Showing papers in "Paleobiology in 1993"

Ten years in the library: new data confirm paleontological patterns.

Abstract: A comparison is made between compilations of times of origination and extinction of fossil marine animal families published in 1982 and 1992. As a result of ten years of library research, half of the information in the compendia has changed: families have been added and deleted, low-resolution stratigraphic data been improved, and intervals of origination and extinction have been altered. Despite these changes, apparent macroevolutionary patterns for the entire marine fauna have remained constant. Diversity curves compiled from the two data bases are very similar, with a goodness-of-fit of 99%; the principal difference is that the 1992 curve averages 13% higher than the older curve. Both numbers and percentages of origination and extinction also match well, with fits ranging from 83% to 95%. All major events of radiation and extinction are identical. Therefore, errors in large paleontological data bases and arbitrariness of included taxa are not necessarily impediments to the analysis of pattern in the fossil record, so long as the data are sufficiently numerous.

Discordance and concordance between morphological and taxonomic diversity

Abstract: Morphological and taxonomic diversity each provide insight into the expansion and contraction of major biological groups, while the nature of the relationship between these two aspects of diversity also has important implications for evolutionary mechanisms. In this paper, I compare morphological and taxonomic diversity within the classes Blastoidea and Trilobita, and within the trilobite clades Libristoma, Asaphina, Proetida, Phacopida, and Scutelluina. Blastoid morphology is quantified with homologous landmarks on the theca, and trilobite form is measured with a Fourier description of the cranidium. Morphological diversity is measured as the total variance among forms in morphological space (proportional to the mean squared distance among forms). Blastoid taxonomic diversity is based on published compilation of stratigraphic ranges of genera. The Zoological Record was used to determine the number of new species of trilobites described since the publication of the Treatise; temporal patterns in species richness are similar to those for generic richness based on the Treatise, suggesting a common underlying signal. Morphological variety and taxonomic richness often increase together during the initial diver- sification of a clade. This pattern is consistent with diffusion through morphospace, although some form of adaptive radiation cannot be ruled out. Morphological diversity varies little throughout much of the history of Proetida, a pattern that may suggest major constraints on the magnitude and direction of evolution, and that agrees with the perception of Proetida as a morphologically con- servative group. Two major patterns are seen during the decline of clades. In Blastoidea, Trilobita, Libristoma, and Asaphina, morphological diversity is maintained at substantial levels, and in fact continues to increase, even in the face of striking reductions in taxonomic richness. This pattern suggests continued diffusion through morphospace and taxonomic attrition that is effectively non- selective with respect to morphology. In Phacopida, Scutelluina, and to some extent in Proetida, morphological diversity decreases along with taxonomic diversity. This pattern suggests hetero- geneities such as elevated extinction and/or reduced origination in certain regions of morphospace. As found previously for the echinoderm subphylum Blastozoa, all studied clades of trilobites except Proetida show maximal morphological diversity in the Mid-Late Ordovician and maximal taxonomic diversity sometime during the Ordovician, suggesting some degree of common control on diver- sification patterns in these groups.

Seafood through time; changes in biomass, energetics, and productivity in the marine ecosystem

Abstract: The biomass of marine consumers increased during the Phanerozoic. This is indicated by the increase in both fleshiness and average size of individuals of dominant organisms, coupled with the conservative estimate that dominant organisms in the Cenozoic are at least as abundant as those in the Paleozoic. As faunal dominants replaced one another during the Phanerozoic the general level of metabolic activity increased due to both increase in basal metabolism and increase in more energetic modes of life. This demonstrates that the expenditure of energy by marine consumers has increased with time as well. There is a time lag in the expansion of more energetic life habits from environmental settings known to have high food supply into regions expected to have lower rates of food supply (e.g., bivalves into offshore carbonate environments or deep bur- rowing deposit feeders into the full range of shelf environments), and a time lag in diversification of energetic modes of life (e.g., predation or deep burrowing deposit feeding) for long intervals after they first appeared. This suggests that the supply of food increased across the whole spectrum of marine habitats during the Phanerozoic. The great diversification of specialized predators es- pecially suggests that biomass increase took place all the way down the food chain to the level of primary production. The development of plant life on land and the impact of land vegetation on stimulating productivity in coastal marine settings, coupled with the transfer of organic material and nutrients from coastal regions to the open ocean, and the increase through time in diversity and abundance of oceanic phytoplankton all point to increased productivity in the oceans through the Phanerozoic.

