Showing papers in "Paleobiology in 1999"

Titanosaurs and the origin of wide-gauge trackways; a biomechanical and systematic perspective on sauropod locomotion

Abstract: Two major ichnotypes of sauropod trackways have been described: "narrow-gauge," in which both manus and pes prints approach or intersect the trackway midline, and "wide-gauge," in which these prints are well apart from the midline. This gauge disparity could be the result of differences in behavior, body size, or morphology between the respective trackmakers. However, the biomechanics of locomotion in large terrestrial vertebrates suggest that sauropods were prob- ably restricted in locomotor behavior, and the lack of systematic size differences between footprint gauges argues against body-size-related influences. We argue that skeletal morphology is respon- sible for gauge differences and integrate data from locomotor biomechanics and systematics with the track record to predict the hindlimb morphology of wide-gauge trackmakers. Broader foot stances in large, graviportal animals entail predictable mechanical consequences and hindlimb modifications. These could include outwardly angled femora, offset knee condyles, and a more eccentric femoral midshaft cross-section. A survey of sauropod hindlimb morphology reveals that these features are synapomorphies of titanosaurs, suggesting that they were the makers of wide- gauge trackways. The temporal and geographic distribution of titanosaurs is consistent with this hypothesis because wide-gauge trackways predominate during the Cretaceous and are found worldwide. Additional appendicular synapomorphies of titanosaurs are interpreted in light of identifying these animals as wide-gauge trackmakers. We suggest that titanosaurs may have used a bipedal stance more frequently than did other sauropods. These correlations between ichnology, biomechanics, and systematics imply that titanosaurs were unique among sauropods in having a more varied repertoire of locomotor habits.

Generalizing and extending the eigenshape method of shape space visualization and analysis

Abstract: Outline-based morphometric methods have been more or less restricted to the consideration of closed curves and plagued by problems related to the maintenance of close biological correspondence across all forms within a sample. Methods developed herein generalize and extend the eigenshape method of outline analysis along the following lines: (1) consideration of open curves, (2) improvement of interobject correspondence via incorporation of information provided by landmarks, and (3) extension to the analysis of three-dimensional (open and closed) curves. In addition, techniques for using eigenshape results to create models of shape variation and for more consistently assessing the digital resolution necessary to represent an object are discussed and illustrated. These improvements are then placed in context via discussions of previous attempts to extend morphometric outline analysis methods, the relation between landmark and outline-based morphometric methods, the use of morphometric analyses to test biological hypotheses, and the nature of morphometric shape spaces (with special reference to studies of morphological disparity).

Variation in dinosaur skeletochronology indicators: implications for age assessment and physiology

Abstract: Twelve different bones from the skeleton of the holotype specimen of the hadrosaurian dinosaur Hypacrosaurus stebingeri were thin-sectioned to evaluate the significance of lines of ar- rested growth (LAGs) in age assessments. The presence of an external fundamental system (EFS) at the external surface of the cortex and mature epiphyses indicate that the Hypacrosaurus specimen had reached adulthood and growth had slowed considerably from earlier stages. The number of LAGs varied from none in the pedal phalanx to as many as eight in the tibia and femur. Most el- ements had experienced considerable Haversian reconstruction that had most likely obliterated many LAGs. The tibia was found to have experienced the least amount of reconstruction, but was still not optimal for skeletochronology because the LAGs were difficult to count near the periosteal surface. Additionally, the numbers of LAGs within the EFS vary considerably around the circum- ference of a single element and among elements. Counting LAGs from a single bone to assess ske- letochronology appears to be unreliable, particularly when a fundamental system exists. Because LAGs are plesiomorphic for tetrapods, and because they are present in over a dozen orders of mammals, they have no particular physiological meaning that can be generalized to par- ticular amniote groups without independent physiological evidence. Descriptions of dinosaur physiology as "intermediate" between the physiology of living reptiles and that of living birds and mammals may or may not be valid, but cannot be based reliably on the presence of LAGs.

Comparing palynological abundance and diversity; implications for biotic replacement during the Cretaceous angiosperm radiation

