Arietites obtusus specimen (P 2467), photographed by Paul Mayer. © The Field Museum.
The Field Museum has a blog post about ammonites and Thanksgiving.
What do Thanksgiving and a fossil ammonite have in common?
In ancient times, the Egyptians, Greeks, and Romans associated the coiled horns of rams with gods, power, virility, fertility, and abundance. The cornucopia—a conical wicker basket with a never-ending supply of food flowing from it—comes from Latin cornu copiae or “horn of plenty.” The Greeks and Romans both used the cornucopia as a symbol of the harvest, prosperity, and abundance.
In paleontology, Pliny the Elder (in 79 AD) collected some strange rocks near Pompeii that he called ammonis cornua ("horns of Ammon") after the ancient Egyptian and Greek god Ammon who had tightly spiraled ram horns growing out of his head. These were fossil ammonoids, shells of an extinct marine animal related to chambered nautiloids, octopus, and squid (cephalopods). The ammonoid animal, a squid-like creature, secreted and lived in these coiled shells. Today the only cephalopod that lives in a shell is the chambered nautilus.
This specimen is the fossil ammonoid Arietites obtusus (P 2467). It was collected from Jurassic rocks near Lyme Regis, England, and is about 195 million years old. As nautiloid and ammonoid shells grow, they chamber off part of the shell with walls called septa. The septa in nautiloids are straight and smooth; in ammonoids, the septa are convoluted and resemble a fern or flame. You can see the internal septa pattern on the far right edge of this specimen, where the outside shell material has eroded away. It looks like a white line forming a pointy flame-like pattern. This specimen (not the fruit) was also on display in the 1893 World Columbian Exposition in Chicago.
Currently, there are seven ammonoid specimens on display in our Evolving Planet exhibition including one slab that has at least 50 smaller ammonoids on it. There is also one large ammonoid specimen behind the entrance desk of the Crown Family PlayLab.