Phylogenies and angiosperm diversification

Abstract: Approaches to patterns of diversification based on counting taxa at a given rank can be misleading, even when all taxa are monophyletic. Such "rank-based" approaches are unable to reflect a hierarchy of evolutionary events because taxa of the same rank cannot be nested within one another. Phylogenetic trees specify an order of origination of characters and clades and can therefore be used in some cases to test hypotheses on causal relationships between characters and changes in diversity. "Tree-thinking" also clarifies discussions of the age of groups, by distinguishing between splitting of the stem-lineage from its sister group and splitting of the crown-group into extant clades. Cladistic evidence that Pentoxylon, Bennettitales, and Gnetales are the sister group of angiosperms implies that the angiosperm line (angiophytes) existed by the Late Triassic. The presence of primitive members of five basic angiosperm clades indicates that the crown-group (angiosperms) had begun to diversify by the mid-Early Cretaceous (Barremian-Aptian), but not necessarily much earlier. The greatest unresolved issue raised by cladistic analyses concerns the fact that the angiosperm tree can be rooted in two almost equally parsimonious positions. Trees rooted near Magnoliales (among "woody magnoliids") suggest that the angiosperm radiation may have been triggered by the origin of intrinsic traits, e.g., a fast-growing, rhizomatous habit in the paleoherb and eudicot subgroup. However, trees rooted among paleoherbs, which are favored by rRNA data, imply that these traits are basic for angiosperms as a whole. This could mean that the crown-group originated not long before its radiation, or, if it did originate earlier, that its radiation was delayed due to extrinsic factors. Such factors could be a trend from environmental homogeneity and stability in the Jurassic to renewed tectonic activity and disturbance in the Early Cretaceous. Potentially relevant pre- Cretaceous fossils cannot be placed with confidence, but may be located along the stem-lineage (stem angiophytes); their generally paleoherb-like features favor the paleoherb rooting. The history of angiophytes may parallel that of Gnetales: some diversification of the stem-lineage in the Late Triassic, near disappearance in the Jurassic, and vigorous radiation of the crown-group in the Early Cretaceous.

Contributions of individual taxa to overall morphological disparity

Abstract: Two methods are discussed for assessing the contributions of subgroups to the morpho- logical disparity of the larger group containing them. (1) Given an ordination of points representing specimens or species in morphological space, morphological disparity of the entire group is measured as the average squared distance of points from the centroid. The contribution that a subgroup makes to morphological disparity is measured as the average squared distance of its points from the overall centroid (not the subgroup centroid), weighted by the subgroup sample size relative to the total group sample size. Thus, morphological disparity of a group can be additively partitioned into the disparity components of its subgroups, and the relative contributions of these subgroups can be assessed quantitatively. (2) An alternative approach is to compare morphological disparity of a group to the disparity it would have if a certain subgroup were omitted. If the resulting disparity differs substantially from the original disparity, then the subgroup in question is considered to have a significant effect on morphological disparity. Because some subgroups are very centralized in mor- phological space, omitting them can cause an increase in morphological disparity when disparity is measured as the average dissimilarity among species. In general, relatively large subgroups that are located peripherally in morphospace make the greatest contributions to morphological disparity, and failure to sample smaller groups often has little effect on disparity estimates. The two methods are applied to morphological disparity in trilobites, partitioned at different levels in the taxonomic hierarchy. Results of the two methods are intuitively reasonable and largely in agreement, and point to the predominance of Early Cambrian olenelloids, Cambro-Ordovician Libristoma, Ordo- vician Asaphina and Cheirurina, Siluro-Devonian Phacopida and Phacopina, and Devonian Proetida.

Time and taphonomy; quantitative estimates of time-averaging and stratigraphic disorder in a shallow marine habitat

Abstract: We examined the radiocarbon age, taphonomic condition and stratigraphic position of shells of the venerid bivalve Chione spp. from the tidal flats of Bahia la Choya, Sonora, Mexico. Shells in Bahia la Choya are time-averaged. Thirty shells yielded radiocarbon dates from modern (A.D. 1950 or younger) to 3569 years before present. The median calendar age of inner flat shells is 483 years; the median age of tidal channel shells is 427 years. We interpret such long shell survival to be the result of frequent shallow burial. Such burial retards bioerosion of shells. The taphonomic condition of shells varied with environment. Shells from the surface of the inner flats were better preserved than shells from the tidal channel. Shells are more likely to be physically worn and biologically degraded in the waters of the channel than on the quieter and more frequently exposed inner tidal flat. Taphonomic condition is an unreliable indicator of a shell's time-since- death. Poorly-preserved shells on the inner flats tended to be old, but in general shell condition was much more variable than shell age. A shell's condition is more likely the result of its total residence time on the surface than its time-since-death (surface time plus burial time). Two composite short (44 cm and 50 cm) cores revealed varying degrees of stratigraphic disorder (the departure from perfect correlation between relative stratigraphic position and relative age). One of eight shells in the inner flats core was disordered; four of nine shells in the tidal channel were disordered. The actual age range of surface shells approximates the age range of shells in cores. Stratigraphic disorder is a consequence of both time-averaging and physical and biogenic mixing. Time-averaging controls the degree of precision possible in paleoecological studies. Environ- mental changes and ecological phenomena occurring within a span of 3500 years would not be recognized in deposits like those of Bahia la Choya. Time-averaging and stratigraphic disorder also constrain the temporal resolution possible in microstratigraphic studies of evolution. The extent of time-averaging and stratigraphic disorder will dictate an appropriate sample interval. In order to prevent temporal overlap between successive samples in deposits like Bahia la Choya, sample spacing should not be less than approximately 0.5 m.

