The use of computer tomography in paleontologic research

The cave hyena Crocuta crocuta spelaea is quite common in European caves. Its fossil record—even if not nearly as rich as that of the cave bear—has led to common theories about its life and habitat in glacial Europe. Different systematic characteristics were used for comparison of these fossil hyenas with recent living hyenas in Africa and Asia. Some of these studies produced good results, using both cranial and post-cranial fea- tures. One special trait was discovered in living hyaenids even before the analysis of fossil material. In all of the recent hyaenine hyaenids (which comprise of Crocuta crocuta crocuta,Hyaena hyaena and Parahyaena brunnea) there are very large developed nasal sinuses overlapping the cranial region of the skull.
The nasal sinus cavities are common in every land living mammal to a greater or lesser extent. In carnivores the frontal sinus is normally well developed but thins out in the dorsal area. The sinal cavities of carnivores normally overlap the endocranium by about one third. In hyaenine hyaenids the dorsal part of the sinal cavities reaches far over the endocranium, sometimes overlapping it completely. The background of this unique feature is not known, though some more or less plausible theories exist.
The same vaulting of the skull can be found in fossil specimens of Crocuta crocuta spelaea. The development of the cavities is similar to recent hyenas, but some small differences are visible with the unaided eye. Upon this a theory was built to compare the sinal cavities in fossil and recent material in search of another taxonomic or systematic feature.
The main problem for a long time was the impossibility of measuring these cavities in any rational way. Unlike the endocranial cavity which is well accessible through the foramen magnum, the sinal cavities lack such a simple access route. For a long time the only way to acquire data about these traits was using roentgen technology or breaking open the skull to get access to it. While x-rays where at least useful to measure distances, the three-dimensional features of the nasal sinuses where completely lost. Cutting a skull open to get direct access to the cavities was, on the other hand, not an option for precious fossil specimens, and thus also an unavailable method.
With the invention of computer tomography in the late 1970’s a new possibility was opened up for acquiring data about these unusual skull-traits. With CT-technology it was possible for the first time to make exact three-dimensional doubles of the scanned object without damaging it. Especially scanning inanimate objects, like the different specimens we studied, yields very good results for further research.

We scanned 17 skulls of recent hyenas (15 spottet hyenas and 2 striped hyenas) and 5 skulls of fossil cave hyenas with the computer tomograph and produced virtual endocasts of the sinal cavities and the brain cavities. We then compared these virtual endocasts by descriptive and statistic means.
You can see some of the resulting images below, to get an impression of the work. The images display photographs of the original skulls with corresponding virtual endocast of the nasal and frontal cavities.

The complete work was incorporated into a master thesis, you can find here:
[1.3MB] Comparison of Crocuta crocuta crocuta and Crocuta crocuta spelaea through computer tomography