Journal of Paleontology, 92(5), 2018, p. 911–919 Copyright © 2018, The Paleontological Society 0022-3360/18/0088-0906 doi: 10.1017/jpa.2018.12


Paleobiology of the basal hydrochoerine Cardiomys Ameghino, 1885 (Rodentia, Caviomorpha, late Miocene, South America) as inferred from its postcranial anatomy


Adriana M. Candela,1 Nahuel A. Muñoz,2 and César M. García-Esponda3


1CONICET, División Paleontología Vertebrados, Museo de La Plata, Paseo del Bosque,B1900FWA La Plata, Argentina ⟨acandela@fcnym.unlp.edu.ar⟩ 2CONICET, División Paleontología Vertebrados, Museo de La Plata, Unidades de Investigación Anexo Museo, Facultad de Ciencias Naturales y


Museo, Universidad Nacional de La Plata, Avenida 122 y 60, B1900FWA LA Plata, Argentina ⟨nahuelmunoz@fcnym.unlp.edu.ar⟩ 3Cátedra Zoología III Vertebrados, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, Avenida 122 y 60, B1900FWA La Plata, Argentina ⟨cesponda@fcnym.unlp.edu.ar⟩


Abstract.—Extinct Hydrochoerinae traditionally included within ‘Cardiomyinae’ (Cavioidea, Caviidae) are caviomorph rodents well represented in the late Miocene to late Pliocene of Argentina, but their paleobiology has received little scientific attention. The postcranium of these rodents is poorly known and has not been considered in morphofunctional or systematic studies. Here, we provide the first description of the postcranium of the basal hydrochoerine Cardiomys Ameghino, 1885, based on a well-preserved specimen from the late Miocene of Central Argentina, and evaluate its paleobiological and systematic implications. A morphofunctional study and a character mapping analysis were performed. We concluded that most of its postcranial features are neither adaptations to a specialized cursoriality, as in some extant cavioids, nor major modifications associated with swimming, as in extant capybaras. Cardiomys exhibits several features (high humeral distal articular surface, perforated olecranon fossa, proximal portion of radius cranially located with respect to the ulna, subrectangular-shaped radial head with flattened ulnar facet, calcaneocuboid joint distally located with respect to the astragalonavicular joint) that allow us to interpret it as an ambulatory caviid. Among cavioids, some features of Cardiomys are more similar to those of Hydrochoerus Brisson, 1762 (lateral coronoid process reduced, humeral capitular tail well differentiated, capitular tail facet of the radial head well developed and relatively short craniodistally, plantar process of the navicular massive and short). Other postcranial features (relatively longer and more gracile third metatarsal and phalanges, straight caudal border of the ulna) suggest that Cardiomys would have been a generalized hydrochoerine, as also indicated by its dental and cranial characters.


Introduction


Extinct Hydrochoerinae (Caviidae, Cavioidea; sensu Madozzo- Jaén and Pérez, 2017) known as ‘cardiomyines’ encompass medium-sized caviomorph rodents, mainly characterized by ever-growing teeth, p4 composed of three prisms, P4–M2 and


m1–m3 formed by two heart-shaped prisms with accessory flexi/ids, M3 multiprismatic, and a broad palate (Vucetich et al., 2011; Pérez et al., 2014). They are first known from the middle Miocene of Patagonia (Vucetich and Pérez, 2011), reaching their greatest taxonomic diversity during the late Miocene–late Pliocene of Argentina (Rovereto, 1914; Kraglievich, 1927, 1940; Pascual, 1961; Pascual and Bondesio, 1963; Pascual et al., 1966; Vucetich et al., 2011), with additional reports from the Neogene of Bolivia (Anaya and MacFadden, 1995), Vene- zuela (Vucetich et al., 2010), and Brazil (Kerber et al., 2017). Late Miocene and Pliocene ‘cardiomyines’ are represented by several species included in the genera Cardiomys, Caviodon Ameghino, 1885 (including Lelongia Kraglievich, 1930b), Procardiomys Pascual, 1961, and Xenocardia Pascual and


Bondesio, 1963, all of which are known from abundant cranial and dental remains. Traditionally, these genera were included within the subfamily Cardiomyinae of Caviidae (Rovereto, 1914; Pascual, 1961; Pascual et al., 1966; Mones, 1986; McKenna and Bell, 1997). Later, the cardiomyines were considered Hydrochoeridae (e.g., Vucetich and Pérez, 2011; Vucetich et al., 2011). More recently, cladistic analyses (Madozzo-Jaén and Pérez, 2017; Pérez et al., 2017b) recovered Caviodon, Cardiomys, Xenocardia, and Procardiomys as basal Hydrochoerinae within the family Caviidae, but the monophyly of ‘Cardiomyinae’ (as originally defined) was not recognized. The postcranial anatomy of ‘cardiomyines’ is poorly known and their paleobiology was scarcely scrutinized. Only a few fragmentary postcranial bones of Caviodon cuyano Vucetich et al., 2011 (Pliocene of Mendoza Province) have been descri- bed (Vucetich et al., 2011). Moreover, the postcranium of these rodents was not used as source of characters either in systematic analyses or to infer probable locomotor behavior. In this contribution, we present the first description of postcranial remains of Cardiomys. The specimen studied comes


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