In the latest issue of Nature is a report on a pretty amazing transitional fossil: Pulija darwini, a relative of modern seals, but one that was a “pre-seal” in that it walked on land. It was related to but not on the direct line of ancestry to modern pinnipeds. Pujila appears to have been much like a large otter. It’s already been covered amply on several other blogs, so I’ll just refer you to the official Pujila website (be sure to manipulate the three-dimensional model and the three dimensional skull), which has all the information, and a disquisition on the beast on Ed Yong’s blog Not Exactly Rocket Science.
Reconstuction of animal from Pujila website, reconstruction of skeleton from Nature paper
A semi-aquatic Arctic mammalian carnivore from the Miocene epoch and origin of Pinnipedia
Natalia Rybczynski, Mary R. Dawson & Richard H. Tedford
Summary of the article: Modern pinnipeds (seals, sea lions and the walrus) are semi-aquatic, generally marine carnivores the limbs of which have been modified into flippers. Recent phylogenetic studies using morphological and molecular evidence support pinniped monophyly, and suggest a sister relationship with ursoids (for example bears) or musteloids (the clade that includes skunks, badgers, weasels and otters). Although the position of pinnipeds within modern carnivores appears moderately well resolved, fossil evidence of the morphological steps leading from a terrestrial ancestor to the modern marine forms has been weak or contentious. The earliest well-represented fossil pinniped is Enaliarctos, a marine form with flippers, which had appeared on the northwestern shores of North America by the early Miocene epoch. Here we report the discovery of a nearly complete skeleton of a new semi-aquatic carnivore from an early Miocene lake deposit in Nunavut, Canada, that represents a morphological link in early pinniped evolution. The new taxon retains a long tail and the proportions of its fore- and hindlimbs are more similar to those of modern terrestrial carnivores than to modern pinnipeds. Morphological traits indicative of semi-aquatic adaptation include a forelimb with a prominent deltopectoral ridge on the humerus, a posterodorsally expanded scapula, a pelvis with relatively short ilium, a shortened femur and flattened phalanges, suggestive of webbing. The new fossil shows evidence of pinniped affinities and similarities to the early Oligocene Amphicticeps from Asia and the late Oligocene and Miocene Potamotherium from Europe. The discovery suggests that the evolution of pinnipeds included a freshwater transitional phase, and may support the hypothesis that the Arctic was an early centre of pinniped evolution.