Despite substantial advances in plate tectonic modeling in the last three decades, the postulated position of terranes in the Paleozoic has seldom been validated by faunal data. Fewer studies still have attempted a quantitative approach to distance based on explicit data sets. As a test case, we examine the position of Avalonia in the Ordovician (Arenig, Llanvirn, early Caradoc, and Ashgill) to mid-Silurian (Wenlock) with respect to Laurentia, Baltica, and West Gondwana. Using synoptic lists of 623 trilobite genera and 622 brachiopod genera for these four plates, summarized as Venn diagrams, we have devised proportional indices of mean endemism (ME, normalized by individual plate faunas to eliminate area biogeographic effects) and complementarity (C) for objective paleobiogeographic comparisons. These can discriminate the relative position of Avalonia by assessing the optimal arrangement of inter-centroid distances (measured as great circles) between relevant pairs of continental masses. The proportional indices are used to estimate the “goodness-of-fit” of the faunal data to two widely used dynamic plate tectonic models for these time slices, those of Smith and Rush (1998) and Ross and Scotese (1997). Our faunal data are more consistent with the latter model, which we use to suggest relationships between faunal indices for the five time slices and new rescaled inter-centroid distances between all six plate pairs. We have examined linear and exponential models in relation to continental separation for these indices. For our generic data, the linear model fits distinctly better overall. The fits of indices generated by using independent trilobite and brachiopod lists are mostly similar to each other at each time slice and for a given plate, reflecting a common biogeographic signal; however, the indices vary across the time slices. Combining groups into the same matrix in a “total evidence” analysis performs better still as a measure of distance for mean endemism in the “Scotese” plate model. Four-plate mean endemism performs much better than complementarity as an indicator of pairwise distance for either plate model in the test case.

Cell division is a key biological process in growth, morphogenesis, and reproduction. Despite our improved understanding of the genetics and dynamics of cell division in all major groups of living organisms, paleontological evidence for cell division is largely restricted to silicified (and some carbonaceous) algae and vascular plants where three-dimensional observation is possible. Animal cell division has been documented in the fossil record to a lesser extent; however, such knowledge is highly desirable in the recently revitalized field of evolutionary developmental biology. Two fundamentally different mitotic cell division topologies are preserved in late Neoproterozoic Doushantuo phosphorites (ca. 550–600 million years old) in South China. Doushantuo algal cells (∼20 μm in diameter) are successively cleaved by mitotic division planes that are offset but not deformed by subsequent cytokinesis. Mitotic division planes in successively cleaving Doushantuo animal embryos (several hundred microns in diameter) are also offset. However, in sharp contrast to Doushantuo algae, Doushantuo animal blastomeres repeatedly shift to mechanically stable configurations by disturbing preexisting division planes. This divergence reflects the underlying cytological and developmental differences between algae and animals. Specifically, the presence/absence of rigid cell walls and different cytokinetic mechanisms, coupled with mechanics at mitotic offsets, contribute to the diverging mitotic topologies in Doushantuo algae and animal embryos. These findings not only confirm previous interpretation of Doushantuo fossils but also provide direct paleontological evidence of cell movement in the development of these early animal fossils.

