Showing papers in "Paleobiology in 1991"

Anatomy of an invasion: the trans-Arctic interchange

Abstract: When the Bering Strait between Alaska and Siberia opened about 3.5 Ma during the early Pliocene, cool-temperate and polar marine species were able to move between the North Pacific and Arctic-Atlantic basins. In order to investigate the extent, pattern, and dynamics of this trans- Arctic interchange, I reviewed the Recent and fossil distributions of post-Miocene shell-bearing Mollusca in each of five northern regions: (1) the northeastern Atlantic (Lofoten Islands to the eastern entrance of the English Channel and the northern entrance of the Irish Sea), (2) northwestern Atlantic (southern Labrador to Cape Cod), (3) northeastern Pacific (Bering Strait to Puget Sound), (4) northwestern Pacific (Bering Strait to Hokkaido and the northern Sea of Japan), and (5) Arctic (areas north of the Lofoten Islands, southern Labrador, and Bering Strait). I have identified 295 molluscan species that either took part in the interchange or are descended from taxa that did. Of these, 261 are of Pacific origin, whereas only 34 are of Arctic-Atlantic origin. Various analyses of the pattern of invasion confirm earlier work, indicating that there is a strong bias in favor of species with a Pacific origin. A geographical analysis of invaders implies that, although trans-Arctic interchange contributed to a homogenization of the biotas of the northern oceans, significant barriers to dispersal exist and have existed for trans-Arctic invaders within the Arctic-Atlantic basin. Nevertheless, trans-Arctic invaders in the Atlantic have significantly broader geographical ranges than do taxa with a pre- Pliocene history in the Atlantic. Among the possible explanations for the asymmetry of trans-Arctic invasion, two hypotheses were explicitly tested. The null hypothesis of diversity states that the number of invaders from a biota is proportional to the total number of species in that biota. Estimates of Recent molluscan diversity show that the North Pacific is 1.5 to 2.7 times richer than is the Arctic-Atlantic, depending on how faunistic comparisons are made. This difference in diversity is much smaller than is the asymmetry of trans-Arctic invasion in favor of Pacific species. Rough estimates of regional Pliocene diversity suggest that differences in diversity during the Pliocene were smaller than they are in the Recent fauna. The null hypothesis was therefore rejected. The hypothesis of ecological opportunity states that the number of invaders to a region is pro- portional to the number of species that became extinct there. The post-Early Pliocene magnitude of extinction was lowest in the North Pacific, intermediate in the northeastern Atlantic, and probably highest in the northwestern Atlantic. The absolute number and faunistic importance of post-Early Pliocene invaders (including trans-Arctic species, as well as taxa previously confined to warm- temperate waters and western Atlantic species that previously occurred only in the eastern Atlantic) was lowest in the North Pacific, intermediate in the northeastern Atlantic, and highest in the northwestern Atlantic. Further support for the hypothesis of ecological opportunity comes from the finding that hard-bottom communities, especially those in the northwestern Atlantic, show a higher representation of molluscan species of Pacific origin, and are likely to have been more affected by climatic events, than were communities on unconsolidated sandy and muddy bottoms. Support for the hypothesis does not rule out other explanations for the observed asymmetry of trans-Arctic invasion. A preliminary study of species-level evolution within lineages of trans-Arctic invaders indicates that anagenesis and cladogenesis have been more frequent among groups with Pacific origins than among those with Atlantic origins, and that the regions within the Arctic-Atlantic basin with the highest absolute number and faunistic representation of invaders (western Atlantic and Arctic) are the regions in which speciation has been least common among the invaders. The asymmetry of invasion is therefore distinct from the asymmetry of species-level evolution of invaders in the various northern marine regions.

Ecogeography and the Great American Interchange

Abstract: When the isthmian land bridge triggered the Great American Interchange, a large majority of land-mammal families crossed reciprocally between North and South America at about 2.5 Ma (i.e., Late Pliocene). Initially land-mammal dynamics proceeded as predicted by equilibrium theory, with roughly equal reciprocal mingling on both continents. Also as predicted, the impact of the interchange faded in North America after about 1 m.y. In South America, contrary to such predic- tions, the interchange became decidedly unbalanced: during the Pleistocene, groups of North American origin continued to diversify at exponential rates. Whereas only about 10% of North American genera are derived from southern immigrants, more than half of the modern mammalian fauna of South America, measured at the generic level, stems from northern immigrants. In addition, extinctions more severely decimated interchange taxa in North America, where six families were lost, than in South America, where only two immigrant families became extinct. This paper presents a two-phase ecogeographic model to explain the asymmetrical results of the land-mammal interchange. During the humid interglacial phase, the tropics were dominated by rain forests, and the principal biotic movement was from Amazonia to Central America and southern Mexico. During the more arid glacial phase, savanna habitats extended broadly right through tropical latitudes. Because the source area in the temperate north was six times as large as that in the south, immigrants from the north outnumbered those from the south. One prediction of this hypothesis is that immigrants from the north generally should reach higher latitudes in South America than the opposing contingent of land-mammal taxa in North America. Another prediction is that suc- cessful interchange families from the north should experience much of their phylogenetic diver- sification in low latitudes of North America before the interchange. Insofar as these predictions can be tested, they appear to be upheld.

