Leedsichthys
Leedsichthys was a giant pachycormid (an extinct group of Mesozoic bony fish) that lived in the oceans of the Middle Jurassic period. The closest living relative of the pachycormids is the bowfin, Amia calva, but this is only very distantly related.
The name Leedsichthys means "Leeds' fish", after the fossil collector Alfred Nicholson Leeds, who discovered it before 1886 near Peterborough, England. The fossils found by Leeds gave the fish the species epithet problematicus, because the remains were so fragmented that they were extremely hard to recognize and interpret.
Unfortunately, although the remains of over seventy individuals have been found, these are usually partial and fragmentary. This has made it difficult to estimate its length. Arthur Smith Woodward, who described the specimen in 1889, estimated it to be 30 feet (around 9 metres) long, by comparing the tail of Leedsichthys with another pachycormid, Hypsocormus. In 1986, Martill compared the bones of Leedsichthys to a pachycormid that he had recently discovered, but the unusual proportions of that specimen gave a wide range of possible sizes. More recent estimates, from documentation of historical finds and the excavation of the most complete specimen ever from the Star Pit near Whittlesey, Peterborough, support Smith Woodward's figures of between 30 and 33 feet (9 and 10 meters). Recent work on growth ring structures within the remains of Leedsichthys have also indicated that it would have taken 21-25 years to reach these lengths, and isolated elements from other specimens indicate that a maximum size of just over 53 feet (16 metres) is not unreasonable.
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