Evolutionary trends of Protypotherium (Interatheriidae, Notoungulata) lineage throughout the Miocene of South America

Abstract

Protypotherium (Mammalia, Notoungulata, lnteratheriinae) is a well-known and very diverse genus of extinct native ungulates of South America, widely distributed from southern to middle latitudes of Argentina, Chile, and Bolivia. This genus exhibits distinctive species throughout the Miocene to the beginning of the Pliocene that display an interesting size pattern. The large sample of specimens studied during several years of research allows us to analyze the shape and size of upper and lower molars for nine species of Protypotherium, in order to test the hypothesis of reduction of size ranges preserving a general tooth morphology as a response to climate deterioration, documented in South America by a marked reduction of temperature that occurred during Miocene times. Elliptic Fourier analyses were used to capture the shape of the occlusal morphology and the centroid size was also retained for subsequent analyses. Our results demonstrate that: 1) a similar morphological tooth pattern is observed among all species; 2) tooth shape variation is not associated with a change in size; and 3) there is a tendency to increase the size and decrease the number of species. This striking pattern could be correlated with a global trend to lower temperatures, which indicates a deterioration of paleoenvironmental conditions. A conservative tooth pattern, together with an increase of size and a reduction in number of species were the main evolutionary and ecological tendencies accounted in Protypotherium from the early to late Miocene-beginning of the Pliocene, which were accompanied by a latitudinal displacement from Patagonia to northern areas at the end of the Miocene.