A recent study reveals an intriguing aspect of evolutionary adaptation in prehistoric marine ecosystems, focusing on the immense size of ancient ammonites. Ammonites, extinct coil-shelled mollusks, exhibited a distinct frilled suture line.

While most ammonites averaged half a meter in diameter, one species, Parapuzosia seppenradensis, stood out with diameters reaching 1.5 to 1.8 meters.

The research, conducted by a team from Germany, Mexico, and the U.K., aimed to unravel why P. seppenradensis grew exceptionally large.

The study involved examining 154 specimens of two ammonite species: P. seppenradensis and Parapuzosia leptophylla. Evidence suggested that P. seppenradensis evolved from P. leptophylla after the latter migrated from western Europe to the Americas.

While the researchers couldn’t pinpoint the exact reason for the size increase, they observed that many mosasaurs, considered the main predators of ammonites, also grew larger during the same period.

The researchers propose that larger P. seppenradensis individuals were harder for mosasaurs to consume, leading to their increased survival and reproduction.

However, the theory encounters a complication, as subsequent research revealed that mosasaurs continued to grow even as P. seppenradensis reached its peak size. Eventually, P. seppenradensis started to decrease in size for unknown reasons.

Despite this, the study underscores the dynamic interplay between predator and prey in prehistoric marine ecosystems, showcasing the fascinating adaptations that occurred over millions of years.