Iterative evolution of hypercarnivory in canids (Mammalia: Carnivora): evolutionary interactions among sympatric predators

Abstract: Convergent evolution of hypercarnivorous adaptations in canids has occurred a number of times in the last 40 m.y. among distantly related taxa. The adaptations include an increase in carnassial blade length, reduction or loss of post-carnassial molars, and transformation of the talonid of the lower first molar from a basinlike depression into a trenchant, bladelike cusp. Although the diversity of these specialized canids is typically low in past and present communities, it was un- usually high during the Late Oligocene of North America and the Pleistocene of South America. These two comparable events provide an opportunity for exploring possible causes of the evolution of hypercarnivory in canids. Plots of generic diversity against time for North American predators reveal a roughly inverse relationship between the number of hypercarnivorous canid taxa and the numbers of other hypercarnivores, such as creodonts, nimravids, mustelids, and amphicyonids. Similarly, the radiation of hypercarnivorous canids in South America occurred at a time of relatively low diversity of other hypercarnivores. Analysis of trophic diversity within the North American carnivore paleoguild before, during, and after the Late Oligocene reveals considerable taxonomic turnover among carnivores because of immigration and speciation. Late Oligocene hypercarnivorous canids appear to have been replaced first by amphicyonids and large mustelids, and then by felids. Despite the repeated tendency of canids to evolve adaptations for hypercarnivory, a canid has yet to appear that is completely catlike, that is, without any post-carnassial molars. This possible constraint on morphological evolution in canids is argued to have resulted, paradoxically, in in- creased flexibility over evolutionary time and a great potential for rapid diversification and clade survivorship. Finally, it is suggested that the iterative pattern of specialization of the lower molars for meat-slicing that is seen in all families of carnivores, past and present, is probably a result of intraspecific competition for food, perhaps among littermates. This intraspecific selective force is countered by competition among species, since there are limits on the number of sympatric hy- percarnivorous species within a single community.

The disparity of the Burgess Shale arthropod fauna and the limits of cladistic analysis: why we must strive to quantify morphospace

Abstract: Three major arguments have been raised against the crucial claim, documented by Whit- tington and colleagues for the Burgess Shale fauna, and so contrary to traditional views, that disparity of anatomical design reached an early maximum in the history of multicellular life: (1) the presence of many early taxa with low membership and high rank is an artifact of naming; (2) cladistic analysis of Burgess arthropods negates the claim for greater early disparity; and (3) Whittington's argument is a retrospective fallacy based on assigning high rank to differentia only by virtue of their later capacity to define major branches. I show that all these arguments are either false or illogical, and that the claim for increased early disparity is justified: (1) Taxonomic rank is an artifact, but no one has ever based a claim for greater disparity on this false criterion. (2) Cladistics can only deal with branching order, whereas disparity is a phenetic issue. These two legitimate aspects of evolutionary "relationship" are logically distinct. The rooting of a cladogram only illustrates monophyletic ancestry (which no one doubts, as we are not creationists), and cannot measure disparity. (3) The active stabilization of the differentia of Baupldne (for genetic and developmental reasons only dimly understood) provides a powerful rationale for weighting these characters in considerations of disparity; nothing had so stabilized in the Burgess fauna. If these differentia were steadily changing contingencies, rather than actively stabilized features with "deep" architectural status, then the retrospective argument would be justified. Although the three arguments are wrong, the claim for greater early disparity cannot be confidently established until we develop quantitative techniques for the characterization of morphospace and its differential filling through time. This is a dauntingly difficult problem, much harder than cladistic ordering, but not intractable.

A kill curve for Phanerozoic marine species.

Abstract: A kill curve for Phanerozoic species is developed from an analysis of the stratigraphic ranges of 17,621 genera, as compiled by Sepkoski. The kill curve shows that a typical species' risk of extinction varies greatly, with most time intervals being characterized by very low risk. The mean extinction rate of 0.25/m.y. is thus a mixture of long periods of negligible extinction and occasional pulses of much higher rate. Because the kill curve is merely a description of the fossil record, it does not speak directly to the causes of extinction. The kill curve may be useful, however, to li inverted question markmit choices of extinction mechanisms.

Incumbent replacement: evidence for long-term evolutionary progress

Abstract: Evolutionary progress is a trend that relaxes trade-off rules. It begins with the evolution of a key adaptation. It continues with the spread of the key adaptation as the clade that contains it replaces some older clade that lacks it. Key adaptations are those that allow for improvement in at least one organismal function at a reduced fitness cost in other functions. Replacement almost certainly involves more than pure chance. It may not often involve com- petitive extinction. Instead, species from the new clade produce new species to replace already extinct species from the old clade. The key adaptation gives them a higher competitive speciation rate than old-clade sources of replacement. The process, termed incumbent replacement, proceeds at a rate limited by extinction rate. Thus, replacement often seems linked to mass extinction events. The incumbent-replacement hypothesis explains what we know about the replacement of straight- neck turtles (Amphichelydia) by those that can flex their necks and protect their heads in their shells. This replacement occurred four or five times in different biotic provinces. It happened as long ago as the Cretaceous in Eurasia, and as recently as the Pleistocene in mainland Australia. It was accomplished in Gondwanaland by turtles flexing their necks sideways (Pleurodira), and in the north by those flexing their necks into an S-curve (Cryptodira). As is typical of replacements, amphichelydian replacement took millions of years to accomplish wherever it occurred, and much of it in North America took place in a burst associated with and immediately subsequent to a mass extinction.

