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Re: Re: ribs

>Mickey's question stirred a similar question in me. I have been curious about
>the function of the "riblets" down the belly of T.rex and family. They seem
>small and fragile to present very much protection against a Triceratops'
>for instance :) and if T.rex rested on its belly, you would think that its own
>weight would break these 'ribs' (or were they flexible?). They are not
>curved, but seem to twist to make sharp projections that would seem dangerous
>to its owner (or were they twisted during fossilization?).

These "riblets" are called gastralia, and are sometimes referred to as the
"belly ribs".  They are a primitive feature associated with the muscles of
the belly and chest.  The reason dinosaurs had them is that they hadn't lost
them (I know that sounds like a cheat of an answer, but unless a character
is modified, it will stay on in its descendants).  Gastralia can still be
found in many living reptiles - look at the skeleton of almost any lizard if
you access to one.  Many groups have lost gastralia throughout vertebrate
history, including mammals.

I don't know about the "pointy" ones you've seen, but generally gastral ribs
are paired (in some cases in three rows) and so can move along jointed

Thomas R. HOLTZ
Vertebrate Paleontologist, Dept. of Geology
Email:Thomas_R_HOLTZ@umail.umd.edu (th81)