It has been contended that Reif's odontode regulation theory is a rival and alternative to Stensiö and ørvig's lepidomorial theory as means of explaining the evolution of development of the vertebrate dermal and oral skeleton. The lepidomorial theory is a pattern-based theory that provides a homological framework that goes further than the odontode regulation theory in comparing dental papillae and their products, and it provides an explanatory mechanism for such relationships a posteriori. In contrast, the odontode regulation theory is process-based and observes only developmental similarity, providing no means of identifying homologies beyond this. The lepidomorial theory is superior to the odontode regulation theory in its ability to trace homology through the evolution of development of the dermal and oral skeleton. The criteria proposed to identify homology between scales—either within a given individual or taxon, or between different individuals or taxa—are, primarily, vascular architecture and, secondarily, external morphology. External morphology may be excluded on Reif's argument for the overarching principle of differentiation, a hypothesis supported by recent advances in the understanding of dental morphogenesis. Vascular architecture is potentially useful but appears to be determined by tooth/scale morphology rather than reflecting historical (phylogenetic) constraint. Data on the development of epithelial appendages, including teeth, scales, and feathers, indicate that individual primordia develop through progressive differentiation of originally larger, homogenous morphogenetic fields. Thus, there is no mechanism of ontogenetic developmental concrescence, just differentiation. Phylogenetic patterns of concrescence and differentiation are similarly achieved through ontogenetic developmental differentiation, or a lack thereof. In practice, however, it is not possible to distinguish between patterns of phylogenetic concrescence and differentiation because there is no means of identifying homology between individual elements within a squamation, or a dentition (in almost all instances). Thus, phylogenetic patterns of increase and decrease in the numbers of elements constituting dentitions or dermal elements are best described as such; further attempts to constrain precise underlying patterns remain without constraint and outside the realms of scientific enquiry. The application of the homology concept in the dermal and visceral skeletons is explored and it is determined that odontodes are serial homologs, conform only to the biological homology concept at this level of observation, and are devoid of phylogenetic meaning. It is concluded that Reif's theory is close to a universal theory of the evolution of development for the dermoskeleton and dentition, and additional components of theory, including the regulatory basis of temporal and spatial patterning, are tested and extended in light of data on the development of the chick feather array. Finally, the dermoskeleton is identified as an exemplary system for examining the regulatory basis of patterning and morphogenesis as it encompasses and surpasses the repertoire of established model organ systems.

Cruising speeds of Mesozoic marine reptiles have been estimated in the past by using a mathematical model of energetic equilibrium during steady swimming. This method suffered from a significant tendency to overestimate speeds of extant cetaceans for no clear reason, which raised questions about the validity of the approach itself. The present study identifies the factors that caused this shortcoming and proposes corrections and some additional modifications. These include the use of more accurate body shape models, updated metabolic rate models, and optimal rather than critical swimming speeds. The amended method successfully approximates published optimal speeds of several extant marine vertebrates, including cetaceans, showing that the basic framework of the energetic approach is valid. With this confirmation, the method was applied to Mesozoic marine reptiles, by assuming three different metabolic rate categories known in extant swimming vertebrates (i.e., average ectothermic, raised ectothermic, and marine endothermic levels). The results support previous inferences about the relative cruising capabilities of Mesozoic marine reptiles (i.e., ichthyosaurs > plesiosaurs > mosasaurs). Stenopterygius, a thunniform ichthyosaur, was probably capable of cruising at a speed at least comparable to those reported for some extant thunniform teleosts with similar diets (~1 m/second).

Traditionally, the distinction between meraspis and holaspis among trilobites has been based on the achievement of the full adult complement of thoracic segments. Using a large sample (over 700 specimens collected from a single bed) we explore the utility of employing the ontogenetic trajectory of the cranidium as an alternative means to differentiate trilobite growth stages. This method is particularly useful for species represented solely by exuviae and disarticulated individuals. We use geometric morphometrics to examine shape change among cranidia ranging in size from 0.9 mm to 11.6 mm in cephalic length. The 114 measured specimens exhibit a rather continuous gradation in size in which no distinct instars are evident.

The meraspid and holaspid specimens exhibit allometry when partial warp scores and uniform components of shape derived from thin-plate spline analysis are regressed onto log centroid size. To describe allometric shape change, deformation vectors from the smallest to the largest specimen in both ontogenetic stages are presented in three different superimposition settings by using a new software program. We have concluded that a new superimposition method (the Sliding Baseline Registration) is a useful tool for visualizing allometry in organisms that contain an axis of symmetry. As a result, we conclude that allometry is evident in meraspides and holaspides, but the degree of allometry in holaspides is very small relative to that in meraspides. The boundary between meraspis and holaspis in Triarthrus becki appears to correspond to a large change in the rate of ontogenetic change, but neither to a change in the direction of that trajectory nor to a cessation of ontogenetic change. This boundary also corresponds to a cranidium centroid size that matches well previous determinations that holaspis begins at about 2.8 mm in cephalic length.

