Fossil Information Research Articles

An evaluation of fossil tip-dating versus node-age calibrations in tetraodontiform fishes (Teleostei: Percomorphaceae)

Time-calibrated phylogenies based on molecular data provide a framework for comparative studies. Calibration methods to combine fossil information with molecular phylogenies are, however, under active development, often generating disagreement about the best way to incorporate paleontological data into these analyses. This study provides an empirical comparison of the most widely used approach based on node-dating priors for relaxed clocks implemented in the programs BEAST and MrBayes, with two recently proposed improvements: one using a new fossilized birth–death process model for node dating (implemented in the program DPPDiv), and the other using a total-evidence or tip-dating method (implemented in MrBayes and BEAST). These methods are applied herein to tetraodontiform fishes, a diverse group of living and extinct taxa that features one of the most extensive fossil records among teleosts. Previous estimates of time-calibrated phylogenies of tetraodontiforms using node-dating methods reported disparate estimates for their age of origin, ranging from the late Jurassic to the early Paleocene (ca. 150–59Ma). We analyzed a comprehensive dataset with 16 loci and 210 morphological characters, including 131 taxa (95 extant and 36 fossil species) representing all families of fossil and extant tetraodontiforms, under different molecular clock calibration approaches. Results from node-dating methods produced consistently younger ages than the tip-dating approaches. The older ages inferred by tip dating imply an unlikely early-late Jurassic (ca. 185–119Ma) origin for this order and the existence of extended ghost lineages in their fossil record. Node-based methods, by contrast, produce time estimates that are more consistent with the stratigraphic record, suggesting a late Cretaceous (ca. 86–96Ma) origin. We show that the precision of clade age estimates using tip dating increases with the number of fossils analyzed and with the proximity of fossil taxa to the node under assessment. This study suggests that current implementations of tip dating may overestimate ages of divergence in calibrated phylogenies. It also provides a comprehensive phylogenetic framework for tetraodontiform systematics and future comparative studies.

The fossilized birth-death process for coherent calibration of divergence-time estimates.

Time-calibrated species phylogenies are critical for addressing a wide range of questions in evolutionary biology, such as those that elucidate historical biogeography or uncover patterns of coevolution and diversification. Because molecular sequence data are not informative on absolute time, external data--most commonly, fossil age estimates--are required to calibrate estimates of species divergence dates. For Bayesian divergence time methods, the common practice for calibration using fossil information involves placing arbitrarily chosen parametric distributions on internal nodes, often disregarding most of the information in the fossil record. We introduce the "fossilized birth-death" (FBD) process--a model for calibrating divergence time estimates in a Bayesian framework, explicitly acknowledging that extant species and fossils are part of the same macroevolutionary process. Under this model, absolute node age estimates are calibrated by a single diversification model and arbitrary calibration densities are not necessary. Moreover, the FBD model allows for inclusion of all available fossils. We performed analyses of simulated data and show that node age estimation under the FBD model results in robust and accurate estimates of species divergence times with realistic measures of statistical uncertainty, overcoming major limitations of standard divergence time estimation methods. We used this model to estimate the speciation times for a dataset composed of all living bears, indicating that the genus Ursus diversified in the Late Miocene to Middle Pliocene.

Bayesian Estimation of Speciation and Extinction from Incomplete Fossil Occurrence Data

The temporal dynamics of species diversity are shaped by variations in the rates of speciation and extinction, and there is a long history of inferring these rates using first and last appearances of taxa in the fossil record. Understanding diversity dynamics critically depends on unbiased estimates of the unobserved times of speciation and extinction for all lineages, but the inference of these parameters is challenging due to the complex nature of the available data. Here, we present a new probabilistic framework to jointly estimate species-specific times of speciation and extinction and the rates of the underlying birth-death process based on the fossil record. The rates are allowed to vary through time independently of each other, and the probability of preservation and sampling is explicitly incorporated in the model to estimate the true lifespan of each lineage. We implement a Bayesian algorithm to assess the presence of rate shifts by exploring alternative diversification models. Tests on a range of simulated data sets reveal the accuracy and robustness of our approach against violations of the underlying assumptions and various degrees of data incompleteness. Finally, we demonstrate the application of our method with the diversification of the mammal family Rhinocerotidae and reveal a complex history of repeated and independent temporal shifts of both speciation and extinction rates, leading to the expansion and subsequent decline of the group. The estimated parameters of the birth-death process implemented here are directly comparable with those obtained from dated molecular phylogenies. Thus, our model represents a step towards integrating phylogenetic and fossil information to infer macroevolutionary processes.

