Recently discovered fossils of Leedsichthys – the biggest fish that ever swam in oceans – show that the prehistoric creature could grow to 26 – 30 feet (8-9 m) in two decades and reach 54 feet (16.5 m) in length in 38 years.
Leedsichtys problematicus (Dmitry Bogdanov / CC BY 3.0).
Leedsichthys was a huge bony, plankton-eating fish that lived in the Middle Jurassic period around 165 million years ago. A number of skeletal remains of the creature have been uncovered over the years but haven’t preserved well, meaning no-one was really sure just how large the fish could grow.
To fill this gap, paleontologists from United Kingdom and Canada studied various remains of Leedsichthys, including a new specimen unearthed near Peterborough, UK.
“What we have demonstrated here is that a small adult Leedsichthys of 26 – 30 feet (8-9 m) could reach that length within around 20 years, whereas after 38 years it would be around 54 feet (16.5 m) long – possibly even outgrowing today’s massive whale sharks,” explained Prof Jeff Liston from National Museums Scotland, who with colleagues reported the findings in the volume Mesozoic Fishes 5: Global Diversity and Evolution.
“This fish was a pioneer for the ecological niche filled today by mammals, like blue whales, and cartilaginous fish, such as manta rays, basking sharks, whale sharks.”
“Before then, vertebrate suspension-feeders did not get larger than 1.6 feet (50 cm) in length. Something important had changed. The existence of these large suspension-feeding fish at this time is highly significant, as it would seem to be clear evidence of a major change in plankton populations in Earth’s oceans of Jurassic Earth – a ‘smoking gun’ that something new, widespread and highly edible was around – possibly related to the first appearance of small crustaceans called copepods.”
“This has implications for our understanding of biological productivity in modern oceans, and how that productivity has changed over time.”
Leedsichthys was around for at least ten million years in the Middle and Upper Jurassic. Although its relatives, all pachycormid fish, continued to successfully suspension feed on plankton through the rest of the Age of the Dinosaurs until the end of the Cretaceous 66 million years ago, the largest examples were in the 13 – 20 feet (4-6 m) range, and never again quite in the same league as Leedsichthys.
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Bibliographic information: Gloria Arratia et al. 2013. Mesozoic Fishes 5 – Global Diversity and Evolution. Proceedings of the international meeting Saltillo, 2010. Hardcover. ISBN 978-3-89937-159-8
