A lizard, a petrified log and a dinosaur

By Jeff Mitton

Every once in a while, an experience reminds us that great gulfs of time preceded the present, times when the world was very different.

I was hiking in the Bisti/De-Na-Zin Wilderness, enjoying the hoodoos created by vagaries of deposition carved by wind and water. Most of the immediate area was intricate patterns of white, tan and brown, so a brightly colored column of rock caught my eye.

To my delight, I found that it was a lichen-encrusted petrified log, about 2 feet in diameter and 5 feet long.

This log was at the bottom of a small hill, and looking up, I saw that another segment of the log was at the top of the hill. I clambered up to take a photograph, but was distracted by an ornate tree lizard,Urosaurus ornatus, basking at the base of the petrified log.

This portion of the wilderness was devoid of plants, and the lizard was the first vertebrate that I had seen since dawn. It struck me first as humorous and then as ironic that the only tree that the ornate tree lizard could find was a 74-million-year-old fossil.

The immense span of time separating the lives of the ancient conifer and the sentient lizard captured my imagination for the next hour, as I sat with the lizard and the tree to eat my breakfast.

The San Juan Basin is about 100 miles across and has eight wilderness areas or badlands; it might be the hoodoo capital of the world. Hoodoos, or sculpted pillars of stone, balance immense table rocks, or mudstones, or even petrified logs. The basin's striking scenery and exposed strata have attracted many geologists, so the history of the area is well known.

The Bisti has changed dramatically over time. At different times, it has been dotted with lakes, an ocean shore, a lush tropical forest and modern desert. When the fossilized log was upright and photosynthesizing, the area was covered by a forest of cypress-like conifers, somewhat similar to the trees in the swamps of Louisiana, South Carolina and Georgia.

The ornate tree lizard had not yet evolved, but the Bisti beast prowled among the trees.

Fossilized fragments of the Bisti beast were found as early as 1990, but in 1998, Paul Sealey, a museum volunteer, found a nearly complete adult skeleton. It was 29 feet long and obviously a relative of Tyrannosaurus rex. In 2010, the dinosaur was officially named Bistieversor sealeyi, the first name a combination of the place it was discovered andeversor, meaning destroyer. The second name honors the discoverer.

It is hard to imagine the Bisti, a colorful eroded landscape with rock layers mineralized to shades of tan, brown, red, orange, purple, white and black, as a lush conifer forest, moist, shady and dank. It is also difficult to reconcile the scaly creatures that have rested beside the conifer when it was alive and now that it has turned to stone.

The Bisti beast was a top carnivore, a predator 29 feet long that would have needed many large prey to survive. So when the tree was alive, numerous dinosaurs would have been nearby.

Today, the scaly creature is a diminutive tree lizard, barely 5 inches long, scratching out a living by skittering after insects.

Jeff Mitton (mitton@colorado.edu) is a professor in the Department of Ecology and Evolutionary Biology at the University of Colorado. This column originally appeared in the Boulder Camera.

Feb. 18, 2011