This Volume marks the inaugural issue of the Paleontological Society Papers. This series, established by The Paleontological Society in 1996, replaces the Paleontological Society Short Course Notes, which ceased to be published in November 1995, and the Paleontological Society Special Publications, which ceased to be published in June 1996. Most of the contributions in the new series are invited papers presented at the Short Courses on Paleontology sponsored by the Society at the annual meetings of the Geological Society of America.

Because of their prodigious abilities for rapid calcification, corals today and in the past have been principal reef builders. The mere mention of corals evokes colorful and vivid image of tropical settings, swaying palm trees, and the crash of waves against the coral-dominated, biologically complex edifice we call the reef. Most geologists, educators, and students are aware of new developments in ecology and evolution of modern and ancient reefs, but they are probably less aware of studies of corals that build reefs. Understanding ancient examples rests on a foundation of modern coral biology and taxonomy. This volume summarizes the 1996 Paleontological Society Short course “Paleobiology and Biology of Corals.” Twelve international authors present current and cutting-edge topics in coral research.

This article is a summary of the main points about the evolution of corals put forward in Veron (1995). The main points presented are first, a family tree of the Scleractinia; second, an analysis of genera and their present-day global distributions, age patterns and diversity, including the Cenozoic fossil record; third, coral species and their global distributions, species determination in fossils of Pliocene to Recent age, their geologic history and geographic characteristics; fourth, the theoretical aspects of coral evolution based on surface circulation vicariance, reticulate evolution, and the nature and origin of species. For non-biologists, important concepts and terms are noted in bold and are defined in a glossary at the end of the text.

The evolutionary history of scleractinian corals, based on morphological taxonomy and inferences from the fossil record, has been poorly understood. Molecular techniques developed over the past ten years are now being used to gain a new perspective on scleractinian phylogeny. DNA sequences, mitochondrial genome structure, and morphological characters support a basal position for the Anthozoa in the phylum Cnidaria. Mitochondrial and nuclear DNA sequences suggest a relatively derived position of the order Scleractinia within the class Anthozoa. Mitochondrial and nuclear DNA sequences have provided a new hypothesis for evolution within the Scleractinia that is different from hypotheses based on morphological characters of extant and fossil taxa. Groupings within the two major lineages defined by molecular data do not correspond to morphological suborder groupings although groupings of genera within families do correspond to traditional taxonomy. This new molecular hypothesis suggests that the Scleractinia are represented by two major lineages that diverged from each other before the appearance of the scleractinian skeleton in the fossil record. This divergence time supports the hypotheses that the Scleractinia are not related to the Rugosa of the Paleozoic and that the scleractinian skeleton has evolved more than once. These two major lineages may represent two architectural strategies within the Scleractinia that have led to their great morphological diversity.

New morphometric methods for distinguishing morphologically similar species of Recent colonial scleractinian corals involve the analysis of three dimensional landmarks digitized on calical surfaces. Variables suitable for multivariate statistical analysis are derived from the landmark data by applying various geometrical techniques, including Bookstein size and shape coordinates and generalized resistant fitting. Cluster analyses of these variables and study of the relative positions of replicates from the same colony on the resulting dendrograms are used to recognize clusters of colonies representing morphospecies. Comparisons with the results of genetic analyses on the same specimens suggest that these morphospecies correspond closely with biological species.

Although slightly less effective, similar analyses of two dimensional landmark data collected on thin sections of the same specimens also distinguish species, and suggest that biological species can be approximated in the fossil record. Multivariate statistical analyses show that variables derived from two dimensional landmarks can be used to trace the stratigraphic ranges of these fossil species. The appropriate method for tracing ranges depends of the evenness of sampling in different geologic horizons. Preliminary comparisons of observed stratigraphic ranges determined by this approach with those determined by cladistic analysis suggest that overall patterns in evolutionary rates through geologic time are the same for both approaches. Thus, nontraditional morphologic characters determined by subsequent examination of morphometrically-defined species have potential for providing sufficient resolution for phylogenetic analysis.

Within a family, genera are usually separated on the basis of their colonial structure. The periodic occurrence of transgeneric highly variable specific units (spectra) in the fossil record poses nomenclatural and phylogenetic problems. A detailed example among Jurassic montlivaltiids is presented in this paper involving the genera Montlivaltia, Coenotheca, Thecosmilia, Latiphyllia and Complexastrea. These spectra are related to peculiar unstable nonreefal environments and are characterized by the dominance of young stages of the colonial growth (astogeny). The arising nomenclatural difficulties are solved by way of spectral nomenclature which allows naming morphological types, as well as taxonomic units and keeping some stability within the general frame of nominal taxa. Genera correspond to grades (solitary, thamnasterioid, phaceloid, meandroid, cerioid) rather than clades and the colonial structure is a labile character. Several alternative phylogenetic hypotheses are proposed, among which, some can renew our vision of this group and emphasize that the iterative production of generic-level shapes is best explained by mean of heterochronic processes. It is suggested that testing of these hypotheses be extended to other families such as Microsolenidae, Stylophyllidae or Fungiidae.

