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Tucson Tales II.



Tucson Tales II. "Birds of a feather"

One of the reasons the Tucson show is a fun place to be is the
"birds of a feather" factor. Many attendees share a common
interest in natural history and jump at the chance to discuss
the hot topics of today.

One of these topics is actually an old topic that has been revived
in recent years, the bird-dinosaur connection. Of the many impromptu
discussions I had at Tucson, the several bird-dino talks I shared with
other attendees was the most interesting for me. In this "Tucson Tale",
I'll give a short background of the debate and present some new ideas
which are highly speculative, but fun nonetheless.

The conventional wisdom of today is simple. Birds _are_ dinosaurs.
Protoavis has drawn a steady barrage of fire ever since Sankar
Chattergee first proposed it as the earliest bird. The debate has
been an enlightening one in many ways, as the participants have
had a difficult time staying purely scientific in their exchanges.
Some have delivered scathing attacks on Chattergees field
methodology, promptness of publication, and poor science.
Others have defended Chattergee in the light of the seemingly
overzealous criticism of his work.

One camp is led by the so called "cladists", such as Kevin Padian
(U of Cal/Berkeley) and Jaques Gauthier (Cal Acad of Science).
They are pioneers in computer-aided cladistic analytical techniques.
They've spent alot of time in past years assembling a large body of
evidence that in their eyes demonstrates that birds _are_ dinosaurs.
Another major voice advocating the strong dino-bird link is John
Ostrom (Yale, Peabody Museum), who actually laid the foundations
for the modern dino-bird interpretations in the 1970's. He noticed
strong anatomical similarities between archaeopteryx and a dinosaur
he had excavated some years earlier, deinonychus.

The other camp (currently the minority view) is that birds are actually
more closely related to the crocodilians. This view is held by ornitho-
logist Larry Martin (U of Kansas). He believes that the true ancestral 
stock to modern birds is to be found in the thecodontia, and Protoavis 
as described by Chattergee generally fits within the scope of his theory. 
He does not, however, agree with Sankar's conclusion that Protoavis was 
a feathered flyer.

---
One morning at the Quality Inn (Tucson) I went to the lobby and picked
up some informational booklets. One of them was called the "Big Rocks
Trader". While flipping through it I noticed an article entitled 
"Scientist and Son find Ostrich Dinosaur". It turns out that the 
scientist is none other than Sankar Chattergee!

They claim to have found:

        - a toothless therapod they refer to as an ostrich dinosaur
          (I assume it's an ornithomimid).
        - they named it Shuvosaurus inexpectatus after Sankar's son
          Shuvo, and described it as a seed and nut eating therapod.
        - it's claimed to be the oldest known "ostrich dinosaur",
          dating to the triassic at around 225 mya.

  [ALERT] This predates other ornithomimid fossils by ~140 MILLION yrs.

Does anyone else see a pattern to Chattergees work? First, he finds
a fossil that has features one would expect from a cretaceous bird
(I refer to Protoavis), but it comes from triassic mudstones near
Lubbock and thus pushes back the date of the earliest bird by around
70 million years. Now, he finds an ornithomimid which predates any
other by 140 million years in those same mudstones. The simplest
explanation for this is that he is actually finding a typical cretaceous
faunal assemblage and somehow misdating the fossils. There are geological
mechanisms(such as sinkholes/caves or unusual faulting and displacement)
that can redeposit fossils from a younger sediment layer to an older one 
and not be obvious, even to experienced fieldworkers. Might Sankar be 
finding some renegade cretaceous fossils in the otherwise triassic horizon?

So what are the implications _IF_ this hypothesis is correct?

a) Sankar Chattergee

        - is correct that Protoavis is a bird displaying somewhat
          advanced avian features.
        - is incorrect that this bird is of triassic age (225 mya).

[comment] Chattergee may be a better scientist than the cladists
          have given him credit for, his major mistake would be
          the misdating of fossils. He also may have shown the
          the least amount of bias in terms of how he interpreted
          Protoavis, he called it as he saw it.

b) The "Cladists"

        - are correct that Protoavis is not the earliest bird.
        - may be incorrect that Protoavis is not a bird fossil
          but represents several different non-bird animals.

[comment] They may have let their biases get in the way of their
          scientific methodology themselves. They were adamant
          that a triassic bird could not exist (because birds _are_
          dinosaurs and you can't be as old as you ancestor) and they
          resorted to methods other than what the evidence warranted.
          Of all the criticisms about Chattergee and Protoavis, none
          of the cladists have suggested misdating as an explanation.
          They seemed determined to show it wasn't a bird no matter
          what it looked like, when perhaps they should have been
          questioning the AGE of the fossil, not it's affinity. If 
          Protoavis was presented to them as a cretaceous fossil, they 
          may well have have embraced it as a bird and trumpeted it 
          as further evidence for the dino-bird connection.
        
c) Larry Martin

        - is correct that Protoavis is a bird fossil.
        - might be incorrect that Protoavis could not fly.

[comment] Although he could accept a triassic bird, a full-flighted
          triassic bird might not have been within his expectations.
          In fairness, he actually didn't totally rule out flight,
          he just didn't see sufficient evidence to convice him that
          the feather "nodes" reported by Chattergee were real.
          Under pressure, he gets high marks for recognizing the
          truly avian characters and agreeing with the bird classification.
                
Here's a few questions to stimulate some discussion:

        1) Which classes share a closer common ancestor, birds-dinos
            or birds-crocodilia?

[This may seem to have already been decided in favor of the birds-dinos
but don't bet the farm before checking out Larry Martin's work.]

        2) At what approximate point in _geological_ history does the avian
            ancestor share a common ancestor with the dinosauria?

[Some of the cladists have suggested cretaceous, as the dinosaurs most
birdlike in the cladistic analyses are of cretaceous age, but what about
a fully flight-feathered archaeopteryx in the jurassic and modern DNA
analysis suggesting that a proto-bird ancestor most likely existed much
earlier than archie?  Don't rule out a thecodont as the dino-bird close
common ancestor just yet.]

        3) How many of the bird-dino anatomical similarities (characters)
           are attributable to convergence vs inherited from a common
           ancestor?

[The cladists tend to lean heavy toward the common ancestor but beware,
bipedalism and the occupation of same niches may complicate things.]

End Tucson Tales II.