The ontogeny of Pteranodon and other pterosaurs

Abstract: Immature specimens of the Late Cretaceous pterosaur Pteranodon were identified using three size-independent criteria: (1) fusion of various cranial and postcranial elements; (2) degree of epiphyseal ossification; and (3) bone grain or degree of ossification of limb-bone shafts. Immature individuals make up 15% of available specimens of Pteranodon and do not differ significantly in size from mature individuals. This and the extensive fusion of the mature skeleton suggest that Pteranodon had determinate growth. The bone of limb-bone shafts of immature individuals is fibro-lamellar bone, which suggests that they grew rapidly to adult size. The size-independent criteria can also be used to identify immature and mature individuals of other pterosaur taxa, and other large pterodactyloids also probably exhibited rapid determinate growth.

Decay and preservation of polychaetes: taphonomic thresholds in soft-bodied organisms

Abstract: A series of experiments was carried out to investigate the nature and controls (oxygen, microbial populations, agitation) on the degradation of soft tissues. Decay was monitored in terms of morphological change, weight loss, and change in chemical composition in the polychaete Nereis virens. Polychaetes include a range of tissue types of differing chemical composition and preservation potential: muscle, cuticle, setae, and jaws. Regardless of conditions, all the muscle had broken down and fluid loss through the ruptured cuticle had reduced the carcass to two dimensions within 8 days at 20?C. In most cases some cuticle, in addition to the jaws and setae, remained after 30 days. Where oxygen was completely eliminated, the rate of decay of the more volatile issues was signif- icantly reduced. The degree of both osmotic uptake of water by the carcass and changes in water pH differed depending on whether the system was open or closed to oxygen diffusion. Autolytic and chemical processes are not sufficient to fully degrade the carcass in the absence of bacteria. Where internal bacteria are present, the presence or absence of water column bacteria made little difference to decay rate. Initial degradation (in the first 3 days) affects mainly the lipid fraction and the collagen of the cuticle. Later decay reduces the nonsoluble protein and increases the relative proportion of refractory structural components (tanned chitin and collagen) to more than 95% by day 30. Thus, only the sclerotized tissues are likely to survive beyond 30 days in the absence of early diagenetic mineralization. The sequence of degradation predicted from the relative decay resistance of macromolecules in the sedimentary record (protein carbohydrate lipid) is not, therefore, a consistent indicator of the preservation potential of structural tissues which incorporate them. The experiments reveal five stages in the decay of polychaete carcasses; whole/shriveled, flaccid, unsupported gut, cuticle sac, jaws and setae. All are represented in the fossil record. This allows an estimation of how far decay proceeded before it was halted by the fossilization process. The most complete preservations occur in the Cambrian where the Burgess Shale preserves evidence of muscle tissues. Traces of the gut and cuticle are more widely preserved, as at Mazon Creek, Gres a Voltzia, Solnhofen, and Hakel. Preservation varies within Konservat-Lagerstatten. The most com- mon whole body preservation includes only the more recalcitrant tissues, jaws (where present) and setae, with an impression of the body outline. The stage of decay can be used as a taphonomic threshold, to provide an indication of how significantly the diversity of an exceptionally preserved biota is likely to have been reduced by taphonomic loss.

Le Clactonien : mise en application d'une nouvelle méthode de débitage s'inscrivant dans la variabilité des systèmes de production lithique du paléolithique ancien

Abstract: Apres un siecle de definitions, le Clactonien reste obscur et incompris : industrie a eclats ou a chopping-tools ? Les analyses technologiques du Paleolithique ancien et moyen tendent actuellement vers une approche systemique des chaines operatoires. Les industries dites clactoniennes seront etudiees dans cette optique, leur place dans la variabilite des methodes de debitage anterieures au Levallois sera discutee.

The potentials and limitations of dicotyledonous wood anatomy for climatic reconstructions

Abstract: The incidences of selected features of dicotyledonous wood that are believed to be of ecologic and/or phylogenetic significance (distinct growth rings, narrow and wide vessel diameter, high and low vessel frequencies, scalariform perforations, tangential vessel arrangement, ring porosity, and helical wall thickenings) were plotted through time (Cretaceous-Recent). There are marked differences between the Cretaceous and Tertiary in the frequency of all wood anatomical features. Incidences of features that are associated with markedly seasonal climates in extant floras do not approach modern levels until the Neogene. Correlations of wood anatomical features with ecology do not appear to have been constant through time, because in the Cretaceous different features provide conflicting information about the climate. Throughout the Tertiary the southern hemisphere/tropical and the northern hemisphere/temperate regions differed in the incidences of ecologically significant features and these differences are similar to those in the Recent flora. Pos- sibilities for reliably using dicotyledonous wood for climatic reconstructions appear restricted to the Tertiary and Quaternary. However, at present the fossil wood record for most epochs and regions is too limited to permit detailed reconstructions of their past climate.

Numerical experiments with model monophyletic and paraphyletic taxa

Abstract: The problem of how accurately paraphyletic taxa versus monophyletic (i.e., holophyletic) groups (clades) capture underlying species patterns of diversity and extinction is explored with Monte Carlo simulations. Phylogenies are modeled as stochastic trees. Paraphyletic taxa are defined in an arbitrary manner by randomly choosing progenitors and clustering all descendants not belonging to other taxa. These taxa are then examined to determine which are clades, and the remaining paraphyletic groups are dissected to discover monophyletic subgroups. Comparisons of diversity patterns and extinction rates between modeled taxa and lineages indicate that paraphyletic groups can adequately capture lineage information under a variety of conditions of diversification and mass extinction. This suggests that these groups constitute more than mere "taxonomic noise" in this context. But, strictly monophyletic groups perform somewhat better, especially with regard to mass extinctions. However, when low levels of paleontologic sampling are simulated, the veracity of clades deteriorates, especially with respect to diversity, and modeled paraphyletic taxa often capture more information about underlying lineages. Thus, for studies of diversity and taxic evolution in the fossil record, traditional paleontologic genera and families need not be rejected in favor of cladistically-defined taxa.

