Massive Ancient Armored Fish Fed Like A Basking Shark

Titanichthys by Mark Witton

Rachael Funnell 20 May 2020, 11:06

New research published in the journal Royal Society Open Science reveals the giant armored fish Titanichthys probably fed in a similar way to modern-day basking sharks. The leviathan filtered the oceans 380 million years ago, feeding on tiny plankton in a strategy called "continuous ram feeding".

Continuous ram feeding sees modern-day basking sharks sweep through the water with their enormous mouths agape, which can be around 1 meter (3 feet) wide. By “ramming” lots of water through their mouths they can efficiently filter the water for tiny food effectively acting as a living colander for krill.

Titanichthys was previously thought to have been a suspension feeder, which encompasses ram feeding, owing to its enormous lower jaws. However, the theory had never been confirmed as no fossilized evidence of suspension feeding structures, such as the elongated projections that cover the gills of modern-day suspension feeding fish, has ever been found.

Scientists from the University of Bristol and the University of Zurich decided to investigate the question using biomechanical analysis to compare the lower jaw of Titanichthys with the jaws of other species. They used Finite Element Analysis (FEA) to virtually apply forces to the different species’ jawbones to determine if under pressure they’d be more likely to break or bend. The findings revealed that the lower jaw of Titanichthys couldn’t withstand the same force as other chomping placoderm species such as Dunkleosteus.

Lower jawbone measuring 96cm from the Southern Maïder basin, Morocco. The specimen is nearly complete, excluding the anteriormost tip. It lacks both dentition and shearing surfaces. Photographed at the University of Zurich. Coatham et al, 2020, Royal Society Open Science

The more delicate structure of Titanichthys jaw means that, despite their enormous size and armored body, it’s unlikely they could handle larger prey items meaning they’d need to feed on large quantities of small prey, just like basking sharks. The comparison is further supported by the researchers’ analysis of the distribution of stress across the jaws of Titanichthys and basking sharks, which showed similar patterns.

“We have found that Titanichthys was very likely to have been a suspension-feeder, showing that its lower jaw was considerably less mechanically robust than those of other placoderm species that fed on large or hard-shelled prey,” said lead author Sam Coatham from the University of Bristol's School of Earth Sciences in a statement. "Consequently, those feeding strategies (common amongst its relatives) would probably have not been available for Titanichthys."

Fossils used in the study, as they were found in Morocco. C. Klug

If it wasn’t obvious with a name like “Titanic”, Titanichthys was a giant. The species has long been considered one of the largest animals of the Devonian and while its exact size isn’t known, it likely exceeded 5 meters (16 feet) in length. This again draws comparisons with modern-day basking sharks which are, at maturity, around the same length.

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