Extinct

Pawson, David L., 2007, Phylum Echinodermata *, Zootaxa 1668, pp. 749-764 : 757-758

Other Extinct Classes of Echinoderms

A useful and comprehensive classification of fossil echinoderm groups is provided by Simms et al. (1993). Mooi (2001) discussed ( Figure 3 ) and critically assessed publications on fossil echinoderms for the period 1980-2000. Ausich and Webster (in press) undoubtedly contains comprehensive summaries of the status of most fossil echinoderm groups, along with an extensive list of references.

Loven’s law and ray homologies are described in echinoids, ophiuroids , edrioasteroids, and an ophiocistioid by Hotchkiss (1995). In a related study with broad implications, Sumrall & Wray (2007) discuss pentamerous symmetry and its origin in the 30 Cambrian-Ordovician clades of echinoderms.

Shu et al. (2004) describe, and Smith (2004b) comments on, what are believed to be ancestral echinoderms (“velulocystids”) from the Lower Cambrian of China ( Figure 4 ). The vetulocystids have a globose theca and a tail. Smith (2004a) studied phylogeny of deuterostomes, and anatomy of carpoids, and concluded that early deuterostomes with a stereom skeleton and gill slits may have existed, but it is not likely that sterom and a notochord co-occurred. These conclusions support in part (gill slits), and disagree in part (notochord) with the ideas of Jefferies et al. (1996). David et al. (1999), applying the extraxial/axial theory, regard the four non-pentamerous classes comprising the homalozoans as early echinoderms, but not indicative of the plesiomorphic morphology of the phylum. Further, the Homalozoa is not a monophyletic assemblage. Lefebvre (2007) studied in detail the palaeobiogeography and palaeoecology of cornutes and mitrates. Parsley (1999), using a cladistic approach, determined that the Cincta (Homostelea) are blastozoans.

Ophiocistioids have been reviewed by Haude (2004), and Reich & Haude (2004).

Dominguez-Alonso (1999) presented new data on the structure of ctenocystoids and proposed a new approach to the early evolution of echinoderms.

Figures

FIGURE 3. Phylogenetic hypothesis of fossil and extant echinoderms. From Mooi (2001), q. v. Published with permission.

FIGURE 4. Phylogeny of early deuterostomes. From Shu et al. (2004), q. v. Published with permission.