Temperature and extinction in the sea; a physiologist's view

Abstract: Climatic change has long been regarded as an important factor in evolutionary history. In particular, periods of enhanced extinction in marine taxa (especially those from warmer waters) have frequently been linked to decreases in seawater temperature. Studies of the physiology of marine invertebrates and fish alive today have revealed well-developed abilities to cope with temperature change, and there would thus appear to be a dichotomy between the rates of temperature change associated with extinction in geological history and the very much faster rates (by several orders of magnitude) with which many marine organisms can cope today. Nevertheless, evidence from ecology and biogeography indicates that temperature, or some temperature-associated factor, does play a significant role in determining the limits to performance, and hence distribution. The resolution of the dichotomy between the evidence from paleontology and physiology may come through a consideration of the role of the previous evolutionary history of the fauna, the influence of sudden temperature events, or the impact of climatic change on individual competitive ability, community structure, and ecosystem functioning. Studies of the energetics of marine invertebrates in relation to temperature and the evolutionary history of polar faunas indicate that we should beware of anthropocentric judgements in attempting to understand the role of climatic change in evolutionary history, and be critical in distinguishing the role of temperature per se from temperature-associated ecological factors. Present evidence suggests that climatic change in the sea, at least at the rates currently believed to be typical, is unlikely to cause extinction by direct physiological impact. It is more likely that extinction is caused by ecological factors; temperature change is thus only one of several factors that may promote those ecological changes that are currently the best candidates for the proximate cause of extinction in the sea.

Survivorship analysis of Paleozoic Crinoidea: effect of filter morphology on evolutionary rates

Abstract: The evolutionary rates of Paleozoic Crinoidea were obtained using dynamic survivorship analysis. The stratigraphic ranges of 838 genera were used in the analyses, revealing a mean generic duration of 12.0 m.y. and a mean species duration of 6.7 m.y., values within the range of longevities reported for other taxa. Further analyses showed differences in evolutionary rates among crinoid taxa: camerate species and genera were shorter-lived than species and genera of flexibles and inadunates. This pattern may result from ecological differences among these taxa: an energy budget equation solved for crinoids with various filter morphologies revealed that crinoids with fine-mesh filters require higher current velocities to supply them with sufficient particulate nutrients than do crinoids with coarse- mesh filters. A hypothesis stipulating that these differences control the distribution of crinoids among different environments is supported by patterns of occurrence of Mississippian crinoids: the pinnulate camerates (fine filter) dominate higher energy settings while the non-pinnulate inadu- nates and flexibles (coarse filter) are found in all environments. The "specialized" pinnulate crinoids may therefore be more prone to speciation and extinction than the non-pinnulate "generalists," thus accounting for the observed differences in the evolutionary rates of the three subclasses. The above hypothesis was tested by comparing evolutionary rates of two morphological groups: fine-filtered crinoids (camerates) and coarse-filtered crinoids (non-pinnulate Paleozoic crinoids). As

Taxonomic evolution in North American Neogene horses (subfamily Equinae); the rise and fall of an adaptive radiation

Abstract: The 18 m.y. history of the subfamily Equinae (exclusive of Archaeohippus and “ Parahippus ”) in North America consisted of a 3-m.y. radiation phase, a 9-m.y. steady-state diversity phase, and a 6-m.y. reduction phase. During the steady-state phase, species richness varied between 14 and 20, with two maxima at about 13.5 and 6.5 Ma. Species richness of the tribes Hipparionini and Equini was about equal through the middle Miocene, but hipparionines consistently had more species in the late Miocene and early Pliocene. Overall mean species duration was 3.2 m.y. ( n = 50), or an average extinction rate of 0.31 m.y. -1 During the radiation phase, speciation rates were very high (0.5 to 1.4 m.y. -1 ), while extinction rates were low ( -1 ). Speciation and extinction rates both averaged about 0.15 m.y. -1 during the steady-state phase, with extinction rates having more variation. Extinction rates increased fourfold during the reduction phase, while speciation rates declined slightly. Late Hemphillian extinctions affected both tribes severely, not just the three-toed hipparionines, and were correlated with global climatic change.

