The earliest dispersal of humans into North America is a contentious subject, and proposed early ... more The earliest dispersal of humans into North America is a contentious subject, and proposed early sites are required to meet the following criteria for acceptance: (1) archaeological evidence is found in a clearly defined and undisturbed geologic context; (2) age is determined by reliable radiometric dating; (3) multiple lines of evidence from interdisciplinary studies provide consistent results; and (4) unquestionable artefacts are found in primary context. Here we describe the Cerutti Mastodon (CM) site, an archaeological site from the early late Pleistocene epoch, where in situ hammerstones and stone anvils occur in spatio-temporal association with fragmentary remains of a single mastodon (Mammut americanum). The CM site contains spiral-fractured bone and molar fragments, indicating that breakage occured while fresh. Several of these fragments also preserve evidence of percussion. The occurrence and distribution of bone, molar and stone refits suggest that breakage occurred at the site of burial. Five large cobbles (hammerstones and anvils) in the CM bone bed display use-wear and impact marks, and are hydraulically anomalous relative to the low-energy context of the enclosing sandy silt stratum. (230)Th/U radiometric analysis of multiple bone specimens using diffusion-adsorption-decay dating models indicates a burial date of 130.7 ± 9.4 thousand years ago. These findings confirm the presence of an unidentified species of Homo at the CM site during the last interglacial period (MIS 5e; early late Pleistocene), indicating that humans with manual dexterity and the experiential knowledge to use hammerstones and anvils processed mastodon limb bones for marrow extraction and/or raw material for tool production. Systematic proboscidean bone reduction, evident at the CM site, fits within a broader pattern of Palaeolithic bone percussion technology in Africa, Eurasia and North America. The CM site is, to our knowledge, the oldest in situ, well-documented archaeological site in North America and, as such, substantially revises the timing of arrival of Homo into the Americas.
Epithelial-mesenchymal interactions guide tooth development through its early stages and establis... more Epithelial-mesenchymal interactions guide tooth development through its early stages and establish the morphology of the dentin surface upon which enamel will be deposited. Starting with the onset of amelogenesis beneath the future cusp tips, the shape of the enamel layer covering the crown is determined by five growth parameters: the (1) appositional growth rate, (2) duration of appositional growth (at the cusp tip), (3) ameloblast extension rate, (4) duration of ameloblast extension, and (5) spreading rate of appositional termination. Appositional growth occurs at a mineralization front along the ameloblast distal membrane in which amorphous calcium phosphate (ACP) ribbons form and lengthen. The ACP ribbons convert into hydroxyapatite crystallites as the ribbons elongate. Appositional growth involves a secretory cycle that is reflected in a series of incremental lines. A potentially important function of enamel proteins is to ensure alignment of successive mineral increments on the tips of enamel ribbons deposited in the previous cycle, causing the crystallites to lengthen with each cycle. Enamel hardens in a maturation process that involves mineral deposition onto the sides of existing crystallites until they interlock with adjacent crystallites. Neutralization of acidity generated by hydroxyapatite formation is a key part of the mechanism. Here we review the growth parameters that determine the shape of the enamel crown as well as the mechanisms of enamel appositional growth and maturation.
