For more than a century, the mystery of the true size of a gigantic dinosaur-era fish, Leedsichthys, seemed like the one that got away for paleontologists.

However, a new study may have solved the problem. The study documented an ancient whopper Leedsichthys that may be the largest fish ever found at 16.5 meters (54 feet). The longest living fish, a whale shark, ever documented stretched 12.7 meters (41.5 feet).

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The Jurassic giant, Leedsichthys problematicus, received its name because scientists couldn’t estimate the true size of the fish. Fossil hunters uncovered the first Leedsichthys fossils in the late 1800s. The fish’s remains later turned up as far apart as England and Chile.

However, much of the skeleton of Leedsichthys, including the vertebra needed to know the animal’s length, was made of cartilage. Cartilage doesn’t fossilize easily, so paleontologists had to guess from the bones of the skull, gills, fins and a few other parts.

The problem was that the gills of the fish would have grown proportionately larger than the rest of the fish, because of the gills’ need to absorb enough oxygen, according to a 2005 study by Jeff Liston of the National Museums Scotland. Therefore, estimates from the size of the gills couldn’t be trusted.

Liston made Leedsichthys his own Moby Dick and spent a decade tracking down the truth behind the whale of a fish. In 2007, he estimated that most Leedsichthys ranged from seven to twelve meters long. His most recent research may have finally harpooned the ultimate size of the ancient fish.

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Liston’s recent study examined fossils from many Leedsichthys, including a particular specimen that he estimates reached 16.5 meters (54 feet). Bone analysis of that Leedsichthys suggest the fish took forty-five years to reach that length.

Leedsichthys grew to 1.6 meters long in their first years. After approximately 20 years, they hit eight to nine meters, according to the new study.

Like the giants of the modern oceans, Leedsichthys reached gigantic proportions feeding on tiny marine creatures, plankton.

“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,” said Liston in a press release.

IMAGE: Artist’s conception of Leedsichthys (Dmitry Bogdanov, Wikimedia Commons)