There are two types of skulls found in caecilians zygokrotaphic and stegokrotaphic. This study aimed to test which skull was better suited for a fossorial lifestyle. The study involved capturing adults of six different caecilian species with three of each skull type. The caecilians were killed and their skulls were scanned into a computer modeling program. From their all zygokrotaphic skulls were changed to stegokrotaphic and additionally akinetic (more voxels than stegokrotaphic and possibly present in Paleozoic caecilian ) and vice versa. They then measured forces on the skulls at different skull angle positionings to see which skulls were best adapted. The skulls were first rotated so that in lateral view the rostral tip of the nasal capsule was in line with the farthest tip of the occipital condyles. This was defined as 0 degrees. The skulls were then rotated from –15 degrees to +15 degrees all during simulated burrowing. All species were found to have an optimal angle between 0 and 6 degrees. It was found that the different skull types did not show a measurable difference in terms of burrowing performance. However the akinetic skulls were found to have overall lower energy straining ability explaining why they are no longer found in present day caecilians. It was also found that the ventral skull bones were most likely to evolve to meet the demands of support in burrowing as they bared most of the force. This is very interesting research combining the power of new technology with addressing much older evolutionary questions. There has been a lot of debate in the field of herpetology as to which skull type zygokrotaphic or stegokrotaphic is ancestral. This study supports that the stegokrotaphic did not evolve from ancestral zygokrotaphic skull to better support burrowing as was the previous skull of thought.
Thomas Kleinteich, Hillary C. Maddin, Julia Herzen, Felix Beckmann and Adam P. Summers
Journal of Experimental Biology
http://jeb.biologists.org.nuncio.cofc.edu/content/215/5/833.full.pdf+html
1 comment:
Very interesting research! How do the two skull types differ? Is one more ossified or reinforced (and would therefore have been predicted to be better suited for burrowing)?
Post a Comment