Cartesian coordinates in two-dimensional bone histology images

Palaeohistologists who work with well-preserved hominin cortical bone can examine two-dimensional (2D) histology images for quantitative parameters of secondary osteons and Haversian canals to reconstruct past bone remodelling. Standard techniques in this space include area measurements and counts of histology components recorded from an image. The ‘point-count’ technique involves counting all the items (e.g., secondary osteons, osteocyte lacunae) of interest per image area. The open access image analysis software ImageJ/ FIJI facilitates this technique in a user-friendly way. Raw data points are captured and can be saved in a spreadsheet. Aside from the total number of counts, the software also issues Cartesian (XY) coordinates locating each counted point. These XY coordinates are typically neglected within palaeohistological approaches due their assumed irrelevance to research questions of bone remodelling significance. We provide a short evaluation of XY coordinates captured by ImageJ/FIJI from 2D bone histology images, and a protocol for a simple calculation of XY distances that follow the path of point counting. We focus on osteocyte lacunae which serve as a proxy for osteoblast-osteocyte conversion in live bone by replicating the protocol on a bone sample from a Medieval English individual. We discuss the potential of XY coordinates for reconstructing the proximity of osteocyte lacunae and related bone remodelling activity through exchange of nutrients by neighbouring cells. We recommend palaeohistologists report XY coordinate data in their results to ensure better hominin palaeobiology characterisation

Twenty years online! A brief history of palaeontologia electronica

This issue marks the 20th anniversary of Palaeontologia Electronica (PE). From modest beginnings as a series of discussions on the PaleoNet listserver in 1996, it has become a well-recognised venue for publication and dissemination of research, techniques, and resources in palaeontology. The journal has many “firsts” to its credit, from the first species named on the internet, the first scientific journal with a plain-language abstract, and the first PDF “reprints” in palaeontology. Over 20 years PE also tried many new approaches that weren’t subsequently adopted by the broader scientific community, such as audio abstracts and animated journal covers. This anniversary issue gives us an opportunity to look back at the beginnings of the journal, its initial aims and aspirations, and to chronicle its evolution. It is as much a reflection of the changing nature of PE as it is a reminder of the larger scale changes that have taken place in the world of palaeontology, the internet, and our community over the past two decades

Taphonomic and zooarchaeological investigations at the middle Pleistocene site of Ti's al Ghadah, western Nefud Desert, Saudi Arabia

In recent years, the Arabian Peninsula has emerged as a key region for elucidating hominin and faunal evolution and dispersals between Africa and Eurasia. Central to this research is the middle Pleistocene site of Ti's al Ghadah (TAG) which has yielded a diverse and abundant fossil faunal assemblage and the earliest chronometrically dated evidence for hominins in this part of the world. Here, we present the first detailed taphonomic study of the large Unit 5 fossil assemblage from the site. We aim to assess which actor/s were responsible for the accumulation of the assemblage and evaluate evidence that might be consistent with the accumulation of fauna by hominins. We also describe, for the first time, fossils and lithic artefacts from stratigraphic horizons not previously considered, providing taphonomic insights into their accumulation. The taphonomic work shows that the Unit 5 faunal assemblage was accumulated by ambush predators, likely large felids and hominins, in a lake side environment, and that carcasses were subsequently scavenged by more durophagus carnivores such as hyenas and canids. Less can be reliably said regarding the newly described fossil assemblages given their poor preservation and significant wind abrasion, but large carnivores again appear to have played a role, and hominins probably played a role in the accumulation of at least one of these. This study provides the first detail insights into the interplay between hominins, carnivores, and herbivores in Arabia, and suggests that watering holes have been a focus on the Arabian landscape for resources since the middle Pleistocene

Extinction of eastern Sahul megafauna coincides with sustained environmental deterioration