Marine biotic interchange between the northern and southern hemispheres

Abstract: Patterns of bipolar or antitropical distributions occur in a diverse array of marine invertebrate, vertebrate, and plant groups in the eastern Pacific Ocean. Available geologic and paleontological evidence does not support vicariance as a process in the creation of these distributions but instead favors biotic interchange between hemispheres. Moreover, the timing of these events suggests several breaches (both northward and southward) of the tropics rather than a single event. The fossil record is extremely important in delimiting potential hypotheses and allowing correlation with vicariance events. The congruence of some interchanges with major regional tectonic activity and others with Pleistocene glaciations is not surprising and argues for a plurality of mechanisms. Extinction of endemic taxa following interchange among marine invertebrates is rare, and none of the antitropical distributions reviewed here suggests that the arrival of a taxon in the adjoining hemisphere resulted in the extinction of an endemic taxon. Instead, interchange and endemic taxa coexist. In contrast to the extinction patterns, the patterns of radiations are extremely diverse with some immigrant taxa undergoing remarkable radiations, whereas other taxa are represented by single species. Temperate nearshore rocky communities in both the northern and southern hemispheres appear to be mosaics of species that share common ancestry (because of interchange), are cosmopolitan, and have independent origins within the region. Although some communities appear to be organized around products of interchange (e.g., kelp forests of California and Chile), only the taxa have immigrated; linkages and interactions between species are independent and locally derived.

Deep-water taphonomy of vertebrate carcasses: a whale skeleton in the bathyal Santa Catalina Basin

Abstract: Taphonomic processes in deep-water environments differ markedly from those in shallow waters. These differences are illustrated by the preservational style of a large cetacean skeleton lying at the bottom of the Santa Catalina Basin in 1,240 m of water. The degree of skeletal articulation contrasts with that documented in the shallow North Sea where gas-filled, buoyant carcasses dis- articulated during flotation. Increased hydrostatic pressure at greater depth is presumed to have prevented the whale carcass from floating and promoted increased levels of preservation. We present a model that relates gas evolution during decay to carcass buoyancy with depth. Application of this model may ultimately allow the degree of skeletal articulation to be used as a rough index of paleobathymetry.

Bias of the paleobotanical record as a consequence of variations in the chemical composition of higher vascular plant cuticles

Abstract: The impact of the variations in the chemical composition of higher vascular plant cuticles on their fossil record is usually not considered in paleobotanical and, more particularly, taphonomic studies. Here we address the subject with reference to the chemical characterization of insoluble cuticular matrices of a large variety of recent and fossil cuticles. The cuticles were analyzed using Curie-point pyrolysis-gas chromatographic techniques. Cuticular matrices of extant higher plants consist either of the biopolyester cutin, the insoluble, non-hydrolyzable polymethylenic biopolymer cutan, or a mixture of both biopolymers. In fossil cuticles an additional cuticular matrix type consisting of cutan and cutin-derived material is recognized. On the basis of the variations in their chemical composition and the different behavior of the cuticular constituents (viz., cutin and cutan) during diagenesis, it is concluded that the paleobotanical record of cuticles will be biased toward taxa originally having a significant amount of cutan in their cuticular matrix.

Biased extinction and evolutionary trends

Abstract: The directionality of long-term trends can be strongly biased by forces intrinsic to a clade. Trends in body size and skeletal shape may be dictated more by variations in survivorship that reflect differences in ecology than by long-term directional changes in the environment. Hence, mass extinctions can help drive evolutionary trends by selectively eliminating some morphologies and permitting the survivors to found the next radiation.Examples include repeated trends toward larger maximum body size and the evolution of keeled species from those with globose tests in planktonic foraminifera. Both the trends in size and shape develop because small species with globose tests are significantly more resistant to extinction than species that are large or have peripheral keels. Hence, the survivors of both the Cretaceous-Tertiary and Eocene-Oligocene extinction episodes are small, unkeeled taxa. Large species and species with keels evolved convergently after both mass extinctions as the founders radiated anew.Comparison of three radiations of planktonic foraminifera suggest that the convergent evolution of similar test shapes and sizes is not due to synchronous changes in oceanography that track evolutionary trends. Instead, the reestablishment of habitat heterogeneity is needed to permit the ensuing radiation to unfold rather than to closely guide its progress. Similar evolutionary trends will develop in each radiation as long as the founders have similar morphology and the evolution of variants present in the previous radiation is not precluded by the environment.

Calibrating the paleothermometer: climate, communities, and the evolution of size

Abstract: Studies in the past 20 years have often interpreted size fluctuations in fossil mammal remains as a response to climatic change, in accord with Bergmann's rule. However, such paleo- ecological inference requires careful consideration of changes in community composition that could cause ecological character displacement or release. Recent size gradients of mammals should be screened for the possibility of character displacement if fossil size gradients are to be used as a "paleothermometer" for past climate. The use of teeth in paleontological studies as a measure of body size presents a further complication; for several carnivore guilds, it appears that competitive pressures act most strongly on tooth size. Teeth may therefore inaccurately estimate body size, even if body size accurately indicates climatic conditions. In the fossil record different species exhibit different size patterns under the same conditions of climatic change, and the same species may show diametrically opposite size fluctuations under similar conditions of climatic change, in different regions.

