Potential hybrid fossil crinoids, Eretmocrinus magnificus x Eretmocrinus praegravis, are identified from the Lower Mississippian Fort Payne Formation of south-central Kentucky. These are the first fossil hybrid crinoids identified, and one of very few examples of hybrids recognized in the fossil record. Eretmocrinus magnificus x E. praegravis specimens have shapes and calyx plate sculpturing that are morphologically intermediate between well-defined, distinct parent species. Suspected hybrids occur at localities where parent species co-occur and where the parent species are the most abundant; the hybrids occur at what may have been the distributional margins of the parent species; and the mixture of characters on suspected hybrids seems to be morphogenetically partitioned. Parent species are derived from separate lineages within Eretmocrinus, and hybridization is the most probable explanation for these morphologically intermediate specimens. This example highlights the need to consider hybridization as a potential interpretation of intermediate morphologies among fossils and raises questions concerning the impact of hybridization for our interpretation of the fossil record and the role of hybridization in the evolutionary process.

The Plio-Pleistocene planktic foraminiferal sequence of the Globorotalia (Globoconella) puncticulata-inflata clade in Deep Sea Drilling Project Site 588, dated at 4.36 Ma to 0.05 Ma, records the branching history of the G. inflata lineage from the ancestral G. puncticulata lineage. The gradational nature of the divergence and the enormous morphological variability inherent in the G. inflata lineage have elicited different views on taxonomy and phylogeny of this clade. A pattern recognition technique, soft independent modeling of class analog (SIMCA), was used as an objective quantitative stratophenetic methodology to reconstruct the phylogenetic history.

Typical specimens of two species, G. puncticulata and G. inflata, were identified from a stratigraphic level dated at 2.76 Ma. Principal component models were built to characterize the morphometric patterns of the two morphotypes using SIMCA. The Globoconella specimens of the next lower and higher adjacent stratigraphic levels were evaluated against the models and classified into one of the two morphotypes. The newly classified specimens were then used to build new models for further tracing of lineages in lower and upper sections, respectively. Progression of such training and classification procedures through stratigraphic intervals resulted in a reconstruction of the evolutionary patterns of the two lineages. Cladogenesis gave rise to the descendant lineage, G. inflata, at about 3.5 Ma. The two co-existing species, G. inflata and G. puncticulata, differ only in size and show similarity in most characters at the beginning of their divergence. Other characters began to diverge later, at various rates. The gradients between planktic and benthic foraminiferal δ18O values show a continuous increase during the late Pliocene. The succession from G. puncticulata to G. inflata during the same time correlates with the progressively increased vertical stratification in temperature of surface waters. Globorotalia puncticulata became extinct at 2.35 Ma when the temperature gradient further increased, corresponding to the onset of extensive glaciation in the Northern Hemisphere.

The fundamental goal of biochronology is ordering taxonomic first and last appearance events. The most useful biochronologic data are of the form “the first appearance event of one taxon predates the last appearance event of a second taxon” (FAE < LAE). FAE < LAE data sets are unusually reliable because they converge on a unique solution with greater sampling. The fact that the FAE of one taxon i < the LAE of another taxon j always can be inferred either if i is found lower than j in a stratigraphic section, or if i and j co-occur in at least one taxonomic list. Thus, FAE < LAE data accurately synthesize two disparate sources of information: routine biostratigraphic observations and taxonomic lists that may have no stratigraphic context. Appearance event ordination, the new method introduced here, is intended to summarize FAE < LAE data. The algorithm is founded on the following parsimony criterion: arrangements of FAEs and LAEs should always imply FAEi < LAEj when this is known, and otherwise imply LAEj < FAEi whenever possible. The technique differs from others related to correspondence analysis in its use of FAE < LAE data and explicit definition as a parsimony method. The algorithm is even more unique in that it uses different subsets of FAEi < LAEj statements at each iterative step, converging on separate sets of scores for the FAEs and LAEs. After arranging either the FAEs or the LAEs on the basis of their scores, the other set of scores can be discarded and the best arrangement of the remaining events can be inferred directly. An analysis of the Plio-Pleistocene mammalian record in the Lake Turkana region is used to illustrate the method. Biochronologic resolution on the order of 0.2-1.5 m.y. is achieved. The Turkana species lists by themselves demonstrate enough FAEi < LAEj relationships to resolve the basic biochronologic pattern, but stratigraphic information is still of great use.