Abstract: The Cretaceous radiation of angiosperms initiated a major reorganization of terrestrial plant communities as dominance by pteridophytic and gymnospermic groups eventually gave way to dominance by angiosperms. Previously, patterns of biotic replacement have been assessed using measures based on taxonomic diversity data. However, using measures of both abundance and diversity to investigate replacement patterns provides more information about macroecological change in the fossil record than either can provide alone. Analyses of an updated and expanded database of North American palynological samples from Cretaceous sediments document a rapid increase in angiosperm diversity and abundance within individual fossil palynofloras (representing local/subregional vegetation). New analyses of floristic diversity patterns support previous results and indicate that the decline of free-sporing plants is more pronounced than the decline of gymnosperms. In contrast, analyses of abundance data appear to show that the decline of gymnosperms is far more pronounced than the decline of free-sporing plants. Detailed examination of both data sets segregated by paleolatitude shows that this apparent contradiction reflects biogeographical differences in the patterns of vegetational change (e.g., free-sporing plants declined in abundance at lower latitudes) as well as sampling bias (e.g., greater sampling in the northern region in the Late Cretaceous). Analyses accounting for these biases support the conclusion that as angiosperms radiated, free-sporing plants rather than gymnosperms (in this case, mainly conifers) experienced the most pronounced decline. A thorough understanding of the Cretaceous radiation of angiosperms will require both abundance and diversity data. It also will require expanding the analyses presented here into other geographic regions as well as sampling more completely at all spatial scales.

Morphological diversity in the evolutionary radiation of Paleozoic and post-Paleozoic crinoids

Abstract: The Paleozoic and post-Paleozoic radiations of crinoids present an opportunity to explore genomic and ecological explanations for patterns of morphologic diversification. Analysis of discrete-character data that cover the principal features of the crinoid skeleton shows that both Paleozoic and post-Paleozoic increases in morphological disparity were abrupt; this is consistent with rapid exploitation of open ecological opportunities in both cases. For the post-Paleozoic, this result is sensitive to some aspects of data analysis and sampling, so it cannot be regarded as unequivocal. The deceleration in morphological diversification within each radiation is consistent with an observed decline in rates of taxonomic origination as well as with the attainment of functional or structural limits. Despite these similarities in the two radiations, Paleozoic crinoids exploited a wider range of morphological designs than did their post-Paleozoic successors. Post-Paleozoic crinoids exploited a wide range of ecological strategies despite being stereotyped in many aspects of form. This difference between the radiations is consistent with an increase in the rigidity of genetic and developmental systems. The range of post-Paleozoic designs is not in essence a subset of the Paleozoic spectrum. The two radiations resulted in morphological distributions that are largely nonoverlapping, perhaps reflecting a different range of ecological strategies.

Estimating the masses and centers of mass of extinct animals by 3-d mathematical slicing

Abstract: A mathematical-computational method for determining the volume, mass, and center of mass of any bilaterally symmetric organism is presented. Cavities within the body of an organism such as lungs are easily accommodated by this method. Sagittal and frontal profiles, obtained from tracings of "fleshed-out" skeletal reconstructions, are used to provide limits for defining transverse slices of the body. Any internal cavities are defined by their own sagittal and frontal profiles. The computations consist of mathematically slicing the body and any cavities into independent sets of transverse laminae and computing their masses, centroids, and moments with respect to the three coordinate axes. Further calculations produce the masses and the (x, y, z) coordinates for the centers of mass of the body, any cavities, and the body+cavities. Predicted body masses of large, extant mammals (elephant, giraffe, hippopotamus, and rhinoceros) are in close agreement with actual body masses. New, lower estimates for body masses of selected large dinosaurs, based on modern skeletal reconstructions, are also presented, along with numerical estimates of their centers of mass. This method is an improvement over earlier ones that relied on measuring displaced volumes of water or sand by scale models to estimate the masses, and suspending models by threads to estimate their centers of mass.

Early Animal Husbandry in the Northern Levant

Abstract: Que ce soient les arguments morphometriques ou. d'autres plus indirects, la domestication du mouton et fort probablement celle de la chevre prend place durant, le PPNB ancien dans les piemonts sud du Taurus. Meme si l'elevage se generalise dans le Levant Nord, au cours du PPNB moyen, les frequences de chevres et de moutons ne depassent pas 30 % des restes osseux de cette periode. Ainsi, l'introduction de ces petits ruminants dans l'economie de ces sites anciens parait moins « revolutionnaire » que l'expression « Revolution Neolithique » ne l'implique. Au cours du PPNB moyen, deux autres especes acquierent un statut domestique dans deux regions differentes : Bos dans le bassin du moyen Euphrate et Sus dans le sud-est de la Turquie. A la fin du. PPNB l'elevage du betail formait une importante composante de l'economie de subsistance humaine dans tout le Levant nord. A l'exception d''Ovis qui semble avoir ete introduit dans le Levant sud a partir du Nord, les modalites du processus de diffusion des animaux de ferme depuis leur(s) centre(s) de domestication vers les regions adjacentes, ont encore besoin d'etre etudiees. Meme si nous sommes assures que les changements socioculturels du 11e et du 10e millenaire ВС calibre se complexifient et que les societes socialement stratifiees du Levant nord bâtissent l'arriere-plan culturel, dans lequel la domestication des caprines prend place, nous continuons encore a nous interroger sur les causes de l'introduction du betail dans l'economie du Neolithique preceramique. En. nous fondant sur les evidences archeozoologiques et paleobotaniques, les changements climatiques de grande amplitude et/ou les deteriorations du milieu nous paraissent maintenant improbables dans cette region. Ceci nous renforce dans l'idee que les facteurs socioculturels ont ete a l'origine du changement d'exploitation des animaux.

