Burrowing dinosaurs are also cool. Honest.

I figured that the internet would be awash with palaeoart of Oryctodromeus cubicularis, the small, Blackleaf Formation hypsilophodontid famous for living in family groups within burrows of their own creation (Varricchio et al. 2007). A quick Google image search, thought I, would reveal dozens of images of Oryctodromeus sitting in dens, digging, hanging out in family groups and all that sort of stuff. I was even expecting to make some sharp comments about minor clichés and tropes in the way Oryctodromeus was depicted. Turns out, however, that there aren't many pictures of this dinosaur at all. On reflection, I guess I Oryctodromeus doesn't meet the three Big Criteria for Palaeoartistic Attention: a) it doesn't really have anything to do with bird evolution; b) it doesn't bear any fancy teeth, claws or spikes and c) it wasn't very big. But I still think this is crazy. It was found in a fickin' burrow of its own making. Palaeonerds, artistic and otherwise, spend hours speculating about what sort of interesting behaviour dinosaurs may have got up to, and then one with incontrovertible interesting behaviour is discovered and... we - myself included - don't do much with it, really. Even the PR associated with its discovery favoured a straightforward illustration of an Oryctodromeus head rather than something more exciting, like a depiction of one digging a hole or drowning in its burrow. How odd.

With that in mind, here's a set of Oryctodromeus to help their much needed PR campaign. Rather than showing an Oryctodromeus burrow in section, as is common to the few depictions of this animal that exist, I wanted to draw them as we may see them in life, hanging out at their burrow entrance in a Lower Cretaceous woodland. The burrowing adaptations of the animals, which are clear and obvious across much of the Oryctodromeus skeleton, are not really discernible here, save for their broad, shovelling snouts which I've adorned with thickened scales to resist shovelling abrasion. This is deliberate, however. Much of the burrowing anatomy of Oryctodromeus reflects relatively minor changes to the hypsilophodontid bauplan and they probably didn't look radically different from other hypsilophodontids with their skin and (possibly) fuzz obscuring their skeletons. In addition to their reinforced snouts, we may have noticed that Oryctodromeus had slightly bulkier forelimb anatomy compared to other hypsilophodontids, as these seem to have been their digging limbs (instead of the hindlimbs, as with the rhynchosaurs we met here). Their hindquarters may also have been a little chunkier, as they seem reinforced to provide a stable digging platform. Otherwise, they probably looked much like other members of their clan. Indeed, the overall similarity of Oryctodromeus to other hypsilophodontids suggested to Varricchio et al. (2007) that burrowing behaviours may not be unique to this member of the group.

Much was made of the assemblage of bones found within the Blackleaf Oryctodromeus burrow. The incomplete skeletons, presumably reflecting animals that died within a burrow shortly before or during a flood, represent two juvenile and one adult individual, and additional discoveries of this species (sadly, not in burrows) hint at even larger Oryctodromeus communities of mixed maturity (Krumenacker et al. 2011). I wanted to bring this out in the painting, so have drawn an entire family, with  two adults and two juveniles perched atop the head of one parent (did dinosaurs carry their children? Perhaps, seeing as many reptiles and mammals  ferry their offspring about when they're especially small). I realised that I'd accidentally made the adults rather different in size rather late in painting the image, but I decided to run with this mistake rather than correct it. First thoughts may be that this could be written off as sexual dimorphism, but I thought it may be better explained though another means: teenage mothers. The early development of reproductive bone histologies in dinosaurs suggests that they, like reptiles, became sexually mature well before they reached their maximum size (generally, no later than halfway to their maximum proportions - Lee and Werning 2008) so it doesn't seem unlikely that some dinosaur couples would be rather mismatched in terms of size if young and old formed breeding partnerships.

