Staurikosaurus
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Extinct (fossil)
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| Staurikosaurus pricei Colbert, 1970 |
Staurikosaurus is a genus of dinosaur.
[edit] Discovery
There exists only a single specimen of Staurikosaurus ("Lizard of the Southern Cross"), recovered from the Santa Maria formation in Rio Grande do Sul, southern Brazil. The name refers to the star constellation "The Southern Cross", only visible in the southern hemisphere - when Staurikosaurus was found in 1970, it was unusual to find dinosaurs in the southern hemisphere. It was first described by Edwin H. Colbert, working at the American Museum of Natural History.
[edit] Description
Staurikosaurus was a small theropod from the Middle Triassic, 231 to 225 million years ago - specifically the Carnian age. It is one of the earliest dinosaurs that is known. At just two metres in length, 80 cm tall and weighing just thirty kilograms, Staurikosaurus was tiny in comparison to later theropods like Megalosaurus. Although its teeth and posture suggest it was an omnivore, some paleontologists prefer to classify Staurikosaurus as a sauropod like the later Diplodocus due to its prosauropod-like skeleton. It seems to represent a transition period as one of these sub-orders evolved from the other. However, another fossil (as yet unnamed) was found in 1984 in Arizona's Painted Desert that was such a typical prosauropod that it seems that the group evolved before Staurikosaurus. Newer research seems to confirm that Staurikosaurus and the related Eoraptor and Herrerasaurus are definite theropods and evolved after the sauropod line had split from theropoda.
There exists very incomplete fossil record of Staurikosaurus, consisting most of the spine, the legs and the large lower jaw. However, dating from such an early period in the dinosaurs' history and being otherwise so primitive, most of Staurikosaurus' other features as being primitive also can be reconstructed. For example, Staurikosaurus is usually depicted with five toes and five fingers - very simple features of an unspecialised dinosaur. However, since the skeletal structure of the legs is known, it can be seen that Staurikosaurus was a quick runner for its size. It also had just two vertebrae joining the pelvis to the spine, a distinctly primitive arrangement. The tail would have been long and thin to balance the border - later sauropods had larger, shorter tails relative to their weight.
The recovered mandible suggests that sliding joint of the jaw allowed it to move backwards and forwards, as well as up and down. Thus smaller prey could be worked backwards towards Staurikosaurus' throat, along its small and backwards-curving teeth. This feature is common in theropods of the time, but disappears in later theropods who presumably had no need for efficiency in eating smaller prey.
[edit] Classification
- Order - Saurischia
- Sub-order - Theropoda (Subject to some debate - see above)
- Family - Staurikosauridae
Since one specimen of Staurikosaurus exists, evidently only one species is known. That is Colbert's original S. pricei. This is named for Colbert's fellow paleontologist Llewellyn Ivor Price. However, there are some related staurikosaurids, such as Chindesaurus bryansmalli, named by Murray & Long in 1985. This was from a similar time period and has been found in Arizona and New Mexico. This suggests that staurikosaurids spread widely across Central Pangaea.