Taking advantage of time-averaging

Abstract: One of the major obstacles in dealing with any form of data derived from fossils is the effects of time-averaging, which are the result of mixing the remains of organisms that did not live contemporaneously. Although this process results in loss of temporal resolution, it also serves to filter out short-term variations. Temporal resolution of a collection depends not only on the range of fossil ages, but also on their frequency distribution. Previous studies of marine molluscs indicate that most shells in an accumulation are relatively young. Such a distribution of shell ages can be fit by an exponential curve (assuming both a constant probability of shell loss and a constant rate of shell addition), which implies that 90% of the shells were added during the last 50% of the time interval represented by the collection. That is to say, differences between two collections can be discerned even if they overlap 50% in time, because the proportion of shells with shared ages is only 10%. Applying the exponential model to previously published data suggests that long-term rates of destruction are controlled by how frequently shells from the taphonomically active zone are re-exposed to rapid destruction. To take advantage of the “noise-filtering” property of time-averaging, samples need to be large enough to catch the full range of environmental variation recorded by an accumulation. A simple probability formula indicates that samples of easily achievable size can give satisfactory time-averaged results depending on the level of confidence and sampling density defined by the researcher.

Animal domestication in the Southern Levant.

Abstract: Dans cet article, sept chercheurs travaillant au Levant sud presentent leur approche de la domestication animale dans cette region, ainsi que de nouvelles donnees. Ils prennent en compte toute la periode concernee par ce phenomene, des premieres communautes sedentaires natoufiennes jusqu 'a l'arrivee des premiers caprines domestiques durant le PPNB moyen/recent. De plus, la domestication du bœuf et du cochon par les societes du PPNC est discutee, de meme que l'est le developpement d'economies pastorales durant le PPNC et le Neolithique a poterie, alors que l'elevage ovicaprin etait introduit dans les regions desertiques situees plus au sud et a l 'est. Cet article examine egalement les differents processus impliques dans la domestication animale, l'hypothese de la domestication locale face a celle de l'introduction, dans cette region, d'animaux d'elevage, ainsi que l'influence des conditions environnementales tres particulieres du Sud Levant sur le processus de domestication.

Origination preceding extinction during late Cenozoic turnover of Caribbean reefs

Abstract: Statistical analyses of occurrence data derived from new collections through scattered Caribbean sections indicate that increased speciation preceded a pulse of extinction during regional turnover of the Caribbean reef coral fauna in Plio-Pleistocene time. The data are based on samples that were newly collected and identified to species using standardized procedures. Age-dates were assigned using high-resolution chronostratigraphic methods. The results show that coral species with a wide range of ecological traits originated and were added to the species pool as much as 1- 2 million years before extinction peaked at the end of the turnover interval. Local assemblages consisted of a mix of extinct and living species, which varied in composition but not in richness. Extinction was selective and resulted in a faunal shift to the large, fast-growing species that dom- inate Caribbean reefs today. The unusual relationship between origination and extinction may have been caused by changes in oceanic circulation associated with emergence of the Central American Isthmus, followed by the onset of Northern Hemisphere glaciation. The pattern of origination pre- ceding extinction may have been responsible for the stability of reef ecosystems during the intense climatic fluctuations of the late Pleistocene, and for the composition and structure of modern Ca- ribbean reef ecosystems.

Discordant morphological disparity and taxonomic diversity during the cretaceous angiosperm radiation : north american pollen record

Abstract: The Cretaceous angiosperm radiation offers an opportunity to examine patterns of morphological evolution in terrestrial plants and to compare them with patterns previously observed during radiations of marine animals. Focusing on evolution among angiosperm pollen types, I used average pairwise dissimilarity and total variance to describe changing morphological varieties (disparity) through the Cretaceous and Paleocene in North America. Angiosperm species diversity shows an approximately tenfold increase through this interval, but this taxonomic diversification is not matched by a comparable change in morphological disparity. Partitioning of morphological disparity among major pollen groups shows that most of the variance is contributed by eudicots from the Albian onwards. Constant disparity across the Cretaceous/Tertiary boundary despite decreased taxonomic diversity suggests that the Cretaceous/Tertiary extinction was not selective with respect to the pollen morphological characters analyzed here. The two measures of disparity show similar patterns. The overall pattern is robust to changes in character weighting, indicating that no one set of characters or weighting scheme is driving the pattern. Analyses of older data indicate that the initial burst of disparity in the Aptian could be due in part to analytical time-averaging. The observed incongruence between taxonomic diversity and morphological disparity suggests that morphological evolution in pollen was characterized by larger jumps early and smaller jumps later on, and is similar to that found in several groups of marine invertebrates.

