[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Dino dimorphism (Was More tyrant Q & A's)

>Yikes!!  Please be careful of what the dimorphism evidence suggests.  The
>data suggest that one morphotype, interpreted by some as the male, is more
>gracile (i.e., for the same body size, it had more slender bones).  That's
>it.  We do not yet at present have sufficient sample size to establish
>which, if either, sex grew to the largest size.  Just because the specimen
>FMNH PR2081 ("Sue") is a robust form, and is currently the largest known
>specimen, doesn't really count for much: the next two biggest specimens are
>gracile morphs.  Beware of small sample sizes!!

This is an important point that many have missed in the dimorphism debate -
"large" relates to size, while "robust" is a *shape* issue that can be
independent of size.  Giraffe leg bones are more gracile than mole leg
bones, but the former is certainly larger than the latter.

As it turns out, female birds of prey may be larger, but they're usually
more gracile.  (There are some other complications - for example, the size
difference in living raptors diminishes with (a) the amount of carrion in
the diet and (b) the amount of time spent on the ground rather than flying.
Reversed dimorphism is actually quite rare in birds outside Falconiformes
and Strigiformes - some, but not all, ratites, as well as a couple of
seabird lineages, whistling ducks, and a few others.)


Christopher Brochu
Department of Geology
Field Museum of Natural History
Roosevelt Road at Lake Shore Drive
Chicago, IL 60605