Eodromaeus

Eodromaeus was named by Ricardo N. Martínez, Paul C. Sereno, Oscar A. Alcober, Carina E. Colombi, Paul R. Renne, Isabel P. Montañez and Brian S. Currie in 2011 and the type species is Eodromaeus murphi. The generic name is derived from the Greek words Eos ("Dawn", "Early") and Dromaeus ("Runner"). The specific name honors Jim Murphy, who used to work the area nearby where the fossils were found.[1]

Artistic restoration

Fossils from Eodromaeus were first discovered in 1996 by Argentinean paleontologist Ricardo N. Martinez and Earthwatch volunteer Jim Murphy, and it was first believed that the fossils were a new species of Eoraptor. However, as the researchers started to take a closer look at the fossils, they found that it had many skeletal features which were absent in Eoraptor,[3] and they understood that it came from a new genus.

Eodromaeus is known from the holotype PVSJ 560, a nearly complete articulated skeleton recovered from the Valle de la Luna Member of the top of the Ischigualasto Formation, and the referred materials PVSJ 534, PVSJ 561, PVSJ 562 and PVSJ 877 from Valle de la Luna, La Peña and Cancha de Bochas Members of Ischigualasto, dating to the early Carnian faunal stage of the early Late Triassic, about 232–229 million years ago.[1]

Size comparison between Eodromaeus and a human.

Skeleton of Eodromaeus murphi, known remains depicted in white and light grey, unknown in dark grey.

Eodromaeus was a relatively small dinosaur, with a total length of about 1.2 metres (3.9 ft) from nose to tail, and a weight of about 5 kilograms (11 lb). The trunk was long and slender. It is unknown how fast Eodromaeus could run, but it has been suggested to about 30 kilometres per hour (19 mph).[4] It is a basal carnivorous theropod. The forelimbs were much shorter than the hindlimbs, ending in hands with 5 digits. Digits IV and V (the ring finger and little finger in humans) were very reduced in size.[1]

Restoration

Eodromaeus is regarded as one of the earliest members of Theropoda, the group that includes the carnivorous dinosaurs. The discovery of Eodromaeus lead some to believe that Eoraptor (typically regarded as a theropod) likely represented one of the most basal sauropodomorphs, the group that includes animals like Apatosaurus.[1] This has since been questioned however, with Bergman and Sues reclaiming Eoraptor as a theropod, like Eodromaeus.[5] This relationship was also recovered in the large analyses of early dinosaurs and other dinosauromorphs that were carried out by Baron, Norman and Barrett (2017).[6]

Cladogram after Martinez et al., 2011:[1]

• Eodromaeus skeleton.
• Eodromaeus skull.
• Video: “Video: Fast, "Nasty" Little Dinosaur Discovered.” National Geographic January 13, 2011.