Showing papers in "Paleobiology in 1998"

High-resolution estimates of temporal mixing within shell beds: the evils and virtues of time-averaging

Abstract: This study quantifies the fine structure of time-averaging by using large samples of dated shells collected from within individual strata. Time-averaging results in both good and bad news for interpreting bioclastic deposits.Nine samples of shells were collected from four Holocene cheniers on the Colorado Delta (Gulf of California) and 165 shells of the bivalve Chione fluctifraga were dated using 14C-calibrated amino acid racemization (D-alloisoleucine/L-isoleucine). The age range of shells within samples averages 661 years and, in seven out of nine samples, exceeds 500 years. The sample standard deviation ranges from 73 to 294 years and averages 203 years, far exceeding the dating errors (≪100 years) and potential variation in the life span of Chione (<10 years). Time-averaging is homogeneous among strata within cheniers but varies significantly among cheniers. Age-distributions of dated shells indicate that at 50-year resolution, the samples provide a continuous and uniform record for the entire interval. The actual sample completeness (63.6%) is very close to that predicted by simulations of sampling a 100% complete, uniform record (67.3%).The bad news is that, no matter how carefully collected, data from shell beds may not be suitable for studying processes on timescales shorter than 102 to 103 years; explanations for faunal change that invoke reasoning or models derived from a strictly ecological point of view may rarely be justifiable. Also, notable differences in temporal resolution between the shell beds of seemingly identical origin imply that paleontological patterns (e.g., species diversity) may be affected by cryptic variation in time-averaging. The comparison of our data with time-averaging estimates obtained from other cheniers at coarser sampling resolutions indicates that pooling of samples (analytical time-averaging) can significantly reduce the temporal resolution of paleontological data.The good news is that shell beds can record the optimal type of time-averaging: where paleobiological data are a time-weighted average of the faunal composition from the spectrum of environments that existed during the entire interval of time. Samples from single strata provide a long-term record that is representative of the predominating environments. Within the range of 14C dating, shell beds can provide a complete, high-resolution record, and thus may offer exceptional insights into the environmental and climatic changes of the last 40 thousand years.

Ghost lineages and mammalness : assessing the temporal pattern of character acquisition in the synapsida

Abstract: The origin of mammals has been characterized as a gradual process, a claim based primarily on a well-preserved series of extinct nonmammalian synapsids (“mammal-like reptiles”) that span some 200 million years. In contrast to the origin of many other higher taxa, the origin of mammals from within cynodont-grade therapsids is not considered to coincide with a major morphological change, but rather to be simply the culmination of a series of more and more mammal-like transitional forms. To test these assertions, an asymmetrical cladogram extending from primitive “pelycosaurs” to morganucodontid mammaliaforms was created. Three different methodologies were then used to compare the amount of morphological change between nodes on this cladogram with the minimum missing time interval between each node, as inferred from sister taxon-based ghost lineages. In general, a statistically significant positive relationship was found, indicating that greater numbers of derived features tend to be correlated with longer ghost lineages. A significant correlation between the number of accumulated apomorphies and branching events was also found. Although the rate of character change was variable, in no case was a long ghost lineage associated with few apomorphies. These correlations are consistent with the hypothesis that rapid accumulation of derived features occurred relatively infrequently within the synapsid lineage leading toward mammals and that gradual character evolution predominated.

Using large mammal communities to examine ecological and taxonomic structure and predict vegetation in extant and extinct assemblages

Abstract: Evolutionary paleoecology is the study of paleoecological patterns of organization over time. However, identification of such patterns within modern communities must be made before any study over time can be attempted. This research analyzes mammalian ecological diversity of 31 African localities classified into eight vegetation types: forests, closed woodlands, closed woodland/bushland transition, bushlands, open woodlands, shrublands, grasslands, and deserts. Ecological diversity is measured as the relative proportions of large mammal trophic and locomotor behaviors within communities. Trophic and locomotor adaptations are assigned on the basis of published observations and stomach contents of 184 African mammal species. Communities are accordingly described on the basis of total percentages of mammalian trophic and locomotor adaptations. Since many paleoecology studies have been made using taxonomic uniformitarianism, this study also examines taxonomic community structure to compare with ecologically derived patterns. Results indicate that particular types of vegetation have predictable percentages of arboreal, aquatic, frugivorous, grazing, etc. large mammals. Therefore, these adaptations, because they are predictable in extant assemblages, can be used to predict paleovegetation as well as to portray the community structure of fossil assemblages. Taxonomic groupings also can be used to predict vegetation in extant assemblages, and taxonomic patterns in communities are compared with ecological ones. The mammalian communities of the Pliocene fossil locality Makapansgat, South Africa, are interpreted using these ecological and taxonomic methodologies. Trophic and locomotor adaptations are assigned for Makapansgat fossil mammals through morphological examination of each taxon. Vegetation type is predicted for these fossil localities, but ecological and taxonomic differences in the assemblages differ from extant communities.

