Showing papers in "Paleobiology in 2003"

Paleoecological reconstruction of a lower Pleistocene large mammal community using biogeochemical (δ13C, δ15N, δ18O, Sr:Zn) and ecomorphological approaches

Abstract: Ecomorphological and biogeochemical (trace element, and carbon, nitrogen, and oxygen isotope ratios) analyses have been used for determining the dietary niches and habitat preferences of large mammals from lower Pleistocene deposits at Venta Micena (Guadix-Baza Basin, Spain). The combination of these two approaches takes advantage of the strengths and overcome the weakness of both approaches. The range of δ13Ccollagen values for ungulate species indicates that C3 plants were dominant in the diet of these mammals. δ13Ccollagen values vary among ungulates: perissodactyls have the lowest values and bovids the highest ones, with cervids showing intermediate values. The hypsodonty index measured in lower molar teeth and the relative length of the lower premolar tooth row indicate that the horse, Equus altidens, was a grazing species, whereas the rhino, Stephanorhinus etruscus, was a mixed feeder in open habitats. The similar δ13Ccollagen values shown in both perissodactyls does not reflect differences...

Paleoecology of the oldest known animal communities: Ediacaran assemblages at Mistaken Point, Newfoundland

Abstract: Ediacaran fossils at Mistaken Point, southeastern Newfoundland (terminal Neoproterozoic; 565–575 Ma) represent the oldest known animal communities. In contrast to most Phanerozoic fossil assemblages, in which postmortem transportation, bioturbation, and the accumulation of hardparts obscure community relationships, all fossils in the Mistaken Point assemblages were sessile, soft-bodied organisms that show no evidence of mobility in life or transportation after death. Mistaken Point assemblages are spectacularly preserved on large bedding planes as in situ census populations of hundreds to thousands of fossils, recording the living soft-bodied benthic community at the moment it was smothered by volcanic ash. This unique preservation style allows ecological tests routinely conducted in modern communities (e.g., species richness, abundance, “biomass,” diversity, and evenness, as well as statistical tests of nearest-neighbor interactions) to be applied to the fossil communities. Observed patterns of community variability are consistent with the theory that Mistaken Point fossil surfaces are “snapshots” recording different stages of ecological succession, progressing from communities of low-level feeders (e.g., pectinates and spindles) to frond-dominated communities with complex tiering and spatial structure. The presence of diverse slope communities at Mistaken Point suggests that the deep sea was colonized rapidly during the evolution of complex organisms. Species richness, abundance, and diversity values, as well as levels of intraspecific interaction, all fall within the typical range observed in modern slope communities. These structural similarities imply that ecological processes present in Ediacaran communities at Mistaken Point were strikingly similar to the processes that operate in modern deep-sea animal communities.

Vertebral pneumaticity, air sacs, and the physiology of sauropod dinosaurs

Abstract: The vertebrae of sauropod dinosaurs are characterized by complex architecture involving laminae, fossae, and internal chambers of various shapes and sizes. These structures are interpreted as osteological correlates of a system of air sacs and pneumatic diverticula similar to that of birds. In extant birds, diverticula of the cervical air sacs pneumatize the cervical and anterior thoracic vertebrae. Diverticula of the abdominal air sacs pneumatize the posterior thoracic vertebrae and synsacrum later in ontogeny. This ontogenetic sequence in birds parallels the evolution of vertebral pneumaticity in sauropods. In basal sauropods, only the presacral vertebrae were pneumatized, presumably by diverticula of cervical air sacs similar to those of birds. The sacrum was also pneumatized in most neosauropods, and pneumatization of the proximal caudal vertebrae was achieved independently in Diplodocidae and Titanosauria. Pneumatization of the sacral and caudal vertebrae in neosauropods may indicate the presence of abdominal air sacs. Air sacs and skeletal pneumaticity probably facilitated the evolution of extremely long necks in some sauropod lineages by overcoming respiratory dead space and reducing mass. In addition, pulmonary air sacs may have conveyed to sauropods some of the respiratory and thermoregulatory advantages enjoyed by birds, a possibility that is consistent with the observed rapid growth rates of sauropods.

The ontogenetic dynamics of shape disparity

Abstract: Disparity appears to decrease or remain stable over geological time in numerous groups. This pattern is sometimes explained in terms of developmental constraints, but labile developmental systems might produce the same pattern should novelties interact, counterbalancing their individual effects. We test the hypothesis that counterbalancing can reduce disparity by comparing ontogenies of shape among nine species of piranhas to identify the developmental novelties. All three parameters examined change multiple times, sometimes dramatically. By comparing levels of disparity between species at two developmental phases, at the transition from larval to juvenile phases, and at maximum adult body size, we find that disparity decreases significantly and substantially over ontogeny. That reduction occurs because of, rather than despite, novelties of postlarval morphogenesis. Some interacting novelties are historically independent and affect different developmental phases, others are historically independent and affect the same developmental phase, and still others are historically correlated and affect either the same or different developmental phases. By modeling hypothetical ontogenies, constraining developmental parameters mathematically to one of the observed values, we find that variation in each parameter, taken by itself, and combinations of them taken two at a time, tend to increase disparity. It is the interactions among all three that reduce disparity. In this group divergent ontogenies transform disparate larvae into similar adults.