Details of an Oryctodromeus burrow; from Varricchio et al. 2007

The upper part of the Blackleaf Formation, which contains the only known Oryctodromeus burrow, represents a well-drained, inland floodplain dotted with lakes and small river channels, set in a relatively warm, seasonal climate. The Blackleaf Oryctodromeus burrow is a fairly large structure that exceeds 2 m in length, and thus extended beneath well into the underlying floodplain muds (see Oryctodromeus burrow details, above, from Varricchio et al. 2007). These clays contain evidence that the floodplain was once fairly well vegetated, with their mottled colouring reflecting variable intrasoil microenvironments associated with root activity and layers of carbonate nodules reflecting dessication of soil layers. I figured our burrowers could make use of these plants, using them to conceal their burrows rather than setting their burrow entrance exposed in a wide, open space. Accordingly, the actual entrance to the Oryctodromeus burrow is not seen here, instead being obscured by the roots of a tree. It's not entirely inconspicuous however, as heaps of sediments below the burrow opening mark material ejected by the tunnellers as they expanded and maintained their dwelling (as seen with badger sets). Because the burrow is long enough to extend through several layers of varicoloured clays, the ejected clays are of a rather different colour to the surrounding soils. Setting Oryctodromeus in such a more vegetated setting also helps to break a palaeoart trope noted at Antediluvian Salad: the "dinosaur conveniently framed by vegetation on an empty patch of dirt" meme. This manner of showing extinct animals certainly makes their anatomy clear, but is comically frequent in palaeoart once you start looking for it. I've certainly added a list of images to this trope, and figure it's time to move my animals off their dirty catwalks and behind the mud, vegetation and shadows of real life.

Finally, and on a related note: it seems I've fallen victim to a most foul palaeoart clichés: A Volcano! Behind Dinosaurs!!1! Volcanoes and dinosaurs seem to walk hand-in-hand in some circles, and the dinosaur imagery I was familiar with in my childhood always seemed to have a volcano bubbling away in the background. It seems that the association of angry mountains and dinosaurs is more of a 'popular' notion than a real palaeoart meme however, presumably because most people with genuine interests in palaeontology and geology know that Mesozoic landscapes were not perpetually exploding. I suppose the popular link between volcanoes and dinosaurs stems from ideas that non-avian dinosaur extinction was likely influenced by the extensive volcanism of the Deccan Traps. Or maybe it's because dinosaur fossils are intertwined with geology, of which volcanoes are the flagship popular topic. Or maybe it's simply pandering to the Lava Adds Awesome and Climatic Volcano Backdrop tropes. Whatever the reason for their prevalence in popular palaeoart, the inclusion of a volcano alongside Oryctodromeus is fairly sound: the Blackleaf Oryctodromeus burrow was made in a landscape that was occasionally inundated by volcanic detritus and tuffaceous sediments, blown in from volcanism occurring to the south west in contemporary Idaho. I'm not sure whether the types of volcano shown here - a classic 'cone' volcano - is appropriate, but the temptation to draw a big mountain belching smoke behind some dinosaurs was too much to resist.

Oh, and finally finally, a big thanks to all the people who've stopped by here thus far before I go. This blog is not even two months old, and I've already been visited over 5,500 times. It's very encouraging and flattering to have this taking off so quickly, so thanks for all the visits, comments and linking that must be happening to make this a minor success already.

References

• Krumenacker, L. J., Britt, B. Varricchio, D. J., Scheetz, R. and  Robison, S. 2011. Idaho's first dinosaur identifiable to genus level, Oryctodromeus sp., from the mid-Cretaceous Wayan Formation, and the geological and paleontological setting. Geological Society of America Abstracts with Programs, Vol. 43, No. 4, p. 16
• Lee, A. H. and Werning, S. 2008. Sexual maturity in growing dinosaurs does not fit reptilian growth models. PNAS, 105, 582–587.
• Varricchio, D.  J.,  Martin, A. J., and Katsura, Y. 2007. First trace and body fossil evidence of a burrowing, denning dinosaur. Proceedings of the Royal Society B, 274, 1361–1368.