Crocodilian diversity in space and time; the role of climate in paleoecology and its implication for understanding K/T extinctions

Abstract: The taxonomic diversity of crocodilians (Crocodylia) through the last 100 million years shows a general decline in the number of genera and species to the present day. But this masks a more complex pattern. This is investigated here using a comprehensive database of fossil crocodilians that provides the opportunity to examine spatial and temporal trends, the influence of sampling, and the role of climate in regulating biodiversity. Crown-group crocodilians, comprising the extant families Alligatoridae, Crocodylidae, and Gavialidae, show the following trend: an initial exponential diversification through the Late Cretaceous and Paleocene that is restricted to the Northern Hemisphere until after the K/T boundary; relatively constant diversity from the Paleocene into the middle Eocene that may be an artifact of sampling, which might mask an actual decline in numbers; low diversity during the late Eocene and Oligocene; a second exponential diversification during the Miocene and leveling off in the late Miocene and Pliocene; and a precipitous drop in the Pleistocene and Recent. The coincidence of drops in diversity with global cooling is suggestive of a causal link--during the initial glaciation of Antarctica in the Eocene and Oligocene and the Northern Hemisphere glaciation at the end of the Pliocene. However, matters are complicated in the Northern Hemisphere by the climatic effects of regional uplift. Although the global trend of diversification is unperturbed at the K/T boundary, this is largely due to the exceptionally high rate of origination in the early Paleocene. Nonetheless, the survival of such a demonstrably climate-sensitive group strongly suggests that a climatic explanation for the K/T mass extinctions, especially the demise of the dinosaurs, must be reconsidered.

Locomotion in non-avian dinosaurs: integrating data from hindlimb kinematics, in vivo strains, and bone morphology

Abstract: Analyses of non-avian dinosaur locomotion have been hampered by the lack of an appropriate locomotor analog among extant taxa. Birds, though members of the clade Dinosauria, have undergone significant modifications in hindlimb osteology and musculature. These changes have resulted in a uniquely developed system of limb kinematics (involving a more horizontal femoral posture and knee-dominated limb motion), which precludes the direct use of extant birds as models for non-avian dinosaur locomotion. Analyses of locomotor data from extant birds and mammals suggest a causal link between general hindlimb kinematics, bone strains, and limb bone morphology among these taxa. A model is proposed that relates the amount of torsional loading in femora to bone orientation, such that torsion is maximal in horizontal femora and minimal in vertical femora. Since bone safety factors are lower for torsional shear strains than for longitudinal axial strains, an increase in torsion can potentially affect bone morphology dramatically over evolutionary time. Interpreting the nearly identical limb bone dimensions and limb element proportions of non-avian dinosaurs and mammals in the light of this relationship supports the prediction of similar vertical femoral postures and hip-driven limb kinematics in these two groups. This information can be used to interpret patterns of locomotor evolution within Dinosauria. The evolution of quadrupedalism with large body size and the acquisition of cursorial or graviportal limb morphologies occurred repeatedly but did not affect the underlying uniformity of dinosaur locomotor morphology. Only derived coelurosaurian theropods (paravians) developed significant modifications of the basic dinosaurian patterns of limb use. Changes in theropod hindlimb kinematics and posture apparently began shortly prior to the origin of flight, but did not acquire a characteristically modern avian aspect until after the later acquisition of derived flight characteristics.

Cambrian and recent disparity : the picture from priapulids

Abstract: An understanding of several macroevolutionary trends has been greatly advanced in recent years by a focus on disparity (morphological variety) rather than taxic diversity. A seminal issue has been the nature of the Cambrian Radiation, and the question of whether problematical Cambrian fossils embody a range of anatomical design far exceeding that observed thereafter. Arthropods have hitherto furnished the only case study, revealing comparable levels of Cambrian and Recent disparity. The generality of this observation needs to be tested in other groups, and the priapulid worms provide a well-documented example. Cladistic analysis of morphological characters for priapulids reveals a paraphyletic series of Cambrian taxa below a crown-group of post-Cambrian genera. However, one extant family (the Tubiluchidae) may be more closely related to Cambrian forms or resolve basally. Character-based morphospace analysis demonstrates greater disparity amongst Recent taxa than amongst their Cambrian counterparts. There is relatively little overlap between the regions of morphospace occupied by Cambrian and Recent genera (contrasting with the situation in arthropods). The Tubiluchidae are morphologically intermediate between Cambrian and other Recent families using several measures of phenetic proximity, and they inhabit environments more comparable with their Cambrian cousins. This work confirms the extensive morphological diversification of major clades by the Cambrian but lends no support to models of a post-Cambrian “decimation” of disparity.

Hallan Çemi, pig husbandry, and post-pleistocene adaptations along the Taurus-Zagros Arc (Turkey)

Abstract: Les travaux recents conduits a Hallan Cemi et sur d'autres sites qui se placent en Anatolie orientale sur l'horizon a maisons circulaires indiquent que les flancs du Taurus-Zagros furent un deuxieme centre autochtone de neolithisation en Asie du sud-ouest Des societes tout a fait sedentarisees de chasseurs-cueilleurs etaient presentes dans cette region au Dryas recent Ces groupes etablis en village avaient une subsistance qui ne reposait pas sur l'exploitation des cereales absentes dans cette region au Dryas recent, mais ils s'adapterent a l'exploitation de noix et de legumineuses a laquelle s'ajoutaient la chasse d'ovicaprides et de cerfs, ainsi que les premiers essais d'elevage, y compris celui de cochons Ainsi, ces societes se distinguent-elles de celles qui constituaient les premieres societes sedentaires au Levant Jusqu'a present, les tentatives d'explication du debut de la vie villageoise reposaient uniquement sur des donnees provenant du Levant, seules disponibles Les donnees en provenance ď Anatolie ne se conforment pas a celles du Levant et soulevent ainsi des questions serieuses sur la validite de la generalisation de ces modeles

A likelihood approach for evaluating estimates of phylogenetic relationships among fossil taxa