Biogeographic analyses of the Ediacara biota; a conflict with paleotectonic reconstructions

Abstract: Paleotectonic reconstructions for the late Proterozoic have differed over the timing of the Cordilleran rifting between Laurentia and the East Gondwana cratons. Parsimony Analysis of Endemism (PAE) and phenetic clustering of the "Ediacara biota" were carried out, for comparison with competing paleotectonic hypotheses. All analyses show a common pattern of similarities among biotas. The biotas of Charnwood Forest and Newfoundland consistently group together, while the south Australian biota is closest to those of Baltica, northern Laurentia, and Siberia. The biota of southwest North America, though still poorly known, strikingly resembles that of Na- mibia-not that of northwestern Canada. This pattern is not obviously due to facies-related or pres- ervational bias and is very different from Cambrian biogeographic patterns. The overall pattern is most consistent with the hypothesis that the western margin of Laurentia was in close contact with East Gondwana, with rifting taking place either during or just before the Vendian. This arrange- ment has been previously proposed as a paleotectonic hypothesis; however, most recent paleo- magnetic and structural studies support the alternate hypothesis that this rifting took place more than 100 million years before the Vendian. Resolving this contradiction will require much more data on both organismal distribution and cratonal position.

Mammal remains from the eastern Jordanian Neolithic, and the nature of caprine herding in the steppe

Abstract: Cet article presente les resultats de l'etude de restes de mammiferes provenant de dix sites de l'Est de la Jordanie. Ces sites couvrent les periodes allant du milieu du 10e millenaire jusqu'au 11e millenaire BP et se rattachent au Neolithique pre-ceramique В (Pre-Pottery Neolithic В, PPNB) et au Neolithique recent (Late Neolithic, LN). Ils se situent dans des regions aujourd'hui desertiques et sub -desertiques. Les proportions relatives des restes mammiferes identifies sont donnees pour chaque assemblage osseux, les variabilites chronologiques et geographiques sont soulignees, et le changement majeur observe au debut du Neolithique recent - celui de l'apparition des caprins (moutons et chevres) est discute. A notre avis l'evidence est faible que les sites neolithique de l'est de la Jordanie soient des etablissements ou s'exercent des activites pastorales specialisees, comme cela a ete suggere. En revanche, les habitants de ces sites pratiquaient pour leur subsistance la chasse, le piegeage, la cueillette, la culture des cereales, auxquels s'ajoute au debut du Neolithique recent l'elevage du mouton et de la chevre.

Les premiers pas de la domestication animale à l'ouest de l'Euphrate : Chypre et l'Anatolie centrale

Abstract: Les auteurs exposent les resultats des analyses encore en cours sur deux sites, l'un a Chypre (Shillourokambos), l'autre en Anatolie centrale (Asikh Hoyuk). Ces sites illustrent tous deux, pour des regions pareillement situees a l'Ouest du foyer de domestication de l'Anatolie orientale, les premiers pas de l'elevage au Neolithique preceramique, entre la fin du 9e et le milieu du 8e millenaire av. J.-C. (dates calibrees). A Chypre, il s'agit clairement d'un processus de diffusion puisque differentes especes- appropriees par l'homme {Porc, Daim, Mouton, Chevre, Bœuf...) ont ete deliberement importees du continent des la fin du 9e millenaire. Le processus de domestication en Anatolie centrale semble, en revanche, resulter principalement de l'emergence d'une gestion intensive et tres specialisee des Caprines, dont on ne peut preciser pour l'instant si elle est contemporaine ou posterieure a celles qui sont attestees dans la region Euphrate-Tigre. Dans les deux cas on observe cependant que certaines especes, bien que probablement elevees par les groupes humains, ont conserve une forme sauvage durant plusieurs siecles (populations «pre-domestiques »). Ces constats font par ailleurs ressortir l'importance anthropologique et historique de cette phase «intermediaire» de gestion intensive de populations «pre-domestiques », qui precede l'apparition d'especes pleinement domestiques. Des pistes de recherche archeologique sont degagees pour Chypre, l'Anatolie centrale et occidentale, et l'ensemble du Proche-Orient.

