Alongside trilobites and dinosaurs, ammonites are among the most iconic fossils. They were an extremely diverse group, with scientists estimating that between 10,000 and 20,000 different species of ammonites lived during their nearly 150-million-year reign, from the beginning of the Jurassic Period approximately 200 million years ago to the end of the Cretaceous Period 66 million years ago. Ammonites were cephalopods, a class of mollusk that includes present-day nautilus, octopus, and squid. The genus of ammonite featured here, Parkinsonia, thrived during the Middle Jurassic approximately 170 million years ago, and some of the finest Parkinsonia fos𝄹sils can be found in England and France, as is the case here.

This species of ammonite is named after James Parkinson, the British naturalist and medical doctor best known for his early descriptions of the "Shaking Palsy," i.e., Parkinson's Disease. Parkinson was highly regarded in his time for his book Organic Remains (1804-11) in which he discussed fossil plants and animals, the history of paleontology, and theories of animal creation and extinction decades before the Darwinian revolution in the second half of the 19^th century. Indeed, in the third vol💜ume of his book, Parkinson described an ammonite very similar to the ones displayed here as having, "a discoidal, spiral, multinodular shell, with turns contiguous...the chambers divided by sinuous sep🌜ta."

The outermost layer of ammonite shells was made up of aragonite, a type of calcium carbonate, which provided 🧸strong protection and allowed ammonites to fossilize much more readily than animals that either had a soft shell or lacked a shell. Because ammonites rapidly evolved into new species and their shells were prone to fossilization, they have been crucial for scientists interested in dating the Earth's layers: finding the same species of ammonite in layers of soil thousands of miles apart implies that those layers are from the same time period in Earth's history.