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.
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Source: Phys.org