The Polar Dinosaur Thread- Dinosaurs of the Arctic and Antarctic

Polar dinosaurs are hardly news these days- plenty of fossils of them have been found in both Arctic and Antarctic regions. The mystery here is how exactly did they cope with the freezing winter temperatures, especially those that- like the hadrosaur described in the article- probably lacked insulating feathers or fuzz of any kind. (All hadrosaurs for which skin impressions or fossilized skin are known show exclusively scaly skin, and this polar hadrosaur was apparently very similar to Edmontosaurus- so much that its remains were initially assigned to it. Edmontosaurus is one of the hadrosaurs for which we have scaly skin evidence).

One possibility is that these animals didn´t live in those regions the entire year, rather staying during the warmer summer months and traveling south to avoid the winter temperatures.
The large predators found in the same regions- such as the dwarf tyrannosaur Nanuqsaurus- would've probably followed the herds during their migration to an extent, although let's not forget that a) there is a chance however small that Nanuqsaurus, being a tyrannosaurid, was actually fuzzy, and b), the smaller adult size of Nanuqsaurus compared to other tyrannosaurs suggests it may have coped with scarcer food sources than their relatives. This may actually suggest Nanuqsaurus lived in those Arctic regions all year long, and for about half of the year they had to prey on smaller animals than the hadrosaurs if the latter were really migratory. All speculation here.

Another interesting Arctic dinosaur is Troodon, which is also known from much more southern regions (all the way down to Mexico), but seems to have grown quite large in these polar regions (we see this in modern day animals; bears, cougars, wolves and many others grow bigger the further they live from the Equator).
Troodon was almost certainly fuzzy, and as I've mentioned in another thread, it had a very well developed sense of hearing, with asymmetrical ears to better detect the provenance of the slightest sounds; something we see in owls as well. Combined with its huge forward-facing eyes which probably imply good vision in low-light conditions, this would've been the perfect dinosaur to thrive there even during the long months of darkness.

Also interesting to note; the size difference between the polar Troodon and the tyrannosaur Nanuqsaurus is actually rather small, although the tyrannosaur would've been a much more powerful predator.
Still, this would suggest that, at least during part of the year and assuming there weren´t other larger predators around whose remains we haven´t found yet, this ecosystem could probably not support gigantic predatory dinosaurs like those we see in lower latitudes.

Nanuqsaurus is "A"; lower latitude Troodon is "F" and polar Troodon is "G".



Yet another interesting fact; although dinosaurs and crocodiles coexisted almost everywhere else, there are no remains of crocodiles from these polar regions. This is to be expected as cold-blooded crocodiles are not tolerant of cold temperatures; the important point here is, dinosaurs were. This should be all the evidence needed to put those cold-blooded dinosaur ideas to rest IMO.

There's also Antarctic dinosaurs but their remains are very fragmentary. Perhaps most intriguing is Laellynasaura, a small hypsilophodont-type animal which was originally described as having huge eyes and optic lobes, suggesting it was especially adapted to a dark environment and thus, spent the winter months in the polar forests.
If we consider that a) other hypsilophodonts are known to have lived in burrows, and b) at least one hypsilophodont-type dinosaur has been suggested to have feather-like covering on at least part of its body, then it is perfectly possible that Laellynasaura was very fuzzy to keep warm, but still could seek shelter in a burrow if the temperatures were too low. It has even been suggested that Leallynasaura's very long tail was densely "furred", and used as a sort of scarf or blanket when the animal was at rest- similar to how snow leopards use their tails today.
This probably makes more sense than the naked Laellynasaura from Walking with Dinosaurs, as a small animal without insulation would lose heat like crazy in such an environment. There's also the possibility that some dinosaurs hibernated, however.

So much to be learned...

Linnaeus wrote: »

I'm just wondering: in areas where hot springs are found, can animals hibernate close to the source and keep warm? In subterranean caverns or passages from which the warm water rises?

Yes, at least one species of bat does use geothermically heated caves to hibernate! And now that you mention it, there is some evidence that some sauropod dinosaurs actually used geothermically heated ground to lay their eggs, thus solving the problem of incubation without having to sit on them. This is not without precedents; modern day Galapagos land iguanas climb into volcanic craters to lay their eggs.
Did some dinosaurs hibernate in geothermically heated caves? It's a really interesting suggestion

Linnaeus wrote: »

I did not know previously that Troodon arrived so far north. And he certainly did grow larger in Arctic zones, as did other species. Personally I suspect that such robust species became not only larger, but also chubbier, deliberately putting on a lot of fat by eating abundantly all throughout the year. They may have been intelligent enough to store food, meat and fish especially, in ice. At any rate, the point you made about the ecosystem having to support mainly big predators is thought-provoking . Would the large, constantly carnivores in Arctic regions have been able to find enough food to stay alive?

