Marine reptile

Marine reptiles are special kinds of reptiles that have changed over time to live mostly in water, like in the ocean or near the shore. Only about 100 out of the 12,000 kinds of reptiles alive today are called marine reptiles. Some examples are marine iguanas, sea snakes, sea turtles, and saltwater crocodiles.

The first marine reptile was called Mesosaurus, and it lived during a time called the Permian period. Later, during a time called the Mesozoic era, many more reptiles began living in the sea. These included groups like the ichthyosaurs, plesiosaurs, mosasaurs, and sea turtles. Most of these groups went away at the end of a time called the Cretaceous period, but sea turtles are still around today.

Some marine reptiles, like ichthyosaurs and plesiosaurs, could only live in the water and had their babies there. Others, like sea turtles and saltwater crocodiles, come to land to lay their eggs. Some of these animals also like to rest on land sometimes.

Extant groups

• Sea turtles: There are seven kinds of sea turtles. They live near warm coastal waters but sometimes travel very far, even as far as Scandinavia. Sea turtles usually live alone, but some gather together when it's time to lay eggs. While only seven turtle types live in the ocean, many others live in mixed salt and fresh water areas.
• Sea snakes: Sea snakes are the most common marine reptiles, with over 60 different types. They live in warm waters of the Indian and Pacific oceans, and there are a few reports of them being seen in the Atlantic Ocean. Sea snakes have venom and can be dangerous if attacked, but they usually don’t use much venom unless bothered. They differ from land snakes because their tails are flattened on the sides.
• Marine iguana: Marine iguanas are only found on the Galápagos Islands. They aren’t fully ocean animals. They eat marine plants and spend time in the water, but they lay eggs on land and need to sit in the sun to get warm. This means they can be caught by land predators.
• Saltwater and American crocodiles: No crocodile types truly live in the ocean, but the saltwater crocodile (Crocodylus porosus) can live in salty water and is found in Southeast Asia and Australia. Saltwater crocodiles have special salt glands to remove extra salt from their bodies. They are the biggest crocodile species and therefore the largest reptiles, growing up to six meters long. American crocodiles (Crocodylus acutus) also prefer salty water to fresh water.

Extinct groups

• Ichthyosaurs were marine reptiles with a dolphin-like body shape that lived during the Mesozoic era.
• Sauropterygians were a diverse group of water reptiles adapted for swimming with flippers. This group included the plesiosaurs, nothosaurs, and placodonts.
• Mosasaurs were a group of large, water squamates (relatives of today's lizards and snakes) which became top hunters in the sea towards the end of the Cretaceous period.
• Thalattosaurs were a group of water or partly water reptiles of uncertain family placement within the diapsid group. One subgroup, the thalattosauroids, are known for their unusual downturned snouts and strong teeth.
• Mesosaurs were possibly the first fully water reptilian animals and the only group known from the Paleozoic, though they are technically not true reptiles in the sense of not being part of the diapsid group. These animals from the Permian period looked like long-snouted lizards with newt-like tails and may belong to either Parareptilia or Synapsid groups.
• Thalattosuchians were water crocodylomorphs that lived during the Jurassic period.
• Tanystropheus and related water archosauromorphs lived during the Triassic period.

Adaptation to the marine environment

Main article: Physiology of underwater diving § Aquatic reptiles

Marine reptiles are special kinds of reptiles that have changed over time to live in the water. Only about 100 out of 12,000 reptile species are considered marine reptiles. These include animals like marine iguanas, sea snakes, sea turtles, and saltwater crocodiles. The very first marine reptile was Mesosaurus, which lived during the Permian period of the Paleozoic era.

Conservation

Most marine reptiles are in danger because their homes are being destroyed or they are being caught for other reasons. Almost all sea turtles are in danger because people are taking away their places to lay eggs, and they get caught in fishing nets. Many sea snakes are also in danger because people take their skins and pollution harms them, especially in Asia. Marine iguanas have a very small area where they live, which makes them vulnerable. Saltwater crocodiles, however, are not in as much danger of disappearing.