Wading newts may explain enigmatic tracks - footprints found in sandstone layers within the Grand Canyon

Science News, Jan 4, 1992 by Richard Monastersky

With the help of some wet newts, two California paleontologists have fashioned a theory to explain strange footprints found in sandstone layers within the Grand Canyon and nearby locations. The controversial idea challenges a half-century-old view of the origin of these rocks.

The tracks appear in the Coconino sandstone, a rock layer that forms steep white cliffs toward the top of the canyon. For decades, the Coconino has served as a quintessential example of a sandstone formed by windblown dunes that get buried as one spreads over another. According to this interpretation, the Grand Canyon region may have resembled the Arabian desert when the Coconino rocks formed roughly 270 million years ago.

But Leonard R. Brand and Thu Tang of Loma Linda (Calif.) University propose that animal tracks in the sandstone indicate that much of the Coconino developed underwater. They outline this theory in the December GEOLOGY. "Many of those tracks have characteristics that are just about impossible to explain unless the animal was underwater," Brand told SCIENCE NEWS.

In particular, he notes that these tracks often show animals moving in one direction while their feet point in a different direction. Other tracks start or stop abruptly, with no sign that the animal's missing tracks were covered by some disturbance such as shifting sediments.

Brand suggests that newt-like animals created the tracks while walking underwater and being pushed by a current. To test that theory, he and Tang videotaped living newts walking through a tank with running water. The animals produced tracks with features similar to those in the Coconino, Brand says.

Because the underwater interpretation runs against the geologic mainstream, Brand and Tang have not found a supportive audience among geologists.

"I find it interesting, but I can't believe it. Every other signal screams out: wind deposition,' says David B. Loope, a sedimentologist at the University of Nebraska in Lincoln.

Ralph Hunter of the U.S. Geological Survey in Menlo Park, Calif., agrees that evidence within the Coconino indicates it formed mainly from windblown dunes. Most important, he says, the formation has think laminations consisting of fine sand on the bottom and coarse sand on top. "That is very distinctive and is a very reliable indictaor of deposition by wind ripples," Hunter says.

He suggests taht some of the tracks may indeed have formed underwater in small streams running through a field of windblown dunes. He notes that such streams and ponds develop temporarily after infrequent rains in the Namibian desert of southwest Africa.