Ornithopod trackway in YemenCourtesy Nancy StevensThe first dinosaur tracks discovered on the Arabian Peninsula are presenting science with new information about dinosaur herding behavior, and the global patterns of their evolution.

A series of parallel tracks made by 11 individual sauropods and a set of ornithopod footprints cutting across them was discovered about 28 miles north of Sana'a, the capitol of the Republic of Yemen. The sauropod footprints show varying sizes meaning the trackway was probably made by a herd of both adults and their smaller offspring.

"Smaller individuals had shorter stride lengths, and took more steps to keep up with the larger individuals," said Nancy Stevens, an assistant professor of paleontology at Ohio University in Athens, Ohio. Stevens co-authored the paper with Anne Schulp, a paleontologist at the Netherland’s University of Maastricht. The paper can be found online at PloS ONE.

A sauropod is one those huge, long-necked, small-headed herbivores with an equally long tail. When viewed from the side, sauropods remind you of a gigantic snake with tree-trunk legs digesting an elephant-sized meal. An ornithopod, on the other hand, is a smaller (about the size of a school bus!) plant-eater that walked on two legs (bipedal).

The dinosaurs produced the tracks along the shoreline of an ancient waterway that existed during the Jurassic Period nearly 150 million years ago. "This mudflat would have been like a highway for them, with little tree cover," Anne Schulp said.

Fossils related to these same types of dinosaurs -- and of the same age -- have been found elsewhere in eastern Africa, adding to the contention that they co-existed when the Arabian Peninsula was fully connected to the African continent. Today, the Red Sea separates the two landmasses.

Ichnology is the study of trace fossils, which can be anything created by an animal while it was alive. These include footprints, coprolites (fossil dung), skin impressions, bite marks, signs of burrowing, etc. Non-organic evidence such as ripple marks and raindrops are sometimes included in the study. Footprints are sometimes referred to as ichnites.

By the way, a new exhibit in the Dinosaurs and Fossils gallery here at the Science Museum of Minnesota displays some trackways from the Coconino Formation in Northern Arizona. The tracks are believed to have been preserved in sandstone by a four-legged mammal-like reptile that lived some 260 million years ago during the Permian period. We’ve also covered the science of Ichnology earlier in these pages.

Researchers take tracksite measurementsCourtesy Nancy StevensBack on the Arabian Peninsula, careful measurements were taken of each track and it’s relationship to nearby footprints. Data from print dimensions and stride length can reveal much about the size and speed of the track maker. The sauropod adults were estimated to have reached 10 to 13 feet in height at the hips and shoulders. The longest sauropod trackway, composed of 16 individual prints measured about 16 meters (about 53 feet). Stevens and Schulp believe it could extend even further once the northern end of the trackway’s limestone layer is exposed.

"We have just scratched the surface," Dr. Schulp said. "We're pretty sure there's a lot more to discover out there."

LINKS
Scientific American website story
Glen Kuban’s Ichnology site
Dinosaur Tracking Research Group