Currently, the hammerhead sharks are represented by eight (or nine, depends on who you listen to) species in the Family
Sphyrnidae. Although all of them have the characteristic "
cepahalofoil", the distinctive, flattened head from which the group draws its name, they show a lot of diversity in both size and in the shape of the head. The
bonnethead (
Sphyrna tiburo) reaches lengths of about a meter and has a fairly narrow, spade-shaped
cephalofoil. The great hammerhead (
Sphyrna mokarran), on the other en
d of the spectrum, sports the classic "hammer" and can reach 6 meters in length.
New research appearing in Molecular Phylogenetics and Systematics describes work done by researchers at the University of Colorado and the University of South Florida employing DNA analysis to analyze the family tree of the hammerheads. The researchers used both mitochondrial (4 genes) and nuclear DNA (3 genes) in their examination of the evolutionary history of the group. They discovered that the ancestral hammerhead appeared relatively suddenly some 20 million years ago. It was a big fish, comparable to the larger of the living species. Small size apparently evolved twice in the development of today's smaller sharks. The
cepahalofoil has been strongly acted upon by natural selection to create divergence in the lineages leading to modern hammerheads.
Currently, the hammerhead sharks are represented by eight (or nine, depends on who you listen to) species in the Family Sphyrnidae. Although all of them have the characteristic "cepahalofoil", the distinctive, flattened head from which the group draws its name, they show a lot of diversity in both size and in the shape of the head. The bonnethead (Sphyrna tiburo) reaches lengths of about a meter and has a fairly narrow, spade-shaped cephalofoil. The great hammerhead (Sphyrna mokarran), on the other en
d of the spectrum, sports the classic "hammer" and can reach 6 meters in length. New research appearing in Molecular Phylogenetics and Systematics describes work done by researchers at the University of Colorado and the University of South Florida employing DNA analysis to analyze the family tree of the hammerheads. The researchers used both mitochondrial (4 genes) and nuclear DNA (3 genes) in their examination of the evolutionary history of the group. They discovered that the ancestral hammerhead appeared relatively suddenly some 20 million years ago. It was a big fish, comparable to the larger of the living species. Small size apparently evolved twice in the development of today's smaller sharks. The cepahalofoil has been strongly acted upon by natural selection to create divergence in the lineages leading to modern hammerheads.
No comments:
Post a Comment