Trigonioidea

Scaphotrigonia navis, Low to Middle Jurassic

The Trigonioidea are the sole family of the order Trigonioida within the palaeoheterodonten shells. The vast majority of the species is only known fossil. First representatives of the superfamily appeared in the late Silurian.

Characterization

The housing is roughly triangular with a short rear end. The two flaps are approximately uniform. The vortex projecting well above the body of the housing. The thick aragonitic shell has an outer prismatic layer and an inner pearly -engine position. The exterior is smooth to heavily ribbed. The castle has a large, triangular cardinal tooth in the left valve and an articulated cardinal tooth in the right valve on ( schizodontes lock). There are no Lateralzähne available. The ligament is external and is quite short. The sphincter ganzrandig are approximately the same size ( isomyar ), the Palliallinie. The gills are filibranchiat.

Evolution

The first Trigonioida appear already in the late Silurian and quickly formed a great variety of species (diversity ) from. The different evolutionary lineages are found in several families. The culmination of the development and diversity is achieved in Jurassic and Cretaceous. At the Cretaceous - Tertiary boundary then almost all the lines died out, except for the line that led to the recent genus Neotrigonia.

System

• Order Trigonoida Dall, 1889 Superfamily Trigonioidea Lamarck, 1819 Family Trigoniidae Lamarck, 1819
• Family Eoschizodidae Newell & Boyd, 1975
• Family Schizodidae Newell & Boyd, 1975
• Family Costatoriidae Newell & Boyd, 1975
• Family Myophoriidae Bronn, 1849
• Family Minetrigoniidae Kobayashi, 1954
• Family Eoastartidae Newell & Boyd, 1975
• Family Scaphellinidae Newell & Ciriacks ​​, 1962
• ? Family Trigonioididae Cox, 1952