Rodentia, Cricetidae), a Supposedly Extinct Muroid from the Ecuadorean Quaternary

Mammalia 2017; aop Short Note Pablo Moreno, José Luis Román, Jorge Britoa and Ulyses F.J. Pardiñas* The taxonomic status of Copemyodon ecuadorensis (Rodentia, Cricetidae), a supposedly extinct muroid from the Ecuadorean Quaternary DOI 10.1515/mammalia-2016-0179 fossil record of cricetids in the subcontinent, although very Received December 16, 2016; accepted February 16, 2017 poor compared with its recent diversity, is almost exclu- sively composed by members belonging to the subfamily Abstract: Copemyodon ecuadorensis was described as a (Pardiñas et al. 2002). As an exception, a form unearthed non-sigmodontine extinct cricetid from two rich fossili- from Quaternary deposits in northern Ecuador, the genus ferous localities in northern Ecuador. It was hypothesized Copemyodon Fejfar et al. 1996, was attributed to the as being related to both the fossil genus Copemys and Neotominae (Fejfar et al. 1996). Represented by a single the living Peromyscus and, as such, is an example of an species, Copemyodon ecuadorensis Fejfar 1996, this small independent “copemyine-neotomine” attempt to colo- cricetid was interpreted as morphologically close to the nize South America. Here, we re-study the holotype of C. fossil genus Copemys Wood 1936, but also to the living one ecuadorensis concluding that it cannot be separated from Peromyscus Gloger 1841 (Fejfar et al. 1993, 1996). In this Reithrodontomys (Cricetidae, Neotominae) at a generic systematic scenario and taking into account its isolated level. Copemyodon constitutes a junior synonym of Reithro- occurrence within a dense assemblage of fossil sigmodon- dontomys. There are recent populations of Reithrodontomys tines, Copemyodon was hypothesized as an example of an in Ecuador and most likely it comprises several species. In independent “copemyine-neotomine” attempt to colonize this context, seems convenient to retain ecuadorensis as a South America (Fejfar et al. 1996). species of Reithrodontomys until an appropriate revision Despite its putative importance, Copemyodon was of this genus is performed, although we identify morpho- almost not discussed again after its original description. logical similarities between Reithrodontomys ecuadorensis Probably coined too late to be listed by McKenna and Bell and the nominal form Reithrodontomys soederstroemi. (1997), the genus was virtually ignored by all subsequent Keywords: Copemys; Ecuador; neotominae; treatments (e.g. Patton et al. 2015), only briefly mentioned Reithrodontomys. as linked to the fossil record of Peromyscus (cf. Musser and Carleton 2005) and in a few reviews about the evolution- ary history of the group (e.g. Pardiñas et al. 2002, Zijlstra Muroid rodents are currently represented in South et al. 2014). As an example of the destiny of a plethora of America by three sub-families, with sigmodontines being fossil forms in a universe, currently dominated by mole- the dominant group (Patton et al. 2015). Concordantly, the cular systematics, characteristic of the recent record of sigmodontine rodents, two decades later Copemyodon aPresent address: Mastozoología, Instituto de Ciencias Biológicas integrates a large number of enigmatic taxa. de la Escuela Politécnica Nacional, Quito, Ecuador In their analysis, Fejfar et al. (1996) posited an erro- *Corresponding author: Ulyses F.J. Pardiñas, Instituto de Diversidad y neous biogeographical scenario when they described Evolución Austral (IDEAus-CONICET), Boulevard Brown 2915, Puerto Copemyodon; these authors stated “… the copemyine- Madryn 9120, Argentina, e-mail: [email protected] Pablo Moreno: Mastozoología, Instituto Nacional de Biodiversidad peromyscine group, previously considered to be restricted (INABIO) (MECN), Pasaje Rumipamba 341 y Av. de los Shyris, Casilla to Northern and Central America, and which presence in Postal 170515, Quito, Ecuador South America has never before been reported” (Fejfar José Luis Román: Mastozoología y Paleontología del Instituto de et al. 1996:138). Certainly the “copemyine-peromyscine Ciencias Biológicas de la Escuela Politécnica Nacional, Av. Ladrón group” is a heterodox construction; even in the 1990s de Guevara E-11 253 e Isabel la Católica, Casilla Postal 17-01-2759, Quito, Ecuador because it combines stem cricetids, mostly represented Jorge Brito: División de Mastozoología, Museo Ecuatoriano de Ciencias by Copemys with a large array of crown members now Naturales, Instituto Nacional de Biodiversidad, Quito, Ecuador subsumed within the Neotominae (Carleton and Musser Brought to you by | UCL - University College London Authenticated Download Date | 3/24/17 2:38 AM 2 P. Moreno et al.: Status of Copemyodon ecuadorensis 1984). Beyond this, according to the authoritative view of Patton (2015:58–59), “The Sigmodontinae