Egu General Assembly Conference Abstracts, Apr 29, 2010
Investigations of stable isotope composition of mineralized tissues have added greatly to our kno... more Investigations of stable isotope composition of mineralized tissues have added greatly to our knowledge of past climates and dietary behaviors of organisms, even when they are implemented through 'bulk sampling', in which a single assay yields a single, time-averaged value. Likewise, the practice of 'sclerochronology', which documents periodic structural increments comprising a growth record for accretionary tissues, offers insights into rates of growth and age data at a scale of temporal resolution permitted by the nature of structural increments. We combine both of these approaches to analyze dental tissues of late Pleistocene proboscideans. Tusk dentin typically preserves a record of accretionary growth consisting of histologically distinct increments on daily, approximately weekly, and yearly time scales. Working on polished transverse or longitudinal sections, we mill out a succession of temporally controlled dentin samples bounded by clear structural increments with a known position in the sequence of tusk growth. We further subject each sample (or an aliquot thereof) to multiple compositional analyses - most frequently to assess δ18O and δ13C of hydroxyapatite carbonate, and δ13C and δ15N of collagen. This yields, for each animal and each series of years investigated, a set of parallel compositional time series with a temporal resolution of 1-2 months (or finer if we need additional precision). Patterns in variation of thickness of periodic sub-annual increments yield insight into intra-annual and inter-annual variation of tusk growth rate. This is informative even by itself, but it is still more valuable when coupled with compositional time series. Further, the controls on different stable isotope systems are sufficiently different that the data ensemble yields 'much more than the sum of its parts.' By assessing how compositions and growth rates covary, we monitor with greater confidence changes in local climate, diet, behavior, and health status. We illustrate the potential of this approach with case studies that reveal: season of birth and age of weaning in juvenile mammoths; age of maturation in male mastodons; season of musth in mammoths and mastodons; and season of death and tests of simultaneity of death in mammoths and mastodons. The data provided by histological and stable isotope analyses rarely reveal cause of death directly, but they can, in concert with other observations, affect perceptions of the likelihood of competing interpretations of cause of death. Most important, paleobiological inferences based on these studies can be integrated over broad geographic and temporal scales to show how specific paleobiological traits changed through time, prior to extinction. These studies have great power for investigating causes of extinction because contrasting patterns of change are expected under different hypothesized drivers of extinction.
The effects of climate change are difficult to predict for many marine species because little is ... more The effects of climate change are difficult to predict for many marine species because little is known of their response to climate variations in the past. However, long-term chronologies of growth, a variable that integrates multiple physical and biological factors, are now available for several marine taxa. These allow us to search for climate-driven synchrony in growth across multiple taxa and ecosystems, identifying the key processes driving biological responses at very large spatial scales. We hypothesized that in northwest (NW) Australia, a region that is predicted to be strongly influenced by climate change, the El Niño Southern Oscillation (ENSO) phenomenon would be an important factor influencing the growth patterns of organisms in both marine and terrestrial environments. To test this idea, we analyzed existing growth chronologies of the marine fish Lutjanus argentimaculatus, the coral Porites spp. and the tree Callitris columellaris and developed a new chronology for anot...
Normal development and disturbances caused by disease can be represented by changes in five biolo... more Normal development and disturbances caused by disease can be represented by changes in five biological parameters that characterize enamel formation. “Fossilized” in tooth structure, there is a detailed record of development traced by incremental growth lines. Enamel growth lines represent the configuration of deposited enamel at a succession of stages in its history of apposition. We hypothesize that we can use them to estimate enamel growth parameters and thus model crown development. Objectives: To measure the distances between incremental lines and use the obtained values to construct 2D and 3D models of daily enamel formation. To reveal the importance of each biological parameter in determining crown shape and quantify the extent to which regulatory mechanisms alter these parameters during human crown formation. Methods: Enamel incremental features include daily cross-striations (CS) and long-period (~7-day) striae of Retzius (SR), and surface perikymata. SEM was used to measur...
Climate change is having major effects on the world’s marine ecosystems, and it is predicted that... more Climate change is having major effects on the world’s marine ecosystems, and it is predicted that the severity of this problem will increase rapidly in coming years. For fishes, changes in temperature and current regimes may lead to shifts in distributions and changes in growth rates. Ultimately, this will have major implications for any fished species, since growth, productivity, and sustainable yield of populations are tightly linked. To understand how marine species might respond to climate change, we evaluated responses to past environmental variations by applying dendrochronology methods to otolith growth records from three long-lived (up to 70 years) fishes from the southwestern coast of Australia. The species set included a shallow water (<100 m) carnivore (western blue grouper- Achoerodus gouldii ), a deep water (>250 m) carnivore (hapuku- Polyprion oxygeneios ), and an omnivore (sea sweep- Scorpis aequipinnis ). We compared growth chronologies from these species to se...