The Origins and development of ground stone assemblages in Late Pleistocene Southwest Asia

Abstract: La technologie du mobilier en pierre est generalement consideree comme une condition prealable a la domestication des cereales. Les assemblages du Levant datant du Pleistocene recent et de l'Holocene ancien revelent plusieurs tendances : 1) les outils en pierre polie sont attestes pour la premiere fois au Paleolithique ancien; 2) les recipients/mortiers apparaissent au cours du maximum glaciaire et coincident ainsi avec les echantillons les plus anciens de cereales sauvages connus a ce jour en provenance de sites archeologiques; 3) les assemblages connus sont peu nombreux et restent pauvres jusqu'au Natoufien ancien; 4) les assemblages du Natoufien ancien sont nombreux; certains sont riches et beaucoup presentent une dominante de recipients/mortiers et de pilons; 5) le nombre de meules et de molettes s'accroit au Natoufien recent et plus particulierement au PPNA et au PPNB, epoques ou sont documentees les plus anciennes cereales domestiques. Les donnees ethnographiques et experimentales semblent montrer que la decortication des cereales sauvages au moyen des outils epipaleolithiques devait etre ardue, ce qui pose la question de savoir si les cereales constituaient une source de nourriture "attrayante". Les mortiers et les pilons du Natoufien ancien suggerent une decortication simple des cereales, ainsi que la preparation de nombreux aliments a base d'autres plantes. Ces ustensiles apparaissent dans des rituels funeraires, ce qui pourrait constituer dans le domaine de la nourriture des indices indirects de choix culturels, a une epoque ou la pression de l'environnement se fait plus forte. Les meules et les molettes du Natoufien recent-PPNA suggerent l'intensification de modes d'exploitation pre-existants lors des modifications du milieu qui caracterisent la fin du Pleistocene.

A model of onshore-offshore change in faunal diversity.

Abstract: Onshore-offshore patterns of faunal change occurred at many taxonomic scales during the Paleozoic Era, ranging from replacement of the Cambrian evolutionary fauna by the Paleozoic fauna to the environmental expansion of many orders and classes. A simple mathematical model is constructed to investigate such change. The environmental gradient across the marine shelf-slope is treated as a linear array of discrete habitats, each of which holds a set number of species, as observed in the fossil record. During any interval of time, some portion of the species in each habitat becomes extinct by background processes, with rates of extinction varying among both clades and habitats, as also observed in the record. After extinction, species are replaced from within the habitat and from immediately adjacent habitats, with proportions dependent on surviving species. This model leads to the prediction that extinction-resistant clades will always diversify at the expense of extinction-prone clades. But if extinction intensity is highest in nearshore habitats, extinction-resistant clades will expand preferentially in the onshore direction, build up diversity there, and then diversify outward toward the offshore. Thus, onshore-offshore patterns of diversification may be the expectation for faunal change quite independently of whether or not clades originate onshore. When the model is parameterized for Paleozoic trilobites and brachiopods, numerical solutions exhibit both a pattern of faunal change and a time span for diversification similar to that seen in the fossil record. They also generate structure similar to that seen in global diversification, including logistic patterns of growth, declining origination but constant extinction within clades through time, and declining overall extinction across clades through time.

Enrichment and stability in the Pliocene mammalian fauna of North China

Abstract: The Late Neogene vertebrate fossil record from Yushe Basin presents multiple, superposed assemblages from a single area, spanning roughly the interval of 6-2 Ma. Both large and small mammals show peak species richness in the middle Pliocene but indicate relative faunal stability throughout the Pliocene. Large mammals show turnover, especially extinction, around 5 and 2.5 Ma. Small mammals indicate change (over half of the species and several genera), as well as turnover at the species level, between 4 and 3.4 Ma. The loosely controlled dating of these events does not disprove hypothetical correlation with events in North America and with global climatic shifts. Elements that lack Yushe antecedents, some being long-distance dispersers, appear throughout the section, but with little effect on the resident assemblage. First records of well-documented immi- grants (from North America, Europe, Africa, southern Asia, or high latitudes) generally do not coincide with ecomorph extinctions. Early Pliocene exchange between Asia and North America appears to have been balanced in both directions and involved a small proportion of the fauna. Immigration probably was opportunistic and contributed to faunal enrichment. We interpret the Yushe Pliocene mammalian assemblages as representing a fauna that was stable from ca. 5 to 2.5 Ma and changed mainly by additions and congeneric species substitutions.

Biogeography of early Mesozoic continental tetrapods: patterns and implications

Abstract: The stratigraphic framework for Triassic and Early Jurassic continental strata has greatly changed in recent years. These revised correlations necessitate a review of traditional views of early Mesozoic continental faunal succession and biogeography. We have examined the relationship between tetrapod distribution and paleogeographic context during the Triassic and Early Jurassic on the basis of a data base comprising updated faunal lists for major early Mesozoic assemblages of continental tetrapods. Analysis of these data supports the hypothesis that there were few barriers to biotic interchange among continental tetrapods throughout the Triassic and Early Jurassic. Early Mesozoic tetrapod assemblages are dominated by widely distributed, often cosmopolitan families. Late Triassic patterns of latitudinal variation among tetrapod assemblages appear to be correlated to those seen among terrestrial plants and contrast with the extremely uniform distribution of Early Jurassic continental biotas.

