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, which belonged to a genus that still exists today.

If true, megatooths and great white sharks may have hit jumbo size independently, said study lead author Dana Ehret, a graduate student at the Florida Museum of Natural History.

(Related: "Great White Shark Filmed Breaching at Night -- A First". With video.)

Competition between great whites and megatooths may have contributed to both species' growth, said Ehret, whose study appears this month in the Journal of Vertebrate Paleontology.

The well-preserved specimen, found in 1988 in southwestern Peru, was donated to the Florida museum in 2008.

"It's really outstanding—not like anything we've seen in the fossil record in the past," Ehret said.

—Christine Dell'Amore

这件包括部分的脊柱、头部以及长着222颗牙齿的大嘴的鲨鱼化石标本是迄今人类所知道的最为完整的远古大白鲨化石。

科学家们一直推测认为，身体长达20英尺（6.1米）的大白鲨是史前 ”巨齿鲨”的近亲，这种可怕的生物能够长到50英尺（15.2米）并且嘴宽超过9英尺（2.7米）。

但是从化石上看，大白鲨更接近于现今仍存在的同属于一个类型的灰鲭鲨。 相对于巨齿鲨而言，灰鲭鲨显得没有那么可怕，体型也小一点。

弗罗里达自然历史博物馆的研究生，本次研究的主要发起人Dana Ehret说，如果这一判断正确，那么巨齿鲨和大白鲨应是相互独立的两种大型鲨鱼。

(相关阅读: "Great White Shark Filmed Breaching at Night -- A First"带视频)

Ehret说，大白鲨与巨齿鲨之间的竞争促进了两个不同类型的鲨鱼的生长进化。他的研究成果刊登在了本月的《脊椎动物古生物学》杂志上。

这件保存完好的化石标本是1988年在秘鲁西南部发现的，并于2008年捐赠给了弗罗里达博物馆。

 Ehret说：“这真的很不可思议，这完全不同于我们以前所见过的化石”。

—Christine Dell'Amore

Dana J. Ehret 供图。