Teeth are generally the best-preserved elements among mammal fossil remains and are highly diagnostic characters. Consequently, much mammalian paleontological, systematic, and evolutionary research focuses on teeth, so it is important to understand how they vary and covary with other characters. Dental traits within populations of carnivores appear to be more variable than cranial traits, a pattern that results only partly from their usually smaller size. Furthermore, dental traits, although highly correlated with one another, are not highly correlated with cranial traits, which are also highly correlated with one another. Thus, teeth and cranial bones may be subject to quite different selective pressures and genetic/developmental constraints and may suggest different microevolutionary scenarios. Vestigial teeth show significantly greater variability than expected, reflecting the absence of stabilizing selection.

Four vascular plant lineages, the ferns, sphenopsids, progymnosperms, and seed plants, evolved laminated leaves in the Paleozoic. A principal coordinate analysis of 641 leaf species from North American and European floras ranging in age from Middle Devonian through the end of the Permian shows that the clades followed parallel trajectories of evolution: each clade exhibits rapid radiation of leaf morphologies from simple (and similar) forms in the Late Devonian/Early Carboniferous to diverse, differentiated leaf forms, with strong constraint on further diversification beginning in the mid Carboniferous. Similar morphospace trajectories have been documented in studies of morphological evolution in animals; however, plant fossils present unique opportunities for understanding the developmental processes that underlie such patterns. Detailed comparison of venation in Paleozoic leaves with that of modern leaves for which developmental mechanisms are known suggests developmental interpretations for the origination and early evolution of leaves. The parallel evolution of a marginal meristem by the modification of developmental mechanisms available in the common ancestor of all groups resulted in the pattern of leaf evolution repeated by each clade. Early steps of leaf evolution were followed by constraint on further diversification as the possible elaborations of marginal growth were exhausted. Hypotheses of development in Paleozoic leaves can be tested by the study of living plants with analogous leaf morphologies.

Major C4 grass expansions during the late Miocene in both the Northern and Southern Hemispheres had a major impact on biological communities. We report that the diverse terrestrial fauna of Langebaanweg, South Africa, existed in a local environment that remained C3-dominated during the late Neogene (~5 Ma). In contrast, other Southern Hemisphere sites at similar latitudes show a clear shift to C4 grasslands well before 5 Ma. Our results are based on stable isotope analyses of enamel carbonate from four artiodactyl and two perissodactyl families from this locality. We also provide insight into the evolution of the current Mediterranean climate system in this part of South Africa.

Theropod dinosaurs were, and mammalian carnivores are, the top predators within their respective communities. Beyond that, they seem distinct, differing markedly in body form and ancestry. Nevertheless, some of the same processes that shape mammalian predators and their communities likely were important to dinosaurian predators as well. To explore this, we compared the predatory adaptations of theropod dinosaurs and mammalian carnivores, focusing primarily on aspects of their feeding morphology (skulls, jaws, and teeth). We also examined suites of sympatric species (i.e., ecological guilds) of predatory theropods and mammals, emphasizing species richness and the distribution of body sizes within guilds. The morphological comparisons indicate reduced trophic diversity among theropods relative to carnivorans, as most or all theropods with teeth appear to have been hypercarnivorous. There are no clear analogs of felids, canids, and hyaenids among theropods. Interestingly, theropods parallel canids more so than felids in cranial proportions, and all theropods appear to have had weaker jaws than carnivorans. Given the apparent trophic similarity of theropods and their large body sizes, it was surprising to find that species richness of theropod guilds was as great as or exceeded that observed among mammalian carnivore guilds. Separation by body size appears to be slightly greater among sympatric theropods than carnivorans, but the magnitude of size difference between species is not constant in either group. We suggest that, as in modern carnivoran guilds, smaller theropod species might have adapted to the threats posed by much larger species (e.g., tyrannosaurs) by hunting in groups, feeding rapidly, and avoiding encounters whenever possible. This would have favored improved hunting skills and associated adaptations such as agility, speed, intelligence, and increased sensory awareness.

