Re: DINOSAUR digest 695

[Stephen_Gatesy@Brown.edu (Steve Gatesy)]

On Sun, 21 Jun 1998 Matthew Troutman responded to this question from Tracy
Ford:

>>2). Are tail feathers really needed to fly? I know birds do use them to
>>break and manevor, but just to fly around, is it really needed?
>
>Gatesy and Dial* have done lots of work on this issue.  Basically in a
>bird's body there are three locomotor modules (locomotor
>module="anatomical subregions of the musculoskeletal system that are
>highly integrated and act as functional units during locomotion" Gatesy
>and Middleton 1997;308), pectoral, caudal, and hind limb.  Gatesy and
>Dial have shown that the tail functions as a locomotor module during
>flight..............(my editing)................Gatesy and Dial also
>produce a cladogram based on their observations (and they show
>dromaeosaurs with one locomotor module, they really have two).

I appreciate Mathews clear citation of my work with Ken Dial and Kevin
Middleton- a good lesson to us all on this list.  However, I want to
correct something that may have been unclear and question one of his
assertions.

First, Ken and I did not "produce a cladogram based on their observations".
We merely reproduced a simplified cladogram of Sauria based on the work of
Gauthier, Sereno, Chiappe and others.  We used this cladogram to study
theropod locomotion, not the other way around.  I would never produce an
hypothesis of relationship based on modules or any other single character.
In fact, I've never produced a cladogram for theropods and intend to leave
that to those who do it best.

Second, as we discuss in the Evolution paper and elsewhere, the tail of
dromaeosaurs was more functionally decoupled from the hind limb than in
basal theropods, but not as liberated as in birds.  Designating the tail as
an independent module is a judgement call, but one we would defer until it
took on aerodynamic function.  Obviously, there is a gray area when
discussing concepts such as modules, but a functionally independent tail in
a terrestrial animal is more difficult to identify.

Steve Gatesy

Stephen M. Gatesy
Dept. of Ecology & Evolutionary Biology
Box G-B209
Brown University
Providence, RI 02912
401-863-3770
401-863-7544 (fax)