Réflexions sur l'histoire technique de l'Homme : de l'évolution cognitive à l'évolution culturelle

Abstract: C'est sans doute l'insatisfaction suscitee par les interpretations automatiques en termes de culture, et notamment pour les periodes anciennes, qui nous engage a reviser certaines demarches habituelles de la prehistoire paleolithique en posant le role heuristique central de la technologie lithique. Au coeur de la recherche, la technologie temoigne autant des competences (cognitives) que des performances (culturelles). Cet article est l'essai d'un decoupage « cognitif » de l'evolution technique qui pourrait eclairer, en la recoupant, l'evolution phylogenique des taxons humains, et mieux situer la place residuelle, « en creux » des reelles caracteristiques culturelles. Une evolution en quatre stades est proposee, d'une conception de la « dimension 0 » qui est deja celle des singes anthropoides actuels, a celle de la « 3eme dimension » qui serait celle de l'Homo sapiens sapiens.

Punctuated anagenesis and the importance of stratigraphy to paleobiology

Abstract: The depositional history of Upper Miocene through Recent sediments from DSDP Site 214 (Ninetyeast Ridge, Indian Ocean) is reexamined. Samples of the Globorotalia tumida planktic foraminiferal lineage, originally obtained from these sediments by Malmgren et al. (1983), serve as the empirical basis for the recognition of punctuated anagenesis as a distinct mode of phenotypic evolution and have been the subject of numerous additional investigations. However, conclusions reached by previous authors depend strictly on the validity of the original chronostratigraphic interpretation of these sediments. Graphic correlation analysis of first- and last-appearance datum levels for a total of 41 planktic foraminiferal, radiolarian, and calcareous nannoplankton taxa provides evidence for a more complex depositional history at this deep-sea site than originally believed. Based on a conservative model of variation in the pattern of sediment accumulation rates, the lowermost portion of the studied section (6.5-4.3 Ma) represents an interval of temporally condensed sediment accumulation (1.88 cm/1,000 yr) followed by an interval (4.3-2.8 Ma) of temporally expanded sediment accumulation (3.97 cm/1,000 yr). This interval, in turn, is followed by a depositional hiatus or an extremely condensed interval, at least 800,000 yr in duration, which is followed by another relatively condensed (1.36 cm/1,000 yr) interval from 2.0 Ma-Recent. Although this chronostratigraphic reinterpretation deviates substantially from the original, which recognized Site 214 as being both temporally continuous and exhibiting a constant sediment accumulation rate from the Upper Miocene through the Upper Pliocene, it is more consistent with expectations based on Neogene eustatic sea-level fluctuations and global surveys of Neogene hiatus distributions. Age assignments for samples of the Gr. tumida lineage based on the revised chronostratigraphic model reverse some findings of previous investigators with respect to the distinctiveness of phenotypic evolutionary rates characterizing the transition from Gr. plesiotumida to Gr. tumida. Finally, a brief survey of similar marine invertebrate lineage studies shows that changes in the rate of phenotypic evolution often appear to coincide with major physical changes in the paleoceanographic environment. Such correspondences may be due, at least in part, to the effect of these environmental changes on sediment accumulation rates. Paleobiologists who seek to understand patterns of phenotypic change over time must remove the effects of variations in sediment accumulation rates from their data before evolutionary hypothesis testing and remain aware of the limitations imposed on their interpretations by the uncertain nature of chronostratigraphic inference.

Biomechanics of the jaw apparatus of the gigantic Eocene bird Diatryma: implications for diet and mode of life

Abstract: Discovery of several new specimens of the gigantic Eocene ground bird Diatryma gigantea from the Willwood Formation of northwestern Wyoming, has prompted an analysis of its feeding apparatus and an assessment of the mode of life of this unusual bird. Diatryma exhibits many of the features predicted by biomechanical models to occur in animals delivering large dorsoventral bite forces. Similarly, the mandible of Diatryma, which was modeled as a curved beam, appears well equipped to withstand such forces, especially if they were applied asymmetrically. Interpretation of these size-independent biomechanical properties in light of the large absolute skull size of Diatryma suggests a formidable feeding apparatus. The absence of modern analogues complicates the determination of just how this unique skull morphology correlates with diet. Suggestions that Diatryma was an herbivore seem improbable in that they require the postulation of excessively high safety factors in the construction of the skull. The traditional hypothesis of Diatryma as a carnivorous bird accords as well or better with the data at hand. Carnivory raises the probability of "accidental" encounter with bones, thus explaining the high safety factors. In fact, the skull and mandible of Diatryma are so massive that bone crushing may have been an important behavior. Diatryma could have been a scavenger. However, limb allometry and phylogenetic interpretation of limb propor- tions call into question the picture of Diatryma as a slow, plodding graviportal animal, suggesting that active predation was within its behavioral repertoire.

Les gisements paléontologiques pléistocènes à indices de fréquentation humaine : un nouveau type de comportement de prédation ?

