The basal opening of conodonts

Observations on a number of different species, which range in age from Cambrian to Triassic, confirm that conodonts have at least two kinds of basal openings. The primitive type is a basal cavity which increased in size as the specimen grew larger. The second variety is defined as a pit; its size was relatively constant after the initial stages of growth, although the total size of the specimen bearing it may have increased several times.

This record provided courtesy of AGI/GeoRef.