Abstract: Estimates of phylogenetic relationships among fossil taxa implicitly provide hypotheses about the quality of the fossil record. Phylogenetic inferences also provide hypotheses about character evolution. The likelihood of any hypothesis that makes predictions about two data sets is simply the likelihood of the hypothesis given the first data set times the likelihood of the same hypothesis given the second data set. In this case, data set 1 represents stratigraphy and data set 2 represents morphology. Statistical methods exist for determining the likelihood of hypothesized levels of sampling. The likelihood of a hypothesized amount of character change yielding a particular most-parsimonious solution (i.e, L[hypothesized length | parsimony length] can be evaluated with simulations. A reanalysis of hyaenid phylogeny based on published character and stratigraphic data is presented here, using the maximum likelihood method. Two trees are found, depending on assumptions about ambiguous species, which are 11 and 10 steps longer than the most parsimonious tree (61 or 60 vs. 50 steps). However, the trees invoke far less stratigraphic debt (9 or 12 units vs. 47 units as measured in Mammal Zones). An important feature of the results is that the most likely tree length given hyaenid character data is estimated to be 56 to 62 steps (depending on the model of character evolution) rather than 50 steps. The likelihood tree suggests stronger trends toward bone-crushing specializations than does the parsimony tree and further suggests that high levels of homoplasy caused parsimony to underestimate the true extent of those trends. Simulations based on the character data and fossil record of hyaenids suggest that the maximum likelihood method is better able to estimate correct trees than is parsimony and somewhat better able to do so than previously proposed phylogenetic methods incorporating stratigraphy.

Pointes ou outils triangulaires ? Données fonctionnelles dans le Moustérien levantin [suivi des] Commentaires de J. Shea, A. Marks, J-M Geneste et de la réponse des auteurs

Abstract: Le Mousterien du Proche-Orient est caracterise par un large developpement d'industries de debitage Levallois, axees majoritairement sur la production d'elements triangulaires (pointes Levallois, eclats triangulaires et subtriangulaires), resultant le plus souvent d'une modalite ď exploitation unipolaire convergente. Parmi les outils identifies dans ces industries, les premieres analyses traceologiques avaient mis l'accent sur la presence de pointes de projectiles. Des travaux recents conduisent cependant a nuancer sensiblement la definition fonctionnelle des ensembles consideres, tant sur les criteres de reconnaissance des armatures que sur leur frequence au sein des outillages. La diversite des modes de fonctionnement des produits triangulaires observee dans differents contextes archeologiques levantins souligne, en fait, l'heterogeneite de cette classe d'objets qui ne peut etre vue comme la reponse a une seule categorie de besoins.

Trilobite alpha diversity and the reorganization of Ordovician benthic marine communities

Abstract: The Ordovician saw the transformation of marine benthic communities from the trilobite-based Cambrian Fauna to the brachiopod-dominated Paleozoic Fauna. An evaluation of the changing importance of trilobites during the Ordovician can be made from accurate assessments of taxonomic richness in various habitats. Here we present a new compilation of trilobite alpha diversity based on field collections and survey of the literature. The data indicate that trilobite species richness within nearshore, shallow subtidal, carbonate buildup and deep subtidal shelf environments was essentially constant between the Late Cambrian and the Late Ordovician. The alpha diversity patterns do not support the notion that trilobites became displaced from inner shelf environments during the Ordovician. Rather, the data are consistent with a decline in relative importance of the group through dilution as newly radiating invertebrate groups entered Ordovician paleocommunities. They also imply that direct interactions between elements of the Cambrian and Paleozoic faunas were not involved in the Ordovician reorganization of paleocommunities. Like many other major faunal transitions during the Phanerozoic, the Ordovician radiations appear to have been essentially non-competitive in nature.

Tale of two rhinos; isotopic ecology, paleodiet, and niche differentiation of Aphelops and Teleoceras from the Florida Neogene

Abstract: Carbon (813C) and oxygen (8180) isotopic results are presented from 42 tooth enamel carbonate samples of rhinos (Family Rhinocerotidae) from a sequence of Florida Neogene localities between 9.5 and 4.5 Ma. These data are used to interpret ancient diets and test previous hypotheses of terrestrial / aquatic adaptations of two sympatric rhinos, Aphelops and Teleoceras. The long-limbed, shorter-crowned Aphelops traditionally has been reconstructed as an open-country browser (similar to the modern black rhino), whereas short-limbed, higher-crowned Teleoceras traditionally has been reconstructed as an amphibious grazer (similar to the modern hippo). Between about 9. 5 and 7 Ma the 813C values (all <-11.0%o) from Florida Aphelops and Teleoceras indicate that both rhinos were feeding on C3 plants. This diet probably included a combination of browse and C3 grasses, although the exact proportions for each genus cannot be distinguished isotopically. In contrast, after the late Miocene global carbon shift as represented at 4.5 Ma in Florida, Aphelops was a browser (mean 813C = -11.9%o), whereas Teleoceras was a mixed feeder/C4 grazer (mean 813C = -7.0%o). Oxygen isotopic values indicate that neither Aphelops nor Teleoceras was principally aquatic. Given these new isotopic data, more plausible modern analogs for these two extinct rhinos are, respec- tively, the terrestrial browsing black rhino (Diceros bicornis) and the terrestrial grazing white rhino (Ceratotherium simum), which are sympatric today in Africa.

