The Asteroidea (Echinodermata) of the Muschelkalk (Middle Triassic of Germany)

Abstract

Trichasteropsis Eck, from the Muschelkalk of Germany is the only Triassic asteroid known from more than fragmentary material. Most spécimens representT. weissmanni (Münster) whereasT. senfti ECK,T. bielertorum n. sp., andBerckhemeraster charistikos n. gen. et n. sp., are each known from few individuals.Parsimony analysis hère treats the füll Ordovician to Récent history of the Asteroidea using a somasteroid (a pre-asteroid stelleroid) outgroup. Ambulacral évolution is critical in echinoderm history; the ambulacral arrangement of crown-group asteroids first appears in Paleozoic sister groups, and the subclass Ambuloasteroidea n. subcl. is proposed for Paleozoic and younger taxa with critical ambulacral apomorphies. Muschelkalk asteroids are assigned to the family Trichasteropsiidae n. fam., superorder Forcipulatacea. The recently described Triassic genusNoriaster belongs to the extant family Poraniidae, superorder Valvatacea.Trichasteropsis andNoriaster represent separate major phylogenetic branches of the post-Paleozoic infraclass Neoasteroidea, and together they indicate that diversification of modern-type asteroids was under-way during the Triassic, although the Mesozoic marine révolution largely was a Jurassic and later event. Post-Paleozoic asteroids appear to hâve returned to Paleozoic life modes in spite of new morphological expressions.Trichasteropsis is skeletally robust, suggesting protection from wave impact or predators. It is found in sédiments associated with shell banks but not from within the banks.Trichasteropsis senfti commonly occurs with brachiopods whereasT. weissmanni does not, although brachiopods are found in associated strata. Aspects of morphology of both species are similar to those of récent predatory Asteriidae suggesting similar behavior, but feeding habits ofTrichasteropsis are unverified.