Re: Fossil Discovery Threatens Theory of Birds' Evolution

[Ronald Orenstein <ornstn@home.com>]

> First of all, spirula, ain't a squid, it's a cuttlefish of sorts, and it's
> internal shell looks exactly like an ammonite. quite simply a perfect example
> of convergance giving the appearence of a nearly exact copy.

Cuttlefish are a sort of squid, or at least a member of the Decapoda.  The 
shell of Spirula bears some resemblance to that of an ammonite but is 
hardly "exactly" like one (for example, it does not have the extremely 
complex folding of the septa that is very much a distinguishing feature of 
ammonites). Anyway its spiral shape is a pretty basic one in nature, and 
ammonites and spirula belong in the same class anyway, so the convergence 
involved seems to me interesting but not all that remarkable.  Anyway, I 
still do not see the relevance of your point in bringing it up.


> The graphotite-like colonies we've both mentioned is another example of such
> convergance. I've never said that these look anything like theropods as you
> seem to be saying. Can nearly exact duplicates evolve completely seperately?

Um... I didn't say that either, and the term is "graptolite".  And what are 
graptolites supposed to be convergent to?

I think the answer to your question depends, though, on what you mean by a 
"nearly exact duplicate" and on how complicated the structure is you are 
talling about.  Bumblebee hairs, for example, look very much like mammalian 
hairs, but the resemblance is actually quite superficial and does not 
extend to details of structure or composition.  Is it a "nearly exact 
duplicate" or just a superficially similar (and basically pretty simple) 
structure?

--
Ronald I. Orenstein                           Phone: (905) 820-7886
International Wildlife Coalition              Fax/Modem: (905) 569-0116
1825 Shady Creek Court
Mississauga, Ontario, Canada L5L 3W2          mailto:ornstn@home.com