Divergence Times and the Evolutionary Radiation of New World Monkeys (Platyrrhini, Primates): An Analysis of Fossil and Molecular Data.

The estimation of phylogenetic relationships and divergence times among a group of organisms is a fundamental first step toward understanding its biological diversification. The time of the most recent or last common ancestor (LCA) of extant platyrrhines is one of the most controversial among scholars of primate evolution. Here we use two molecular based approaches to date the initial divergence of the platyrrhine clade, Bayesian estimations under a relaxed-clock model and substitution rate plus generation time and body size, employing the fossil record and genome datasets. We also explore the robustness of our estimations with respect to changes in topology, fossil constraints and substitution rate, and discuss the implications of our findings for understanding the platyrrhine radiation. Our results suggest that fossil constraints, topology and substitution rate have an important influence on our divergence time estimates. Bayesian estimates using conservative but realistic fossil constraints suggest that the LCA of extant platyrrhines existed at ca. 29 Ma, with the 95% confidence limit for the node ranging from 27–31 Ma. The LCA of extant platyrrhine monkeys based on substitution rate corrected by generation time and body size was established between 21–29 Ma. The estimates based on the two approaches used in this study recalibrate the ages of the major platyrrhine clades and corroborate the hypothesis that they constitute very old lineages. These results can help reconcile several controversial points concerning the affinities of key early Miocene fossils that have arisen among paleontologists and molecular systematists. However, they cannot resolve the controversy of whether these fossil species truly belong to the extant lineages or to a stem platyrrhine clade. That question can only be resolved by morphology. Finally, we show that the use of different approaches and well supported fossil information gives a more robust divergence time estimate of a clade.

The real females of human evolution

When "woman-the-gatherer" was first proposed as a counter to "man-the-hunter," we were only beginning to understand the many faces of primate females. In ensuing decades we have learned about the skills and talents of female chimpanzees in tool using, hunting, and transmitting behaviors from one generation to the next as teachers, and across space as newcomers to neighboring communities. The perspective of evolutionary time highlights the continuity of female lives from the origin of mammals to the origin of Homo sapiens. The combination of behavioral, fossil, and archeological information aid in reconstructing key ingredients acquired by females along the way that contributed to the success of our species.

Age, origins and extinctions of the avifauna of Macaronesia: a synthesis of phylogenetic and fossil information

Understanding the age, origins and extinction of oceanic island biota has captivated the interest of evolutionary biologists since Darwin and Wallace. Because oceanic islands are discrete entities of small geographical size but with considerable habitat diversity, they provide ideal templates within which to study evolutionary processes. The peripheral North Atlantic islands, collectively referred to as Macaronesia, are considered a hot spot of biodiversity due to the fact that they contain a large proportion of endemic taxa (ca 25%). Recent molecular studies are providing insight into the patterns of colonization and radiation within the extant avifauna, while paleontological studies have described many extinct avian species, sometimes identifying the causes and chronology of extinction. The aim of this review is to develop an understanding of the evolutionary and biogeographic history of the macaronesian avifauna, combining information from phylogenetic and paleontological studies. We then compare patterns for Macaronesia with those of other oceanic archipelagos to evaluate to what extent patterns may be generalised across regions. Phylogenetic analyses have confirmed the close relationships between endemic macaronesian avifauna and the closest mainland areas (Europe and Africa), however, in contrast to other archipelagos of a similar age, we show that most extant birds appear to have colonized macaronesian archipelagos relatively recently, within the last four million years, despite some islands being approximately 30 million years old. Fossil records support the idea that higher species richness previously existed, with recent dating on bone collagen of selected extinct species suggesting that their extinction coincided with the arrival of aboriginal people ca 2500 years ago in the Canary Islands, or the arrival of Europeans across all the macaronesian islands in the 14th century. It is plausible that these human mediated extinctions may have selectively acted upon older lineages, but there is little evidence available to evaluate this.

