Oryctodromeus burrows were discovered in 2006 in Montana and since then other burrows have been described from Australia. While Anthony Martin, the man responsible for the descriptions of the burrows in America as well as Australia, attributes the Aussie burrows to both a dependence on the earth to hide as well as warm during the theorized long Aussie Cretaceous winter (see leaellynasaura), the Montana burrows would more than likely not have been dug for winter survival as much as simple survival from predators. What else, then, could they have been used for? Certainly running and hiding is enough reason to have a burrow when a slightly larger raptor or a tyrannosaur is trying to end your life; but was there other evidence in the burrow that made the Oryctodromeus burrow find even more important than simply being a burrow? There certainly is and we have the graphics to help understand it.
Adapted from L. Hall/Montana State University
The Montana burrow contained Oryctodromeus skeletal material in a large hollowed out burrow comprised, millions of years later, of sandstone that had, it is thought, originally lined the burrow for comfort, to make a home (a couple of pillows and a sandy carpet, maybe a skylight!) for the small animals. The entrance of the burrow, denoted in the figure above by the letter "U" was just large enough for an adult Oryctodromeus to squeeze in and then meander, probably crouching quite low for a short ways before reaching the larger inner chamber, down to its wider and more open home environment. Using speed to gain distance and then squeezing into a small hole is a somewhat common defensive measure for extant fauna (rabbits, mice, and shrews; to name a few mammals that can use this strategy) and would have certainly worked in dinosaur times for a smaller herbivore which used speed as its initial defensive strategy. However, the home chamber, labeled "CH", also had a surprise for Martin and the team when it was examined; babies! Along with an adult Oryctodromeus two smaller skeletons, announced as juveniles, were also discovered in the hollowed out nest area of the burrow. This evidence points not only at a defensive strategy but also at a family unit living in the burrow. Whether that family unit is theorized to be a single parent unit or that of a collector and protector role for each parent I have not seen yet, however, given evidence from numerous stay at home parents in the existing animal kingdom, it would not amaze me, for one, if the parents either took turns collecting foliage and bringing it to the nest or if it was a mom at home dad out earning food situation. This could also explain a heart-breaking story of loss when a burrow collapsed and a family was lost with one parent outside unable to help its family...
Photo and arrows by Anthony Martin
Let us, for now, try to ignore the sadness either parenting scenario leaves us in with this burrow and skeletons and look at something that Anthony Martin personally points out on his blog entry from which this photo is borrowed. The arrows, according to Martin (which can be seen in the image above as well once one knows to look for them), indicate accessory, or extra burrows. These would not have been used by the Oryctodromeus, but rather by other animals smaller than Oryctodromeus which survived by living in communion with Oryctodromeus, or vice versa. Martin points out in his blog that the gopher tortoise exists in a similar symbiotic community where the tortoise, or another denizen of the community, begins and extends its tunnel and other smaller animals, insects, smaller mammals even, extend tunnels for their own living spaces in the comfort of knowing that their neighbors will not come through their walls and eat them. The arrows in Martin's photo (and t1 and t2 above) point to other burrows found extending from the main Oryctodromeus tunnel. Oryctodromeus was not, then, just a burrow digger, but a community planner and neighborhood builder. Nifty role for a fast little dinosaur.