The Basics:
Chameleons are a family (chamaeleonidae) of old world lizards. They’re found in Africa, the Iberian Peninsula, the southern tip of the Arabian Peninsula, the Eastern Mediterranean, and in the west coast of India. They have also been introduced to warm parts of the USA.Their name has Greek origins and means “ground lions” due to their head crests (not to confuse them with sea lions and sky lions).
Origins and Biology:
Chameleons are at least 100 million years old. Chameleons are likely to have originated from Africa. There are over 160 species of chameleon, many of which don’t change colours. Over half of those species live in Madagascar.
Interesting Bone Structure:
One of the main characteristics of chameleons is that their hind feet are zygodactylous, which usually means they have two fingers that point forward and two fingers that point backwards. This is extremely helpful to climb trees. As you can grip a branch from both sides. There’s a bit of controversy about the word zygodactylous, because it’s mostly used to describe bird feet, and chameleon feet don’t look like bird feet. The main issue is that chameleons have five fingers. So instead of being two fingers opposite two fingers, it’s three opposite two. Another thing to note is that they’re more side by side than front and back. The inner side has three and the outer side has two.
- Chameleons that are in the genus calumma, have little bones protruding from their head.
- They are fluorescent under UV light and can make them very conspicuous to animals that uv vision, like other chameleons.
- They don’t have outer ears but they can feel vibrations between 200 and 600 hz. So they probably can’t hear adults speaking, but could hear children or sounds we consider to be high pitched.
Colour Changing Mechanisms
It’s basically impossible to know how and when some species developed the ability to change colours.The only thing we know for sure is that their colour changes were evolved as a means to communicate with other chameleons of the same species (infraspecific) and not to blend in with the environment.
If anything, when chameleons change colours they become more conspicuous. Similar to peacocks, male chameleons are typically more attractive and colourful than female chameleons.
- Males change to bright colours to show aggression and dark colours to show submission.
- Females can change colour to show if they’re willing to mate with a particular males.
- It’s also possible that chameleons turn darker to absorb more sunlight when they’re cold, but in some cases it can be for camouflage (crypsis)
How Do They Actually Change Colour?
The chameleon’s skin has several layers. The outermost one is transparent.Under that layer there are more layers with pigments called chromatophores.Under the the chromatophores there’s a layer of guanine nanocrystals. The space between the skin changes depending on how the chameleon is feeling. If they’re excited, feel threatened, or scared, they guanine nanocrystals will separate a little bit and will reflect higher wavelength like.
A chill chameleon’s iridophores will reflect blue light, which combines the yellow chromatophores to make the chameleon reflect green light. Or, from our point of view, they make the chameleon green. If they’re excited the guanine nanocrystals will reflect red light, which will combine with the yellow chromatophores to make them look, red, bright orange, or even yellow.
- Think of it like the effect of oil in water. The different colours depend on the thickness of the layer of oil at any given point. It’s pretty much the same principle with the guanine nanocrystals.
There’s a second layer of iridophores that reflects mostly light close to infrared. This is supposed to help in thermoregulation. The more you reflect, the less you absorb. And the more you absorb, the hotter you get. So, in short, chameleon colours depend on the combination of light reflected by crystals and natural pigments.
- Note: If you’re doing additional research, don’t read anything published before 2015. This is a new discovery.
Defence Mechanism with Predators
The Smith’s Dwarf Chameleon (no relation to Morrissey) changes colours when approached by predators.
Two of the main predators are fiscal shrikes (a bird that impales chameleons before eating them) and a snake called boomslang. If the bird shows up they’ll match the colour of the branch very closely, as birds have amazing vision. If they’re approached by the boomslang, they don’t have to try as hard because the snakes vision isn’t as sharp as the birds.
- Fun Fact: Despite not completely changing colours, it still looks more camouflaged to the snake than to the bird.
Their Tongues
There are three main components to the tongue: the sticky part, the tongue bone (hyoid), and the coils of muscle around the bone that launch and retract the tongue.
- Chameleons are slow and feed mostly on fast insects. Luckily their tongue is super fast and sticky.
- A chameleon’s tongue is longer than its body, usually 1.5 to 2 times.
- Smaller chameleons have proportionally longer tongues.
This is a extremely fast mechanism, accelerating to 2500 m/s in less than a tenth of a second. If you accelerated that fast you’d feel about 41 g-forces. More than you’d feel inside a stunt plane at a red bull air show.
- For some smaller chameleons, like the Rhampholeon Spinosus, the tongue can accelerate 265 times faster than gravity. If it was a car it could go from 0 to 100 in 1/100th of a second. That’s the fastest muscle acceleration among vertebrates.
Before the chameleon launches its tongue, muscles around the bone contract, creating elastic recoil. When these muscles are released the tongue shoots forward. If it hits the target, it’s the sticky part of the tongue’s time to do its job.
The Viscous Mucus at the Tip Is 1,000 Thicker than Human Saliva
It is very adhesive and is sticky enough to catch prey that can be a third of the weight of the chameleon (imagine lifting something a third of your weight with your tongue!)
- Viscous adhesion works better when used quickly. The stronger the pull, the stronger the bond.
- Once inside their mouth, the tongue relaxes, and the prey gets released inside their mouth.
Their Eyes
- Chameleons have very distinctive eyes. The eyelids are joined and the pupil only has a pinhole to see through.
The eyes can move independently and can focus on two things at the same time. Because of the eyes range of motion, this effectively gives the chameleon a 360 view range. Despite rarely being able to see the same thing with both eyes (binocular vision), they have great depth perception.
They can spot small prey from up to 10 meters because they have the best amplification among any vertebrate. This is in part due to their negative lens. Our lenses are convex, but theirs are concave, which increases retinal image size, and allows more precise focusing. (I wonder why they don’t make negative film camera lenses)
- They can see ultraviolet light, and apparently it enhances social behaviour.