Ecological conservatism in the “living fossil” Ginkgo

Abstract: The living species Ginkgo biloba is phylogenetically isolated, has a relictual distribution, and is morphologically very similar to Mesozoic and Cenozoic congenerics. To investigate what adaptations may have allowed this lineage to persist with little or no morphological change for over 100 Myr, we analyzed both sedimentological and floral data from 51 latest Cretaceous to mid- dle Miocene Ginkgo-bearing fossil plant sites in North America and northern Europe. The resulting data indicate that throughout the late Cretaceous and Cenozoic Ginkgo was largely confined to dis- turbed streamside and levee environments, where it occurred with a consistent set of other plants. These inferred habitats are surprising because the life-history traits of Ginkgo (e.g., slow growth rate, late reproductive maturity, extended reproductive cycle, large and complex seeds, large and slowly developing embryos) are counter to those considered advantageous in modern disturbed habitats. Many flowering plant lineages first appeared or became common in disturbed riparian habitats, and are inferred to have had reproductive and growth traits (e.g., rapid reproduction, small easily dispersed seeds, rapid growth) suited to such habitats. Paleoecological inferences based on both morphology and sedimentary environments thus support the idea that Ginkgo was displaced in riparian habitats by angiosperms with better adaptations to frequent disturbance.

Quantitative estimates of time-averaging in terebratulid brachiopod shell accumulations from a modern tropical shelf

Abstract: Quantitative estimates of time-averaging in marine shell accumulations available to date are limited primarily to aragonitic mollusk shells. We assessed time-averaging in Holocene assemblages of calcitic brachiopod shells by direct dating of individual specimens of the terebratulid brachiopod Bouchardia rosea. The data were collected from exceptional (brachiopod-rich) shell assemblages, occurring surficially on a tropical mixed carbonate-siliciclastic shelf (the Southeast Brazilian Bight, SW Atlantic), a setting that provides a good climatic and environmental analog for many Paleozoic brachiopod shell beds of North America and Europe. A total of 82 individual brachiopod shells, collected from four shallow (5–25 m) nearshore (<2.5 km from the shore) localities, were dated by using amino acid racemization (D-alloisoleucine/L-isoleucine value) calibrated with five AMS-radiocarbon dates (r2 = 0.933). This is the first study to demonstrate that amino acid racemization methods can provide accurate and ...

Taphonomy and ecology of modern avifaunal remains from Amboseli Park, Kenya

Abstract: Avian skeletal remains occur in many fossil assemblages, and in spite of small sample sizes and incomplete preservation, they may be a source of valuable paleoecological information. In this paper, we examine the taphonomy of a modern avian bone assemblage and test the relationship between ecological data based on avifaunal skeletal remains and known ecological attributes of a living bird community. A total of 54 modern skeletal occurrences and a sample of 126 identifiable bones from Amboseli Park, Kenya, were analyzed for weathering features and skeletal part preservation in order to characterize preservation features and taphonomic biases. Avian remains, with the exception of ostrich, decay more rapidly than adult mammal bones and rarely reach advanced stages of weathering. Breakage and the percentage of anterior limb elements serve as indicators of taphonomic overprinting that may affect paleoecological signals. Using ecomorphic categories including body weight, diet, and habitat, we compared species in the bone assemblage with the living Amboseli avifauna. The documented bone sample is biased toward large body size, representation of open grassland habitats, and grazing or scavenging diets. In spite of this, multidimensional scaling analysis shows that the small faunal sample (16 out of 364 species) in the pre-fossil bone assemblage accurately represents general features of avian ecospace in Amboseli. This provides a measure of the potential fidelity of paleoecological reconstructions based on small samples of avian remains. In the Cenozoic, the utility of avian fossils is enhanced because bird ecomorphology is relatively well known and conservative through time, allowing back-extrapolations of habitat preferences, diet, etc. based on modern taxa.

Land-to-sea transition in early whales: evolution of Eocene Archaeoceti (Cetacea) in relation to skeletal proportions and locomotion of living semiaquatic mammals

