The Dinosaur Wore Bubblewrap – Duane Nash’s brilliant SIGIL idea

The most frightening dinosaur fossil I ever saw was the South American sauropod hatchling with its hairless skin. All it had was nodules … but because its ancestors were obligate bipeds, they must have been warm-blooded… and therefore presumably the hatchling must also have been. Anyway the adult sauropods must have been warm-blooded for their own reasons.

How could they survive without fur or feathers? Did they rely on the warmth of their parents or of the climate? The problem was, it didn’t look like the skin of that hatchling was ever going to bear fluffy insulation, so it didn’t matter that some Protoceratops fossils seemed to show porcupine-style long spines, nor that some small ornithopods seem to have had some kind of fibrous integument.

But now, Duane Nash has had a brilliant idea on how unfuzzy species could still have had insulation: Bubblewrap! Or as he terms it: SIGIL – S.ubdermal I.nterstitial G.ridded I.nsulatory L.ayer(s)

People will be familiar with the nodule-like scales in the skin of some dinosaurs. What if some contained air?!? There are fossils that seem to suggest this. There are also fossils that seem to suggest unfuzzy dinosaurs lived in cold regions – in fact most if not all non-theropod types of dinosaurs seem to have representatives that did so, unfluffed.

Nash introduces Raymond B. Cowles as the worker from 60 and 70 years ago whom he believes edged towards the idea, and views his work partly through the eyes of Scott J. Turner, whom Nash also quotes.

Having read the excerpts he’s offered, I feel Nash needn’t have done so, since I don’t think either Cowles nor Turner really went much in the direction of suggesting sub-surface air insulation. Maybe Nash wanted to imply some support from earlier workers (a ubiquitous custom), perhaps even to let the others share some of the blame if things didn’t go well!

He need have no fear though, since it’s an excellent idea, even if it later goes bad – which I very much doubt. But Turner and Nash do refer to the way Cowles seemed to… jump to his theories. Whatever theories they were is of less interest to me than the comments on how Cowles arrived at them. We now know that theory generation is a highly creative process, and does not rely on the simple cranking of systems of rules and statements that we recall through Euclid’s geometry. That’s deduction – making rules work. Producing theorisation (i.e. making the new rules) is induction when we work out what happenS, or abduction when we work out what happeneD. Neither are what most would see as logical – or even “careful”.

The suspicion of the style of Cowles’ first steps that Nash shows on his own way to probably the most useful insight into ornithischian palaeontology so far this century, by no means indicates a flaw in the final product. The way in which theories arise must not be considered when judging the theory, since the worth of a theory depends only on how well it explains (or is consistent with) the evidence.

Much, much more will be written on all this of course. Here is the final sumarising paragraph of Duane’s blog posting:

Since the gradual and accumulating evidence for widespread endothermy or at least mesothermy in many dinosaurs it has become somewhat anathema to compare dinosaur thermal physiology to ectomthermic reptiles. While mounting evidence suggests the potential for widespread insulatory coats in many, if not all theropod lineages, such evidence is much thinner in many other dinosaur lineages and completely absent in several despite abundant casts and direct skin preservations. Research, thought, or even speculation has been lacking in terms of explaining how such naked skinned dinosaurs insulated themselves given wide distributions up into polar regions. Here is presented a novel hypothesis addressing insulation in such naked skinned species. An anatomical feature referred to as the subdermal interstital gridded insulatory layer(s) – or SIGIL – is outlined and referenced via several lines of evidence. Through vasoconstriction blood flow can be diminished to this layer creating an insulating, vacuum sealed layer of air visceral to the outer skin and which insulated dinosaurs from temperature extremes. Additionally, this layer could be vasodilated and engorged with blood to facilitate heat shedding or heat uptake into or from the environment respectively. This ability to control blood flow to the extremities is likely ancestral to all tetrapods and is a simple co-option of known capabilities in extant ectothermic reptiles. A novel ability to both absorb thermal energy from the environment and create internal heat is inferred for many dinosaurs via the efficient capacity for heat exchange and insulation through SIGIL. The extent of this dual functionality likely varied significantly across families and genera and offers potential insight into efficiently achieving gigantism and fast growth rates with minimal or non-existent parental provisioning of food and at rates much more efficient than other endotherms in terms of food intake. The intricate vascularized osteoderms of several types of dinosaurs are argued to represent the acme of this “dual functionality” and crocodylomorphs are inferred to have a congruent thermal function for their osteoderms as well as secondarily losing this “dual funtionality” in their evolutionary history that they once shared with their extinct archosaurian brethren.

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2 Responses to The Dinosaur Wore Bubblewrap – Duane Nash’s brilliant SIGIL idea

  1. Duane Nash says:

    Thanks for the write up. The reason I went into Cowles was that he was the first to really push the notion that reptiles were masters of their thermal environment and not slaves to it. His theory and the work that it inspired are interesting in and of itself. But I only discovered him when I started researching how and where external blood flow control originated in tetrapods. Since Cowles was one of the first to suggest vaso-constriction or vaso-dilation of the external blood supply originated in stem-tetrapods and not with endothermic animals I thought it fair to give his work some spotlight. Vasoconstriction is key to my idea because this is what pull blood away from the SIGIL and allows the animal to behave more or less like an insulated house or the thermos that keeps your coffee warm.

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