Press Release

Department of Human Genetics
Eccles Institute of Human Genetics
University of Utah

RELEASE DATE: 26 Oct. 1999

contact:
Connie Barth -- (801) 585-6135
Eccles Institute of Human Genetics

Anna Radev -- (212) 850-6484, fax 850-6799 -- aradev@wiley.com
Anatomical Record/New Anatomist

Recent analysis of a fossilized endocast from an Allosaurus skull, and the implications about the nature, behavior and intelligence of dinosaurs, may lend compelling evidence to certain long-standing theories about their existence, relatedness to modern-day species, and possible circumstances precipitating their extinction. A comprehensive analysis of fossilized Allosaurus brain tissue, documented by Scott Rogers, Ph.D., at the Salt Lake City VA Geriatrics Research, Education and Clinical Center, in the October 15 issue of The New Anatomist, presents many clues in the quest to unlock the mysteries of dinosaurs.

Our understanding of the nature and behavior of dinosaurs has relied on fossilized evidence, such as skeletal remains and endocranial cast formations (fossilized casts of the "brain space" inside the skull). Given the rareness of bone fossilization in general and skull fossilization in particular, soft tissue fossilization has proven even harder to find, although it can occur under exceptional conditions. Evidence collected from studying fossils is compared and contrasted with the characteristics of modern day mammalian herbivores and carnivores, allowing researchers to theorize about dinosaur neurobiology and behavior. Fossilized casts (endocasts) often preserve many features from the endocranial space, including location of nerves and blood vessels, as well as the shape and size of the brain, which has traditionally been associated with certain traits, such as a species’ intelligence or ability to adapt to a changing environment.

Dr. Rogers’ recent retrospective analysis of such fossilized remains, uncovered over 30 years ago, is helping to unlock the mysteries of dinosaur survival and extinction, and perhaps provide a better understanding of our own natural world and our own ability to survive. "The implications of this finding opened a new arena regarding the importance of dinosaurs to our understanding of evolution and generated new concepts regarding the origin of birds from extinct dinosaur ancestors," explains Dr. Rogers.

At the Cleveland-Lloyd quarry near Price, Utah, scientists uncovered abundant fossilized skeletal remains, preserved with remarkable detail. Among these was a complete natural endocranial cast. Using new technology, in the form of computer-based imaging and high-resolution optical advancements, Dr. Rogers has probed the endocast in great detail. Spiral computed tomography (CT) scanning has revealed "astounding new insights" into the structure of the Allosaurus brain and its relatedness to existing reptiles and birds, notes Dr. Rogers. He has discerned that the putative brain, which only partially fills the Allosaurus endocast, seems to be almost suspended in the lower portion of the endocast, amazingly consistent with the location of the brain within the skull of modern day reptiles and crocodiles. However, the cerebellum closely approaches the posterior internal endocranial surface, which is consistent with the brain-endocranial relationship found in birds. The dinosaur brain seems to have been a hybrid between avian and reptilian species.

There is also another possible interpretation of this evidence. Because the relationship between the brain and the endocranial space changes with age, and the Allosaurus from which the specimen was removed was not fully grown, this endocast may simply reflect an intermediate state between juvenile and adult brain structures, rather than a combination of features from different modern day species.

The endocast exhibits a notable bulge, consistent with the well-developed optic lobes found in birds, but the bulge does not coincide with the expected location and reflects the presence of considerable internal structures, which is characteristic of reptiles and crocodiles. The vestibular apparatus, which controls balance, is also remarkably similar between the endocast under analysis and the structures present in existing reptiles and crocodiles. The arrangement of this system accommodates rapid movement of the head and suggests that the Allosaurus held its head almost parallel with the ground during normal walking.

The cochlear duct, which coordinates hearing, exceptionally resembles that of crocodiles. This suggests, as notes Dr. Rogers, that Allosaurus was able to hear best at lower frequencies and was less prone to distinguish subtle sounds with higher pitch. Hence, the endocast suggests that the Allosaurus family is linked more closely with present-day reptiles and less directly to birds, a conclusion that poses some challenge to the long-standing hypothesis that dinosaurs are direct ancestors to birds.

According to Dr. Rogers, what may explain this seeming contradiction is that Allosaurus is only one of many species of dinosaurs, including ancestral birds, which are likely to have evolved from a common family, the Archosaurs (ruling reptiles). In relating his findings of Allosaurus to the rise and fall of the Archosaurus family, Dr. Rogers comments that Archosaurs seem to have responded favorably to the relatively mild and environmentally stable Jurassic period, rapidly evolving into many diverse species. Geological changes overtime, combined with alterations in environmental conditions and outside forces no doubt affected the ability of some of these species to survive and flourish while contributing to the extinction of others.

"Evolutionary success can be distilled into two key points: the ability of an organism to adapt both physically and behaviorally" explains Dr. Rogers. Paradoxically, evolutionary mechanisms seem to have been responsible for both Allosaurus’ survival and for its subsequent extinction. Forced to respond to changing demands imposed by their environment, certain species, like the ancestral birds, experienced a progressive increase in the forebrain, accommodating greater cellular density and neurologic complexity. Meanwhile, crocodiles retained a less-elaborated brain and remained largely dependent on sensory acquisition and interpretation.

Dr. Rogers points out that Allosaurus was a dominant carnivore for at least 20 million years, so undoubtedly, it was able to respond to some extent to changes in its surroundings. However, its habitat was that of the open plain, characterized by a relative absence of complex surroundings and little threat from predatorial challenge. Dr. Rogers suggests that the evolution of its brain did not keep up with environmental changes that were taking place, as the climate became more tropical and the Allosaurus habitat became more complex. The author also suspects that new predators, who were better adapted to changing condition may have migrated across land bridges with Asia to challenge Allosaurus for dominance of its terrain.

Dr. Rogers proposes that the fundamental behavioral and physiological traits of Allosaurus that contributed to its survival over a span of 20 million years, may have in the end made Allosaurus too rigid and resistant to change, inevitably leading to its eventual extinction. Darwin’s theory of Natural Selection, which has long ignited controversy and contention amongst leading scientists in the field, may have earned newfound legitimacy in face of the recent analysis of the Allosaurus’ endocast.

"Allosaurus, Crocodiles and Birds: Evolutionary Clues From Spiral Computed Tomography of an Endocast," Scott W. Rogers, Ph.D., THE ANATOMICAL RECORD (New Anatomist) 1999; 257:5, pp. 162-173.