American Oceans

Archelon: The Giant Sea Turtle of the Cretaceous Period

Archelon is a genus of extinct sea turtles that lived during the Late Cretaceous period in North America.

a rendering of what Archelon Ischyros would have looked like

These turtles were among the largest ever known, with some individuals measuring up to 4.5 meters (15 feet) in length and weighing over 2,200 kilograms (4,850 pounds). Archelon had a unique shell structure that allowed it to swim efficiently in the open ocean and dive to great depths.

Archelon is an important species for paleontologists because it provides valuable insights into the evolution of sea turtles.

By studying the structure and function of Archelon’s shell, scientists can learn more about how sea turtles adapted to life in the ocean and how they evolved over time.

Archelon is also a fascinating creature in its own right, representing one of the largest and most impressive animals to ever inhabit the ancient seas.

Archelon Ischyros

the skeleton of Archelon Ischyros in a museum

Archelon ischyros, meaning “mighty turtle”, is a species of extinct sea turtle that lived during the Late Cretaceous period.

It was first discovered in 1895 by Othniel Charles Marsh, a paleontologist, in the Pierre Shale Formation of South Dakota.

The fossils found were a nearly complete carapace, ribs, both femurs, one humerus, and the procoraco scapulars and coracoids.

The species was named by Oliver Perry Hay in 1908, who classified it as the largest known sea turtle species. The genus name “Archelon” means “ruler turtle” in Greek, while the species name “ischyros” means “mighty” in Greek.


Archelon ischyros was a massive sea turtle, with an estimated length of up to 4.5 meters (14.8 feet) from flipper to flipper and a weight of over 2,200 kilograms (4,850 pounds). Its skull was relatively small compared to its body size, and its beak was toothless.

Its neck was long and flexible, allowing it to reach its head to the bottom of the sea floor to feed on mollusks and other invertebrates.

The carapace of Archelon ischyros was the largest of any turtle species, measuring up to 4.9 meters (16 feet) from head to tail.

It was relatively flat and streamlined, with a smooth surface that lacked the ridges and bumps found on the shells of other sea turtles. The tail was relatively short, and the hind limbs were modified into paddle-like flippers for swimming.

Habitat and Lifestyle

Archelon was a giant sea turtle that lived during the Late Cretaceous period. It was well adapted to its marine lifestyle and inhabited the Western Interior Seaway, an inland sea that covered much of North America during the Late Cretaceous.

Archelon was an obligate carnivore and fed on a variety of marine organisms, including fish, jellyfish, and cephalopods.

Diet and Predation

Archelon had a beak that was well-suited for crushing the hard shells of mollusks and other prey items. Its front flippers were also adapted for swimming and catching prey.

Archelon was likely preyed upon by large carnivores such as Cretoxyrhina, a prehistoric shark that lived during the same time period.

Reproduction and Growth

Archelon was a reptile and laid eggs on shore. Its carapace, or shell, was covered in ridges that may have helped it move more efficiently through the water.

The temperature of the sand where the eggs were laid likely determined the sex of the offspring. Archelon grew to be one of the largest sea turtles ever known, with some individuals reaching lengths of over 13 feet.

Archelon lived in a muddy, oxygen-depleted environment. Its lifestyle was adapted to this environment, and it likely spent most of its time swimming near the bottom of the sea.

Climate change and the subsequent changes in sea level likely played a role in the extinction of Archelon and other large marine turtles.

Fossil Records

the skeleton of Archelon Ischyros on display in a museum

Archelon is the largest known sea turtle to have ever existed. It lived during the Late Cretaceous period, approximately 70-80 million years ago.

The fossil record of Archelon provides valuable information about the evolution of sea turtles and their behavior.

Fossil Locations

The majority of Archelon fossils have been found in the Pierre Shale geological formation, which stretches from South Dakota to North Dakota in the USA.

The YPM 3000 specimen, the most complete Archelon fossil, was discovered in South Dakota. Other fossils have been found in different parts of the USA.