Evidently they were, as they lasted long enough in those latitudes to give rise to specialized forms. If the hadrosaurs and other large herbivores (such as Pachyrhinosaurus) were indeed migratory, then the resident carnivores must have based their diet on smaller fry, same as wolves preying on snow hares when there are no caribou.
So if you were a predator living in those latitudes, you had to be large enough to hunt the big prey while they were around (and also, large enough to retain body heat more efficiently and wander longer distances searching for food), but small enough that you wouldn´t starve during the winter months.

If you look at the dinosaurs that lived along with Nanuqsaurus and Troodon, you'll find a hypsilophodont-type creature called Parksosaurus which was about 2-3 meters long- perfect size to make a good meal for either carnivore, should they manage to catch one.
Parksosaurus has strong arms and probably dug burrows, like other hypsilophodonts. So there you have at least one potential prey animal that could conceivably stay all year round.
Also from that region mammal remains are known; Troodon has long been thought of as a specialized mammal hunter. If this view is correct then it may be that Troodon and Nanuqsaurus avoided competing with each other by hunting different prey. It also wouldn´t be surprising if Troodon scavenged tyrannosaur kills. And they did live near water so chances are high they would catch fish and shorebirds whenever they could.

Linnaeus wrote: »

Troodon and most raptors probably hunted in packs; they would have prefered substanzial-sized prey, for the common "banquet" which they would share.

Possible but not certain. There's no evidence that Troodon was a pack hunter. However, it is true that polar Troodon have relatively larger teeth than their southern counterparts, suggesting they were possibly dealing with larger prey. Assuming Troodon did hunt in packs at all, it may have been similar to the wolves, gathering in larger numbers when large herbivores were available, but switching to a more solitary hunting style when limited to smaller prey.

Raptors probably lived in the same regions as well, as suggested by isolated teeth; they have been tentatively assigned to Dromaeosaurus and Saurornitholestes, but let's face it, teeth are rather unreliable. Some raptor teeth found in more southern latitudes have turned out to be from previously unidentified species, and some of them weren´t even dinosaurian at all. So until the teeth are found associated with a skull, I wouldn´t pay them much attention. This also means we don´t know if there were pack-hunting raptors in those regions. In fact, evidence of pack hunting is scarce for raptors in general.

Linnaeus wrote: »

Certain species whose members fought fiercely against each other for mates, territory or food, may even have practiced cannibalism. There is some evidence for this in the species Daspletosaurus.

And Tyrannosaurus, and Gorgosaurus, and many others. Any large carnivore will go cannibal if hungry enough. Hell, even chicken go cannibal if hungry enough.

Linnaeus wrote: »

I've taken a look at Parksosaurus online...He was an attractive dinosaur, slender and swift...Hope that he was fast enough to outrun Nanuqsaurus, Troodon and company. Lovely dinos like Parksosaurus were born to be admired, not devoured!

It could be argued that everything was born to be devoured in one way or another. :B

Linnaeus wrote: »

Please let me know which mammals coexisted with the abovementioned dinosaurs. Did any of them dig out burrows or tunnels? In a dangerous environment in which big predators prevailed,smaller mammals may have burrowed in order to have safe hiding places and also to hibernate during the coldest months.

To my knowledge their remains are fragmentary but represent at least three species of small mammal. Surely here were many more, of course, but their remains wouldn´t fossilize often. It is very likely that many, if not most of them dug burrows; many Mesozoic mammals did (there's even a very interesting fossil site from the late Jurassic I think in which the burrows of unidentified mammals were found to go through and around the skeleton of a sauropod dinosaur which had been laying there for centuries at least; one of the few cases in which a sort of indirect interaction between mammals and dinosaurs is known).

Linnaeus wrote: »

Were there any large-sized mammals living alongside Parksosaurus, Nanuqsaurus and Troodon?

Not likely, or at least not "large" as we would understand it today. Most Mesozoic mammals seem to have been small; the largest North American mammal from the same age as those dinosaurs is Didelphodon, a metatherian.
It was slightly larger than today's North American opossum. Interestingly, this creature was restored as badger-like in Walking with Dinosaurs in the 90s, when it was known by fragmentary remains only:




Instead, new remains show it had an elongated, otter-like body with a massive head similar to that of a Tasmanian devil. Everything seems to suggest it was an aquatic hunter, which is further proof that mammals were more diversified at the time than usually thought.



However, I don´t know if Didelphodon is one of the mammals identified from Alaskan sites. I wouldn´t be surprised if mammals this size or even somewhat larger were present, though; recent finds in China and Africa suggest Mesozoic mammals were not limited to diminutive, mouse or shrew size as previously believed.

Nothing like bison or moose, tho.

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