Since Haeckel's Biogenetic Law (‘ontogeny recapitulates phylogeny’) fell into disrepute early in the twentieth century, there has been intermittent debate, particularly in recent years (de Beer, 1958; Gould, 1977; Alberch et al., 1979; Alberch, 1980; Bonner, 1982; McNamara, 1982a), on the nature of the relationship between an individual's development and phylogenetic history. Important questions under discussion include the following: If a strong causal relationship does exist, what is its nature? How does it work? What is its importance in evolution? How can it be recognized in the fossil record?

Biodiversity is the number and variability of genes, species, and communities in space and time (Norse et al., 1986; Wilson, 1988; Heywood and Baste, 1995). The fundamental question that has governed its study in modern times is Hutchinson's (1959): “Why are there so many kinds of animals?” In more recent decades, a somber subquestion has been added: How many species are dying every year (e.g., Wilson, 1992)?

Currently some controversy exists in the micropaleontological community concerning the statistically correct number of counts required for quantitative examinations, particularly with respect to the effect of variations in the number of species between samples and the significance of varying fractional abundances on the reliability of results. This analysis of the various statistical methods used to determine the number of required counts has shown that the number of species has no relationship to the number of counts required to measure accurately fractional abundances. As part of the study, logarithmic contours plotting percentage abundance against the total number of specimens, which provide abundance errors at a 95 percent confidence level, have been generated. The plot is displayed logarithmically to emphasize the significance of rare microfossil elements that dominate most assemblages, and which are important in many paleoenvironmental studies. Based on the plot, it is recommended that researchers utilize counts of at least 50 for indicator species having a fractional abundance of approximately 50 percent or greater; 300 counts for species which comprise approximately 10 percent of a sample; 500–1,000 counts for species that make up 5 percent of a sample; and counts of several thousand for defining species that comprise 1 percent of a sample. It is important to note, however, that where similar biofacies are involved, higher counts are required to accurately distinguish them. It is also recommended that researchers include fractional error abundances with their estimated abundances to provide an indication of their accuracy.

Trends are the primary phenomenon of macroevolution, but they have often been misinterpreted because an old and deep conceptual error has induced us to misread, as anagenesis in abstracted entities, a pattern that actually records changes in variance by increase or decrease in diversity or disparity among species within clades. These patterns are actually produced by the “entity making and breaking machine” of differential species success, but we misread history as anagenesis because we focus on extreme values (though they may only represent tails in variance of a system), or on measures of central tendency that shift passively as species birth and death work in their differential way. I discuss several examples in two classes: “increase trends” mediated by growth in variance, and “decrease trends” produced by diminution of diversity or disparity. I present two examples in extenso based on original data: threefold occurrence of Cope's rule in planktonic foraminifers as a consequence of increasing species diversity from small founding lineages (increase trend), and disappearance of 400 hitting in baseball as a decrease trend recording symmetrical decline of variance with increasing excellence of play, not the gradual extinction of a valued “thing.” A proper appreciation of trends as changes in variance flows from and into the two most important revisionary themes in modern evolutionary theory: 1) constraint and structure as an antidote to overreliance upon adaptation (questions about why founding lineages tend to be small, and why size ranges are constrained, lie primarily in structural, not adaptational, domains); 2) hierarchy (increase and decrease trends are powered by differential species sorting, not by extrapolated anagenesis of competition among organisms within populations).

Tyrannosaurids are a well-supported clade of very large predatory dinosaurs of Late Cretaceous Asiamerica. Traditional dinosaurian systematics place these animals within the infraorder Carnosauria with the other large theropods (allosaurids, megalosaurids). A new cladistic analysis indicates that the tyrannosaurs were in fact derived members of the Coelurosauria, a group of otherwise small theropods. Despite certain gross cranial similarities with the large predators of the Jurassic and Early Cretaceous, the Late Cretaceous tyrannosaurids are shown to be the sister group to ornithomimids and troodontids, which share a derived condition of the metatarsus. This clade is found to be nested within Maniraptora, which is a more inclusive taxon than previously recognized. The atrophied carpal structure found in tyrannosaurids and ornithomimids is derived from a maniraptoran condition with a large semilunate carpal, rather than from the plesiomorphic theropod morphology.