Morphologic discrimination of species of scleractinian reef corals has long been plagued by a shortage of independent characters and by high ecophenotypic plasticity. Because of these two factors, many species appear to intergrade morphologically. We outline a newly developed protocol for the morphometric recognition of species, which uses size and shape coordinates derived from landmark data. The landmarks consist of spatially homologous points digitized in three dimensions on upper calical surfaces. The approach is more powerful than linear measurements at detecting subtle distinctions among species; and the distinctions are easy to visualize and interpret biologically, which increases the accuracy and resolution of subsequent phylogenetic and large-scale faunal analyses.

As an example, we distinguish morphospecies in collections of Porites made at three Caribbean locations. Size and shape coordinates are analyzed using principal component analysis, average linkage cluster analysis, and a series of iterative discriminant analyses. Positions of different corallites from the same colonies are examined on cluster dendrograms to determine cutoffs for group recognition, and discriminant classifications for different corallites from the same colonies are compared to maximize group assignments. The results yield seven morphospecies, which are generally in 90% agreement with classification of the same animals using allozyme electrophoresis. Measures of corallite size and the relative heights and locations of the pali and septal denticles all reveal unique patterns of variation among morphospecies.

Biostratigraphic applications of Devonian plant macrofossils are unusual because of the rarity of these fossil plants. Moreover, the taxonomic determination of these plants is too often either arguable or impossible. Here is proposed a biostratigraphic method based on a quantification of individual plant characters and not on determination of whole fossils. The method is the following: (1) each biocharacter found at a given locality receives a score according to whether it is primitive or derived, so that the biocharacter score increases with increasing derivation; (2) the biostratigraphic coefficients of well-dated localities are calculated, the biostratigraphic coefficient of a given plant locality being the mean of all the biocharacter scores of this locality; (3) the scores of these well-dated localities are used to build a reference scale to which localities under investigation will be compared. A detailed example is developed for Early Devonian times. Various plant biocharacters of seven fossiliferous outcrops have been quantified and the subsequent scores of these localities are presented. This example shows that biostratigraphic results obtained by using the quantification method are comparable in precision with dating based on palynological assemblage zones. Evolutionary aspects of the method are also discussed.

The Neogene species Petaloconchus sculpturatus presents a contradiction in terms, for it grows whorl “packages” of nearly perfect regularity, but ranks within the most geometrically irregular family of uncoiled gastropods, the Vermetidae. We perform a first biometric study of vermetids (only possible because sufficient regularity of growth permits us to number and identify whorls) to specify and characterize the factors on both sides of this “exquisite tension” between promotion and prevention of recoiling. Promoting factors include the older phyletic heritage of preserved dextral coiling, and the more immediate vermetid (or specifically petaloconchid) features of growth toward open spaces (where regular coiling might proceed in an unimpeded fashion); radular excision of discordant feeding tubes with shaping of the resulting scar so that growth may proceed in conformity with previous whorls; and locking of subsequent whorls upon a keel formed by longitudinal bead-rows of the previous whorl. Preventing factors include prominent phyletic heritage of all vermetids—maximal early irregularity enjoined by discordance between larval and subsequent growth (with teleoconch wrapping itself around the protoconch), thus precluding an ordered substrate to act as a foundation for regular whorl “packages” of intermediary growth—and a set of features specific to this lineage and acting as geometric constraints. In this category, we particularly document the exceedingly low rate of whorl expansion and the consequently wide umbilical space that produces a shell akin to winding a cylindrical coil of narrow-diameter rope around the periphery of a wide circular platform. This complex combination of promoting and preventing factors produces a shell that is tantalizingly close to fully regular, but cannot truly reattain this previous phyletic state—thus providing a fine example of Dollo's Law at the centenary of his formation of irreversibility.

Cantius is an early Eocene adapid primate with an exceptionally well known fossil record. Measurements were recorded to describe the size and shape of upper and lower first molars collected from a measured stratigraphic section in the Clarks Fork Basin of Wyoming. Rates of change of size and shape are quantified by calculating evolutionary rates in standard deviation units per generation (haldanes). Temporal scaling of rates shows that change in size was generated by a significantly nonrandom directional process, while change in shape was generated by a significantly nonrandom stabilizing process. Size change in Cantius is interpreted to be the result of weak directional selection, and shape change is interpreted to be the result of strong stabilizing selection.