Reconstructing cave bear paleoecology from skeletons: A cross-disciplinary study of middle Pleistocene bears from Yarimburgaz Cave, Turkey

Abstract: Cave bears, an extinct subgenus (Spelearctos) of Ursus, were versatile enough to inhabit large areas of the northern hemisphere during the middle and late Pleistocene, yet they had evolved a specialized dentition that emphasized grinding functions, implying a heavy dietary reliance on tough, fibrous foods (i.e., plants). Isotope studies have yielded conflicting results on cave bear diet, however, often without consideration of the provenance of the samples or the possible contradictions that taphonomic and morphologic evidence might pose to dietary interpretations. It is likely that cave bear habits varied somewhat in response to environmental circumstance, and the limits on their abilities to do so remain unknown. If the larger goal of paleontological inquiry is to reconstruct the adaptations of cave bear species, then variation and commonalities among populations must be tracked closely, and the disparate lines of evidence currently available examined together on a case by case basis. Clearly, no single analytical technique can achieve this. By way of example we present the results of a cross-disciplinary collaboration that combines osteometric, isotopic, and taphonomic approaches to studying the paleoecology of a bear assemblage from Yarimburgaz Cave in northwest Turkey. Reference information on the linkages between diet, hibernation, and population structure in modern bears provides test implications for the investigation. Osteometric techniques demonstrate the presence of two coextant middle Pleistocene bear species in the sample–Ursus (Spelearctos) deningeri, a form of cave bear, and U. arctos or brown bear–the former abundant in the sample, the latter rare. An attritional mortality pattern for the bears and the condition of their bones show that most or all of the animals died in the cave from nonviolent causes in the context of hibernation. The study also elucidates several characteristics of the cave bear population in this region. Osteometric techniques show that the adult sex ratio of the cave bears is only slightly skewed toward females. This pattern lies near one extreme of the full range of possible outcomes in modern bear species and can only reflect a strong dietary dependence on seasonally available plants and invertebrates, showing that hibernation was a crucial overwintering strategy for both sexes; the results specifically contradict the possibility of regular, heavy emphasis on large game (hunted or scavenged) as a winter food source. The nature of wear and breakage to the adult cave bear teeth indicates that food frequently was obtained from cryptic sources, requiring digging and prying, and that extensive mastication was necessary, leading to complete obliteration of some cheek tooth crowns in old individuals. The patterns of tooth damage during life corroborate the dietary implications of the adult sex ratio and also argue for a diet rich in tough, abrasive materials such as nuts, tubers, and associated grit. The carbon and oxygen isotopic compositions of cave and brown bear tooth enamel from the site are virtually identical, and there is no evidence of a strong marine signal in either species, despite the cave's proximity to a modern estuary of the Sea of Marmara; nitrogen isotope ratios could not be examined because of poor protein preservation. The isotope results suggest that both bear species were highly omnivorous in the region during the middle Pleistocene and obtained nearly all of their food from terrestrial and fresh-water habitats. Bone pathologies, usually originating from trauma, occur in some of the adult bears, testifying to long lifespans of some individuals in this fossil population. The Yarimburgaz cave bears also exhibit great size dimorphism between the sexes, based on weight-bearing carpal bone dimensions, with adult males attaining roughly twice the body mass of adult females.

La variabilité du débitage discoïde dans la grotte de Fumane (Italie du Nord)

Abstract: Dans la grotte de Fumane, les nombreux niveaux du Paleolithique moyen recent se caracterisent par une importante variabilite techno-economique des ensembles lithiques. L'ensemble du niveau A9, datant de l'lnterpleniglaciaire wurmien, est pris en consideration dans ce travail. Malgre l'absence de remontages, l'etude technologique a permis de comprendre la structure du systeme de production regi principalement par le debitage discoide, et d'identifier deux chaines operatoires, l'une principale, l'autre secondaire, les deux independantes du type de la matiere premiere utilisee (toutes de provenance locale). Malgre l'application rigoureuse des criteres techniques dans la predetermination discoide, on a pu relever que, au cours de la chaine operatoire, on effectuait differents choix et gestes techniques qui determinaient la modification de la morphologie du nucleus. Cette variabilite repond, en tout cas, aux exigences de production visant la realisation des principaux objectifs techniques. Enfin, l'analyse des sous-ensembles lithologiques distingues sur la base de caracteres texturaux et mecaniques du silex, met en relief les problemes rencontres au cours de la production et montre des differences dans l'economie du debitage.

The bio-geometry of mollusc shells

Abstract: The shells of gastropods and cephalopods grow by production of new material, by the mantle, at the lip of the shell I derive a model of shell form that allows us to describe the morphology of a shell in terms of independently definable biological parameters These are (1) the relative rates of shell production at different points around the aperture, (2) the total amount of shell produced per time interval, (3) the growth rate of the aperture, (4) aperture shape, and (5) the orientation of the animal within the shell Describing shell form in these terms allows us to see what biological changes must occur in development in order to change one shell morphology into another and what constraints are associated with particular morphological transformations The model shows that it is developmentally easy to derive a slightly coiled limpet shell from that of a high-spired ancestor, but difficult to take the next step to a fully conical limpet Many, if not most, real gastropod shells are not conical but rather have a convex or concave profile I show that these forms result from a decoupling of shell production rates from the growth rate of the animal within the shell The model also shows how truly different forms, such as vermetid snails and heteromorph ammonites, escaped the confines of spiral growth–sometimes by rotating the body within the shell, and sometimes by taking up a growth strategy that does not constrain them to coil This model is compatible with shell morphometric models that have been widely discussed in the literature but strives toward a different goal: understanding the relationships between the various biological processes involved in shell development

Evolutionary significance of differential species longevity in Osagean-Meramecian (Mississippian) crinoid clades

