My Collection #2

Small Kosmoceras jason on a piece of Oxford Clay with a tiny
belemnite to the left.

These fossils were collected from Must Farm Brick Pit in Whittlesey, near Peterborough in Cambridgeshire, UK in June 2016.

Kosmoceras ammonites are known from Callovian age Oxford Clays of the Late Jurassic Period in Europe. These ammonites therefore date back to around 163 Ma. As with these two fossils, they are commonly found flattened in the clay, rarely it is possible to find three dimensional casts of the shell. The maximum diameter known from fossils is about ten centimetres. There is evidence of sexual dimorphism in these ammonite, the more decorated males have a smaller shell than the females, the purpose of the ornamentation is unknown.

Calcitic Kosmoceras jason from Kings
Dyke Brick Pit.

A larger iridescent Kosmoceras jason on a piece of Oxford Clay

The preserved phragmocone of a belemnite from the
Oxford Clay.

Cylindroteuthis is a belemnite known from the Early Jurassic, ~200 Ma, to the Early Cretaceous, ~140 Ma. This specimen is rather common, being found in Asia, Europe, North America and New Zealand. The calcitic guard of the belemnite is what is commonly found, lengths range from ten centimetres to twenty-two centimetres. Rarer fossils exhibit traces of appendages and an ink sac, showing their relation to squids. The guard would be an internal feature as traces of blood vessels have been found on the surface of the guard. This fossil is not to be confused with the shell of the belemnite, this is found within the guard, as shown in the photo to the right.

The largest of the Cylindroteuthis belemnites in my collection from the Oxford Clay at Kings Dyke Brick Pit.

This is a fragment on a bone from the giant fish Leedsichthys. This member of the pachycormidae is known from Callovian sediments of the late Jurassic. Discovered by Alfred Leeds in 1889 when the Peterborough brick making industry was taking off and quarries were being opened in and around the city, Leeds collected various marine fossils from the Oxford Clay in this time. Fossils have been found in England, France, Germany and Chile. In 2002, another individual was discovered in the Must Farm pit in Whittlesey by students at Portsmouth University. An excavation led by Jeff Liston of Yunnan University, revealed thousands of delicate bones, including the pectoral fin. A lot of the skeleton would have been composed of cartilage and so it doesn't fossilise. Size estimates put the fish at around twelve metres long. It is believed that a spike in planktonic populations were the reason behind the size of the Leedsichthys. Being a filter feeder, water would have been forced through gill rakers that removed the plankton from the water.

A small fragment of Leedsichthys problematicus from the Oxford Clay at Kings Dyke Brick Pit.

The larger and more complete Gryphaea
in my collection.

Also known as the Devil's Toenail, Gryphaea is an extinct genera of bivalve mollusc. Their geological range is from the late Triassic through to the Eocene. These bivalves are some of the more common finds in Jurassic marine deposits of Europe. They possibly lived in small colonies as shown in the photograph to the right. The bivalve had a larger hooked valve and a smaller, flatter lid. The
larger valve would be embedded in the sediment whilst the lid remained exposed. It is one of the only bivalves that have one valve larger than the other.

A broken Gryphaea from the Oxford Clay.

The underside of the above Gryphaea.

Palaeoart: Leedsichthys

Today I've got two pieces of artwork from the same artist and of the same subject. The Jurassic leviathan, Leedsichthys problematicus. The artist is the great Robert Nicholls, the artist of the Ichthyosaur piece that I shared yesterday. I think we can agree that Nicholls is a fantastic artist who really does these animals justice when he brings them back to life in his artwork.

The Leedsichthys is a prehistoric fish of the family pachycormidae, an extinct group of ray finned fish. The animal is known in the Jurassic deposits in the Peterborough area where thousands of fossils have been found in the Oxford Clay quarries. The first was found by local Palaeontologist and farmer, Alfred Leeds, the man the fish is named after. However, in 2002, students from the University of Portsmouth found more remains, a team led by palaeontologists Dr Jeff Liston and Dr Dave Martill uncovered over a thousand bones, making it the most complete specimen to be found despite only finding a small proportion of the animal. Size estimates are around 11 to 14 metres (37 to 49 feet). 

This first piece shows a lone Leedsichthys with an Ichthyosaur in the background. This gives us a nice sense of scale, although the Ichthyosaur is in the background it is clear to see that it is dwarfed by the fish. This raises an interesting question, would smaller animals follow giants like this as a form of protection? Another thing I like about this piece is Nicholls' choice of colouration for the Leedsichthys, a dark dorsal surface and white underneath. This is very similar to the colouration of modern sea animals including Great White Sharks. The sharks of today are coloured as such so that from above they are camoflaged with the murky depths and from beneath they blend in with the bright surface of the water, this makes it more difficult for prey to spot the incoming predator. But Leedsichthys was not a predator, it was a filter feeder like the Whale and Basking sharks of today, this is shown by the giant gape of the fish's mouth which is collecting tiny plankton. The reason for the a peaceful giant like Leedsichthys to be coloured this way is for its own protection, a predator would have difficulty making out the outline of the fish from above or below, making a successful attack more risky.

The seond piece I've chosen is another lone Leedsichthys in the Jurassic Ocean by Robert Nicholls. This time rather than being accompanied by an Ichthyosaur, there is a group of smaller fish surrounding the giant, the species is possibly Caturus. This is interesting as it shows the vast range in size between the two types of fish, which helps to visualise the length of this gentle giant. As with the last piece, it appears that smaller animals are staying close to the Leedsichthys for protection from predators. This behaviour can be seen in fish today that surround Whale Sharks.

Overall, both artworks are impressive in the way they show us the scale of this fascinating fish. If you want to read more about this wonder, then pay a visit to the new website created by a team at Peterborough Museum, the link will be left below.

www.bigjurassicfish.com