|Inoperna bellarugosa Popenoe, 1937 (length 7.3 cm = 73 mm).|
The bivalve genus Inoperna, which belongs to the mytilid family (includes mussels), lived during the Triassic (latest part), and the Jurassic to Cretaceous (a total geologic time range of just over 60 million years). It was globally widespread in warm seas, and it had its widest distribution during the Jurassic. It showed up on California during the Cretaceous.
The genus is characterized by a narrow elongate shell, with nearly parallel dorsal and ventral margins. Its surface is divided by a diagonal ridge, with numerous strong ribs above the ridge and smooth shell beneath the ridge. The shape and ribbing of this genus resembles that of a feather and is very memorable. Individuals of this genus apparently lived on the sea floor and were stationary.
The species shown above is from Turonian strata of Late Cretaceous age in the Santa Ana Mountains, Orange County. As you might remember from my last post, the Turonian (93.5–93 million years ago) was the warmest time of the Cretaceous Period.
The etymology (name derivation) of I. bellarugosa is from bella, Latin for beautiful, and rugosa, Latin for wrinkles. I think that you will agree that it is aptly named.