Abstract: The pattern of differential species longevities among five Osagean-Meramecian crinoid clades is analyzed for its evolutionary significance. Differences in mean species longevity between clades may have resulted from species sorting based on eurytopy (niche breadth). In order to test the relationship between longevity and eurytopy it was first necessary to recognize generalists (eurytopes) vs. specialists (stenotopes) objectively. Three different approaches were used: (1) the ''Eurytopy Index'' (EI), which is a measure of mean number of facies per species; (2) analysis of crinoid functional morphology; and (3) use of canonical discriminant analysis to analyze species distributions between facies in order to separate generalists from specialists. Mean species longev- ity for each clade was evaluated by four different approaches: (1) rarefaction was used to control for differences in sample size, including both species richness and number of occurrences, between clades; (2) potential facies control of species longevity was evaluated by a bootstrap that compared the observed data to a null model where species longevity was limited only by the actual occur- rences of each species known facies through time; (3) uniformity of clade species richness through time was evaluated by the ''Index of Uniformity for Species Richness'' based on the standard de- viation of clade species richness across the time intervals; and (4) potential species range trunca- tions were evaluated by a biostratigraphic gap analysis based on the binomial distribution. The general order of increasing longevity and eurytopy is (from least to most): flexibles, ad- vanced cladids, camerates, disparids, and primitive cladids. In general the pinnulate crinoids (ad- vanced cladids and camerates) were specialists with lower mean species longevity, and the non- pinnulate crinoids (disparids and primitive cladids) were generalists with higher mean species lon- gevity. Pinnulate crinoids were specialized for feeding in high-energy currents and, thus, were limited in their facies distribution and presumably more extinction-prone. The non-pinnulates could feed in both low- and high-energy currents and, thus, were less limited in their facies dis- tribution and presumably less extinction-prone. The flexibles were the exception in that they were non-pinnulate but had the lowest mean species longevity, apparently because they were specialized for deeper-water clastic environments. On average, generalist clades have mean species longevities that at a minimum are up to 45% 1.0 0.7 m.y.) longer than specialist clades. However, greater mean species longevity did not necessarily confer long-term advantages to a clade. The specialist advanced cladids became the dominant crinoid clade of the late Paleozoic and gave rise to the articulate crinoids of the post- Paleozoic. This may have resulted from the more rapid species turnover of stenotopes creating adaptive evolutionary novelties for their clade. Alternatively, it could simply be the result of sto- chastic processes. The finer subdivision of niche space by specialists has led previous workers to predict that spe- cialist clades should have higher species richness than generalist clades. The present study sup- ports this prediction.

Variability, selection, and constraints; development and evolution in viverravid (Carnivora, Mammalia) molar morphology

Abstract: Developmental constraints presumably operate by influencing patterns of variability: when development causes some features to vary more than others and when the level of variability is correlated with evolutionary change, then development can be said to constrain evolution. This idea was tested by examining the relationship between tooth variation and three other factors: developmental processes, tooth function, and evolutionary change. Data came from two lineages of viverravid carnivorans (Viverravidae, Carnivora) from the Paleogene of North America. Variability in cusp position was significantly correlated with position in the developmental cascade, with the amount of intercusp growth (when growth is relatively greater in some cusps than others), and with amount of evolutionary change. This indicates that tooth development exerts a local constraint on phenotypic variability and on the evolutionary response to functional selection, but comparative data suggest that the developmental constraint itself may evolve. Intense directional or stabilizing selection may modify the developmental cascade so that the constraint is either removed or modified to permit new evolutionary patterns. Thus development does not constrain evolution in an absolute sense, but rather introduces modifiable patterns of covariance among crown features. Both development and function seem to play important, intertwined roles in coordinating evolutionary change in mammalian molars.

Speciation and extinction asymmetries in paleontological phylogenies; evidence for evolutionary progress?

Abstract: This paper concerns paleontological phylogenies that have a "budding" configuration, wherein "ancestral" species persist through branching events to coexist with their "descendants." Two principal tests are proposed for detecting patterns within such trees. The first test, called the "ancestor-descendant extinction test," compares the number of cases in which, after a split, the ancestral species became extinct before its descendant with the number of cases in which the descendant became extinct before its ancestor. The second test, called the "ancestor-descendant speciation test," compares the number of cases in which, after a split, the ancestral species gave rise to a further species with the number of cases in which the descendant species gave rise to a further species. The null hypothesis in each case is that the frequencies are equal, as predicted by a random Markovian branching model of evolution. Five stratophenetic species-level phylogenies of three taxonomic groups, planktonic foraminifera, nannofossils, and graptoloids, are examined using these tests, including one (Paleogene planktonic foraminifera) that is presented for the first time. In all cases, the phylogenetic trees are found to be strongly nonrandom. The general pattern, although by no means expressed perfectly in every case, corresponds to a Simpsonian "step-series," in which ancestor taxa are simultaneously more likely to become extinct and less likely to speciate than their coexisting descendants. It is shown that this pattern cannot simply be the result of simple age-dependent factors such as an increasing extinction risk in older taxa. Instead, the very fact that a species has given rise to another appears to increase its future extinction risk and decrease its likelihood of further speciation. Many possible biases may affect the shape of paleontological phylogenies, which are as yet poorly understood and unquantified. One potentially important effect follows from the taxonomic subdivision of gradual chronoclines into artificial morphospecies, such as might conceivably induce a step-series pattern in the phylogeny. Even if this is the partial or entire reason for the observed patterns, it would appear to imply directional evolution in phyletic gradualism. Other possible artifacts are discussed, but they are regarded as probably too weak to produce the observed patterns. If the pattern is not artificial, the fact that three of the best known fossil groups exhibit substantial asymmetries in speciation and extinction argues against the currently popular "nonprogressive" view of evolution. Instead, the evolutionary step-series pattern is consistent with the classical Darwinian concept of the general competitive superiority of newly evolved species over their ancestors and supports the idea of evolutionary progress.

