Seal evolution: Sexual dimorphism in pinnipeds arose around 27 million years ago as climate changed

http://feeds.feedburner.com/~r/sciencedaily/top_news/top_science/~4/4YUCqLF4nHQ

In the world of science, one of the most exciting things a researcher can do is pin down an answer to a widely asked question. This experience came early for Carleton University graduate Thomas Cullen, who made a discovery about pinnipeds — the suborder that makes up seals, sea lions and walruses — while doing research for his Master’s degree under the supervision of Canadian Museum of Nature palaeontologist Dr. Natalia Rybczynski.His discovery, published today in the journal Evolution, relates to sexual dimorphism (a large variance in size between males and females), in a variety of pinniped species. Males in many species of pinnipeds are often much larger than their female counterparts, in some cases more than twice as large, and this has implications for how they mate and behave.Dimorphic pinnipeds such as the Steller’s Sea Lion and Northern Fur Seal typically mate in a harem, with one male pinniped presiding over a larger community of female mates. This behavior is not typically seen in non-dimorphic pinnipeds such as the Ringed Seal, and so sexual dimorphism is intimately linked with mating style.Researchers have long puzzled over both why sexual dimorphism exists in many pinniped species and when this trait evolved. When Cullen examined fossils of an extinct pinniped with Rybczynski, he discovered an incontrovertible answer to the question of when. He was able to examine it there before analyzing the data at Carleton in a lab headed by his other thesis supervisor, Prof. Claudia Schrder-Adams.Skull of Enaliarctos emlongi, an early pinniped ancestor. Cullen examined and analyzed the characteristics of this fossil for his study on the evolution of sexual dimorphism in pinnipeds.”We were examining a fossil of a pinniped that was previously thought to be a juvenile, but we looked at it again and found that, based on its skull structure, it was likely an adult,” says Cullen. This discovery, coupled with analyses comparing this fossil to others of the same species as well as modern dimorphic species, proved that the fossil belonged to a sexually dimorphic species.The fossil in question, the skull of an early pinniped ancestor called Enaliarctos emlongi, was discovered in the late 1980s off the coast of Oregon. …


Read More: Seal evolution: Sexual dimorphism in pinnipeds arose around 27 million years ago as climate changed

#Alternative-Medicine, #Canadian, #Canadianmuseum, #Carleton, #Climate, #Journal, #Northern, #Pregnancy