5-mln yr old shark fossil sheds new light on Great Whites origins

March 13th, 2009 - 3:25 pm ICT by ANI  

Washington, March 13 (ANI): A new study of a preserved 4- to 5-million-year-old shark fossil has shed new light on the great whites origins, and has helped scientists decide which line of species did it evolve from.

For the last 150 years, some paleontologists have concluded the great white shark, Carcharodon carcharias, is a smaller relative of the line that produced Carcharodon megalodon, the largest carnivorous fish known.

Other paleontologists disagree, arguing that the great white shark evolved instead from the broad-toothed mako shark.

The second group contends megalodon, which grew to a length of 60 feet, should have its genus name switched to Carcharocles to reflect its different ancestry.

The new study falls squarely into the mako camp.

It concludes that megalodon and modern white sharks are much more distantly related than paleontologists initially believed.

I think that this specimen will clarify things, said lead author Dana Ehret, a vertebrate paleontology graduate student at the Florida Museum of Natural History located on the UF campus. When we only have isolated teeth to describe, its very hard to come to a definitive conclusion, she added.

The study is based on a remarkably well preserved 4- to 5-million-year-old fossil from Peru of an early white shark species: a complete jaw with 222 teeth intact and 45 vertebrae.

Most ancient shark species are known only from isolated teeth.

Based on tooth size and analysis of growth rings within the vertebrae, the shark was about 20 years old and 17 to 18 feet long, a size in the range of modern white sharks.

Having the teeth in place allows researchers to see important distinguishing characteristics that help determine a fossils genus and species, such as whether a tooth curves toward the outside of the jaw or its midline, Ehret said.

He believes the fossil belongs to a white shark species closely related to Isurus hastalis, a broad-toothed mako shark that probably grew to 27 feet long and lived 9 million to 10 million years ago.

An olive-grove farmer trained in fossil collection discovered it near his home in the desert of southern Peru in 1988. It now belongs to a private collection and was only recently pledged to the Florida Museum of Natural History.

Its the only fossilized partial skull of a white shark thats ever been found, said Gordon Hubbell, the fossils owner and study co-author.

According to vertebrate paleontologist Kenshu Shimada, an associate professor at DePaul University in Chicago, the study strengthens the evolutionary link between the extinct mako and the modern white shark. (ANI)

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