The taxa “Carnosauria” and “Deinonychosauria” (Dromaeosauridae plus Troodontidae) are shown to be polyphyletic, and the Late Jurassic African form Elaphrosaurus is found to be the sister taxon to Abelisauridae rather than a primitive ornithomimosaur. Purported allosaurid-tyrannosaurid synapomorphies are seen to be largely size-related, present in the larger members of both clades, but absent in smaller members of the Tyrannosauridae. The remaining giant tetanurine theropods (Megalosaurus and Torvosaurus) were found to be progressively distant outgroups to an allosaurid-coelurosaur clade. The inclusion of the Tyrannosauridae within Maniraptora suggests a major adaptive radiation of coelurosaurs within Cretaceous Asiamerica comparable to contemporaneous radiations in various herbivorous dinosaurian clades.

New fossils from the Neoproterozoic Ediacara fauna of South Australia are interpreted as the oldest known hexactinellid sponges. They occur within the Ediacara Member of the Rawnsley Quartzite (Pound Subgroup) from several locations in the Flinders Ranges. The new genus, Palaeophragmodictya, is characterized by disc-shaped impressions preserving characteristic spicular networks and is reconstructed as a convex sponge with a peripheral frill and an oscular disc at the apex.

Carbonates and rare shales of the ca 700–800 Ma old Draken Conglomerate Formation, northeastern Spitsbergen, preserve a record of environmental variation within a Neoproterozoic tidal flat/lagoon complex. Forty-two microfossil taxa have been recognized in Draken rocks, and of these, 39 can be characterized in terms of their paleoenvironmental distributions along a gradient from the supratidal zone to permanently submerged lagoons. Supratidal to subtidal trends include: increasing microbenthic diversity, increasing abundance and diversity of included allochthonous (presumably planktonic) elements, decreasing sheath thickness of mat-building organisms (with significant taphonomic consequences), and an increasing sediment/fossil ratio in fossiliferous rocks. Five principal and several minor biofacies can be distinguished. The paleoecological resolution obtainable in the Draken Conglomerate Formation rivals that achieved for most Phanerozoic fossil deposits. It documents the complexity and diversity of Proterozoic coastal ecosystems and indicates that both environment and taphonomy need to be taken into explicit consideration in attempts to understand evolutionary trends in the early fossil record. Three species, Coniunctiophycus majorinum, Myxococcoides distola, and M. chlorelloidea, are described as new; Siphonophycus robustum, Siphonophycus septatum, and Gorgonisphaeridium maximum are proposed as new combinations.

The concept of “land-mammal age” as developed in South America is examined. The “Uquian Land-mammal age” is used as a study case. “Land-mammal age” parataxonomy is here considered methodologically but not conceptually different from chronostratigraphic taxonomy. “Land-mammal ages” in South America are based on stages. However, we consider that accurate biostratigraphic studies must be done in South America for establishing the biostratigraphy and precise boundary stratotypes of most stages-ages. The Uquia outcrops are here considered inadequate as a stratotype. A new South American continental stage-age is proposed. This stage is based on a biostratigraphic scheme. The stratotypes of the stage and biozones are located in the fossiliferous southeastern Buenos Aires Province marine cliffs. The lower boundary stratotype is proposed. The stage-age is probably correlated with the Gauss Chron and the lower Matuyama Chron. Additionally, some major units of Ameghino are validated and a different timing for the arrival of North American mammals to southern South America is presented.