The effects of climate change on predatory fishes in deep shelf areas are difficult to predict be... more The effects of climate change on predatory fishes in deep shelf areas are difficult to predict because complex processes may govern food availability and temperature at depth. We characterised the net impact of recent environmental changes on hapuku (Polyprion oxygeneios), an apex predator found in continental slope habitats (>200 m depth) by using dendrochronology techniques to develop a multi-decadal record of growth from otoliths. Fish were sampled off temperate south-western Australia, a region strongly influenced by the Leeuwin Current, a poleward-flowing, eastern boundary current. The common variance among individual growth records was relatively low (3.4%), but the otolith chronology was positively correlated (r = 0.61, p < 0.02) with sea level at Fremantle, a proxy for the strength of the Leeuwin Current. The Leeuwin Current influences the primary productivity of shelf ecosystems, with a strong current favouring growth in hapuku. Leeuwin Current strength is predicted t...
... E-mail The Corresponding Author , Adam N. Rountrey b , E-mail The Corresponding Author , Jan ... more ... E-mail The Corresponding Author , Adam N. Rountrey b , E-mail The Corresponding Author , Jan van Arkel a , E-mail The Corresponding Author , Joost F. Duivenvoorden ... Tree pollen is represented by Pinus, Picea, Betula, Alnus and low values of Carpinus, Corylus and Ulmus. ...
A well-preserved woolly mammoth calf found in northwest Siberia offers unique opportunities to in... more A well-preserved woolly mammoth calf found in northwest Siberia offers unique opportunities to investigate mammoth anatomy, behavior, life history and taphonomy. Analysis of the fluvial setting where the specimen was found suggests it was derived from eroding bluffs during ice-out flooding in June 2006. It then lay exposed on a point-bar surface until recovery the following May. AMS dating of
The earliest dispersal of humans into North America is a contentious subject, and proposed early ... more The earliest dispersal of humans into North America is a contentious subject, and proposed early sites are required to meet the following criteria for acceptance: (1) archaeological evidence is found in a clearly defined and undisturbed geologic context; (2) age is determined by reliable radiometric dating; (3) multiple lines of evidence from interdisciplinary studies provide consistent results; and (4) unquestionable artefacts are found in primary context. Here we describe the Cerutti Mastodon (CM) site, an archaeological site from the early late Pleistocene epoch, where in situ hammerstones and stone anvils occur in spatio-temporal association with fragmentary remains of a single mastodon (Mammut americanum). The CM site contains spiral-fractured bone and molar fragments, indicating that breakage occured while fresh. Several of these fragments also preserve evidence of percussion. The occurrence and distribution of bone, molar and stone refits suggest that breakage occurred at the site of burial. Five large cobbles (hammerstones and anvils) in the CM bone bed display use-wear and impact marks, and are hydraulically anomalous relative to the low-energy context of the enclosing sandy silt stratum. (230)Th/U radiometric analysis of multiple bone specimens using diffusion-adsorption-decay dating models indicates a burial date of 130.7 ± 9.4 thousand years ago. These findings confirm the presence of an unidentified species of Homo at the CM site during the last interglacial period (MIS 5e; early late Pleistocene), indicating that humans with manual dexterity and the experiential knowledge to use hammerstones and anvils processed mastodon limb bones for marrow extraction and/or raw material for tool production. Systematic proboscidean bone reduction, evident at the CM site, fits within a broader pattern of Palaeolithic bone percussion technology in Africa, Eurasia and North America. The CM site is, to our knowledge, the oldest in situ, well-documented archaeological site in North America and, as such, substantially revises the timing of arrival of Homo into the Americas.