A total-evidence approach to dating with fossils, applied to the early radiation of the hymenoptera.

Phylogenies are usually dated by calibrating interior nodes against the fossil record. This relies on indirect methods that, in the worst case, misrepresent the fossil information. Here, we contrast such node dating with an approach that includes fossils along with the extant taxa in a Bayesian total-evidence analysis. As a test case, we focus on the early radiation of the Hymenoptera, mostly documented by poorly preserved impression fossils that are difficult to place phylogenetically. Specifically, we compare node dating using nine calibration points derived from the fossil record with total-evidence dating based on 343 morphological characters scored for 45 fossil (4--20 complete) and 68 extant taxa. In both cases we use molecular data from seven markers (∼5 kb) for the extant taxa. Because it is difficult to model speciation, extinction, sampling, and fossil preservation realistically, we develop a simple uniform prior for clock trees with fossils, and we use relaxed clock models to accommodate rate variation across the tree. Despite considerable uncertainty in the placement of most fossils, we find that they contribute significantly to the estimation of divergence times in the total-evidence analysis. In particular, the posterior distributions on divergence times are less sensitive to prior assumptions and tend to be more precise than in node dating. The total-evidence analysis also shows that four of the seven Hymenoptera calibration points used in node dating are likely to be based on erroneous or doubtful assumptions about the fossil placement. With respect to the early radiation of Hymenoptera, our results suggest that the crown group dates back to the Carboniferous, ∼309 Ma (95% interval: 291--347 Ma), and diversified into major extant lineages much earlier than previously thought, well before the Triassic. [Bayesian inference; fossil dating; morphological evolution; relaxed clock; statistical phylogenetics.]

INTEGRATING FOSSILS WITH MOLECULAR PHYLOGENIES IMPROVES INFERENCE OF TRAIT EVOLUTION

Comparative biologists often attempt to draw inferences about tempo and mode in evolution by comparing the fit of evolutionary models to phylogenetic comparative data consisting of a molecular phylogeny with branch lengths and trait measurements from extant taxa. These kinds of approaches ignore historical evidence for evolutionary pattern and process contained in the fossil record. In this article, we show through simulation that incorporation of fossil information dramatically improves our ability to distinguish among models of quantitative trait evolution using comparative data. We further suggest a novel Bayesian approach that allows fossil information to be integrated even when explicit phylogenetic hypotheses are lacking for extinct representatives of extant clades. By applying this approach to a comparative dataset comprising body sizes for caniform carnivorans, we show that incorporation of fossil information not only improves ancestral state estimates relative to those derived from extant taxa alone, but also results in preference of a model of evolution with trend toward large body size over alternative models such as Brownian motion or Ornstein-Uhlenbeck processes. Our approach highlights the importance of considering fossil information when making macroevolutionary inference, and provides a way to integrate the kind of sparse fossil information that is available to most evolutionary biologists.

Out‐of‐India dispersal of Paliurus (Rhamnaceae) indicated by combined molecular phylogenetic and fossil evidence

AbstractPaliurus (Rhamnaceae) is a small genus with a narrow and disjunct distribution in East Asia and the Mediterranean. Fossil evidence from the Late Cretaceous to the present suggests it once had a broad geographic distribution, encompassing parts of India, North America, Asia, and Europe. To reconstruct the evolutionary history of Paliurus and understand the origin of the disjunction observed today in the Northern Hemisphere, phylogenetic and biogeographical reconstructions were performed based on ITS, trnL‐F, and rbcL sequences. Paliurus is shown to be a monophyletic genus, which could be divided into two clades as suggested by previous studies. Biogeographical inference integrated with fossil information indicates that the origin and dispersal pattern of the genus coincide with the “Out‐of‐India” hypothesis. The genus may have originated in India or other parts of Gondwana and then dispersed to East Asia after the collision of the Indian subcontinent with Eurasia, and to North America via the Bering land bridge. Paliurus appears to have reached the Mediterranean region in the late Oligocene following closure of the Turgai Strait. The uplift of the Qinghai‐Tibet Plateau and the advent of drying and cooling climates during the Miocene may have fragmented the distribution of the genus, shaping the biogeographical patterns observed today. Paliurus populations in different regions either became extinct or adapted to changes in local ecological conditions following global climatic shifts through geological time.

