How Did Dinosaurs Sleep? Resting Behavior in the Mesozoic

Every animal needs to sleep, and dinosaurs were no exception. But how do you figure out the sleeping habits of animals that have been dead for at least 66 million years? Remarkably, a handful of extraordinary fossils preserve dinosaurs in resting and sleeping positions, and comparisons with their living relatives—birds and crocodilians—fill in the gaps. The picture that emerges is surprisingly detailed.

Fossil Evidence: Dinosaurs Caught Sleeping

Mei long: The Sleeping Dragon

The most famous sleeping dinosaur is Mei long, a small troodontid theropod from Early Cretaceous China. Its name literally means “sleeping dragon” in Chinese, and the name couldn’t be more appropriate:

The holotype fossil preserves the animal in a bird-like sleeping posture: legs tucked beneath the body, head turned back, and snout nestled under one arm
This is virtually identical to how modern birds sleep—tucking the head under a wing to conserve heat
The animal was likely killed suddenly (possibly by volcanic gases) while asleep, preserving its natural resting position
A second Mei long specimen was later found in the exact same sleeping posture, confirming this wasn’t a random death position

This fossil is powerful evidence that the bird-like sleeping posture evolved long before modern birds—at least 125 million years ago.

Sinornithoides: Another Sleeping Troodontid

Sinornithoides, another troodontid from Mongolia, was also found in a resting posture:

Legs folded beneath the body
Arms tucked close to the torso
Head positioned near the chest
The posture is consistent with sleeping or resting and closely resembles Mei long

Changmiania: Buried Alive While Sleeping

In 2020, scientists described Changmiania liaoningensis (meaning “eternal sleeper”), an ornithopod dinosaur from China:

Two specimens were found in identical resting postures—legs tucked, eyes closed, heads resting on the ground
The researchers concluded the animals were buried alive by a sudden volcanic event while sleeping in burrows
This suggests small ornithopod dinosaurs may have slept in underground burrows for protection, similar to modern burrowing animals

How Different Dinosaurs Likely Slept

Small Theropods (Raptors, Troodontids)

Based on fossil evidence and their close relationship to birds:

Sleeping posture: Legs tucked under the body, head turned and resting on or under the arm/wing
Location: On the ground, possibly in sheltered areas (under vegetation, in tree hollows, or in burrows)
Social sleeping: Some may have slept in groups for warmth and protection, like modern penguins and some passerine birds
Feather insulation: Feathered species likely fluffed their plumage while sleeping to trap warm air, just as modern birds do
Duration: Small theropods likely slept for several hours, possibly in multiple bouts (polyphasic sleep) rather than one long period

Large Theropods (T-Rex, Allosaurus)

The sleeping habits of giant predators are more speculative:

Standing or lying down? Large theropods probably slept lying down. Fossil trackways and body impressions show theropods resting on the ground, and standing sleep would require significant energy to maintain balance
Body impressions: A few fossil sites preserve impressions of large theropods resting on the ground—showing the belly, tail, and sometimes hand prints pressed into soft sediment
Sleep duration: Large predators in the modern world (lions, tigers) sleep extensively—up to 18-20 hours per day. Large theropods with infrequent but massive meals may have followed a similar pattern
Vulnerability: A sleeping T-Rex was still an 8-tonne animal. Few predators would have posed a threat to a resting adult, but juveniles may have sought sheltered sleeping spots

Sauropods (Brachiosaurus, Argentinosaurus)

How did 30-meter, 70-tonne animals sleep?

Standing vs. lying: This is debated. Elephants can sleep standing up (supported by locking leg joints) for short naps, but must lie down for deep (REM) sleep. Sauropods may have done the same
Getting up problem: For the largest sauropods, lying down and getting back up would have been a significant physical effort. They may have spent most of their rest time standing and only lay down briefly for deep sleep
Herd protection: Sleeping in herds would have provided safety in numbers, with some individuals remaining alert while others rested
Sleep duration: Modern large herbivores (elephants, giraffes) sleep very little—2-5 hours per day. Giant sauropods may have slept even less, as their enormous bodies required near-constant feeding

Ceratopsians and Hadrosaurs

Medium-to-large herbivores likely had intermediate sleeping strategies:

Triceratops: Probably slept lying on the ground with legs tucked, similar to modern rhinos and hippos. Its horns and frill would have remained upright, providing some defense even while resting
Hadrosaurs: Likely slept in herds, with individuals lying down while others stood watch. Bonebeds showing hadrosaurs in resting positions have been found
Protoceratops: Multiple specimens found in resting postures suggest they slept lying on the ground with legs tucked, possibly in groups

Ankylosaurs and Stegosaurs

Heavily armored dinosaurs had unique considerations:

Ankylosaurus: With armor covering the entire back, sleeping on the belly was the natural choice. Rolling onto the side would have been difficult given the body shape. Their armor provided protection even while asleep
Stegosaurus: The large back plates may have made lying on the side uncomfortable. Stegosaurs likely slept lying on their bellies with legs tucked to the sides

Sleep Cycles and Brain Activity

How Much Did Dinosaurs Sleep?

