Showing papers in "Paleobiology in 2002"

Faunal and environmental change in the late Miocene Siwaliks of northern Pakistan

Abstract: The Siwalik formations of northern Pakistan consist of deposits of ancient rivers that existed throughout the early Miocene through the late Pliocene. The formations are highly fossil- iferous with a diverse array of terrestrial and freshwater vertebrates, which in combination with exceptional lateral exposure and good chronostratigraphic control allows a more detailed and tem- porally resolved study of the sediments and faunas than is typical in terrestrial deposits. Conse- quently the Siwaliks provide an opportunity to document temporal differences in species richness, turnover, and ecological structure in a terrestrial setting, and to investigate how such differences are related to changes in the fluvial system, vegetation, and climate. Here we focus on the interval between 10.7 and 5.7 Ma, a time of significant local tectonic and global climatic change. It is also the interval with the best temporal calibration of Siwalik faunas and most comprehensive data on species occurrences. A methodological focus of this paper is on controlling sampling biases that confound biological and ecological signals. Such biases include uneven sampling through time, differential preservation of larger animals and more durable skeletal elements, errors in age-dating imposed by uncertainties in correlation and paleomagnetic timescale calibrations, and uneven tax- onomic treatment across groups. We attempt to control for them primarily by using a relative-abun- dance model to estimate limits for the first and last appearances from the occurrence data. This model also incorporates uncertainties in age estimates. Because of sampling limitations inherent in the terrestrial fossil record, our 100-Kyr temporal resolution may approach the finest possible level of resolution for studies of vertebrate faunal changes over periods of millions of years. Approximately 40,000 specimens from surface and screenwash collections made at 555 localities form the basis of our study. Sixty percent of the localities have maximum and minimum age esti- mates differing by 100 Kyr or less, 82% by 200 Kyr or less. The fossils represent 115 mammalian species or lineages of ten orders: Insectivora, Scandentia, Primates, Tubulidentata, Proboscidea, Pholidota, Lagomorpha, Perissodactyla, Artiodactyla, and Rodentia. Important taxa omitted from this study include Carnivora, Elephantoidea, and Rhinocerotidae. Because different collecting methods were used for large and small species, they are treated separately in analyses. Small spe- cies include insectivores, tree shrews, rodents, lagomorphs, and small primates. They generally weigh less than 5 kg. The sediments of the study interval were deposited by coexisting fluvial systems, with the larger emergent Nagri system being displaced between 10.1 and 9.0 Ma by an interfan Dhok Pathan sys- tem. In comparison to Nagri floodplains, Dhok Pathan floodplains were less well drained, with smaller rivers having more seasonally variable flow and more frequent avulsions. Paleosol se- quences indicate reorganization of topography and drainage accompanying a transition to a more seasonal climate. A few paleosols may have formed under waterlogged, grassy woodlands, but most formed under drier conditions and more closed vegetation. The oxygen isotopic record also indicates significant change in the patterns of precipitation be- ginning at 9.2 Ma, in what may have been a shift to a drier and more seasonal climate. The carbon isotope record demonstrates that after 8.1 Ma significant amounts of C 4 grasses began to appear and that by 6.8 Ma floodplain habitats included extensive C4 grasslands. Plant communities with predominantly C3 plants were greatly diminished after 7.0 Ma, and those with predominantly C4 plants, which would have been open woodlands or grassy woodlands, appeared as early as 7.4 Ma. Inferred first and last appearances show a constant, low level of faunal turnover throughout the interval 10.7-5.7-Ma, with three short periods of elevated turnover at 10.3, 7.8, and 7.3-7.0 Ma. The three pulses account for nearly 44% of all turnover. Throughout the late Miocene, species richness declined steadily, and diversity and richness indices together with data on body size imply that community ecological structure changed abruptly just after 10 Ma, and then again at 7.8 Ma. Be- tween 10 and 7.8 Ma the large-mammal assemblages were strongly dominated by equids, with more balanced faunas before and after. The pattern of appearance and disappearance is selective with respect to inferred habits of the animals. Species appearing after 9.0 Ma are grazers or typical of more open habitats, whereas many species that disappear can be linked to more closed vege- tation. We presume exceptions to this pattern were animals of the mixed C

