It is amazing to think that one of the original prehistoric animals that helped start the science of paleontology is still one we know very little about. In fact what knowledge we have gained about Ichthyosaurs seems to be because of the incredibly large number that have been discovered. At this date there are more then 80 recorded species if Ichthyosaur, with more being added ever year.

The first Ichthyosaur fossils were unearthed at the start of the 19th century (around 1811), and were quickly recognized for what they were. It was obvious these animals were marine in nature, and just as clearly were not related to fish, nor marine mammals like today's dolphins and whales. It seemed skeletally these creatures were closely related to reptiles, and were given a name accordingly. (Ichthyosaur means fish lizard.)

One important piece of information missing about Ichthyosaurs is just what they evolved from? Early versions (250 M.Y.A) show many similarities between themselves and lizards, making lizards their most probable ancestor. These ichthyosaurs still had necks, slender torsos, and long tails. And none of them had developed a dorsal fin. With such bodies it is thought these marine reptiles swam much like an eel does today (called anguilliform), by undulating their entire bodies from side to side. This swimming style is not unsurprising as swimming reptiles today such as the marine iguanas and crocodiles swim in the same fashion.

These ‘eel' like Ichthyosaurs are usually placed in one of five families in the order ichtyosauria, called shastasauridea.

Next are the Mixosauridae, which seem to be the bridge between the reptile like ichthyosaurs, and the ‘true', dolphin like ichthyosaurs. These ichthyosaurs, typified by Mixosaur, developed streamline bodies and a dorsal fin, but only had the beginnings of a fish like tail or fluke.

By the Jurassic, the third family, ichtyosauridae, started to appear. These had the typical body of an ichthyosaur, with sleek bodies, long porpoise like noses, dorsal fins and a fish like tail fluke. These ichthyosaurs would have swum much like today's tuna (thunniform), sweeping their large tails from side to side in broad, powerful strokes while keeping their heads relatively still. This family includes the ‘type' member, ichthyosaurus , along with ophalmosaurus (renowned for having the biggest eyes of any creature that has ever lived!).

The Stenopterygiidae were the second family of ichthyosaurs to evolve during the Jurassic, and though similar to the ichtyosaurids, there were a few important differences. These ichthyosaurs had smaller heads, and longer, narrower paddles, with only five toes while members of the ichtyosauridae had up to nine toes.

The final family to evolve was the Leptopterygiidae . This family includes members such as temnodontosaurus (sometimes known as Leptopterygius) and the odd looking Eurhinosaurus, whose nose resembles that of a modern sawfish.

The smallest of the ichthyosaurs was Chaohusaurus at around 70 cm, while the largest was around 23 metres. Found in Canada , this unnamed ichthyosaur is still being pulled out of the ground.

With a skull weighing 5.8 tonnes and a body of around 80 tonnes, these dimensions place it close to the size of modern whales, a size previously thought impossible for these reptiles.

The skin colour of some of these animals is also known from some remarkably well-preserved fossils, which have managed to preserve skin pigment. It shows that these animals at least were a deep brown in colour, with lighter colors along their bellies. These well preserved fossils have also shown that ichthyosaurs gave birth to live young. Unlike crocodiles and mosasaurs which had managed to keep a reptilian like body, the ichthyosaurs had truly adapted to life in water. This meant ichthyosaurs could no longer venture on land and lay eggs like other marine reptiles, but must have given birth to live young. The fossil record supports this idea as many specimens have been noted carrying young, with some individuals holding up to three 'pups'.

With their dolphin like bodies it is thought most ‘dolphin' like ichthyosaurs could swim at speeds up to 45 k.p.h, and be capable of maintaining that speed for at least half an hour.

Australia has its fair share of ichthyosaurs as well. The first was discovered in 1865, along the Flinders River in Queensland , with more soon to follow from the northern territory and western Australia . Each find was given an individual name, but recently all Australian ichthyosaurs have been placed under the single genus platypterygius (flat wing flipper), also sometimes called Ochtyosaurus australis. The platypterygius seems to have been the most common of all the worlds' ichthyosaurs, with their remains being found across the globe, including as far away as Russia .

The death of the ichthyosaurs is also a mystery as the fossil record shows them dying out well before the k.t boundary, 65 million years ago. Many reasons have been suggested, including the development of modern sharks. Personally I think the most logical reason is the gradual changing of marine habitats at the time. Not matter how well developed the ichthyosaurs became; they were still reptiles, a cold-blooded animal. This was of no disadvantage during the Triassic and Jurassic as the world was covered with shallow, warm seas (the Triassic was the hottest time in the earths history), but the end of the cretaceous saw the end of these seas. The planet was cooling, while the continents were drifting further apart, creating bigger, deeper oceans. These deep waters started absorbing much of the heat these shallow seas once received, thus making all the worlds oceans colder! With this loss of warm habitat, the ichthyosaurs were doomed. The only warm waters left were in some coastal regions. But these waters in waters were patrolled by giant mosasaurs, making them a dangerous place to call home. It seems the ichthyosaurs may simply have run out of warm places to live, and thus slipped into extinction well before the end of the cretaceous.

It must be said this last paragraph is pure speculation. It is possible that ichthyosaurs were warm blooded, thus voiding the cooling oceans theory. Again, we still have much to learn about these amazing creatures.