Abstract: Skeletal remains of Eocene Archaeoceti provide the only direct and unequivocal evidence of the evolutionary transition of whales from land to sea. Archaeocete skeletons complete enough to be informative about locomotion are rare (principally Rodhocetus and Dorudon), and these deserve to be studied in comparison to the full spectrum of semiaquatic mammals. A principal components analysis of 14 trunk and limb measurements for 50 species of living semiaquatic mammals reduces the observed variation to three informative axes. The first principal axis (PC-I) represents overall size (water mice and shrews have the lowest scores on this axis and the hippopotamus has the highest); the second axis (PC-II) represents a spectrum of aquatic adaptation (seals have the lowest scores and tapirs have the highest); and the third principal axis (PC-III) represents a spectrum ranging from hindlimb- to forelimb-dominated locomotion (sea otters have the lowest scores and the platypus the highest).Dorudon fits poorly into a morphospace defined solely by living semiaquatic mammals; thus a second 53-species set was analyzed, adding an anthracothere to represent an artiodactyl ancestral morphology and two species of archaeocetes to represent successive stages of early whale evolution. This addition has little effect on the first two principal axes but changes the third substantially. PC-III now represents a contrast of lumbus- (and presumably tail-) dominated versus hindlimb-dominated locomotion (Dorudon has the lowest score and Rodhocetus the highest, whereas the otter shrew has the lowest score among living mammals and the desman the highest). Mammals that are more aquatic have a shorter ilium and femur combined with longer manual and pedal phalanges, whereas the reverse is true for more terrestrial taxa. Lumbus- and tail-dominated swimmers tend to have a longer lumbus combined with shorter pedal elements, whereas the reverse is true for hindlimb-dominated swimmers. Trunk and limb proportions of early middle Eocene Rodhocetus are most similar to those of the living, highly aquatic, foot-powered desmans. Trunk and limb proportions of late middle Eocene Dorudon indicate that it was a lumbus-and-tail-powered swimmer specialized in the direction of modern whales. Thus it appears that the land-to-sea transition in whale evolution involved at least two distinct phases of locomotor specialization: (1) hindlimb domination for drag-based pelvic paddling in protocetids (Rodhocetus), with tail elongation for stability, followed by (2) lumbus domination for lift-based caudal undulation and oscillation in basilosaurids (Dorudon). Rates of evolution in both phases of this change of adaptive zone are about an order of magnitude higher than background rates for the timescale involved.

The pattern of evolution in Pleistocene human brain size

Abstract: With a sample of 94 Pleistocene cranial capacities between the time period of 1.8 Ma and 50 Ka now known, we consider the evolution of cranial capacity in Homo, with the null hypothesis that the changes over time are a result of one process. We employ a new method that uses a resam- pling approach to address the limitations imposed on the methods of previous studies. To test the null hypothesis, we examine the distribution of changes in adjacent temporal samples and ask whether there are differences between earlier and later samples. Our analyses do not reject the hypothesis of a single process of brain size change, but they are incompatible with an interpretation of punctuated equilibrium during this period. The results of this paper are difficult to reconcile with the case for cladogenesis in the Homo lineage during the Pleistocene.

Stable isotopes, hypsodonty, and the paleodiet of Hemiauchenia (Mammalia: Camelidae): a morphological specialization creating ecological generalization

Abstract: Morphological adaptations may indicate increased specialization (narrowing of ecolog- ical niche) or expansion of the suite of lifestyles available to an organism (increasing niche breadth). Hypsodonty in mammals generally has been interpreted as a specialization into a grazing niche from a browsing niche. Here I examine the feeding strategy of the extinct hypsodont camel Hem- iauchenia through an analysis of stable carbon isotope values from its tooth enamel, which was used to clarify its feeding strategy and to resolve conflicting interpretations of dental versus muzzle attributes. The paleodiet of Hemiauchenia is then used to test whether hypsodonty correlates to graz- ing within fossil Lamini. This study focuses on fossils from Florida, which is geographically ideal because unlike other regions of the country almost all extant plants on which animals browse use the C3 photosynthetic pathway. In contrast, most of the grasses and sedges utilized by grazers use the C4 photosynthetic pathway. If Hemiauchenia was an obligate grazer, the stable carbon isotope values of tooth enamel should reflect primarily a diet of C4 grass and sedge (.21.3‰). If Hem- iauchenia was mainly a browser, the isotopic value should be considerably more negative reflecting ingestion primarily of C3 browse (,27.9‰). The mean d 13C values for Hemiauchenia during each time interval average more negative than 28.0‰, indicating a dominantly C3 browse diet, and there is no evidence for abandonment of the browsing niche from the Hemphillian through the Ran- cholabrean North American Land Mammal Ages. However, an increase in the range of isotopic values indicates a diet with a higher proportion of C4 grasses and sedges through time. This study therefore suggests that Hemiauchenia was a hypsodont intermediate feeder with preference for browse during the past 5 million years. Hypsodonty is not strictly associated with obligate grazing; instead it may, in this case, represent an adaptation to widen niche breadth that allowed grazing as well as browsing.

Origins and escalation of herbivory in fishes: a functional perspective

Abstract: One of the central goals in paleoecology is to understand the nature and consequences of biotic interactions. In marine systems, it has been argued that one of the major steps in the escalation of biotic interactions was marked by the origins of grazing fishes in the Cenozoic. Here I investigate the origins of herbivory and grazing in marine fishes using analyses of functional morphospace. Closing and opening lever ratios and relative length of the lower jaw are used to construct a plot of functional morphospace, a quantitative description of the potential feeding modes of fishes. Four fish faunas were examined, spanning the Mesozoic and Cenozoic (Triassic, Jurassic, Eocene and Recent). All three fossil faunas are from conservation Lagerstatten in the central Tethys, in the vicinity of coral reefs or coral-bearing hardgrounds. Changes in functional morphospace occupation reveal a marked shift in the Cenozoic, with the appearance of fishes with relatively small forceful jaws. In Recent faunas, this functional morphospace is occupied almost exclusively by grazing herbivores. This taxon-independent morphological signal of herbivory was lacking in the Mesozoic faunas, was first recorded in the Eocene, and persisted throughout the Cenozoic. This suggests that the Cenozoic did indeed witness the appearance and proliferation of herbivory and grazing by marine fishes. The arrival of these piscine herbivores had the potential to fundamentally alter the dynamics of benthic marine communities.

