STL Science Center

STL Science Center

06 August 2014

Shortening and Reducing

The forelimbs of Eodromaeus are shorter than the forelimbs. We expect as much when we are told that an animal is bipedal. We also expect it in theropods, regardless of how basal they might be. As we know and have seen over the past few years here, reduction of digits and shortening of the forelimb in theropods are common evidences in the evolutionary history of theropods. Eodromaeus, despite its rather basal placement on the theropod family tree, was no exception. Digits IV and V on the hands of Eodromaeus were noticeably shorter than the other digits and the forelimbs themselves were noticeably shorter than the hindlimbs. The center of gravity of the animal was shifted backwards toward the hips even further with the long balancing tail extending behind Eodromaeus. All of these characteristics, in addition to a "runner's leg" point toward an animal that may have been rather quick on its feet. Estimates of that speed, however, have not been made at this point through functional studies. Conservative estimates, though, have assumed that a speed of approximately 30 kph (19 mph) is acceptable. This is pretty impressive given its size of approximately 5 kg (11lbs) and 1.2m (3.9 ft) in length and that it was only about as tall as a Border Collie.

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