Pl. IV · Geological Survey
Chapter III
The Jurassic was the high-water mark.
Named ammonite species recorded across five geological periods, 1820–1852
Fig. 1 — Species count by geological period
300
200
100
0
Species recorded
94
Devonian
67
Carboniferous
186
Triassic
342
Jurassic
278
Cretaceous
Peak diversity
342 named species
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Ammonite Fossil Plate
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