Allometric analysis of the size-shape relationships in the Pliocene-Pleistocene planktic foraminiferal Globorotalia (Globoconella) puncticulata-inflata plexus reveals several heterochronic modes underlying the morphological evolution of the clade. The ancestral lineage, G. puncticulata, is a peramorphocline, showing a pre-displacement mode of heterochrony between 3.5 Ma and 3.0 Ma and an acceleration mode from 3.0 to 2.7 Ma. A different peramorphosis process, isometric giantism (hypermorphosis), in the ontogeny of the ancestral stocks of Globoconella occurred at about 3.5 Ma and gave rise to the G. inflata lineage. The descendant lineage, G. inflata, appears to have adopted a paedomorphosis trend by delaying the onset of the neanic stage in ontogeny during the period of 3.5 to 2.35 Ma, resulting in a series of transposition allometries. During the interval of 2.4 to 1.73 Ma, the allometries shifted to the opposite direction, signifying a pre-displacement trend. Evolutionary stasis marks the evolution during 1.73 to 0.25 Ma. Neoteny concluded the final evolutionary stage of the G. inflata lineage during the latest Quaternary (0.26 to 0.05 Ma). The enormous plasticity and fluctuations in morphology of G. inflata are attributed to the highly positive allometric growth during the ontogeny and the wide-range transposing allometries in the phyletic history. The major changes in heterochronic mode coincide with paleoceanographic events, suggesting that the morphological evolution in the Globoconella clade has been modulated by changes in paleoceanographic conditions.

Seven endemic species of skates (Chondrichthyes: Rajidae) represent the only family of elasmobranchs currently known to live in Antarctic continental waters. Many previous authors believed skates colonized Antarctic waters from Patagonia during interglacial periods in the Quaternary. However, recent fossil material collected from the middle Eocene La Meseta Formation of Seymour Island, Antarctic Peninsula, indicates that they may have persisted in Antarctic waters since the Paleogene. Additionally, oceanographic barriers present in the Neogene and Quaternary would have prevented dispersal from southern continents to Antarctica. A revised dispersal scenario, based on skate fossils, biology, paleogeography, and present centers of skate diversity, suggests that skates evolved in the western Tethys and North Boreal seas of western Europe in the Late Cretaceous and early Paleogene and emigrated into Antarctica during the early to middle Eocene via a dispersal corridor along the continental margins of the western Atlantic Ocean. Skates probably populated the Pacific Basin by passing from this dispersal corridor through the Arctic Ocean. Vicariant events, such as opening of the Drake Passage, the development of the Circum-Antarctic Current, and formation of deep and wide basins around Antarctica in the late Paleogene, created barriers that isolated some species of skates in Antarctica and prevented movement of other species of skates into Antarctica from northern areas. Skates are the only group of fishes known to have survived the Oligocene cooling of Antarctica that killed or extirpated the Paleogene ichthyofauna; they persisted by a combination of cold-tolerance, generalized diet, and unspecialized bathymetric and habitat preferences.

Late Paleocene planktic foraminifera exhibit strong positive correlations between carbon isotopic values and test mass, but negative correlations between oxygen isotopic values and test mass. Based on analogy with modern taxa, these trends are probably ecotypic and may or may not apply to an ontogenetic series. Among Acarinina and Morozovella species, the magnitude and direction of these trends resemble those of modern planktic foraminifera with dinoflagellate photosymbionts. This is consistent with current models of photosymbiosis and calcification in planktic foraminifera and suggests that Acarinina and Morozovella relied heavily on photosymbionts for nutrition.

Acarinina and Morozovella species resemble modern, strongly photosymbiotic taxa in their association with low and mid latitude nearsurface water masses. However, their test morphologies differ greatly from those of extant taxa that bear obligate photosymbionts. Earliest Paleocene taxa that exhibit a similar paleohabitat association and similar size-related isotopic trends are characterized by still different test morphologies. These comparisons suggest that (1) throughout geologic time, strong reliance on photosymbiont activity has been closely linked to habitat, but not to test morphology; (2) photosymbiosis has been a common and convergently evolved strategy of planktic foraminifera over geologic time, and (3) modern relationships between planktic foraminiferal test morphology and photosymbiont dependence are largely an artifact of geologically recent phylogenetic relationships and shared ecologic strategies.

