This is the conclusion of a team of researchers from the University of Heidelberg (Germany), who discovered fossils of the gigantic species Parapuzosia seppenradensis both in England and in Mexico.
The history of the largest ammonite in the world
The type specimen of P. seppenradensis unearthed near the German city of Lüdinghausen in 1895 is the largest known ammonite : it has a 1.7 meter wide carapace.
With few specimens of this great size ever found, scientists weren’t sure how this creature got to this length. However, experts found P. seppenradensis and its smaller cousin, P. leptophylla , on both sides of the Atlantic, with widths ranging from 0.1 to 1.48 meters. The truth is that both species have a different growth cycle of five stages, which would explain the range of sizes.
This new work completes the evolutionary history of the cephalopod that lived in the Upper Cretaceous, thanks to the study of 154 ammonite fossils, including a handful of historical specimens and more than 100 newly discovered fossils collected from England and Mexico, the researchers concluded that P. seppenradensis appeared on both sides of the Atlantic Ocean about 80 million years ago and likely evolved from a smaller related species called Parapuzosia leptophylla , which grew to be only 1 meter across. That is, these creatures, with tentacle-like arms and coiled shells, would represent different stages in the ammonite growth cycle.
Why did they grow so much?
Apparently, they would have evolved to such colossal size to avoid being eaten by the fearsome aquatic mosasaurs. Mosasaurs were giant and fearsome marine reptiles that bore powerful jaws and lived roughly the same time as ammonites; some of the largest specimens grew to be 15 meters long.
The biological and evolutionary adaptability of prehistoric species is somewhat complex, but it provides insights into how biodiversity complemented each other. Predation is one of the main drivers of evolutionary pressure and those individuals with traits best suited to survive this stress are more likely to reproduce and pass those traits on to offspring. These ferocious beasts , the mosasaurus , the main predators of the Cretaceous seas, were known to feed on ammonites and their rapid growth during the Upper Cretaceous was very similar to the growth of P. seppenradensis.
“The gigantisms displayed by the two species studied here may be a coevolution of size increase in mosasaurs,” the authors wrote.
However, scientists believe a more detailed analysis is necessary to determine how closely interconnected the two species might have been.
“Currently no other short-term global environmental trend is identified that correlates with the increase in the size of this ammonite across the Santonian-Campanian boundary,” the researchers write.
Referencia: Ontogeny, evolution and palaeogeographic distribution of the world’s largest ammonite Parapuzosia (P.) seppenradensis (Landois, 1895)
Christina Ifrim ,
Wolfgang Stinnesbeck,
Arturo H. González González,
Nils Schorndorf,
Andrew S. Gale
Published: November 10, 2021 PLOS ONE
https://doi.org/10.1371/journal.pone.0258510