We can estimate dinosaur sleep patterns based on modern animals:

Animal Group	Daily Sleep	Pattern
Small birds (living dinosaurs)	10-12 hours	Polyphasic (many short bouts)
Large birds (ostriches, emus)	6-8 hours	Mix of standing naps and lying sleep
Crocodilians	17 hours	Long, deep sleep periods
Large mammals (elephants)	2-4 hours	Short sleep, mostly standing
Large predatory mammals (lions)	18-20 hours	Extended post-meal sleep

Based on this, estimates for dinosaurs:

Small theropods: 8-12 hours, polyphasic
Large theropods: 10-18 hours (more after feeding), mix of dozing and deep sleep
Small herbivores: 6-10 hours, polyphasic with alert periods
Large herbivores: 2-6 hours, mostly standing dozes with brief lying-down periods
Giant sauropods: 2-4 hours, primarily standing naps

Unihemispheric Sleep?

Some modern birds and marine mammals can sleep with one half of the brain at a time, keeping one eye open for predators. Dinosaurs may have done the same:

Birds on the edges of sleeping flocks keep the eye facing outward open and the corresponding brain hemisphere awake
Small prey dinosaurs sleeping in groups may have used the same strategy
This would have allowed herds to maintain vigilance while individual members rested

REM Sleep in Dinosaurs

REM (rapid eye movement) sleep—associated with dreaming in mammals—has been observed in birds and some reptiles:

Since both birds and reptiles show forms of REM sleep, dinosaurs almost certainly experienced it too
REM sleep in birds is typically very short (seconds to minutes) compared to mammals
Dinosaurs likely had brief REM episodes, possibly accompanied by twitching muscles—similar to how sleeping birds and dogs twitch during dreams

Nocturnal vs. Diurnal: When Did Dinosaurs Sleep?

Not all dinosaurs were active during the day:

Velociraptor and other dromaeosaurids had large eyes relative to their skull size, suggesting good night vision and possible nocturnal or crepuscular (dawn/dusk) activity
Troodontids (like Mei long) had among the largest eyes of any dinosaur group, strongly suggesting nocturnal hunting
Scleral rings (bony rings inside the eye) preserved in dinosaur fossils can be measured to estimate pupil size and light sensitivity:
- Large pupils = adapted for low light (nocturnal)
- Small pupils = adapted for bright light (diurnal)
A 2011 study of scleral rings across many dinosaur species found a mix of diurnal, nocturnal, and cathemeral (active at any time) species—just like modern ecosystems

This means the Mesozoic world was active 24 hours a day, with different dinosaur species occupying different time niches, sleeping and waking at different hours.

Sleeping Sites and Nests

Where did dinosaurs choose to sleep?

Burrows: Changmiania and the ornithopod Oryctodromeus show evidence of burrowing, providing safe sleeping shelters
Nests: Oviraptor fossils show adults sleeping on nests while brooding eggs—combining rest with parental care
Tree roosts: Small feathered dinosaurs like Microraptor had grasping feet suitable for perching and may have slept in trees, safe from ground predators
Open ground: Large dinosaurs with few predators likely slept wherever they happened to be, relying on size and armor for protection
Herd centers: Juveniles and smaller individuals likely slept in the center of herds, surrounded by alert adults

Frequently Asked Questions

Q: Did T-Rex snore? A: While we can’t know for sure, many modern animals that breathe through large nasal passages produce sounds during sleep. A sleeping T-Rex may well have produced deep, rumbling breathing sounds—not exactly snoring in the human sense, but potentially audible.

Q: Could dinosaurs dream? A: Very likely. Both birds and reptiles show REM-like sleep states associated with dreaming. Since dinosaurs are ancestral to birds and share common ancestry with reptiles, they almost certainly experienced some form of dream-like brain activity during sleep.

Q: Did any dinosaurs sleep in trees? A: Probably. Small feathered theropods with grasping feet—like Microraptor and early birds—likely roosted in trees. Some may have even slept hanging from branches, though we have no direct fossil evidence of this specific posture.

Q: How do we know dinosaurs didn’t sleep standing up like horses? A: Some likely did—at least for light napping. Horses and elephants can lock their leg joints to sleep standing. Large sauropods may have done the same. However, fossils of small dinosaurs consistently show lying-down resting postures, and even large animals need to lie down for the deepest stages of sleep.

From the curled-up “sleeping dragon” Mei long to the buried-alive Changmiania to sauropods napping on their feet, dinosaur sleep was as varied as the animals themselves. The Mesozoic world was never truly quiet—as some dinosaurs drifted off to sleep, others were just waking up to hunt in the darkness.