Ohtalmosaurus icenicus skull from the Museum of Natural Sciences of Barcelona’s permanent collection ‘Planet Life” collected in Dorset, England | Credit: Talita Bateman — *Ohtalmosaurus icenicus* skull from the Museum of Natural Sciences of Barcelona’s permanent collection ‘Planet Life” collected in Dorset, England | Credit: Talita Bateman

Yes, they were enormous. Yes, they looked like modern dolphins (mammals) or sharks (fish) but they were actually reptiles. And finally, no, they were not dinosaurs. Ichthyosaurs have got to be one of my favourite groups of extinct reptiles and a great example of convergent evolution.

If you visit a natural history or palaeontology museum, you are likely to come across at least one specimen of the ichthyosaur group. This extinct group of aquatic reptiles are distant relatives of modern-day Lepidosauria reptilians, including my beloved tuatara!

They first appeared around 248 million years ago at the beginning of the Triassic period. Fossils suggest that early specimens looked like lizards with flippers, such as the Chaohusaurus (found in China) and the Utatsusaurs (found in Japan). However, they were the first Tetrapod to reach real gigantic sizes. Examples would include specimens of the Shastasauridae family, which first appeared in the middle of the Triassic period (circa 240 million years ago).

I believe that the largest species record so far is the Shonisaurus sikanniensis found in British Columbia, Canada – or at least the largest specimen whose species palaeontologists were able to determine from its remains. This specimen is currently on display at the Royal Tyrrell Museum in Alberta, Canada and is a whopping 21 metres long.

In reality, even bigger species, or at least specimens, are likely to have existed. Dr Dean Lomax wrote an incredibly informative article about Ichthyosaurs back in October 2018 where he discusses his (and his team’s) finding of a giant piece of ichthyosaur jaw bone collected from Somerset in England. This finding suggests that the entire specimen could have measured an estimated 26 metres long. However, because of the fragmented nature of the remains, they were unable to identify the species. If you would like to know more about Ichthyosaurs, I would highly recommend that you read his article!

Now, at the beginning of this blog post, I mentioned that they were not dinosaurs and for many of the people that read my blog, this will be a ‘yeah, duh’ statement. However, I think it’s quite clear that the general public does not necessarily know what a dinosaur is – if it’s big, extinct and resembles an old lizard-like monster in modern-day drawing representations, it’s a dinosaur. We’ve all experienced one form or another of someone pointing at a pterodactyl specimen at a museum or on TV and stating ‘Look at that dinosaur!’.

Ichthyosaurus communis from the Museum of Natural Sciences of Barcelona’s permanent collection ‘Planet Life’ collected in Dorset, England | Credit: Talita Bateman — *Ichthyosaurus communis* from the Museum of Natural Sciences of Barcelona’s permanent collection ‘Planet Life’ collected in Dorset, England | Credit: Talita Bateman

For the most part, the misunderstanding is not that surprising. Most people’s knowledge on the classification of living animals is pretty poor, let alone extinct ones. In my experience, once you start explaining the basic characteristics of a dinosaur – and what makes a dinosaur a dinosaur – people zone out and push it aside as a ‘technicality’ and geek talk. For that reason, I tend to stick to explaining the bare minimum, such as mentioning the straight back legs that were perpendicular to the body, how they were oviparous, etc. Having said that, simply put, dinosaurs have certain characteristics that are not all, or not always, present in other extinct animal groups. The Natural History Museum has a great little summary page that lists the main characteristics of a dinosaur – they define those as:

- They had an upright stance, with legs perpendicular to their body. This is the main feature that sets dinosaurs apart from other reptiles.
- Like other reptiles, they laid eggs.
- With the exception of some birds, for example penguins, dinosaurs lived on land, not in the sea.
- Their skull had a hole between the eye socket and nostril. This feature is shared by all archosaurs.
- Dinosaurs also had two holes behind the eye socket. Large, strong jaw muscles went through the holes to attach directly to the top of the skull. As a result, the jaws were able to open wide and clamp down with more force.

Having listed those characteristics, it’s easy to see why ichthyosaurs were not dinosaurs - physical appearance aside, they were viviparous (gave birth to live young) and aquatic. On top of that, their physical similarities to dolphins and sharks (respectively mammal and fish) are a great example of convergent evolution - where unrelated animals evolve with similar advantageous characteristics that make them more adaptable to their environment. Good living examples of convergent evolution that I often mention are the Australian Thorny Devil Lizard (Moloch horridus) and the American Horned Lizard (Phrynosoma).

I decided to write about Ichthyosaurs after attending TetZooCon 2019, where I found a great little tote bag decorated with drawings of ichthyosaur skeletons. Since I luuuurve ichthyosaurs, the tote has become a daily staple of mine and it reminded me of the two ichthyosaur specimens on display at the Museum of Natural Sciences of Barcelona that I photographed during my visit earlier this year (photographs above). So, what’s your favourite extinct reptile?