Dinosaur body temperatures: the occurrence of endothermy and ectothermy

Abstract: Despite numerous studies, the thermal physiology of dinosaurs remains unresolved. Thus, perhaps the commonly asked question whether dinosaurs were ectotherms or endotherms is inappropriate, and it is more constructive to ask which dinosaurs were likely to have been en- dothermic and which ones ectothermic. Field data from crocodiles over a large size range show that body temperature fluctuations decrease with increasing body mass, and that average daily body temperatures increase with increasing mass. A biophysical model, the biological relevance of which was tested against field data, was used to predict body temperatures of dinosaurs. However, rather than predicting thermal relations of a hypothetical dinosaur, the model considered correct paleogeographical distribution and climate to predict the thermal relations of a large number of dinosaurs known from the fossil record ( .700). Many dinosaurs could have had ''high'' ($308C) and stable (daily amplitude #28C) body temperatures without metabolic heat production even in winter, so it is unlikely that selection pressure would have favored the evolution of elevated resting metabolic rates in those species. Recent evidence of ontogenetic growth rates indicates that even the juveniles of large species (3000-4000 kg) could have had biologically functional body temper- ature ranges during early development. Smaller dinosaurs (,100 kg) at mid to high latitudes (.458) could not have had high and stable body temperatures without metabolic heat production. How- ever, elevated metabolic rates were unlikely to have provided selective advantage in the absence of some form of insulation, so probably insulation was present before endothermy evolved, or else it coevolved with elevated metabolic rates. Superimposing these findings onto a phylogeny of the Dinosauria suggests that endothermy most likely evolved among the Coelurosauria and, to a lesser extent, among the Hypsilophodontidae, but not among the Stegosauridae, Nodosauridae, Anky- losauridae, Hadrosauridae, Ceratopsidae, Prosauropoda, and Sauropoda.

Increase of shell-crushing predation recorded in fossil shell fragmentation

Abstract: The Mesozoic marine revolution focuses on increased predation by durophagous (shell-crushing) predators and the concomitant evolution of prey organisms that occurred in the Mesozoic. Evidence of this predator/prey revolution is found in the appearance and increase of new types of predators that can crush hard shells of prey organisms, and is also found in the morphological changes of prey organisms, such as the appearance of a protective shell morphology of gastropods. We present new data based on the occurrence of shell fragments that indicate a slower increase in durophagous predation than has been considered previously. The results of an experiment on shell abrasion, in which shells were tumbled in barrels with sediments, indicate that incomplete bivalves and gastropods with angular margins from shallow-marine deposits can be considered as good evidence of durophagous predation. Such angular shell fragments are virtually absent from Japanese Mesozoic shell beds, whereas they are occasionally o...

Reconstruction of Tertiary Metasequoia forests. II. Structure, biomass, and productivity of Eocene floodplain forests in the Canadian Arctic

Abstract: Abundant fossil plant remains are preserved in the high-latitude middle Eocene deposits of the Buchanan Lake Formation on Axel Heiberg Island, Nunavut Territory, Canada. Intact leaf litter, logs, and stumps preserved in situ as mummified remains offer an opportunity to determine the structure, biomass, and productivity of two Taxodiaceae-dominated forests that grew north of the Arctic Circle (paleolatitude 75–80°N). We excavated fossil tree trunks and treetops to develop equations that describe the height, structure, and mass of the aboveground components of Eocene-age Metasequoia trees. We combined those data with surveys of in situ stumps to determine the structure, biomass, and productivity of two fossil forests, “N” and “HR.” We calculated a canopy height of 40 ± 3 m for the N forest and 25 m ± 2 m for the HR forest. Buried knots in dissected logs and abundant branch-free bole wood indicate that these were tall, closed-canopy forests. Stem tapers indicate that the overstory was of uniform hei...

Morphological pathways in the evolution of Early and Middle Devonian ammonoids

Abstract: The principal conch parameters—whorl expansion rate, whorl overlap rate, umbilical width, and whorl thickness—of Early and Middle Devonian ammonoids have been extensively investigated. Stratophenetic analyses show long-term trends in the transformations of these characters over long periods of time, but sudden and rapid reversals can also be observed. On the basis of these four quantifiable conch parameters and supplementary qualitative characters, ten ammonoid morphs were distinguished. Reconstruction of the evolutionary history of these morphs reflects the existence of two major phylogenetic lineages, both already visible in Early Devonian faunas. The agoniatitid lineage is characterized by slow character development and leads to the Frasnian gephuroceratids; the anarcestid lineage displays rapid morphological evolution that leads to the late Givetian pharciceratids as well as the Middle and Late Devonian tornoceratids. Morphological evolution is interpreted as partly limited by geometrical and physical constraints.

