TF0323 Ammonite

Parkinsonia parkinsonia

Jurassic

Phylum: Mollusca
Class: Cephalopoda
Subclass: Ammonoidea
Order: Ammonitida

Planispiral
Evolute
Ribs
Ammonitic suture lines

Calcite has replaced aragonite in the skeleton

Beware! The specimen in set 2 has a dark circular hole, which you may be tempted to identify as a siphuncle. However remember that in ammonoids the siphuncle runs around the outer edge of the chambers, so this hole is in the wrong place. It is probably there due to eccentricities of the mineralisation process.

Why is it a dark colour when the rest of the shell is white? Generations of Earth Scientists have made the same mistake, their pencil marks fooling others into making the same error.