The time of origin of whales and the role of behavioral changes in the terrestrial-aquatic transition

Abstract: Addition of the recently discovered fossil Nalacetus to a phylogenetic analysis of basicranial, cranial, dental, postcranial, and soft morphological characters reveals that it is the most basal cetacean, and that mesonychians form the monophyletic sister group to Cetacea. The molars of Nalacetus elucidate transformations in dental morphology that occurred early in the cetacean radiation and clarify certain derived differences in molar cusp position between cetaceans and the extinct clade, Mesonychia, hypothesized to be their sister taxon. Nalacetus and other archaic cetaceans share derived vertically elongate shearing facets on the lower molars. Applying the Extant Phylogenetic Bracket, we advance the hypothesis that these facets are an osteological correlate of aquatic predation. Our functional interpretation of this character and its distribution within Cetacea indicates that a behavioral change in tooth use characterized the origin of the clade. Comparison of the transformation of this dental character with that of the cetacean pelvis indicates that a change in tooth use (feeding behavior) occurred before loss of the ability to engage in terrestrial locomotion.The most parsimonious phylogenetic hypothesis presented here has a significant fit with the stratigraphic record as determined by the Manhattan Stratigraphic Measure, which is corroborated by retention indices of stratigraphic data. Ghost lineages necessitated by the phylogenetic hypothesis extend the stratigraphic range of Cetacea into the middle Paleocene (Torrejonian), ten million years earlier than the oldest cetacean fossil currently known. Primitive features of Nalacetus, the large number of synapomorphies diagnosing Cetacea, and the implied ghost lineage suggest that the early cetacean radiation was much more extensive than has been previously recognized.

Anagenetic evolution, stratophenetic patterns, and random walk models

Abstract: Previous studies have suggested that unbiased random walks may serve as appropriate null hypotheses for the detection of pattern in stratophenetic series. While numerous processes that influence the perceived temporal morphological evolution of a species may yield stratophenetic patterns that conform to the model of a random walk, use of the model as a null hypothesis raises several concerns. First, unbiased random walks are only a subset of a much larger set of random motions, including biased and fractional random walks. Some of these motions could also serve as appropriate null models for stratophenetic patterns. Second, due in part to the fractal nature of random walks, many types of time series begin to resemble random walks statistically as sampling resolution decreases. Therefore, indiscriminate support for unbiased random walks as null hypotheses of stratophenetic pattern leads inevitably to the commitment of Type II errors (incorrect failure to reject a null hypothesis). In this paper we simulate different hypothetical patterns of microevolution using various random walk models and apply the test of the null hypothesis. The frequency of Type II errors increases as stratigraphic completeness decreases, but at a currently unknown rate. Moreover, the test is insensitive to nongradual patterns of anagenesis. We also demonstrate that a previously published approach is closely related to a standard method of fractal time series analysis and represents a good qualitative test of evolutionary pattern. The statistical variation underlying this method, however, is currently unknown, and further work is required to make it a robust quantitative test.

Direct measurement of age in fossil Gryphaea: the solution to a classic problem in heterochrony

Abstract: We have known since Trueman's classic work of 1922 that the Lower Jurassic Gryphaea of Britain exhibit phyletic size increase and heterochronic change in shape. Since Hallam's revisionary work in the 1960s, we have recognized that pronounced and generalized juvenilization of form accompanied this increasing size. This extensive literature provides invertebrate paleontology's most famous example of a biometrically documented, continuous anagenetic trend within a discrete lineage. But Gryphaea has also provoked great frustration because a key datum, required for a full solution, had been theoretically recognized but practically unavailable. We could identify the evolution of shape as paedomorphic, but could not specify the mode of heterochrony for this paedomorphic result because we could not standardize samples by common age or developmental stage.In this paper, we provide sclerochronological data on sizes and shapes at specified ages marked by annual growth bands in two Jurassic sequences of Gryphaea: the classic Lower Jurassic series showing phyletic size increase with paedomorphosis, and an independent Middle–Upper Jurassic series illustrating neither size increase nor heterochrony. We prove that size increase in the classic series occurs entirely by faster growth (larger descendant sizes at the same ages as ancestors), and not by extended age (for descendants lived no longer than ancestors). The well-marked paedomorphosis of form probably arose as a correlated consequence of growing larger by extending and maintaining rapid juvenile growth rates—thus marking the heterochronic mode as a case of neoteny. The independent upper sequence, acting as a different replicate in a natural experiment, shows neither size increase nor heterochrony but does exhibit (in contrast with the classic sequence) evolution toward greater longevity.Hallam's flow tank experiments indicated a strong adaptive advantage in shell stability for both larger size and paedomorphic form. Neotenous development provides an evolutionary pathway to the simultaneous acquisition of both favored traits—thus showing that “constraints” due to “correlations of growth” (Darwin's own phrase for the phenomenon) may be positive in promoting joint evolutionary advantages, and not only neutral (in carrying spandrels along with primary adaptations), or negative (by imposing inadaptive “baggage” upon trends in form through developmental correlation with selected traits).

