Tuesday, November 20, 2012

[Paleomammalogy • 2012] the Miocene mammal Necrolestes patagonensis from Patagonia, Argentina, demonstrates the survival of a Mesozoic nontherian lineage into the late Cenozoic of South America


The Miocene mammal Necrolestes patagonensis ventures out of its burrow 16 million years ago in Patagonia, present-day Argentina. Necrolestes is now recognized as a member of a group long thought to have become extinct shortly after the extinction of the large dinosaurs at the end of the Cretaceous period. Credit: Reconstruction by Jorge Gonzalez, copyright Guillermo W. Rougier 

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. 

Keywords: anatomy, paleontology, vertebrate, fossorial

Guillermo W. Rougier, John R. Wible, Robin M. D. Beck and Sebastian Apesteguía. 2012. The Miocene mammal Necrolestes demonstrates the survival of a Mesozoic nontherian lineage into the late Cenozoic of South America. Proceedings of the National Academy of Sciences of the United States of America. in press. doi:10.1073/pnas.1212997109


After 121 years, identification of 'grave robber' fossil solves a paleontological enigma 
An international team of researchers, including Carnegie Museum of Natural History scientist John Wible, has resolved the evolutionary relationships of Necrolestes patagonensis, whose name translates into "grave robber," referring to its burrowing and underground lifestyle. This much-debated fossil mammal from South America has been a paleontological riddle for more than 100 years.

Scientific perseverance, a recent fossil discovery, and comparative anatomical analysis helped researchers to correctly place the strange 16-million-year-old Necrolestes, with its upturned snout and large limbs for digging, in the mammal evolutionary tree. This finding unexpectedly moves forward the endpoint for the fossil's evolutionary lineage by 45 million years, showing that this family of mammals survived the extinction event that marked the end of the Age of Dinosaurs. This is an example of the Lazarus effect, in which a group of organisms is found to have survived far longer than originally thought. Situating Necrolestes among its relatives in the fossil record answers one long-held question, but creates others; it reminds us that there is a lot we don't yet know about the global impacts of the massive extinction event 65 million years ago and it challenges assumptions that the well-documented effects that occurred in western North America were experienced globally. 

After 121 years, identification of 'grave robber' fossil solves a paleontological enigma http://phys.org/news/2012-11-years-identification-grave-robber-fossil.html via @physorg_com

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