Ammonites – Summary of Research

Figure: Jurassic Coast Trust. (2020). Ammonite.

I have been very excited to learn more about ammonites for my External Brief project. While I knew of their existence due to their infamous status in the prehistoric sphere, I never knew how complex their lives were, and even how much is still unknown about them!

Ammonites are “a large and diverse group of creatures that arose during the Devonian period, which began about 416 million years ago” (McKeever, n.d). I have been very lucky to talk to Dr Steve Etches, the founder of The Etches Collection, who helped to explain to me what these creatures looked like in the past. They varied widely around the globe, such as in characteristics including shape and size, though in the Kimmeridge area where The Etches Collection is based, only species with tight curls have been found. The biggest of these reached sizes of around 50-60cm, though on average they reached around 30cm diameter. Females were larger than males. (Etches, S. 2020)

Interestingly, there is a lot of conjecture when it comes to some aspects of ammonites. For instance, palaeontologists cannot claim what the head of the creatures looked like, as there have never been any fossilised ammonite living parts found. Similarly, experts can only theorise what the shell looked like in terms of colouring, or what the ammonite fed on. Many palaeontologists look to the sister groups of the ammonite, such as the nautilus and cuttlefish for clues. (Etches, S. 2020)

These prehistoric creatures had a fascinating buoyancy system inside their shells that helped to regulate their movement. Their shells had very complex, separate little chambers, which they filled with water. The more water in the shells, the greater their density, thus they would sink. Likewise, if water were to be removed, the ammonite would be lighter than the water around it, thus it would rise.

Neutral buoyancy could also be reached when the “buoyant shell… compensates for the dense soft parts of the organism. This is achieved when total mass of organism = total mass of displaced water. At neutral buoyancy, the ammonite would neither rise nor sink.

I am very excited to portray this concept in the form of a model. I am especially looking forward to studying the formation of the chambers inside the shells – they are far more complex than I thought they were originally!


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