Around 140 million years ago, a certain Mei long lay down to sleep. The feathery duck-sized dinosaur, a troodontid of the early Cretaceous period, adopted a pose common to modern-day birds: Head nestled beneath a winglike forelimb, hind limbs tucked underneath its body. Unfortunately for this particular creature, its bedtime coincided with some disastrous event that buried it alive, forever preserving the unlucky theropod in its state of rest.
It’s next to impossible to know how the dinosaurs slept. Though the body of paleontologic knowledge grows with each day, full skeletons are rare, and those that are razed are often in what’s referred to as the death pose: Neck tilted back, tail curled upward. No one’s quite agreed what causes the death pose, but most paleontologists suspect it’s the result of contortions that occurred during or after the animal’s demise. And since we can’t exactly observe dinosaurs in the act of sleeping, we’re left more or less in the dark. Which is what makes Mei long, Chinese for “soundly sleeping dragon,” so exciting.
Scientists have unearthed two Mei long specimens in apparent slumber: The first was described in 2004 by Xing Xu and Mark Norrell; the second was described in 2012 by Chunling Gao and four co-authors. One of these is Eric Morschhauser, a professor at Drexel University who told Van Winkle’s that Mei long is unique among dinosaur skeletons.
“There are a number of positions associated with processes that happen after death,” Morschhauser said. “All kinds of things affect how dinosaurs are found in the field. They get torn apart, things happen with the muscles after death. But this arrangement — where the arms are folded up at the side, the elbows are a little bit out, and the head is curled back and tucked behind one of the elbows — is exciting because it’s a position that shouldn’t be associated with any other processes.” Any processes other than sleep, that is.
Morschhauser said that Mei long’s posture offers yet another commonality between dinosaurs and birds, which may deepen our understanding of Mei long and its relatives.
“There’s a lot of other features that tie meat-eating dinosaurs to birds,” he said. “Skeletal features, feathers and now this sleeping position, which could be implicated in sleeping with a very low surface area exposed: If you’ve got a relatively high body temperature and need to keep it that way, it’s a good position to be in, because you’re minimizing exposure to the outside environment.”
Mei long had some kind of feathered or feather-like insulation and, according to Morschhauser and his team, this position would reinforces that notion:“Why would you arch the head over the arm unless you actually had insulation on that arm?”
The precise circumstances of Mei long’s death remain an open question, however. David Varricchio, a professor at the University of Montana and one of Morschhauser’s co-authors, dismissed early speculation that his specimen perished was buried in volcanic ashfall.
“Some people said ‘oh, it’s volcanic deposits,” but if you look at the sediments, it’s not raining hot volcanic ash on these animals,” he said. “Some people said ‘oh, maybe it’s a mudslide,’ and I find that hard to believe. It seems that should orient animals in all sorts of different directions — there’d be this thick slurry of mud and rock. It’s hard for me to imagine that they’d all end up belly-down.”
And yet Mei long’s posture does seem to reflect “the death of a living animal,” according to Varricchio. “It seems like the animal was either somehow buried alive or was unmodified after it died,” he said, noting that similar belly-down specimens typically show signs of postmortem snacking by scavengers. Both Mei long specimens, however, were preserved unmolested.
“I wonder if they were in burrows or dens,” Varricchio said. “I’m maybe obsessed with that theory. I don’t really have any firsthand field documentation — you could look for changes in the rocks surrounding the specimens, but these rocks are kinda collected without any field data. So I could see it being curled up in a den, sleeping in that den, and then it either perishes or is buried alive.”
We may never know how Mei long died, whether its larger relatives slept similarly or if they all had anxiety dreams about their teeth falling out. But the soundly sleeping dragon is a unique glimpse into the nocturnal lives of dinosaurs, and proof that they still sleep among us today — just head over to the local duckpond and see for yourself.