0 an extinct sea creature (= one that no longer exists) often found as a fossil (= an animal turned into rock), with a flat, spiral shell -- 菊石（鸚鵡螺的化石）
This siltstone unit lies upon a conspicuous erosion surface highlighted by angular chips of phosphatized pebbles and ammonites.
The central part begins with ammonite-bearing crinoidal limestones and black pillow basalts.
Cladistic techniques have been applied to many fossil groups but ammonites remain largely understudied in this way.
Detailed collecting through 15 sections across the basin has facilitated a major revision of the ammonite zonation.
The fauna is limited to ammonites and a species of epifaunal bivalve.
This method can therefore be used to compare the morphological signal of ammonites with other physical or chemical signals.
We note, however, that ammonites have not been recorded from the 1.8 m of strata below the proposed boundary level.
The sudden appearance of these genera represents a major reinvasion of the basin by neocomitid ammonites.
