A new Echimyidae (Rodentia, Hystricomorpha) from the late Miocene of southern South America

Abstract

Dental nomenclature follows Marivaux et al. (2004), Antoine et al. (2012), and homologies of crests are after Verzi et al. (2016). References of publications that include at least partial descriptions of the listed characters are indicated. Ten new characters are listed at the end.Character 1. Premaxillary septum separating incisive foramina (Verzi, 2001): with posterior ends of premaxillae joined medially, forming a pointed or rounded projection which may join an anterior apophysis of the maxilla (0); with posterior ends of premaxillae divergent, each one forming a small lateral apophysis (1).Character 2. Lateral walls of incisive foramina (or of the corresponding cavity in case of partially obliterated foramina) (Verzi, 2008): with concave margins (0); with protruding medial walls of premaxillae producing anteriorly convergent margins (1); margins very narrow or not developed posterior to premaxillary-maxillary suture (2).Character 3. Premaxillary-maxillary suture at medial margin of incisive foramen (Verzi, 2008;Verzi et al., 2010): level with the portion of the suture located lateral to the foramen (0); displaced anteriorly (1); displaced posteriorly (2).Character 4. Medial margins of maxillary fossae (Olivares et al., 2012): separated (0); approximating each other or fused along the midline and generally forming a crest (1).Character 5. External margins of incisive foramina posterior to premaxillary-maxillary suture: separated (0); very close or fused to each other (1). Character 6. Anterior portion of premaxilla anterior to incisive alveolus in lateral view (Carvalho and Salles, 2004;Olivares et al., 2012): low to very low (0); high, forms the ventrolateral side of a tube that is dorsally completed by the nasal (1).Character 7. Alveolar margins of M1-M2: level with palatal bridge, or ventral and forming acute alveolar margins (0); dorsal to the palatal bridge, forming wide to moderately convex, sometimes swollen, margins (1).Character 8. Protuberance on maxilla ventral to bottom of alveolar sheath of I1: absent (0); present and located at the level of the external alveolar margin of DP4 (1); present and located at the level of the external alveolar margin between DP4 and M1 (2). Character 9. Lateral flange of canal for infraorbital nerve in zygomatic root (Verzi ,2008;Verzi et al., 2010): with dorsal margin free or slightly in contact with bottom of alveolar sheath of upper incisor (0); with dorsal margin joined to bottom of alveolar sheath of upper incisor (1).Character 10. Lacrimal foramen: opens into the orbital portion of the lacrimal (0); opens into the maxilla (1).Character 11. Portion of maxilla surrounding foramen into lacrimal canal: with a suture posterior to the foramen (0); continuous around foramen (1).Character 12. Foramen into nasolacrimal canal: open on side of the base of rostrum or anterior portion of orbital region, visible in lateral view (0); open on medial side of maxillary lamina posterior to incisor alveolar sheath, on the margin of sphenopalatine fissure, and oriented posteriorly to...

Unravelling the distinctive craniomandibular morphology of the Plio‐PleistoceneEumysopsin the evolutionary setting of South American octodontoid rodents (Hystricomorpha)

“…; Olivares et al . ). In addition, the low position of the zygoma adjusted to this particular orbital morphology results in an equally low craniomandibular joint and consequently a low condylar process in the mandible (Olivares et al .…”

“…, ; Olivares et al . ). The relationships among genera were also congruent with results of molecular phylogenies (Galewski et al .…”

“…Its craniomandibular and dental traits, including large orbits and marked hypsodonty, have been interpreted as adaptations to open habitats (Olivares & Verzi ; Olivares et al . ). Remarkably, however, this distinctive morphology is not shared with extant echimyids from open environments or with southern octodontoids, but only with the partially preserved Myocastorini Ullumys from the late Miocene of southern South America (Olivares et al .…”

“…Remarkably, however, this distinctive morphology is not shared with extant echimyids from open environments or with southern octodontoids, but only with the partially preserved Myocastorini Ullumys from the late Miocene of southern South America (Olivares et al . ).…”

“…Specifically, our goal is to test whether the craniomandibular morphology of Eumysops is divergent within the clade Echimyidae, and even Octodontoidea, as has been suggested in previous qualitative analyses (Olivares et al . ). Considering that the evolution of cranial and mandibular disparity in caviomorphs has shown to be driven by both ecological factors and phylogenetic structure (Perez et al .…”