Adding Megalochelys to the Turtle Montage (Patreon)

Hello again, noble patrons. I hope you're all doing well in these most unusual times.

To business: as you might recall from recent posts here, I've been illustrating new turtles for the Big Book's enormous reptile chapter (the turtle section of which is pretty massive in itself). I finally got round to reconstructing the immense Asian land tortoise Megalochelys, a long-lived taxon that was alive during the Miocene, Pliocene and Pleistocene and lived from central Asia (and perhaps eastern Europe) in the west to Indonesia in the east. There are several Megalochelys species, and the biggest individuals of the biggest species (M. atlas) have a curved carapace length (CCL) of over 2 m and an estimated mass of over 900 kg. There are suggestions of even bigger individuals (in 2015, Ren Hirayama and colleagues reported one with a carapace length of 2.7 m!) but it's difficult to determine there if the authors are talking about straight-line carapace length or CCL, which makes a big difference. Whatever,  Megalochelys was very big, and I really wanted it to loom like a giant near the back of the turtle montage I've been building. Keep reading to see how that plan worked out...

My plan was to draw Megalochelys BIG, so I had it filling up the better part of a whole sheet of A4. I began by tracing over the more complete shells of this turtle: an especially good one (about 2 m long) was published by Erick Setiyabudi in 2016. Here it is...

An especially interesting feature of Megalochelys is that it has a massive, thick, robust, bilobed structure at the anterior end of the plaston, formed by the paired epiplastra. These are about 15 cm thick. When covered in their scutes (the gulars), they would have been even bigger. They were narrow from side to side to give lots of room for forelimb movement, but they were so similar to the forked epiplastra of some living tortoises (like Centrochelys) that they were surely used in intraspecific combat. The idea of two of these giant pushing and shoving with their ploughshare-like plastron edges is a compelling one that really needs depiction in  palaeoart - I've seen one drawing which hints that it might be going on, but nothing compelling or dynamic. Here are the epiplastra from a  Megalochelys cf. sivalensis specimen described by  Setiyabudi  in 2009...

I incorporated this impressive feature into my building reconstruction, but the fact that I showed the animal in side view means that their interesting shape is mostly obscured.

Some shells of these tortoises are well enough preserved that we can determine the position of their scutes (the scutes - some experts call them scales - do not align with the underlying bones of the shell), so I added those next. I then used the known limb bones to reconstruct the lengths of the limbs, and deliberately gave the animal a relatively erect limb carriage where the legs are held in column-like fashion, this being based on the way the humeral heads fit into the scapulacoroid glenoid. Megalochelys was a continental turtle, not an island-dwelling one... which led me to wonder if it might be especially well protected on the limbs, as are some big, continental tortoises of today (like the Centrochelys African spurred tortoises). I added thorn-like scales and large. polygonal scales, and I think they look pretty good.

What else? We have skull material for Megalochelys. Not only does this allow us to work out how large (or small) the head was relative to the rest of the animal (it was about similar in length to the humerus, so over 30 cm long in a very large individual), we also know that this was a tortoise with a short, deep snout and deep nasal region. In other words, the head was shaped very much like that of the living Aldabran giant tortoises, and I used these animals as models for the look of the head here. Here's how things came together - apologies for the poor lighting of these photos, they were hastily snapped in between other project and I didn't have time to do scans or take professional images...

So we're left with the image you've seen at the top of the article. The final job was to import it into the building (and still in-prep) montage, and here's how it currently looks....

Thanks as always for your support -- more soon!