Abstract: La presentation de quelques sites meridionaux possedant en commun une association entre un assemblage faunique d'origine non-anthropique et de rares vestiges lithiques amene a s'interroger sur leur signification Trois categories sont distinguees qui toutes semblent concourir a restituer un comportement de type charognage controle et actif : les repaires de carnivores speleens, les avens et les gisements de plein air Une chronologie de ce comportement avec ces implications evolutives est mis en relation avec la division tripartite du paleolithique moyen

Faunal interchange and Miocene terrestrial vertebrates of southern Asia

Abstract: Problems of stratigraphic completeness and poor temporal resolution make analysis of faunal change in terrestrial sequences difficult. The fluvial Neogene Siwalik formations of India and Pakistan are an exception. They contain a long vertebrate record and have good chronostrati- graphic control, making it possible to assess the influence of biotic interchange on Siwalik fossil communities. In Pakistan, the interval between 18 and 7 Ma has been most intensively studied and changes in diversity and relative abundance of ruminant artiodactyls and muroid rodents are documented with temporal resolution of 200,000 years. Within this interval, diversity varies con- siderably, including an abrupt rise in species number between 15 and 13 Ma, followed by a decline in ruminant diversity after 12 Ma and a decline in muroid diversity in two steps at 13 and 10 Ma. Significant changes in relative abundance of taxa include an increase in bovids between 16.5 and 15 Ma, a decrease in tragulids after 9 Ma, and a very abrupt increase in murids at 12 Ma. Megacri- cetodontine rodents also decrease significantly at 12 Ma, and smaller declines -re recorded among myocricetodontine and copemyine rodents after 16 Ma. An increase of dendromurine rodents at 15.5 Ma is also observed. There is also a trend of progressive size increase among giraffoids and bovids throughout the sequence. We have also investigated relationships between biotic interchange and diversity, body size, and relative abundance, concluding that (1) the rapid increase in ruminant and muroid diversity was largely due to immigration, whereas in situ speciation had only a secondary role; (2) during intervals of increasing diversity, resident lineages did not have higher than average rates of in situ speciation; (3) during intervals with rising diversity, greater extinction did not accompany increased immi- gration; (4) during intervals with falling diversity, there may have been greater extinction in recently invading lineages; and (5) change in diversity was independent of changes in relative abundance and body size.

Living and fossil scallop shells as airfoils: an experimental study

Abstract: Selected shell specimens of extant and fossil streamlined pectinids, which have or pre- sumably had level-swimming ability, were examined experimentally to elucidate their hydrody- namic properties, in particular, airfoil efficiency estimated by lift-drag ratio. Using a stationary water tank for nautical engineering, lift and drag forces were measured at various attack angles. Of the examined species, Amusium japonicum, which is characterized by an unusually shiny surface, upward- cambered commissure and sharpened trailing edge, is the most efficient level swimmer and has the lowest drag coefficient and the highest value of lift-drag ratio at any attack angle. Amussiopecten praesignis from the Plio-Pleistocene may have swum horizontally because its airfoil efficiency is superior to that of a living level swimmer, Placopecten magellanicus. Although its shell shape is analogous to that of Placopecten, Camptonectes (Maclearnia) cinctus from the Lower Cretaceous shows a much inferior efficiency and a significant flow separation from the surface. Bernoulli's effect in convex-upward species may contribute to increase lift, but a certain attack angle is always required for level flight. The strategy of level swimming probably evolved independently in several pecti- nacean lineages in which swimming rather than shell robustness became the preferred defense against predators. One problem that must be solved is that some feedback mechanism is required to check pitching, rolling, and yawing of the shell to attain stability in level flight.

Landmark-based morphometrics of spiral accretionary growth

Abstract: Many organisms continue to grow their skeletons throughout ontogeny. In the shells of molluscs, protists, and brachiopods and in bovid horns, accretionary spiral growth provides a detailed and continuous growth history. Although a shell may be described as a single static form, the overall morphology is a summation of the ongoing accretionary process. For this reason, an explicitly ontogenetic characterization of form provides insight into the final form achieved. Anal- ysis of landmark transformations offers direct access to major components of morphological variation, both among adult individuals and through an individual's ontogeny. Parameters of preconceived, abstract geometric models can also be used to characterize morphological variation, but there is no guarantee that these parameters will coincide with the major features of shape variation. In order to locate landmarks at equivalent ontogenetic stages, features that indicate ontogenetic stage of coiled forms must be identified (e.g., growth increments, age, size, whorls). The gastropod Epitonium (Nitidiscala) tinctum exhibits prominent varices that provide landmark locations throughout ontogeny. Recent specimens of this species were obtained from three localities in Baja, Mexico. The morphological variation among individuals, treated as whole shells and within individual ontog- enies, was analyzed using shape coordinates of landmark configurations. Deformation of shape is expressed in the uniform and nonuniform shape subspaces. The empirical components of shape variation found are similar to those generated by two parameters of an equiangular spiral: 0, the angle between consecutive varices, and W, the whorl expansion rate. The distribution of individuals is examined within morphospaces constructed from these shape features. Three scales of analysis are necessary to characterize adequately the shape variation within and among specimens. The smallest scale is equivalent to increment-by-increment changes in 0 and W. The middle scale comprises variation equivalent to whorls resulting from systematic changes in 0 and W during an individual's ontogeny. Finally, there is the overall ontogenetic trajectory. Mean shape must be a function of initial shape and ontogenetic trajectory in shape. Mean forms that are found to have similar shapes at the same arbitrary growth increment may achieve that shape in different ways.

