New materials of Argentoconodon fariasorum (Mammaliaformes, Triconodontidae) from the Jurassic of Argentina and its bearing on triconodont phylogeny

摘要

Argentoconodon fariasorum is the only triconodont from the Jurassic of South America. Originally described on the basis of an upper molariform, A. fariasorum is now known by several specimens, including one that preserves most of its dentition, upper and lower jaws, and several postcranial elements. Close anatomical similarity exists between Argentoconodon fariasorum, Ichthyoconodon jaworowskorum, from the Cretaceous of Morocco, and the likely Jurassic Volaticotherium antiquus, from China. The results of a phylogenetic analysis including most taxa relevant to addressing triconodont phylogenetic relationships show Argentoconodon and Volaticotherium as a clade, which in turn is more closely related to Ichthyoconodon than to any other taxon. Our most parsimonious hypotheses support a triconodontid ancestry for Argentoconodon, Ichthyoconodon, and Volaticotherium as members of the monophyletic traditional subfamily Alticonodontinae. The inclusion of Argentoconodon among alticonodontines extends the geographical and temporal distribution of this triconodont subfamily to the South American Early Jurassic, resulting in extensive ghost lineages for many triconodontid groups. Postcranial similarities between Argentoconodon and Volaticotherium make it possible that the Argentinean taxon might have had gliding capabilities; if this is the case, our cladistic analysis highlights the possible existence of a gliding clade of triconodonts of wide distribution from at least as early as the Early Jurassic.