Taphonomic analysis of large mammals recovered from the Pleistocene Rancho La Brea tar seeps

Abstract: The asphalt deposits of Rancho La Brea are well known for preserving a prolific and diverse Late Pleistocene fauna. However, little taphonomic research has been done on these collections. To better understand the formation of this impressive assemblage, a taphonomic study of the bones of the large mammals from one asphalt deposit, Pit 91, was carried out, and results are presented here. The predominance of carnivore specimens in the Rancho La Brea deposits has long been explained by a scenario in which a prey animal was trapped in asphalt and attracted large numbers of carnivores who became trapped in turn. Hypotheses generated from this scenario were tested by collecting taphonomic data on over 18,000 specimens. Weathering data indicate that elements were deposited fairly rapidly. However, patterns of skeletal part representation for the seven most common species demonstrate that complete skeletons are not present. Water transport is ruled out as the primary process responsible for removing skeletal elements based on abrasion data. Instead, the feeding activity of carnivores (ravaging) appears to have been an important factor in the formation of the assemblage.

Comparative geographic and environmental diversity dynamics of gastropods and bivalves during the Ordovician Radiation

Abstract: Bivalves and gastropods, prominent members of the Modern Evolutionary Fauna, are traditionally noted for sharing remarkably similar global diversity trajectories and environmental distributions throughout the Phanerozoic. By comparing their fossil occurrences at several scales within a finely resolved geographic, environmental, and temporal framework, it is possible to eval- uate whether such similarities are caused primarily by intrinsic macroevolutionary factors or ex- trinsic ecological factors. Using a database of 7779 global gastropod and bivalve genus occurrences, we investigate the geographical and environmental attributes of bivalves and gastropods during the Ordovician Period at scales ranging from global, to a comparison among five paleocontinents, to an intracontinental comparison of four regions within Laurentia. Although both classes shared statistically indistinguishable global diversity trajectories and broadly similar environmental dis- tributions during the Ordovician, their environmental distributions differed in several significant features. Furthermore, the diversity trajectories and environmental distributions of these classes differed significantly among paleocontinents and among regions within Laurentia. Bivalves were consistently most diverse in deeper water, siliciclastic-rich settings in higher-latitude paleoconti- nents whereas gastropods were consistently most diverse in shallower, carbonate-rich settings in more-equatorial paleocontinents. Notably, these environmental differences were robust to chang- ing physical parameters within paleocontinents, with each class consistently tracking its preferred environmental setting. These results suggest that environmental factors played significant, albeit distinct, roles in the Ordovician diversifications of gastropods and bivalves. However, their similar global diversity trajectories suggest that shared, intrinsic macroevolutionary attributes also may have played an important role in the evolution of these classes during the Ordovician Radiation.

Metabolic rate of late Holocene freshwater fish: evidence from δ13C values of otoliths

Abstract: We examine patterns of intra-otolith variation in δ13C values of fossil Aplodinotus grunniens (freshwater drum) otoliths recovered from an archeological site in northeast Tennessee. We find three repeatable patterns: an initial increase early in ontogeny followed by relatively stable δ13C values as the fish ages, an initial strong covariation between seasonal δ18O and δ13C values, and a decrease with age in the magnitude of seasonal change in δ13C values. These last two observations are illustrated by seasonal least-squares linear regressions between δ13C and δ18O values that tend to progressively decrease in r2 value and slope with fish age. These patterns are evaluated by using a mass balance model in which otolith δ13C values are derived from dissolved inorganic carbon of ambient water mixing with carbon derived from metabolic processes. The proportion of metabolically derived carbon is found to be the dominant factor controlling intra-otolith variation in δ13C values. Thus, the difference between maximum and minimum δ13C values from a single otolith (δ13Cmax–min) is postulated to reflect the total change in metabolic rate over the lifetime of a fish. δ13Cmax–min values significantly and negatively covary with average δ18O(CaCO3) values, suggesting either a higher total change in metabolic rate over the lifetime of a fish in cooler climates characterized by shorter growing seasons, or a decrease in summer/winter precipitation ratio. A proxy for metabolic rate preserved in otoliths would facilitate the understanding of evolutionary history in physiological traits of fishes and improve our understanding of bioenergetics.