Fossil gaps inferred from phylogenies alter the apparent nature of diversification in dragonflies and their relatives.

BackgroundThe fossil record has suggested that clade growth may differ in marine and terrestrial taxa, supporting equilibrial models in the former and expansionist models in the latter. However, incomplete sampling may bias findings based on fossil data alone. To attempt to correct for such bias, we assemble phylogenetic supertrees on one of the oldest clades of insects, the Odonatoidea (dragonflies, damselflies and their extinct relatives), using MRP and MRC. We use the trees to determine when, and in what clades, changes in taxonomic richness have occurred. We then test whether equilibrial or expansionist models are supported by fossil data alone, and whether findings differ when phylogenetic information is used to infer gaps in the fossil record.ResultsThere is broad agreement in family-level relationships between both supertrees, though with some uncertainty along the backbone of the tree regarding dragonflies (Anisoptera). "Anisozygoptera" are shown to be paraphyletic when fossil information is taken into account. In both trees, decreases in net diversification are associated with species-poor extant families (Neopetaliidae, Hemiphlebiidae), and an upshift is associated with Calopterygidae + Polythoridae. When ghost ranges are inferred from the fossil record, many families are shown to have much earlier origination dates. In a phylogenetic context, the number of family-level lineages is shown to be up to twice as high as the fossil record alone suggests through the Cretaceous and Cenozoic, and a logistic increase in richness is detected in contrast to an exponential increase indicated by fossils alone.ConclusionsOur analysis supports the notion that taxa, which appear to have diversified exponentially using fossil data, may in fact have diversified more logistically. This in turn suggests that one of the major apparent differences between the marine and terrestrial fossil record may simply be an artifact of incomplete sampling. Our results also support previous notions that adult colouration plays an important role in odonate radiation, and that Anisozygoptera should be grouped in a single inclusive taxon with Anisoptera, separate from Zygoptera.

When was the Large Magellanic Cloud accreted on to the Galaxy?

Using fully self-consistent N-body models for the dynamical evolution of the Large Magellanic Cloud (LMC) in the Galaxy, we show that if the LMC initially has an extended old stellar halo before its commencement of tidal interaction with the Galaxy, physical properties of the stars stripped from the LMC stellar halo can have fossil information as to when and where the LMC was accreted onto the Galaxy for the first time. If the epoch of the first LMC accretion onto the Galaxy from outside its viriral radius is more than ~4 Gyr ago (i.e., at least two pericenter passages), the stars stripped from the stellar halo of the LMC can form an irregular polar ring or a thick disk with a size of ~100 kpc and rotational kinematics. On the other hand, if the LMC was first accreted onto the Galaxy quite recently (~ 2 Gyr ago), the stripped stars form shorter leading and trailing stellar stream at R=50-120 kpc. Also distributions of the stripped stars in phase space between the two cases can be significantly different. The derived differences in structure and kinematics of the stripped stars therefore suggest that if we compare the observed three-dimensional (3D) distribution and kinematics of the outer Galactic stellar halo along the polar-axis, then we can give strong constraints on the past orbit of the LMC. We find that the orbital properties of the LMC in the successful formation models of the Magellanic Stream (MS) are consistent with those predicted from recent LambdaCDM cosmological simulations. We conclude that the LMC was accreted onto the Galaxy more than ~4 Gyr ago so that interaction between the LMC, the Small Magellanic Cloud (SMC), and the Galaxy could form the MS and its Leading Arms (LAs).

Fossil Cross-validation of the Dated Ant Phylogeny (Hymenoptera: Formicidae)

As molecular clock methods become more widely used it has become apparent that careful consideration of fossil minimum calibrations is essential. Not only is it necessary to be certain of the taxonomic identity of the fossils and correct placement within the phylogenetic tree, recent studies have suggested that when multiple fossils are available consideration of conflict among fossils must also be taken into account. In this study we investigate whether any of the 43 fossils used by Moreau, et al. (2006) are “inconsistent” and how this affects the results of molecular clock dating analyses and inferred diversification patterns. After considering each of the 43 fossils in turn, following the methods of Near and colleagues (Near & Sanderson, 2004; Near et al., 2005), we found that five fossils are considered to be “inconsistent.” After removing these fossils and reanalyzing the data, we found that excluding these minimum age fossil calibration points did not have a considerable effect on the results. Comparing lineages-through-time plots demonstrate that not only are similar ages recovered, but also that the previously inferred significant shift in diversification rates within the ant phylogeny is not an artifact of the “inconsistent” fossils. These findings suggest that all available fossil information should be included in molecular clock analyses.

