A fascinating study reveals that the immense size of ancient ammonites was a response to their predators’ growth, a remarkable example of evolutionary adaptation in prehistoric marine ecosystems
The specimen was collected in 1894 near Seppenrade. LWL-Museum for Natural History , Münster. Photo: CI. Scale: 100 mm. Credit: Ifrim et al., 2021, PLOS ONE, CC-BY 4.0 (creativecommons.org/licenses/by/4.0/) A small team of researchers from Germany, Mexico and the U.K. has found evidence suggesting that the reason a species of ammonite grew into giants was because of the increasing size of the mosasaurs that fed on them. In their paper posted on the open-access site PLOS ONE , the group describes their detailed study of 154 specimens of two species of ammonite fossils and what they learned about them. Ammonites are a kind of coil-shelled mollusk that went extinct millions of years ago. They were notable for their distinctive frilled suture lines. Prior research has shown that the average ammonite was no more than half a meter in diameter. But one species stands out—Parapuzosia seppenradensis, a species that could grow to have a diameter as large as 1.5 to 1.8 meters...