A rays-as-appendages model for the origin of pentamerism in echinoderms

Abstract: -A new hypothesis concerning the evolutionary origin of pentameral symmetry in echinoderms is presented. The BA-A-BA pattern of Loven's law in echinoids and the 2-1-2 symmetry of the edrioasteroid Stromatocystites appear to be morphogenetically related, and this pattern appears to be locked into development. This pattern may have originated from a unirayed 0-1-0, -A-, ancestor. I propose that a duplication of the uniray occurred and resulted in the addition of a pair of rays that followed Bateson's rules of symmetry to form a three-rayed 0-1-2, -A-BA, construction. This change occurred on the side that corresponds to the left side of the organism. This event made the individual asymmetric with respect to its anterior-posterior axis. Therefore I propose that morphogenetic regulation of bilaterality of the organism then led to homeotic expression of a mirror-image pair of rays on the opposite side. These two morphogenetic steps achieved the 2-1-2, BA-A-BA pattern. "Appendage status" of rays is assumed necessary to invoke the Batesonian mirror-image duplications of the model. Three robust morphological characters emerge from the "rays-as-appendages" model: (1) 2-1-2, BAo-A-BA, organization; (2) "locked-in" pentamerism; and (3) a 2-3 pattern of right and left rays. Results based on ray homology research are presented for echinoids, asteroids, ophiuroids, edrioasteroids, ophiocistioids, and holothurians. I speculate that helicoplacoids may have 0-1-2 triradiate construction, and that solutes may have 0-1-0 uniray construction. The model has limits; it does not explain 1-1, or 2-1, or 2-2 or 1-1-1 organization of ambulacra. Frederick H. C. Hotchkiss. 26 Sherry Road, Harvard, Massachusetts 01451. E-mail: hotchkissf@panametrics.com Accepted: 12 January 1998

La variabilité du débitage discoïde dans la grotte de Fumane (Italie du Nord)/The variability of discoid production at the grotte de Fumane

Abstract: Dans la grotte de Fumane, les nombreux niveaux du Paleolithique moyen recent se caracterisent par une importante variabilite techno-economique des ensembles lithiques. L'ensemble du niveau A9, datant de l'Interpleniglaciaire wurmien, est pris en consideration dans ce travail. Malgre l'absence de remontages, l'etude technologique a permis de comprendre la structure du systeme de production regi principalement par le debitage discoide, et d'identifier deux chaines operatoires, l'une principale, l'autre secondaire, les deux independantes du type de la matiere premiere utilisee (toutes de provenance locale). Malgre l'application rigoureuse des criteres techniques dans la predetermination discoide, on a pu relever que, au cours de la chaine operatoire, on effectuait differents choix et gestes techniques qui determinaient la modification de la morphologie du nucleus. Cette variabilite repond, en tout cas, aux exigences de production visant la realisation des principaux objectifs techniques. Enfin, l'analyse des sous-ensembles lithologiques distingues sur la base de caracteres texturaux et mecaniques du silex, met en relief les problemes rencontres au cours de la production et montre des differences dans l'economie du debitage.

Differences between evolution of mean form and evolution of new morphotypes : an example from late cretaceous planktonic foraminifera

Abstract: Morphological evolution in the Late Cretaceous (Maastrichtian) Contusotruncana lineage of planktonic foraminifera was studied at DSDP Sites 525 (South Atlantic) and 384 (North Atlantic). A multivariable approach was used to separate aspects of form controlled by geographical variation (size, spiral roundness of the test, percentage of kummerform specimens) from those due to changes that occurred simultaneously in geographically distant populations of the lineage (shell conicity, number of chambers in the last whorl). A gradual increase in mean shell conicity was observed over the last 3 million years of the Cre- taceous. It arose from the combination of a rapid development of highly conical shells after 68.5 Ma and a long-term trend of progressive disappearance of the ancestral morphotype. Therefore, despite the gradual change in ''mean form,'' the morphological evolution in the Contusotruncana lineage differs from the classical image of phyletic gradualism. The gradual increase in mean shell conicity in the lineage was accompanied by a remarkable decrease in its absolute abundance (shell accumulation rate), suggesting that the changes in shell morphology might not have been neutral with respect to natural selection. Apparently, gradual change in ''mean form'' of fossil lineages does not require an equally gradual development of morphological novelties. It may be caused by natural selection operating on a constant range of variation in populations living in environments without geographical barriers.

Independent testing of a paleobiological hypothesis; the optical design of two Ordovician pelagic trilobites reveals their relative paleobathymetry

Abstract: -Evidence that can be used to interpret the life habits of extinct organisms usually takes three forms: functional analysis, analogy with living organisms, and geological evidence. Independent quantitative tests for habit are rarely available. A theory of optimum eye design originally derived for living aquatic arthropods provides quantitative data that are used to test previous suppositions about the life habits of two Ordovician pelagic trilobites: that the telephinid trilobite Carolinites was epipelagic while the cyclopygid Pricyclopyge was mesopelagic. Optimum compound eye design theory uses measured lens diameters and interommatidial angles to determine the "eye parameter" (p), which can be used to gauge approximate optimum level of illumination for the eyes of these trilobites. The eye parameter provides an independent test for their relative paleobathymetry. Values of the eye parameter measured in the dorso-ventral direction across two eyes of Carolinites killaryensis utahensis were found to have medians of 2.13 and 3.24. Values measured in the antero-posterior direction have medians of 3.17 and 4.86 for the two eyes. Values measured in the dorso-ventral direction across two eyes of Pricyclopyge binodosa have medians of 4.23 and 4.98, while values measured in the antero-posterior direction have medians of 7.06 and 8.31. Eye parameters are higher in Pricyclopyge than in Carolinites, the difference statistically significant at p = 0.05. The eyes of Pricyclopyge are optimally designed for lower levels of illumination than are those of Carolinites. This accords with the previous interpretations of the former trilobite as mesopelagic and the latter as epipelagic. Tim McCormick and Richard A. Fortey. Department of Palaeontology, The Natural History Museum, Cromwell Road, London SW7 5BD, United Kingdom. E-mail: timm@nhm.ac.uk and raf@nhm.ac.uk Accepted: 4 December 1997