Leanchoilia guts and the interpretation of three-dimensional structures in Burgess Shale-type fossils

Abstract: The Burgess Shale arthropod Leanchoilia superlata Walcott 1912, commonly preserves a three-dimensional axial structure generally interpreted as gut contents. Thin-section examination shows this instead to be phosphatized biserially repeated midgut glands, including exceptional preservation of subcellular features. The preferential mineralization of these structures is related to their unusually high chemical reactivity and probably to an internal source of phosphate. Sub-millimetric lineations previously interpreted as annular musculature are in fact planar, sometimes radially arranged, subdivisions of these glands. Ventral rows of isolated phosphate patches appear to represent the same tissue.In extant arthropods, extensively developed midgut glands are related to a rich but infrequent diet with a primary function in storage. Their conspicuous occurrence in unambiguous fossil predators such as Sidneyia and Laggania (Anomalocaris) suggests they served a similar role in the Cambrian; by extension, their conspicuous occurrence in Leanchoilia suggests it was a predator or scavenger.Phosphatized midguts with a structure essentially indistinguishable from that of Leanchoilia are also found in Burgess Shale Odaraia, Canadaspis, Perspicaris, Sidneyia, Anomalocaris, and Opabinia. All are characterized by a distinctive sub-millimetric arrangement of planar elements that is not found in extant arthropods or trilobites, suggesting they diverged before the last common ancestor of extant forms; i.e., they represent stem-group arthropods.Three-dimensionally preserved guts are widely preserved in the Lower Cambrian Chengjiang biota but, unlike those in the Burgess Shale, appear to be filled with sediment. Although generally interpreted as evidence of deposit feeding, the form of these structures points to early permineralization of (sediment-free) midgut glands that were subsequently altered to clay minerals. There is no evidence of deposit feeding in the Chengjiang; indeed, there is a case to be made for deposit feeding not being generally exploited generally until after the Cambrian.Fossils with three-dimensionally preserved axes from the Lower Cambrian Sirius Passet biota have been interpreted as lobopodians; however, most of the putative lobopodian features find alternative interpretations as aspects of Leanchoilia-type midgut glands. Although Kerygmachela is reliably identified as a stem-group arthropod, its phylogenetic position remains unresolved owing to the non-preservation of critical external features and to the plesiomorphic nature of its Leanchoilia-type midgut.

Evolution of developmental potential and the multiple independent origins of leaves in Paleozoic vascular plants

Abstract: 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 Car- boniferous 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.

Inferring predation intensity in the marine fossil record

Abstract: Accurate estimates of predation intensity, the frequency of mortality from predation, are critical to studies of the evolution of species in response to predation, and to studies of predator-prey systems in general. Most commonly used indirect proxies for predation intensity in the fossil record have logistical or theoretical problems. Direct proxies, using actual traces of predatory activity, such as drilling and repair scars, may hold more promise. However, these direct proxies often have been used in conjunction with optimal foraging models, and in this context, the underlying assumptions and predictions of optimal foraging are examined. Results from theoretical models using optimal foraging suggest that (1) the ratio of internal shell volume to shell thickness of prey (benefit/cost ratio) may be a questionable measurement of prey “value” to the predator, as it fails to account adequately for energetic cost to the predator during pursuit and grappling; (2) drilling and repair frequency are inv...