Evaluation of Bayesian Models of Substitution Rate Evolution—Parental Guidance versus Mutual Independence

We have evaluated the performance of two classes of probabilistic models for substitution rate variation over phylogenetic trees. In the first class, branch rates are considered to be independent and identically distributed (i.i.d.) stochastic variables. Three versions with respect to the underlying distribution (Gamma, Inverse Gaussian, and LogNormal) are considered. The i.i.d. models are compared with the autocorrelated (AC) model, where rates of adjacent nodes in the tree are AC, so that a node rate is LogNormal distributed around the rate of the parent node. The performance of different models is evaluated using three empirical data sets. For all data sets, it was clear that all tested models extracted substantial knowledge from data when posterior divergence time distributions were compared with the prior distributions and, furthermore, that they clearly outperformed a molecular clock. Moreover, the descriptive power of the i.i.d. models, as evaluated by Bayes factors, was either equal to or clearly better than that of the AC model. The latter effect increased with extended taxon sampling. Likewise, under none of the models could we find compelling evidence, in any of the data sets, for rate correlation between adjacent branches/nodes. These findings challenge previous suggestions of universality of autocorrelation in sequence evolution. We also performed an additional comparison with a divergence time prior including calibration information from fossil evidence. Adding fossil information to the prior had negligible effect on Bayes factors and mainly affected the width of the posterior distribution of the divergence times, whereas the relative position of the mean divergence times were largely unaffected.

What Do Molecular Clocks Tell Us About the Evolution of Ants?

Within the last decade, the interest in using molecular clock methods for divergence dating has greatly increased, including within the ant community. Due to the rich fossil record of ants and the ever-increasing amount of molecular data available, the ants have become the focus of several divergence dating studies (summarized in Moreau 2009). The fossil record of ants dates back ~ 100 million years (Grimaldi et al. 2002; Perrichot et al. 2007) and in some formations contains thousands of individual ant fossils (Dlussky and Rasnitsyn 2009), providing numerous fossils to serve as minimum calibration points in molecular clock analyses. The first attempt to use a molecular clock to date the age of modern ants was implemented by Crozier et al. (1997) using only sequence divergence information between six ant species and a vespid wasp; the results suggested a Jurassic origin for the crown group ants. The first major attempt to incorporate fossil information into a large-scale divergence dating study on the phylogeny of the ants was completed by Moreau et al. (2006), and recovered an age of 140-168 million years for modern ants. Later that same year; Brady et al. (2006) also published a phylogeny of the ants including molecular clock analyses recovering an age of 115-135 million years for the crown group ants. Although these two studies used the same molecular clock method (penalized likelihood, which requires at least one fixed node in the phylogeny), similar fossil information, and similar molecular data, the different ages recovered for modern ants are likely due to the fixed maximum age placed on the root node of each study (Moreau and Bell, unpublished). To determine if newer Bayesian divergence dating methods (Drummond and Rambaut 2007), which do not require a fixed dated node within the phylogeny and also allow for simultaneous estimation of the topology during inference, are more stable across analyses, the molecular data of Moreau et al. (2006), Brady et al. (2006), and Rabeling etal. (2008) were combined. Within a Bayesian framework using 45 fossils as minimum age constraints across the ant phylogeny. these combined data were subjected to three separate molecular clock analyses: 1) topology constrained to the maximum likelihood tree with 185 million years as the maximum age for the root node (following Brady et al. 2006); 2) topology constrained to the maximum likelihood tree and no maximum age for the root node; and 3) topology simultaneously estimated during molecular clock analysis and root node constrained to a maximum age of 185 million years. The results of these analyses suggest that regardless of whether the root node or topology were constrained, a stable age of 139-148 million years is inferred for the crown group ants (Moreau and Bell, unpublished). In addition to providing a date for nodes of interest across a phylogeny, divergence dating can inform biogeographic reconstruction. Ree and Smith (2008) have created Lagrange, a maximum likelihoodbased ancestral range reconstruction method which can account for dispersal probability across time. For example, ifa taxonomic group of interest includes species distributed across Africa and South America, a chronogram (phylogeny with branch lengths proportional to time) and the known distributions for each terminal taxa can be used to specify the probability of dispersal between these (and other) biogeographic areas across time. In the case of Africa and South America at 195 million years, dispersal between these landmasses would likely be given a probability of 1.0 because the continents were in direct contact, whereas dispersal probability decreases toward the present as the continents drift apart. Using the current distributions of each included ant genus and dated chronogram, ancestral range evolution was inferred across the ant phylogeny. Interestingly, the Neotropics are inferred to have played a major role in the evolutionary history of the modern ants. As the Neotropics are currently home to more species and genera of ants, this provides an intriguing picture of ant evolution, and for the first time the biogeographic history of the Formicidae has been inferred using statistical methods (Moreau and Bell, unpublished). Divergence dating also allows for the inference of patterns of diversification across groups of interest. These can include Lineages