Modern vertebrate tracks from Lake Manyara, Tanzania and their paleobiological implications

Abstract: We studied mammal and bird track formation at the northern edge of Lake Manyara, Tanzania, to develop models for interpreting fossil tracks and trackways. Lake Manyara is a closed-basin, alkaline lake in the East African Rift System. The area has a high vertebrate diversity, allowing us to investigate tracks in an environment similar to that of many ancient track-bearing sequences. Three study sites, two on mud flats adjacent to the lake margin and a third on a delta floodplain, provided contrasting environments in which to assess the types of biological data that can potentially be extracted from fossil trackways.Our censuses of mammals and their tracks revealed that most species that occur within the study area leave a track record, and that common species leave abundant tracks, although numbers of trackways are not proportional to numbers of individuals. Logarithmic increases in track sampling area yield a linear increase in the proportion of both the medium and large-sized local mammals represented in a track record. Transect vs. area mapping methods produced different censusing results, probably because of differences in monitoring periods and areal coverage.We developed a model of expected track production rates that incorporates activity budget and stride length data in addition to abundance data. By using these additional variables in a study of diurnal birds, we obtained a much better estimator relating track abundance to trackmaker abundance than that provided by census data alone. Proportions of different types of tracks predicted by the model differ significantly from the observed proportions, almost certainly because of microenvironmental differences between the censusing and track counting localities. Censuses of fossil tracks will be biased toward greater numbers of depositional-environment generalists and away from habitat-specific species.Trackways of migratory animals were dominantly shoreline-parallel, whereas trackways of sedentary species were more variable. A strong shoreline-parallel environmental zonation at the Alkaline Flats site exerted an influence on trackmaker distribution patterns, initial track formation, and track preservation. Variations in habitat usage by different species, as well as species abundance and directionality of movement, were all important in determining the number of preservable tracks a species produced within a given environmental zone.Fossil trackways are time-averaged, although over entirely different temporal scales than are bones. Unlike bones, tracks are not space-averaged. Therefore, wherever possible, fossil track and bone studies should be used to complement each other, as they provide fundamentally different pictures of paleocommunities. Tracks provide “snapshot” views of localized assemblages of organisms useful in reconstructing autecological relationships, whereas bones yield a broader image of a local fauna in which seasonal and microenvironmental variation are more commonly smoothed out.

The first 2 million years after the Cretaceous-Tertiary boundary in east Texas: rate and paleoecology of the molluscan recovery

Abstract: Analysis of molluscan collections from a 3+ my interval around the Cretaceous-Tertiary (K-T) interval in east Texas suggests that molluscs suffered an extinction at or near the K-T boundary, followed by a prolonged period of stress which lasted through the PO and Pla planktic foraminiferal zones The stressed period was characterized by low species richness, low abundances of individuals, high species turnover and a dominance of deposit feeders Species richness and the relative abun- dance of deposit feeders generally track the 13C depletion curve suggesting that the stress was caused by a lack of primary production A stable, relatively diverse, suspension feeding molluscan com- munity was reestablished less than two million years after the K-T boundary The total number of species within the habitat did not recover to Cretaceous levels within the study interval

Competition, clade replacement, and a history of cyclostome and cheilostome bryozoan diversity

Abstract: One of the striking yet scarcely documented episodes of clade replacement in the post- Paleozoic fossil record is the decline of cyclostome Bryozoa and the corresponding, rapid diversi- fication of cheilostome Bryozoa. These clades are closely associated morphologically and phylo- genetically, and their ecological similarities have previously led to the inference that competition was a primary cause of the overt pattern of replacement. Alternatively, previous compilations of bryozoan families and genera have implied that extinctions at the Cretaceous/Tertiary boundary differentially affected cyclostomes, and thus were also an important factor in the transition. We first evaluated the ecological context for competition between the two clades, then updated and reexamined the history of absolute family diversity for bryozoans in consecutive geologic stages from Jurassic to Recent. The resulting trends echo the patterns shown in earlier family level com- pilations, but indicate a slight shift in the frequency of cheilostome family originations from Late Cretaceous to early Paleogene. The relative fall in cyclostome family diversity at the Cretaceous/ Tertiary boundary is significantly less than shown in earlier genus level compilations. We then assessed these various compilations of absolute diversity by analyzing species counts and percentages in 728 fossil assemblages, primarily from North America and Europe, over the same time interval. Cyclostome species overwhelmingly dominate assemblages from Jurassic through Cenomanian, then decline significantly in average percentage dominance through the Campanian. Cheilostomes are predominant in Campanian and later assemblages. Cyclostome species percentages do decrease overall through the Tertiary, but this decrease is small and non-uniform, varying around 30%, with a sharp drop in the Late Neogene. Our within-assemblage results indicate that as cheilostomes radiate, their mean species diversity, maximum diversity, and variance all increase, thereby ac- counting for much of the decline in average percentage of cyclostomes within assemblages. While this result does not exclude a role for competition, an hypothesis of relative decline in cyclostome species richness based on competitive extinction alone seems unlikely. Further, despite decreases in absolute species counts following end-Cretaceous extinctions, within-assemblage percentages of cheilostome or cyclostome species show only slight change relative to one another. Comparison of these and earlier diversity compilations indicates that the dynamics of bryozoan clade replacement may be perceived differently at different ecologic scales or taxonomic ranks.

