Palaeothentid Marsupials of the Salla Beds of Bolivia (Late Oligocene): Two New Species and Insights into the Post-Eocene Radiation of Palaeothentoids

摘要

We report the finding of new remains of palaeothentid marsupials (Paucituberculata: Marsupialia) from the late Oligocene of Salla, Bolivia (Deseadan South American Land Mammal Age). These fossils represent two new taxa, Antawallathentes illimani and Antawallathentes quimsacruza, increasing the known number of Deseadan palaeothentoid species to 11. Antawallathentes illimani is represented by two incomplete skulls and A. quimsacruza is known only from the holotype, a partial mandible with p3 - m4. Our phylogenetic analysis, based on a data matrix modified from that of Abello, suggests that the two new Salla species are members of the Palaeothentidae (sensu stricto) and are more closely related to each other than they are to other known palaeothentids. Although these new taxa inidicate a greater diversity of Deseadan palaeothentoids than previously appreciated, nowhere in the Deseadan are palaeothentoids abundant, as they are in later Colhuehuapian and Santacrucian faunas. Thus, Deseadan palaeothentoid species richness, coupled with the observation that these palaeothentoids are numerically few in Deseadan faunas, permits the development of a general outline of the post-Eocene palaeothentoid radiation. This may be summarized as follows: 1) EOB Pulse that began near the Eocene/Oligocene Boundary; 2) Deseadan Diversification, increased species richness without large population sizes; and 3) Early Miocene Diversification, increased species richness with local abundances. This Colhuehuapian to Santacrucian diversity with local abundences declined after the Santacrucian. Palaeothentoids are unknown after the Laventan SALMA.