#integument

As a Paleoartist, is there anything you can say on this? Because I don't know nearly enough.

Oh boi, this is a tricky one.

Cranial ornaments come in all kinds of shapes, sizes and surface textures. For Allosaurus it seems likely that they simply had keratin sheets on top of the lacrinal crests, at least that's what the rough surface and striations suggest. However it also seems like air sacs were reaching up from the antorbital fenestra

This is how I would reconstruct that part of Allosaurus in the moment.

There could have been more though, you can see in this photo of the skull of Big Al II that this animal had large opening behind the lacrinal crests, so there could have been other structures involved.

Maybe even better to look at is this 3d scan of Arkhane, from Brussels.

This could have been related to theroregulation, more display structures or simply further weight reduction.

There is quite a bit of wiggle room when it comes to the interpretation of dinosaur facial features and there is way too much already published and at the same time too little to put it all into a single blog post.

Also not all dinosaurus follow this patters, the cranial crests of oviraptorosaurs show no good indication for keratin crests for example. So it's better to say good bye to cassowary interpretations of these animals and instead cover them in skin and/or inflatable sacs, because these hollow chambers appear to be extensions of the sinuses. (my version of Corythoraptor on the right, Citipati from Wikipedia on the left.)

And then again in other theropods like Abelisaurs we see very rugose skull tops but without the striations you see on the lacrinals of Allosaurus, potentially indicating large scales. Here my, slightly over the top, interpretation of Skorpiovenator. And even then: within abelisaurus you have stuff like Carnotaurus which shows clear signs of keratin sheets on its horns.

This all has been complicated in recent years with new methods in bone histology, because as it turns out the internal structure of a bone can tell us stuff about it's outside, that's how we for example found out that Amargosaurus neck spines were no horns and probably conected with soft tissue, or that the osteoderms of notosuchians were covered by skin like in leatherback turtles.

Going back to Allosaurus and other allosauroids. Keratin sheets, scales, air sacs, all these were probably present in these animals, but their exact distribution is still a question of debate.

Here a paper from a few years back that maps para-nasal sinuses in extent and extinct archosaurus which gives you a little idea how complex their internal anatomy could get

What would you choose: fur, scales, or feathers?

Human skin is truly amazing. Did you know it's the biggest organ of our bodies? If we "took off" our skin, it would weigh around 4 kg! 😮 

Still, for fantasy or sci-fi worldbuilding purposes, you might want to explore other options: For example, what would you choose: fur, scales, or feathers? 

Fur serves for camouflage, temperature regulation (especially when cold), and enhancing the sense of touch. Maybe your sentient beings with fur evolved in cold worlds that need the extra layer or live in an environment when they can be easily hunted down by predators.

Scales are useless for thermal regulation but protect the body from water loss and abrasion when moving in terrestrial mediums. In aquatic mediums, they reduce friction with water and allow the animal to move or swim faster. So your sentient beings with scales might be amphibians or live underwater.

And finally, feathers. It was thought that only birds had feathers, but now it's believed that some dinosaurs also had feathers. Feathers are necessary for insulation, temperature regulation, and flight. Your sentient beings with feathers may not necessarily fly. Still, they can be useful for insulation and communication. For example, a particular feather pattern may be the equivalent of a name. Or, they may also use a sort of feather display to find their significant other. 😉

Another curious option that I didn't want to leave behind is the exoskeleton. Unlike vertebrates, who have their skeletons on the inside, arthropods have them outside, covering their bodies. Exoskeletons primarily protect the insect with a hard protein coat; however, they limit how big they can grow. So, sentient beings with exoskeletons might have rigid movements compared to vertebrate beings and may grow slower and not as big as other beings in your world. But the tradeoff is that they would wear "armors,"  probably with the beautiful iridescent colors of the insect world.

~ Integument ~

Spring 2018 (April)

Nikon D5300 w/ Nikon AF-P NIKKOR 18-55mm lense

A paper came out last night describing skin impressions from Tyrannosaurus rex and some of its close relatives, purporting to show that tyrannosaurids were scaly rather than feathered.

