How Can a Creature With Rock Armor Also Have an Inflating Head?

Question

Globold are darkeye dragons with some rather unusual traits. Their bodies are more or less cylindrical, with a rounded chest and a sloping back, with two small arms and two big legs and a tail like a theropod, and plates of rock all over their bodies like a mutant armadillo-all over, that is, except on their head.

Now, this is where it gets weird fast. The head of a Globold is green and rubbery, smooth yet studded with bone-white spines, with a mouth that comes down and turns upward in a toothy grin, like a crocodile emoji but gumdrop-shaped. When a Globold is angry, it can raise these spines up and inflate its head up to twice or even thrice its original size, and at this point its head becomes a dangerous weapon.

Normally, a Globold's head is sort of like a water bed or a water-filled glove, relatively amorphous and too flexible to do much harm, but inflated, its head stiffens and acts more akin to a rock and can be used like a mace to smash the odd adventurer. In this state, it is also capable of releasing pressure by firing its spines, one by one or all at once, or by using its lungs and the air trapped inside its head to let loose an explosive roar that sends people flying like leaves in the wind.

These abilities are the result of magic expanding upon inflation's normal capabilities, but in order for them to exist, Globold have to be able to inflate in the first place. So my question is, how can a creature with rock armor also have an inflating head?

Specifications:

1. The best answer will take into account that in order for Globold to live, they must have something holding them up, and that something must enable inflation. Or in other words, in order for their head to hold its shape, before and after inflating, there must be some kind of support system that enables inflation, can support rock armor, and keeps the head gumdrop-shaped. For example:

• Octopi 'skeleton': muscle attached to muscle, that's how octopi support themselves. This would also explain a Globold head's relative flexibility and inherent strength, it would be due to relaxed or tightened muscles. However, I'm not sure how well that would work with rock armor.
• Pufferfish, one of the main inspirations for Globold, have reduced skeletons that enable their inflation, but I'm not too excited about a potential boss dragon having such a exploitable weakness as a reduced skull. How would it even survive with that?
• Mice or sperm whales have segmented skeletons or flexible ribs, which enable them to squeeze through small spaces or survive deep-sea pressure pressure respectively. I like the idea, as it would likely enable a Globold's mouth to grow with the rest of the head as I have envisioned,, but am too much of a biology amateur to know if that would work with the segmented, gray rock armor covering the rest of a Globold's body.

2. In order for a Globold's head to inflate, it must not have armor on its head, which means that either head armor is a neutral trait (it doesn't impact survival) or there is a really good reason for the head to not have armor. That's my understanding of natural selection and genetic traits, anyway, and the best answer should take those things into account.

3. Don't be afraid to ask questions if you need clarification on something, I appreciate feedback!

Notes:

@Joachim: Yes, the head needs to be durable. Their environment is known as the Rocky Highlands, it's a series of canyons, ridges of rock, and so forth that could really hurt one's head, and besides that Highland Scerafin, being bipedal with telescoping necks and lancelike snouts, are perfectly capable of lancing a Globold's head. As for the skeleton, you see my problem; and for what's it's worth, if the scaly-foot snail can have metal armor, why not a Globold with rock armor?

@Dan: As a Globold's head must either be protected by quick reflexes or be capable of taking a collision or crash into the rocks around it, as well as tanking hits from a Scerafin, it's likely to evolve into a formidable weapon. I understand this is strange, and that it is problematic biologically. That's why I'm asking this question.

@Join JBH on Codidact: Thank you, that's the point of the question! The problem is that a Globold's entire body is armored except for the head, which can inflate! I know having the head unarmored, thereby making it a vulnerability, is weird, so I'm asking how it could work enough to not get selected out of the population!

Answer 1

Folded scales, wrinkly skin.

What you described isn't out of the ordinary. In fact I know a simple solution to make it work. Origami! The principle of folding structures to allow for greater surface area or vise versa.

You described Globolds as having no scales on their heads. I disagree. They have tiny scales on their green heads which gives the illusion of having no scales. Up close, the skin would look like a lizards but from further away it looks smooth and soft. The head can nonetheless inflate without tearing the skin. How?

The secret lies in the scales themselves. Instead of being like tiles on a roof, the scales are squashed together like an accordion. When the skin is pulled these scales unfold. This is the microscopic detail that most miss when face to face with a Globold.

How does the head bulge?

Erectile tissue is any tissue that is capable of stiffening or engorging with blood. During sexual arousal, sexual erectile tissue experiences increased blood flow and becomes engorged with blood, enlargening and/or stiffening.

Globolds aren't quite like rams. Their heads are bigger, they are stronger and therefore they receive a stronger impact on their noggin. They need some shock absorption, which is where the erectile tissue comes in. While this means their headbutts will be cushioned, the horns on their head serve as the main weapon anyway.

Visually, when they bulge their head pulsates along with their heartbeat, signifying they are ready to attack. It's not as fast as a puffing up but it's more resistant. There's no bursting or popping their head. If the idea of erectile tissue in their head makes you uncomfortable though I have alternatives.

I have a theory as to why they can inflate:

A combination of unfortunate genetics and sexual selection. Lacking armour on a body part is completely random. Usually though, the stomach is more prone to being left exposed. The reason is to preserve mobility. The head being unarmored would be a random mutation. Perhaps they swallow their prey whole like a snake and need flexible skin to do so. Either that or they feed on carcasses and like vultures have exposed heads to prevent bacterial growth.

Biology is a lottery. Unfavourable traits can often be compensated for with a change in tactics. Hermit crabs, for example, hide their tails in a shell. Globolds might, for example, burry their heads to protect them from attacks.

Sexual selection would also come into play in making this a widespread trait. Flexible skin means the head can be inflated. This would serve as a sexual display to impress females and intimidate competitors. The spikes on the head would be a result of this rivalry. They can pierce the inflated head. Also the bigger the head the further the spikes can reach, improving chances of victory while also making it harder to be penetrated.