A paleoecological paradox: the habitat and dietary preferences of the extinct tethythere Desmostylus, inferred from stable isotope analysis

Abstract: The Desmostylia, an extinct order of mammals related to sirenians and proboscideans, are known from the late Oligocene to late Miocene of the North Pacific. Though often categorized as marine mammals on the basis of fossil occurrences in nearshore deposits, reconstructions of desmostylian habitat and dietary preferences have been somewhat speculative because morpho- logical and sedimentological information is limited. We analyzed the carbon, oxygen, and stron- tium isotope compositions of enamel from Desmostylus and co-occurring terrestrial and marine taxa from middle Miocene sites in California to address the debate surrounding desmostylian ecol- ogy. The d 13C value of tooth enamel can be used as a proxy for diet. Desmostylus had much higher d13C values than coeval terrestrial or marine mammals, suggesting a unique diet that most likely consisted of aquatic vegetation. Modern aquatic mammals tend to exhibit lower variability in d18O values than terrestrial mammals. Both fossil marine mammals and Desmostylus exhibited low d18O variability, suggesting that Desmostylus spent a large amount of time in water. Finally, the Sr isotope composition of marine organisms reflects that of the ocean and is relatively invariant when com- pared with values for animals from land. Sr isotope values for Desmostylus were similar to those for terrestrial, rather than marine, mammals, suggesting Desmostylus was spending time in estu- arine or freshwater environments. Together, isotopic data suggest that Desmostylus was an aquatic herbivore that spent a considerable portion of its life foraging in estuarine and freshwater ecosys- tems.

Confidence limits on fossil ranges that account for facies changes

Abstract: A drawback to most existing methods of calculating confidence limits on fossil ranges is their assumption that the probability of collecting a taxon through a stratigraphic section is constant. Marshall (1997) described an approach that would circumvent this problem, but it requires knowing the probability of collection as a function of stratigraphic position. Multivariate paleoecological methods, such as detrended correspondence analysis (DCA), offer a means of estimating these probabilities. DCA axis 1 sample scores can be used to quantify facies change through a stratigraphic section, and to calculate the probability of collection of a taxon relative to DCA axis 1. From these two, the probability of collection of each taxon can be estimated for each horizon in the measured section. This approach is applied here to the Upper Ordovician Kope Formation of the Cincinnati, Ohio, area to distinguish between disappearances of taxa that are driven by facies change and taxon rarity and those that represent true regional extinction. This new approach to confidence limits could also be applied to test the synchroneity of extinction or origination at large-scale turnover events, such as mass extinctions and the turnover pulses that bound episodes of faunal stasis.

Evidence for advanced carnivory in fossil armadillos (Mammalia: Xenarthra: Dasypodidae)

Abstract: The euphractine Macroeuphractus outesi, from the late Pliocene Chapadmalalan SALMA of Buenos Aires Province, Argentina, is one of the largest dasypodids known. Its skull preserves features remarkable for an armadillo. Its complete dental arcade and large caniniform teeth have received attention in the literature as indicative of scavenging behavior. This report considers the degree of carnivory within the context of the generally omnivorous feeding behavior of euphractine armadillos through morphological and biomechanical analyses. Morphological analyses reveal that the main differences between M. outesi and other euphractines are the enlargement of the cranium, particularly of the temporal fossa; more prominent muscular scars for origin of the temporalis muscle; a more expanded rostrum, particularly in dorsoventral height; a more powerful anterior dentition, especially in the great enlargement and caniniform modification of M2; and a deeper and more robust zygomatic arch. Biomechanical analyses ...

An alternative method for predicting body mass: the case of the Pleistocene marsupial lion

Abstract: Accurate estimates of body mass in fossil taxa are fundamental to paleobiological reconstruction. Predictive equations derived from correlation with craniodental and body mass data in extant taxa are the most commonly used, but they can be unreliable for species whose morphology departs widely from that of living relatives. Estimates based on proximal limb-bone circumference data are more accurate but are inapplicable where postcranial remains are unknown. In this study we assess the efficacy of predicting body mass in Australian fossil marsupials by using an alternative correlate, endocranial volume. Body mass estimates for a species with highly unusual craniodental anatomy, the Pleistocene marsupial lion (Thylacoleo carnifex), fall within the range determined on the basis of proximal limb-bone circumference data, whereas estimates based on dental data are highly dubious. For all marsupial taxa considered, allometric relationships have small confidence intervals, and percent prediction errors are comparable to those of the best predictors using craniodental data. Although application is limited in some respects, this method may provide a useful means of estimating body mass for species with atypical craniodental or postcranial morphologies and taxa unrepresented by postcranial remains. A trend toward increased encephalization may constrain the method's predictive power with respect to many, but not all, placental clades.

