About Eodromaeus
| Scientific Name (Genus) | Eodromaeus |
| Meaning of Name | Dawn runner ēōs (dawn) [Greek] - dromaeus (runner) [Greek] |
| Classification | Saurischia, Theropoda |
| Total Length | Approx. 1.2m |
| Diet | Carnivorous |
| Period | Late Triassic (approx. 232-229 mya) |
| Species | Eodromaeus murphi |
| Year of Publication | 2011 |
| Genus Description Paper | A Basal Dinosaur from the Dawn of the Dinosaur Era in Southwestern Pangaea. Science 331(6014). Martinez, R.N., Sereno, P.C., Alcober, O.A., et al. 2011. |
Characteristics
Eodromaeus was one of the earliest known theropod dinosaurs, living in what is now Argentina during the Late Triassic. True to its name, 'dawn runner,' it was a very lightweight and slender creature, about 1.2 meters long and weighing around 5 kg, capable of running swiftly on its two hind legs.
The most important features of Eodromaeus are found in its skull and teeth. The upper jaw was lined with long, sharp fangs, already possessing the basic characteristics of carnivorous dinosaurs that would lead to large theropods like Tyrannosaurus and Allosaurus. It is believed to have hunted insects and small reptiles, using its long tail for balance.
It had five fingers on its hands, but the fourth and fifth were very small, suggesting that mainly three fingers were used for grasping. This 'three-fingered hand' is another feature common to later theropods.
Powered by DALL-E3, 2025.
The Split from Eoraptor
Fossils of Eodromaeus were originally thought to belong to Eoraptor, which was found in the same geological formation. However, detailed research in 2011 revealed definitive differences between the two.
The biggest difference is the shape of the teeth. While Eodromaeus has the sharp teeth of a typical carnivorous dinosaur, Eoraptor possesses teeth adapted for both carnivory and herbivory (heterodonty). This discovery led researchers to conclude that Eoraptor, previously considered an early theropod, was actually a very primitive member of the Sauropodomorpha (the group that would lead to giant herbivorous dinosaurs like Brachiosaurus).
In other words, these two types of dinosaurs, living at the same time and place, had already embarked on different evolutionary paths at the dawn of the dinosaur age: the 'carnivorous theropods' and the 'herbivorous/omnivorous sauropodomorphs.' The discovery of Eodromaeus became a crucial milestone in understanding the early evolutionary divergence of dinosaurs.
Discovery and Research
The holotype specimen of Eodromaeus (PVSJ 560) was discovered in 1996 in the Ischigualasto Formation (nicknamed the "Valley of the Moon") in San Juan Province, Argentina, by Ricardo Martínez, a member of a team led by Paul Sereno from the University of Chicago. Initially, it was considered a new specimen of Eoraptor, but as cleaning work progressed in the lab, clear differences in the skull and hand structure became apparent.
After more than a decade of detailed analysis, it was described as a new genus and species, Eodromaeus murphi, in 2011 by Martinez, Sereno, Alcober, and others in the prestigious scientific journal "Science." The species name "murphi" was given in honor of James Murphy, a philanthropist who supported the research.
This discovery provided conclusive evidence that the two major dinosaur groups, Saurischia (theropods and sauropodomorphs), had diverged very early in the dinosaur age, making an impact significant enough to rewrite textbooks on dinosaur evolutionary history.