Larry Rinehart knew he'd discovered something interesting when he saw the tiny set of teeth lurking between fossil remains of some of the first dinosaurs to appear on Earth.

The sharp, delicate and deadly looking jaw, which is smaller than a dime, ended up belonging to an entirely new genus and species of 205 million-year-old reptile, said Rinehart, preparator at the New Mexico Museum of Natural History and Science.

"When I first saw it, I could tell it was a small reptile that was different from anything else," Rinehart said. "I might not have found it at all if I wasn't preparing the whole block of fossils under a microscope."

The creature was hidden in a 4,000-pound chunk of rock called the Coelophysis Block, which is now on display at the museum's Triassic Hall. That block, which came from a quarry in Ghost Ranch, holds the remains of at least 24 early 7-foot-tall dinosaurs called Coelophysis.

But the fact that the tiny companion of those dinosaurs hadn't yet been discovered isn't even the most interesting thing about it, said Spencer Lucas, a paleontologist and interim director of the museum.

The lizardlike animal, named Whitakersaurus bermani, is also one of only a handful of fossils of tiny creatures that have been discovered from that time, and one that could lead to a much better understanding of the truly massive diversity of creatures that existed in the Triassic, a time period that started around 248 million years ago, Lucas said.

"There's a story here of these smaller animals that we don't have yet because we just don't have enough fossil record of them," he said. "We're just beginning to tap into that record. And one thing this tells us is we need to look harder for remains of the massive diversity of creatures that lived beneath the feet of the dinosaurs."

The lizardlike creature could be a relative of true lizards, which didn't appear until millions of years later. And it could be related to some of the first frogs and snakes that leaped and squiggled their way across the ancient landscape, Lucas said.

Today, the animal, classified as a sphenodont, only has one real descendant: a burrowing, insect-eating, living-fossil called a tuatara, which is found in New Zealand.

Because the teeth of Whitakersaurus were the only preserved part of the animal, it's impossible to tell whether the ancient creature burrowed like the tuatara or lived scurrying through the trees or in the underbrush of the tropical forest that existed in New Mexico at that time, Lucas said.

To get that information, scientists would have to find some preserved limbs, which may yet be lurking in other chunks of rock taken from Ghost Ranch, he said.

"What we do know about this guy is he's the most complete sphenodont ever found in North America," Lucas said. "And we also know from the teeth, which come in different shapes, that there was something going on with what it was eating."

Creatures with different sets of teeth use molars, canines and other shapes to chop, grind or chew food. So the interesting variety of teeth in Whitakersaurus' jaw indicates that perhaps it was evolving to eat varied food sources, perhaps not just insects, Lucas said. "It suggests it was eating a new food item, or it was eating differently somehow," he said.

As part of the ecosystem, this "sphenodont McNugget" was probably also a food source for some of the small dinosaurs like Coelophysis that lived at that time, Lucas said.

But that said, it's the tiny creatures like Whitakersaurus that play a much larger role in the evolutionary process than their bigger, more well-known dinosaur companions, he said.

"Today, if you think about it, most of the biomass on Earth isn't these large animals, like buffalo or giraffes," Lucas said. "There's more biomass beneath the feet of those animals than there is in all the large animals roaming around. And that was the same in the Triassic."

It's only in the last 20 years or so that sorting techniques, microscopes and other technologies have become available to make it easier to find those little animals, he said.

And the study of small creatures from the distant past is likely to become a major source of new finds in paleontology because of that, Lucas said. "This is a lost world," he said. "This is where the action is — this is where a lot of new discoveries are going to be made."

Those discoveries are critical, Lucas added, because it can give us a more complete picture of what that time was really like. "So when we look at dinosaurs, because the fossils are bigger and they're easier to find, we've ended up with a skewed picture of the time in which they lived," he said. "Alongside the dinosaurs, there are probably hundreds of other species just of these sphenodonts that are still waiting to be discovered. We need to find them so we can really understand what was going on at that time."

Lucas, Rinehart, Andrew Heckert, a geology professor at Appalachian State University, and Adrian Hunt, the former director of the museum, published a paper this month on the discovery of Whitakersaurus in the British journal Palaeontology.

Contact Sue Vorenberg at 986-3072 or svorenberg@sfnewmexican.com.