我来我网
https://5come5.cn
 
您尚未 登录  注册 | 菠菜 | 软件站 | 音乐站 | 邮箱1 | 邮箱2 | 风格选择 | 更多 » 
 

本页主题: Ancient Megafish Had First Bite Strong Enough to Snap Prey in Half 显示签名 | 打印 | 加为IE收藏 | 收藏主题 | 上一主题 | 下一主题

妖刀村正



贝尔诺勋章
性别: 帅哥 状态: 该用户目前不在线
头衔: stay hungry stay foolish
等级: 希望之光
发贴: 1691
威望: 5
浮云: 1126
在线等级:
注册时间: 2005-10-19
最后登陆: 2010-04-15

5come5帮你背单词 [ outer /'autə/ a. 外部的,外层的 ]


Ancient Megafish Had First Bite Strong Enough to Snap Prey in Half

Did someone say "jaws"? Forget the great white shark: a 400-million-year-old, multiton fish may have had a bite powerful enough to chop a shark--or just about anything else--clean in two. To determine its strength, researchers reconstructed the ancient creature's jaw muscles from the grooves of a well-preserved fossil.

A well-known denizen of museum displays, Dunkleosteus terrelli could have exerted up to 1,200 pounds of force with its bite, the investigators estimate. When applied along its jagged snapping-turtle-like jaws, such a force would translate to about 8,000 pounds of pressure per square inch, the researchers find. "It was probably the first vertebrate that was able to fragment its prey before swallowing," says zoologist Mark Westneat of the Field Museum in Chicago.



Dunkleosteus grew up to 33 feet long and was the largest of a group of armor-plated predatory fish, the placoderms. The top ocean predator of the time, its prey could have included early sharks, large nautiluslike mollusks, arthropods and other placoderms, Westneat says.

A strong bite would have helped the "Dunk" contend with such armored fare, says paleontologist Gregory Erickson of Florida State University, who was not involved in the research. "You had to crack fairly thick pieces of shell or thick pieces of bony armor," he says. The estimated bite force of Dunkleosteus is comparable to that of a hyena or lion, and is probably stronger than that of a shark, he notes. "It'll go right through bone," he says of such a bite. "It's like a hot knife through butter."

To reconstruct the size of the Dunk's jaw muscles, Westneat and his colleague Philip Anderson, a graduate student at the University of Chicago, made foam rubber casts of the muscle cavities in a Dunkleosteus skull replica. The length and cross section of each muscle allowed them to calculate maximum contraction forces based on the typical strength of a modern vertebrate muscle.

The researchers combined these values with a two-dimensional simulation of the fish's jaws, which fossils indicate could pivot at several points. Muscles on the top rear of the head and under the chin might have pulled its jaws open or held them in place so crisscrossing muscles in the cheeks could slam them shut. Such a multipivot system, in which some hinges stay still and others rotate, is highly efficient at transmitting force, the researchers observe in a paper published online November 28 in Biology Letters.

The muscle placement and pivot points of the jaw suggest Dunkleosteus may have sucked prey into its mouth before biting, like an extremely large-mouthed bass, the researchers note. Suction might have helped it contend with agile prey such as sharks, they observe.

Despite its bone-crushing bite and dominance of the seas, Dunkleosteus died out after 100 million years for unknown reasons. It would not be the last word in chompers, however. Today's large alligators can generate 3,000 pounds of bite force, and the Tyrannosaurus rex probably outdid that, Erickson says. --JR Minkel
顶端 Posted: 2006-12-13 21:10 | [楼 主]
我来我网·5come5 Forum » 外语乐园

Total 0.007174(s) query 4, Time now is:12-28 17:29, Gzip enabled
Powered by PHPWind v5.3, Localized by 5come5 Tech Team, 黔ICP备16009856号