December 3, 2012 in Features

Rock Doc: A truly ugly discovery

E. Kirsten Peters
 

Science often advances by fits and starts. And sometimes new discoveries lurk in dusty old drawers of samples.

Such was the case at Harvard University where for about 50 years a sample from Africa lay quietly awaiting insightful review. The man who looked at it with fresh eyes was Paul Sereno, a famous dinosaur expert from the University of Chicago who is National Geographic explorer in residence at Harvard.

The dino, called Pegomastax africanus, was little, measuring less than 2 feet long and weighing less than a cat. But boy was it an ugly herbivore.

It had a beak like a parrot. Far behind the beak were some tall, very sharp teeth. The way the teeth are worn seems to indicate they scraped against each other as the dino used its jaws, meaning the impressive teeth were self-sharpening. Pego also had a fine pair of “stabbing” canine teeth behind its beak and in front of its slicing dentition.

Just a few dino fossils mix herbivorous and carnivorous teeth the way Pego did. It’s possible that such dinosaurs ate plants but also insects or the occasional piece of meat. But Sereno argues that damage to the teeth indicate they were used for fighting rather than eating.

Besides the 200 million-year-old sample from Africa, scientists have recently unearthed something similar from China. (China has become a gold mine for fossil discovery in recent years.) The Chinese specimen was found in lake sediments covered in volcanic ash back at the time the animal lived. This animal, it’s clear, had another interesting feature besides a bizarre combination of teeth and a beak. The specimen preserved hundred of bristles covering the dinosaur’s body, a bit like a porcupine is covered by bristles today.

Sereno and others believe the African dino had the same bristles, they just didn’t get preserved with the dino’s bones.

What this all means is that the Pego had four noteworthy features: a beak, stabbing canines, self-sharpening slicing teeth, and bristles. Not bad for a little guy.

But Pegomastax and the genus to which it belonged didn’t fare well through time. As the Jurassic period was ending, the most advanced members of the group disappeared.

“Perhaps they were too specialized for their own good,” Sereno speculated to Time. “Changing climate and plant life may have done them in.”

Dinosaurs, obviously, are all extinct. But many of them saw at least some of their genes go through the final extinction boundary of the Late Cretaceous 65 million years ago. That’s because, according to modern theory, the dinosaurs are the ancestors of birds.

But that’s not the case for the ugly little Pego dinosaur. It might seem to be related to a parrot (or even a porcupine) but scientists say that evolution had to come up with those body parts from scratch, inventing anew features that had been explored long ago by a small but complex dinosaur.

E. Kirsten Peters, a native of the rural Northwest, was trained as a geologist at Princeton and Harvard. Her most recent book is “The Whole Story of Climate,” just published by Prometheus Books. This column is a service of the College of Agricultural, Human and Natural Resource Sciences at Washington State University.

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