Phylogenetic relationships and palaeobiology of a new xenungulate (Mammalia: Eutheria) from the Palaeogene of Argentina

BERGQVIST, LILIAN P.; GELFO, JAVIER N.; GARCÍA-LÓPEZ, DANIEL A.

JOURNAL OF SYSTEMATIC PALAEONTOLOGY

CAMBRIDGE UNIV PRESS

Año: 2020 p. 1 - 15

1477-2019

Xenungulates are a peculiar group of bilophodont ungulates, widespread over South America during the Paleocene andearly Eocene. Here we describe, illustrate and analyse a new Xenungulata, Rodcania kakan gen. et sp. nov., the firstfrom the lower latitudes of Argentina. It was recovered from the Rıo Loro Formation (Tucuman Province), for which aPaleocene age was estimated. The material comprises a fragment of the left dentary with an incomplete m2, eroded overthe enamel surface, and an almost complete m3. Both teeth share with Xenungulata strong enamel, vertically orientedHunter?Schreger bands (HSB), and wear facets sloping distally. Rodcania kakan differs from other xenungulates in them3 trigonid, simplified and mesiodistally short; absence of a paraconid; more oblique protolophid in relation to themesiodistal axis and a straight cristid obliqua, pointing to the protoconid position; and has a wider and longer talonid. Aphylogenetic analysis of 13 species and 36 craniodental characters recovered R. kakan as a basal member of theCarodniidae, supported by 10 synapomorphies in the four most parsimonious trees. The body mass estimation of the RıoLoro Fauna and of the rest of the xenungulate taxa revealed that R. kakan is the largest mammal of the Rıo Loroassemblage, weighing around 165 kg and with a size comparable to Carodnia feruglioi. The increase in body massshowed no clear relation with evolutionary trends in xenungulates.