Organisms from all five phylogenetic kingdoms form minerals. No less than 60 different mineral types are known, to date, to be formed by organisms and these are located at a wide variety of tissue sites and fulfill a host of different functions (Lowenstam and Weiner, 1989). A prominent and well known function of biogenic minerals is to provide mechanical strength to skeletons and often at the same time to act as a reservoir for the supply of ions necessary for vital metabolic functions. A characteristic of the mineral component of most skeletons is that it is formed under unusually well controlled conditions, such that the mineral form bears no morphological resemblance to its inorganic counterpart. This is, for the most part, achieved by inducing the minerals to precipitate in preformed spaces located by complex assemblies of macromolecules or vesicles or in some cases by combinations of both.

The number of cell types present in a metazoan body is a reasonable metric of its complexity. If evolutionary progress is defined as increase in complexity, from “lower” to “higher” forms, then progress occurs as cell-type numbers are increased. Using a lumper's definition of cell type, living metazoans range from 4 (placozoans) to over 210 (higher mammals) somatic cell types. The earliest fossil traces may be 580 my old and require an organism of about 30 cell types, while the primitive members of higher invertebrate phyla, appearing near 525 my ago, require about 50 cell types, an increase of about 0.3 cell type/my. Average Phanerozoic cell-type increase was about 0.4 cell type/my. These estimates are indistinguishable considering their crudity, and imply an origin of metazoans between about 645 and 680 my ago. While it may have been episodic rather than gradual, evolutionary progress would seem to have continued throughout metazoan history.

The Cambrian “explosion” occurred chiefly among organisms of 50 or so cell types, but so far as one can judge represented no major leap in the complexity of body plans. Rather it was characterized by a radiation of a number of clades that were at about this same level of complexity, one that permitted the construction of a rich variety of body plans, within a few million years. The diversity of the daughter body types was thus spectacularly broad. Though it may have been only a locus on a sweeping trend of continuing progress, the Cambrian explosion was something special in the history of life.

Concomitant with the rise in cell type numbers during the late Precambrian, the genetic regulatory apparatus that characterizes most metazoans was assembled, involving a cascading, hierarchical system of genes with feedback mechanisms and with informational systems that are not directly encoded. This flexible and open-ended regulatory architecture underlies evolutionary progress in metazoans, and permitted the evolution of cell differentiation. It may prove possible to judge the steps in the assembly of this regulatory system from the early metazoan record of body types, and conversely, it may prove possible to reconstruct the pattern of divergence of clades and the rise of body types as comparative data on pattern-formation systems become available for a variety of major taxa.

Pleistocene-Holocene sedimentary rocks, which outcrop along the northern Gulf of California coast in the vicinity of Puerto Peñasco, Sonora, have a very heterogeneous, mixed carbonateclastic composition. Carbonate grains are primarily molluscan, echinoderm, bryozoan and calcareous algal fragments. Terrigenous grains are primarily silicate minerals (e.g., quartz and feldspar) derived from three nearby igneous prominences (the basaltic Punta Peñasco and Cerro Prieto and the granitic Punta Pelicano).

Porosity of the sedimentary rocks, which commonly exceeds 50% in many units, may be intergranular and/or moldic. Cements in eolianite, precipitated within the vadose zone, are mainly of the meniscus spar type at grain contacts. Cements in beachrock, precipitated within the intertidal or shallow subtidal zone, include isopachous calcite spar and/or acicular aragonite.

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.

It seems likely that I was invited to contribute to this course because I am a renegade geologist. Many years ago I was lured by the attractions of living animals and switched to zoology. Later I became interested in the possibility of using immunological methods to assess evolutionary relationships among shrews, moles, hedgehogs, tree-shrews, elephant-shrews, otter-shrews, golden-moles and tenrecs, and I set a graduate student onto this project. We also sought to explore the relationships between these so-called ‘Insectivora’ and other orders of mammals, using immunological techniques to estimate crude biochemical distances between the serum proteins of representative species.

