CROCODILES
SKULL
American Alligator & Saltwater Crocodile
The eyes, ears and nostrils of crocodilians are positioned for use while the rest of the
body is submerged. They have a well-developed bony palate, formed from several skull
bones, similar to mammals.
Crocodiles and alligators have an enlarged tooth near the front of the lower jaw,
analogous to the canine in a mammal. In crocodiles this tooth tends to protrude,
whereas in alligators it is normally more or less hidden in the living animal, fitting into a
socket in the upper jaw.
1. American Alligator skull, lateral view
2. Saltwater Crocodile skull, lateral view
3. Alligator & Crocodile skulls, ventral view
JAWS
MORPHOLOGY
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.
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.
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 i
Estuarine crocodiles are identified by their long, well-toothed
snout, eyes and nostrils set atop the head, thick skin with
embedded bony plates, long muscular tail, streamlined
body and short limbs with clawed webbed feet.
Adults typically have a heavy build and range in colour
from golden tan to grey or almost black, with irregular
darker mottling. Juveniles are brightly patterned and are
generally pale tan in colour, with black stripes and spots
on the body and tail. The underside of the animal is
generally cream coloured.