sp. and Eleutherokomma'' sp. It is likely that
Tenticospirifer, that itself appeared during early
Givetian, includes the ancestor of
Cyrtospirifer.
Cyrtospirifer first occurs in western Europe in the Late Givetian.
Tenticospirifer has a relatively narrow hinge line and an inflated and thick shell in common with two of the oldest species known,
C. verneuiliformis and
C. aperturatus. This group dominated during the late Givetian, but was replaced by other species, such as
C. syringothyriformis and
C. verneuili which have wide hinge lines and thinner shells. == Description ==