Description and Classification

Mei was a tiny dinosaur, estimated to be only about 53 centimeters (21 inches) in length, roughly the size of a modern duck. It had a lightweight skeleton, long legs for its size, and many features similar to modern birds. These characteristics suggest it was an agile and quick-moving animal.

Mei belongs to the family Troodontidae, a group of small to medium-sized theropod dinosaurs known for their relatively large brains, large eyes, and sharp teeth. Troodontids like Mei are considered very closely related to birds, sharing many anatomical similarities. Other members of this group include dinosaurs like Troodon and Stenonychosaurus. The only known species is Mei long, which means “sleeping dragon.”

Distinguishing Features

Mei is notable for several unique characteristics:

• Sleeping Posture: The most famous feature of Mei is the “sleeping” position in which its fossils were found. The type specimen, and later a second one, was preserved with its body curled up, its tail wrapped around it, and its head tucked under one of its forelimbs. This posture is nearly identical to the way many modern birds roost and sleep, providing strong evidence that this behavior evolved in dinosaurs before the origin of birds.
• Small Size: Mei is one of the smallest known non-avian adult dinosaurs, highlighting the diversity in size among theropods during the Cretaceous period.
• Extremely Bird-like Anatomy: Beyond the sleeping posture, Mei possessed numerous skeletal features that are very bird-like, further supporting its close evolutionary relationship with birds. This includes a light build and long, slender legs.
• Large Nasal Openings: It had proportionally very large openings for its nostrils in its skull.

Paleoenvironment and Diet

Mei lived in what is now Liaoning Province, China, during the Early Cretaceous. This area, famous for the Yixian Formation, was characterized by a diverse ecosystem with lakes, forests, and active volcanoes. The fine volcanic ash from eruptions in the area led to the exceptional preservation of many fossils, including those of Mei, often capturing details of soft tissues like feathers and even life poses.

As a troodontid, Mei was likely a carnivore or an omnivore. Its small size and sharp teeth suggest it probably hunted small animals such as lizards, insects, and possibly small mammals. It might have also eaten eggs or supplemented its diet with some plant material. Mei shared its environment with many other dinosaurs, including other small feathered theropods like Sinosauropteryx and Caudipteryx, the plant-eating Psittacosaurus, and early birds like Confuciusornis.

Significance and Ongoing Research

The discovery of Mei has been highly significant for paleontology. The stunningly preserved sleeping posture provides direct fossil evidence of complex, bird-like behaviors in non-avian dinosaurs. This suggests that many traits we associate with birds today actually originated much earlier in their dinosaur ancestors.

Mei fossils also contribute to our understanding of troodontid anatomy and the evolution of bird characteristics. The three-dimensional preservation of some specimens allows for detailed study. It is believed that the Mei specimens were rapidly buried by volcanic ash while they were sleeping, which is why they were preserved in such a lifelike pose.

Ongoing research on Mei and other troodontids continues to explore their biology, behavior, and their place in the dinosaur family tree. Scientists study these fossils to learn more about dinosaur metabolism, the evolution of feathers (though direct feather impressions are not perfectly preserved with Mei, other troodontids are known to be feathered), and the dynamic ecosystems of the Early Cretaceous period.