The Ammonite Pavement

I love the Jurassic Coast. I went to Lyme regis as a child (evidently due to the photos) although I don't remember much of it. My parents, however, like to claim this is where my love for rocks and fossils began. I remember a specific story book my mum would read to me and my sister before bed about Mary Anning and her dog fossil hunting along he cliffs in Lyme egis, so have always had fond thoughts of the place. Since studying geology, I've done a whole uni field course in Dorset, really getting to now the rocks of the Jurassic Coast and the workings of the Wessex Basin as an oil province, as well as becoming familiar once again with the Jurassic Coast as my my family and I tackle the challenge of walking the South West Coast Path (which I have ish documented on here, and there will be more to come...).

Me at the ammonite pavement on a field trip in 2022, and as a child circa 2007?

On the most recent leg of the SW Coast Path we started in Lyme Regis and walked for 3 days east to Weymouth, stopping at West Bay and Abbotsbury on the way. I was super hyped about this because it meant I could go back to the ammonite pavement perhaps the coolest geological site the UK has to offer (in my opinion) before we began our walk. The ammonite pavement is located towards the western end of Monmouth beach, a 10 min walk out of the main town of Lyme Regis. It gets its name because the ground you are walking on is literally COVERED in ammonite fossils. Ammonites are my favourite fossils (fun fact my sister and I both have an ammonite tattooed on our ankles somewhat in reference to holidays spent in Lyme Regis, somewhat in reference to my late grandfather who was a keen collector of fossils), so this place is really cool to me.

The rock that makes up the ammonite pavement is a limestone ledge that sticks out onto the beach below the crumbling cliffs. Lyme Regis itself sits on very fossiliferous rock of Lower Jurassic age. These rocks were deposited in a deep ocean which is why they are host to so many marine fossils - not just ammonites ( a group of marine molluscs) but also belemnites, plesiosaurs, and ichthyosaurs - which Mary Anning was able to find. The rocks deposited when this area of the world was deep underwater are known as the Blue Lias and have a very distinctive appearance of a dark blue/grey colour. This is because of their high organic content and low clastic input (aka they have lots of bits of dead plants/animals and not much sandy stuff). For this reason the Blue Lias acts as a source of oil to the Wessex Basin which is the oil province that lies in Dorset. Here in Lyme Regis though, the Blue Lias is exposed at outcrop and you can see all the fossils, hence the ammonite pavement exists.

Pictures of the Blue Lias rock formation and my helpful? annotations from our second year field course

The rocks int this raea of Dorset are really very cool - I actually did my masters research focused around rocks from a cliff in Charmouth called the Belemnite Marls (you can read all about that in previous blog posts) but the really cool bit that I want to share is the ammonites themselves . Ammonites are just really cool! They are extinct marine molluscs that lived between the Devonian and the Cretaceous so about 420 - 60 million years ago. They had these coiled up shells made of aragonite that fossilise easily. Their lives consisted of floating about in the ocean, adjusting their height in the water column by changing how much air was in the different chambers in their shell, and eating little animals, mostly zooplankton.

The main species of ammonite seen on the ammonite pavement is Coroniceras, and in this case they can be up to 70 centimetres in diameter which is pretty huge, far bigger than found in most other places!

The large ammonites seen in the ammonite pavement (I took all these pics - how cool!)

One of the things I found most interesting when learning about ammonites was that you can identify the type of ammonite based on what is called its suture line, the sort of wiggly pattern you see on the shell. Below are some of my notes from first year invertebrate paleobiology at uni showing the different suture lines of goniatites, ceratites, and ammonites as well as the morphology of ammonite shells.

Notes form second year invertebrate paleobiology lectures

Finally, I couldn't write about ammonites and Lyme Regis without touching on Mary Anning herself. She is basically the (in my world) OG woman in geology and was a big inspiration for me. Mary Anning lived, collected, and studied fossils in Lyme Regis in the 19th century. Her father, Richard, was a carpenter/cabinet maker and an amateur fossil hunter. Being a woman in the 19th Century, Mary had little access to a formal education but she was able to read and through a combination of books, and fossil hunting with her father, she taught herself geology and anatomy. When her dad suddenly died of tuberculosis Mary, at the age of 11, was encouraged to keep hunting fossils and help pay off her family's debt through selling them. Between 1811 and 1812, when Mary was just 12 years old, her and her brother found a strange looking fossilised skull. At the time, Darwin had not yet published his theory of evolution by natural selection, so the idea of fossils was mysterious and their origin debated. It took Mary several months to uncover the five metre outline of the skeleton of this lizard type creature, which was later identified to be an Ichthyosaur. This was not the first Ichthyosaur fossil to be found but it was the first to be described in scientific literature (in a paper titled Some account of the fossil remains of an animal more nearly allied to fishes than any of the other classes of animals published in 1814 by Sir Everard Home, a member of the Royal Society of London). In 1823, Mary then discovered the first complete skeleton of a Plesiosaur. Later, in 1828, she discovered a jumble of bones consisting of a long tail and wings which were eventually attributed to belonging to a Dimorphodon, making it the first pterosaur fossil discovered outside of Germany.

By selling her finds, Mary not only contributed to her family's income but helped to fuel public interest in geology and paleontology. Despite her huge contribution to the field, even the Geological Society of London refused to accept her as a member in her life time. They didn't accept women until 1908, common for scientific societies at the time but a real shame nonetheless. In 2022, 11 year old Evie Swire, a resident of Lyme Regis and her mum campaigned to get a statute of Mary Anning in the town to recognise her contribution to geology and paleobiology and so she could serve as a role model for others. Below is a picture of me with that statue.

Me posing as the icon that is Mary Anning next to her statue on my recent trip to Lyme Regis