Crocodilian Biology Database - Teeth (Egg tooth)

Egg tooth

Morphology / Head: Egg tooth is essential during hatching, after which it is reabsorbed.

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Head; Egg Tooth

TYPE:	Temporary modified epidermis
FUNCTION:	To assist in hatching, splitting the inner membrane and cracking the outer membrane of the egg. It is not a true tooth, and it is resorbed a few weeks after hatching.
INVOLVING:	Epidermis at the tip of the upper jaw is modified into a paired, horny point.

The inside of a crocodile egg is a great place to develop, but after more than two months trapped in this small, ovoid shell the fully developed embryo needs to get out fast before its oxygen demands become too great. Hatching is actually a much more difficult task than you might imagine, but the baby crocodile has developed ways to make the process easier. The most obvious of these is the presence of the egg tooth to help break out of the egg.

The photograph on the right shows clearly the position of the egg tooth (circled in red) on the crocodile's upper jaw. Despite its name, the "egg tooth" is not actually a true tooth made from bone. Instead, it is a modified piece of skin - a toughened, horny piece of epidermis which forms during development of the embryo. The "tooth" is actually paired. It's not as sharp as a bony tooth, but it is normally very effective at cutting through egg membrane.

Crocodile eggs, unlike other reptile eggs, consist of a soft, inner membrane and a hard, calcified outer membrane - very similar to a bird's egg. So how does the crocodile use its egg tooth to break out? When the time comes to emerge, the crocodile normally rubs the tip of its snout up and down against the inner membrane of the egg. The sharp egg tooth slices apart the inner membrane, and the hatchling can then push its nose forwards forcefully to crack the outer membrane.
Hatchling saltwater crocodile emerging from egg

Hatchling saltwater crocodile emerging from egg

This event, where the baby crocodile pierces the eggshell membrane and sticks its snout out into the air, is called "pipping" (see right). The hatchling may remain in this position for several hours, although normally when the adult female opens the nest in response to hatching calls from the eggs, her vibrations stimulate the eggs to hatch rapidly. Some eggs do not always hatch immediately, even when the female is present, and so she picks them up within her jaws to gently squash the shell between her tongue and the roof of the mouth, encouraging the hatchling to emerge. Without her presence, some of these eggs may not hatch at all. If the nesting conditions are slightly dry, for example, the inner membrane becomes dehydrated and leathery. In this case, the crocodile trapped inside the egg may not be able to split open the toughened membrane using its egg tooth. Without assistance, the small crocodile will suffocate and die within its prison.

resorbed egg tooth

After the crocodile has successfully hatched, the egg tooth becomes completely redundant - it is only ever used for a brief but important moment in the crocodile's life. The photograph on the left shows a small saltwater crocodile four weeks after hatching - the egg tooth has been almost completely resorbed, and in a few more weeks there will be no trace of it.