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 Eoraptor

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PostSubject: Eoraptor    Wed Oct 12, 2016 3:13 pm

Here is some information about Eoraptor from Wikipedia:

Quote :
Eoraptor was one of the world's earliest dinosaurs that lived ca. 231.4 million years ago, during the latter part of the Triassic Period in Western Gondwana, what is now the northwestern region of Argentina. It was a small sized, lightly-built, ground-dwelling, two-legged bipedal saurischian. It is known from several well-preserved skeletons. When first described in 1993, it was considered to be one of the earliest, if not the earliest known dinosaur. Eoraptor has heterodont dentition, suggesting that it was omnivorous, and that this feeding strategy had evolved early on in dinosaurs.

Eoraptor had a slender body that grew to about 1 meter in length, with an estimated weight of about 10 kilograms. It had a lightly built skull with a slightly enlarged external naris. Like the coelophysoids which would appear millions of years later, Eoraptor had a kink in its upper jaws, between the maxilla and the premaxilla. Sereno et al. (2013) observed that the lower jaw had a mid-mandibular joint. It ran digitigrade, and upright on its hind legs. The femur of the holotype specimen PVSJ 512 of Eoraptor is 152 mm, and the tibia is 157 mm, suggesting that it was a fast runner. Its forelimbs are only half the length of its hindlimbs, which would suggest that it was an obligate biped. All of its long bones have hollow shafts. Eoraptor had five digits on each 'hand', the three longest of which ended in large claws and were presumably used to handle prey. Scientists have surmised that the fourth and fifth digits were too tiny to be of any use in hunting. The ilium is supported by three sacral vertebrae, unlike that of the coeval Herrerasaurus which is supported by only two sacrals, a basal trait. Eoraptor had vertebral centra that are hollow, a feature present in some of its ancestors.

Eoraptor is thought to have been an omnivore. It was a swift sprinter and, upon catching its prey, it would use claws and teeth to tear the prey apart. Unlike later, carnivorous dinosaurs, it lacked a sliding joint at the articulation of the lower jaw, with which to hold large prey. Furthermore, only some of its teeth were curved and saw-edged, unlike those in a later predator's mouth. The unique heterodont dentition of Eoraptor (Sereno et al., 1993) consists of both serrated, recurved teeth in the maxillae (upper jaws), like the teeth of theropods, and leaf-shaped teeth in the dentary (lower jaw), like the teeth of basal sauropodomorphs. Eoraptor had 4 teeth in the premaxilla and 18 teeth in the maxilla, a dental formula not dissimilar to that of Herrerasaurus. Tweet (2003) noted that the variability observed in the teeth (heterodonty) of Eoraptor, suggests that it descended from ancestors that were omnivorous, or it was itself omnivorous.


Currie (1997) found Eoraptor anatomically closer to what would be considered the ancestral morphotype of both saurischian and ornithischian dinosaurs. In 2011, as part of the team that described Eodromaeus, Martinez and others found Eoraptor to be a basal sauropodomorph, with characteristic features for that group. Michael Benton has expressed his hesitation to this, and claims that it is "quite a shift" to remove Eoraptor from the theropods and then place it in Sauropodomorpha. A subsequent study by Apaldetti, Martinez, Alcober, and Pol published in 2011 found Eoraptor to be a saurischian close to sauropodomorphs and theropods, though was unable to resolve which of the two branches, if either, it fell within. Sereno et al. (2013) redescribed the holotype skeleton and concluded that Eoraptor was not a theropod but a basal sauropodomorph, consistent with the earlier observation made by Martinez et al. (2011).

Sereno (1993) noted that Eoraptor was found in "close association" with therapsids, rauisuchians, archosaurs, Saurosuchus and the dinosaurs Herrerasaurus and Pisanosaurus, all of whom lived in its paleoenvironment. Herbivores were represented by rhynchosaurs such as Hyperodapedon (a beaked reptile); aetosaurs (spiny armored reptiles); cynodonts like Probelesodon, kannemeyeriid dicynodonts (stocky, front-heavy beaked quadrupedal animals) such as Ischigualastia; and traversodontids (somewhat similar in overall form to dicynodonts, but lacking beaks) such as Exaeretodon. These non-dinosaurian herbivores were much more abundant than early dinosaurs. Dinosaur fossils, including those of Eoraptor only represent approximately 6% of the total sample that has been recovered from the Ischigualasto Formation (Rogers et al., 1993), which suggests that dinosaurs were less numerous than other tetrapods









What do you, guys, think about this dinosaur's classification? I was actually thinking that it is a theropod, and I was really surprised to find out that it is not. Like, I would be okey with its classification as a basal saurischian.. But a sauropodomorph? Seriously?
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PostSubject: Re: Eoraptor    Wed Oct 12, 2016 3:54 pm

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