Although ammonites have been extinct for 65 million years, newly published data based on 35 years of field work and analysis is providing invaluable insights into their paleobiology. Ammonites, shelled mollusks closely related to modern day nautilus and squids, inhabited the oceans for nearly 350 million years. Specimens found in the rock record of the ancient seaway that covered North America during the Cretaceous Period demonstrate that these animals thrived at cold methane seeps at the bottom of the sea, consumed small prey, and often survived predation attempts.
"Our field work has resulted in the discovery of exceptionally well preserved ammonites at ancient methane seeps, which permit new insights into the mode of life and habitat of these organisms," says Neil Landman, curator in the Division of Paleontology at the American Museum of Natural History. "The picture that emerges is that these ammonites had little in common ecologically with either modern nautilus or most modern coleoids. This forces us to reexamine our thinking about the ecology of ancient marine systems and how the extinction of ammonites ultimately impacted the modern marine biota."
About 70 million years ago, dinosaurs roamed the continents, the Atlantic Ocean was much narrower than today, and what is now North America was divided in half by a broad inland sea that covered much of the continent. This epicontinental sea was, according to new discoveries, partly covered by cold methane seeps of gas bubbling up from sediments below. These seeps were like underwater oases that attracted a host of organismsbacteria, sponges, gastropods, bivalves, sea urchins, and even sea lilies that attached to the veneer of calcite that formed on the bottom at the seep sites. Ammonites were also abundant at the seeps.
"What astonishes me is that I have walked over these fossil deposits for years without ever realizing that they were the sites of cold methane seeps," says Land
|Contact: Kristin Elise Phillips|
American Museum of Natural History