Abstract: Explanations for the Upper Pleistocene extinction of megafauna from Sahul (Australia and New Guinea) remain unresolved. Extinction hypotheses have advanced climate or human-driven scenarios, in spite of over three quarters of Sahul lacking reliable biogeographic or chronologic data. Here we present new megafauna from north-eastern Australia that suffered extinction sometime after 40,100 (±1700) years ago. Megafauna fossils preserved alongside leaves, seeds, pollen and insects, indicate a sclerophyllous forest with heathy understorey that was home to aquatic and terrestrial carnivorous reptiles and megaherbivores, including the world’s largest kangaroo. Megafauna species diversity is greater compared to southern sites of similar age, which is contrary to expectations if extinctions followed proposed migration routes for people across Sahul. Our results do not support rapid or synchronous human-mediated continental-wide extinction, or the proposed timing of peak extinction events. Instead, megafauna extinctions coincide with regionally staggered spatio-temporal deterioration in hydroclimate coupled with sustained environmental change

Speleological and environmental history of Lida Ajer cave, western Sumatra

Some of the earliest evidence for the presence of modern humans in rainforests has come from the fossil deposits of Lida Ajer in Sumatra. Two human teeth from this cave were estimated to be 73–63 thousand years old, which is significantly older than some estimates of modern human migration out of Africa based on genetic data. The deposits were interpreted as being associated with a rainforest environment based largely on the presence of abundant orangutan fossils. As well as the main fossil-bearing chamber, fossil-bearing passages are present below a sinkhole, although the relationship between the different fossil deposits has only been tenuously established. Here, we provide significant new sedimentological, geochronological and palaeoecological data aimed at reconstructing the speleological and environmental history of the cave and the clastic and fossil deposits therein. Our data suggest that the Lida Ajer fossils were deposited during Marine Isotope Stage 4, with fossils from the lower passages older than the main fossil chamber. Our use of stable carbon and oxygen isotope analyses of mammalian tooth enamel demonstrates that early humans probably occupied a closed-canopy forest very similar to those present in the region today, although the fossil orangutans may have occupied a slightly different niche. This article is part of the theme issue ‘Tropical forests in the deep human past’

The origins and persistence of Homo floresiensis on Flores: biogeographical and ecological perspectives

The finding of archaeological evidence predating 1 Ma and a small hominin species (Homo floresiensis) on Flores, Indonesia, has stimulated much research on its origins and ancestry. Here we take a different approach and examine two key questions – 1) how did the ancestors of H. floresiensis reach Flores and 2) what are the prospects and difficulties of estimating the likelihood of hominin persistence for over 1 million years on a small island? With regard to the first question, on the basis of the biogeography we conclude that the mammalian, avian, and reptilian fauna on Flores arrived from a number of sources including Java, Sulawesi and Sahul. Many of the terrestrial taxa were able to float or swim (e.g. stegodons, giant tortoises and the Komodo dragon), while the rodents and hominins probably accidentally rafted from Sulawesi, following the prevailing currents. The precise route by which hominins arrived on Flores cannot at present be determined, although a route from South Asia through Indochina, Sulawesi and hence Flores is tentatively supported on the basis of zoogeography. With regards to the second question, we find the archaeological record equivocal. A basic energetics model shows that a greater number of small-bodied hominins could persist on Flores than larger-bodied hominins (whether H. floresiensis is a dwarfed species or a descendent of an early small-bodied ancestor is immaterial here), which may in part explain their apparent long-term success. Yet the frequent tsunamis and volcanic eruptions in the region would certainly have affected all the taxa on the island, and at least one turnover event is recorded, when Stegodon sondaari became extinct. The question of the likelihood of persistence may be unanswerable until we know much more about the biology of H. floresiensis

Homo sapiens in Arabia by 85,000 years ago.

Understanding the timing and character of the expansion of Homo sapiens out of Africa is critical for inferring the colonization and admixture processes that underpin global population history. It has been argued that dispersal out of Africa had an early phase, particularly ~130-90 thousand years ago (ka), that reached only the East Mediterranean Levant, and a later phase, ~60-50 ka, that extended across the diverse environments of Eurasia to Sahul. However, recent findings from East Asia and Sahul challenge this model. Here we show that H. sapiens was in the Arabian Peninsula before 85 ka. We describe the Al Wusta-1 (AW-1) intermediate phalanx from the site of Al Wusta in the Nefud desert, Saudi Arabia. AW-1 is the oldest directly dated fossil of our species outside Africa and the Levant. The palaeoenvironmental context of Al Wusta demonstrates that H. sapiens using Middle Palaeolithic stone tools dispersed into Arabia during a phase of increased precipitation driven by orbital forcing, in association with a primarily African fauna. A Bayesian model incorporating independent chronometric age estimates indicates a chronology for Al Wusta of ~95-86 ka, which we correlate with a humid episode in the later part of Marine Isotope Stage 5 known from various regional records. Al Wusta shows that early dispersals were more spatially and temporally extensive than previously thought. Early H. sapiens dispersals out of Africa were not limited to winter rainfall-fed Levantine Mediterranean woodlands immediately adjacent to Africa, but extended deep into the semi-arid grasslands of Arabia, facilitated by periods of enhanced monsoonal rainfall