Paleobiogeographical extinction patterns of Permian brachiopods in the Asian-western Pacific region

Abstract: Spatial and temporal variations in biological diversity are critical in understanding the role of biogeographical regulation (if any) on mass extinctions. An analysis based on a latest da- tabase of the stratigraphic ranges of 89 Permian brachiopod families, 422 genera, and 2059 species within the Boreal, Paleoequatorial, and Gondwanan Realms in the Asian-western Pacific region suggests two discrete mass extinctions, each possibly with different causes. Using species/family rarefaction analysis, we constructed diversity curves for late Artinskian-Kungurian, Roadian-Wor- dian, Capitanian, and Wuchiapingian intervals for filtering out uneven sampling intensities. The end-Changhsingian (latest Permian) extinction eliminated 87-90% of genera and 94-96% of species of Brachiopoda. The timing of the end-Changhsingian extinction of brachiopods in the carbonate settings of South China and southern Tibet indicates that brachiopods suffered a rapid extinction within a short interval just below the Permian/Triassic boundary. In comparison, the end-Guadalupian/late Guadalupian extinction is less profound and varies temporally in different realms. Brachiopods in the western Pacific sector of the Boreal Realm nearly disappeared by the end-Guadalupian but experienced a relatively long-term press extinction span- ning the entire Guadalupian in the Gondwanan Realm. The end-Guadalupian brachiopod diversity fall is not well reflected at the timescale used here in the Paleoequatorial Realm because the life- depleted early Wuchiapingian was overlapped by a rapid radiation phase in the late Wuchiapin- gian. The Guadalupian fall appears to be related to the dramatic reduction of habitat area for the brachiopods, which itself is associated with the withdrawal of seawater from continental Pangea and the closure of the Sino-Mongolian seaway by the end-Guadalupian.

The evolution of plesiosaur and pliosaur morphotypes in the Plesiosauria (Reptilia: Sauropterygia)

Abstract: 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.

Evolution of taxonomic diversity gradients in the marine realm: a comparison of Late Jurassic and Recent bivalve faunas

Abstract: We still have much to learn about the evolution of taxonomic diversity gradients through geologic time. For example, have latitudinal gradients always been as steep as they are now, or is this a phenomenon linked to some form of Cenozoic global climatic differentiation? The fossil record offers potential to address this sort of problem, and this study reconstructs latitudinal diversity gradients for the last (Tithonian) stage of the Jurassic period using marine bivalves. At this time of relative global warmth, bivalves were cosmopolitan in their distribution and the commonest element within macrobenthic assemblages. Analysis of 31 regional bivalve faunas demonstrates that Tithonian latitudinal gradients were present in both hemispheres, though on a much smaller magnitude than today. The record of the Northern Hemisphere gradient is more complete and shows a steep fall in values at the tropical/temperate boundary; the Southern Hemisphere gradient exhibits a more regular decline in diversity with i...

New evidence for the lack of C4 grassland expansions during the early Pliocene at Langebaanweg, South Africa

Abstract: Major C 4 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 C 3 -dominated during the late Neogene (∼5 Ma). In contrast, other Southern Hemisphere sites at similar latitudes show a clear shift to C 4 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.

Holocene Paleoecology and Prehistory in Highland Southern Arabia

Abstract: Dans une haute region desertique hyper-aride de la peninsule arabe, le projet « RASA » a conduit dans le Wadi Sana, une prospection systematique permettant de reconnaitre tout vestige archeologique. Il fut fait appel aux methodes de la geologie et de la paleoecologie pour developper et enregistrer la sequence Holocene aussi bien des paleo-environnements que des activites humaines des hautes terres du Yemen Sud. La phase humide reconnue au debut de l 'Holocene (ca. 10 000-6 000 cal. BP) temoigne d'une vegetation plus dense, d'une population plus importante et d'une meilleure exploitation des terres qu 'a l'Holocene recent. Les chasseurs-cueilleurs du debut de l 'Holocene ont fait appel a des strategies qui leur permettent de developper leurs ressources telles que les brulis et le controle des inondations. De telles strategies permirent de passer a l'elevage et a l'agriculture lorsque, a l 'Holocene moyen, on constate des changements de l 'environnement. Nos recherches suggerent que dans la peninsule arabique, les pratiques de l 'agriculture purent commencer des le Ve millenaire ВС, tres probablement dans des conditions environnementales fort differentes de celles d'aujourd'hui. Nous laissons ouvertes les questions relatives a la nature des cultures et, par ailleurs, au devenir des premiers agriculteurs lorsque l'environnement devint aride.

