Did Dinosaurs Sleep at Night?

Did Dinosaurs Sleep at Night?

2021-01-12 14:37:00

From museum halls to movie screens, we love seeing dinosaurs at their brightest. All those teeth, claws, spines, horns, and other weird decorations have provided a lot of inspiration for dramatic – and often brutal – Mesozoic scenes over the years. But the lives of dinosaurs were not simply "Red in tooth and claw. These once real animals had many other concerns in their daily lives – such as resting, napping and sleeping.

Before we get into how dinosaurs said goodnight, though, it's worth asking when dinosaurs snooze. Today, animals are usually active, either during the day, at night, or at dawn and dusk. And in 2011, paleontologists Lars Schmitz and Ryosuke Motani suggested that different non-avian dinosaurs were also active at different times of the day.

Schmitz and Motani examined delicate eye bones of different dinosaurs to see how those structures called scleral rings related to when the reptiles may have been active. The bones indicate not only how big the eyes were, but also how much light they let in. Following this logic, the researchers found that large, herbivorous dinosaurs like the duckbill Corythosaurus probably stomped in the morning and & # 39; around at night while predators like the infamous Velociraptor stalked the night.

But dinosaurs eventually stopped their daily activities, whether they were active at night or during the day. A growing collection of fossils shows how they did that.

How dinosaurs say goodnight

For example, when a sleepy bird of prey went to sleep, the dinosaur probably assumed a familiar pose. Rare skeletons and trace fossils – or impressions made by once living dinosaurs – indicate that at least some dinosaurs shuffled their feet under them, folded their arms and leaned their heads on their back, as do some dormant birds today. Nearly a century ago, paleontologist Charles Lewis Camp described the bones of a tiny, carnivorous dinosaur named Segisaurus found with his arms and legs underneath.

Since then, several other finds have surfaced. In the Jurassic Rock of southern Utah there is a body impression of a great one, Dilophosaurus-like dinosaur that sat down to rest, shuffled forward, and settled in. From the way the dinosaur sat to how it held its hands, this carnivore behaved in a very bird-like manner, despite living more than 40 million years before the first birds evolved. Better yet, paleontologists have also described the fossil of a tiny, raptor-like dinosaur called May long it slept – curled up and snugly – while ashes buried the unfortunate animal. The name translates to "sleeping dragon".

Here the dinosaur Dilophosaurus wetherilli hangs in a bird-like pose. (Credit: Heather Kyoht Luterman)

To date, most of the resting dinosaur finds were from strange, parrot-like dinosaurs called oviraptorosaurs. "We have far more resting oviraptorids than any other group of dinosaurs," said University of Edinburgh paleontologist Greg Funston, who notes that there are more than half a dozen published specimens. Last year, Funston and colleagues published yet another example: juveniles of a new oviraptorosaurus named Oksoko which were found in the classical resting position.

So far, most of the finds relate to a particular branch of the dinosaur family tree – the theropods, which includes birds. A rare counterexample is the name of a herbivorous dinosaur Changmiania which was named in 2020 after a pair of skeletons found in rolled-up resting positions, which depict dinosaurs buried in a collapsing burrow. But when it comes to favorite giants like Triceratops, Stegosaurus, Apatosaurus and others, those dinosaurs may have been too big to leave any clues. “There is probably a limit to how big an animal can get before it cannot be buried alive,” says Funston. So paleontologists are unlikely to have one Brachiosaurus who perished while dozing off.

The local environment also plays a role. “In areas such as Mongolia's Gobi Desert, which is an oviraptorid hotspot, some rocks come from desert environments where animals can more easily be buried alive,” said Funston. Large sand dunes near where the dinosaurs nested could suddenly collapse and bury them at rest, a special circumstance not found in many other places.

Trace fossils can be useful here. Dinosaurs have left their marks and impressions, as well as bones. The trick would be to recognize them. "If some dinosaurs were to lie in completely horizontal positions, the tracks from that behavior could be so large and messy that we would have a hard time recognizing them as track fossils," said Emory University paleontologist Anthony Martin. Thinking on a dinosaur scale isn't always easy.

Nonetheless, paleontologists are still working on the quieter side of dinosaur life. This month, paleontologists suggested they find traces made by a rest Tyrannosaurus pushing himself off the ground with his forearms. Martin is skeptical of the identification, noting that the tracks may be unrelated impressions, but he is still glad that other researchers are reminding dinosaurs to do things other than bite each other. "Dinosaurs weren't always moving, chasing, or chasing," says Martin. & # 39; Sometimes they had to stop, watch and listen. Or just chill. "


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