Choristodera

Long ago, many reptiles lived in the water.

These animals had many shapes. Some looked like big crocodiles with long snouts. They used their sharp teeth to catch fish.

Other types were small like lizards. Some even had very long necks. They lived in warm lands like North America and Asia. Some had webbed feet to help them swim.

These creatures were very different from each other. It is fun to see how they lived!

Choristoderes were a group of reptiles that lived long ago.

They lived in freshwater, like rivers and lakes. Most lived in warm places. They can be found in fossils from North America, Asia, and Europe.

These animals came in many shapes. Some were big and looked like crocodiles. We call these neochoristoderes. One type, Champsosaurus, had a long, thin snout. It had small, sharp teeth to catch fish.

Other types were smaller and looked like lizards. Some had very long necks, much like a plesiosaur.

Scientists study their bones to learn how they lived. Most had small scales on their skin. Some had webbed feet to help them swim.

A type called Hyphalosaurus might have used its tail like a fin.

We also learn about how they grew. Some fossils show babies inside their mothers. This means they might have given birth to live young. Other fossils show eggs with thin shells. This suggests they laid eggs on land. Some types might have even cared for their babies after they hatched.

Choristoderes were a special group of reptiles that lived a very long time ago.

These animals lived in freshwater places like rivers and lakes. They mostly lived in warm areas across the Northern Hemisphere. We find their fossils in North America, Asia, and Europe.

Some scientists think they might have lived in North Africa too. These reptiles were very different from each other in how they looked. Some were huge, while others were very small.

These animals had many different body shapes. The most famous ones are called neochoristoderes.

These looked a lot like modern crocodiles or gharials. They had long, thin snouts with small, sharp teeth. They likely used these teeth to catch fish in the water. Other types were called non-neochoristoderes.

These were mostly small and looked like lizards. However, some of them had very long necks like a plesiosaur.

Scientists have been studying these reptiles for a long time. Edward Drinker Cope first named the group in 1876. He described a type called Champsosaurus from Montana. In 1877, Paul Gervais described another type called Simoedosaurus from France.

For over one hundred years, we only knew about those two. Then, new fossils were found in the late 20th century. Soviet-Mongolian teams found new types in Mongolia starting in the late 1970s. Susan E. Evans also described new fossils from Britain between 1989 and 1991.

There is a wide range of sizes among these reptiles. The smallest ones, like Cteniogenys, were only about 20 centimeters long.

The largest known one was named Kosmodraco dakotensis. This big animal is estimated to have been around 3 meters long. Most choristoderes had simple, pointy teeth. Many also had many teeth on the roof of their mouths. These teeth helped them move and handle their food.

We can learn how they moved by looking at their skin and feet. Some fossils, like Monjurosuchus, show small, overlapping scales.

This animal also had webbed feet for swimming. Hyphalosaurus had scales too, and its tail might have worked like a fin.

We even found tracks in South Korea that might be from these animals. These tracks show five fingers and traces of webbing. This helps us picture how they walked near the water.

Choristodera is an extinct order of semiaquatic diapsid reptiles. The name comes from Greek words meaning "separated neck." These animals lived in the Northern Hemisphere for millions of years. Their history spans from the Middle Jurassic or possibly the Triassic to the Miocene. This means they lived from about 168 million years ago until 20 or 11.6 million years ago.

They were mostly found in North America, Asia, and Europe. Some scientists believe they may have also lived in North Africa. They are generally considered to be derived neodiapsids. This makes them close relatives or members of the group known as Sauria.

Scientists identify choristoderes through several unique physical traits, called synapomorphies. One major trait is a special bone in the skull called a neomorph. This is a new bone found in the dermatocranium that is not in other reptiles. Their skulls also have specific openings called temporal fenestrae. In neochoristoderes, these openings are very large and give the skull a heart shape.

These reptiles also had gastralia, which are rib-like bones located in the abdomen. Their teeth are usually conical and sub-thecodont, meaning they sit in shallow sockets. Most choristoderes also had teeth on the roof of their mouths, called palatal teeth. These teeth helped them manipulate food using their tongues.

Choristoderes show great variety in their body shapes. The most famous group is the neochoristoderes. These animals resembled modern crocodilians, specifically the long-snouted gharial. They had long, thin snouts filled with small, sharp, conical teeth.

Other members are called non-neochoristoderes. Most of these were small and lizard-like. However, some had very long necks similar to the marine reptile plesiosaur. This group includes animals like Hyphalosaurus and Shokawa. Because the lizard-like shape is the ancestral form, the non-neochoristodere group is considered paraphyletic.

Discovery of these animals has happened in stages. Edward Drinker Cope first established the order in 1876. He described Champsosaurus from the Late Cretaceous of Montana. In 1877, Paul Gervais described Simoedosaurus from France. For over a century, these were the only two recognized types. This changed in the late 20th century when new fossils were found. Soviet-Mongolian teams discovered new taxa in Mongolia starting in the late 1970s. Between 1989 and 1991, Susan E. Evans described new material of Cteniogenys from Britain. This helped scientists realize that some choristoderes were small and lizard-like rather than crocodile-like.

Size differences among choristoderes are quite large. The smallest genera, such as Cteniogenys and Lazarussuchus, were only about 20 centimeters long.

On the other end of the scale, the largest known member was Kosmodraco dakotensis. This animal is estimated to have reached a total length of around 3 meters. Their environments were also specific. They are found exclusively in freshwater deposits. They lived in warm temperate climates. During the Late Cretaceous, some neochoristoderes even lived in the high Canadian Arctic because the earth was extremely warm then.

We can learn about their lives from exceptionally preserved fossils. The specimen of Monjurosuchus shows pleated skin and small, overlapping scales.

It also shows evidence of webbed feet. Hyphalosaurus had scales of different shapes and a tail that likely acted as a fin.

Some fossils even show what they ate. A Hyphalosaurus specimen contained small rib bones, suggesting it ate vertebrates like small fish. There is also a Monjurosuchus specimen with seven juvenile skulls in its abdomen. Some suggest this shows cannibalism, but others believe they might be late-stage embryos. Scientists also found five-fingered tracks in South Korea that likely belong to choristoderans.

Reproduction in choristoderes was also diverse. Evidence from Hyphalosaurus suggests they might have been viviparous, meaning they gave birth to live young. This is based on a specimen with 18 fully developed embryos. However, other specimens show they also had soft-shelled eggs. This might mean they were ovoviviparous, where eggs hatch shortly after being laid. Other animals, like Ikechosaurus, appear to have been oviparous, laying eggs on land. Some fossils, like Philydrosaurus, show juveniles near adults. This suggests that some species may have provided parental care to their young.