Ammonites were a successful group of extinct marine mollusks that flourished in the world’s oceans for hundreds of millions of years. Their fossils, characterized by intricate coiled shells, are frequently found globally, offering a glimpse into prehistoric marine ecosystems. These ancient creatures exhibited a vast range of sizes, leading many to wonder just how large they could grow. This exploration reveals the identity of the largest known ammonite ever found.
What Exactly Are Ammonites
Ammonites were predatory animals belonging to the cephalopod class, making them distant relatives of modern squid, octopuses, and the chambered nautilus. The defining feature of this group was the external shell, typically coiled in a flat spiral resembling a ram’s horn. The animal lived only in the largest, outermost chamber of the shell, which was open to the sea.
The interior of the shell was divided into smaller chambers, separated by walls called septa. The animal controlled its buoyancy by regulating the amount of gas and fluid within these sealed compartments, allowing it to move vertically through the water column. Ammonites dominated the seas throughout the Mesozoic Era, particularly during the Jurassic and Cretaceous periods, before their extinction 66 million years ago. Their widespread distribution makes their fossil shells highly valuable to geologists for dating rock layers.
Identifying the Largest Ammonite Ever Found
The largest ammonite specimen yet discovered belongs to the species Parapuzosia seppenradensis from the Late Cretaceous seas. The actual fossil, which is incomplete, currently measures approximately 1.8 meters (5.9 feet) in diameter. This massive specimen was unearthed in 1895 near Seppenrade, Germany, and is now housed in the Museum of Natural History in Münster.
Since the fossil lacks its entire living chamber, paleontologists estimate the complete shell could have reached a diameter between 2.5 and 3.5 meters (8.2 to 11.5 feet). Based on these estimations, the full-grown animal, including its soft body and shell, is thought to have weighed approximately 1,455 kilograms (3,208 pounds). The scale of this fossil places it among the largest invertebrates known from the geologic record.
Understanding Ammonite Gigantism
The immense size achieved by species like Parapuzosia seppenradensis is part of a broader biological phenomenon known as Cretaceous Giantism. This period saw many marine animals, including other cephalopods and predators, evolve to enormous proportions. The drive toward gigantism in ammonites is theorized to be connected to environmental conditions.
One factor may have been the high productivity and warmer global temperatures of the Late Cretaceous, which led to increased nutrient availability in the oceans. A primary hypothesis links the size increase to an evolutionary arms race with predators, particularly the large marine reptiles known as mosasaurs. Growing to a gigantic size would have provided protection against these hunters.