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| Audouliceras Heteromorph Ammonite |
Audouliceras belongs firmly in the second camp.
This wonderfully eccentric Cretaceous ammonite abandoned the classic tight spiral that most of its kin wore so elegantly and instead opted for something that looks, at first glance, like a shell having second thoughts.
Its whorls uncoil, loop, and flare in ways that feel almost rebellious — as though the blueprint for “proper ammonite” was politely ignored.
Audouliceras lived during the Late Cretaceous, roughly 100–90 million years ago, when warm epicontinental seas flooded vast stretches of the globe.
In North America, its fossils are found in marine sediments laid down by the Western Interior Seaway — that immense inland ocean that once split the continent in two.
Beautiful specimens have turned up in Cretaceous deposits of Alberta, British Columbia, Montana, and the U.S. Great Plains, preserved in shales and sandstones that were once quiet seafloors.
Across the Atlantic realm, relatives occur in European Cretaceous deposits as well, reflecting the broad distribution of ammonites in the world’s warm, shallow seas.
These were not shoreline creatures; Audouliceras drifted or swam in open marine environments, buoyed by gas-filled chambers within its shell. Like other ammonites, it controlled its position in the water column through a siphuncle — a delicate tube threading through its chambers, regulating buoyancy with remarkable precision.
What did it eat? Likely small crustaceans, plankton, and other tiny drifting life. Its soft body would have extended from the final chamber, equipped with tentacles and a beak-like mouth similar to that of modern squids and nautiluses.
Heteromorph ammonites are often interpreted as slower, more vertical drifters compared to their tightly coiled cousins — perhaps hovering, bobbing, or gently pulsing through the water column rather than actively cruising.
And the seas they inhabited? Oh, they were anything but quiet.
Audouliceras shared its world with formidable predators and strange contemporaries. Giant marine reptiles patrolled the waters — long-necked plesiosaurs, sleek mosasaurs, and swift ichthyosaurs in earlier intervals.
Sharks like Cretoxyrhina cruised the depths. Teleost fishes flashed through sunlit waters. Other ammonites — some tightly coiled, some extravagantly uncoiled — drifted alongside them, along with belemnites and rudist bivalves building reef-like structures on the seafloor.
In the fossil record, Audouliceras appears in Upper Cretaceous marine strata, often serving as a useful biostratigraphic marker. Ammonites evolved rapidly and had wide geographic ranges, making them excellent timekeepers for geologists.
When you find Audouliceras in a rock layer, you are almost certainly standing in the Late Cretaceous.
Heteromorph ammonites like this one remind us that evolution is not a straight line toward efficiency or elegance. It experiments. It loops. It spirals outward and occasionally lets go of symmetry altogether.
And then — at the end of the Cretaceous, 66 million years ago — they vanished with the non-avian dinosaurs, casualties of the mass extinction that closed the chapter on the Mesozoic.
What remains are these curious, uncoiled shells in stone — records of a warm sea long gone, and of a lineage that was never afraid to look a little different.
