Dinosaur Tracks Shed Light on Sauropod Evolution

John Roach
for National Geographic News
May 30, 2002

Dinosaur tracks made on the edge of a coastal plain 163 million years ago in middle England are providing a team of researchers with new insights into the evolution and behavior of sauropods.

Sauropods are the group of plant-eating dinosaurs distinguished by their long necks and tails. They include some of the largest creatures ever to walk on Earth.

An analysis of about 40 tracks of varying sizes indicates that they were made by a mixed herd of sauropods, concludes a group of researchers reporting in the May 31 issue of Science. One of the species represented in the tracks was a titanosaur, a dinosaur group that researchers didn't think had emerged for another 12 million years.

Track Investigations

The tracks, which were found in a limestone quarry near Oxford, can be divided into two distinct types: those that have a wide gap between the left and right feet and those that have very little space, if any at all, between the left and right feet.

Julia Day, a paleontologist at the University of Cambridge in England, and colleagues analyzed these tracks to try and determine which species made them.

"Different groupings of dinosaurs are defined on the basis of unique characteristics. This can also be applied to the trackways," said Day.

According to the researchers, each of the tracks contains characteristics that distinguish them as those made by sauropods. For example, the front footprints indicate the metacarpals—the hand bones on people—were held in a semicircular arrangement unique to sauropods.

While there is not enough detail among the narrow tracks to enable the scientists to discern what species of sauropod made what track, the wide gauge tracks were clearly made by titanosaurs, the researchers conclude.

The wide tracks do not contain an impression of a claw on the front foot, whereas the narrow tracks do as do another group of nearby tracks previously reported by Day's team to belong to theropod dinosaurs.

Other researchers have shown that this claw is reduced in brachiosaurs, the sister group to titanosaurs. The claw is believed to be completely lost in titanosaurs.

Continued on Next Page >>




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