"Is it possible that non-avian dinosaurs nest in small self-dug, or captured caves? and if yes, what species would be suitable for this behaviour?
These were the questions which grew into my mind when I thought about nest forms.
I finally choose Epidexipteryx. Why?
Let’s begin with the environment of E. hui. The specimen was found in china, inner Mongolia, within the Daohugou beds which are between 168 and 152 million years old. It was a wet ecosystem with lakes and streams, it was the home of the first known aquatic mammal, Castorocauda, which was maybe also a digging animal.
Volcanic ashes are known from the fossil beds, a material which may form huge river banks and small canyons, here an example: [link] an environment.
Epidenxipteryx may used such walls to build its own holes. The animal is really small (25 cm without the tailfeahters) and light (160 g). The long fingers and possible presence of grasping claws, like Epidendrosaurs (I would have chosen this species, but we just know juveniles), make a climbing lifestyle practicable. The teeth are not visible here because I cover them with lips (inspired by Quilongs Masiakasaurus) but they were huge for an animal of this size and may help to dig into the clay of the cliff. In addition a short tail, like found at Epidenxipteryx, could be useful; even if I have reconstructed the animal here with the iconic four tail feathers it’s possible that these were just seasonal phenomenons which disappear after mating.”