Trophic classification. Appreciation of the ecologic functions of echinoderms is derived from an understanding of the diverse feeding methods and food preferences found within the group. Echinoderms are dominantly benthonic marine organisms but exploit a wide variety of food resources on the bottom, within the sediment, and from the water masses near the bottom (Table 1). The only echinoderms that are not strictly benthonic are some of the elasipodid holothurians, which have been captured at the surface and swimming above the bottom at great depth (Barnes et al., 1976). By rhythmic undulations of a fan of oral tentacles these bizarre holothurians capture suspended food particles from the water mass near the sea floor. Their anomalous form and habits, so far removed from the typical sea cucumber, serve to emphasize that holothurians and all other echinoderms cannot be readily characterized by a single trophic classification for each group. Each major living group of echinoderms has diversified in feeding methods and/or food preferences.

Echinoderms are a moderately successful phylum today with five classes and about 6,000 living species. They are found in all marine environments from the intertidal zone down to the bottom of deep-sea trenches. Because most echinoderms have a stable calcite skeleton made up of many distinctively-shaped plates, spines, stem and arm segments, and other parts, echinoderms have the potential to produce a long and rich fossil record, and we find this to be true. Although our knowledge of this record is far from complete, some past echinoderm faunas may have approached present-day echinoderm communities in number of coexisting genera and species. Also, many classes of echinoderms are known only from the fossil record, and as many as 12–13 classes may have occurred together at some times in the past. Although they have a wide ecologic range today, most fossil echinoderms are found in rocks representing shallow-water, subtidal, marine environments, either past continental shelves or epicontinental seas.

Definitions.– Taphonomy is the study of what happens to an organism from the time of its death until it is discovered as a fossil. Whereas paleoecology deals with the interactions between an organism and its environment during life, taphonomy is concerned with post-mortem processes such as disarticulation, predation, transportation, and diagenetic alteration. Biostratinomy (formerly biostratonomy) is the part of taphonomy which covers the history of the organism from death to final burial of the remains. The chemical, physical, and biological processes which affect these remains after burial are dealt with in studies of diagenesis. The relationship of these disciplines is shown in Figure 1.

The chief economic use of biostratigraphic data is short distance temporal correlation within or between petroleum bearing areas and is based primarily on subsurface sampling. Of greater overall importance, the stratigraphic distribution of countless fossil organisms has permitted widespread approximation of time equivalence and forms the basis for recognitiion of the fundamental subdivisions of the geologic time scale. Echinoderm remains are common constituents of marine sedimentary rocks, especially during much of the Paleozoic; they rarely have been studied in such a manner as to become a widely used tool in biostratigraphic zonation. The common problems associated with the detailed stratigraphic study of echinoderms involve many of the “classic” characteristics of biostratigraphically useful organisms:

Crinozoans and Blastozoans typically occur in very diverse epifaunal suspension feeding communities. In Lower Mississippian rocks of Indiana, as many of 155 benthonic invertebrate species lived in a single community (Ausich, Kammer, & Lane, 1979; Lane, 1973, Ausich & Lane, 1980). How did so many species co-exist? According to current ecological literature each species should have occupied a separate niche. If so, what limiting factors controlled niche differentiation within these communities?

Discussions of evolutionary theory in paleontology include the topics of overall diversity through time, the tempo and mode of evolution, and the consequences of the parallel between ontogeny and phylogeny. The first of these topics – diversity through time and the significance of major echinoderm radiations and extinctions – is the subject of other discussions in this short course and will not be considered here. Detailed evolutionary studies using echinoderms are complicated by the compound nature of their skeleton which tends to disarticulate very rapidly after death. Complete specimens usually reflect rapid burial, and large populations may be relatively rare in many stratigraphic sequences. Possible exceptions include the carboniferous blastoid Pentremites and various Teriary echinoid lineages. Indeed Paul (1977b) has concluded that the fossil record of echinoderms would seem to be of little use in testing evolutionary ideas. While not numerous, studies of echinoderms have contributed to evolutionary theory and selected cases will be discussed below.

The initial explosive radiation of echinoderms in the Cambrian and Ordovician is very likely the single most spectacular evolutionary pattern shown by echinoderms during their long fossil record. This radiation involved 19–20 echinoderm classes and lasted from the Early Cambrian (perhaps latest Precambrian) to the end of the Middle Ordovician. It is important because in many ways this initial radiation determined the entire Paleozoic record for echinoderms. In addition, it is almost a textbook example of a major adaptive radiation (Raup and Stanley, 1978, p. 307, 357–360), and also fits nicely the two-stage metazoan diversification model for the Early Paleozoic outlined by Sepkoski (1979).

