The fish in question, with the ammonite located just below its spine.
Ars Technica has a story about an interesting fish fossil. A fossil fish, Pachycormus macropterus, from Germany shows that even fish sometimes bite off more than they can eat... This particular fish fossil has a fossilized ammonite in its belly. The fossil was found in the Fischer Quarry in Zell unter Aichelberg, Germany and dates to the Jurassic Period, more than 170 million years ago. See more detail in a paper published in the journal Gelological Magazine.
“This work is part of a larger project studying the evolution and palaeoecology of fishes from the Early Jurassic of Germany,” Maxwell explained. “We were interested in looking at stomach contents in these fishes in order to understand where they fit in the Early Jurassic food web and whether different fishes living in the same environment during the Early Jurassic had similar diets.”
That inquiry brought them directly to this fossil.
Maxwell said that it “fossilized in a very particular way, retaining a lot of the original mother-of-pearl shine of the shell material. This is very unusual for fossils from this locality and is likely a function of the shell being protected from the external environment inside the body of the fish. This can help us to assess whether a shell is truly preserved in an animal’s stomach in future finds.”
