Part 2 of a 5 part series: for part 1 click here!

Banner image: a) Pliosaur - Liopleurodon b) Plesiosaur, The Fossils of the Oxford Clay by The Palaeontological Association (1)

Let's journey to the Millennium Country Park's very own marine Jurassic Park...!

By Duncan Willox ǀ Local geology enthusiast and poet

Now we’re a little deeper, what else can you see?

You might spot a familiar looking creature with coiled shell called an ammonite, although they are different species from those that you’ll find in Lyme Regis in Dorset or around Whitby in Yorkshire. As you can see, they are related to present day squid & octopus with their tentacles used to grasp their prey. Ammonites can only travel backwards- that’s because they move by expelling a jet of water from the front end of their shells. A bit of a design fault you might think; imagine trying to drive around our dear M25 in a car that can only go backwards! Despite that huge challenge (mercifully for them - not the M25, I don’t mean) ammonites were very successful over many millennia, evolving through many hundreds of species until extinction also struck them at the end of the Cretaceous period. Much the same can be said for their close relatives, the belemnites, those cigar-shaped tentacled creatures that are swarming past us at the moment.

Images: Ammonite (top) and Belemnite (bottom), Fossils of the Whitby Coast - a photographic guide by Dean R Lomax

Of course, there are also many fish.

You’d be likely to see the giant fish Leedsichthys, believed to have grown up to 16 metres in length, making it the biggest species of fish to have ever lived - just imagine a fish longer than a double-decker bus! Some lived to be more than 50 years old.

Anyone hoping to see the water foam from a clash of the titans between Leedsichthys and, say, a pliosaur, will be disappointed because it is thought that this fish probably fed primarily on plankton. If so, it wouldn’t have been able to trouble a pliosaur with anything more fatal than an irritating suck.

If you take a closer look at the seafloor you can see it’s made up of fine sediment. Best not to try and stand on it, as you’ll get a bad case of that sinking feeling - and my doctor has repeatedly advised that at my age I shouldn’t be trying to pull people out of the upper Jurassic seabed!

As you’d expect there are lots of shelled animals down here, some looking quite like shells you might see on our beaches: particularly creatures with snail-like shells (gastropods) and others with flat 2 halved cockle-like shells (Bivalves). There’s also thick beds of the oyster shell, Gryphaea (I’ll tell you more about them later) as well as fish and sharks down here, including Asteracanthus, a very common shark. Disappointingly for fans of the film ‘Jaws’, Asteracanthus had flat teeth used for crushing its prey of exclusively shellfish.

For geologists this is actually the most exciting place in the world because this is where it all happens. No, I don’t mean the best shellfish dinner parties! This is where a creature, having finally given up life’s struggles, is buried in the soupy seafloor sediment and thus the fossilisation journey begins. That journey over many millions of years may end in the palm of a geologist’s hand.

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(1) Kelly, S. (1992). D. M. Martill & J. D. Hudson 1991. Fossils of the Oxford Clay. Palaeontological Association Field Guide to Fossils, number 4. 286 pp. London: The Palaeontological Association. Price £15 (paperback). ISBN 0 901702 46 3. Geological Magazine, 129(3), 374-375. doi:10.1017/S001675680001935X