with small members of the genus Mazama and South American populations of O. virginianus , but the horizontal ramus is taller in lateral view. The possible taxonomic significance of this latter characteristic is not known.