Morphological phylogeny and divergence times of the Octodontidae (Rodentia, Hystricomorpha)

VERZI, D.H.; OLIVARES, A.I.; MORGAN, C.C.

San Juan

Congreso; IV Congreso Latinoamericano Paleontología Vertebrados; 2011

IMCN UNSJ

The family Octodontidae Waterhouse, 1839 (Degus, Coruros, Viscacha-rats, Tuco-tucos) comprises an assemblage of living South American rodents of southern origin, with essentially fossorial to subterranean habit. The boundaries and age of the family and subordinate taxa in the fossil record remain controversial. A phylogenetic analysis (parsimony analysis by implicit enumeration using TNT 1.1, Goloboff et al., 2008a, b) of living and extinct Octodontoidea, including living Echimyidae as outgroups, was performed on a matrix of craniomandibular and dental characters (partially based on Verzi, 2001, 2008). The modified Stratigraphic Manhattan Measure (MSM*, Pol and Norell, 2001) was used both to assess the fit between the stratigraphic record and the resulting phylogeny and to optimize divergence times. The analysis resulted in a single tree in which Octodontidae was monophyletic (and strongly supported), and so were the sister clades Octodontinae Waterhouse, 1839 and Ctenomyinae Lesson, 1842. The tree topology for the living genera is consistent with molecular phylogenies (Gallardo and Kirsch, 2001; Honeycutt et al., 2003), except for the position of Octodontomys Palmer, 1903 within the Octodontinae. Stem Ctenomyinae included extinct genera previously assigned to the family Echimyidae Gray, 1825. Estimated divergence times suggested a Deseadan age (late Oligocene, >25 Ma) for the Octodontinae-Ctenomyinae dichotomy, and temporally extended stem groups for each of these clades. Differentiation (recognized by the independent acquisition of molar euhypsodonty) and subsequent branching of the modern Octodontinae and Ctenomyinae would have occurred at different times in these clades during the Huayquerian (late Miocene), occurring earlier in Octodontinae. Among the Ctenomyinae, a more recent split (early Pliocene) would have given rise to the living Ctenomys Blainville, 1826. The most recent Octodontinae divergences at the genus level, estimated to have occurred during the Montehermosan (early Pliocene, ca. 5 Ma), corresponded to the fossorial mesic-adapted representatives. These results suggest a timing of the Octodontinae-Ctenomyinae split similar to molecular estimates and much older than previously assumed from fossils, whereas the more recent divergences of Octodontinae are older than those inferred using molecular evidence.