Groundbreaking Fossil Finds: Tiny T. Rex Ancestor and Saber-Toothed Herbivore

Paleontologists have recently uncovered the fossils of two small creatures that defied some basic “dinosaur rules”, and which have provided unique insights into the evolution of both carnivorous and plant-eating creatures.  Eodromaeus, christened the Dawn Runner, resembled a pint-sized Tyrannosaurus, and likely gave rise to the most ferocious predator of ancient times, T rex.  Tiarajudens eccentricus, on the other hand, ate plants yet was equipped with long, pointed fang-like teeth – a “saber-toothed cow” of sorts.

The Dawn Runner, Eodromaeus,

This 4-foot-long, 10-15 pound fellow likely made up in ferocity what it lacked in size.  Pondering its image (please see photo of skeleton and artist’s recreation in article below), I can’t help but think that “prehistoric herpers” would have surely made a pet of this one!  Of course, dinosaurs and humans did not inhabit earth at the same time, but if we had…

The Dawn Runner’s skeleton was unearthed in an area known as the Valley of the Moon, at the foot of the Andes Mountains in Argentina (please see photo…this valley is aptly named!). Studies of it are expected to provide a rare glimpse into the earliest days of the meat eating dinosaurs.  As we now far more about the dinosaurs demise than their origins, paleontologists are pleased with this possibility.

Long of neck and tail, and able to run on its rear legs, the Dawn Runner may be the first in the line of creatures that culminated with the mighty T. rex.  Also found near the Dawn Runner were the remains of small plant-eaters, such as Eoraptor, upon which the sawed off “terrible lizard” likely fed.

A Saber-Toothed Vegetarian, Tiarajudens eccentricus

To the formidable predators that stalked Brazil 250 million years ago, Tiarajudens might at first have appeared to be an easy mark.  Only dog-sized, it was a small beast for the times, yet it was stocky and so would provide a decent meal.  However, the little creature was not defenseless…it sported two huge fang-like teeth that were totally out-of-character for a vegetarian.

Paleontologists theorize that Tiarajudens displayed these teeth, which resembled those sported by Saber-Toothed Tigers (please see photo and recreation in article below) to ward off potential predators before they attacked; perhaps they were functional in battle as well.  The sabers might also have found use in territorial disputes with others of its kind, and could possibly have helped Tiarajudens to pull branches within reach when feeding.  The rest of its teeth were similar to those evolved by other plant-eaters.

Tiarajudens’ line died out in time, but its fossils offer a unique look at the origins of canine teeth.  The group in which it is classified, the Theraspids, are believed to have featured in the evolution of today’s mammals.  Today, saber-bearing plant eaters are rare but not unknown; please see this photo of Musk Deer skulls for a modern-day example (I have worked with these creatures – the only time I used gloves when handling deer!).