The Patagonian fossil mammal Necrolestes: a Neogene survivor of Dryolestoidea

NICOLÁS R. CHIMENTO; FEDERICO L. AGNOLIN; FERNANDO E. NOVAS

Revista Museo Argentino de Ciencias Naturales

Museo Argentino de Ciencias Naturales

Año: 2012 p. 1 - 47

1514-5158

Necrolestes is an enigmatic Miocene South American mammal that is the size of a shrew, the phylogenetic relationships of which constituted a matter of debate since its original description in 1891. This taxon has been variously related to the Chrysochloroidea, Palaeanodonta, Xenarthra, Gondwanatheria, and Metatheria. However, Necrolestes exhibits fossorial adaptations in combination with cranial, postcranial, and dental features that are remarkably plesiomorphic for a therian mammal. This led several authors to consider Necrolestes as a Theria incertae sedis, Tribosphenida incertae sedis, and even as a Mammalia incertae sedis. We present evidence in support that Necrolestes belongs to the Dryolestoidea, an extinct group of basal cladotherians that were abundant and widespread from the Late Jurassic through the Late Cretaceous. Recent discoveries demonstrated that the South American continent was a cradle for the evolutionary radiation of dryolestoid mammals at the end of the Cretaceous. Moreover, it become evident that some of these early mammals persisted across the K-P boundary, as illustrated by the peligrotheriid dryolestoid Peligrotherium, documented in Paleocene beds of Patagonia. A comprehensive cladistic analysis of living and fossil mammals depicts Necrolestes as a member of the dryolestoid subclade Meridiolestida, thus amplifying the morphological disparity of this lineage of southern dryolestoids, including dog-sized bunodontian forms (i.e., Peligrotherium), alongside with small-sized insectivores (i.e., Necrolestes). Present study solves the enigma that for the last 120 years surrounded the phylogenetic relationships of the bizarre mammal Necrolestes, also demonstrating the unexpected survival of South American dryolestoids up to Miocene times.