Channel4.com Text Only

[ Text Only: Homepage ]
[ Graphical: Channel4 Homepage ]

Big Monster Dig

Leedsichthys: the big fish

Leedsichthys: the big fish | Leedsichthys | Resources

Leedsichthys

The biggest fish in the sea
Most people regard the great white shark as a big fish, and with a total (authenticated) maximum length of around six metres, it is. It's far from the biggest fish in the sea, however: that title belongs to the whale shark, a filter-feeding giant that reaches an incredible 12 metres.

During the Jurassic, though, there swam a fish that may have put even the whale shark to shame, yet it is hardly heard of, little studied, and only known to a handful of palaeontologists. This fish is Leedsichthys problematicus, a behemoth that probably approached a length of 30 metres – about the same length as a blue whale (which is a mammal).

First discovery
Unlike the whale shark (which, like all sharks, is a cartilaginous fish), Leedsichthys was a bony fish and hence part of the same group as herring, perch and trout. Not a new discovery, it was first found late in the 1800s by Alfred Leeds, a farmer and avid collector of the fossils of the Oxford Clay, a Jurassic mudrock that has produced hundreds of well-preserved marine reptiles, fish and other fossils.

Most of Leeds' Oxford Clay fossils were sold to what is now the Natural History Museum in London, where they were studied by Arthur Smith Woodward, an expert on fossil fishes. Woodward named and described Leedsichthys in 1889 and, though thinking initially that it might be related to sturgeons, he later realised that it was a member of an extinct group called the pachycormidae.

What Leedsichthys looked like
Given that Leedsichthys is not known from complete skeletons, this classification has allowed experts to make several educated guesses about what the whole fish looked like. Pachycormids known from complete skeletons have a streamlined body shape suggestive of fast-swimming, a strongly forked tail and stiff, scythe-like pectoral fins.

Luckily, a nearly complete tail is known for Leedsichthys: it is a remarkable five metres from tip to tip. But because some kinds of pachycormids are relatively short-bodied, while others are relatively long-bodied, estimates of the total length for Leedsichthys have varied between 10 and 30 metres. A new Leedsichthys specimen from Whittlesey, in Cambridgeshire, excavated during the summer of 2002, is probably the most complete yet found. Preliminary results indicate that a total length of around 30 metres is more accurate than the lower estimates.

Diet and predators
In Leedsichthys, the rod-like gill bones called gill rakers supported millions of tiny needle-like teeth. These formed an effective filtering device and would have allowed Leedsichthys to strain small crustaceans, fish and other animals out of the water as it swam along. Leedsichthys was therefore a Jurassic version of the whale shark or the blue whale.

A fish the size of Leedsichthys would have been an important component of Jurassic marine ecosystems. It would have consumed literally tonnes of plankton. Its dung would have fertilised the sea floor, and during the breeding season thousands of fish and other animals would have feasted on the millions of eggs produced by Leedsichthys females.

Baby and juvenile Leedsichthys would have been preyed upon by predatory bony fish, sharks, and an assortment of marine reptiles. When a Leedsichthys died, moreover, its body would have provided tonnes of flesh for many hundreds of scavengers. As the biggest fish ever, it is likely then that Leedsichthys played one of the biggest roles in Jurassic marine life.

Top of page

Graphical version

[ Text Only: Homepage ]
[ Graphical: Channel4 Homepage ]
[ Contact Us ]
[ Access Advice ]

[ HTML 4.01 TR Approved ]