|>> A great puzzle. But be careful. Was it Thomas Rich who recently talked about hard evidence of a permafrost in home range of Lilyianasaura (sp?)?<<
>>Permafrost!?! Really? Cool... :-) *Leaellynasaura*, named after Rich's daughter Lea Ellyn.<<
Yes...... it was in Science not too long ago: _Enhanced: Polar Dinosaurs_ Thomas H. Rich, Patricia Vickers-Rich, Roland A. Gangloff.
Basically the article talked about how an old scenario that was used to try to explain the presence of polar dinosaurs..... doesn't gel with the data. The scenario encompassed how it was once thought that the inclination of the Earth's rotational axis may have been substantially different during the Mesozoic than it is today. This would have resulted in warmer climates and more even day length through the year at the higher latitudes. They obviously were still thinking over grown iguanas. BUT.... Theoretical investigations have suggested that except for the usual and well-understood variation by a few degrees that does take place on a scale of thousands of years, the inclination of the Earth axis has remained much the same relative to the plane of the ecliptic. This means that polar dinosaurs and their associated biota would have had to deal with the same types of extremes of day length through the year that characterize these types of latitudes today.
BUT... of course the annual temperatures were different at these high latitudes in the Mesozoic then they are today. For the North Slope, a mean annual temperature curve spanning the last 35 million years of the Cretaceous has been constructed based on the leaf shapes of flowering plants. Basically you had a maximum temperature of 13C and a minimum temperature of 2 to 8C. Today for example, the mean annual temperature in Portland, Oregon, is 12C, and in Calgary, Alberta, it is 4C. What is really interesting is that the dinosaurs on the North Slope closely resemble the contemporaneous ones farther south in Alberta, Montana, and Wyoming. BUT.... there existed a profound difference in the animals living along side them. The North Slope has an absence of the ectothermic animals such as lizards and crocodilians. But in the south, these animals encompass a substantial part of the fauna. All of this, of course, lends credence to endothermic dinosaurs of one form or another.
Now, what is really neat is that in southeastern Australia, you find evidence for the presence of permafrost, ice wedges, and hummocky ground in association with dinosaur-bearing deposits during the late Early Cretaceous (105 to 115 million years ago). What this means is that the dinosaurs lived there when mean annual temperatures ranged between -6ºC and +3ºC. There have been Oxygen isotope studies performed that have given a mean annual temperature of -2º ± 5ºC for the same deposits. Look at it this way.... Today, the modern mean annual temperature of Fairbanks is -2.9ºC. What is weird and has yet to be explained, is that the diversity of the late Early Cretaceous flora in southeastern Australia, and the oddly large size of some of the trees, far exceed what is found in these types of cold environments today.
Just like Jahren remarked about his 45 myo metasequoias on Axel Heilberg Island, it could very well be that in southeastern Australia, and even in Alaska, these plants could have had some type of different metabolism or strategies no longer found or used in plants today, that allowed them to survive in such cold, dark conditions.
What is also interesting is that Hypsilophodontids make up half of the dinosaurs found in southeastern Australia... these being your Leaellynasaura. This is important because it's been noted that they are rare for the most part in other parts of the world. The Rich article talked about how after looking at a brain endocast of the Leaellynasaura, you can see that they possessed enlarged optic lobes. When you compare the Leaellynasaura endocast to those of lower latitude hypsilophodontids, it becomes apparent that the Leaellynasaura had a more pronounced visual acuity. And when you combine this with the histological evidence that shows how their bones were constantly growing and that they were thus active throughout the year,.... you come to the conclusion that the Leaellynasaura were well adapted to polar conditions, even though they had to deal with about a 3 month long polar night.
As for the probability of seasonal migrations...... When you take a peak at the North American polar dinosaurs, which were predominately made up of ceratopsians and hadrosaurids, it has been thought that these animals only occupied the higher latitudes only during certain times of the year. This might be possible.... but take a look at an article by Gregory S Paul in _The Dinosaur Encyclopedia_ edited by Currie and Padian. It's entitled _Migration_ and it basically says that these supposed migrations to and fro from Alaska to warmer southern areas would require distances around 6000-9000 km round trip! That's like taking a round trip from New York to Los Angeles. This type of scenario obviously brings about what can only be called insurmountable energy problems for a reptilian dinosaur... and even if they were endothermic, dinosaurs didn't have the specialized, energy efficient limbs to take on this type of migration which is larger then that taken by any migratory mammal. As Paul states in his article, dinosaurs were most likely migrating moderate distances throughout the year to seek the best intraregional conditions so as to try to keep exploitation of food resources in one place to a minimum. Of course there is much more too this..... so, your best bet is to read the article if you can.
This type of migration, even a modest one at that, is very unlikely for the dinosaurs that were living in southeastern Australia. This is because of their small size and because seaways to the north blocked their passage to lower latitudes.
All of this is why I made that little remark about thermal underwear and dinosaurs in Alaska.
And that's about it.