Natural History

Natural History

View full screen - View 1 of Lot 19. A Split Ammonite.

A Split Ammonite

Lot Closed

December 3, 07:19 PM GMT


22,000 - 24,000 USD

Lot Details


A Split Ammonite

Pachydiscus (Neodesmoceras) japonicus

Late Cretaceous (approx. 72 million years ago)

Menabe Region, Madagascar

21 by 16 by 4¾ inches (53.5 x 40.75 x 12 cm) and 21 by 16 by 3¾ inches (53.5 x 40.75 x 9.5 cm). Together 80 pounds (36.3 kg).

This superb split and polished ammonite fossil exhibits ambers, tan, and deep browns, its highly-whirled chambers filled with calcite geodes. Exceptional.

While dinosaurs ruled the land during the Late Cretaceous, the ammonite genus Pachydiscus (aka "thick disc") could be found flourishing in oceans worldwide.

Ammonites were a type of cephalopod—the taxonomic class that includes today's octopus, nautilus, and squid. Much like a submarine, they employed gas and fluid-filled chambers to regulate their position in the water column. The animals themselves lived only in the outermost compartment, employing their tubular siphuncle to connect its chambers along their shell's ventral surface.

Pachydiscus fossils are an important index species in the stratigraphic record of the history of life on Earth, as they are used as the "defining biological marker" for the beginning of the Maastrichtian Stage, starting 72.1 ± 0.2 million years ago. The specimen offered here is even more remarkable, as evidenced by the calcified geodes that have taken up residence within each of the Pachydiscus fossil's chambers.