Researchers Studying Jurassic Fish Fossils Baffled to Find They Suffered a Rather Unusual Death — By Choking

Examination of a set of Tharsis fossils has revealed to researchers a possible cause of death for some of these creatures. This shocking cause of death was swallowing belemnites (squid-like cephalopods), and then choking to death because of it, as reported by Phys. Tharsis is the extinct genus of late Jurassic fish, and their remains are mostly found in the marine fossil deposits of the Solnhofen Plattenkalk (Solnhofen Limestone), Germany. The analyzed remains were also from Solnhofen Plattenkalk. Belemnite fossils are also present in the area, but they are fewer than in Tharsis. Before this study, nobody knew about this possible cause of death. Findings regarding this revelation have been published in Scientific Reports.

Placement of Tharsis Fossils

The Tharsis fish, which were suspected to have undergone choking, seemed to be subadults. The subjects were embedded in Solnhofen Plattenkalk (Solnhofen Limestone), situated at Eichstätt-Solnhofen basins. In the late Jurassic, these basins were a part of the Solnhofen archipelago, which supposedly had an environment that exhibited low oxygen levels and high salinity. Both of these factors are unsuitable for life, but still, Eichstätt-Solnhofen basins have a treasure house of fossils, with numerous specimens of Tharsis. "Tharsis is the second most common genus in the Solnhofen Archipelago with some 4,200 specimens that Martin Ebert, the first author of the paper, has actually seen in various collections," Dr. Martina Kölbl-Ebert, second author of the study, explained.

Uncanny Discovery in the Fossils

Researchers found belemnites in the throats of four Tharsis fossils among the examined specimens. Belemnite remains have mostly been found in the Plattenkalk basin. Belemnites are cephalopods that existed during the Jurassic and Cretaceous periods. Despite having known about Tharsis fossils for years, this pattern had gone unnoticed. Kölbl-Ebert believes it happens because the specimens are so numerous that experts often only focus on the most well-preserved ones to get insights. The first author, Dr. Martin Ebert, was examining 4,200 specimens due to his interest in statistics and ecology, and stumbled upon this discovery.

How did Tharsis eat Belemnites?

Belemnites mostly lived in the open sea and could not survive in low-oxygen environments, like the Solnhofen archipelago. Hence, researchers speculate that when Tharsis fishes came across belemnites, the latter were already dead. Past examinations have proven Tharsis to be micro-carnivore. This eating habit implies that they might be swallowing algae, bacterial growth, or remnants of dead tissue from their habitat. If belemnites were dead, algae may have grown on their body. Researchers believe that seeing a belemnite along with a food resource could have made Tharsis think that it was also a food item. "We assume from present-day experience that such floating objects are quickly overgrown with algae and bacteria, thus for the fish they smell and taste like food," Kölbl-Ebert shared.

The tip of the belemnite would fit into the mouth of Tharsis, but as they would have swallowed the cephalopods, it would have become increasingly difficult to keep it down. They must have tried to expel the belemnite out but failed. While taking into consideration modern observations, researchers believe the fish were dead within hours, due to oxygen deprivation.