Re: Ratio of Saurischians/Ornithischians

[Amado Narvaez <anarvaez@umd5.umd.edu>]

On Tue, 20 Jun 1995, Paul Willis wrote:

> I'm not sure that the ratio of members of one clade verses the numbers of
> another clade have any significance. I can't see that there could be any
> useful result from asking why there are so many species of bird compared to
> the number of crocodiles in the world. Their differential success is
> independant of their relationship to the other group. Similarly, why would
> there be a relationship between the number of saurischians to
> ornithischians? Have I missed some subtle point here?

The saurischian/ornithischian question came to mind while I was debating 
whether to teach this distinction to the kindergarteners at my school. It 
was to be part of a sorting exercise, where they were to take a set of 
dinosaurs from the Carnegie models and sort them as "lizard-hipped" or 
"bird-hipped." There seemed to be a predominance of saurischians, 
especially in the Jurassic. The natural curiosity of children leads to 
the question "Why?" For example, did plant-eating ornithischians adapt to 
the food of flowering plants better than most saurischians, which might 
account for the seeming rise of ornithischians in the Cretaceous? (And I 
admit -- I'm a "big" kid myself -- and I want to know why.)

Of course, part of the explanation might be that the selection in the 
Carnegie series slants the statistics in one direction over the other.

While on the subject of lizard and bird hips -- Any suggestions for how 
to explain to primary level kids that birds evolved from lizard-hipped 
dinosaurs and NOT bird-hipped? Do I tell them that "bird-hipped" was an 
unfortunate choice of words based on superficial similarities (re-phrased 
of course in terms and metaphors that they can understand)?

Finally, demographics of a population is just... interesting. Even if 
there is no real reason that saurischians outnumber ornithischians (or 
vice versa), the information would be... interesting. Whether the 
information would be useful in any way is debatable. 

Curiously,
Amado Narvaez
anarvaez@umd5.umd.edu