Was this prehistoric giant the largest coelacanth to ever swim in ancient waters?

Nature · Published 3 October 2026 Swipe more like this →

In short: Mawsonia was a massive prehistoric fish that thrived in freshwater and brackish habitats across three continents. While some estimates suggest it reached lengths of over five meters, paleontologists remain cautious about these figures. This enigmatic creature, first identified in 1907, continues to challenge our understanding of ancient aquatic ecosystems.

First described by Arthur Smith Woodward in 1907, Mawsonia represents one of the most significant genera of extinct coelacanths. These fish inhabited diverse regions across South America, Africa, and North America, specifically within the area known as Appalachia. Their temporal range was extensive, spanning from the late Jurassic period through the mid-Cretaceous, roughly 152 to 96 million years ago.

The physical scale of Mawsonia is a subject of ongoing scientific debate. While some specimens suggest lengths reaching 5.3 meters, these figures are largely derived from fragmentary skull remains, such as the quadrate bone. A 2024 study highlights that such large size estimates require skepticism, as they rely on uncertain scaling relationships between specific bones and the total body length of the animal. Regardless of the exact maximum, it was among the largest coelacanths, rivaled only by the related genus Trachymetopon.

The biology of Mawsonia presents several mysteries. Instead of traditional teeth, the interior of its mouth featured small denticles measuring one to two millimeters. Researchers hypothesize that these structures might have been used for durophagy—crushing hard-shelled prey like snails and crabs—or that the fish utilized suction to swallow its food whole. Furthermore, the taxonomy of the genus remains fluid; while many species were historically proposed, recent research, including a 2014 thesis by Léo Fragoso, suggests that some, such as M. brasiliensis, remain valid, while others have been reassigned to different genera entirely.

The distribution of Mawsonia fossils provides a window into the ancient world, with remains found in formations ranging from the Bahia Group in Brazil to the Kem Kem Group in Morocco. These findings underscore the genus's ability to occupy varied freshwater and brackish environments across millions of years, cementing its status as a fascinating, albeit elusive, subject of vertebrate paleontology.

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