Mammal-like occlusion in conodonts

Abstract: Conodont element function and feeding mechanisms are of considerable paleobiological importance, yet many details remain poorly understood and speculative. Analysis based on mor- phology, physical juxtaposition, and patterns of surface damage and microwear on pairs of Pa el- ements from individuals of Idiognathodus indicates that these elements crushed food by rotational closure, which brought the oral surfaces into complex interpenetrative occlusion. Other molariform conodont elements also functioned in this manner. Occlusion of this complexity is unique among nonmammalian vertebrates, and is all the more surprising given that conodonts lacked jaws. In addition to enhanced understanding of food processing in conodonts, our analysis suggests that many details of conodont Pa element morphology, which underpin taxonomy and biostratigraphy, can now be interpreted in a paleobiological, functional context.

Animal Domestication in the Zagros : A Review of Past and Current Research.

Abstract: Pendant plus de cinquante ans, la region du Zagros que couvre de nos jours l'Iran et V Iraq fut reconnue comme ayant ete l'un des centres primaires et independants de la domestication animale, particulierement celle des moutons et des chevres. Commencant avec les travaux conduits par R. Braidwood et les chercheurs qui l 'entouraient, un certain nombre de fouilles avaient pour objectif de mettre en evidence comment s 'etait effectuee dans cette zone la transition entre la chasse et l 'elevage. Les etudes archeoz.oologiqu.es, reellement des travaux pionniers, sur les restes animaux tracerent alors avec succes les grandes lignes de la domestication des caprines dans le Zagros. Cependant, compte tenu de la diversite des approches et des perspectives des differents chercheurs engages dans ces recherches, il n 'y a encore guere de consensus tant sur le temps que prit la domestication que sur la periode, la localisation et les causes de celle du mouton et de la chevre dans cette region. De plus, les premieres tentatives pour dater ce processus furent faites au tout debut des datations par le radiocarbone ; trop souvent ces datations ne permirent pas de se faire une idee claire de la ou se placaient dans cette region sur le plan temporel les sites cles du debut de l'Holocene. Cet article resume les premiers efforts accomplis pour suivre le cours de la domestication animale dans le Zagros. Il presente aussi les premiers resultats d'une recherche recente qui tend a re-analyser et a redater toutes les collections pouvant apporter des elements sur l'origine de la domestication dans le Zagros. Utilisant une nouvelle methode qui a permis de tracer les etapes initiales du processus de domestication, cette etude demontre que la domestication de la chevre prit place dans les hauteurs la ou la chevre a son habitat naturel et ce, aux alentours de 9 000 uncal BP, et qu 'ensuite elle s 'etendit vers des zones plus marginales. Le mouton domestique, lui, semble avoir ete introduit plus tard dans cette region, probablement depuis le lieu de sa domestication originale, le nord et l'ouest du croissant fertile.

Biomasse d'ongulés au paléolithique et inférences sur la démographie

Abstract: Fonde sur des donnees fossiles et actuelles, ce travail traite essentiellement des variations de la biomasse des Ongules au cours de la derniere periode de recession du froid: de 18 000 a 11 000 BP. Plusieurs ecosystemes successifs ont ete mis en evidence, chacun avec leur propre biomasse d'Ongules. Du systeme le plus contraignant (autour de 18 000 BP) au systeme le plus favorable (vers 13 000 BP), la biomasse augmente dans un rapport de 1 a 23; elle chute brutalement ensuite. Il a ete retenu que la densite des predateurs humains a varie de la meme facon partant d'une valeur proche de 0 vers 18 000 BP, atteignant plus de 17 habitants par 100 km 2 vers 13 000 BP et chutant fortement ensuite. L'effectif maximum de la population humaine d'Europe habitant le nord de l'arc alpin de la Pologne jusqu'aux confins ouest de la peninsule a pu etre estime a pres de 250 000 individus. La variation de la biomasse des Ongules lors des deux periodes anterieures de recession du froid (passage stade 4-stade 3 et passage stade 6-stade 5) est egalement discutee.

Kombewa et alii

Abstract: Kombewa et alii. This is about a general thought concerning the cores on a flake and their occurrence during the Lower and Middle Paleolithic in the Bassin Aquitain.

