Cassianellidae is a small extinct

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

of prehistoric bivalves which lived from the

Middle Triassic In the geologic timescale, the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided in chronostratigraphy. The Middle Triassic spans the time between Ma and ...

, Ladinian stage through the

Late Triassic The Late Triassic is the third and final epoch of the Triassic Period in the geologic time scale, spanning the time between Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch and followed by the Early Jurassic Epoch. ...

Norian stage.The Paleobiology Database Cassianellidae entry
accessed 2 January 2012 It has been suggested that the family may have evolved from the related family Bakevelliidae. Bakevelliidae species are found in North America, South America, Europe, the Middle East, and Asia. Living a stationary life attached to substrate in marine and brackish environments, they formed shells of an

aragonite Aragonite is a carbonate mineral, one of the three most common naturally occurring crystal forms of calcium carbonate, (the other forms being the minerals calcite and vaterite). It is formed by biological and physical processes, including pre ...

composition with a low amount of magnesium calcite. The family Cassianellidae was named by K. Ichikawa in 1958.

Description

The cassianellids are noted for being restricted to the Triassic only, going extinct during the end Triassic extinction event. They are thought to have a close relationship to the longer lived family Bakevelliidae and it is possible the cassianellids may have even evolved from one of the early Triassic bakevelliid genera. As is found in the Bakevelliidae genus '' Kobayashites'' and the Isognomonidae genus '' Lithiotis'', cassianellids are distinguished by the presence of a larval septum which is retained in the adult shell morphology. Also notable for the entire family is the presence of a primitive alivincular type ligament, termed an alivincular-areate ligament. This form of ligament was widely found in many of the Triassic bivalve families but evolution of more refined ligament systems resulted in the shift away from the alivincular-areate system. Only a few modern families, such as

Gryphaeidae The Gryphaeidae, common name the foam oysters or honeycomb oysters, are a family of marine bivalve mollusks. This family of bivalves is very well represented in the fossil record, however the number of living species is very few. All species h ...

, still retain the alivincular-areate ligament system. Several of the genera, such as '' Cassianella'', have a widespread distribution. In contrast, '' Lilangina'' is known only from Asia, and '' Septihoernesia'' from the middle Triassic of northern Italy.

Taxonomy

Cassianellidae Ichikawa, 1958 *Genus '' Burckhardtia'' Frech, 1907 *Genus '' Cassianella'' Beyrich, 1862 (synonyms = ''Acinophorus'' Meek, 1864, ''Gryphorhynchus'' Meek, 1864) *Genus '' Hoernesiella'' Gugenberger, 1934 *Genus '' Lilangina'' Diener, 1906 *Genus '' Reubenia'' Cox, 1924 *Genus '' Septihoernesia'' Cox, 1964

References

{{Taxonbar, from=Q5049346 Prehistoric bivalve families Triassic bivalves Ladinian first appearances Norian extinctions Pteriida