Fossil Cross-Validation of the Dated Ant Phylogeny (Hymenoptera: Formicidae)

As molecular clock methods become more widely used it has become apparent that careful consideration of fossil minimum calibrations is essential. Not only is it necessary to be certain of the taxonomic identity of the fossils and correct placement within the phylogenetic tree, recent studies have suggested that when multiple fossils are available consideration of whether any of the fossils are in conflict must also be taken into account. In this study we investigate whether any of the 43 fossils used by Moreau, et al. (2006) are “inconsistent” and how this affects the results of molecular clock dating analyses and inferred diversification patterns. After considering each of the 43 fossils in turn, following the methods of Near and colleagues (Near and Sanderson, 2004; Near et al., 2005), we found that five fossils are considered to be “inconsistent.” After removing these fossils and reanalyzing the data, we found that excluding these minimum age fossil calibration points did not have a significant effect on the results. Comparing lineage-through-time plots demonstrate that not only are similar ages recovered, but also that the significant shift in diversification rates within the ant phylogeny is not an artifact of the “inconsistent” fossils. These findings suggest that all available fossil information should be included in molecular clock analyses.

The virtual and physical preparation of the Collard plesiosaur from Bridgwater Bay, Somerset, UK

The 'Collard Plesiosaur', found in 2003 in Bridgwater Bay on the Somerset coast is the only complete and fully articulated plesiosaur skeleton to have been found in Britain for over 100 years. The 1.5 metre long specimen was preserved in the finegrained and thinly laminated Lower Liassic Kilve Shales. This lithology is susceptible to fluctuations in humidity, severely compromising the integrity of specimens once dry. The priorities for the project were to arrest shale delamination caused by environmental fluctuations and to prepare the specimen for research. The specimen appeared to be mostly well fossilised in a homogeneous, un-cemented matrix, offering excellent potential for non-destructive recovery of fossil information using conventional X-radiography and Computed Tomography before the preparation commenced. Despite the skeleton being variably mineralised, the analyses yielded very detailed images. This 'virtual preparation' helped to inform the subsequent physical preparation, with the conventional radiographs proving most useful. In addition, the project demonstrated that such analyses are not just useful for guiding preparation but also for recording material that might be removed during preparation and highlighting details not visible to the naked eye or that remain buried. During preparation, experimental attempts to consolidate matrix samples were unsuccessful - the shale layers distorted and delaminated. However, the adhesive Paraloid B72 was successfully applied to the sides of the specimen blocks in liberal quantities, providing a useful partial barrier to future changes in atmospheric relative humidity. Scalpels were found to be the most appropriate tools for preparing the specimen, removing one paper-thin layer of shale at a time.

Estimating divergence times among subfamilies in Nymphalidae

The mitochondrial cytochrome oxidase subunit I (COI) gene and the nuclear elongation factor 1α (EF-1α) gene were sequenced from 13 species of Nymphalidae. Phylogenetic trees of Nymphalidae, which is the largest family in butterflies, were constructed based on the sequences determined from 13 species sequenced in our laboratory and an additional 43 species obtained from GenBank using the maximum likelihood (ML) and Bayesian methods. Relative-rate tests between lineages in these phylogenetic trees were performed. On the basis of the results of the relative-rate tests and fossil information of Satyrinae, Nymphalinae and Biblidinae, the average divergence times among the subfamilies are estimated as 44.2–87.1 million years ago (Ma). These results will be helpful for better understanding of the origin and evolution of this family, as well as the divergence time of butterflies and other complex taxa.

