We all knew that a great many dinosaurs were airheads, but were we presuming too much about what was going on in and around their gorgeous skulls? In their paper The Frontoparietal Fossa and Dorsotemporal Fenestra of Archosaurs and Their Significance for Interpretations of Vascular and Muscular Anatomy in Dinosaurs, published in The Anatomical Record, Holliday et al. look at the anatomy of existing archosaurs and apply their findings to an aspect of dinosaur cranial anatomy that we’d always taken for granted. The big old holes in the tops of dinosaur skulls were previously assumed to be filled with extensions of the jaw muscles, giving the animals an enhanced bite, even though the muscles would have to contort in unlikely ways for that to happen, and the fossils don’t really indicate it. As the abstract puts it,
“Relevant anatomical features argue for rejection of the default hypothesis—that the fossa was muscular—due to a complete lack of osteological correlates reflective of muscle attachment. The most supported inference of soft tissues is that the frontoparietal fossa contained a large vascular structure and adipose tissue.”
So, study of extant archosaurs and of dinosaur fossils suggests that some of the space was filled with blood vessels and fat, with all sorts of interesting implications for dinosaur metabolism and head adornments. (This was naturally reduced to ‘T. rex had inbuilt air conditioning’ by many of those toiling on the media coalface.)
But where does World Famous Palaeoartist Brian Engh™ fit into all this? Well, he was commissioned to illustrate the paper, of course. Dr Casey Holliday himself had the idea of using ‘thermal imaging’ to illustrate the ideas outlined in the paper, and so Brian set to work depicting Daspletosaurus and Deinosuchus together – as if captured by a thermal imaging camera.
It’s an unusual piece in many ways, not least because in the past Brian has mostly portrayed dinosaurs in a naturalistic light; one might imagine that suddenly having to depict them through the eyes of a thermal imaging machine might be a real challenge. However, Brian notes that
“It was surprisingly a much easier illustration to render than my natural light illustrations, in large part because it’s figurative, with less emphasis on surface detailing, and the color palette is limited, but also because the technique I came up with made it pretty quick to render in Photoshop. Basically I drew in graphite but I detailed from the colder areas down. In other words, the darkest parts of my graphite drawing were the areas that would be coolest. Areas I wanted to ‘glow’ hot when it was colored I left blank. In Photoshop I then made the lighter values more transparent, and color tinted the darker values. The end result is a pretty simple composite, with a warm to cooler color gradient for each animal underneath a slightly cooler surface detail layer with its own gradients.”
On a more philosophical level, Brian also found replicating thermography “fun” because
“…it uses bright attractive colors to visualize something we all feel on some level. We all feel our body heat emanate from our bodies and those of people and pets we’re close to, we feel cool air hit the insides of our mouths when we breathe in, we feel the warmth when we breathe out…Thermography uses appealing colors to show that thing we all feel, and to a degree I think the result hearkens back to the mesmerizing appeal of staring into a campfire at night (which we also feel as heat on our bodies).”
Enjoyable it may be, but in contrast to most palaeoart, pseudo-thermography is an attempt to replicate an effect generated by a machine. The majority of palaeoart attempts to make the viewer feel like they are seeing the subject though their own eyes, even when it is stylised. (As I’ve argued many a time, stylised palaeoart can often feel more ‘real’ than attempts at photorealism.) I put this to Brian, and he pointed out (quite rightly) that it is all artifice anyway, and much of it is generated through machines. As he put it,
“I don’t really see mimicking the imagery generated by a machine as any different than looking at any other photo reference or mimicking the look or technique of any other art created with traditional means. It’s all technology. What I attempted to do with this image is present a thermographic image that’s actually a bit more detailed than the images produced by thermographic cameras, which tend to be a bit grainy and low-resolution.”
So – as you may well have noticed – Brian’s piece is actually substantially more detailed than a real thermographic image. Eat your heart out, Predator. But while it’s simple enough (sort of) to go out and acquire thermographic images of living crocodilians, how did Brian decide upon the heat map of his crouching tyrannosaur? Well, in that case, he drew upon the thermographic photography that Holliday et al. had produced during their research. Apparently, these were largely taken in the St Augustine Alligator Farm Zoological Park in Florida, so take a bow, there. Quelle surprise: Daspletosaurus‘ glowing yellow bits were based on those of birds, as photographed at St Augustine, “because the histological data for large tyrannosaurs shows high metabolic rates and phylogenetics place these giant coeleurosaurs much closer to birds than crocs”. Quite right.
You may not have noticed, but the Daspletosaurus in Brian’s piece also has a very fine layer of feathers over its body, resembling hairs. Rather controversial in light of those tiny skin patches that have received so much publicity, and prompted Mark Witton to have another crack at restoring T. rex (as if he needed an excuse). It’s probably best to quote Brian at length here.
“We went with a thin covering of plumage over most of the animal because Yutyrannus is the best preserved example of a large tyrannosauroid we’ve yet found, and also because it’s fun to show the insulating effect of the plumage in an image about thermography. There are a lot of really simplistic views and discussion of thermoregulation in the paleo community (including published papers about fossil animals) and the prevailing thinking in the paleo community is that large bodied animals struggled to shed heat and thus were likely all naked. This is not based on any real rigorous data, [emphasis added for extra controversy baiting] as there are many modern large bodied animals with extensive fur or plumage, and there’s no clear correlation between body size increasing and a loss of feathers or hair. There’s a growing body of evidence that feathers and hair act as a buffer against sudden temperature changes, and this is beneficial to animals of many body sizes in many environments. Part of the takeaway of this whole thermography work is that there is a LOT of work to do with regards to animal metabolism and body temperature, and the picture is complex and nuanced, with numerous adaptations in various parts of these animals bodies, all evolving in concert to result in the external (or thermographic) image we see of the living animal.”
Blimey, Brian. You’re going to get the place kicking off.
Before you all leave angry angry comments explaining why he’s wrong, Brian would like to point out that he’s very keen on other people exploring these sorts of techniques in palaeoart, and will be posting a video on his YouTube channel to that end shortly. He’s also got the hashtag #thermalpaleoart going on social media, so do go and have a look. I’d like to thank Brian both for sharing all this and answering my daft questions, and Casey Holliday, William Ruger Porter, Kent A Vliet and Lawrence Witmer (who he?) for their excellent paper. Congratulations all.
There’ll probably be more from Brian soon. You know how it is.