Intersite comparison suggests that the stable isotopic signals of narrowly constrained size fractions of a late Paleocene Acarinina or Morozovella species can be used to reconstruct the magnitude and direction of relative variation in equilibrium stable isotopic values throughout its geographic and temporal range. This is supported by analogy with extant photosymbiotic taxa. However, since photosynthetic depletion of 12C leaves 13C-enriched HCO3-for calcification, the carbon isotopic values of Acarinina and Morozovella tests may have been consistently greater than paleoseawater values. Failure to account for this effect could lead to overestimation of late Paleocene marine productivity.

Ediacaran fossils are taphonomically similar to impressions of fossil plants common in quartz sandstones, and the relief of the fossils suggests that they were as resistant to compaction during burial as some kinds of Pennsylvanian tree trunks. Fossils of jellyfish are known from siderite nodules and fine-grained limestone, and even in these compaction-resistant media were more compressed during burial than were the Vendobionta. Vendobionta were constructed of materials that responded to burial compaction in a way intermediate between conifer and lycopsid logs. This comparative taphonomic study thus falsifies the concept of Vendobionta as thin soft-bodied creatures such as worms and jellyfish.

Lichens, with their structural chitin, present a viable model for the observed preservational style of Vendobionta, as well as for a variety of other features that now can be reassessed from this new perspective. The diversity of Ediacaran body plans can be compared with the variety of form in fungi, algae, and lichens. The large size (ca. 1 m) of some Ediacaran fossils is reasonable for sessile photosynthetic symbioses, and much bigger than associated burrows of metazoans not preserved. Microscopic tubular structures and darkly pigmented cells in permineralized late Precambrian fossils from Namibia and China are also compatible with interpretation as lichens. The presumed marine habitat of Ediacaran fossils is not crucial to interpretation as lichens, because fungi and lichens live in the sea as well as on land.

More than 300 coots (Fulica americana) became frozen in Spring Lake, Tazewell County, Illinois, on December 1, 1985. This catastrophic event permitted 8 weeks of taphonomic observations, which showed that ice forms a stable substrate which permits terrestrial taphonomic processes to be imprinted on lacustrine deposits. Bird and mammal scavengers attacked coot carcasses in different manners, resulting in distinct disarticulation sequences. Bird scavengers preferentially fed on the head, neck, and breast-wing complex, causing early disarticulation of bones in these areas, late loss of hindlimb joints, and minimal bone damage. In contrast, mammal scavengers concentrated their attention on the hindlimb and tail region, resulting in bone breakage and early disarticulation of these body parts, but late disarticulation of the breast-wing complex. These data demonstrate that scavenger-specific feeding behaviors significantly influence disarticulation patterns early in assemblage formation, while anatomy may exert increasingly greater influence on disarticulation patterns as carasses become less attractive to scavengers. Finally, because taphonomic processes change in intensity and type through time, bone frequency and modification patterns will vary according to the time at which the patterns are arrested by burial. Thus, bone frequency and modification patterns should provide an index to the relative importance of specific biotic agents and of anatomy in fossil disarticulation patterns as well as an estimate of the time between death and burial.

Paleoecologists have long sought to obtain estimates of the sizes of extinct populations. However, even in ideal cases, accurate counts of individuals have been hampered by the fact that many organisms disarticulate after death and leave their remains in the form of multiple, separated parts. We here analyze the problem of estimating numbers of individuals from collections of parts by developing a general counting theory that elucidates the major contributing variables. We discover that the number of unique individuals of a particular species that are represented in a fossil collection can be described by an intricate set of relationships among (1) the number of body parts that were recovered, (2) the number of body parts that were possessed by organisms belonging to that species, and (3) the number of individuals of that species that served as the source of the parts from which the paleontological sample was obtained (the size of the “sampling domain”). The “minimum number of individuals” and “maximum number of individuals” methods currently used by paleontologists to count individuals emerge as end members in our more general counting theory. The theory shows that the numbers of individuals of a species that are represented in a sample of body parts is fully tractable, at least in a theoretical sense, in terms of the variables just mentioned. The bad news is that the size of the “sampling domain” for a species can never be known exactly, thus placing a very real limit on our ability to count individuals rigorously. The good news is that one can often make a reasonable guess regarding the size of the sampling domain, and can therefore make a more thoroughly informed choice regarding how to estimate numbers of individuals. By isolating the variables involved in determining the numbers of individuals in paleontological samples, we are led to a better appreciation of the limits, and the possibilities, that are inherent in the fossil record.