Wednesday, May 18, 2005

Megalodon and Great White Sharks: Part Two

So the question becomes, if Megalodon did not evolve into great whites ( i.e., if they were not a chronospecies) then what happened to cause them to go extinct? One site argues that it was competition with great whites. Specifically, early great whites were outcompeting/preying on juvenile Megalodon which caused Megalodon to go extinct. As the cheetah post, of a few days ago, shows high infant mortality came be overcome. It is adult survivorship that is important. Another theory has it that oceanic temperature cooled off around the end of the Pliocene. My own hypothesis on the subject is that they were outcompeted by early killer whales (which go back at least 5 million years). Killer whales are warm blooded and travel in packs - which makes them efficient predators. They frequently team up to kill larger whales (such as blue whales)and occasionally eat great white sized sharks. They are, approximately, the same size as Megalodon and would have been trying to fill the same niche. What would it take to confirm my hypothesis and how can I broaden it into a theory? That is a subject for another post.

In the meantime, awhile back I had written a post on killer whales. Killer whales (in the Pacific Northwest, that is) are divided into three different forms: residents, transients and offshores. These three forms differ in morphology, ecology, behavior, and genetic composition and,it should be added, cultural behavior. The resident population is divided into northern and southern residents and thes two populations are reproductively isolated from each other even though there is a partial overlap in territory. I am wondering if this is the beginnings of a sympatric speciation event?