The recent discovery of a semi-dino-fossil in New Mexico from Triassic rekindled the dispute about when and how the first true dinosaurs took over the top of the food chain.

In the history of ancient Earth, Triassic is considered one of the most agitated periods, since it marks the transition between the Permian (the last “remnant” of the Paleozoic era) and the famous Jurassic, with its exploding bio-diversity. During Triassic, Earth was still dominated by Pangaea, the mammoth continent from which all of today’s continents have emerged, and which influenced world’s climate in a totally different way.

However, the notable aspect that most paleontologists speak of when dealing with Triassic is the catastrophic and still unexplained bio-cataclysm that determined the disappearance of 96 percent of all marine species and 70 percent of land vertebrate species. Sometimes called the Great Dying, this massive extinction happened around 251 million years ago and it took more than 6 million years for the bio-diversity to recover.

So that means that around 215 million years ago, when the animal whose stoned remains have recently been discovered in New Mexico died, life on Earth should have thrived again, with new species of more powerful animals dominating the vastness of the planetary ocean and the green tropical woods that spread way beyond the Tropics.

Surprisingly, the fossil finding suggests that “older” species of animals, thought extinct after the Great Dying, continued to co-exist with their “newer” and better adapted relatives, the dinosaurs.

The first true dinosaurs were thought to have emerged about 230 million years ago (roughly 20 million years after the Triassic extinction) and were not at all as impressive as Hollywood movies try to portray them: a dino-ancestor called Eoraptor was the size of a modern day dog and was not a predator, although it did consume meat. However, because Eoraptor's skeleton shows some advanced skeletal features, older dinosaurs may yet be found.

The 215 million years fossil from New Mexico shows that it took true dinosaurs a whole lot more to break loose from their “degraded” ancestors and conquer the food chain, during the Jurassic. Most paleontologists believe that “dinosaur-wannabes” (or "basal dinosauromorphs," ) like the Eoraptor were suppressed by their evolved relatives, in the virtue of “survival of the fittest” law. Turns out they co-existed for quite a while: around 15 to 20 million years.

"When dinosaurs first evolved, they were not very common and they were pretty small," said Randall Irmis of the University of California-Berkeley, who worked on the study.

"So they're not the dominant predators or creatures on land at all during most of the Triassic. And it's only really until the Jurassic when they really explode in diversity and reach these huge sizes that we're so familiar with," Irmis added.

"For the first time, we're finding the earliest dinosaurs and their closest relatives together," paleontologist Kevin Padian of the University of California-Berkeley, one of the researchers, said in a telephone interview with Reuters.

"That tells us that the transition to the beginning of the age of dinosaurs was not a very-rapid affair and that, therefore, it wasn't instant competitive superiority."