Does global diversity mean anything

Abstract: A major goal of paleobiological research since the early 1960s has been the reconstruction in quantitative terms of the history of biological diversity. Spearheaded by Valentine (1969), Raup (1972, 1976a,b), and Sepkoski (1979, 1981, 1984, 1990, 1993), this effort has yielded estimates of global diversity through time, as well as calculations of global rates and magnitudes of extinction and diversification. A consensus emerging in the early 1980s (Sepkoski et al. 1981) indicated that global marine invertebrate diversity rose through the Cambrian and Ordovician periods to a plateau, which with brief extinction-related interruptions was maintained from the mid-Paleozoic to the mid-Mesozoic. Beginning in the Cretaceous, diversity rose again, reaching a peak in the late Neogene. The five mass extinctions of the Phanerozoic, and more or less distinct episodes of diversification, were identified and distinguished from many lesser events (Raup and Sepkoski 1982). Comparable studies, with varying results, were conducted on land vertebrates (Benton 1985, 1989), land plants (Knoll et al. 1979; Niklas et al. 1980, 1983; Tiffney 1981; Knoll 1984), early protistans (Knoll 1994), insects (Labandeira and Sepkoski 1993), and life as a whole (Van Valen 1984, 1985; Van Valen and Maiorana 1985; Signor 1990; Valentine et al. 1991; Benton 1995; Courtillot and Gaudemer 1996; Miller and Foote 1996). Recent analyses of diversity through time (Alroy et al. 2001), utilizing several different methodological protocols for handling sampling biases and taxon counting, have called some of the earlier work into question. Alroy and colleagues tentatively propose that global genus-level marine diversity reached plateaus of similar magnitude during the mid-Paleozoic and in the Cretaceous to Recent interval, with no detectable rise in diversity during the latter interval. Commenting on the new study, …

Temporal and Spatial Variation in Neolithic Caprine Exploitation Strategies : a Case Study of Fauna from the Site of Yiftah'el (Israel)

Abstract: Trois differentes strategies d'exploitation animale ont coexiste durant la periode du PPNB moyen dans le sud du Levant. La premiere caracterise les sites de la vallee du Jourdain et des regions adjacentes. Elle correspond a un proto-elevage de chevres (morphologie identique a celle des formes sauvages) qui domine les assemblages fauniques. La seconde strategie, qui correspond a une chasse a la gazelle ainsi qu 'une frequence de chevres sauvages moins elevee que dans la vallee du Jourdain, est localisee dans la partie occidentale de la region mediterraneenne. Comme dans le cas precedent, la morphologie des os de Capra ne se distingue pas de ceux des animaux sauvages. La troisieme strategie s 'observe dans les regions arides des deserts du Sinai, de Judee et de la partie orientale de la Jordanie. Elle reflete une forte continuite des traditions epipaleolithiques de chasse et de cueillette, comprenant exclusivement des especes sauvages. L'analyse de la faune neolithique de Yiftah'el (Basse Galilee, Israel) a ete entreprise dans le but de tester si les variations des strategies de subsistance inter-site refletent une introduction de chevres domestiques et leur dispersion graduelle ou, au contraire, une domestication autochtone. Les resultats montrent une evolution chronologique graduelle du spectre faunique, des âges d'abattage et de la taille des chevres, trois facteurs qui, combines, prouvent la domestication locale de Capra.

Demography of late Miocene rhinoceroses (Teleoceras proterum and Aphelops malacorhinus) from Florida: linking mortality and sociality in fossil assemblages

Abstract: Among polygynous mammals, a heightened risk of mortality is linked to the intensity of intragender competition and life-history stages, such as sexual maturity, where inexperienced individuals are vulnerable to the aggressive behaviors of dominant individuals. In this respect, the age- and sex-specific mortality patterns found in fossil assemblages could be informative of soci- ality in extinct species. This possibility was explored by comparing the age- and sex-specific de- mography of attritional rhinoceros assemblages, Teleoceras proterum (n 5 2) and Aphelops malacor- hinus (n 5 1), from pond and fluvial sedimentary facies of the late Miocene of Florida, with modern skeletal assemblages of extant rhinos and other large mammals. Subadult and young adult males (between 15-40% of potential life span) numerically dominate the Teleoceras assemblages, indicating a disproportionately high frequency of localized young male mortality. The estimated age-specific mortality rates indicate elevated mortality risks among males at an age equivalent to the years encompassing male physiological and social maturity in modern rhinos, a pattern that suggests a high frequency of socially mediated mortality. Age-specific mor- tality rate curves of modern black rhino populations are essentially identical. A high frequency of intraspecific fight-related mortality characterizes modern rhinos and strongly suggests that ele- vated Teleoceras mortality was influenced by intragender competition. Although Teleoceras is widely believed to have been the analog of extant Hippopotamus, mortality rates of young males are not elevated in a modern Hippopotamus population. The Aphelops assemblage is not significantly male- biased and does not indicate elevated mortality rates of young males, suggesting that aspects of Aphelops sociality differed from modern rhinos. Although the nature of Aphelops sociality is not clear, aggression toward young males may have been less extreme or less frequent in Aphelops pop- ulations.

Mapping the origin of faunal assemblages using strontium isotopes

Abstract: One of the greatest challenges in using faunal assemblages to make ecological or paleo- ecological interpretations is determining the spatial scale over which such analyses are applicable. As a result, it has been difficult to use these assemblages to test hypotheses about spatial and tem- poral variability in populations. Here we show that it is possible to use strontium (Sr) isotopes from bones and vegetation to statistically constrain the area sampled in two Holocene predator accumulations in northeastern Yellowstone National Park, Wyoming. Previous studies have used these sites to elucidate local population responses to climatic change, by assuming that the speci- mens originated within ;5 km of the site. We used Sr analyses to construct a likelihood curve that describes the probability that our samples were collected within a given radius of each site. Our results indicate that the specimens in both sites were derived from non-overlapping populations and that the collection radius has not changed detectably over the past 3000 years. This work un- derscores the promise of this technique for ascribing source areas to paleontological, biological, and ecological specimens.