Comparative physiology of suspension-feeding in living brachiopods and bivalves: evolutionary implications

Abstract: This paper presents scaling equations relating suspension-feeding rates to body size for articulate brachiopods and bivalve molluscs, two classes which represent a significant component of the fossil record of marine benthic communities. Clearance (feeding) rates of five species of living articulate brachiopods and three species of epifaunal suspension-feeding bivalve molluscs collected from mid-latitude fjords of Newfoundland and New Zealand were measured in similar experimental conditions. In comparisons within and between the two classes, we found that both plectolophous and spirolophous brachiopods had significantly lower feeding rates than mytilids, which are filibranchs, but that a sympatric primitive eulamellibranch veneroid bivalve had rates comparable to the brachiopods. Articulate brachiopods do not appear to feed effectively at the high algal concentrations which bivalves can exploit. The data on comparative suspension-feeding rates support the hypothesis that past changes in diversity and distribution of bivalves and brachiopods may be related to an overall increase in energy flux and escalation of metabolic rates during the Phanerozoic.

Levels of selection and macroevolutionary patterns in the turritellid gastropods

Abstract: This analysis examines the evolution of the greater diversity of species with non-plank- tonic larval types relative to species with planktonic larval types in the turritellid gastropods. This sort of trend has been documented in both the fossil and recent biota of several gastropod families. Two mechanisms for generating diversity gradients in larval types have been proposed in the literature. The first, species selection, focuses on the population biology of larval types. The second proposes that factors in development that are mediated by organismal adaptation are responsible. Turritellids have been cited as a classic example of species selection. In order to examine the relevance of these two proposed mechanisms, a phylogenetic analysis of the turritellids using molecular sequence data was performed to determine the evolution of larval types in this clade. The resultant phylogeny suggests that species selection is not the only process driving the trend toward increasing numbers of non-planktonic species through time. Developmental processes, apart from those in- volving organismal adaptation (except in the trivial sense), are implicated as playing a role in this trend. In particular, these processes may involve changes in the timing of germ-line sequestration in organisms. Germ-line sequestration governs how accessible organisms are to heritable variation during ontogeny. Embryological evidence from gastropods suggests that non-planktonic species have early germ-line sequestration relative to planktonic species, making them more resistant to developmental change. Thus, non-planktonic lineages will only rarely revert to a planktonic larval mode.

Late Quaternary climate in the Eastern Mediterranean Region.

Abstract: Pour aborder l'histoire climatique du Quaternaire superieur au Proche-Orient, il s'avere necessaire de reevaluer la chronologie des diagrammes polliniques de Grece et Syrie, precedemment publies, qui sont ici selectionnes. On admet que des spectres polliniques specifiques et identiques sont synchrones. La chronologie absolue est basee sur des dates AMS (Spectrometrie de Masse par Accelerateur) d'une carotte marine en Adriatique, dont le diagramme pol Unique peut etre carre le avec ceux de Grece, puis de Syrie. La succession de deux evenements marqueurs est largement observee : une phase ou l'abondance du pollen d'Herbacees, principalement des Chenopodiacees issues d'un milieu desertique, est la plus elevee de tout le Quaternaire superieur, et qui est identifiee comme Dryas Recent, date 11 000-10,000 ans B.P. Puis, une phase ou le pollen de Pistacia, un arbre typiquement mediterraneen, est present, de 9,000 a 6,000 ans B.P. L'abondance du pollen de Pistacia est maxima de 9,000 a 8,000 ou 7 500 B.P. Celle du pollen de Chene caducifolie croit rapidement a partir de 10,000 ans B.P. jusqu'a une valeur maxima en meme temps que le Pistacia. Ce dernier disparait pendant quelques centaines d'annees, puis reapparait avec des valeurs inferieures au maximum precedent, jusqu'a 6,000 ans B.P. Apres 6 500 ans B.P, divers arbres temperes a feuilles caduques atteignent une abondance pollinique maxima. Le Dryas Recent est interprete comme tres aride et froid. L'augmentation du Chene apres 10,000 ans B.P. indique une augmentation des precipitations, jusque vers 650 mm, dont une partie en ete, et de la temperature moyenne annuelle. La phase du maximum de Pistacia est un Optimum climatique thermique avec des hivers sans gelees. Les arbres cadu- cifolies divers indiquent des precipitations encore ou meme plus abondantes, y compris en ete, mais aussi des hivers plus froids, qui eliminent le Pistacia. Cette evolution de la vegetation et du climat concerne les bordures nord et est de la Mediterranee orientale. La comparaison avec celle des aires continentales et oceaniques peripheriques exclut la possibilite qu'aucune region du Proche-Orient puisse avoir eu une histoire climatique completement opposee.

The Yarmukian Culture in Israel.

Abstract: Les resultats des fouilles recentes et l'analyse du materiel provenant des fouilles anciennes ont permis notre comprehension de la culture yarmoukienne en Israel. Des habitations rondes ou rectangulaires, parfois de grandes sont associees a de nombreuses fosses, caracteristiques de l'habitat varmoukien. La poterie est la plus ancienne produite cette partie du Levant. Son decor, incise et peint, est particulierement caracteristique. Des outils en silex et des objets en en basalte ont ete trouves ainsi que de tres nombreuses figurines qui sont parfois d'une grande qualite artistique.

From foraging to herding in the Negev and Sinai : the Early to Late Neolithic transition.

