How Did Young Survive Winter?

[Rogue1stClass]

The Hell Creek formation 66 million years ago was a subtropical forest, right? Most of modern Florida is a subtropical forest, too, down to the Orlando area where it turns into savanna and eventual tropics, and it gets cold here. Snow is rare, but freezes are common enough that the reptiles and tropical mammals that have been introduced in the southern parts can't survive up here. All of the bigger native reptiles here disappear into burrows in the winter, while the mammals and birds develop thicker insulation.

I know there isn't much evidence for insulation on non-theropod dinosaurs, but they would have to have it, wouldn't they? The hatchlings would be tiny, and it would be a long time before something like Triceratops and Edmontosaurus would grow big enough to rely on their size alone. I'm not convinced that something like Thescelosaurus ever would. They can't all have burrowed and gone dormant when it got cold. If they had a nesting strategy like birds and rodents, they would have to keep that up for years, and it's not like an Alamosaurus would really be able to curl up with its chicks to keep them warm.

I know I'm not the only person to have ever thought of this before. What are the theories?

[Dinoguy2]

The Hell Creek formation 66 million years ago was a subtropical forest, right? Most of modern Florida is a subtropical forest, too, down to the Orlando area where it turns into savanna and eventual tropics, and it gets cold here. Snow is rare, but freezes are common enough that the reptiles and tropical mammals that have been introduced in the southern parts can't survive up here. All of the bigger native reptiles here disappear into burrows in the winter, while the mammals and birds develop thicker insulation.

I know there isn't much evidence for insulation on non-theropod dinosaurs, but they would have to have it, wouldn't they? The hatchlings would be tiny, and it would be a long time before something like Triceratops and Edmontosaurus would grow big enough to rely on their size alone. I'm not convinced that something like Thescelosaurus ever would. They can't all have burrowed and gone dormant when it got cold. If they had a nesting strategy like birds and rodents, they would have to keep that up for years, and it's not like an Alamosaurus would really be able to curl up with its chicks to keep them warm.

I know I'm not the only person to have ever thought of this before. What are the theories?

Dinosaurs grew fast enough that if they were born in the spring, they'd probably be large enough come winter to survive without having to burrow or have insulation in a semi-tropical ecosystem, especially if they were endothermic. Lizards are a bad example, because they're ectotherms. Dinosaurs were at the very least mesotherms. The smallest dinosaurs at the time were theropods and small ornithischians, which were probably insulated as well.

Here's a recent study of growth in Maiasaura. If the Hell Creek species Edmontosaurus annectens was similar, they would have been pretty large by the end of their first year. A 1 year old Maiasaura was almost 400kg, and Edmontosaurus could grow larger as an adult, so its babies probably grew even faster. It's reasonable to think that a baby Edmontosaurus annectens would weigh nearly half a ton before it ever met its first winter!


Thescelosaurus was pretty big. I don't think there's any data on how fast it grew, but as another ornithopod it's reasonable to think it would have been at least the size of a large fox by the end of its first year. There's also ample evidence that small ornithischians were burrowers, and not just Oryctodromeus (Drinker has been found in burrows, as has Psittacosaurus, so it was probably a common behavior among small ornithischian species). I'd bet Leptoceratops, the smallest HC ornithischian, probably lived in burrows.


Also, notice the mortality rate in the first image. 90% of baby ornithopods did not survive their first year, whether by predation or the elements. So the basic answer to the question of "how did these hatchlings survive?" would be "they mostly didn't."

As for Alamosaurus, they certainly didn't curl up with their chicks. All evidence we have demonstrates that sauropods abandoned their eggs either before or shortly after hatching. Baby titanosaurs probably grew very fast, just like ornithopods. Add to that the fact that Alamosaurus did not live in Hell Creek. Same time period, but only in the formations of the southern US. No Late Cretaceous sauropods have ever been found north of Utah. No natural barrier is known to have existed, so it must have been a climate/ecological barrier keeping them out of the northern US and Canada. Maybe it was too cold.

[Rogue1stClass]

Wow! That's an incredible answer! Thank you! I'm impressed!

The only reservation I have is just how fast bare skin sheds heat in cold air. Even a little bit of insulation of some kind would drastically improve their chances of surviving weeks of near freezing temperatures, but it would have to be something that could be shed in the summer. Feathers, fat, even a layer of slime like hippos secrete. Or maybe they did just all die out except the exceptionally lucky individual. I honestly can't imagine the kind of plant life that could sustain that kind of growth cycle and feed the massive adults and gravid females.

I had just picked Alamosaurus because it was the most ridiculous example, but that does make a lot of sense. Their necks and tails would give them a lot of surface area for their volume, which would make them more susceptible to cold than compact animals like hadrosaurs and ceratopsians.

Thanks again. I really didn't expect this detailed of an answer for a question I came up with while freezing in my garage late at night.

[Dinoguy2]

Wow! That's an incredible answer! Thank you! I'm impressed!

The only reservation I have is just how fast bare skin sheds heat in cold air. Even a little bit of insulation of some kind would drastically improve their chances of surviving weeks of near freezing temperatures, but it would have to be something that could be shed in the summer. Feathers, fat, even a layer of slime like hippos secrete. Or maybe they did just all die out except the exceptionally lucky individual. I honestly can't imagine the kind of plant life that could sustain that kind of growth cycle and feed the massive adults and gravid females.

I had just picked Alamosaurus because it was the most ridiculous example, but that does make a lot of sense. Their necks and tails would give them a lot of surface area for their volume, which would make them more susceptible to cold than compact animals like hadrosaurs and ceratopsians.

Thanks again. I really didn't expect this detailed of an answer for a question I came up with while freezing in my garage late at night.

Glad I could help! Regarding bare skin, keep in mind it's not really bare, it's covered in scales which would seal in some heat, and may have been quite thick in some species. An extra layer of fat over the winter would help too.

The exception is hadrosaur skin, which is very weird. It appears to be very thin and stretchy/wrinkly but also very tough. It's been speculated that there must have been something very odd about its structure given how often it fossilizes compared to all other kinds of dinosaur skin (it's weird to find an articulated hadrosaur fossil without at least some patches of skin preserved, and of course we have several mummies from a variety of species). So we don't really know what kind of properties their skin might have had in terms of insulation.