The Prehistoric Large Sea Turtle Archelon

Archelon is the best known large sea turtle from ancient times. Its impressive size has fired the imagination of many a child. I know it did for me.

Archelon Is Different From Modern Turtles

AS you can see from the pictures, Archelon has that most defining of turtle features, a shell that is made from the back bone and ribs. You can also see that the shoulder blades and pelvis are inside the ribcage; turtles are the only creatures that have this feature.

Its top shell (carapace) and bottom shell (plastron) are not full bone protection as in most modern turtles. Their shell and other features of the body show them to be most closely related to today's sea-going Leatherback turtles, though the connection is distant.

Archelon Is Not The Oldest Turtle

Its name means "ancient turtle", and when it was discovered it was the oldest and most primitive large sea turtle fossil yet discovered. In recent decades other specimens of this and other ancient turtle species have come to light that show Archelon as part of an already well developed order of animals.

In fact, this creature evolved around 150 million years after the first primitive turtle ancestors.

The most ancient turtle like animal found so far in fossil form is the half-shelled and toothed Odontochelys semi-testacea (the name just means half shelled and toothed turtle!).

Not That Big
In Its Day

While the fossils of Archelon certainly impress, this turtle was nothing special in its day. There were many predators in the seas at that time, such as the sea going giant Mosasaur Tylosaurus and the ancient crocodile-like Sarcosuchus for whom Archelon would have been no more than a good size snack.

Imagine It
Laying Eggs

Given that ancient reptiles laid eggs and that all turtles alive today still do this, it's a good bet that Archelon also behaved in this way.

I can imagine this enormous female turtle crawling up a Cretaceous beach at night, digging her nest chamber with her back flippers, laying a clutch of large eggs and then carefully covering the nest before making her way back to the dark water.

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