A new South American archaic ungulate and new insight for the early diversification of the South American native ungulates

Abstract

Palaeogene South American faunas include enigmatic ungulates that cannot be classified unequivocallywithin any of the main South American (SA) Native Ungulates clades (Litopterna, Notoungulata,Astrapotheria, Pyrotheria and Xenungulata) because they retain plesiomorphic features, resemblingLaurasian ‘archaic ungulates’ traditionally classified within the order ‘Condylarthra’. Most SA ‘condylarths’are known by partial dental series and isolated teeth and unassociated postcranial remains, hamperingcomparisons with better-known ungulates. Here, we describe a nearly complete skull and associatedmandible of an SA ‘condylarth’, Talquinodus puertai gen. et sp. nov., preserving most of the dentition andbasicranium, derived from middle Eocene rocks of the Sarmiento Formation at Central Patagonia.Talquinodus shows a combination of plesiomorphic traits (complete dentition with bunolophodont cheekteeth, ring like ectotympanic, retention of stapedial system, etc.), combined with some autapomorphies, asthe reduction of the m3 talonid. Our phylogenetic analyses support consistently that Talquinodus belongs tothe SA radiation of Euungulata along with Litopterna, Notoungulata and Astrapotheria. However, theinternal relationships could not be resolved unambiguously: Talquinodus could be a didolodontid relatedto the origin of Litopterna, or could be part of a separate radiation of South American archaic ungulates,along Depaulacoutoia, Lamegoia and Escribania, with no descendants in post-Eocene faunas.