 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 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 study in the March 12 issue of the Journal of Vertebrate Paleontology falls squarely into the mako camp. It concludes 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, it's very hard to come to a definitive conclusion."
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 fossil's 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.
The specimen-which includes part of the spinal column, the head, jaws lined with 222 teeth-is the most complete fossil known of an ancient great white shark.
Scientists had long assumed that great whites—which can reach lengths of 20 feet (6.1 meters)-were close kin of the prehistoric "megatooth" sharks, frightening creatures that grew up to 50 feet (15.2 meters) long and had jaws more than 9 feet (2.7 meters) wide.
But a new look at the fossil suggests that great whites are more closely related to the less fearsome and smaller mako shark, a species that still exists today.
SOURCELabels: fossil, shark, species origin |
