Eutrephoceras Nautilus Cluster | Fox Hills | Montana

Discovered in the Late Cretaceous-aged Fox Hills Formation of Montana, this fossil Nautilus (Eutrephoceras) is a beautifully preserved relic from an ancient seaway that once covered much of central North America. Dating back approximately 66–70 million years, this specimen represents one of the last surviving nautiloid species from the Mesozoic Era.

These elegant, coiled shells are often found in sandy marine sediments that once formed the seafloor of the Western Interior Seaway. Many feature intricate internal chambers and may retain traces of their original pearlescent nacre—an iridescent reminder of the life this cephalopod once led.

Eutrephoceras was a slow-moving marine predator, using its buoyant shell and tentacled arms to hunt small fish and invertebrates. Its close relatives still exist today, making the Nautilus one of Earth’s longest-living fossil lineages.

Each specimen from the Fox Hills Formation is a unique window into a dynamic prehistoric ocean ecosystem, making it a striking and scientifically significant addition to any collection.