Following rediscovery of the sclerosponges (Hartman 1969, 1979; Hartman and Goreau, 1970, 1975) and recognition of their similarities to the stromatoporoids (Hartman and Goreau, 1970, p. 221–228), classification and interpretation of fossil Porifera have undergone major revisions during the past ten years. Our interpretation of the “edges” of the phylum have been considerably expanded.

Resolution of deep evolutionary problems, including the origin of the metazoa and the morphologic evolution of higher taxa within the metazoa, have long been sought in the developmental sequence. Haeckel's gastraea theory is perhaps the best example of this endeavor. Since Haeckel's time it has become apparent that the early evolution of animal life cannot be read directly from the developmental sequence. Ontogeny itself evolves making it difficult to even identify homologies in the early development between many phyla and classes. However, all may not be lost; during metazoan development gene expression must be localized in order to differentiate cell types in the body during development. It is this regionalized transcription and translation to protein product that differentiates cell types, organ systems, and the morphologic features that we can identify in the fossil record. The functional importance of the genes in question, and the fact that portions of the protein products of these genes must bind to DNA in order to perform their switching function, leads to extreme sequence conservation. This permits the identification and comparison of homologous genes important in the development of divergent taxa even after the passage of the entire Phanerozoic. If these genes retain a pattern of expression in development as well as conservation of the DNA sequence, then we can identify a homologous process derived from the development of the shared ancestor of the two taxa.

This approach can be used to address the homology of metameric units. Preliminary results indicate that the segmentation gene engrailed is expressed in chiton trochophores in associated with each of the developing plate fields. The engrailed gene is known to control segmentation processes in arthropods and annelids. Evidently the plates in chitons evolved from serial features in a shared ancestor of annelids, arthropods and molluscs. This indicates that the serial features found in molluscs are ancestral (plesiomorphic), and that the evolution of the mollusca has involved the loss or reduction of serial features rather than their de novo evolution in chitons and monoplacophorans as has been suggested by a number of neontologists. The fossil record suggests successive reduction of serial features in molluscs. This paleontological interpretation now finds support in developmental genetics.

Developmental genetics also provides a basis for evolution of body plans. Unusual preoral appendages have evolved in chelicerates, Burgess Shale arthropods such as Yohoia and Leanchoilia, and non arthropod forms such as Opabinia and Tullimonstrum. The differentiation of the vertebral column of vertebrates and the segments of arthropods are controlled by homologous genes that are expressed in a anterior to posterior sequence. Out of place (ectopic) expression of posterior genes in the anterior region produces posterior features in the antennal field of arthropods and in the most anterior vertebrae of the vertebrates. This potential for conversion of anterior features was present in the shared ancestor of vertebrates and arthropods. Thus evolution of novel anterior features resulting from ectopic expression could occur in both deuterostomes and protostomes and may account for a range of novel fossil forms. This suggests that parallel evolution of unusual anterior features could occur, and the presence of these features may not be the best character to use in a phylogenetic analyses.

Taxonomic databases are important tools in the study of faunal diversity and evolution. The usefulness of the inferences drawn from these databases is diminished when the role of environment is not considered. Analysis of the foraminiferal database at the genus and family levels is used to demonstrate the effect of water depth on presumed changes in taxonomic diversity and evolutionary turnover rates.

This paleoenvironmental effect is particularly noticeable when foraminiferal faunas of the late Paleozoic and the Mesozoic and Cenozoic intervals are compared. The late Paleozoic fauna is dominated by the Fusulinina and shallow-water (0–200 m) Textularuna. Standing diversity fluctuates greatly, and evolutionary turnover is high. This reflects short-term fluctuations in sea level which led to the rapid formation and destruction of narrow ecological niches. Evolutionary turnover appears to be related to reef growth during this time. This trend may also reflect an increased number of k-selected specialists which serve as proxy indicators for a slow-circulating oligotrophic ocean system. Shallow-water taxa may also be predisposed to extinction due to their reliance on symbiotic algae. The extinction event at the end of the Permian resulted in the loss of almost 70% of the standing generic diversity. This included the complete loss of the Fusulinina as well as a number of shallow-water textularids. Cohort survivorship curves are steep and taxon ages short during this time.