Of mice and men. Biological markers for long-term sedentism : a reply

Abstract: La brusque apparition d'especes commensales autour des habitations resulte des longues occupations natoufiennes au Sud-Levant ; elle trouve son explication par la possibilite pour les especes animales de trouver de facon permanente de la nourriture et/ou des abris. Ces isolats encouragerent la modification in situ de certaines especes (Mus domesticus, Passer domesticus, Canis familiaris). Les premieres preuves de manipulations genetiques et d'abattage intentionnel selon le sexe (dans ce cas Gazella gazella, Bovidae) peuvent etre percues sur les sites natoufiens. Une diminution significative de la taille (allometrique et disproportionnelle) ne peut s'expliquer que par une pression anthropogenique de longue duree sur l'environnement au sein d'une zone geographique relativement limitee. Ces consequences biologiques de la sedentarite sont clairement refletees par les donnees paleontologiques telles que les frequences et la taphonomie des microvertebres ou le comportement des predateurs.

Ornament Styles of the Indus Valley Tradition : Evidence from Recent Excavations at Harappa, Pakistan

Abstract: Les fouilles recentes effectuees a Harappa, a Mehrgarh, et sur d'autres sites au Pakistan et en Inde offrent des possibilites nouvelles pour l'etude des parures de la Civilisation de l'Indus. Les methodes utilisees pour l'elude des parures de la tradition Indus sont presentees et commentees rapidement, ainsi que le sont quelques exemples de parures specifiques, produit elabore du travail des artisans de l 'Indus qui allient les materiaux precieux, la pierre, les coquillages et la faience. On copiait aussi ces parures dans des materiaux d'obtention plus facile tels que la steatite ou la terre cuite. Grâce au contexte archeologique, mais aussi a des comparaisons avec la fonction de parures specifiques decrites dans les textes anciens et les traditions populaires de l'Asie du sud, sont etudiees aussi les implications sociales et rituelles de parures specifiques.

Probabilities of origination, persistence, and extinction of families of marine invertebrate life

Abstract: -In this paper we model the process of taxonomic evolution as a Galton-Watson branching process in discrete time and, using maximum likelihood, develop methods to estimate the probabilities of origination, persistence, and extinction of fossil taxa. We use the methods to estimate the probabilities of origination, persistence, and extinction of families (1) within 135 orders of marine invertebrate organisms, (2) within 12 phyla, and (3) within all marine invertebrate life (independently of the suprafamilial classification). Most orders, including the arcoid bivalves, the dentaloid scaphopods, the orders of chitins, and many others, have relatively low probabilities of familial origination and extinction. The various ammonoid and trilobite orders, and some others, have high probabilities of origination and extinction. Among the phyla, the Archaeocyatha have the highest probabilities of familial origination and extinction, and the Annelida the lowest, with the more typical phyla of shelly organisms clustering near the high end of the probability scale. The Porifera and Protozoa also have low probabilities but not as low as the Annelida. The estimated origination and extinction probabilities for families within all marine invertebrate life are 0.470 and 0.452 per stage, resp&ctively, values that are at the high end of the probability scale. We have also estimated the probabilities of ultimate extinction (extinction of all families) of the supertaxa. By analyzing the changes of the diversity during each stratigraphic stage separately, we have also determined the trajectories of the estimated origination and extinction probabilities for families within all marine invertebrate life. The estimated origination probability is relatively high in association with the expansion of the Cambrian and Paleozoic evolutionary faunas and declines to more normal levels for the remainder of the Phanerozoic. The trajectory of the estimated extinction probability is from nearly zero early in the Phanerozoic to more normal levels later, showing clearly defined peaks in association with the five Phanerozoic mass-extinction events. The terminal Cretaceous mass extinction is the only one of the five that was not preceded by a monotonic decline of origination probability or by a series of stages with low origination probability. It appears to have been a unique, singular event. Because the mathematical theory we employ as a model corresponds so closely to the processes of taxonomic evolution as we understand them, we believe that the theory provides a reasonable model of biological reality. Norman L. Gilinsky. Department of Geological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061 I. J. Good. Department of Statistics, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061 Accepted: January 16, 1991

Growth form in Silurian heliolitid corals: the influence of genetics and environment

Abstract: Colony growth form in some Silurian heliolitid corals is analyzed by the measurement of their shape in profile. Data are presented for seven species, Stelliporella parvistella, Heliolites interstinctus, H. megastoma, H. daintreei, H. spongodes, Propora tubulata, and Plasmopora scita from three localities in Gotland, Sweden, and three localities in England. Intraspecific growth-form variation is presented on triangle diagrams. These plots allow variation to be compared between species present at each locality and between localities for each species. Results indicate that the overall potential for growth-form variation is genetically controlled and that levels of response to envi- ronmental stimuli may differ markedly between species. Stelliporella parvistella is a very plastic species, the only one developing branching growth in addition to other growth forms. Heliolites interstinctus is much less variable, dominantly tabular, domal, and low bulbous in form, but dem- onstrates a similar response. Propora tubulata has a tightly constrained bulbous growth form that shows little variation between localities. The other species are represented by few specimens, most of which parallel H. interstinctus. The likely moderating influences of light levels, substrate type, sedimentation rate, energy levels, and other variables on growth-form variation and species range are considered. The main environmental factor including ecophenotypic response is concluded to be sedimentation rate. A close correlation between this factor and growth form in S. parvistella indicates that form in this species is a particularly sensitive indicator of sedimentation rate and substrate conditions. No simple equations can be made between specific environments and one particular growth form in these corals.

