Mamenchisaurus tail club, again
March 30, 2010
In color, this time, with multiple views, thanks to Xing et al. (2009). They also did a finite element analysis of the tail club and concluded that it was a fairly pathetic weapon. Xing et al. closed by supporting the contention of Ye et al. (2001) that the tail club was a sensory organ. As they stated at the end of the abstract:
The tail club of Mamenchisaurus hochuanensis probably also had limitations as a defense weapon and was more possibly a sensory organ to improve nerve conduction velocity to enhance the capacity for sensory perception of its surroundings.
One thing Xing et al. (2009) cite in support of this is the expanded neural canal inside the club, which they compare to the sacral enlargement in stegosaurs and to the glycogen bodies of birds. They rule out a glycogen body on the grounds that the sacral enlargement in stegosaurs is much bigger than the brain volume, whereas the neural canal enlargement in the M. hochuanensis tail club is much smaller (if you don’t follow that logic, don’t worry, neither do I).
I’m not sure what to make of this thing. On one hand, it would be nice to have more than one club available to rule out the possibility that it’s just a weird paleopathology. On the other hand, it looks oddly regular to be pathological, and the definitive clubs in Shunosaurus and Omeisaurus are at least weak support for this being a genuine feature, although the clubs of the former taxa look very different.
Furthermore, I don’t understand how the authors can rule out the presence of a glycogen body based on the size of the neural expansion alone–especially since the functions of glycogen bodies in extant taxa are very poorly understood (as you may remember from this dustup). Nor can I fathom how a titchy little nerve bundle–if such existed–down at the end of the tail could do much to improve nerve conduction velocity up the rest of the tail. Either my understanding of neuroscience is completely shot, or this hypothesis…lacks support. I am open to being enlightened either way.
Finally, I am disappointed that the authors didn’t pursue the cutting-edge pseudohead hypothesis that has figured prominently here and elsewhere in the blogosphere. There’s a Nobel lurking in there, I just know it.
- Xing, L, Ye, Y., Shu, C., Peng, G., and You, H. 2009. Structure, orientation, and finite element analysis of the tail club of Mamenchisaurus hochuanensis. Acta Geologica Sinica 83(6):1031-1040.
- Ye, Y., Ouyang, H., and Fu, Q.-M. 2001. New material of Mamenchisaurus hochuanensis from Zigong, Sichuan. Vertebrata PalAsiatica 39(4):266-271.