Two major groups of corals have essentially continuous records from the Early Ordovician (Tabulata) and Middle Ordovician (Rugosa) to the end of the Permian. A third major group, the living Scleractinia, range from Middle Triassic to Holocene. Additional groups have shorter ranges within the Paleozoic. The origins and relationships of these groups have been discussed for over 100 years. Relations between the Rugosa and Scleractinia have attracted the greatest interest because of their morphologic similarities and the time sequence. Arguments involve the significance of serial versus cyclic septal insertion, calcitic versus aragonitic skeletal mineralogy, and the time gap between the last rugosans and first scleractinians (there are no known Lower Triassic corals). Discussions of relationships among the various Paleozoic groups are commonly based on detailed morphological comparisons because of their overlapping stratigraphic ranges.

Recent work on the living corals and anemones supports a closer relationship between groups than is suggested by placing them in different orders or suborders. The paleontological record of “anemones” is slight, but it is reasonable to assume that one or more groups of skeletonless zoantharians persisted through long parts of the Phanerozoic. It is suggested that the major groups of zoantharian corals originated through the development of skeletons in various anemone groups at several different times.

The extinct Paleozoic coral groups Rugosa and Tabulata suffer from confused systematics because of extreme morphological variation, pervasive homoplasy, and relatively simple skeletal morphology. Morphological variation occurs within individuals or colonies, between individuals within a population, and between populations. Variation at each level may have both genetic and ecologic components. Homoplasy is very abundant and extended sequences of parallel or convergent character transformations have led to the recognition of “recurrent evolutionary trends” in many lineages.

Morphological variation causes much difficulty in the recognition and characterization of coral species and homoplasy is problematic for phylogeny reconstruction. Improved coral systematics require a more holistic approach to both taxonomy and phylogeny analysis, including: 1) population-based species concepts, as opposed to typological approaches; 2) use of more quantitative techniques in species discrimination and description; 3) more attention to subtle morphological elements, such as microstructure; 4) description of ecological settings (depositional environments) to aid in analysis of behavior and to help unravel ecophenotypic plasticity; and 5) use of stratigraphic and geographic distribution data in phylogeny analysis, because skeletal morphology is inadequate by itself.

Modern understanding of skeletal microstructure in fossil corals builds on knowledge of structure and biomineralization in modern corals and diagenesis of carbonate skeletons. It is agreed that the skeleton of living stony corals, the Scleractinia, is made of fibrous aragonite, with growth of biocrystals generally according to rules of crystal growth as observed in inorganic aragonite, but here controlled by organic matrix. Fossil scleractinians all apparently fit the same model of biomineralization seen in living corals, although some early taxa (Triassic) lack septal trabeculae, rod-like framework structures typical of all living and most fossil septate corals.

Paleozoic corals, both septate Rugosa and non-septate Tabulata, had a skeleton of calcite, most likely low-magnesium calcite, thus had diagenetic histories differing considerably from the aragonitic Scleractinia. Agreement is lacking as to whether a single structural motif can be defined for the calcitic corals, that is, whether the Rugosa and Tabulata originally had a calcitic skeleton built of fibrous biocrystals, analogous to the scleractinians, or whether some others originally had a non-fibrous, lamellar skeletal microstructure. The disagreement hinges on whether both of these basic configurations are biogenic, or whether the latter is sometimes or always diagenetic in origin. The presence of matrix control over biomineralization in Rugosa and Tabulata is yet to be proven, but will play an important role in models for biocrystallization in these older cnidarians. Details of diagenetic history and modification of structures in these calcitic corals likewise warrant investigation to improve our ability to interpret the Paleozoic corals.

Skeleton microstructure of Recent scleractinians proves to be a valuable suprageneric taxonomical criterion, and the same has been stated with respect to Mesezoic corals where skeletonal preservation is aragonite. In paleontological practice, septal microstructure is decisive in discrimination of taxa among homeomorphic genera of different families. Similarities of microstructural features of some Recent and fossil corals encompass the genera in common taxa of higher ranks and allow for reconstruction of their presumed phylogeny.

Data on extant and fossil corals are analyzed. The characteristics of the organisms are divided into five basic units of data: morphology, ecology, taxonomical relations, stratigraphical, and (paleo-) geographical occurrence. Six data complexes are derived from these units. Their relationships are defined and the database structures designed on the basis of the Entity-Relationship-Model. The data structures are described in detail and advice is given for building up databases. The various opportunities of querying the database and particularly of assessing the data are thoroughly discussed. Data obtainable by transactions on the stratigraphical and (paleo-) geographical distribution of the organisms are considered. Finally, the database on Mesozoic corals compiled by the author is introduced and some preliminary results as well as future projects are presented.

There is a fundamental ecologic differentiation between zooxanthellate and non-zooxanthellate corals. This paper reviews factors which govern the stable carbon and oxygen isotopic composition of these groups of corals. Although the stable carbon and oxygen isotope compositions of coral skeletons are strongly influenced by environmental and physiological factors, the precise mechanisms remain a matter of debate. In particular the oxygen isotopic composition is known to be governed by the temperature and the oxygen isotopic composition of the water and perhaps also by kinetic factors. In contrast the carbon isotopic composition is controlled by a combination of photosynthesis, respiration, autotrophy, heterotrophy, and the isotopic composition of dissolved inorganic carbon. Using a combination of carbon and oxygen isotopes it is possible to distinguish zooxanthellate from non-zooxanthellate corals.

Manuscripts submitted to the Paleontological Society Papers must conform strictly to guidelines in order to ensure timely publication of each volume. Manuscripts, to be included in the series, should be no more than 25 single-spaced pages in length, and submitted to the volume editor by February 15 of the intended year of publication.