Necrolestes: A Nontherian mammal from the Miocene

The Miocene mammal Necrolestes demonstrates the survival of a Mesozoic nontherian lineage into the late Cenozoic of South America

Authors:

1. Guillermo W. Rougier (a,b,*)
2. John R. Wible (b)
3. Robin M. D. Beck (c)
4. Sebastian Apesteguía (d,e)

*. To whom correspondence should be addressed. E-mail: grougier@louisville.edu

Affiliations:

a. Department of Anatomical Sciences and Neurobiology, University of Louisville, Louisville, KY 40202

b. Section of Mammals, Carnegie Museum of Natural History, Pittsburgh, PA 15206

c. School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW, Australia

d. CEBBAD–Fundación de Historia Natural ‘Félix de Azara’, Universidad Maimónides, 1405 Buenos Aires, Argentina

e. Consejo Nacional de Investigaciones Científicas y Técnicas de Argentina, C1033AAJ Buenos Aires, Argentina


Abstract:

The early Miocene mammal Necrolestes patagonensis from Patagonia, Argentina, was described in 1891 as the only known extinct placental “insectivore” from South America (SA). Since then, and despite the discovery of additional well-preserved material, the systematic status of Necrolestes has remained in flux, with earlier studies leaning toward placental affinities and more recent ones endorsing either therian or specifically metatherian relationships. We have further prepared the best-preserved specimens of Necrolestes and compared them with newly discovered nontribosphenic Mesozoic mammals from Argentina; based on this, we conclude that Necrolestes is related neither to marsupials nor placentals but is a late-surviving member of the recently recognized nontherian clade Meridiolestida, which is currently known only from SA. This conclusion is supported by a morphological phylogenetic analysis that includes a broad sampling of therian and nontherian taxa and that places Necrolestes within Meridiolestida. Thus, Necrolestes is a remnant of the highly endemic Mesozoic fauna of nontribosphenic mammals in SA and extends the known record of meridiolestidans by almost 45 million years. Together with other likely relictual mammals from earlier in the Cenozoic of SA and Antarctica, Necrolestes demonstrates the ecological diversity of mammals and the mosaic pattern of fauna replacement in SA during the Cenozoic. In contrast to northern continents, the Cenozoic faunal history of SA was characterized by a long period of interaction between endemic mammalian lineages of Mesozoic origin and metatherian and eutherian lineages that probably dispersed to SA during the latest Cretaceous or earliest Paleocene.