The classification of echinoderms at class-rank and higher has been a topic of considerable dispute for well over a century. We will confine our analysis to the more ‘modern’ classification schemes which have advocates among currently active paleontologists and neontologists, in particular those of Bather/Lankester, 1900; and Fell/Moore 1966 (Figs. 1 and 2). Detailed explanations of these schemes may be found in most major works on invertebrate paleontology and neontology. Comparisons of other schemes are given in Tables 1 and 2.

The Subphylum Homalozoa is divided into four classes, which while having similar morphological features, are at best distantly related. All classes exhibit flattened thecae, are bilateral to relatively asymmetrical and apparently were surface detritus feeders or low level suspension feeders. Many homalozoans display thick marginal plates with smaller central plates on dorsal and ventral surfaces, possibly to augment gut and/or cloacal pumping.

Blastozoan echinoderms include several classes of stalked echinoderms with a combined stratigraphic range from Lower Cambrian to Upper Permian. Ranges of constituent classes tend to be much shorter, except for the Blastoidea, which are known from the Middle Ordovician (Broadhead, 1980) to the Upper Permian (Breimer & Macurda, 1972).

The blastoids are a widespread and long ranged class of echinoderms. Their taxonomic diversity is low at their first appearance (M. Ordovician?; Silurian) and geographically restricted but they had become more diverse and cosmopolitan by the Devonian. They were widespread until the end of the Paleozoic. Approximately eighty genera and several hundred species are known. Most blastoids were attached to the substrate but several experimented with an eleutherozoic life style. Blastoids were passive filter feeders, usually living in shallow water (5–50m) communitites. The preservation of parts of most of the principal organ systems in the theca allows detailed studies of the evolution and functional morphology of blastoids.

Paracrinoids were originally grouped together under the Orders Varicata (recumbent arms) and Brachiata (arms free standing) by Jaekel, 1900 and essentially the same groups were elevated to the Class Paracrinoidea by Regnell, 1945. Various authors have added genera to the class but the group was ill defined until Parsley and Mintz, 1975, re-defined it, establishing two orders based on the presence or absence of thecal pores rather than free standing or recumbent arms. The nature of the basals, peristomals, geometry and position of the gonopore and hydropore, thecal asymmetry makeup of the transverse uniserial pinnulated arms and the geometry and composition of the column are also important taxobases.

Fossil crinoid studies have been extensively summarized in the most recent volumes on echinoderms in the Treatise on Invertebrate Paleontology (Moore and Teichert, 1978), less than 2 years ago. It would be presumptuous of us to try to provide a summary of the three Treatise volumes on crinoids in 15 typescript pages.

The edrioasteroids (seat stars) are a small but diverse group of Paleozoic (Lower Cambrian through Pennsylvanian) echinoderms known to include five morphologically distinct types of thecal construction. Domal and clavate thecae predominate, although some are globoid and others axially elongate. Adult thecal diameters range from 6 – 7 mm to approximately 9 cm, but 15 – 30 mm is the norm. Edrioasteroids are not common fossils, although when proper conditions for preservation existed, entire populations were often fossilized so that hundreds or even thousands of specimens can be recovered through excavation. Apparently, preservation depended upon catastrophic kills, most of which seem to have resulted from storm-deposited mud deeply burying the entire substrate surface area.

Among the living echinoderms, holothurians are generally regarded as “poor relations” of the other groups. The color and symmetry of sea-stars and the complexity of echinoids usually elicit expressions of admiration from casual observers; the reactions to holothurians usually involves a considerable degree of revulsion. The generally soft-bodied holothurians, with their reduced skeleton and leathery to gelatinous body walls, are consequently less well known than many other echinoderm groups.

In accordance with the stated purpose of this short course to bring non-specialists up to date on advances in echinoderm paleontology, these notes build on what may be considered common knowledge of the Paleozoic Asterozoa. They are intended to be additions to information available in most paleontology textbooks and to update and comment on information presented in the Asterozoans section of the Treatise on Invertebrate Paleontology (hereafter referred to as the Treatise) written by Spencer and Wright (1966). Some reiteration herein of earlier works is necessary, however, to understand the current status of investigations on Paleozoic Asterozoa. Oral presentation during the short course will assume you are familiar with the material presented here.

The post-Paleozoic Asterozoa include the Asteroidea and the Ophiuroidea. Various workers believe the arguments in support of a common Paleozoic ancestry for the two are very strong and rank them as subclasses of the class Stelleroidea. Other workers feel asteroids and ophiuroids are worthy of class-level recognition, either stressing their disparate early development or because living representatives are thought to be distinctive at the class level on par with the other living classes.