Leedsichthys – Getting Shrunk Down to Size
There seems to be a trend in palaeontology, perhaps it is the public’s obsession with the fastest, the fiercest, the biggest and such like, but over the years a number of extinct genera have been subjected to a shrinking effect once more is known about them. Liopleurodon for example, portrayed by the BBC as the largest carnivore of all time, weighing a colossal 150 Tonnes, an exaggeration given the fossil evidence. Now even a gentle filter feeder such as Leedsichthys (Leedsichthys problematicus) has been subjected to a shrinking ray.
Leedsichthys was a member of the Pachycormidae, a group of ray-finned fishes. The first fossils of this Jurassic fish were discovered in the mid 1880’s near Peterborough (Cambridgeshire, England), although something like seventy fossils of this marine giant are known, they are all very incomplete and fragmentary. The best evidence for claiming this fish to be the largest ever comes from reconstructions as scientists try to piece together what remains of the fish they do have. As the skeleton of Leedsichthys was made of cartilage and not bone, it is very difficult to piece together what fragments scientists do have. However, thanks in part to a chance discovery of a reasonable number of Leedsichthys fossils found in a cupboard in a Glasgow museum, lengths of up to 27 metres have been ascribed.
Is Leedsichthys the largest fish that ever lived? To read more about this ancient creature, a marine giant from the Age of Reptiles: Leedsichthys – The Largest Fish Ever?
Formerly described by many scientists as “Blue Whale sized”, the problem occurs as scientists attempt to scale up Leedsichthys by comparing what elements of the skeleton are known with more complete but much smaller Pachycormidae specimens. Based on simple comparisons some researchers have concluded that certain individuals, perhaps females; could reach sizes in excess of 35 metres, however, recent research has indicated that Leedsichthys was probably nearer to 35 feet long than 35 metres, with one or two exceptional individuals reaching lengths of 55 feet or more. This would put this extinct animal in the size bracket of the extant Whale Shark (Rhincodon typus), largest living fish on the planet.
Recently, the discovery of more fossils of filter feeding fish has enabled scientists to “plug” an evolutionary gap in ancient eco-systems, as up until recently, there was very little fossil evidence to indicate the presence of large plankton feeding vertebrates between the time of Leedsichthys and the evolution of modern fishes and baleen whales to fill this ecological niche.
To read an article about this: Evidence of a “Leedsichthys Legacy” – Fossil Discovery fills 100 million year old Gap.