Epithelial-mesenchymal interactions guide tooth development through its early stages and establis... more Epithelial-mesenchymal interactions guide tooth development through its early stages and establish the morphology of the dentin surface upon which enamel will be deposited. Starting with the onset of amelogenesis beneath the future cusp tips, the shape of the enamel layer covering the crown is determined by five growth parameters: the (1) appositional growth rate, (2) duration of appositional growth (at the cusp tip), (3) ameloblast extension rate, (4) duration of ameloblast extension, and (5) spreading rate of appositional termination. Appositional growth occurs at a mineralization front along the ameloblast distal membrane in which amorphous calcium phosphate (ACP) ribbons form and lengthen. The ACP ribbons convert into hydroxyapatite crystallites as the ribbons elongate. Appositional growth involves a secretory cycle that is reflected in a series of incremental lines. A potentially important function of enamel proteins is to ensure alignment of successive mineral increments on the tips of enamel ribbons deposited in the previous cycle, causing the crystallites to lengthen with each cycle. Enamel hardens in a maturation process that involves mineral deposition onto the sides of existing crystallites until they interlock with adjacent crystallites. Neutralization of acidity generated by hydroxyapatite formation is a key part of the mechanism. Here we review the growth parameters that determine the shape of the enamel crown as well as the mechanisms of enamel appositional growth and maturation.
Egu General Assembly Conference Abstracts, Apr 29, 2010
Investigations of stable isotope composition of mineralized tissues have added greatly to our kno... more Investigations of stable isotope composition of mineralized tissues have added greatly to our knowledge of past climates and dietary behaviors of organisms, even when they are implemented through 'bulk sampling', in which a single assay yields a single, time-averaged value. Likewise, the practice of 'sclerochronology', which documents periodic structural increments comprising a growth record for accretionary tissues, offers insights into rates of growth and age data at a scale of temporal resolution permitted by the nature of structural increments. We combine both of these approaches to analyze dental tissues of late Pleistocene proboscideans. Tusk dentin typically preserves a record of accretionary growth consisting of histologically distinct increments on daily, approximately weekly, and yearly time scales. Working on polished transverse or longitudinal sections, we mill out a succession of temporally controlled dentin samples bounded by clear structural increments with a known position in the sequence of tusk growth. We further subject each sample (or an aliquot thereof) to multiple compositional analyses - most frequently to assess δ18O and δ13C of hydroxyapatite carbonate, and δ13C and δ15N of collagen. This yields, for each animal and each series of years investigated, a set of parallel compositional time series with a temporal resolution of 1-2 months (or finer if we need additional precision). Patterns in variation of thickness of periodic sub-annual increments yield insight into intra-annual and inter-annual variation of tusk growth rate. This is informative even by itself, but it is still more valuable when coupled with compositional time series. Further, the controls on different stable isotope systems are sufficiently different that the data ensemble yields 'much more than the sum of its parts.' By assessing how compositions and growth rates covary, we monitor with greater confidence changes in local climate, diet, behavior, and health status. We illustrate the potential of this approach with case studies that reveal: season of birth and age of weaning in juvenile mammoths; age of maturation in male mastodons; season of musth in mammoths and mastodons; and season of death and tests of simultaneity of death in mammoths and mastodons. The data provided by histological and stable isotope analyses rarely reveal cause of death directly, but they can, in concert with other observations, affect perceptions of the likelihood of competing interpretations of cause of death. Most important, paleobiological inferences based on these studies can be integrated over broad geographic and temporal scales to show how specific paleobiological traits changed through time, prior to extinction. These studies have great power for investigating causes of extinction because contrasting patterns of change are expected under different hypothesized drivers of extinction.