Some of the relatively recent literature correlating morphological variation in benthic foraminifera with environmental parameters such as temperature, salinity, carbonate solubility, depth, nutrition, substrate, dissolved oxygen, illumination, pollution, water motion, trace elements, and rapid environmental fluctuation is reviewed. It appears some variables (most notably depth) are recorded more frequently, which may affect some conclusions. Although each variable is treated separately, it appears that almost no variables act independently on test morphologies. In reviewing the literature, it becomes clear that there are many individual trends, especially with shell ornamentation, but few broad ones, and that it is almost impossible, with exception of some of the larger reef-dwelling, symbiont-bearing foraminifera, to predict how any species will react to various parameters. The broad trends concern thinning or thickening of carbonate tests with changing carbonate availability, temperature, and salinity. It appears that many observations of morphological changes within species may not be recorded in the literature, perhaps because authors did not recognize the importance of small details that would be of importance at a later time.

Tidal cycles are reflected in daily growth-increment sequences in shells of many Recent and fossil mollusks. Living specimens of the bivalve Mercenaria mercenaria were notched at the growing edge of the shell and planted intertidally in Barnstable Harbor, Massachusetts. Shells from two lots, killed at intervals of 368 and 723 days after planting, show the same number of small growth increments as there were days from notching to killing. Superimposed on daily growth record are effects of winter (thin daily increments) and tides (14-day cycles of thick and thin daily increments). Comparison of Barnstable tide record with the first year's growth shows that, for each 14-day cycle, thin daily increments form during neap tides and thicker daily increments form during spring tides. Although tidal patterns are present in subtidal Mercenaria shells, they are rarely as pronounced as in intertidal ones. Spawning patterns differ from winter patterns; they are expressed in the shell by an interruption of regular deposition followed by a series of thin daily increments. Continuous sequences of bidaily patterns, one thick daily increment followed by a relatively thin one, are common in M. mercenaria.

The clearest 14-day cycles of deposition were seen in shells of the bivalve Tridacna squamosa. Each daily neap-tide increment is a simple layer consisting of a dark and light zone. Each daily spring-tide increment is a complex layer consisting of two light-dark alternations separated by a depositional break that is more pronounced than the breaks delimiting daily intervals. Preliminary results of growth-increment counts in fossils show a generally decreasing trend of the mean values of days per lunar month toward the Recent. The Pennsylvanian value is 30.07 ± 0.08, a figure that is in general agreement with those of Scrutton (1964), who counted 30.59 days per month on Devonian corals, and Barker (1966), who reported more than 30 days per month in Pennsylvanian bivalves.

When extracting or cleaning phosphatic fossils using acetic acid, the solutions must be buffered with calcium acetate to a pH greater than 3.6 for conodont and many fish taxa, and to a slightly greater pH for some conulariid, shark, and some fish taxa. Diagrams of the changes in pH and density during dissolution, rate of dissolution, and productivity per liter of acid provide a means for selecting the economically optimal process, monitoring the progress, and adjusting the composition of the solution when necessary.

Discovery of fossils of the Ediacara biota near the top of the Spitzkopf Member at farm Swartpunt extends the known range of these remains in Namibia more than 600 m to near the sub-Cambrian unconformity. The fossiliferous beds occur approximately 100 m above a volcanic ash dated at 543 ± 1 Ma, and thus may be the youngest Proterozoic Ediacara-type fossils reported anywhere in the world. Fossils are preserved within and on the tops of dm-thick beds of storm-deposited sandstone at two stratigraphic levels; the environment is interpreted as open marine, generally calm but with episodic disruptions by storm waves, and probably within the euphotic zone. The presence of Pteridinium carolinaense (St. Jean), which is also known from the classic sections in Ediacara and the White Sea among others, reinforces evidence from geochronology and chemostratigraphy that the Swartpunt section is terminal Neoproterozoic in age. The new genus and species Swartpuntia germsi is a large, multifoliate frond that exhibits at least three quilted petaloids. Macroscopically, Swartpuntia resembles Pteridinium and Ediacara-type fronds such as Charniodiscus traditionally interpreted as Cnidaria, whereas microscopically it exhibits segmentation that is remarkably similar to that of the putative worm Dickinsonia. Combination of diagnostic characters of these supposedly disparate groups in a single species suggests that many species of quilted Ediacaran organisms were more similar to each other than they were to any modern groups, and provides support for the concept of the “Vendobionta” as a late Neoproterozoic group of mainly multifoliate organisms with a distinctive quilted segmentation.

