It doesn't take an expert to describe the basic features of a hammerhead shark. After all, their distinctive and bizarre head is included in their name outright. But just where exactly did the head come from in the context of Hammerhead evolution in the past? Well, as luck would have it, some researchers at the University of Colorado Boulder (long way from the ocean, eh?) published a paper this past week on a genetic analysis of Hammerhead phylogeny. In said study, they analyzed the mitochondrial and nuclear DNA of species of Hammerhead from all over the world, and constructed a phylogenetic tree of their relatedness and origin. What the tree revealed was that the first Hammerhead likely first evolved in the Miocene epoch, 20 million years ago. It was a large shark, probably closest in appearance to the Great Hammerhead of modern oceans. From there though, small size in these sharks evolved twice, independently. The results today are the small bonnethead shark of the Caribbean, and the similarly diminished winghead shark of northern Australia. For a rehash of these details in a more journalistic and complete fashion, you can read the full article here:
http://www.eurekalert.org/pub_releases/2010-05/uoca-hss051810.php
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