Re: Dinosaur sex

["Steve Brusatte" <dinoland@mailcity.com>]

On Thu, 11 May 2000 12:18:42   Paleoworld wrote:
>After discovering a specimen how do you deduce which sex the dinosaur belonged 
>to?
>Thanks...

This is a good question, and one that was just mentioned in that CNN Sue 
article (Larson thinks Sue was female).

Here are a few highlights of the dinosaur sex debate:

*In 1924 O. Abel proposed that differences in the head crests of Canadian 
lambeosaurines might be accounted for by the sex of the individual.

*In 1991 Ralph Molnar suggested that the presence or absence of a rugosity 
(bone that is enlarged by wrinkles or ridges) on the postorbital could be a 
sexual difference.  But, like Abel, he didn't assign these differences to a 
particular sex.

*While looking a a bone bed of Syntarsus rhodesiensis (Jurassic theropods) 
Michael Raath found that as these dinosaurs reached maturity, their skeletons 
developed into two forms: a heavy and light morphotype.  He found that the 
robust individuals outnumbered the light ones, and concluded that they must be 
female.  

*Ken Carpenter first proposed the existance of sexual morphotypes in 
Tyrannosaurus rex.  He identified differences based upon the humerus and 
ischium, and also found robust and gracile morphotypes.  He also concluded that 
the robust type represented females.  This was based on the shape of the 
ischium in the robust form, which he believes allowed for a wider passage for 
laying eggs.

*Larson and Eberhard Frey found that the first chevron (bone connecting to the 
underside of the vertebrae) is connected to the second caudal vertebrae in 
males, but to the third in females.  In other words, males had an extra 
chevron.  The extra chevron, he proposed, was used as an anchor or base for 
muscles that controlled the penis.  This was seen in crocodiles, and it is 
implied that it may also hold true for dinosaurs.

All of these theories can be read about in several papers by Larson, Carpenter, 
and Molnar, especially Larson's book 'The Rex Files.'

Steve

Steve Brusatte
Dino Land Paleontology
http://www.geocities.com/stegob


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