The Echinoid Directory

 Crown group echinoids with:

• Test small, composed of two columns of ambulacral and interambulacral plates in each zone; plates firmly sutured;
• Apical disc loosely bound to corona; generally missing;
• Ambulacral plating simple, pore-pairs uniserial;
• Interambulacral plates with single large primary tubercle; tubercle with massive mamelon, either imperforate or with small rudimentary pore and with no surrounding platform; mamelons increasing in size adapically;
• No perignathic girdle.

Triassic (Anisian-Norian), Europe, North and South America.

This small group of Triassic echinoids has the basic test architecture of the crown group, with biserial plating in ambulacral and interambulacral zones. However, they have simple ambulacral plating and lack a well developed perignathic girdle and thus cannot be placed with certainty into either the Cidaroidea (which have a perignathic girdle of apophyses) or the Euechinoidea (which have a perignathic girdle of auricles and compounding of ambulacral plating). They seem to form a small clade that thrived and diversified in the reefal environments of the Middle to Late Triassic. Triadocidaridae differ from Paurocidaridae and Serpianotiaridae in having non-crenulate tubercles.

The most detailed accounts of this group are to be found in Kier (1977, 1984).

Kier, P. M. 1977. Triassic echinoids. Smithsonian Contributions to Paleobiology 30, 1-88.

Kier, P. M. 1984. Echinoids from the Triassic (St Cassian) of Italy, their lantern supports, and a revised phylogeny of Triassic echinoids. Smithsonian Contributions to Paleobiology 56, 1-41.

Smith, A. B. 1990. Echinoid evolution from the Triassic to Lower Jurassic. Cahiers de la Universite Catholique Lyon, Serie Science 3, 79-117.