Early Neolithic use of upland areas of Wadi El-Yabis : preliminary evidence from the excavations of 'Iraq Ed-Dubb, Jordan

Abstract: Les fouilles qui se sont deroulees dans la grotte d'Iraq ed-Dubb (grotte de l'Ours), situee dans les montagnes boisees du Wadi El-Yabis, en Jordanie du nord-ouest, ont revele la presence de constructions en pierre et d'autres restes de culture materielle dates par le C14 de 9.950 +/- 100 BP. Parmi les restes materiels de cette occupation PPNA, ont ete mis au jour une construction ovale en pierre au sol en terre battue et deux sepultures, et recueillis des restes de faune abondants et de plantes carbonisees en bon etat de conservation. L'analyse preliminaire de l'assemblage lithique indique que le gisement est contemporain d'autres sites neolithiques anciens fouilles dans la Vallee du Jourdain, et qu'il se caracterise par un industrie de microlithes et de lamelles, avec des pointes ďEl-Khiam, des segments de cercle et des troncatures Hagdud. Les fouilles en cours dans la grotte ont livre de precieux renseignements sur l'exploitation des zones de plateaux au cours du neolithique Preceramique par les chasseurs/cueille urs, alors que l'on assiste aux debuts de l'agriculture dans la Vallee du Jourdain.

Seasonality and gazelle hunting at Hayonim Cave : new evidence for "sedentism" during the Natufian

Abstract: L'identification des saisons d'occupation des sites archeologiques reste un probleme majeur pour les archeologues, et l'un des points essentiels de l'etude des changements des strategies d'acquisition des ressources de chasseurs-cueilleurs. L'application de l'analyse des depots cementeux a l'interpretation de l'occupation saisonniere des sites est presentee ici. L'exemple ďHayonim montre que les chasseurs-cueilleurs du natoufien ont occupe le site durant toute l'annee, contrairement a leurs predecesseurs qui, durant le Kebarien, ne semblent l'avoir utilise qu'entre les mois de novembre et de fevrier. L'apport de ces donnees est discute dans le cadre des origines de la sedentarisation preagricole qui s'est produite au Levant a la fin du natoufien.

Nouvelles analyses d'obsidiennes du Proche-Orient : modèle de géochimie des magmas utilisé pour la recherche archéologique

Abstract: Les recherches sur les origines des obsidiennes sont effectuees sur 52 echantillons geologiques et archeologiques, au moyen d'analyses chimiques multi-elementaires : 27 elements majeurs et traces doses par spectrometrie d'emission d'etincelle, de flamme et de plasma (ICP). Ces analyses sont exploitees en utilisant le modele de geochimie des magmas : fusion partielle, cristallisation fractionnee, coefficients de partage. Leurs caracteres specifiques conduisent a s'interesser tout particulierement aux elements, dits « hygromagmaphiles », qui se concentrent dans un magma au cours de son evolution. Ce sont ici quatre lanthanides, ; La, Ce, Yb, Lu, ainsi que Y, Zr, Nb et Zn. ; Cinq echantillons, choisis dans les familles geochimiques de Bingol, ont en outre ete testes par thermoluminescence, tests qui ont conduit a une chronologie relative en trois temps : deux coulees successives avec, pour la plus ancienne, un âge probablement tres superieur a 1 million d'annees et un echantillon artificiellement chauffe vers 8 000 BP. ; La methode conduit a considerer deux types de criteres permettant d'attribuer des objets a un meme site geologique. 1) Identite des compositions chimiques, en particulier en elements hygromagmaphiles : provenance d'une meme coulee. 2) Compositions chimiques differentes, mais conservation des rapports entre elements hygromagmaphiles : provenance de coulees successives issues d'un meme magma. C'est ainsi que les deux familles de Bingol sont confirmees et expliquees : elles sont comagmatiques et correspondent a des coulees d'âges differents, lesquels sont confirmes par les tests de thermoluminescence. Un echantillon est par ailleurs repere qui pourrait provenir d'une troisieme coulee de Bingol qu'il serait interessant de rechercher sur le terrain. ; Ces analyses montrent l'importance particuliere du gite anatolien de Bingol dans l'approvisionnement en obsidienne des villages neolithiques (PPNB) et chalcolithiques, non seulement dans le Taurus et en Haute Mesopotamie, mais bien plus au Sud, dans une oasis du desert syrien (El Kowm).

The Analysis of Mammalian bones from Basta, a Pre-Pottery Neolithic site in Jordan : problems and potential

Abstract: Les fouilles recentes sur le site de Basta (region de Petra, Jordanie) ont produit un assemblage faunique tres riche (plus de 100 000 os), datant du 7e millenaire avant notre ere. Les analyses archeozoologiques ont donne des resultats preliminaires inattendus: l'economie a Basta est fondee avant tout sur l'elevage d'ovicaprines; la chasse se concentre sur les gazelles, les onagres, les ânes sauvages africains et d'autres ongules; carnivores et rongeurs sont plus rares. L'assemblage faunique temoigne de l'existence et de l'exploitation, non loin du site, de divers biotopes comportant chacun sa faune specifique : steppe semi-aride, collines, wadis avec leurs forets et regions montagneuses. Les resultats obtenus aident a combler certaines lacunes concernant aussi bien la domestication des animaux, la distribution prehistorique des ongules et d'autres especes que l'economie d'un village pre-ceramique du sud du Levant.