The polar dinosaurs revealing ancient secrets • Hacker News Board

Re: The polar dinosaurs revealing ancient secrets

#11

Post by dogma1138 » Sun, Dec 04, 2022, 1:09 PM UTC

adrian_b wrote: post #9

ComputerGuru wrote: post #4

Earlier quoted context omitted.

Without commenting on anything else in your reply, > Other counter evidence is that some species were just too darn big to be endothermic and at that size would have high enough internal temperatures to cook themselves. I don’t understand. Isn’t the existence of the (obviously endothermic) blue whale enough to obviate that argument, at least on its own?

The blue whale and all its relatives have a very good thermal insulation made of a thick fat layer. This allows it to keep a constant internal temperature even in the cold water. In terrestrial conditions, a very big animal has the reverse problem, of cooling its body, which is more difficult than keeping it warm, which needs only insulation. Cooling requires body parts with very large area and energy lost with pumpi…

This impacted both land and oceanic dinosaurs at least in certain periods.

During the Cretaceous period the ocean temperature was 35c and the north and south poles were tropical rain forests devoid of any ice.

Re: The polar dinosaurs revealing ancient secrets

#12

Post by dogma1138 » Sun, Dec 04, 2022, 1:12 PM UTC

ComputerGuru wrote: post #4

dogma1138 wrote: post #3

Earlier quoted context omitted.

The amount of evidence for them being endothermic is about as much as for them poikilothermic. The bone evidence specifically is not particularly convincing on its own, it based on some microscopic analysis which indicates that (some) dinosaurs grew too fast to be poikilothermic but it’s far for being conclusive. Other counter evidence is that some species were just too darn big to be endothermic and at that size wou…

Without commenting on anything else in your reply, > Other counter evidence is that some species were just too darn big to be endothermic and at that size would have high enough internal temperatures to cook themselves. I don’t understand. Isn’t the existence of the (obviously endothermic) blue whale enough to obviate that argument, at least on its own?

Blue whales didn’t had to live when the ocean temperature was on average 35c.

On land as someone else mentioned very large warm blooded animals need ways to cool themselves this is why elephants have huge ears and why they spray water on themselves when ever possible.

Marine mammals need to worry today about insulating themselves in order to not to loose heat, marine dinosaurs would need to worry about their insides cooking.

Re: The polar dinosaurs revealing ancient secrets

#13

Post by dogma1138 » Sun, Dec 04, 2022, 5:18 PM UTC

adrian_b wrote: post #8

dogma1138 wrote: post #3

Earlier quoted context omitted.

The amount of evidence for them being endothermic is about as much as for them poikilothermic. The bone evidence specifically is not particularly convincing on its own, it based on some microscopic analysis which indicates that (some) dinosaurs grew too fast to be poikilothermic but it’s far for being conclusive. Other counter evidence is that some species were just too darn big to be endothermic and at that size wou…

There are also some studies that have shown many deep similarities between endothermy in birds and endothermy in mammals, which do not seem very likely to be the result of parallel evolution. So there are chances that actually endothermy was developed in the common ancestor of all amniotes. If that would be true, then various branches have reverted to poikilothermy, like modern crocodiles, turtles, lizards and snakes…

I mostly agree with this, the point was that dinosaurs being warm blooded as a general rule isn’t well established or to be more exact no one is trying to establish it.

Dinosaurs span 165 million years there is enough room on an evolutionary time scale for them to take any shape and form.

That said the climate for much of their reign was very different, you probably didn’t had warm blooded aquatic life when the oceans were at 35c and finding dinosaurs in polar regions isn’t a proof for them being warm blooded as those region were tropical rain forests for about 90M years.

Re: The polar dinosaurs revealing ancient secrets

#14

Post by ComputerGuru » Wed, Dec 07, 2022, 10:41 PM UTC

dogma1138 wrote: post #10

ComputerGuru wrote: post #7

Earlier quoted context omitted.

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.

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.

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.