Estimation of low-latitude paleoclimates using fossil angiosperm leaves: examples from the Miocene Tugen Hills, Kenya

Abstract: 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...

Variation and covariation of skulls and teeth: modern carnivores and the interpretation of fossil mammals

Abstract: 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.

Les fossiles de Cro-Magnon (Les Eyzies-de-Tayac, Dordogne) : nouvelles données sur leur position chronologique et leur attribution culturelle

Abstract: Les squelettes de Cro-Magnon decouverts en 1868 pres des Eyzies-de-Tayac (Dordogne) sont generalement attribues a l’Aurignacien et date de 30 000 BP en reference aux datations C14 des niveaux aurignaciens de l’abri Pataud (Dordogne).Une datation par la methode du carbone 14 en SMA (27 680 ± 270 BP , Beta – 157439) d’une des coquilles de littorine qui leur etait associee demontre que ces fossiles humains seraient dates d’au plus 28 000 BP. Ce resultat demontre que la sepulture de Cro-Magnon ne correspond pas a une sepulture de l’Aurignacien ancien. Plusieurs indices culturels et la datation plaident en faveur d’une attribution a la culture gravettienne.

Size patterns through time: the case of the Early Jurassic ammonite radiation

Abstract: The shell size of 1236 ammonite species representing all known Early Jurassic faunas is analyzed. Size patterns are studied for the entire period and then at the biozone scale for the first four stages of the Jurassic (28 Myr), during which ammonites recovered from the crisis at the Tri- assic/Jurassic (T/J) boundary. Our analysis reveals that (1) a size continuum (normal distribution from ''dwarfs'' to ''giants'') exists for all Early Jurassic ammonites; (2) although there are no sus- tained trends (e.g., no Cope's rule), the succession is not monotonous and patterns may differ con- spicuously from one biozone to the next; and (3) increases and decreases in size range are the most frequent evolutionary styles of size change. The only pattern that can be connected with a particular episode of Early Jurassic ammonite history is the initial increase in size disparity during the first four biozones attributable to phyletic radiation after the T/J crisis. Subsequent correlations with environmental constraints (e.g., sea-level changes), although suspected, cannot be shown.

Evolution of development of the vertebrate dermal and oral skeletons: unraveling concepts, regulatory theories, and homologies

Abstract: It has been contended that Reif's odontode regulation theory is a rival and alternative to Stensioand Orvig'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 pos- teriori. 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, pri- marily, 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 (phy- logenetic) 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 sim- ilarly achieved through ontogenetic developmental differentiation, or a lack thereof. In practice, how- ever, it is not possible to distinguish between patterns of phylogenetic concrescence and differenti- ation because there is no means of identifying homology between individual elements within a squa- mation, 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 skel- etons is explored and it is determined that odontodes are serial homologs, conform only to the bio- logical 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.

Time-averaging, evolution, and morphologic variation

Abstract: Many fossil assemblages are time-averaged, with multiple generations of organisms mixed into a single stratigraphic horizon. A time-averaged sample of a taxon should be more var- iable than a single-generation sample if enough morphologic change occurred during the interval of time-averaging. Time-averaging may also alter correlations between morphologic variables and obscure allometric relationships in an evolving population. To investigate these issues, we esti- mated the variability of six modern, single-generation samples of the bivalve Mercenaria campe- chiensis using Procrustes analysis and compared them with several time-averaged Pleistocene sam- ples of M. campechiensis and M. permagna. Both the modern and the fossil samples ranged in var- iability, but these ranges were virtually identical. Morphology was quite stable over the hundreds to many thousands of years that passed as the assemblages accumulated, and the variabilities of the fossil samples could be used to estimate single-generation variability. At one fossil locality, the environment and paleocommunity changed partway through the collection interval; the morphol- ogy of Mercenaria appears stable above and below the transition but changes across it. This change is similar in magnitude to the differences between geographically separated modern populations, whereas temporal variation within single environmental settings is distinctly less than geographic variation. Analytical time-averaging (the mixing of fossils from different horizons) between paleo- communities increased variability slightly (but not significantly) above that found in living pop- ulations. While its constituent populations appear stable on millennial timescales, M. campechiensis has been evolutionarily static since at least the early to middle Pleistocene.

