Kosmoceras jason Ammonites
Ammonidea, Kosmoceratidae
Geological Time: Jurassic, Callovian Stage (160 m.y.a)
Size (25.4 mm = 1 inch): 60 mm and 49 mm diameter Matrix: 125 mm by 85 mm
Fossil Site: Oxford Clay, England
Fossil Code: 9838
Price: Sold
 Description:
A magnificent pair of fossil specimens of the ammonite Kosmoceras
jason of the Callovian Stage (160 m.y.a) deposits of England. Ammonites
of this degree of preservation are difficult to come across. These
specimens represent an example of sexual dimorphism in ammonites,
displaying both a macroconch (large shell) and microconch (small shell).
Since examples of the macroconch have been found with eggs, they are
presumed to be the females. The microconch in addition to being somewhat
smaller, has more ornate knobs and spines, as well as often displaying
a structure known as the lappet at the front of the living chamber.
The lappet is thought to have been a display structure which allowed
other ammonites to tell “the boys from the girls”. There
are a number of impressions of others on the reverse. As in modern
day cephalopods these may have been part of a mass spawning such as
is seen in some squids today. Once mating and egg laying is completed,
the adults expire. |