The effects of climate change are difficult to predict for many marine species because little is ... more The effects of climate change are difficult to predict for many marine species because little is known of their response to climate variations in the past. However, long-term chronologies of growth, a variable that integrates multiple physical and biological factors, are now available for several marine taxa. These allow us to search for climate-driven synchrony in growth across multiple taxa and ecosystems, identifying the key processes driving biological responses at very large spatial scales. We hypothesized that in northwest (NW) Australia, a region that is predicted to be strongly influenced by climate change, the El Niño Southern Oscillation (ENSO) phenomenon would be an important factor influencing the growth patterns of organisms in both marine and terrestrial environments. To test this idea, we analyzed existing growth chronologies of the marine fish Lutjanus argentimaculatus, the coral Porites spp. and the tree Callitris columellaris and developed a new chronology for anot...
Normal development and disturbances caused by disease can be represented by changes in five biolo... more Normal development and disturbances caused by disease can be represented by changes in five biological parameters that characterize enamel formation. “Fossilized” in tooth structure, there is a detailed record of development traced by incremental growth lines. Enamel growth lines represent the configuration of deposited enamel at a succession of stages in its history of apposition. We hypothesize that we can use them to estimate enamel growth parameters and thus model crown development. Objectives: To measure the distances between incremental lines and use the obtained values to construct 2D and 3D models of daily enamel formation. To reveal the importance of each biological parameter in determining crown shape and quantify the extent to which regulatory mechanisms alter these parameters during human crown formation. Methods: Enamel incremental features include daily cross-striations (CS) and long-period (~7-day) striae of Retzius (SR), and surface perikymata. SEM was used to measur...
Climate change is having major effects on the world’s marine ecosystems, and it is predicted that... more Climate change is having major effects on the world’s marine ecosystems, and it is predicted that the severity of this problem will increase rapidly in coming years. For fishes, changes in temperature and current regimes may lead to shifts in distributions and changes in growth rates. Ultimately, this will have major implications for any fished species, since growth, productivity, and sustainable yield of populations are tightly linked. To understand how marine species might respond to climate change, we evaluated responses to past environmental variations by applying dendrochronology methods to otolith growth records from three long-lived (up to 70 years) fishes from the southwestern coast of Australia. The species set included a shallow water (<100 m) carnivore (western blue grouper- Achoerodus gouldii ), a deep water (>250 m) carnivore (hapuku- Polyprion oxygeneios ), and an omnivore (sea sweep- Scorpis aequipinnis ). We compared growth chronologies from these species to se...
The effects of climate change on predatory fishes in deep shelf areas are difficult to predict be... more The effects of climate change on predatory fishes in deep shelf areas are difficult to predict because complex processes may govern food availability and temperature at depth. We characterised the net impact of recent environmental changes on hapuku (Polyprion oxygeneios), an apex predator found in continental slope habitats (>200 m depth) by using dendrochronology techniques to develop a multi-decadal record of growth from otoliths. Fish were sampled off temperate south-western Australia, a region strongly influenced by the Leeuwin Current, a poleward-flowing, eastern boundary current. The common variance among individual growth records was relatively low (3.4%), but the otolith chronology was positively correlated (r = 0.61, p < 0.02) with sea level at Fremantle, a proxy for the strength of the Leeuwin Current. The Leeuwin Current influences the primary productivity of shelf ecosystems, with a strong current favouring growth in hapuku. Leeuwin Current strength is predicted t...
... E-mail The Corresponding Author , Adam N. Rountrey b , E-mail The Corresponding Author , Jan ... more ... E-mail The Corresponding Author , Adam N. Rountrey b , E-mail The Corresponding Author , Jan van Arkel a , E-mail The Corresponding Author , Joost F. Duivenvoorden ... Tree pollen is represented by Pinus, Picea, Betula, Alnus and low values of Carpinus, Corylus and Ulmus. ...
A well-preserved woolly mammoth calf found in northwest Siberia offers unique opportunities to in... more A well-preserved woolly mammoth calf found in northwest Siberia offers unique opportunities to investigate mammoth anatomy, behavior, life history and taphonomy. Analysis of the fluvial setting where the specimen was found suggests it was derived from eroding bluffs during ice-out flooding in June 2006. It then lay exposed on a point-bar surface until recovery the following May. AMS dating of
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