How, where and when did dinos sleep?

Linnaeus

Now, this may seem to be a silly question, but I think it has been insufficiently raised and discussed in palaeontological circles: just exactly how, where and when did dinos sleep?

One of the few fossils we have of a sleeping dinosaur is the little troodontid Mei long, another marvel from that immense treasure trove which is Liaoning Province. Mei, meaning "soundly asleep" in Chinese, according to the Wikipedia article "is a young juvenile...(discovered) with the snout nestled beneath one of the forelimbs and the legs neatly folded beneath the body, similar to the roosting position of modern birds". The question is, would this sleeping position have been common to adult Mei long dinosaurs as well, or only to juveniles? A bit difficult to imagine a fully grown troodontid curling up in this way...How might adult theropods have slept? Huge ones, like Allosaurus and T-Rex, would have knelt or squatted down? I can't imagine them in such a position. Did they recline, more or less as humans do? T-Rex had such short,almost useless arms that, if he had managed to lie down, I don't think he could have used those arms as support in raising himself up again!

Prehistoric reptilian quadrupeds preparing to sleep may have tucked their legs under their bodies as camels do today. But I suspect that some of the larger bipeds may have had to sleep standing up, like horses.

Dinos that lived in herds or packs might have assigned guard duty to one or more members of the group at night. But not all dinosaurs would have slept when the sun went down...They might have rested during the hottest part of the day, and gone out prowling for food at night. I would appreciate more info on this theme, with which I am not very familiar.

As for WHERE they slept, we tend to imagine most dinos just sleeping out in the open...But I'm sure that their snoozing places and habits would have depended greatly upon environmental/climatic conditions, and would have varied from species to species. As I suggested previously, some dinos may have hibernated for prolonged periods. Smaller species would surely have made use of burrows or tunnels, even caves. I doubt that any would have ventured up to the mountains, as many wild species do today...But who knows? Certain dinos may even have climbed up to the heights in order to escape predators and to enjoy a bit of peace and quiet.;)

Adam Khor

Linnaeus wrote: »

Now, this may seem to be a silly question, but I think it has been insufficiently raised and discussed in palaeontological circles: just exactly how, where and when did dinos sleep?

It's actually an interesting question. I've often wondered the same (also, what did they dream about? )

Linnaeus wrote: »

One of the few fossils we have of a sleeping dinosaur is Mei long, (discovered) with the snout nestled beneath one of the forelimbs and the legs neatly folded beneath the body, similar to the roosting position of modern birds". The question is, would this sleeping position have been common to adult Mei long dinosaurs as well, or only to juveniles? A bit difficult to imagine a fully grown troodontid curling up in this way...

Depends on the troodontid really; IIRC, adult Mei long are believed to have been about duck-sized, so it wouldn´t be strange if they slept in the same position as the juveniles. In fact, it is most likely, as this particular position helps reduce loss of body heat. Mei long is not the only theropod found in a sleeping position, by the way; the original Sinornithoides specimen (another small troodontid) was too.
A specimen of the very early Guaibasaurus was also found in a similar resting posture, meaning this was not a Cretaceous "invention". (If it ain´t broke...)

On the other hand, the larger ones may have slept like modern day ostriches:





Or emus:





Bigger size means body heat is not so easily lost, so they wouldn´t need to curl up in a ball. You see the same with mammals today; for example, lions tend to sleep all oustretched whereas house cats curl up to keep warm.

It has been suggested that the large pubic boot of some giant theropods (T. rex included) was used to support the animal's weight in a resting position, either when lying down or sitting. I wouldn't be surprised if they were able to sleep in either position.





Take a look at this:

http://ix.cs.uoregon.edu/~kent/paleontology/Tyrannosaurus/images/up-1e.jpg

There's a possibility that some of the very large dinosaurs could sleep while standing up. There was a study not long ago that spoke of a sort of locking mechanism similar to that of horses in giant sauropods (at least I remember reading something like that). Makes sense in a way, since a 70 plus ton sauropod would probably be very slow to get up, and that would be a major disadvantage when there were large, hungry theropods about. Modern day giraffes usually sleep standing but may lie down if they're feeling confident enough (for example, in captivity where they don´t have to worry about being attacked in their sleep).

As for where they slept, the little ones apparently sought cover in burrows (Psittacosaurus, various hypsilophodonts). Semiaquatic dinosaurs may have slept partially or even completely submerged, like crocodiles, hippos or even tapirs (known to take naps underwater).
Giant herbivores may have been similar to modern day elephants, which sleep lying down, usually near a tree or termite mound for protection and comfort.

If you look at large animals today, very few are okay with sleeping on the open; lions are a notorious example, and they probably only do it because they're apex predators and relatively safe from attack.
The very largest theropods may have been confident enough to sleep wherever they wanted.

Adam Khor

@Linnaeus, I think we discussed the possibility that dinosaurs (some of them anyway) could have used caves to hide from the cold; here's an interesting article on giant Aldabra tortoises doing just that, but to escape intense heat. Even though tortoises are ectothermic and dinosaurs were seemingly not, I thought it was interesting. As with dinosaurs, you wouldn´t precisely think of a tortoise if asked to list animals that seek shelter in caves.

http://news.nationalgeographic.com/2016/02/160212-caves-giant-tortoises-animals-science-seychelles/?utm_source=Facebook&utm_medium=Social&utm_content=link_fb20160212news-seychellestortoise&utm_campaign=Content&sf20859090=1

Linnaeus

Thank you, Adam, for your very interesting comments and for the photos.