Biophysical constraints on the thermal ecology of dinosaurs

Abstract: A physical, model-based approach to body temperatures in dinosaurs allows us to pre- dict what ranges of body temperatures and what thermoregulatory strategies were available to those dinosaurs. We argue that 1. The huge range of body sizes in the dinosaurs likely resulted in very different thermal problems and strategies for animals at either end of this size continuum. 2. Body temperatures of the smallest adult dinosaurs and of hatchlings and small juveniles would have been largely insensitive to metabolic rates in the absence of insulation. The smallest an- imals in which metabolic heating resulted in predicted body temperatures 2 2?C above oper- ative temperatures (TJ) weigh 10 kg. Body temperature would respond rapidly enough to

Morphological evolution of the murine rodent Paraethomys in response to climatic variations (Mio-Pleistocene of North Africa)

Abstract: The North African murine rodent Paraethomys evolved as an anagenetic lineage from the late Miocene until its extinction in the late-middle Pleistocene. A Fourier analysis of the outlines of the first upper and lower molars of this rodent was used to quantify the evolutionary patterns of this lineage and to compare evolutionary patterns to the climatic record. Morphological evolu- tion and long-term environmental variations are strongly correlated. A change in molar shape, which may be related to the development of a more grass-eating diet, corresponds to the global cooling beginning around 3 Ma and the subsequent increase in aridity in North Africa. Concur- rently, size increased, which may be related to increased masticatory efficiency or to metabolic ad- aptation to the cooler environmental conditions according to Bergmann's rule. This adaptive re- sponse to changing environmental conditions corresponds to an acceleration of evolutionary rates in the lineage. The modalities of the evolutionary response in size and shape are probably con- trolled by intrinsic factors such as different genetic determinisms for both characters.

Decline in extinction rates and scale invariance in the fossil record

Abstract: We show that the decline in the extinction rate during the Phanerozoic can be accurately described by a logarithmic fit to the cumulative total extinction. This implies that extinction intensity is falling off approximately as the reciprocal of time. We demonstrate that this observation alone is sufficient to explain the existence of the proposed power-law forms in the distribution of the sizes of extinction events and in the power spectrum of Phanerozoic extinction, results that previously have been explained by appealing to self-organized critical theories of evolutionary dynamics.

Heterochrony; beyond words

Abstract: “It's not all heterochrony.” Raff (1996)“Heterochrony … explains everything.” McNamara (1997)Few evolutionary topics have generated more confusion and controversy than heterochrony. Commonly defined as “evolution via change in rate or timing of development,” heterchrony has historically become associated with genocidal ideologies, simple-minded theories of evolution, and a bloated, baroque jargon describing patterns produced by largely unknown mechanisms. With a track record like that, perhaps the most surprising aspect of heterochrony is its continued, even rapid, growth as an area of productive scientific inquiry. For example, the number of papers devoted to heterochronic topics continues to increase in many evolutionary journals and books (reviews in Reilly et al. 1997; Klingenberg 1998), including those devoted to human development (Bogin 1997) and evolution (Vrba 1998; McKinney 1998; Parker and McKinney 1999).

Biomasse d'Ongulés au Paléolithique et inférences sur la démographie/Ungulate Biomass During the Paleolithic Period and Inferences Concerning Human Demography

Abstract: Fonde sur des donnees fossiles et actuelles, ce travail traite essentiellement des variations de la biomasse des Ongules au cours de la derniere periode de recession du froid : de 18 000 a 11 000 BP. Plusieurs ecosystemes successifs ont ete mis en evidence, chacun avec leur propre biomasse d'Ongules. Du systeme le plus contraignant (autour de 18 000 BP) au systeme le plus favorable (vers 13 000 BP), la biomasse augmente dans un rapport de 1 a 23 ; elle chute brutalement ensuite. Il a ete retenu que la densite des predateurs humains a varie de la meme facon partant d'une valeur proche de 0 vers 18 000 BP, atteignant plus de 17 habitants par 100 km2 vers 13 000 BP et chutant fortement ensuite. L'effectif maximum de la population humaine d'Europe habitant le nord de l'arc alpin de la Pologne jusqu'aux confins ouest de la peninsule a pu etre estime a pres de 250 000 individus. La variation de la biomasse des Ongules lors des deux periodes anterieures de recession du froid (passage stade 4-stade 3 et passage stade 6-stade 5) est egalement discutee.