The remarkable “evolution” of the reconstructions of Anomalocaris, the extraordinary predator from the 515 million year old Middle Cambrian Burgess Shale of British Columbia, reflects the dramatic changes in our interpretation of early animal life on Earth over the past 100 years. Beginning in 1892 with a claw identified as the abdomen and tail of a phyllocarid crustacean, parts of Anomalocaris have been described variously as a jellyfish, a sea-cucumber, a polychaete worm, a composite of a jellyfish and sponge, or have been attached to other arthropods as appendages. Charles D. Walcott collected complete specimens of Anomalocaris nathorsti between 1911 and 1917, and a Geological Survey of Canada party collected an almost complete specimen of Anomalocaris canadensis in 1966 or 1967, but neither species was adequately described until 1985. At that time they were interpreted by Whittington and Briggs to be representatives of “a hitherto unknown phylum.”

Here, using recently collected specimens, the two species are newly reconstructed and described in the genera Anomalocaris and Laggania, and interpreted to be members of an extinct arthropod class, Dinocarida, and order Radiodonta, new to science. The long history of inaccurate reconstruction and mistaken identification of Anomalocaris and Laggania exemplifies our great difficulty in visualizing and classifying, from fossil remains, the many Cambrian animals with no apparent living descendants.

Ichnofacies stand today as one of the more elegant but widely misunderstood concepts in ichnology, especially where paleobathymetry is concerned. Marine ichnofacies are not intended to be paleobathometers, as some workers continue to imply (e.g., Lockley et al., 1987; Ekdale, 1988); rather, they are archetypical facies models based upon recurring ichnocoenoses (Frey and Pemberton, 1984, 1985, 1987). If a particular ichnocoenose tends to occur repeatedly within a given bathymetric setting, so much the better; but water depth per se is rarely, if ever, a governing factor. Ichnocoenoses and ichnofacies, therefore, are best viewed in the context of actual depositional conditions or environmental gradients, wherever they occur (Figure 1).

When each of the Avalon-, Ediacara-, and Nama-type fossil assemblages are tracked through geological time, there appear to be changes in species composition and diversity, almost synchronized between different sedimentary environments, allowing a subdivision of the late Ediacaran into the Redkinian, Belomorian and Kotlinian geological time intervals. The Redkinian (580–559 Ma) is characterized by first appearance of both eumetazoan traces and macroscopic organisms (frondomorphs and vendobionts) in a form of Avalon-type communities in the inner shelf environment, whereas coeval Ediacara-type communities remained depauperate. The Belomorian (559–550 Ma) is marked by the advent of eumetazoan burrowing activity in the inner shelf, diversification of frondomorphs, migration of vendobionts from the inner shelf into higher energy environments, and appearance of tribrachiomorphs and bilateralomorphs. Ediacaran organisms formed distinctive ecological associations that coexisted in the low-energy inner shelf (Avalon-type communities), in the wave- and current-agitated shoreface (Ediacara-type communities), and in the high-energy distributary systems (Nama-type communities). The Kotlinian (550–540 Ma) witnessed an expansion of the burrowing activity into wave- and current-agitated shoreface, disappearance of vendobionts, tribrachiomorphs and bilateralomorphs in wave- and current-agitated shoreface, together with a drop in frondomorph diversity. High-energy distributary channel systems of prodeltas served as refugia for Nama-type communities that survived until the end of the Ediacaran and disappeared when the burrowing activity reached high-energy environments. This pattern is interpreted as an expression of ecosystem engineering by eumetazoans, with the Ediacaran organisms being progressively outcompeted by bilaterians.

