In Depth
Enaliarctos has been commonly included in books about prehistoric animals where it is credited as being the first pinniped, the groups that seals, sea lions and walruses all belong to. The 2009 description of Puijila however has taken some of the limelight away since this is even more primitive pinneped in form that more clearly shows the transition between land living ancestors and more aquatic descendants. One often overlooked fact however is that some remains of Enaliarctos actually come from the late Oligocene period which means that they actually predate the Puijila type specimen. Despite this Puijila almost certainly does represent a more primitive form of pinneped than Enaliarctos, but it does suggest that they continued to survive in their existing form despite the advancements made by other genera such as Enaliarctos.
One key area of study concerning Enaliarctos is how it swam. Today sea lions and fur seals (those with external ears) swim with only their front limbs, while true seals (those with just ear holes rather than eternal ear lobes) swim with only the rear limbs. Enaliarctos however seems to have swum with both fore and hind limbs, an idea supported by biomechanical study. This indicates that as early pinnepeds evolved to be better suited to swimming they initially swam with all fore limbs until they specialised down one form of locomotion other the other.
Aside from locomotion another trait that reveals the primitive nature of Enaliarctos is the dentition. Modern pinnepeds have teeth for crunching and puncturing, but Enaliarctos also retained slicing teeth towards the back of the mouth. This has been taken as an indication that would have had to return to land to eat the animals that it caught at sea. Enaliarctos was well adapted for hunting under water as evidenced by spaces for large eyes, well developed whiskers and hearing that had developed to work well under the water.
Further Reading
– The Enaliarctinae: A new group of extinct aquatic Carnivora and a consideration of the origin of the Otariidae. – Bulletin of the American Museum of Natural History, 151(3), 203-284. – E. Mitchell & R. H. Tedford – 1973. – Skeleton of the oldest known pinniped, Enaliarctos mealsi. – Science 244:60-62. – A. Berta, C.E. Ray & A.R. Wyss – 1989. – New Enaliarctos* (Pinnipedimorpha) from the Miocene of Oregon and the role of “Enaliarctids” in Pinniped Phylogeny. – Smithsonian Contributions to Paleobiology 69. – A. Berta – 1991.
