STL Science Center

STL Science Center

18 January 2014

Skulls and Horns

Photo by Bob Ainsworth (Oklahoma Museum of Natural History)
The horns I mentioned yesterday consist of dorsal extensions of the lacrimals which make up the posterior boundary of the antorbital fenestra and the anterior boundary of the orbits. Much of the rest of the skull is typical of theropods, though there are characteristics of the skull that are unique to Allosaurus. The fleshed out Allosaurus appears slightly less ostentatious than the skull does as far as horns are concerned; however, the horns are not all that crazy and extended to begin with, so ostentatious appears a bit extreme in describing them. As with other theropods with cranial ornamentation, these could have been species and individual specific anatomical characters that influenced sexual selection and intimidation of rivals. There is no evidence that suggests these horns had any indicative features related to sexual dimorphism. In fact, the only noted sexually dimorphic characters are found in the pelvic region of the skeleton.

©Charles R. Knight
The Allosaurs of Charles R. Knight did not have horns on their lacrimals. That seems rather strange given that the lacrimals of Allosaurus were always there and known after the first skulls were completely recovered. Some small ridge detail is evident in this image, as in other Knight depictions of Allosaurus, but it was a normal system of illustrating Allosaurus at the time (see Rudolph Zallinger's version also). The ridge details visible in the Allosaurus of Knight are indeed small, but are there. The body has issues as well, but we are only worrying about the skull here, and there really are not that many problems with the old illustrations of the skull. The massive ear membrane may or may not be ccurate, but we will not worry about that until we have a mummified Allosaurus to compare it to.

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