Alatoconchidae
Alatoconchidae is an extinct family of prehistoric bivalves that lived in the early to middle Permian period. Genera belonging to Alatoconchidae are characterized by their shell that is strongly compressed in the dorsoventral direction. Some species reached large sizes of as much as long. It is hypothesized that some species in this family got energy from chemosynthetic bacteria. Occurrence Fossil records of Alatoconchidae are known from the early to middle Permian. They are found in shallow marine carbonates across widely separated areas, such as Croatia, Tunisia, Oman, Afghanistan, Iran, Thailand, Malaysia, Philippines, Japan, Alaska and South China. History In 1968, Shikamaia akasakaensis from Japan, named after palaeontologist Shikama Tokio, is described, but due to its unique shape and fragmentary fossil preservation, it was originally classified as Animalia incertae sedis. The Alatoconchidae family was created in 1973, and included genus Alatoconcha. Morphology According to form of Shikamaia perakensis, the shell is compressed in the dorsal ventral direction, and is elongated in the anterior-posterior direction. The posterior half of the shell consists only of the wing-like flat flanges, which have a very compressed cross-section. Its anatomical feature is close to modern cardiid, like Corculum cardissa. Paleoecology It is theorized that one of