Response of tropical vegetation to Paleogene warming

Abstract: The late Paleocene-early Eocene transition was characterized by a long period of global warming that culminated with the highest temperatures of the Cenozoic. This interval is associated with a significant increase in plant diversity in temperate latitudes. However, data from tropical regions remain largely unknown. The record of pollen and spore diversity across the late Paleocene to the early middle Eocene of eight sections in central and eastern Colombia was analyzed. Several techniques, including range-through method, rarefaction, bootstrap, detrended correspondence analysis, and Shannon index, were used to assess the significance of the observed diversity pattern. The palynofloral record indicates that the lower to middle Eocene contains a significantly higher palynofloral diversity than the underlying upper Paleocene strata. This pattern is maintained after accounting for sample size, number of samples/time unit, lithofacies, and depositional systems. Eocene palynofloras have higher alpha and beta diversities and a higher equitability than Paleocene palynofloras. This increase in diversity is the product of a gradual increase in the rate of first appearances and a gradual decrease in the rate of last appearances. The early to middle Eocene increase in diversity, as well as the increase in spore abundance and diversity, suggests that tropical (equatorial) climate became wetter during the early to middle Eocene. This interpretation favors causes for early Eocene warming that do not involve significant increases in greenhouse gases. Samples from strata associated with the Paleocene/Eocene thermal maximum were barren for palynomorphs, and the effects of this climatic event on tropical vegetation remains uncertain.

The early formation of the skull in extant and Paleozoic amphibians

Abstract: 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 se- quence 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, squa- mosals, 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 .T he 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 branchio- saurids, 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 dif- ference between salamanders and branchiosaurids is that the morphology of the latter is much less affected by developmental perturbations, such as larval specializations and metamorphosis.

Finite-element analysis of simulated ammonoid septa (extinct Cephalopoda): septal and sutural complexities do not reduce strength

Abstract: 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.

Swimming speed estimation of extinct marine reptiles: energetic approach revisited

Abstract: 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 lev- els). The results support previous inferences about the relative cruising capabilities of Mesozoic marine reptiles (i.e., ichthyosaurs . plesiosaurs . mosasaurs). Stenopterygius, a thunniform ich- thyosaur, 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).

Mitotic topologies and mechanics of Neoproterozoic algae and animal embryos

Abstract: 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.

Le gisement pléistocène moyen de Galeria Pesada (Estrémadure, Portugal) : premiers résultats

Abstract: Les fouilles de la grotte de Galeria Pesada (complexe karstique d’Almonda, Torres Novas) livrent de riches assemblages lithiques et osseux dates du Pleistocene moyen final (fouilles 1997-1999). Les ensembles lithiques sont caracterises par une combinaison d’outils classiques de l’Acheuleen, d’une abondante serie d’outils bifaciaux (foliaces, petits bifaces asymetriques, Keilmesser, etc.) et de nombreux racloirs, souvent en quartz. Cette industrie n’a pas d’equivalent jusqu’a present dans la Peninsule iberique. Elle est associee a une faune dominee par les Cervides et les Equides dont les ossements presentent un fort pourcentage de marques de boucherie, demontrant une exploitation intensive (consommation) des carcasses par les anciens hominides.