Evolutionary trends and the origin of the mammalian lower jaw

Abstract: The single bony element forming the lower jaw of living mammals, the dentary, has been interpreted as representing the culmination of a long and gradual evolutionary trend. Numerous fossil nonmammalian synapsids (“mammal-like reptiles”) show varying degrees of enlargement of the dentary and concomitant reduction in the postdentary bones. To quantitatively reexamine patterns of morphological change in the evolution of the mammalian lower jaw, measurement and discrete character data were collected from 322 fossil synapsid mandibles spanning Late Carboniferous through Jurassic time. Measurements confirm that the relative contribution of the dentary increased in theriodont (advanced therapsid) evolution with regard to both stratigraphic and phylogenetic position. However, dentary enlargement and postdentary reduction failed to typify all therapsid subclades. Qualitative characters of the mandible were used to quantify morphological similarity with regard to the early mammal Morganucodon . Analyses contrasting stratigraphic and phylogenetic position with mammalian similarity indicate that mandibular evolution was primarily conservative, with only anomodont therapsids evolving substantial morphological novelty. Scaling analyses comparing the area of the dentary and postdentary regions to jaw length uniformly show isometry or slight positive allometry, although cynodont therapsids have a smaller postdentary region than any other therapsid subgroup. These results suggest that body size decreases cannot fully explain the reduction of the postdentary bones. Finally, step size bias was tested as a mechanism for explaining long-term trends. Qualitative data reveal no significant difference in the magnitude of character changes occurring in mammalian and nonmammalian directions.

An Aurignacian «Garden of Eden» in southern Germany ? An alternative interpretation of the Geissenklösterle and a critique of the Kulturpumpe model

Abstract: New radiocarbon dates and results of new analyses from Geissenklosterle (Conard and Bolus JHE, 40: 331-71) were recently used to suggest that the Aurignacian of the Swabian Jura dates back to 40 ka BP and that this evidence supports the Kulturpumpe model according to which cultural innovations of the Aurignacian and Gravettian in Swabia predate similar developments in the remainder of Europe. Here we conduct a critical analysis of new and old evidence, discuss the relevance of Conard and Bolus’s hypothesis of a “Middle Paleolithic Dating Anomaly” to explain inconsistencies in the 14C determinations for Geissenklosterle, and conclude that the earliest Aurignacian occupation of this site does not predate ca 36.5 ka BP and probably took place between 35 and 33 ka BP. This interpretation is consistent with what we know about the taphonomy and environmental context of the site, with the technology and typology of the bone and lithic assemblages from its Aurignacian levels, and conforms well to the 14C dates on faunal remains modified by humans found therein. This interpretation is also consistent with the pattern of radiocarbon dates for the Aurignacian as a whole suggesting that the emergence of this technocomplex dates to ca 36.5 ka BP ; that the process appears to our eyes as simultaneous is to be expected in the first place due to the poor resolution of available dating methods. Modern behavior as inferred from the use of objects of personal ornamentation is documented in the Châtelperronian and the Initial Upper Paleolithic of the Levant; both predate the Aurignacian chronometrically and stratigraphically. The emergence of the Aurignacian and of modern behavior in Eurasia were considered for a long time as one and the same problem, but it is now clear that these are two independent issues that must be considered separately.

Global databases will yield reliable measures of global biodiversity

Abstract: For decades, paleobiologists have treated global diversity estimation as a straightforward problem (Miller 2000): count up the known higher taxa in each geological time interval, make a diversity curve, and go straight ahead to analyzing and interpreting the trends. However, global diversity curves recently have come under attack from all sides. Some researchers argue that although traditional curves are strongly affected by sampling biases (e.g., Smith 2001; Peters and Foote 2002), these biases can be corrected by assembling large, locality-level databases with detailed contextual information (Alroy et al. 2001). Others point to the large gap between true total global richness and the meager head counts the fossil record has to offer, and conclude that workers should focus exclusively on local and regional diversity (Jackson and Johnson 2001). Here I argue that although further fieldwork surely is needed, understanding global diversity in the short term remains a tractable goal—as long as we move quickly to build a discipline-wide, globally extensive paleontological database.

Estimation of stratigraphic ranges when fossil finds are not randomly distributed

Abstract: Existing methods for point and interval estimation of the endpoints of the stratigraphic range of a fossil taxon under continuous sampling assume that the mean density of finds is constant over the stratigraphic range. These methods can perform badly when this mean density is not constant. Most seriously, if mean density declines toward the endpoint of interest, then the true coverage of the confidence interval for the true endpoint can be far below its nominal level, giving a false impression of estimation precision. Simple point and interval estimates that are designed to avoid this problem are presented. These methods are illustrated with the fossil record of two species of the Caribbean bryozoan Metrarabdotos.