A rare fossil reveals behavior that may have been shared between dinosaurs and birds

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Death in the wilderness is often brutal and violent. But for a small, bird-like dinosaur of the late Cretaceous period, the end of its life was relatively peaceful, as it curled up to take a nap and never woke up.

This is what scientists explained from the position of the dinosaur’s fossil skeleton. With the creature’s head resting on its limbs and its tail wrapped snugly around its body, its relaxed posture resembles that of Modern birds In a quiescent state, suggesting that these dinosaurs not only looked like birds, but may have even acted like them.

Paleontologists have excavated a dinosaur’s skull and nearly complete skeleton in the Gobi Desert in the Barun Guyot Formation in Mongolia, and that most of the bones are still arranged in the animal’s original death position, researchers reported Wednesday in the journal. One plus.

The animal’s long neck wrapped around the right side of its torso, and its head was tucked close to its side, resting above the right knee. The hind limbs were tucked under, and most of the tail was curved around the left side of the body.

The study’s authors identified it as an alvarezsaurid, a small species Theropods (bipedal carnivorous dinosaur) with a long tail and legs and short forelimbs. Alvarezosaurids are part of a larger group of dinosaurs called maniraptorans, which includes birds and the bird-like dinosaurs that were their closest relatives.

The tiny Alvarezsaur’s posture mimicked that of two other dinosaur fossils found in Mongolia that were also curled up in bird-like sleeping positions: Sinornithoides yungii and Mei longi. These are two types of dinosaurs, another type of dinosaur in the maniraptoran group, which is more closely related to birds than Alvarezsaurus.

The new fossil suggests that this sleeping behavior may have been more common than expected among non-avian relatives of the first birds, the researchers report.

“We’ve all seen ducks sleeping with their heads tucked under their wings. Then you see this little dinosaur in the same sleeping position,” said paleontologist Dr. Jingmai O’Connor, associate curator of fossil reptiles at the Field Museum of Natural History in Chicago.

“This is concrete evidence of behaviors that today are unique among birds. Now, we can actually say that this is not a unique trait for birds,” O’Connor, who was not involved in the study, told CNN.

Scientists who examined the fossil decided it was a species new to science and gave it a ferocious name: Jaculinykus yaruui. The genus name comes from jaculus, a mythical dragon, and onykus, which means claw in ancient Greek, while its species name stems from yaruu, the Mongolian word for hasty or quick.

Jaculinykus yaruui lived about 70 million years ago at the end of the Stone Age Cretaceous period It was just over 3 feet long (about 145 million to 66 million years ago) from nose to tip of tail, said lead study author and paleontologist Kohta Kubo, a doctoral candidate in Hokkaido University’s Paleobiology Research Group. Japan.

“This specimen was considered a partial skeleton when it was discovered, but after it was prepared, it represents a nearly complete, detailed skeleton that maintains its lifelike posture,” Kubo told CNN in an email. “It is the first definitive record of this posture in alvarezosaurs as well as early branching maniraptoran dinosaurs.”

The closest relative of Jaculinykus yaruui is a small alvarezsaurid called Shuvuuia deserti, Kubo said. Among its distinguishing features are the shape of its nostrils, the connection of the jaw muscles to the skull, and the shapes of the bones of its limbs.

“It’s a beautiful specimen, and it’s always exciting to have new diversity in dinosaurs, especially in alvarezosaurids,” O’Connor said.

Alvarezsaurids are not the most well-known group of dinosaurs, but they have long fascinated scientists with their dramatically short forearms and hands, which in some species ended in a single massive toe sprouting a spike-like claw.

“These types of fossils that are so well preserved that they record behaviors are extremely rare,” O’Connor said. “It’s great that we have some additional evidence that definitely shows that this sleeping position was more widespread.”

In modern birds, this behavior helps them maintain body heat; It likely served a similar purpose to maniraptor dinosaurs, which also curled up at bedtime, according to the study. Over the course of its evolution, Alvarezsaurus shrunk in size. This “radical miniaturization” may have led non-avian dinosaurs to adopt the same thermoregulation strategy as their avian cousins, Kubo said.

Furthermore, the tiny, sleepy Jaculinykus yaruui “highlights that this bird-like thermoregulatory behavior evolved before the advent of powered flight.” “Jaculinykus is an important example that alvarezsaurids possess more similarities to living birds – not only in bone features but also in behavioral traits.”

Mindy Weisberger is a science writer and media producer whose work has appeared in Live Science, Scientific American, and How It Works.