Abstract: Au 8L millenaire В. Р., on assiste dans la bordure occidentale du Neguev et dans le sud de la plaine cotiere d'Israel a l'emergence d'une premiere forme d'economie pastorale, fondee sur l'elevage de la chevre. Des contacts paraissent alors s'etablir avec la vallee du Nil. Des couteaux bifaces, frequents dans le Tuwailien y refletent peut-etre l'introduction de l'economie pastorale. Les sites du pourtour du massif central du Neguev, et du Sinai oriental ont livre un grand nombre de haches. On trouve trace egalement dans la seconde moitie du 8e millenaire B.P. d'activites specialisees : extraction de l'asphalte a Mazad Mazzal, fabrique de perles a Beer Ada, etc. Ce developpement se poursuit au 7e millenaire B.P, une innovation etant les sanctuaires de plein air du Neguev meridional. A la fin du 7 millenaire B.P, le Qatifien du Neguev septentrional s'etend jusqu'a la Arava; cette entite, la seule que l'on puisse definir, represente une transition vers le Chalcolithique.

PPNC ADAPTATIONS IN THE FIRST HALF OF THE 6th MILLENNIUM B.C.

Abstract: In the central and southern Levant, the sustained PPNB subsistence strategy of combined farming and herding during the early 7th millennium (MPPNB) incurred severe damage to the ecological systems around the agricultural settlements, which eventually led to widespread abandonment of villages beginning as early as 6,500 B.C. Late 7th millennium (LPPNB) responses to cope with these local disturbances are poorly documented throughout the region. By the early 6th millennium, a restructuring of the subsistence economy into incipiently segregated farming and pastoral sectors allowed continued permanent settlement of the central and southern Levant, although the economic transformation resulted in fundamental realignments of the cultural base. This distinctive ensemble of socioeconomic and sociocultural adaptations is termed the Pre-Pottery Neolithic С (PPNC). ( RESUME - La strategie de subsistance combinant agriculture et elevage, maintenue au PPNB pendant le debut du 7e millenaire (MPPNB) dans la partie centrale et meridionale du Levant, a gravement compromis les equilibres ecologiques dans le voisinage des etablissements agricoles, ce qui a mene sans doute a l'abandon generalise des villages des 6 500 B.C. Les solutions apportees vers la fin du 7e millenaire (LPPNB) sont mal connues dans la region. Vers le debut du 6e millenaire, une restructuration de l'economie de subsistance par un debut de separation des secteurs agricole et pastoral a permis une occupation sedentaire continue du Levant central et meridional, bien que la transformation economique ait provoque des reajustements fondamentaux du cadre culturel. Cet ensemble distinct d'adaptations socio-economiques et culturelles est designe par le terme de Neolithique preceramique С (PPNC).

A faster-paced world?: contrasts in biovolume and life-process rates in cyclostome (Class Stenolaemata) and cheilostome (Class Gymnolaemata) bryozoans

Abstract: Zooids of cheilostome bryozoans are on average substantially more robust than are zooids of cyclostome bryozoans. The differences include greater number, length, and cross-sectional area of tentacles, plus a more extensively developed funiculus. Median values for mouth size and cilia- generated feeding current velocity are greater for cheilostomes than for cyclostomes so that cheilo- stomes have the potential for greater intake of nutrient energy per unit time, which may explain their apparently higher growth rates. For unit area of substrate occupied, the Cheilostomata (Class Gymnolaemata; members of the post-Paleozoic fauna) contain greater biomass and apparently gen- erate greater energy flow than do the Cyclostomata, which are the only extant order of the Class Stenolaemata (characteristic of the Paleozoic fauna).

The problem of changes in levallois technique during the technological transition from the middle to upper palaeolithic

Abstract: La technologie du debitage {eclats primaires) ainsi que les particularites des industries Levallois et de celles de la periode de transition Paleolithique moyen-Paleolithique superieur au Proche-Orient (Levant sud) d'une part, en Europe centrale et en Europe de l'est {Moravie meridionale et Ukraine occidentale) d'autre part, sont discutees dans cet article. Suit une analyse des liens "generiques" eventuels entre les industries Levallois du Paleolithique moyen et les industries de transition. Des elements de ressemblance et de difference entre les industries contemporaines d'Europe et du Proche-Orient sont evalues, tenant compte des changements de strategie des sequences de reduction des nucleus et des typologies depuis les industries du Paleolithique moyen jusqu'aux industries de transition.

The importance of phylogenetic analysis for the assessment of species turnover: a case history of Paleocene mammals in North America

