A newly described dinosaur from Mongolia reveals sleeping poses shared with modern birds
An international team of paleontologists from Japan, Mongolia, and the United States has identified a new dinosaur species that slept in a position strikingly similar to today’s birds. The find is documented in a study published in an issue of the journal PLOS One, signaling a notable link between ancient and modern sleeping postures.
Fossils were recovered during excavations in Mongolia’s vast Gobi Desert, a site long famous for extraordinary dinosaur discoveries. The animal belongs to the family Alvarezsauridae, a lineage of small, bipedal carnivores. The researchers named the species Jaculinykus yaruui, a moniker that translates roughly to “little fast dragon.” Radiometric and comparative analyses place this species in the late Cretaceous period, about 71 million years ago.
Estimations suggest Jaculinykus yaruui stood roughly one meter tall and carried a body mass near 30 kilograms during life. The fossil’s most compelling feature is its resting posture. The neck and tail are lowered, and the hind legs are tucked beneath the body, a configuration that mirrors modern birds when they prepare to sleep. This arrangement appears to have provided stability and comfort for the animal while it rested in its natural environment.
The researchers note that contemporary birds curl up during sleep not only for warmth but also for protection and energy conservation. The discovery implies that ancient relatives of birds may have used similar strategies to curtail heat loss and maintain bodily warmth during rest, suggesting behavioral parallels that stretch back to the throne of the dinosaurs.
In the broader context of paleontology, this finding contributes to a growing body of evidence that links bird-like sleeping behavior to their theropod ancestors. It also reinforces the understanding that certain life-history traits seen in modern birds have deep roots in the dinosaur lineage, reinforcing their evolutionary connection and the continuity of life over tens of millions of years. Scholars cite the Gobi fossil as an important data point in discussions about the evolution of resting behavior and metabolic regulation among early birds and their close relatives (evidence summarized in comparative studies by researchers in Mongolia, Japan, and North America).
The discovery of Jaculinykus yaruui underlines the value of continued fieldwork in arid landscapes and the importance of international collaboration in paleontology. Ongoing analysis of the specimen, including its skeletal proportions and possible feather impressions, aims to shed further light on how this small predator lived, hunted, and eventually slept within its ecosystem. While the fossil record always leaves some questions unanswered, this find adds a new chapter to the story of how sleeping behavior emerged and persisted among the dinosaurs and their bird descendants, bridging millions of years of natural history (as discussed by contemporary researchers and summarized in recent reviews).