182 million-year-old fish fossil reveals its cause of death

The presence of ammonite in the stomach fossil

The analysis of the preserved stomach residue indicated that this fish had devoured a variety of prey before dying. 

The evidence showcased it had eaten small mollusks and other tiny fish.

Notably, the stomach fossil included traces of a big, shelled organism ammonite conch – around 10 centimeters across. 

The close fossil inspection revealed that the ammonite was not digested by the fish, and it perished shortly after gulping the entire creature. 

This is mostly because the ammonite was too large for fish to consume all at once. 

The team also speculates that the fish may have inadvertently swallowed the organism, causing it to become stuck in its mouth. Once inside, the fish was unable to expel the ammonite from its mouth, forcing it to swallow it. 

The ammonite's shell then could have blocked passage to the intestine, leading to either congestion or internal bleeding. And in any case, the fish would have died within a couple of hours.

After its death, the fish sank to the seafloor and was eventually buried under the sediments. 

Where it was preserved, along with its stomach contents, for millions of years. And now found by scientists. 

The results have been reported in the journal Geological Magazine.

Study abstract:

A remarkable specimen of the actinopterygian fish Pachycormus macropterus from the Early Jurassic (Toarcian) Posidonienschiefer Formation of Germany exceptionally preserves an unusually large ammonite inside its gut. The ammonite was swallowed by the fish, likely by accident, and represents the first direct evidence for an actinopterygian fish consuming an ammonoid. Exceptional aragonite preservation of the conch retaining partial nacreous lustre, combined with only minor acid etching of the shell, strongly indicates that the ammonite was ingested immediately prior to and was directly responsible for the fish’s death. The fish’s stomach provided a microenvironment protecting the aragonite from chemical dissolution.