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>If more or less modern-style birds go back as far as the jurassic, what
>then, and where, is the link between birds and those dinos that have the
>most bird-like features? And weren't most of these dinos from the
>cretaceous? Is archeopteryx now out of the loop?
1) There are no modern-style birds of the Jurassic, nor in the Cretaceous.
Archaeopteryx is barely avian, sharing only a few cranial features with
birds that are not found in dromaeosaurids (feathers may or may not have
been present in the latter).
2) The record of small theropods (and indeed for most dinosaurs) of the
Middle Jurassic quite frankly sucks rocks. It's not until the Late
Jurassic that the record picks up again, and the advanced coelurosaurs are
definately present by then.
3) It is true that the dromaeosaurids (that group of theropods which shares
the most derived features with birds) are known mostly from the Cretaceous,
but potential dromaeosaurid fossils are known from the Late Jurassic.
Additionally, absence of evidence (of dromaeosaurids in the Middle
Jurassic) is not evidence of absence.
[This particular argument, "no dromaeosaurs are positively identified
before the Cretaceous", is a favorite of anti-dinosaur origin stalwarts.
Nevertheless, their own favorite "ancestor", cursorial/arboreal small
crocodylomorphs, are also not known from this time period. The reason is
probably not because neither group was around, but because there are very
few good fossil sites of Middle Jurassic age].
4) There is still no positive evidence that removes Archaeopteryx from an
ancestral position for birds.
Thomas R. Holtz, Jr.
Vertebrate Paleontologist in Exile Phone: 703-648-5280
U.S. Geological Survey FAX: 703-648-5420
Branch of Paleontology & Stratigraphy
MS 970 National Center
Reston, VA 22092