A paper has come out that examines dinosaurs’ sense of smell by using computed tomography (CT) to measure the size of the relative size of dinosaurs’ olfactory bulbs, part of the brain that deals with the sense of smell. This is one example of the really interesting paleontological questions that can be addressed with modern imaging techniques (hint into my NSF proposal…).
The olfactory bulb is a part of the brain that deals with smell. Quite simply, the larger the olfactory bulb, the greater an organism’s reliance upon smelling. As a group, primates rely less on scent than many other mammals, and so their olfactory bulbs are relatively small. Humans have a greatly reduced bulb compared to other primates. Prosimians, the most primitive primates, have much larger bulbs than other primates. Thus, scent plays a larger role for their ecology, possibly due to the fact that many are nocturnal (there’s less light at night, but smells always abound).
This dinosaur study used this logic to infer that Tyrannosaurus rex (probably the ‘sexiest,’ most over hyped dinosaur ever) had a very strong sense of smell. This has important implications about T. rex–was it nocturnal (like all those scenes in Jurassic Park…)? Did scent play an important social role (like modern scent-marking mammals including prosimians)?
Also cool was how the team examined olfactory bulb and brain size. The importance of an scent can be inferred based on an animal’s olfactory bulb size relative to the size of the entire brain. The study used endocasts (naturally preserved impressions of surfaces) of brains and CT scans of skulls to estimate these sizes. This illustrates the usefulness of computed tomography in paleontology. It can be difficult to study certain aspects of fossils non-invasively. By CT scanning a fossil, a digital 3D image of it is created, and this allows researchers to examine all the surfaces (including interior) of the bone, with much better accuracy and resolution than X-rays. In this way, researchers can create ‘virtual’ endocasts, among other things. CT scanning also makes bone (and other material) of different densities distinguishable, so that fossil teeth and the insides of bones can be examined without having to damage them.
CT data are becoming very important not just in medical imaging, but also biological anthropology (Dana knows lots!). Many anthropologists, including the team I met in Vienna this summer, are using CT data to reconstruct fragmentary fossils, uncover tooth shapes in fossil hominins, study brain evolution with ‘virtual’ endocasts, and many other things. This is a very exciting time for anthropology and paleontology, as modern medical imaging techniques have made it possible to address (and ask) research questions that were not possible in the past. In fact, my current NSF graduate research fellowship proposal is seeks to develop a new method for studying cranial variation using CT scans. If I get it (fingers crossed), I’ll keep you all updated with how the research goes. Here’s hoping!
Zelinitsky D, Therrien T and Koboyashi Y. Olfactory acuity in theropods: paleobiological and evolutionary implications. Proceedings of the Royal Academy B. Corrected proof, in press.