This graphic shows where these skin impressions were found, as well as four skin impressions of unknown position (shown at bottom left). You may note that these impressions are very, very small and cover only a small part of the body.

Taking a closer look at the hips and tail, however, does reveal something interesting: a small skin impression shows scales over the hips. Unlike the tail, neck, and belly impressions, this is from a place that is shown as feathered in, for example, the Saurian T. rex. 

Does this mean that Tyrannosaurus was scaly after all? We don’t know. As the paper itself notes, the back could have had a “cape” of feathers, and some fossils, such as Juravenator, show that scales and feathers can be intermixed. Maybe there were feathers between the scales that fell off before fossilization. However, this paper does make a fully-feathered Tyrannosaurus seem less likely than before.

Both feather and scale fans should be happy about this paper: there’s new evidence of scaly skin on tyrannosaurs for the latter, so scaly tyrannosaurs are scientifically justifiable again, but that evidence also doesn’t rule out a mostly-feathered body, so feather fans can keep drawing fluffy tyrants.

See also: my similar post on Carnotaurus.

After having a look at Thomas Carr’s paper, I used the weekend for doing some paleo scribbles with the attempt to interpret their findings.

So, I got three variants down.

“Gesichtsfliese” (Face tiles, the initial title is a German word I came up with)

“Scaly Pride”

“Keratin on my Skin”

One depicts a rather regular arrangement of the “large flat scales” as it is called in the paper, a bit similar to a floor with tiles (”Fliese” in German)

The second one is closer to the life reconstruction in the paper, but instead, I tried to make the transitions from large scales to armored and less textured skin smoother. In the illustration in the paper, I find the part over the postorbital fenestrae a bit too shrinkwrapped and it looks like as if the Daspletosaurus had some kind of skin transplantation. I also tried to make the jaw muscle more prominent, because it looked rather thin.

🦭 Seal Syringoma 🦭

This is definitely the sealiest thing I have observed in a histology slide

i❤️histo

A syringoma is a benign tumor of sweat glands. There a two types of sweat gland in the skin: eccrine (merocrine) and apocrine.

Eccrine sweat glands are the most common and are found all over the body, they secrete the regular type of sweat you are familiar with and are particularly dense on the palms of the hands and soles of the feet (it's your eccrine sweat glands responsible for those nervous sweaty palms and those sweaty feet in hot sockless shoes). Eccrine sweat is largely for thermoregulation (to help you cool down when hot).

Apocrine sweat glands are found mainly in the pubic regions (groin, axilla/armpit) and they secrete the type of sweat that quickly gets stinky after exercise because bacteria love to feast on this more oily secretion.

🧠 Pinkus & The Brain 🧠

The fibroepithelial patterning in this unusual, basal cell carcinoma variant (Pinkus tumor) looks like it has a mind of its own!

i♡histo

This is a biopsy of a big pink lump that was removed from the surface of the skin. You can tell it is skin because you can see the keratinized stratified squamous surface epithelium (the epidermis) lining the 'head', 'nose', 'mouth' and 'chin'; and you can see sebaceous glands and sweat glands in the connective tissue dermis.

The layered cells and keratin of the epidermis provides us with essential protection from the hostile external environment in which we live. It's a physical barrier between us and the outside world.

However, to perform this role the cells of the epidermis (called keratinocytes) sacrifice themselves (they die) in order to release their protective keratin onto the surface of the epithelium. Dead keratinocytes and old, dry keratin are constantly shed from the surface and as a result must be constantly replaced by division of basal keratinocytes in the deepest layer of your epidermis (the basal layer/stratum basale).

Sometimes these dividing cells can undergo cancerous changes, often as a result of exposure to UV light, causing them to divide uncontrollably forming a tumor called a basal cell carcinoma (BCC). In the microscope, BCC often has a distinct pattern that pathologists can identify - islands of epithelial cells surrounded by palisading rows of the dividing basal keratinocytes.

This particular example though, looks different. It still contains those epithelial cells with their palisades of basal cells but instead of forming islands they form interconnected strands of epithelium with the spaces between filled with fibrous material - in this instance making it look like a brain in the skin.