Burrowing dinosaurs

There is something wonderful about a bunch of people being drawn together by something that is at best obscure and at worst ridiculously geeky. It's the kind of feeling you get at a Scrabble tournament, or a They Might Be Giants concert and it's a feeling I experienced today as I attended the 11th Australian Vertebrate Palaeontology Conference at Museum Victoria. You may laugh, you may scoff. You may point at me and throw things at me and shout 'Ha ha, poindexter!' - but what the hell did you do with your day? Back off and stop throwing stuff at me. One particularly interesting article of palaeontological note was brought to my attention - a paper describing a new species of dinosaur from Montana. The authors, David Varrachio, Tony Martin and Yoshihiro Katsura named the new dinosaur Oryctodromeus cubicularis, a small bipedal herbivore belonging to a group called the Hypsilophodonts. As they were excavating the fossilised dinosaur skeleton out of a mudstone layer it became apparent that it was inside a strange sandstone structure within the rock. This sandstone layer was the den of Oryctodromeus, the first dinosaur known to exhibit burrowing behaviour. In fact, in addition to an adult skeleton there were also two juvenile skeletons within the burrow as well. The presence of an adult with juveniles strongly suggests close parental care in this species, something which is suspected to be quite common amongst dinosaurs but for which there is not a lot of direct evidence. In this single fossil find you can see a snapshot of life for a particular species of dinosaur that lived between 99 - 93 million years ago. But why did Oryctodromeus burrow? Many animals today dig burrows for a variety of different reasons; to escape extremes of hot and cold, to avoid predators and to raise their young. It's probable that Oryctodromeus was a burrower for all these reasons. The undeniable existence of burrowing behaviours in some dinosaur species raises some interesting questions about the final mass extinction that wiped the group out at the end of the Cretaceous 65 million years ago. It is generally accepted that this extinction event was kick-started by a huge asteroid colliding with the earth, devastating a large area of the planet from the impact and throwing up a huge dust layer which blocked out sunlight and halted photosynthesis of plants. Of the groups that made it through the Cretaceous extinction (such as mammals), survival has often been attributed to them finding suitable shelter from climatic extremes. Burrowing dinosaurs would surely be in this category and could have theoretically survived the mass extinction but Oryctodromeus is known from the early Late Cretaceous not the late Late Cretaceous. Further excavations may reveal more burrowers from younger localities nearer the end of the Cretaceous, now that we know what to look for. Interestingly the authors suggest that burrowing may have been a behavioural adaptation for dinosaurs living in polar environments - such as the Hypsilophodonts known from the Cretaceous rocks of Victoria, Australia. We haven't found any conclusive evidence for them yet, but if you see a fossilised burrow that looks like it was dug by something the size of a wallaby give me an email.

Science Daily article about Oryctodromeus