Multiple regression models were developed for seasonal test inputs to, and preservation of, marsh foraminiferal assemblages for a two-year period at Bombay Hook National Wildlife Refuge (BHNWR; Smyrna, Delaware). Seasonal assemblages were quite variable and yielded poor regression models. However, signal/noise ratios were amplified using artificially time-averaged (ATA) assemblages, in which separate dead and live abundances of the most abundant species were summed for all seasons. Regression models that used ATA species abundances to retrodict original sample depths accounted for up to ~99% (p < 0.0001) and ~91% (p < 0.023) of the variation of dead and live ATA assemblages, respectively, and usually retrodicted sample depths within 2–3 cm of actual depths.

Artificially time-averaged assemblages were also used to extract multidecadal- to centennial-scale sea-level signals from near-surface assemblages at BHNWR formed during the past few centuries. The BHNWR sea-level curve closely resembles one previously published for marshes in Clinton, Connecticut (also based on foraminifera). The technique of artificial time-averaging therefore links the temporal scales of ecology and paleobiology by extracting high-resolution paleoenvironmental signals preserved in the fossil record.

The dichotomy between short-necked, large-headed “pliosaurs” and long-necked, small-headed “plesiosaurs” has formed the basis of plesiosaur taxonomy for over one hundred years. Recent work has cast doubt on the taxonomic validity of this dichotomy, suggesting that the pliosaur morphotype may have evolved independently in more than one clade. This paper quantifies the variation in body proportion in the clade Plesiosauria using principal component analysis and demonstrates that the traditional plesiosaur/pliosaur dichotomy is an oversimplified view of the range of morphologies present in the group. The topology of the clade is mapped into the morphospace, demonstrating that the pliosaur morphotype evolved three times from two different regions of morphospace. Both the range of body morphologies displayed by plesiosaurs and the evolutionary history of those morphologies, are more complex than previously supposed.

The Dominican Republic amber, as a data set for ecological investigation, is subject to unique biases. To understand the paleoecology of Hispaniola during the Miocene it is not sufficient only to identify the amber inclusions, the biases of entrapment also need to be elucidated. This study compares the spider (Araneae) fauna from Recent Neotropical rainforests with assemblages from Dominican Republic amber deposits. This comparison demonstrates that the site of the original resin secretion is farther removed from the ground layer than has previously been suggested. In many spider families, particularly the web weavers, mature males lead an active lifestyle as they roam in search of the more sedentary females. Male spiders are significantly more common as amber inclusions than females. When the sex ratios of preserved spiders are examined in relation to the predation strategies of their extant relatives, at family level, wandering spiders appear more susceptible to entombment than sedentary spiders. This implies that spiders, and presumably other co-occurring organisms, were trapped primarily by wandering onto sticky resin rather than by being engulfed passively by less viscous, flowing resin.

Finite-element analysis of circular septum models indicates that (1) anticlastic fluting weakened the last septa of the same radius of curvature by a factor of about 2.5 relative to the tensile stresses in a sphere of nacre, (2) septa with ammonitic sutures were stronger than those with goniatitic sutures of the same thickness, and (3) septa with more “complex” ammonitic sutures were stronger at the edge between lobes and saddles than “simple” ones. These results contradict recent claims that ammonoid septa became weaker as sutural complexity increased from goniatitic through ammonitic, so that the most complex sutures were limited to the shallowest habitats. The smaller marginal flutes of complex septa were relatively strong, allowing them to be thinner than the central septum and still act as elastic wall supports. Many Mesozoic ammonoids with highly sinuous sutures occurred in deep epeiric and open-ocean habitats, whereas it is those with secondarily reduced, ceratitic sutures that were typically associated with restricted shallow basins.