comprise the vast majority of cricetid rodents in South America, representing a large radiation. Only single species of Reithrodontomys and of Isthmomys of the otherwise highly diverse and mostly Northern or Middle American Neotom- inae… and of Tylomys of the lesser diverse Middle Ameri- can Tylomyinae… extend into South America. Neotomine and tylomyine taxa are limited to western Colombia and adjacent Ecuador”. In brief, Fejfar et al. (1993, 1996) overlooked the occurrence of the neotomine genus Reithro- dontomys Giglioli 1874 in Ecuador, formerly recognized by most authors since Thomas (1898), described Reithrodon- tomys soederstroemi with type locality in Quito. When described by Fejfar et al. (1996:139), the holotype of Copemyodon ecuadorensis was referred as “Holo- type: lower left jaw with m1–3, temporarily stored at the Department of Earth Sciences of the University of Flor- ence”. Now, this material is correctly labeled as holotype under the number MECN 129, in the paleontological collections of the Museo Ecuatoriano de Ciencias Naturales (Quito, Ecuador). The correspondence of MECN 129 with Figure 1: Comparison among the left m1–3 in occlusal view of the the material figured by Fejfar et al. (1996: figures 2 and neotomines Copemyodon ecuadorensis (A = MECN 129, holotype; 3) is beyond doubt. In addition, several upper and lower La Calera, Bolívar, Carchi, Ecuador; Holocene), Reithrodontomys = toothrows, cranial fragments and isolated molars origi- mexicanus soederstroemi (B MECN 1135; Quebrada Pistud, Carchi, Ecuador; Recent) and Reithrodontomys mexicanus milleri (C = MEPN nally referred by Fejfar et al. 1996 to Copemyodon are also 6416; Pinantura, Antisana, Pichincha, Ecuador; Recent). available for study in MECN collections (see Appendix 1). Scale = 1 mm. The holotype of Copemyodon ecuadorensis is a left dentary with m1–3 (molar nomenclature used here follows Reig 1977) and the horizontal ramus well pre- by “labially shifted, asymmetric and wide anterocone” served although both the angular and coronoid pro- and large mesolophs. All these dental traits were con- cesses are broken and the incisor is missing. According sidered as “very unique and primitive”. Probably guided to the degree of wear of the molars, it belongs to a mod- by the incorrect presumption that the authors had at the erately adult individual (Figure 1). It was recovered at La unique South American neotomine, Fejfar et al. (1993, Calera (0°30′04.74″N, 77°51′4 7. 3 3 ″W, 2710 m) in a profile 1996) focused the comparisons to the widespread living described near Cantón Bolivar in the province of Carchi, genus of the subfamily, Peromyscus. They also compared northern Ecuador. The holotype of C. ecuadorensis, as the fossil Ecuadorean material to the Nearctic but extinct well as abundant additional material referred for this form, Copemys. These comparisons overlooked a basic rule taxon, include a late Holocene small mammal assemblage in any taxonomic approach to first check the living assem- representing several sigmodontine rodents, lagomorphs, blage at the local and regional scales to look for potential and soricomorphs (see Fejfar et al. 1993). A single speci- candidates for comparison. When such is done, Copemyo- men also attributed to Copemyodon was recovered at don is indistinguishable from Reithrodontomys and Cope- Quebrada Cuesaca (0°31′04.17″N, 77°53′13.53″W, 2640 m), myodon ecuadorensis is very close to the forms contained a late Pleistocene-Holocene assemblage recovered very in the Reithrodontomys mexicanus species group (reviewed near to La Calera (see Fejfar et al. 1993, 1996). by Arellano 2015; figure 1). Beyond the general agreement Fejfar et al. (1996:139) described Copemyodon as a that we found between the morphology of the material “medium sized cricetid” with lower brachydont molars referred to Copemyodon and several recent specimens of displaying main cusps in alternate pattern and having R. mexicanus species group from Ecuador (see Appendix bisected anteroconid, a “drop-like” mesostylid and an 1), additional confirmation of our taxonomic hypothesis is “ectolophid or ectostylid regularly joining the anterior derived from the incisor morphology. Reithrodontomys, as side of hypolophid”. The upper molars were highlighted a genus, is diagnosed by the presence of a well-developed Brought to you by | UCL - University College London Authenticated Download Date | 3/24/17 2:38 AM P. Moreno et al.: Status of Copemyodon ecuadorensis 3 Table 1: Dental measurements (in mm) of Copemyodon ecuadorensis (MECN 129, holotype; left lower jaw from La Calera, Bolívar, Ecuador; Holocene) and the living neotomine Reithrodontomys mexicanus (Ecuadorean specimens). C. ecuadorensis R. m. eremicus R. m. soedertroemi (n = 8) R. m. milleri (n = 9) m1, length

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