Cretaceous Foraminifera and the evolutionary history of planktic photosymbiosis

Abstract: Ecotypic correlations between stable isotopic signals and skeletal size indicate that some Late Cretaceous serial planktic foraminifera were strongly photosymbiotic. In contrast, coeval trochospiral planktic foraminifera do not exhibit the isotope/size signatures that typify strongly photosymbiotic species. Comparison to Cenozoic taxa demonstrates that photosymbiosis has recurred throughout planktic foraminiferal history and has evolved independently in superfamilies characterized by very different gross skeletal morphologies. The historical contingency of that evolution is illustrated by the consequences of the Cretaceous/Paleogene mass extinction, which terminated the Cretaceous lineages of photosymbiotic planktic foraminifera but did not permanently extinguish photosymbiont reliance by planktic foraminifera.

Ontogeny of Trimerocephalus lelievrei (Trilobita, Phacopida), a representative of the Late Devonian phacopine paedomorphocline; a morphometric approach

Abstract: A detailed morphometric approach based on size and on outline analyses has been used on an exceptionally well-preserved assemblage of silicified trilobite exuvia, recovered from a Late Devonian limestone from southeastern Morocco. The material comprises a series of late larval to postlarval growth stages belonging to a single phacopine species, Trimerocephalus lelievrei Cronier and Feist, 1997. Plurimodality of size distribution has allowed us to discriminate postlarval instars. Distinct dimensional classes of isolated parts are obtained using the intertooth distances on the posterior pygidial margin and the internotch distances in the cephalic vincular furrow, which are functionally linked during trilobite enrollment. Morphometric analysis of development permitted demonstration of progressive shape change in agreement with ontogenetic ordination and a comparison of the timing of size and shape changes. The main shape changes appear to occur early in development, and once the "adult" morphology is obtained, size increases significantly. The growth rate during ontogeny is estimated by analogy with extant deep-sea crustaceans. Exponential size increase resulting from constant duration of intermolt periods may be regarded as a life history strategy to compete in a nutrient-impoverished offshore environment. The particular phacopine mode of molting, which involves the opening of the neck joint after ankylosis of the facial sutures, occurred in Trimerocephalus lelievrei between the first two postlarval instars, later than in its ancestor. Trimerocephalus lelievrei occupies an intermediate position within the phacopine paedomorphocline as indicated by the delayed onset of ankylosis.

Constructional morphology, origin, and evolution of the gastropod operculum

Abstract: Gastropod opercula are classified here on a new morphogenetic basis, which distinguishes three main types: (1) flexiclaudent spiral (mostly multispiral) operculum, the shape of which does not coincide with that of the aperture, (2) rigiclaudent spiral (usually paucispiral) operculum, the shape of which fits that of the aperture, and (3) rigiclaudent concentric operculum, also aperture-fitting. The first type fits by flexing into the aperture and is secreted when the soft parts are partly or wholly extended (i.e., when the operculum is not in a closed position). The other two types do not flex upon retraction (except at the very margin) and grow when the operculum closes over the aperture, with or without rotation. A study of opercular types at the family level confirms the systematic and evolutionary significance of opercula. Types 1 and 2 are the only ones present in archaeogastropods, Type 1 being predominant. Opercula (if present) in Neritopsina are always rigiclaudent. Within Caenogastropoda, Type 2 predominates; the only flexiclaudent spiral opercula are found in certain basal cerithioidean families. Concentric opercula are predominant in higher neotaenioglossans and exclusive in neogastropods. Except for one family, opercula in Heterostropha are always rigiclaudent spiral. Morphological, systematic, and histological criteria point to the flexiclaudent spiral operculum as the ancestral form. This leads us to propose the “periostracum shaving” model in prosobranchs to account for the origin of this kind of operculum. According to this model, in the earliest trochospiral gastropods the periostracum ceased to serve a shell-formation function at the band of overlap between whorls (the parietal band). The periostracal band was then extruded from the shell to constitute an incipient operculum, taking on the appearance of a spiral strip coiling opposite to the shell. The parietal segment of the periostracal groove migrated toward the epipodium and became independent from the rest of the mantle. The concomitant development of an opercular disc allowed the successive turns of periostracal strip to seal together. In this way, a spiral operculum emerged, coiling counterclockwise without matching the aperture shape. During the course of prosobranch evolution, rigiclaudent spiral opercula emerged several times from the ancestral flexiclaudent type, although they were always restricted to apertures with a spiral-shaped outer (labral) edge. Such opercula enlarged the range of shell morphologies for which the operculum constituted an efficient protective barrier to include those of neritoidean or naticoidean type. The onset of calcification in opercula took place with the rigiclaudent type. Concentric opercula also evolved independently from rigiclaudent spiral opercula in several gastropod groups, thus further broadening the spectrum of apertures and, hence, of shell morphologies using opercula for protection. From the standpoint of adaptation, the concentric type was probably the only one available to neogastropods having long and wide siphonal canals.

