LET SLEEPING DINOS LIE
FOSSIL EVIDENCE POINTS SCIENTISTS TOWARD DIFFERENT THEORIES ABOUT HOW THESE PREHISTORIC CREATURES LIKELY SNOOZED.
CLOSE YOUR eyes and imagine a snoozing triceratops or a T. rex taking a siesta. How, exactly, did these prehistoric beasts sleep? For scientists, it’s difficult to say — largely because most dinosaurs didn’t die that way.
In other words, the only way we can know how a dinosaur slept would be if they fossilized in a sleeping position, but finding a dinosaur in a sleeping position is uncommon. Most fossils we’ve found show dinosaurs in a classic “death pose,” as shown at the upper right, their bodies contorted as they brace for their imminent demise.
Still, a few key specimens found in recent years have provided some clues into the sleeping world of these ancient creatures.
SCOTT PERSONS, a paleontologist at the College of Charleston in Charleston, South Carolina, notes that scientists are continuing to learn from these rare fossils. “In a few specific cases, we know a great deal about how dinosaurs would have slept because we found the skeletons of sleeping dinosaurs,” he says. These specimens, he continues, are reminiscent of those found in Pompeii, meaning that they were buried very quickly by volcanic ash, preserving them for millions of years in a peaceful sleeping pose.
In a recent example, scientists documented an Alvarezsaurid dinosaur found in Mongolia in a sleeping position in a study published in PLOS ONE in 2023. Alvarezsauridae was a small family of dinosaurs about the size of a flightless bird. The specimen was found in a sleeping position, all curled up with its neck and tail wrapped around its body.
“The fossil was hunkered down, with legs and arms folded,” says Persons, who was not involved with the study. “[It’s] one of the most adorable fossils that you ever did see.”
Other fossils from sleeping dinosaurs have been unearthed in similar states; in one case, curled up in an underground burrow. Two Ornithopod specimens — two-legged herbivores that lived some 125 million years ago — were found in the Lujiatun Beds in Northeast China, according to a 2020 study in PeerJ Life & Environment.
Animals that tend to sleep curled up are likely concerned with retaining body heat. This means they’re less likely to sleep spread out like crocodiles or lizards, who both get their heat from external sources. These animals burn ample energy producing heat so they would want to keep it tightly held within their bodies while they slept. This was true of both the Alvarezsauridae and the Ornithopod specimens.
EVEN WITH those illuminating finds, there’s still lots scientists don’t know about sleeping dinosaurs. For example, how did the huge, long-necked sauropods sleep? Did they snooze curled up and lying down, or did they sleep standing up for protection and to ensure proper blood flow?
“Modern giraffes, for example, sleep standing up with their necks still fully extended,” says Persons. “If they slept curled up, their powerful hearts would send too much blood to their heads and cause them to black out.” Additionally, while there’s no research to prove this, Persons notes that it’s been suggested that the large pubic bone among Tyrannosaurus rex was “basically a kickstand” to hold it up while the monstrous predator dozed.
It’s also hard to know how dinosaurs in general slept because there were so many different varieties. The animals of today all sleep in different ways depending on the species, and this was likely true of dinosaurs — some curled up, some burrowed, some standing, and others spread out. Thus, the sleeping rituals of these prehistoric creatures still largely remain a mystery, with the exception of those few that met their end as they slumbered.