World fossil society’s founder Riffin T Sajeev and  his brother Russel T.Sajeev proposed that,The Rastellum (Arcostrea) genus in cavery basin geological area may have originated in late Jurassic with adaptive modifications like high toothed commissure. The reason for such adaptation is the existence of high energy environment with heavy sedimentation. Hence the possibility of various adaptations on the alectryonia cannot be ruled out. The functional importance of high toothed commissure was broadly discussed on the Cretaceous representatives of Arctostrea.

Rastellum Carrinata fossil

They suggested that, the alectryonia and liostrea originated around upper Triassic and passed through various era. But the derivation of arcostrea happened in the late Jurassic due to the high energy muddy environment in the seabed. The adaptations like high toothed commissure shows that, the sedimentation and particle density in the water were very high. In cavery basin such situation may sustained from late jurassic. Then oyster families that lived in that area accepts various adaptations and becomes a new genus named Rastellum (arcostrea). The genus arcoatrea extinct in the late cretaceous, but the genus alectryonia continued further.

Ref: Occurrence of Arcostrea: Existence of high energy Paleoenvironment in Cauvery basin, India during Late Jurassic. (http://worldfossilsociety.org/resources/)