Micro Methods for Megafauna: Novel Approaches to Late Quaternary Extinctions and Their Contributions to Faunal Conservation in the Anthropocene

Drivers of Late Quaternary megafaunal extinctions are relevant to modern conservation policy in a world of growing human population density, climate change, and faunal decline. Traditional debates tend toward global solutions, blaming either dramatic climate change or dispersals of Homo sapiens to new regions. Inherent limitations to archaeological and paleontological data sets often require reliance on scant, poorly resolved lines of evidence. However, recent developments in scientific technologies allow for more local, context-specific approaches. In the present article, we highlight how developments in five such methodologies (radiocarbon approaches, stable isotope analysis, ancient DNA, ancient proteomics, microscopy) have helped drive detailed analysis of specific megafaunal species, their particular ecological settings, and responses to new competitors or predators, climate change, and other external phenomena. The detailed case studies of faunal community composition, extinction chronologies, and demographic trends enabled by these methods examine megafaunal extinctions at scales appropriate for practical understanding of threats against particular species in their habitats today. </section

Understanding morphological variation in the extant koala as a framework for identification of species boundaries in extinct koalas (Phascolarctidae; Marsupialia)

We document morphological variation (both geographical and sexual) in the dentition of the extant koala, Phascolarctos cinereus, in order to facilitate discrimination of species boundaries in extinct phascolarctids. Considerable variation is evident in dental structures previously used to diagnose several phascolarctid fossil species. Consistent patterns of morphological variation are not evident between sexes or geographic regions, with variation as great between samples as within them. Metric variation is evident between the sexes in upper molar dimensions with Victorian (southern) males significantly larger than Victorian females, although this is not reflected in lower molar dimensions or in the Queensland (northern) sample. Male koalas from southern populations generally display significantly larger molars than their northern counterparts; however this trend is not evident in female upper molar dimensions. In both males and females, some, but not all, lower molar dimensions are larger in southern populations than northern. In light of these results, a systematic revision of species of Litokoala suggests L. dicktedfordi' is a junior synonym of L. kutjamarpensis, and the poorly known L. thurmerae is regarded to be a nomen dubium. Further, we describe a partial cranium of a new species of koala from Early Miocene sediments in the Riversleigh World Heritage Area, northern Australia. Litokoala dicksmithi sp. nov. is the fifth koala species recorded from the diverse rainforest assemblages of Riversleigh and the third species referred to the Oligo-Miocene genus Litokoala. Aspects of cranial morphology, including a shortened robust rostrum and broad, irregular nasal aperture, confirm placement of Litokoala as sister taxon to the modern genus Phascolarctos. Relatively large orbits and small body size suggest the possibility that L. dicksmithi was nocturnal, had enhanced visual acuity, and was a more agile arboreal species than the relatively sedentary extant koala

Direct dating of Pleistocene stegodon from Timor Island, East Nusa Tenggara

Stegodons are a commonly recovered extinct proboscidean (elephants and allies) from the Pleistocene record of Southeast Asian oceanic islands. Estimates on when stegodons arrived on individual islands and the timings of their extinctions are poorly constrained due to few reported direct geochronological analyses of their remains. Here we report on uranium-series dating of a stegodon tusk recovered from the Ainaro Gravels of Timor. The six dates obtained indicate the local presence of stegodons in Timor at or before 130 ka, significantly pre-dating the earliest evidence of humans on the island. On the basis of current data, we find no evidence for significant environmental changes or the presence of modern humans in the region during that time. Thus, we do not consider either of these factors to have contributed significantly to their extinction. In the absence of these, we propose that their extinction was possibly the result of long-term demographic and genetic declines associated with an isolated island population