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Re: Ancestors and descendants (story for Nick)



Ken Kinman wrote:

Although
there would be some shared features between the deinonychus and the bird, I
think I would be even more struck by the large number of differences between
the bird and all the saurischians.

This is true. The "phenetic gap" (as you put it) between, say _Ceratosaurus_ and a pigeon is quite large (although how you put a value on it, I'll never understand). However, the number of differences between _Deinonychus_ and _Archaeopteryx_ are far fewer. Of the differences you listed (below) between a modern bird and _Deinonychus_, very few apply to _Archaeopteryx_. Many are not seen in Cretaceous birds. Yet you excise all the Aves - including _Archaeopteryx_ - from the Theropoda.



    Look at this thing, it's arms have turned into wings, it's lost its
front claws and teeth.  For Heaven's sake, there's hardly any tail
left---just a stubby little pygostyle.  It has a laterally facing shoulder
joint and the feathers are asymmetric, I bet this beastie can fly.
[snip]
Oh yes, and look at all these flight adaptations, deep thorax with a
strut-shaped coracoid, a triosseal canal with the tendon of the
supracoracoideus muscle (great for wing rotation). See the elastic furcula,
deep sternal keel, and look at those pectoral muscles----this is a very
strong flier (those pterodactyls will be so jealous).

Yes, the pterodactyls will be *very* jealous. Despite the profound changes to their skeleton and the presence of body hair*, Ken Kinman won't give them their own Class. Yet those new-fangled, upstart flying theropods do. Confound them!!


* (hair-like integumentary structures, present in at least some pterosaurs.)

With all these
derived features, we can hardly call this a dinosaur even if it does share
some features with them. This bird beastie has been doing some serious evolving.

Grrr.

I think you may be missing the point. Ken, you are subjectively separating a descendent group from its ancestors - birds from theropods. And (as far as I can tell) you are doing so on the basis of certain perceived evolutionary novelties which somehow denotes that birds have achieved some higher level of existence than mere reptiles.

The modern bird form represents a cumulation of the novelties you mention, all of which were acquired step by step. Birds didn't appear by some sudden gust of evolution - _Archaeopteryx_ and other fosil birds show this. (And besides, evolution doesn't work like that.) Here you are with your mental calipers, trying to measure "phenetic gaps" between related families, trying to determine into which Order (or Class) each family should belong to. What a messy process! And such a darn waste of time and effort!

This thing
is almost as weird as that hairy mammal thing we found last week---you know,
the one with the three shrunken jaw bones shoved up into it ears,

What if a fossil therapsid shows two "shrunken jaw bones" in its ears, and the third in the process of migrating there? Is it a mammal or a reptile? How much agonising will you go through in measuring these s-called "phenetic gaps" to determine which Class it belongs in?


This "Eclecto-Cladistic" method (or whatever it's called) combines the *worst* aspects of Linnaean and cladistic phylogenies. It retains the clunky and subjective hierarchies of the past, but lacks the explicit representation of relationships inherent in cladistics. And don't try and tell me that because Linnaean hierarchies have been around for hundreds of years it's a good reason to keep them. You could use the same argument in favor of slavery.

Rant complete.


Tim

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