Holocene thecideide brachiopods from the north‐western Pacific Ocean: Systematics, life habits and ontogeny

A new species of the lacazelline brachiopod genus Ospreyella is described from shallow cryptic habitats in Palau, western Caroline Islands and Arnd Atoll, Pohnpei, eastern Caroline Islands, north‐western Pacific Ocean. This new taxon, here named Ospreyella palauensis, and representing the third discovery of a species of Ospreyella from the Indo‐Pacific region, is compared with the other two recently described extant species of the genus, O. depressa Lüter from the Great Barrier Reef, Australia, and O. maldiviana Logan from the Maldive Islands, northern Indian Ocean. An ontogenetic sequence is described for the new species and compared with those previously described for other Holocene lacazellines. Additionally, a study of ontogenetic stages in Thecidellina congregata from Saipan in the Northern Mariana Islands shows early‐stage similarities to those of the new species and other lacazellines. These observations on development in extant forms provide important analogies for comparison with ontogenetic stages in ancestral fossil forms and information which may be useful in reconstructing thecideide phylogenetic history.

Robert M. Kleinpell: Founder of the Berkeley School of Stratigraphic Paleontology

Robert M. Kleinpell (1905-1986) has been called the founder of a ‘Berkeley School of West Coast Cenozoic Stratigraphic Paleontology’. Through his personal experiences in carrying out oil exploration in California's Cenozoic stratigraphic successions, his extensive inquiry into the fundamentals of stratigraphic paleontology, and his teaching activity while held in a Japanese prison camp during World War II, Kleinpell developed the basic ingredients for his school of stratigraphic paleontology. His school attracted numbers of students interested in obtaining employment in the oil industry when Kleinpell joined the Department of Paleontology at University of California, Berkeley, in 1953. Kleinpell told his students that the first step toward a basic understanding of stratigraphic geology came from field mapping and recording of all relevant data. The data included collecting fossils from precisely-positioned stratigraphic levels. The fossil occurrence information was then plotted carefully to ascertain associations of taxa that appeared to be unique. The associations that appeared to be unique in time, based on their stratigraphic positions (Kleinpell came to term these ‘congregations’), were used to recognize zones and stages. Kleinpell was firm in his conviction that the zones and stages that he and his students recognized in American West Coast Cenozoic strata were closely similar in principle to the zones and Zonengruppe of Albert Oppel who had worked with ammonite faunas in the European Jurassic. Kleinpell did not publish a diagram or definition of the zones that he espoused because, he said, Oppel had already defined that type of zone. Hollis Hedberg, Kleinpell's former fellow-student in graduate study at Stanford, did include a discussion of the ‘zone’ of Oppel and Kleinpell in the 1976 International Stratigraphic Guide. Subsequent international and American stratigraphic guides and codes have omitted Hedberg's discussion and illustration of the Oppel zone. The West Coast Cenozoic zones and stages, recognized using the methodology established by Oppel, are a primary characteristic of the Berkeley School of Stratigraphic Paleontology.

A gharial from the Oligocene of Puerto Rico: transoceanic dispersal in the history of a non-marine reptile

The Indian gharial (Gavialis gangeticus) is not found in saltwater, but the geographical distribution of fossil relatives suggests a derivation from ancestors that lived in, or were at least able to withstand, saline conditions. Here, we describe a new Oligocene gharial, Aktiogavialis puertoricensis, from deltaic-coastal deposits of northern Puerto Rico. It is related to a clade of Neogene gharials otherwise restricted to South America. Its geological and geographical settings, along with its phylogenetic relationships, are consistent with two scenarios: (i) that a single trans-Atlantic dispersal event during the Tertiary explains the South American Neogene gharial assemblage and (ii) that stem gharials were coastal animals and their current restriction to freshwater settings is a comparatively recent environmental shift for the group. This discovery highlights the importance of including fossil information in a phylogenetic context when assessing the ecological history of modern organisms.