Re: So Just How Much Could They Bend Their Tail?

[Gerrit Hanenburg <G.Hanenburg@inter.NL.net>]

> > Actually, the tail of Velociraptor appears to have been rather flexible, at
> > least in lateral direction, despite the elongated prezygapophyses. The tail
> > of specimen IGM 100/986 has been preserved in an S-shaped curve.
> >
> > Norell, M.A. & Makovicky, P.J. (1999). Important Features of the
> > Dromaeosaurid Skeleton II: Information from Newly Collected Specimens of
> > Velociraptor mongoliensis. American Museum Novitates 3282: 1-45.
> Its was very flexible indeed, the base of the tail was capable of bending 
> ninety degrees in most directions, and it perhaps severed as balancing rod 
> for changing direction quickly, just as modern cheetahs use their long 
> tails. And to make the tail even more capable of doing so, they had bony 
> tendons along the tail to stiffen it up.

Well, the dynamic stabilizer hypothesis is the usual explanation. However, 
the character appears to be restricted to Dromaeosauridae (AFAIK it has 
been observed in Deinonychus, Velociraptor, Sinornithosaurus, and the 
unnamed specimen NGMC 91described by Ji et al. (2001)), but there are many 
other theropods with an anatomy that suggests a certain degree of 
cursoriality which lack the character. And specimen IGM 100/986 suggests 
that mobility was not restricted to the base of the tail. Also, in NGMC 91 
the tail is clearly lined with a featherlike integument, which seems to 
weaken the dynamic stabilizer hypothesis as this would have significantly 
increased air resistence.

Ji, Q. et al. (2001). The distribution of integumentary structures in a 
feathered dinosaur. Nature  410: 1084-1088.

Gerrit