Miocene
Lincoln Creek Formation
Grays Harbor County, WA, USA
Extremely rare complete 26mm nautiloid preserved in translucent chalcedony.

Nautiloid, Cephalopod.

Aturia is a nautiloid genus known from the Paleocene to Miocene of various sites worldwide but it is a common find nowhere.

Nautiloids flourished during the Ordovician Period, a time when they constituted the dominant predatory animals and developed an extraordinary diversity of shell shapes and sizes.  At least 2,500 species of fossil nautiloids are known but only a handful of species survive to the present day.

Sutures (or suture lines) are visible as a series of narrow wavy lines on the surface of the shell, and they appear where each septum contacts the wall of the outer shell.  The sutures of nautiloids are simple in shape, being either straight or slightly curved.  This differs from the “zigzag” sutures of the goniatites and the highly complex sutures of the ammonites.

Chalcedony replacement sometimes offers an unusual and attractive level of translucence to a fossil as in this specimen – see photo. Tough to get one this complete too.