Chemical composition and lead isotopy of metal objects from the "royal" tomb and other related finds at Arslantepe, Eastern Anatolia

Abstract: Cet article traite d'objets en metal, de scories et de minerais provenant du centre urbain ď Arslantepe. La majorite des objets analyses ont ete trouves dans la tombe « royale » niveau VI В1 (debut du Bronze ancien I), quelques autres appartiennent au tresor palatial du temple niveau VI A (Uruk recent). Les scories et les minerais proviennent de differents loci et niveaux. Les metaux peuvent etre classes en cuivre (arsenieux), cuivre arsenieux a haute teneur en nickel, argent, plomb et en un nouveau type d'alliage argent-cuivre. Des artefacts en bronze stannifere n'apparaissent pas parmi les objets retrouves. En nous fondant sur les analyses des isotopes du plomb, nous suggerons que les objets argent-cuivre resultent du melange intentionnel de deux metaux, et apportent donc ainsi la plus ancienne preuve des pratiques d'alliage en Anatolie orientale. Pour produire la couleur argent vif de ces objets, la technique de reduction de la dorure (gilty depletion) fut utilisee. Les armes de la tombe « royale » et du tresor palatial, sont en cuivre arsenieux. Ces analyses isotopiques du plomb tendent a confirmer les suggestions, deja emises sur le plan archeologique, qu 'elles etaient importees de Transcaucasie. Les objets en metal trouves a Arslantepe (Bronze ancien) etaient en partie produits sur le site a partir de minerais importes, et en partie importes comme produits finis. Ils representent donc probablement un systeme commercial a deux niveaux : un echange de produits sur le marche, et un niveau eleve du don-echange parmi les elites.

Cyanobacterial blooms as the cause of a Pleistocene large mammal assemblage

Abstract: We investigated the petrography and biochemistry of varved sediments from a Pleistocene mass occurrence of fossil vertebrates in the lake basin of Neumark-Nord (Sachsen-Anhalt, Germany). The carbonate portions of the varves appear to be cyanobacterial layers that have been decomposed by benthic bacteria. The biochemical results obtained by absorption spectroscopy and RP-HPLC with UV-detection show that pigments, and probably toxins, characteristic for cyanobacteria are preserved in the sediment. The results of this study indicate the presence in the lake of large amounts of toxic cyanobacteria that probably occurred in seasonal blooms. It seems likely that these toxic cyanobacterial blooms caused the mass death of the large mammals preserved at the Neumark-Nord locality. This model may explain comparable lithologies and vertebrate occurrences in other Tertiary lake sediments such as the Messel oil shale.

Fabriques des niveaux archéologiques : méthode et premier bilan des apports à l’étude taphonomique des sites paléolithiques

Abstract: Des progres significatifs ont ete realises au cours de la derniere decennie dans l’analyse des fabriques en contexte archeologique, c’est-a-dire dans l’analyse de l’orientation et du pendage du grand axe des objets. Ils concernent a la fois l’exploitation statistique des mesures, la constitution d’un referentiel sur les mecanismes sedimentaires naturels ainsi que l’accroissement du nombre de sites etudies. Ces travaux montrent que les fabriques constituent un outil efficace pour aborder les processus de formation des niveaux paleolithiques. Elles permettent notamment de discriminer clairement les niveaux ayant subi des pedoturbations importantes dues a l’activite biologique et au retrait-gonflement des argiles ou les niveaux affectes par la solifluxion en contexte periglaciaire. Dans l’etat actuel des connaissances, les fabriques utilisees seules ne permettent pas d’estimer reellement l’ampleur des perturbations et doivent pour cela etre confrontees avec d’autres arguments archeologiques et geologiques.

