Eoraptor
Name: Eoraptor
(Dawn thief).
Phonetic: E-owe-rap-tore.
Named By: Sereno, Forster, Rogers &
Monetta - 1993.
Classification: Chordata, Reptilia, Dinosauria,
Saurischia, Eusaurischia.
Species: E. lunensis (type).
Diet: Possibly an omnivore.
Size: 1 meter long.
Known locations: Argentina - Ischigualasto
Formation.
Time period: Ladinian of the Triassic.
Fossil representation: Many specimens, some of
which are very well preserved.
Eoraptor
stands out not only for being one of the first dinosaurs to ever walk
the Earth, but because palaeontologists cannot conclusively agree on
where to place it in relation to other dinosaurs. Initially Eoraptor
was classed as a theropod because of its bipedal stance and narrow
build, but the sauropodomorphs
(which would go on to evolve into
giant quadrupedal dinosaurs like Apatosaurus
and Brachiosaurus)
were
also bipedal with a similar body plan in their early stages of
development. To confuse things further, Eoraptor
had two main types
of teeth, those of a carnivore and a herbivore. This is why
Eoraptor has in the past been classed as a theropod
by some and
sauropodomorph by others, and why in 2011 it was classed again as
a eusaurischid, a position that places it between these two groups.
The
combination of the two types of teeth has been seen to suggest that
Eoraptor was a generalist omnivore that adapted to
the availability of
different food and prey. Still, Eoraptor may
have had a preference
for one type of diet but still feeding upon another type to balance out
nutritional deficiencies that were in the other. Eoraptor
also lacked
specialist carnivore adaptations such as a sliding jaw joint, which
meant that Eoraptor would have been limited to
small prey animals such
as insects and lizards.
Despite
potentially carnivorous aspects of its diet, Eoraptor
was not the
dominant hunter of its day, and may itself have been prey to the
larger Herrerasaurus
that is also known from the
same time and
formation.
Further reading
- Primitive dinosaur skeleton from Argentina and the early evolution of
Dinosauria. Nature 361:64-66 - P. C. Sereno, C. A. Forster, R. R.
Rogers & A. M. Monetta - 1993.
- Osteology of Eoraptor lunensis (Dinosauria,
Sauropodomorpha). Basal
sauropodomorphs and the vertebrate fossil record of the Ischigualasto
Formation (Late Triassic: Carnian-Norian) of Argentina. - Journal of
Vertebrate Paleontology Memoir 12: 83-179 - Paul C. Sereno, Ricardo N.
Mart�nez & Oscar A. Alcober - 2013.
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