Fueling the hearths in India : the role of dung in paleoethnobotanical interpretation

Abstract: Lors de l'analyse des restes de moissons provenant de sites archeologiques, les paleobotanistes se heurtent souvent au probleme d'identification des graines trouvees dans des contextes qui ont pu contenir du combustible. Cet article presente les resultats de recherches ethnoarcheologiques - production et utilisation du fumier par les societes agricoles traditionnelles - conduites en Inde afin d'aider a l'identification de l'origine de graines recueillies dans les contextes archeologiques. L'effort a porte en particulier sur la distinction qu'il convient d'etablir en Inde entre des activites effectuees dans les foyers et a leur proximite, sur les differences entre les divers types de foyers et de combustibles, et sur la nature du fumier. Ces nouveaux resultats s 'ajoutant a des etudes plus anciennes ayant porte sur les foyers alimentes avec du fumier vont permettre aux paleoethnobotanistes d'elargir la gamme des possibilites qu'il leur faudra tester.

The masticatory apparatus of the armadillo Eutatus (Mammalia, Cingulata) and some allied genera: paleobiology and evolution

Abstract: The eutatines are a group of fossil armadillos traditionally regarded as herbivorous due to the particular morphology of the skull and teeth. Nevertheless, they have never been the subject of a detailed morpho-functional analysis. The masticatory apparatus of Eutatus (late Pliocene-early Holocene) is analyzed and compared with other eutatines (Proeutatus and Stenotatus from the Mio- cene, and Doellotatus and Ringueletia from the Pliocene) and with living armadillos (Euphractus and Dasypus). The masticatory muscles were reconstructed from origin and insertion scars; the occlusal pattern and mandibular movements were determined through the study of the craniomandibular joint, the shape and arrangement of the teeth and the symphysis, and the moment arms of the lines of action of the masseter and temporalis muscles were estimated. Skull and mandible shapes were compared using the Procrustean method Resistant-Fit Theta-Rho-Analysis (RFTRA). The analysis of the masticatory apparatus of the eutatines allows us to state that Eutatus and Proeutatus exhibit the most specialized morphology known for an herbivore with an armadillo-like skull pattern. Ad- ditionally, we can identify a morphological group from the Miocene Stenotatus to the Pleistocene Eutatus, including the Pliocene Doellotatus and Ringueletia as intermediate stages of a morphological line; Proeutatus deviates from this pattern. This morphological separation may reflect an early di- chotomy within the well-defined clade of eutatines.

Témoignages d'un traitement thermique des feuilles de laurier dans le Solutréen supérieur de la grotte du Parpalló (Gandia, Espagne)/Testimonios de un tratamiento térmico de las ojas de Laurel en el Solutrense superior de la cueva del Parpalló/Evidence for thermal treatment of Laurel Leaf points in the Upper Solutrean of the grotte du Parpalló

Abstract: Testimonios de un tratamiento termico de las ojas de Laurel en el Solutrense superior de la cueva del Parpallo. Veinte anos despues del descubrimiento del primer testimonio de un tratamiento termico en el Solutrense de Laugerie-Haute, queremos presentar en este articulo, mediante el ejemplo de las hojas de laurel, las pruebas tangibles de su utilizacion tambien en el Solutrense superior de la cueva del Parpallo. Consideradas desde un punto de vista tecnologico, estas pruebas ayudan a reforzar el origen solutrense de la entidad tipologica a la que pertenecen, mas conocida con el nombre generico de Solutrense de facies iberica. Y desde un punto de vista tecnico, nos permiten ampliar la extension del fenomeno "tratamiento termico" en el Solutrense. Su utilizacion atestiguada en Portugal y fuertemente presumida en Andalucia, parece pues que los limites espacio-temporales de este fenomeno coinciden con los generalmente atribuidos a esta entidad crono-cultural.

Détermination de l'âge des chevaux fossiles et établissement des classes d'âge/Age determination of fossil horses and the establishment of age classes

Abstract: Si la connaissance de l'âge de la mort des animaux qui proviennent des sites prehistoriques repose encore souvent sur l'examen de l'usure dentaire, il n'est pas raisonnable de se satisfaire des âges bruts obtenus car ils sont entaches d'erreur et/ou d'imprecisions. De plus tous les auteurs s'accordent pour reconnaitre que passe 8 ans, il devient extremement difficile de determiner l'âge d'un Cheval. Ce travail fait le point sur l'ensemble de ces difficultes et definit 5 classes d'âge basees sur la sequence eruption/usure des dents a la fois labiales et jugales.

Settlement patterns, polities and regional complexity in the Southeast Arabian Iron Age

Abstract: L'analyse des donnees sur l'environnement et le « mode de vie » a l'Age du Fer en Arabie du Sud-Est met en valeur l 'existence d'une serie d 'etablissements de piemont auxquels etaient associes des systemes d'irrigation, les possibilites d'une agriculture intensive et les moyens de controler et defendre ces ressources. Ces donnees, combinees a celles fournies par l'histoire, permettent d'entrevoir des systemes politiquement complexes, limites a un environnement tres precis. L'orientation de la recherche sur le terrain en Arabie du Sud-Est a conduit a surestimer l'importance de ces etablissements en termes de hierarchies regionales et d'interactions de pouvoir. L'examen de sites localises dans d'autres environnements, combine a l'analyse de la repartition des vestiges materiels, suggere que les etablissements de piemont n'exercaient pas de domination economique et politique sur l'ensemble de la region.