Transformations of society : the changing role of ritual and symbolism in the PPNB and the PN in the Levant, Syria and south-east Anatolia

Abstract: Les societes du Neolithique preceramique В (PPNB) et du Neolithique ceramique (PN) du Levant nord, Syrie et Anatolie du Sud-Est, sont ici abordees du point du vue du rituel et du symbolisme. Alors que le rituel est, au PPNB, modele par la communaute et s 'exprime au travers d 'un symbolisme dominant, vitalite et association homme-animal, il apparait, au Neolithique ceramique, profondement marque par la domesticite. Une hierarchie sociale claire ne peut etre mise en evidence ni au PPNB, ni au PN, a l 'exception de probables reunions de village. Le rituel communautaire au PPNB et la decoration de la ceramique au PN sont consideres comme des systemes (symboliques), regulateurs des societes etudiees. L 'emergence a partir du fonds PPNB de la societe du Neolithique ceramique -probablement constituee de paysans, mais aussi de pasteurs nomades et de chasseurs-cueilleurs - semble le resultat de l'interaction de facteurs socio-economiques complexes.

Characters in context: molluscan shells and the forces that mold them

Abstract: The characters and body parts of organisms are shaped by mechanical forces at two temporal scales. At the ontogenetic scale, the relevant forces are those of every day, exerted by muscles, other metabolism-powered processes, and normal interactions between the body and the external environment. At the phylogenetic scale, forces are strong enough to kill some individuals or to cause reproductive failure. These forces act more intermittently. I explore these ideas by examining the characters of molluscan shells, which grow by the addition of skeletal material along the rim of the open end of a hollow, conical tube that is closed at its narrow (apical) end. In the idealized case of a null shell, the skeleton is a right circular cone, in which the magnitude and direction of growth are the same at each point along the rim. The rate of expansion of the cone is determined by the shell-builder's metabolism. Real shell-builders are exposed to, and themselves exert, forces that affect shell shape. These fo...

L’habitat moustérien de « La Folie » (Poitiers, Vienne) : synthèse des premiers résultats

Abstract: Le gisement mousterien de La Folie illustre un campement de plein air en bordure du Clain d’une rare qualite de preservation. Plusieurs structures ont ete mises au jour (structures empierrees, zone de combustion, trou de poteau avec calage…) revelant une organisation de l’espace claire, avec des zones d’activites bien delimitees. Ce gisement constitue un exemple exceptionnel pour cette periode en Europe occidentale.

Quantifying paleogeography using biogeography: a test case for the Ordovician and Silurian of Avalonia based on brachiopods and trilobites

Abstract: 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.

Dinosaurian and mammalian predators compared

Abstract: 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.

La redécouverte du nouveau-né néandertalien Le Moustier 2

Abstract: En 1996, des ossements d’un perinatal sont retrouves dans les reserves du Musee National de Prehistoire avec les collections des abris du Moustier (Dordogne). Certains sont isoles, d’autres sont pris dans de petites mottes de sediment. Assez vite, il apparait que ces vestiges peuvent etre ceux mis au jour par D. Peyrony dans l’abri inferieur. En 1997, le Musee National de Prehistoire nous confie la fouille des mottes et l’etude des vestiges. A l’issue de la fouille (fin 2000), nous proposons la reconstitution d’un squelette de perinatal exceptionnellement bien conserve. L’etude, morphologique et metrique, preliminaire, des vestiges osseux nous assure que nous sommes en presence d’un Neandertalien. Considerant sa classe d’âge, certains de ses ossements sont uniques dans les annales de la Paleontologie humaine. De surcroit, la fouille des mottes de sediment s’est accompagnee de l’enregistrement de donnees qui permettront de preciser la position de segments du corps dans la tombe. Enfin, cette decouverte remet en cause le nombre d’individus presents dans le gisement de La Ferrassie et l’existence de l’unique sepulture double du Mousterien d’Europe. En ce qui concerne les predecesseurs des Hommes modernes d’Europe, Le Moustier 2 represente donc la plus importante decouverte paleoanthropologique faite en France depuis ces vingt-cinq dernieres annees et en Perigord depuis 1961. Son etude permettra de nombreuses avancees en anthropologie biologique, sur l’ontogenie des Neandertaliens et les pratiques funeraires mousteriennes.