Pojetaia is an extinct genus of early bivalves,[1] one of two genera in the extinct family Fordillidae.[2] The genus is known solely from Early to Middle Cambrian fossils found in North America, Greenland, Europe, North Africa, Asia, and Australia.[2][3] The genus currently contains two accepted species, Pojetaia runnegari, the type species, and Pojetaia sarhroensis, though up to seven species have been proposed. The genera Buluniella, Jellia, and Oryzoconcha are all considered synonyms of Pojetaia.
Description[]
Pojetaia are small bivalves with valves that are subequal in size and suboval in shape. In size Pojetaia specimens reach a total shell length of less than 2 millimetres (0.079 in) and a height of 25 millimetres (0.98 in).[2][4] The shells are compressed laterally and the back edge is slightly broadened. The rear adductor is more developed and larger than the front adductor, with the pallial muscles arranged in partially connected series along the valve margins.[2] The ligament is usually straight with an umbo which is central to subcentral and each valve possessing between one and two teeth, with a total of no more than three teeth on a specimen. The exterior of the shells shows faint ribbing and fine comarginal growth lines.[2] The inner shell layers of Fordilla and Pojetaia species both consist of layers of carbonate which is akin to the laminar aragonite layer found in extant monoplacophora.[5] The structuring is similar to shell layering found in the extinct genera Anabarella and Watsonella, which is thought to suggest that members of the phylum Mollusca developed nacre independently several times.[5] Due to the size and age of the fossil specimens, Pojetaia are included as part of the Turkish Small shelly fauna.
Affinity[]
Pojetaia and Fordilla appear to form a clade, but whether this is in the stem or crown group of Bivalvia is unconstrained by the available evidence.