The vomeronasal (VN) system is a pheromone-processing sensory system of tetrapods. Tetrapods use pheromones to communicate territorial boundaries, reproductive status, sex, and species identity. Presumed impressions of VN bulbs on phytosaur frontals led to a claim that phytosaurs possessed the VN system. However, in extant crocodilians, which lack the VN system, the corresponding impressions are associated not with cerebral tissue but with the ophthalmic nerves. Phytosaur head morphology was not conducive to pheromone collection. The extant phylogenetic bracket suggests that all extinct archosaurs, including phytosaurs, lacked the VN system. Without the pheromonal sense, they would not have used chemical means to convey territorial boundaries, reproductive status, sex, and species identity. Instead, they would have used visual, acoustic, and tactile cues, as in extant archosaurs and other tetrapods in which the VN sense is reduced or absent.

Understanding of evolutionary changes in the vertebrate skull is greatly influenced by the knowledge of ontogeny. Extant amphibians are an outstanding example in this field, because their life cycles are complex and have been intensively studied. At the same time, fossil material of Paleozoic amphibians has become available that sheds light on the ontogeny of a long-extinct clade, prompting comparison with recent forms. In this paper, the formation of the skull of a Paleozoic amphibian (the branchiosaurid temnospondyl Apateon) is analyzed in comparison with that of an extant salamander (the hynobiid Ranodon). Both temporal patterns (sequence of ossification) and spatial patterns (morphological changes) are described. The general results are that (1) the sequence of ossification is similar in many aspects, and (2) most dermal bones share fundamental similarities in morphogenesis, although sometimes the morphological result in adults may differ conspicuously.

The comparison reveals that the parasphenoid, premaxillae, maxillae, frontals, parietals, squamosals, and prefrontals are strikingly similar in their mode of growth. In particular, the appearance of the earliest primordia and the subsequent stages of morphological transformation are almost identical. The development of the pterygoids and nasals is different in the earliest stages, but the ontogenetic trajectories converge in later stages. In Ranodon and other transforming urodeles, the pterygoids and vomers experience extensive resorption during metamorphic climax, whereas in branchiosaurids the morphology of this region remains stable throughout ontogeny.

In the sequence of cranial ossifications, the early appearance of the premaxilla and tooth-bearing elements of the palate characterize both genera, but the maxilla forms much later in Ranodon. The ectopterygoid, absent in all salamanders, is the last palatal element to appear in branchiosaurids. In the skull roof, the parietals, frontals, and squamosals are the first bones to form in both groups. Conversely, the circumorbital elements and tabular are among the last ossifications in branchiosaurids, and the prefrontal and lacrimal (the only circumorbital bones present in salamanders) form within the same interval in urodele ontogeny. The septomaxilla is the last dermal element to ossify in both groups. Comparison with caecilians and anurans indicates that salamanders are much more similar to Paleozoic branchiosaurids than to other extant lissamphibians. A major difference between salamanders and branchiosaurids is that the morphology of the latter is much less affected by developmental perturbations, such as larval specializations and metamorphosis.

In the last decade, several statistical models have been proposed to quantify the relationships among leaf morphological characters and climate parameters. The models, based on modern plants and climate from varying geographic areas, and derived using varied statistical analyses, were intended for paleoclimatic reconstruction based on the morphological characters of fossil leaves. The goal of the research presented here is to evaluate these and newly constructed models in order to estimate past climate in tropical Africa from fossil leaves. Models found to estimate current climate most accurately using modern African leaf assemblages are used to estimate past climate from fossil leaves at three middle and late Miocene paleobotanical sites in the Tugen Hills, Kenya.