We who love palaeontology often dream of the past. Dinosaurs, who WERE the past, might have dreamed of the future: of us, for example! Troodon may even have imagined a distant moment when his brainy descendants would have evolved into anthropoid geniuses who became palaeontologists and unearthed the bones of Homo Megabyticus! Oh well, so much for fantasy...;)

Dinosaurs may well have sought out caves, deep tunnels and shady forests as resting places in summer (refuges against sultry heat). In winter, as we discussed previously, they would have used thermally heated locations if they were lucky enough to find them. I don't think they would have ventured too close to active volcanoes, though. But I wonder if, in the future, palaeontologists may discover a kind of dinosaur Pompeii: an open place near a semi-dormant volcano where ancient creatures gathered to keep warm, but from which they were not able to escape in time when a lava eruption began in serious. Imagine a graveyard of beasts hardened into statues by volcanic ash. That would be something astonishing: perfectly preserved casts of dinos and other prehistoric animals, with clear impressions of scales, skin, feathers, fur and all.

Dinosaurs, in order to preserve the species, may have mated twice or more in one year. If so, some of the wee babies may have hatched in winter. This brings up the question of what kind of shelter these families with delicate newborn tots would have found in the more inclement seasons.

Perhaps one reason why relatively few fossils of once widely thriving species have been found is that the creatures literally went underground for lengthy periods of the year,for the purposes of safety or hibernation: into the deeper tunnels under the earth where palaeontologists' spades seldom reach.

Adam Khor

Linnaeus wrote: »

But I wonder if, in the future, palaeontologists may discover a kind of dinosaur Pompeii: an open place near a semi-dormant volcano where ancient creatures gathered to keep warm, but from which they were not able to escape in time when a lava eruption began in serious. Imagine a graveyard of beasts hardened into statues by volcanic ash. That would be something astonishing: perfectly preserved casts of dinos and other prehistoric animals, with clear impressions of scales, skin, feathers, fur and all.

The famous Liaoning fossils are pretty much that. Many of them preserve scales, fur, feathers, food remains, even sometimes traces of their internal organs. That's where the sleeping Mei long comes from.

Linnaeus wrote: »

If so, some of the wee babies may have hatched in winter. This brings up the question of what kind of shelter these families with delicate newborn tots would have found in the more inclement seasons.

Winter was rather mild during most of the Mesozoic but there were indeed colder periods; the Liaoning fossils come from one of those periods. Obviously a lot of baby dinosaurs (theropods at least) were quite fuzzy to protect themselves from the cold, whereas others such as Psittacosaurus apparently sought shelter in burrows. One interesting find was that of 34 baby Psittacosaurus all of the same age, which apparently died together when their burrow collapsed.
Living in groups would've offered not only safety from predators (such as the mammal Repenomamus known to have dined on baby dinosaurs) but also from the cold, as sleeping closely together in a burrow would've helped them keep warm.

Other dinos such as hypsilophodont-type ornithopods are also known to have used burrows.

Linnaeus

Just a few remarks here:

Your idea about the large pubic boot of T-Rex et al seems logical. However, in the resting position in which the theropod's skeleton is represented in the illustration, the neck is unsupported. In sleep, the dino's head may have slumped unto his upper chest; but if not, slumbering might have been uncomfortable. I've tried manipulating a flexible T-Rex putty model into several pre-sleep positions. The one which seems most plausible (and most comfortable for him!) is this: T-Rex would have supported one side of his body against a tree trunk. Then, slowly, he would have bent his knees, into an almost sitting position. He would have slept in this way, head and torso supported against the trunk, which would also have been useful in helping him to rise again. T-Rex's body was not as lithe and supple as that of human beings; what is more, his short arms were nearly atrophied, and would have been of little or no help to him in trying to get up from a reclining or sitting position.

Linnaeus

Another remark: Pompei and Liaoning present two very different phenomena. At Liaoning, we have a huge number of SKELETAL remains, bearing frequent impressions of external features such as feathers, scales etc. At Pompei, we have three-dimensional BODIES, superbly preserved by a covering of ash and lava. These complete casts seem to be rounded statues, fallen to the ground. Even fruit, vegetables, loaves of bread have been "fossilized" in this amazingly naturalistic way. This is the kind of "graveyard" I would hope to find in a palaeontological context.

Adam Khor

So they're not exactly the same, but similar. Unless I'm remembering this totally wrong, the people and animals at Pompeii were covered on volcanic ash which then hardened into a porous shell, meaning the soft tissue of the bodies rotted away leaving basically just the skeleton inside. So they're not really full bodies, they're casts surrounding the petrified(?) skeletons.

Some of the Liaoning dinos may have died buried by floods of rainwater mixed with volcanic ash (lahars) and not necessarily by the actual pyroclastic flows, but many of them were still preserved in three dimensions, unlike the usually flattened fossils you find elsewhere. I'd say it's about as close to a dinosaur Pompeii as we have.

Linnaeus

Absolutely right about the Pompeian victims being CASTS of bodies; the soft parts disintegrated. But the three-dimensionality of the casts has preserved with remarkable clarity details of those bodies.

I think that a dinosaur, thus preserved, has not yet been discovered.

Adam Khor

But we do have fossilized dinosaur mummies, which is just as good if not better.









(ok, the last one is a Holocene dino, but still cool...)

Capt'n Midnight

Back in the day there were dinos in the polar forests. So six months of darkness.