Preservation and Examination

Archelon fossils are usually preserved as flattened, fossilized shells, plastrons, and bones. The fossils are often incomplete, with some missing parts such as the skull. The thoracic vertebrae and sacrum are commonly found in the fossil record.

Archelon fossils have been studied extensively by American paleontologist Samuel Paul Welles and others.

The examination of the fossils has revealed that Archelon had a unique way of swimming, likely using its powerful front flippers to propel itself through the water.

The fossils of Archelon have also provided insight into its nesting behavior. Fossilized nests and eggs have not been found, but the examination of other fossilized sea turtles, such as Microstega and the ruler turtle, has given scientists an idea of what Archelon’s nests might have looked like.

Comparative Anatomy and Evolution

a skeleton of Archelon Ischyros hanging in a museum

Archelon was a massive turtle that lived during the Late Cretaceous period, around 70 million years ago.

It is believed to be the largest turtle that ever existed, with a shell that could measure up to 4.5 meters in length.

Archelon belonged to the family Protostegidae, which also includes other prehistoric turtles such as Protostega and Desmatochelys.

Comparison with Modern Turtles

Archelon’s shell was significantly different from that of modern turtles. Its shell was flatter and more streamlined, which would have helped it swim faster in the water.

Additionally, Archelon’s shell lacked the fused bones that modern turtles have, which would have given it more flexibility in its movements.

Archelon also had a hooked beak, which it likely used to catch and eat crustaceans and other small marine animals.

This is in contrast to modern sea turtles, such as the leatherback sea turtle, which have a more pointed beak that they use to eat jellyfish.

Evolution and Extinction

Archelon was part of a group of reptiles called Testudines, which includes all modern turtles.

Testudines is a subgroup of the larger group Reptilia, which also includes dinosaurs, plesiosaurs, and mosasaurs.

During the Late Cretaceous period, the climate was cooling and sea levels were dropping. This likely had a significant impact on Archelon and other marine reptiles, as their habitats were shrinking.

Additionally, competition from other marine animals may have contributed to Archelon’s extinction.

Research history on Archelon has been ongoing since its discovery in the late 1800s by George Reber Wieland in Wyoming.

The first complete skeleton of Archelon was discovered in 1979 and is now housed at the University of Alabama Museum of Natural History.

Archelon’s taxonomy has been the subject of debate, with some researchers suggesting that it should be classified in its own family, Archelonidae, rather than Protostegidae.

Regardless of its classification, Archelon remains an important part of the evolutionary history of turtles and is a fascinating example of the diversity of life that existed during the Late Cretaceous epoch.

Frequently Asked Questions

Where did Archelon live?

Archelon was a prehistoric sea turtle that lived during the Late Cretaceous period, approximately 70 to 80 million years ago.

It is believed that Archelon lived in the shallow seas that covered much of what is now North America.

What did Archelon eat?

Archelon was a carnivore and its diet consisted mainly of jellyfish, squid, and other small marine animals. It had a beak-like structure that it used to crush the shells of its prey.

Why was the Archelon so big?

Archelon was one of the largest sea turtles that ever existed, with a shell that could grow up to 13 feet in length.

The reason for its large size is not entirely clear, but it is believed that it may have been an adaptation to its environment, allowing it to better compete for resources and avoid predators.

What is the largest turtle that ever existed?

Archelon is one of the largest turtles that ever existed, but it is not the largest. The honor of being the largest turtle goes to the Archelon’s distant relative, the Archelonoides, which could grow up to 16 feet in length.

Did Archelon lay eggs?

Yes, Archelon was an egg-laying reptile. It is believed that it would have laid its eggs on sandy beaches, much like modern-day sea turtles.

Archelon vs leatherback?

Archelon and the leatherback turtle are both prehistoric sea turtles, but they are not closely related.

While Archelon had a hard, bony shell, the leatherback turtle has a soft, leathery shell. Additionally, the leatherback turtle is still alive today, while Archelon went extinct millions of years ago.

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