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.”
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.