Giant armored fish specializing in open mouth waiting for bait

Titanichthys has long been known as one of the largest animals in the Devonian period, living in the ocean 380 million years ago. The exact size of this species is difficult to determine, but certainly longer than 5 m. Like a exposed shark, Titanichthys's lower jaw is over a meter long. However, unlike Dunkleosteus, an equally large armored fish, researchers have previously found no evidence of Titanichthys eating. While Dunkleosteus's lower jaw has clear fangs and crushed plates, the Titanichthys's lower jaw is quite narrow, lacking teeth or sharp edges suitable for bite activity.

Titanichthys is a giant whale species that lived in the late Devonian. (Photo: Mark Witton).

As a result, researchers from Britain and Switzerland think that Titanichthys are a kind of wait-for-eat, feeding small zooplankton by swimming slowly with their mouth wide open in the water to catch large amounts of phytoplankton. This technique is called continuous eating. However, this is still an uncertain speculation because there is no evidence of fossils about the structure of the jaw suitable for such feeding as long-drawn combs like modern sharks.

Instead, the team sought to indirectly answer the question through biomechanical analysis to compare the mandibles of Titanichthys with other species. They published their findings on May 19 in the journal Royal Society Open Science. Research leader Sam Coatham conducted the analysis while studying for his PhD in paleontology at the Earth Science School at the University of Bristol.

"We found that Titanichthys were more likely to be feeding by waiting. Their lower jaw was less mechanically rugged than those of large-sized or hard-shelled prey. Other popular foraging tactics may not be suitable for Titanichthys, " Coatham said.

The Titanichthys fossils  used in the study were found in the Sahara Desert in Morocco by co-author Christian Klug, a scientist at the University of Zurich. The team tested the force used to test the jaw's toughness, using a technique called Finite Element Analysis (FEA) to assess how the jaw is prone to breaking or bending. The results revealed that the lower jaw of Titanichthys was much less resistant and more fragile than other species of mackerel, including Dunkleosteus. Therefore, the Titanichthys jaws may not be able to withstand the high pressures associated with large prey hunting tactics. Further analysis showed that the distribution of pressure in the Titanichthys jaws and exposed sharks have many similarities.