Ammonoidea is a group of hard shelled squid-like cephalopods that lived in the late Paleozoic, Mesozoic and very early Cenozoic eras, which included the famous ammonites. Their distinctive feature is a hard outer shell, twisted in most species, which make them similar to modern Nautilus. However, in the family Baculitidae the shell is more straight, and in Turrilitidae it has the shape of a voluminous spiral like in several snails. Most species were free-swimming predators, although turrilitids may have lived on the seafloor. Along with belemnites and nautilids, ammonites are the most numerous prehistoric cephalopods known from fossils.
Ophiceras medium (sakuntala), an Early Triassic species
Ammonoids first appeared during the Paleozoic, but began to flourish only during the Mesozoic. Their fossilized shells are found so often that various species and species cosplexes of ammonites are used as markers of the boundaries of stratigraphic units. For example, the first appearance of the Psiloceras spelae tirolicum is related to the beginning of the Hettangian age and the whole Jurassic period.[1] The biggest ammonite was the Late Cretaceous Parapuzosia with shell diameter of about 2 m.
The ammonites began to decline at the end of the Cretaceous, and died-out during the K-T extinction alongside the non-avian dinosaurs, the giant marine reptiles like Mosasaurus, and others. The main theory is that unlike the modern Nautilus, which lays several smaller clutches of eggs on the sea floor, the ammonites had only one big clutch of eggs during the lifetime, and their young lived in the upper waters of the seas, alongside other plankton - and died-out alongside it when the meteorite hit.
In Popular Culture[]
- Jurassic ammonites appear in Walking with Dinosaurs.
- An indeterminate ammonite can be seen in the end of the first episode of Primeval.
- Ammonites appeared in Jurassic World: The Game as a legendary aquatic creature, alongside the Baculites, in which it is a super rare aquatic creature.
- Ammonites appeared in Jurassic Park Builder.
- Ammonites appeared on Dinosaur Train.
- Ammonites appeared in Jurassic World: Fallen Kingdom.
- Ammonites appeared on Dinosaur King.
- 3 Cretaceous ammonite genera are represented in Fossil Fighters: Champions.