[andrewl]

I’m really getting out of my area of expertise on this, but could the fact that whales live immersed in a heat sink be a factor? They’re the most massive animal that’s ever lived (as far as is known). Maybe an animal that size can only be endothermic if it lives in the water.

[Edit: the blue whale is the most massive animal known.]

[ComputerGuru]

Yes, I considered that. I think it's a very valid possibility and likely GP's argument is applicable to the titan dinosaur species. However in the context of this article, we're discussing much smaller ("regular mammal-sized") dinosaurs living in polar conditions, where the calculus changes enough that this discussion is rather besides the point.

[dogma1138]

The polar regions used to be warm rainforests up-to as recently as about 50m years ago.

The temperature of the oceans during the Cretaceous was 35c.

Finding dinosaurs in Antarctica or Lapland doesn’t mean anything really since those areas used to be quite warmer than most tropical regions we have today.

[ComputerGuru]

The article claims that the areas where fossils were found had winters with temperatures just above freezing, and that some evidence (fossilized young, growth patterns in bones, etc) indicates that the species lived there year-round rather than only migrating there during the warmer months.