Isoetes beestonii new species is the most ancient known species of this living genus. In earliest Triassic shales of the Sydney and Bowen Basins of Australia it is locally abundant as circlets of transversely wrinkled leaves. It was heterosporous with megaspores of Maiturisporites rewanensis and microspores of Lundbladispora sp. cf. L. springsurensis.

Isoetes thus predates Pleuromeia from which it has been thought to have evolved. Australian Pleuromeia-like subarborescent lycopsids are here reviewed as whole plants, with names based on fertile structures, and include Cylostrobus sydneyensis Helby and Martin from the Sydney Basin, Pleuromeia dubia (Seward) Retallack from the Sydney and Canning Basins, and Cylostrobus indicus (Lele) new combination and Pleuromeia sternbergii (Münster) Corda for Germar, newly recorded from the Canning Basin.

There are in addition an array of cormose lycopsids that formed compact conelike plants when fertile, intermediate in stature between Isoetes and Pleuromeia. One of these is Tomiostrobus australis (Ash) Sadovnikov, formerly regarded as a cone, but here reinterpreted as a small pioneering plant of oligotrophic lakes and ponds, like Isoetes. Its megaspores are Horstisporites and its microspores are the stratigraphically important Aratrisporites tenuispinosus. Other similar forms are Tomiostrobus polaris (Lundblad) new combination from the early Triassic of Greenland, T. mirabilis (Snigirevskaya) new combination from the early Triassic of the Tunguska Basin of Siberia, T. taimyrica (Sadovnikov) new combination from the Early Triassic of the Taimyr region of Siberia, Lepacyclotes ermayinensis (Wang) new combination from the middle Triassic of China, L. convexus (Brik) new combination from the middle-late Triassic of Kazachstan, and L. zeilleri (Fliche) new combination from the middle Triassic of France and Germany.

The diversity of isoetaleans in early Triassic floras and the weak vascular system of permineralized Tomiostrobus and Pleuromeia contradict the traditional view that Isoetes evolved by reduction in size from Pleuromeia and that its opportunistic life style allowed it to avoid plant competition. It is now more likely that Isoetaceae were weedy survivors of Permian-Triassic extinctions. The adaptive radiation and decline of Triassic quillworts matches the recovery from near-extinction, then decline of therapsid reptiles, for which these plants may have been an important food.

Tidal rhythmites of the Tonganoxie Sandstone Member (Stranger Formation, Douglas Group) at Buildex Quarry, eastern Kansas, contain a relatively diverse ichnofauna. The assemblage includes arthropod locomotion (Dendroidichnites irregulare, Diplichnites gouldi types A and B, Diplopodichnus biformis, Kouphichnium isp., Mirandaichnium famatinense, and Stiaria intermedia), resting (Tonganoxichnus buildexensis) and feeding traces (Stiallia pilosa, Tonganoxichnus ottawensis); grazing traces (Gordia indianaensis, Helminthoidichnites tenuis, Helminthopsis hieroglyphica); feeding structures (Circulichnis montanus, Treptichnus bifurcus, Treptichnus pollardi, irregular networks), fish traces (Undichna britannica, Undichna simplicitas), tetrapod trackways, and root traces. The taxonomy of some of these ichnotaxa is briefly reviewed and emended diagnoses for Gordia indianaensis and Helminthoidichnites tenuis are proposed. Additionally, the combined name Dendroidichnites irregulare is proposed for nested chevron trackways. Traces previously regarded as produced by isopods are reinterpreted as myriapod trackways (D. gouldi type B). Trackways formerly interpreted as limulid crawling and swimming traces are assigned herein to Kouphichnium isp and Dendroidichnites irregulare, respectively.

Taphonomic analysis suggests that most grazing and feeding traces were formed before the arthropod trackways and resting traces. Grazing/feeding traces were formed in a soft, probably submerged substrate. Conversely, the majority of trackways and resting traces probably were produced subaerially in a firmer, dewatered and desiccated sediment.

