Implications of lantern morphology for the phylogeny of post paleozoic echinoids

Smith, A.B.

Palaeontology 24(4): 799-801

1981


ISSN/ISBN: 0031-0239
Accession: 005639458

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Abstract
Aristotle's lanterns of the Liassic echinoids Diademopsis tomesii (Wright) and Eodiadema aff. minutum (Buckman) are described and compared with those of living echinoids. Diademopsis has a primitive lantern and weakly grooved teeth. The ultrastructure of these teeth is well preserved. It is shown how Recent grooved, keeled and diamond-shaped teeth could be derived from a tooth of this construction. Eodiadema has diamond-shape teeth of a type previously known only in irregular echinoids, and its lantern is intermediate in form between the regular Diademopsis type of lantern and 2 types of irregular echinoid lantern (cassiduloid and holectypoid). The evolution of tooth and lantern in post-Palaeozoic echinoids is outlined, and is the basis for constructing a phylogeny. All living echinoids form a monophyletic group in which stem-group includes archaeocidarids and some miocidarids as its most advanced members. Cidarids are the monophyletic primitive sister group to the euechinoids and, within the Euechinoidea, echinothurioids are the primitive sister group to all others. Irregular echinoids are a monophyletic group with a stem group that includes Eodiadema as 1 of its members. Irregular echinoids are separated into 3 groups: eognathostomates, neognathostomates and atelostomates. Eognathostomates, comprising pygasteroids and holectypoids, are the primitive sister group of all other irregluar echinoids. Cassiduloids and clypeasteroids are grouped together as neognathostomates; spatangoids and holasteroids are placed in the atelostomates. Echinaceans are another monophyletic group in which most primitive members belong to the Pseudodiadematidae. Echinaceans and irregulars both evolved from an aulodont ancestor.