Re: [asa] Did dinosaurs become chickens?

This is informative. Thanks.

My general reading in recent years leaves me with the impression that not all expert paleontogists buy into the bird-from-dinosaur idea. I'd appreciate a comment on the status of that controversy.

Don

  ----- Original Message -----
  From: kbmill@ksu.edu<mailto:kbmill@ksu.edu>
  To: asa@calvin.edu<mailto:asa@calvin.edu>
  Sent: Friday, January 30, 2009 8:41 AM
  Subject: Re: [asa] Did dinosaurs become chickens?

> A naive question. How can dinosaurs evolve into chickens if the
> extinction of dinosaurs occurred suddenly?

  Two different questions, I will respond to the one above first.
  Taxonomy is the procedure for assigning names to species and to groups
  of species. The field of systematics involves developing the criteria
  by which organisms are grouped into a heirarchy of categories. There
  are different competing methodologies for how this is done. The most
  influential systematics being used today is cladistics. Using
  cladistic proceedures, birds (all birds) are a subset of the dinosaur
  group. In this classification, birds ARE dinosaurs. Therefore,
  dinosaurs as a group did not go extinct at the end of the Cretaceous.
  However, if you used the older "evolutionary" classification system or
  the still older Linnean classification system , birds were grouped as a
  separate class. Using that classification, dinosaurs did go extinct.
  It is important to understand that classifying birds in a separate
  group does not imply that they are unrelated to dinosaurs.

  In response to the question in your subject line: The fossil evidence
  for the evolution of birds from the maniraptoran group of dinosaurs
  (Oviraptors, Troodontids, Therizinosaurs, Dromaeosaurids) is very
  extensive and rapidly increasing. There are now numerous dinosaur
  specimens that show transitional characters with the earliest birds.
  Various maniraptoran dinosaurs (especially the Dromaeosaurids)exhibit
  nearly all of the diagnostic skeletal features of the earliest
  unquestioned birds. As with other cases in which there is a good
  fossil record, there are specimens whose proper classification is in
  question. Paleontologists talk of avian and non-avian dinosaurs - the
  the distinctions are sometimes very subtle and disputed. The origin of
  birds from maniraptoran dinosaurs has been given increased support with
  the discovery of non-avian dinosaurs with various filamentous and
  feather-like body coverings. Some even have true feathers, and a few
  (eg Microraptor) may have been capable of gliding flight.

  I discuss some of this in my book chapter on transitional forms in
  "Perspectives on an Evolving Creation." However, even since the
  publication of that book in 2004, there have been many new fossil
  discoveries that have further filled in and illuminated the
  maniraptoran - bird transition.

  Keith

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Received on Sat Jan 31 02:51:49 2009