Thread: Black Tongues in (Certain) African Mammals

Reading Handa's surprise to my three year old, he became interested in why the giraffe's tongue is black. He also asked what colour tongue do the other animals have.

Giraffe:



Antelope:



Okapi:



(ok so there isn't an okapi in Handa's surprise)

Does anyone know if there is any selection pressure that has caused a number of African mammals to have black tongues? (And how I'd explain it to a three year old!)

This is a pure guess:

Black tongues will only be found on herbivores. Only herbivores spend a considerable amount of time with their tongues exposed outwith the mouth. This is the only external piece of the animal that is unprotected by hair. Therefore this is feature to avoid sunburned tongues.

I going to guess the colour somehow correlates to specialised myocytes in the tongue required for such long tongues.

Other than that, genetic drift?

Those animals are all pretty closely related too, it could just be a combination of genetic drift and close relatedness of those species. Most mammals have red tongues, it's not impossible that there could be some sort of selective pressure involved though.

http://en.wikipedia.org/wiki/Pecora

Edit: On second thought I'm thinking their tongues may be highly keratinized or has a layer of collagen, like the hide of a rhino or elephant, for protection against particularly rough plant material.

I've no idea why some tongues are black. They are seen in other animals too such as Polar Bears and some breeds of dog, such as the Chow Chow.

I know that Polar Bears have black skin too. Don't know about Giraffes though.

I thought I read some time back that the polar bear black skin and white (actually translucent and hollow) fur combination was an adaptation for warmth.

I know the chow is a breed from the spitz family (along with the husky, malamute, and other cold climate adapted dogs).

I wonder if you shaved a chow down if their skin is black like a polar bear's?

I'm completely speculating, of course.

This makes me think of the breed of asian chickens that have black pigmented bones. I believe the roosters have black testicles as well. I saw a bi-color chicken testicle soup which contained 50% black testicles and I just assume they were from the same kind of chicken that has black bones. I suppose artificial selection could have produced this but I really don't know. There must be many such oddities out there.

It would be helpful to know what is underlying the colour of the tongue, e.g. a pigment such as melanin. Protection from excess exposure to sunlight has been suggested, my first thought was that perhaps the dark colour promotes sunlight absorption - this might provide some selective advantage.

All speculation unfortunately.

According to the Sandiego Zoo's website the tongue is maybe dark to protect against sunburns, so that likely means the colour is caused by melanin. So, Ophi may have guessed right.

They have large papillae and thick saliva to protect against the rough plant material they eat. So, that at least isn't what's leading to the dark colour.

I was able to find these citations, but don't have access to that journal.

Lahkar, K., A. Chakraborty and M. Bhattacharya. 1989. Gross anatomical observations on the tongue of giraffe. Indian Veterinary Journal, 66(10):954-957.

-----, M. Bhattacharya and A. Chakraborty. 1992. Histomorphological study on the tongue of the giraffe. Indian Veterinary Journal, 69(6):523-526.

Originally Posted by i_feel_tiredsleepy

According to the Sandiego Zoo's website the tongue is maybe dark to protect against sunburns, so that likely means the colour is caused by melanin. So, Ophi may have guessed right.

I'm famous for it. :wink: