Speaker
Dr
Burkhard Schillinger
(Heinz Maier-Leibnitz Zentrum (FRM II))
Description
Only little is known about the brain antomy of the mammalian forerunners, the non-mammalian therapsids, because the brain reconstruction is faced with several problems. The first is that soft-tissue is not preserved. Consequently, information about the shape of the brain can only be deduced from the surrounding bony cavity. A second problem is that the brain cavities of most therapsids were only incompletely ossified. Therefore, the forebrain of most therapsids is only known from slight impressions on the underside of the skull roof. Moreover, it seems likely that the brain often did not fully fill in the braincase as it is also the case in modern turtles and reptiles. Furthermore, nerves and blood vessels were often covered by the meninges and did not leave impressions in the braincase. Consequently, the vascular system of the therapsid brain is almost completely unknown. Finally, fossil skulls are usually filled with sediment and cannot be studied from external. Mechanical preparation is often impossible to avoid destruction of the valuable specimens. For this reasons it is useful to search for therapsid species with well ossified braincases, in which the brain was in close contact to the surrounding bones by means of non-destructive methods for investigation such as neutron radiography.
One “needle in the haystack” we found was the dicynodont *Diictodon feliceps*. A specimen of *Diictodon* investigated at the facility ANTARES at FRM2 in Munich clearly showed impressions of several blood vessels on the inner surface of the braincase. This is an indication for a close contact between the brain and the braincase and enabled us to reconstruct hitherto unknown parts of the vascular system. In this context, the nature of a controversially discussed depression in the braincase, the “unossified zone”, could be clarified. The neutron tomographic images clearly showed that the unossified zone was a terminal chamber of several blood vessels at the level of the hindbrain. Furthermore, the course of another blood vessel, the prootic sinus, could be reconstructed and several passages of cranial nerves could be identified, which penetrated the braincase (Laaß et al., 2017).
Another example is the dicynodont therapsid *Kawingasaurus fossilis*. Neutron tomography showed that *Kawingasaurus* possessed an almost completely ossified braincase. Brain structures such as the cerebral hemispheres left sharp impressions in the brain cavity, which enabled a less hypothetical reconstruction of the forebrain for the first time (Laaß and Kaestner, 2017).
Finally, it can be stated that neutron tomography is a very useful tool in palaeoneurology for the investigation and virtual reconstruction of cranial endocasts of fossil skulls.
References:
Laaß M, Kaestner A. 2017. Evidence for convergent evolution of a neocortex-like structure in a late Permian therapsid. Journal of Morphology. 2017;00:000–000. https://doi.org/10.1002/jmor.20712
Laaß, M., Schillinger, B., & Kaestner, A. 2017. What did the “unossified zone” of the non-mammalian therapsid braincase house? Journal of Morphology. doi:10.1002/jmor.20583.
Primary author
Mr
Michael Laaß
(University Duisburg/Essen)
Co-author
Dr
Burkhard Schillinger
(Heinz Maier-Leibnitz Zentrum (FRM II))