Abstract: During the latest Cretaceous and the Paleocene in western North America, disappearance rates for mammalian genera track appearance rates, both reaching their peak in the early Paleocene (Puercan) following the extinction of non-avian dinosaurs. Some of the disappearances during this time were pseudoextinctions that resulted when ancestral species disappeared during speciation. Species-level cladistic analyses and a well-constrained biostratigraphic framework are required to study this form of pseudoextinction. Cladistic analyses show that monophyly cannot be estab- lished or rejected for some species because these species lack autapomorphies (uniquely derived character states) that unite their constituent members. Such taxa, termed metaspecies, are potential ancestors to species and higher clades with which they share a node in the cladogram. A hypothetical species-level cladistic analysis coupled with three different hypothetical biostra- tigraphies shows how different models of speciation (bifurcation, budding, or anagenesis) result in very different patterns of true versus pseudoextinction. Depending on the speciation model, true extinction can be overestimated by as much as a factor of four, raising the specter of mass extinction. Species-level studies for three early Tertiary mammalian taxa-taeniodont eutherians, taeniolabidid multituberculates, and periptychid ungulates-use the same procedures. They show that almost 25% of disappearances during the early Paleocene (Puercan) for species in the analysis were pseu- doextinctions of metaspecies. Budding and anagenetic-like peripatric speciation, but not bifurcation, are seen in the three examples. Equating disappearance to true extinction can profoundly affect interpretations of faunal turnover, especially during mass extinctions or major faunal reorganizations. Some authors use pseudoex- tinction to describe the taxonomic rather than evolutionary disappearance of nonmonophyletic groups. Pseudoextinction, as used here refers only to the evolutionary disappearance of metaspecies via speciation. Both usages seem appropriate but should not be confounded.

Diversity changes in lycopsid and aquatic fern megaspores through geologic time

Abstract: Quantitative data on lycopsid and aquatic fern megaspore taxa recovered from Carboniferous, Mesozoic, and Tertiary strata have been compiled in order to analyze the changes in diversity of the two groups of fossil plants that produced them. Numbers of species of lycopsid megaspores are similar in the Carboniferous and Mesozoic, whereas the diversity of megafossils is much lower in post-Paleozoic deposits. Our data suggest that lycopsids were more diverse in the Mesozoic than previously thought and that there is a preservational bias against the megafossils, because the plants were probably mainly herbaceous. Heterosporous aquatic ferns first appeared in the Neocomian and gradually diversified until the early Late Cretaceous, after which their numbers remained relatively stable, whereas the variety of lycopsids declined dramatically during the Late Cretaceous. These changes occurred at a time of rapid angiosperm diversification. The reduced diversity of the lycopsids may have been caused by the invasion of their aquatic and damp forest-floor habitats by heterosporous ferns and by aquatic and herbaceous angiosperms. These diversity changes do not seem to be directly related to the global events at the Cretaceous-Tertiary boundary, but the relatively few samples available and the resulting range truncation would make detection of such correlations difficult.

Evolution of sexually dimorphic characters in peccaries (Mammalia, Tayassuidae)

Abstract: Cladistic analysis of osteological and dental characters in a monophyletic group of Miocene and younger tayassuids demonstrates a pattern of changes in the degree of sexual dimorphism in canine tooth diameter and zygomatic arch width, and in phenotypic correlations between these characters. Primitively, tayassuids have canine teeth that are sexually dimorphic and discretely bimodal in size, and zygomatic arches that are narrow in both sexes. Many late Miocene and Pliocene tayassuids have broad, winglike zygomatic processes. In some species, these processes are large in both sexes, but in others, those of females are much smaller than those of males. The presence of large processes in both sexes is primitive relative to the condition of strong sexual dimorphism. In five separate clades, the zygomatic processes of both sexes become reduced in size, and the degree of sexual dimorphism in canine size becomes reduced as well. The pattern is congruent with predictions derived from a theoretical model of the evolution of sexual dimorphism, and it further indicates the emergence of a new phenotypic correlation between two previously uncorrelated characters, canine size and zygoma size. The advent of this new correlation coincides with the advent of pronounced sexual dimorphism in zygomatic processes. Although such a pattern could be explained by genetically modifying phenotypic expression of homologous characters in one sex or the other, an epigenetic modification of expression is equally plausible: the evolution of sexual dimorphism in homologous characters could be accomplished by placing phenotypic expression of an originally monomorphic character under the control of steroid sex hormones. This hypothesis is consistent with evidence from many vertebrate groups, and it provides testable predictions.

Un mode de production inédit au Paléolithique moyen dans l'industrie du niveau 6e du Pucheuil (Seine-Maritime)

Abstract: L'une des series Paleolithique moyen du gisement du Pucheuil se caracterise par une production secondaire originale, realisee a partir des sous- produits de la chaine operatoire principale (Levallois). Ses specificites techniques ainsi que la chronologie des operations de debitage sont successivement decrites.

The taphonomy of Maastrichtian inoceramids in the Basque region of France and Spain and the pattern of their decline and disappearance

Abstract: -After having been very abundant in the Early Maastrichtian Globotruncana gansseri zone, Inoceramus remains disappear from five stratigraphic sections in the Basque region of France and Spain in the lower Abathomphalus mayaroensis zone, 2.5 m.y. before the Cretaceous-Tertiary boundary. Several lines of evidence demonstrate that these shell fragments are preserved in place and accurately record the pattern of the decline and disappearance of the group. The dominant taphonomic process seems to have been passive disaggregation of the shell as shell proteins decayed. The resulting shell fragments were dispersed only locally by burrowing organisms. Shell fragments decline in abundance over tens of meters of section and there are subtle differences between sections which suggests Inoceramus was eliminated by gradual changes in ecological conditions that affected the basin roughly simultaneously but with some geographic variability. Kenneth G. MacLeod. Department of Geological Sciences, AJ-20, University of Washington, Seattle, Washington 98195 William N. Orr. Department of Geological Sciences, University of Oregon, Eugene, Oregon 97403 Accented: December 10. 1992