Cranial anatomy of the earliest marsupials and the origin of opossums.

Background: The early evolution of living marsupials is poorly understood in part because the early offshoots of this group are known almost exclusively from jaws and teeth. Filling this gap is essential for a better understanding of the phylogenetic relationships among living marsupials, the biogeographic pathways that led to their current distribution as well as the successive evolutionary steps that led to their current diversity, habits and various specializations that distinguish them from placental mammals.

Methodology/principal Findings: Here we report the first skull of a 55 million year old peradectid marsupial from the early Eocene of North America and exceptionally preserved skeletons of an Oligocene herpetotheriid, both representing critical groups to understand early marsupial evolution.

Exceptionally preserved North American Paleogene metatherians: adaptations and discovery of a major gap in the opossum fossil record.

A major gap in our knowledge of the evolution of marsupial mammals concerns the Paleogene of the northern continents, a critical time and place to link the early history of metatherians in Asia and North America with the more recent diversification in South America and Australia. We studied new exceptionally well-preserved partial skeletons of the Early Oligocene fossil Herpetotherium from the White River Formation in Wyoming, which allowed us to test the relationships of this taxon and examine its adaptations. Herpetotheriidae, with a fossil record extending from the Cretaceous to the Miocene, has traditionally been allied with opossums (Didelphidae) based on fragmentary material, mainly dentitions.

A comprehensive morphological analysis of talpid moles (Mammalia) phylogenetic relationships.

Some talpid moles show one of the most specialized suites of morphological characters seen among small mammals. Fossorial and more generalized shrew-looking moles inhabit both North America and Eurasia but these land masses share none of the same genera. One of the central questions of mole evolution has been that of how many times specialized fossorial habits evolved.

First combined cladistic analysis of marsupial mammal interrelationships.

We combine osteological, dental, and soft tissue data with sequences from three nuclear and five mitochondrial genes, sampling all major living clades of marsupials plus several extinct taxa, to perform a simultaneous analysis of marsupial interrelationships. These data were analyzed using direct optimization and sensitivity analysis on a parallel supercomputing cluster, and compared with trees produced with conventional parsimony and likelihood algorithms using a static alignment. A major issue in marsupial phylogeny is the relationships among australidelphians.

The anatomy of the world's largest extinct rodent.

Phoberomys is reported to be the largest rodent that ever existed, although it has been known only from isolated teeth and fragmentary postcranial bones. An exceptionally complete skeleton of Phoberomys pattersoni was discovered in a rich locality of fossil vertebrates in the Upper Miocene of Venezuela. Reliable body mass estimates yield approximately 700 kilograms, more than 10 times the mass of the largest living rodent, the capybara.

A Report on "One Day Symposium on Numerical Cladistics".

A recent symposium on numerical cladistics held at the American Museum of Natural History in New York City, addressed novel methods for searching tree space, applications of randomizations in cladistic analysis, and data management. One of the major concerns in systematics is that of finding the global optimum in tree length. The space to search is complex because it includes many local optima.