Marine reptile

Marine reptiles are special kinds of reptiles that have changed to live mostly in water, like in the ocean or near the shore. Only about 100 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.
• 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.

Extinct groups

• Ichthyosaurs were marine reptiles shaped like dolphins. They lived during the Mesozoic era.
• Sauropterygians were water reptiles with flippers for swimming. This group included the plesiosaurs, nothosaurs, and placodonts.
• Mosasaurs were large, water squamates related to today's lizards and snakes. They were top hunters in the sea near the end of the Cretaceous period.
• Thalattosaurs were water or partly water reptiles. Their family placement is unsure within the diapsid group. One subgroup, the thalattosauroids, had unusual downturned snouts and strong teeth.
• Mesosaurs were possibly the first fully water reptiles. They are the only group known from the Paleozoic, though they are not true reptiles as they are not part of the diapsid group. These animals from the Permian period looked like lizards with long snouts and newt-like tails. They 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 live in the water. These include animals like marine iguanas, sea snakes, sea turtles, and saltwater crocodiles. The very first marine reptile was Mesosaurus, which lived long ago during the Permian period.

Conservation

Most marine reptiles are in danger because their homes are being destroyed or they are being caught. Almost all sea turtles are in danger because people take 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. 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.