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Re: How Did Hadrosaurs Survive?



Tim Donovan wrote:

>    With the exception of that Hell Creek lambeosaur recently reported. But
> it was found stratigraphically low, and certainly seems rare, so maybe
> lambeosaurs were essentially gone by the Lancian.
    I have had a chance to discuss this specimen with the authors of that
poster twice. They are good fellas who are doing a responsible job with very
little material, but I can't say they have an open-and-shut case. I'd rather
not discuss my opinion, nor the details in public, since it isn't my work.
Let's just say that IT ISN'T PUBLISHED, therefore IT ISN'T SCIENCE. I
recommend you avoid using this data. And yes, for the record, abstracts,
IMHO, are not really published (they aren't peer-reviewed, you can't name
new taxa in them, etc.). I know there are some cases where an abstract
simply presents small, unequivocal bits of information, and there isn't much
point in ignoring it... this is NOT such a case.

>    It has been known for years that Buffetaut identified an ankylosaur
> specimen from the Wangshi as Pinacosaurus, [...]
       And what was the basis for this identification? As I recall, the
specimen (discussed in the 6th Mesozoic Terrestrial Ecosystems volume) is
the butt-end of a vertebral column originally identified by Wiman as
hadrosaurian. There might be more... I found this reference:

    BUFFETAUT E. (1995): An ankylosaurid dinosaur from the Upper Cretaceous
of Shandong (China). Geol.Mag. 132(6): 683-692

     ...but this appears to be a non-existant paper (!). If you know of
more, I'd very much like to hear of it.

    In any case, have you considered why Buffetaut might have called it
Pinacosaurus, and do you think his identification is reasonable? Not that I
don't think postcrania can be diagnostic, but if that dinobutt is all there
is, do you really consider the evidence sufficient for ankylosaur
identification? For that matter, what is your opinion of land vertebrate
biostraigraphy? Even if this is the same species as in Mongolia, are you
willing to base your theories on a correlation drawn from the co-occurence
of a single taxon? If I look in the biogeography section of The Dinosauria,
and note that Edmontonia longiceps and Euplocephalus tutus are present in
both the Judith River and Horseshoe Canyon formations, should I then
confidently correlate these units?

> [...] which argues for a Barungoyotian
> age i.e. early Barungoyotian, inasmuch as Pinacosaurus was apparently
> supplanted by Saichania and Tarchia in the Barungoyotian beds which
directly
> underlie the Nemegt.
    Supplanted, or perhaps its range simply shifted... vertebrates don't
exist in the stratigraphic record in only one dimension (up). The patchy
distribution of living vertebrates in two dimensions, and uncertainties
regarding facies associations of land vertebrate fossils in three
dimensions, are two of the many reasons why land vertebrate biostratigraphy
is untrustworthy.

> Lambeosaurs ranged well inland in Mongolia since the
> time of Bactrosaurus, and [...]
    You may not be up on the most recent literature: Bactrosaurus is almost
certainly not a lambeosaurine. Godfroit et al. put the big spike in the
vampire's chest in 1998. I don't know of anyone who seriously works on
hadrosaurs who clings to the idea that it might be a lambeosaurine, but it
is possible SOMEONE still doubts (the truth is out there, after all).

> probably continued to do so in the Barungoyotian
> period, given tracks at Abdrant Nuru and elsewhere.
    I wouldn't be surprised. The little buggers get in everywhere! :)

>  If the Wangshi and
> Tsagayan were of Nemegtian age, why didn't their primitive lambeosaurs
range
> into Omnigov etc?
    What primitive lambeosaurines? I see these units as having nice, happy,
freaked-out, possibly Parasaurolophus-like, perfectly bizarre lambies. What,
would you say, is primitive for a lambeosaurine? Just curious...

> They must have been supplanted by a Nemegtian community
> composed largely of American immigrants such as Saurolophus c mid
> Maastrichtian.
    You seem awfully sure of this. Bear in mind that the stratigraphy and
systematics of Asian dinosaurs is in its infancy. I really wouldn't hang too
much inference on the signs and portents wedged into the loose cracks of
papers written over a period of decades, during which time modern methods
were themselves in their infancy. At best, the situation in Asia is poorly
understood. It is nice to construct biogeographic models to guide
research... we all do it. However, I would advise against becoming so
wrapped up in models based on such poor primary data. Especially when some
of that data is land vertebrate biostratigraphy...

    I don't mean to be mean: we all want to make sense of dinosaur
biogeography in general, and specifically what was going on in Asia.
However, the data really aren't there to support hard-and-fast conclusions,
much to everyone's distaste (including mine). Rest assured, people are
working on the problem. That doesn't mean you shouldn't continue to explore
the data, just try to consider it in a (very) critical context. :)

    Hope this helps,

    Wagner