Regression models derived from predictor data having a majority of sites from higher than 25°N-S latitude consistently overestimate mean annual precipitation at modern African sites by an average of 990 mm. A pronounced cold season, as at high latitudes, has an inhibitory effect on leaf size, the primary correlate of rainfall, and may negatively affect the accuracy with which models derived from high latitudes estimate rainfall in the Tropics, which lack a cold season. Models derived from data sets consisting of samples from 25°N-S latitude yield similar and more accurate estimates for mean annual precipitation at modern African sites, expressing the predominant relationship between yearly or seasonal rainfall and leaf size at lower latitudes. Models that estimate temperature parameters, whether derived from high or low latitudes, were found to be inaccurate with modern tropical African samples. The hypothesis is proposed that non-entire margins, the primary correlate with temperature, are more likely to be present on the leaves of deciduous plants, whether they lose their leaves because of cold (at high latitudes) or seasonal drought (at low latitudes). Generally, this study indicates that modern predictor data sets from which models are drawn should be representative of the predominant climate parameters expected among fossil sites.

Four regression models are approximately equal in their ability to estimate accurately mean annual precipitation at the modern African sites. They are derived from African data or combinations of African plus other low-latitude data and provide consistent rainfall reconstructions at the three fossil sites. Estimates are 955 ± 29 to 1185 ± 96 mm/yr for Kabarsero (12.6 Ma), 490 ± 46 to 693 ± 32 mm/yr for Waril (9–10 Ma), and 730 ± 30 to 1019 ± 32 mm/yr for Kapturo. Wet-months precipitation estimates are 857 ± 30 mm/yr for Kabarsero, 437 ± 30 for Waril, and 627 ± 30 for Kapturo.

These are the first quantitative estimates of climate for the Miocene of East Africa. The seasonally dry climate inferred for Waril may indicate that the Asian monsoon was established by about 9–10 Ma. Alternatively, the seasonally dry climate may reflect local topographic changes caused by rift valley development. However, the plant localities suggest that, although progressive drying may have been a trend during the Tertiary, there was not a unidirectional change from forested to open environments in the Kenya rift between 12.6 and 6.8 Ma, the time interval just prior to the origin of hominids.

Exceptional examples of planispiral ammonites that were infested by epizoans during life display alterations of their normal coiling. Most commonly, the epizoan(s) settled on the venter of the ammonite and constituted an obstacle for the whorl tube grown one whorl later; this caused lateral deviation of the whorl tube and tilting of the ammonoid because of changes in the hydrostatic condition; from here on, the whorl tube periodically crossed the venter of the preceding whorl, thereby producing a zigzag coiling pattern. Some epizoans, which were particularly centered on the midventer, provoked detachment between whorls. In a few cases, lateral placement of the epizoan did not directly obstruct the normal growth path of the ammonite but induced a trochospiral coiling pattern. Both the zigzag and the trochospiral pattern were created when the ammonite tried to maintain the growth direction within the vertical plane at the same time as whorls remained in contact along a differentiated dorsal epithelium. The aperture reacted to changes in growth direction, to maintain also a permanent angle with the vertical direction. Growth direction, then, was a major morphogenetic parameter in ammonites, because it contained the necessary instructions for correct shell coiling. The model based on the observation of fabricational defects has been tested by a theoretical model by which the different situations so far observed are simulated and in which the parameters are the morphogenetic instructions inferred to have been present in the biological system.

In the late 1930s and early 1940s, a professionally disparate group of biologists forged an evolutionary synthesis that placed natural selection at the center of the changes in genes and in morphology that have produced the diversity of organisms in the biosphere. The chief architects of this famous synthesis included population geneticists, zoologists, botanists, and paleontologists, but not developmental biologists. Among the tenets of the synthesis was the finding that evolution generally proceeded in populations by selection from among a variety of alleles of structural genes that were provided by various forms of mutation, and which had small but cumulative effects. Some workers concluded that even the evolution of major novelties, such as the distinctive body-plans of different animal phyla, could be produced by the accumulation of such small changes in gene products. Whether the high rates of morphological change inferred from the fossil record could have actually been achieved by these processes alone was not clear.