Wednesday, 10 August 2011

Endothermania!

This is very strange. No sooner have I published the previous post on warm blooded dinosaurs than none other than Greg Paul made a very interesting contribution on the DML. In it, he refers to a paper by Spicer and Herman (2010) that was looking at the Late Cretaceous environment of the Arctic by using plant fossils to determine the conditions at the time.

Migrating dinosaurs are something that has been alluded to in this blog on more than one occasion, usually to explain the occurrence of monotaxic bonebeds that may sometimes contain the remains of hundreds, perhaps thousands of animals. One of these migrations has been suggested to explain animals whose fossils have been recovered from the northern Alaskan slope, in as much that perhaps they spent the summer in northern latitudes during a time of plenty and then returned south before the Winter set in.

Paul points out that conditions in these latitudes were never that warm, with average July temperatures of 50° Fahrenheit (10°c), occasionally hitting 70°f (21°c). A blanket of cloud covered the land, only with occasional breaks, and this combination of average cool temperatures and very little sun were not exactly ideal conditions for ectothermic reptiles and Paul points out that there have been no remains found of crocodile, lizard or turtle on the Alaskan slope.

Winter at these latitudes was hard, at least three months without sun, perpetual darkness and prolonged sub-zero temperatures. Paul interprets these conditions as evidence that dinosaurs were well equipped to deal with such conditions, regardless of whether they were small or large animals, and cites bone histology that displays fast growth which is on a par with dinosaurs living in warmer climates.

And, as Paul points out, there would be no point for dinosaurs at lower latitudes to migrate north since it would be sunnier, warmer and there would be more food simply by remaining where they were. The dinosaurs of the north were resident all year round and maximised the summer season by consuming as much food as possible in preparation for the colder months ahead.

Paul interprets this as powerful evidence of endothermic dinosaurs with a high metabolism that were able to survive in many different environments and suggests that the Spicer paper is, more or less, the final nail in the coffin for those who persist with any notion of ectothermian dinosaurs.

Firstly, it has to be said that Greg Paul loves to throw a notion into the ring to provoke a reaction and this has certainly been the case with this one – just take a look at the follow up emails at the DML, still going strong. Secondly, even if you subscribe to the suggestion that there was no north to south migration, this does not mean that there was not any migration of some description. Surely the huge herds of both ceratopsians and hadrosaurs would have had to keep on the move to some extent otherwise local vegetation would have been quickly exhausted. This is one of those big mysteries that is one of the hot topics of the moment since there appears to be no obvious answer.

It is also worth pointing out that no matter how well sampled a formation may be, something will always turn up that surprises you and it is always a possibility that other reptilian remains have simply not yet been discovered, but this does seem unlikely. As I mentioned earlier, for a full gamut of argument and counter-argument, head over to the DML. Regardless of the evidence, Greg Paul, just like Bob Bakker, loves to get his ideas out there and really stoke up the palaeoworld, which in turn promotes healthy discussion, and I think that can only be a good thing.

Lastly, Paul’s summation echoes my own final words from the previous blog post:

And the hypothesis of low metabolic rate dinosaurs is dead, dead, dead. Bakker was right.”

Amen.

Reference

Spicer, R. A. and Herman, A. B. (2010). The late Cretaceous environment of the Arctic: A quantitative reassessment based on plant fossils. Palaeogeography, Palaeoclimatology, Palaeoecology, 295(3-4), pp.423–442.



5 comments:

Alessio said...

For once i have to agree with Gregory Paul, long live active, kickass dinosaurs! ;)

Herman Diaz said...

"Secondly, even if you subscribe to the suggestion that there was no north to south migration, this does not mean that there was not any migration of some description. Surely the huge herds of both ceratopsians and hadrosaurs would have had to keep on the move to some extent otherwise local vegetation would have been quickly exhausted. This is one of those big mysteries that is one of the hot topics of the moment since there appears to be no obvious answer."

Did you think of "Dinosaur Odyssey" (See the paragraph w/highlighted words: http://books.google.com/books?id=RDq5Szn7afoC&pg=PA250&dq=%22notwithstanding+the+evidence+for+small%22&hl=en&ei=avhFTpiXJ8LqgQeu_-3GBg&sa=X&oi=book_result&ct=result&resnum=1&ved=0CCoQ6AEwAA#v=onepage&q=%22notwithstanding%20the%20evidence%20for%20small%22&f=false ) when you read that too?

"Regardless of the evidence, Greg Paul, just like Bob Bakker, loves to get his ideas out there and really stoke up the palaeoworld, which in turn promotes healthy discussion, and I think that can only be a good thing."

Unlike Bakker, it's hard to take Paul seriously as a good source nowadays. In fact, 1 could argue that Paul's the new David Peters (I.e. A talented paleoartist gone mad &, as a result, the butt of internet jokes).

Mark Wildman said...

Well I have read Dinosaur Odyssey and reviewed it here on the blog but migratory dinosaurs and food supply have been an issue for years - Sampson simply put it into the limelight again (there's more to come on this in the not too distant future by the way).

Like I said, I like to think of Greg Paul as a bit of a loose cannon who pops up now and then to instigate discussion. It's also worth pointing out that Paul has also been vindicated by the recent Xu paper on Archaeopteryx that more or less validates his assertion, back in the mid-80's, that Archaeopteryx was actually a basal dromaeosaurid as opposed to being avialian. So I wouldn't write off Paul just yet!

Herman Diaz said...

"Well I have read Dinosaur Odyssey and reviewed it here on the blog but migratory dinosaurs and food supply have been an issue for years - Sampson simply put it into the limelight again (there's more to come on this in the not too distant future by the way)."

I just meant b/c what you & Paul said reminded of the aforementioned "Dinosaur Odyssey" paragraph (Specifically, migration from North to South & vice versa vs. migration w/in the North & South).

"It's also worth pointing out that Paul has also been vindicated by the recent Xu paper on Archaeopteryx that more or less validates his assertion, back in the mid-80's, that Archaeopteryx was actually a basal dromaeosaurid as opposed to being avialian. So I wouldn't write off Paul just yet!"

I wouldn't say that yet, given the following quote. However, I do get what you're saying. Archaeopteryx having hyperextendable 2nd toes is a good example of that. I didn't say that I've stopped taking him seriously altogether, just that it's gotten harder to take him seriously, given his actions in recent years (E.g. The copyright-related diatribes on DML, the text in his field guide, etc).

Quoting Holtz ( http://dml.cmnh.org/2011Jul/msg00338.html ): "Statistical support for this position is not tremendously strong, so this
is by no means written in stone. (Indeed I know of at least one study
coming soon which will turn all of this inside out: however, that paper
lacks the Xiaotingia zhengi data)."

Mark Wildman said...

Yes, I agree that the Archaeopteryx issue is certainly far from resolved. I simply believe that Paul still has much to offer but I confess that the image/copyright saga, on the DML, left a little to be desired.

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