One of my favorite fossils. Too cute.
When: Early Cretaceous (~125 million years)
Where: Liaoning, China
What: Mei is a paravian dinosaur. Paraves is the clade comprised of birds and two families of non-avian dinsaurs; Troodontidae and Dromaeosauridae. As Mei is a fairly basal member of the troodontids, it is not very far removed from the common ancestor of all paravians. Its bird-like heritage can be easily seen in this extraordinary articulated fossil shown above. This specimen was found in a sleeping pose, which is very much like the resting posture of many modern birds, with the legs folded underneath the body and the head folded back and resting on the shoulder. It is this pose that gives the taxon its full name: Mei long, which translates to ‘sleeping dragon’. This animal is a sub-adult, determined via the ends of its bones not yet being fused, and would be roughly 21 inches (~53 cm) long, if it was not curled up as it is.
The find of a basal troodontid in this pose gives us far more information than just when the sleeping posture was adapted by this clade. It has been determined that modern birds commonly sleep like this to preserve their body heat, covering up the areas that are most prone to radiating heat. If Mei long and its kin were not ‘warm blooded’ than there would be no benefit to sleeping in this pose. Thus, this provides another compelling bit of evidence that the ‘warm bloodedness’ of modern birds was present in their mesozoic non-avian relatives.