Disparity and constraint in olenelloid trilobites and the Cambrian Radiation

Abstract: The Cambrian Radiation marks the appearance of representatives of virtually all major skeletonized phyla in the fossil record and clearly represents a fundamental episode in the history of life. Furthermore, the tempo and mode of this evolutionary event have been the subject of intense debate. One area that has been debated is how so many phylum-level body plans can have evolved in such a geologically brief period. Some have argued that there was enhanced morphological flexibility and fewer evolutionary constraints at this time, leading to greater morphological disparity of Early Cambrian faunas. Others have claimed that this is not true because the evolution of most of the animal phyla significantly predates the radiation or because they failed to detect a signature of decreasing morphological disparity through time. At present, the higher-level patterns of diversification during this time period and the relevant implications for Early Cambrian uniqueness are areas of active research interest and debate. Recognizing this debate, we used both a phylogenetic and a morphometric framework to study whether there is a signature of increasing morphological constraint and decreasing flexibility through time within one of the clades that is a significant constituent of the Early Cambrian biota, specifically, the olenelloid trilobites. In this species-rich clade, we found no evidence that morphological changes were becoming either increasingly constrained or less flexible in one of the dominant Early Cambrian metazoan clades as it passed through the Cambrian Radiation.

The stratigraphic distribution of graptolites in the classic upper Middle Ordovician Utica Shale of New York State; an evolutionary succession or a response to relative sea-level change?

Abstract: The stratigraphic distribution of graptoloid species within the upper Middle Ordovician strata of New York State represents a complex pattern of origination, extinction, faunal migration, and fluctuating relative abundances. In particular, the observed patterns of species turnover at graptolite biozone boundaries are apparently strongly correlated with lithofacies, sampling strat- egies, and the depositional effects of relative sea-level change. Vertical facies changes that occur within third-order depositional sequences and fourth- or fifth- order parasequences are mirrored by changes in the graptoloid faunal composition. Large-scale -faunal turnovers at biozone boundaries tend to occur either at sequence boundaries or at flooding surfaces within sequences (e.g., the base of Highstand System Tracts). The base of the Corynoides americanus and Climacograptus (D.) spiniferus Zones coincide with major onlap events, and the Or- thograptus ruedenianiii Zone fauna appears just below a Lowstand Systems Tract. Within individual biozones, smaller-scale changes such as the fluctuating relative abundances of graptoloid species coincide with higher-order parasequence cyclicity. These distribution patterns resemble recent computer-generated models for the sequence stratigraphic distribution of hypothetical taxa. By combining good biogeographic control with a detailed sampling program, we are able to see through the patterns attributable to depositional cyclicity and identify the different components of faunal turnover (migration, speciation, and extinction).

New Discovery of a Neanderthal Child Burial from the Dederiyeh Cave in Syria

Abstract: Une seconde sepulture d'enfant neanderthalien a ete mise au jour dans la grotte de Dederiyeh en Syrie lors de la campagne de fouilles 1997-1998. Les restes humains ont ete deposes dans une fosse creusee dans un niveau mousterien. Des observations preliminaires indiquent que le squelette de cet enfant partage de nombreux traits anatomiques avec celui de l'enfant decouvert en 1993 dans une premiere sepulture et que les deux individus relevent de la meme classe d'âge, ayant tous deux autour de deux ans. Bien qu'incompletement preserve, le squelette nouvellement decouvert est le premier provenant de Syrie qui apporte des informations sur la morphologie faciale.

On the dual nature of chance in evolutionary biology and paleobiology

Abstract: The identification of randomness and nonrandomness is a perennial problem in evolu- tionary research. Stochastic thinking in evolutionary biology and paleobiology has solidified the use of a statistical notion of chance, but the idea of chance in evolutionary studies goes beyond statistics. A duality arises from the use of a statistical meaning on the one hand, and a more strictly evolutionary meaning on the other. The former implies a combination of indiscriminate sampling and unpredictability due to multiple causes; the latter codifies independence from adaptation and the directionality imposed by natural selection. Often these meanings are kept separate in evolu- tionary research, used in isolation according to the empirical situation or the goal of the investigator (recognition of pattern versus process). I argue that evolutionary studies in general and paleobi- ological studies in particular can benefit from the simultaneous application of statistical and evo- lutionary notions of chance. Following some background on the notion of chance and its use, I dis- cuss a series of examples in which insight can be gained by explicit consideration of both meanings. Thus, typologies of extinction become clearer when phenomena like wanton extinction are made explicit; exaptive radiations are exposed as an alternative to adaptive radiations; the possible non- adaptive nature of deterministic chaos becomes sensible; the nonrandomness of community-assem- bly is put into question; parallel taxonomies of sorting rooted in different notions of nonrandom- ness are suggested as a means of facilitating understanding of relationships across the hierarchy; developmental constraints and self-organization are more easily distinguished from selective con- straints; and a new term, "incidentals," is suggested to refer to both exaptations and nonaptations. Finally, I point to ways in which the dichotomy between chance and necessity can be approached in evolutionary theory, by showing that the dual nature of chance in evolution entails a distinction between functional and structural necessity, and that chance ultimately becomes a unifying concept for a number of criticisms to neo-Darwinism.