Tuesday, October 21, 2008

Rock records dino 'dance floor'

Footprints (R Seiler)
Print collections are known elsewhere but the scale here is impressive

Scientists have identified an amazing collection of dinosaur footprints on the Arizona-Utah border in the US.

There are so many prints - more than 1,000 - that geologists have dubbed the site "a dinosaur dance floor".

Located within the Vermilion Cliffs National Monument, the marks were long thought simply to be potholes gouged out of the rock by years of erosion.

A paper describing the 190-million-year-old footprints is published in the palaeontology journal Palaios.

"Get out there and try stepping in their footsteps, and you feel like you are playing the game 'Dance Dance Revolution' that teenagers dance on," says Professor Marjorie Chan from the University of Utah.

"This kind of reminded me of that - a dinosaur dance floor - because there are so many tracks and a variety of different tracks."

"There must have been more than one kind of dinosaur there," she adds. "It was a place that attracted a crowd, kind of like a dance floor."

Dinosaur tail marks illustrated by a diabram  (W.Seiler)
Dinosaur tail marks are rare. The diagram better illustrates the drag movement

The site covers about a third of a hectare and records dinosaur movements around what was probably a watering hole during the Early Jurassic Period, when the US south-west was covered with a field of sand dunes larger than the Sahara Desert.

Footprints (N.Miller)
The prints will eventually erode away

Original here

Investigation of the site reveals at least four dinosaur species were present, with the animals ranging from adults to youngsters.

"The different size tracks [2.5-50cm] may tell us that we are seeing mothers walking around with babies," says Winston Seiler, who worked on the project.

As well as footprints, the site also records tail-drag marks - which are up to seven metres in length.

The scientists say the dinosaur prints were locked into sandstone after being covered by shifting dunes.

They became exposed through erosion and will eventually disappear through erosion, too.

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