The diversity increase over the past 245 million years has largely been due to the addition of deep-water (200-10,000 m) taxa. This was particularly true during the Late Cretaceous and early Eocene, and may reflect the relatively high eustatic sea level during those intervals. The relationship between reef development and evolutionary turnover rates is less clear during this time interval. Although the extinction event that marked the end of the Cretaceous resulted in a greater loss in absolute taxonomic diversity than occurred at the end of the Permian, the relative loss in generic diversity was only about 21% due to the large number of deep-water taxa. When the entire fauna is considered, cohort survivorship curves are less steep and taxon ages are longer than in the late Paleozoic, but when only the shallow-water taxa are considered, the results are similar to those for the late Paleozoic.

The oldest-known dinosaurs (Herrerasaurus, Pisanosaurus) occur within the Ischigualasto Formation. Recent work in the formation has brought to light significant new material, including the complete skeleton of a new primitive dinosaur. We sketch below the paleoenvironment and faunal succession during the range of these early dinosaurs, and review some of the taphonomic factors that shaped their fossil record.

The Ischigualasto Formation (Carnian?) is included within the Agua de la Peña Group, a series of continental Triassic deposits exposed in the Ischigualasto-Ville Union Basin of northwest Argentina. Ischigualasto sediments rest unconformably upon the carbonaceous fluvial/lacustrine Los Rastros Formation; this contact is characterized locally by marked angular discordance. The upper contact is gradational into red-beds of the Los Colorados Formation. Medium- to coarse-grained conglomeratic sandstones, siltstones, and silty mudstones dominate the section. Sand bodies are characterized by medium- to large-scale trough cross-stratification and broad lenticular/narrow sheet geometries, and are interpreted as deposits of shallow, low-sinuosity streams. Siltstones and mudstones show pervasive evidence of soil development, including root traces, nodular caliche horizons, and pedogenic slickensides. Deposits attributable to lacustrine/paludal sedimentation are scarce, and freshwater vertebrates and invertebrates are extremely rare. These data suggest an upland depositional setting on a low-relief alluvial plain with seasonal climate.

The Ischigualasto vertebrate fauna includes archosaurs, rhynchosaurs, traversodontid and carnivorous cynodonts, and temnospondyl amphibians. Rhynchosaurs dominate (relative specimen abundance) in the lower half of the section, but are absent from the upper half. Traversodontid cynodonts occur throughout the formation, but are much more abundant up-section. Archosaurs, carnivorous cynodonts, and particularly temnospondyls are rare throughout, with dinosaurs limited to the lower half. No major stratigraphic or sedimentologic changes occur up-section, and there is no evidence for significant shifts in physical or chemical taphonomic processes. Thus, trends in relative taxon abundance likely record a true biotic signal (e.g., local extinction, immigration) rather than a taphonomically-driven preservational bias.

Fossils are preserved as isolated carcasses or disarticulated elements, most often in fine-grained overbank facies. Bone beds and microsites are conspicuously absent. Temnospondyl remains were found within a local carbonaceous lens developed upon a sand body, suggesting autochthonous burial in an abandoned-channel setting. Isolated skulls, particularly those of the traversodontid Exaeretodon, are extremely common. Fifteen isolated crania of this cynodont were mapped in a single stratum with limited areal exposure. Abundant preservation of isolated therapsid crania has also been reported in the Beaufort Series (Permo-Triassic) of the Karoo Basin, South Africa (Smith, 1980). Post-disarticulation hydrodynamic sorting (enhanced by scavenging?) of an areally dispersed mass-mortality assemblage may explain this unusual occurrence.