The Buildex Quarry ichnofauna records the activity of a terrestrial and freshwater biota. The presence of this assemblage in tidal rhythmites is consistent with deposition on tidal flats in the most proximal zone of the inner estuary, between the maximum landward limit of tidal currents and the salinity limit further towards the sea.

The impetus for writing this paper has come from many people who have shown an interest in the device we describe; prior to this paper, we had no reference to provide for interested parties. The original device was described in Elmgren (1973) and illustrated in Thomas (1986). These papers are not readily available to many micropaleontologists; hence, we felt the need to redescribe it here with a few modifications. Traditionally, foraminiferal researchers, especially those working in fossil deposits, work on samples that are first processed and then dried. To split these dry samples to aliquots of manageable numbers of foraminifera, they use the well-known “Otto” microsplitter, which provides accurate splits plus or minus 10–20 percent.

Turtles have served as a model system for molecular divergence dating studies using fossil calibrations. However, because some parts of the fossil record of turtles are very well known, divergence age estimates from molecular phylogenies often do not differ greatly from those observed directly from the fossil record alone. Also, the phylogenetic position and age of turtle fossil calibrations used in previous studies have not been adequately justified. We provide the first explicitly justified minimum and soft maximum age constraints on 22 clades of turtles following best practice protocols. Using these data we undertook a Bayesian relaxed molecular clock analysis establishing a timescale for the evolution of crown Testudines that we exploit in attempting to address evolutionary questions that cannot be resolved with fossils alone. Some of these questions, such as whether the turtle crown originated in the Triassic or Jurassic, cannot be resolved by our analysis. However, our results generate novel age-of-origination estimates for clades within crown Testudines. Finally, we compare our fossil calibrations and posterior age estimates to those from other studies, revealing substantial differences in results and interpretation.

The lowest Cambrian of Avalon, or Placentian Series, is a relatively thick sequence (1,400 m) in southeastern Newfoundland. A newly proposed body fossil zonation supplements an existing trace fossil zonation of the lower part of the Placentian Series and includes strata to the top of the sub-trilobitic Lower Cambrian.

The Sabellidites cambriensis Zone brackets the Precambrian–Cambrian boundary and comprises peritidal and wave-influenced subtidal facies deposited during deepening through the lower part of the Chapel Island Formation. Younger “Ladatheca” cylindrica Zone strata include the deepest facies of the Chapel Island Formation. The base of the overlying Watsonella crosbyi Zone (a post-Nemakit Daldyn and pre-Tommotian equivalent) is significantly diachronous because the diagnostic mollusks were preferentially preserved in pyritiferous offshore muds rather than in coeval nearshore muds. High diversity, upper Watsonella crosbyi Zone faunas (18 species) are limited to peritidal limestones of member 4 and are dominated by calcareous small shelly fossils. A thick interval (ca. 430 m) without body fossils and an important episode of block faulting that led to 750 m of differential erosion preceded deposition of the lower part of the Bonavista Group (=Sunnaginia imbricata Zone, an interval considered to be largely older than the Tommotian). Although much Early Cambrian time may be lost as a result of erosion at Random Formation–Bonavista Group unconformities, many Watsonella crosbyi Zone species reappear in the Sunnaginia imbricata Zone. Shoaling accompanied the immigration event defining the base of the Camenella baltica Zone, and an unconformity following regional offlap marks the top of the Placentian Series.

Calcareous, and not phosphatic, composition is most common in earliest Cambrian shelly remains. Little evidence suggests that a global, Precambrian–Cambrian boundary interval “phosphogenic” event either resulted in deposition of local phosphate deposits in the Tethyan region or had a role in the appearance of mineralized skeletons.

Twenty metazoans and problematica and an alga are illustrated from the Chapel Island Formation. Bemella? vonbitteri Landing n. sp. and Halkieria stonei Landing n. sp. are described. The monoplacophoran Archaeospira? avalonensis Landing n. sp. has right-and left-handed conchs comparable to those of Archaeospira (=Yangtzespira) from China. Anabarites is the senior generic synonym of Tiksitheca.