Miocene
Lincoln Creek Formation
Grays Harbor County, WA, USA
Extremely rare near complete 35mm nautiloid preserved in chalcedony
Nautiloid,  Cephalopod.

Nautiloids flourished during the Ordovician Period when they constituted the main predatory animals and developed an extraordinary diversity of shell shapes.  At least 2,500 species of fossil nautiloids are known from across geologic time 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.

The lighter areas of the chalcedony is translucent in some specimens – a preservational artifact rarely seen in a fossil