Wednesday, April 22, 2009

Missing link to the pinnipeds

From Nature magazine, via Scientific Blogging, news of a missing link in the fossil record of the evolution of pinnipeds: Puijila Darwini - 'Missing Link' In Evolution Of Seals, Sea Lions And Walruses.
Modern seals, sea lions, and walruses all have flippers—limb adaptations for swimming in water. These adaptations evolved over time, as some terrestrial animals moved to a semi-aquatic lifestyle. Until now, the morphological evidence for this transition from land to water was weak.

Skeletal illustration of Puijila darwini
Skeletal illustration of Puijila darwini. Credit: Mark A. Klingler/Carnegie
Museum of Natural History

"The remarkably preserved skeleton of Puijila had heavy limbs, indicative of well developed muscles, and flattened phalanges which suggests that the feet were webbed, but not flippers. This animal was likely adept at both swimming and walking on land. For swimming it paddled with both front and hind limbs. Puijila is the evolutionary evidence we have been lacking for so long," says Mary Dawson, curator emeritus of Carnegie Museum of Natural History.

Portions of the Puijila darwini specimen were found in 2007 in deposits that accumulated in what was a crater lake in coastal Devon Island, Nunavut, Canada. A subsequent visit in 2008 yielded the basicranium, an important structure for determining taxonomic relationships.

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