The Paleo Burrows in the Evolution Underground

Orictodromius was also a curser, which means digging runner. The authors of this paper say that if we look at analogies to day running animals that create burrows tend to do so for a pretty specific reason. They create them as dens for rearing their young. A den provides a place to protect the young while they're growing and still vulnerable. Some had partially or wholly filled with sediment but others remained quite open. These were cut in a variety of soft igneous, metamorphic and set bedrock.