Morphological evaluation of genetic evidence for a Pleistocene extirpation of eastern African impala

Palaeontology typically relies on fossil studies, in particular morphological differences, to reconstruct and interpret patterns of vertebrate evolution. However, genetic studies of population histories of extant species provide data about past population events (e.g. local extinctions, recolonisations) which are equally relevant to palaeontological questions. This study used morphological traits to evaluate a hypothesis based on genetic evidence that southern African impala (Aepyceros melampus) are the founder population for all other living African impala populations, after an eastern African extirpation event dating to around 200 000 years ago. Measurements of three horn metrics and the presence or absence of a particular dental trait were compared across four regional impala samples. Eastern African impala possess a unique combination of larger horns and a signiicantly higher occurrence of entostyles when compared to other impala populations. These traits are likely to have characterised a small group of founding impala which recolonised this region. This pattern appears consistent with the genetic evidence that a subset of the southern African impala gave rise to the eastern African populations. Other species with complex population histories, such as wildebeest, eland, topi and hartebeest may also therefore be expected to express variation in certain morphological traits in the fossil record because of similar patterns of recolonisations. The process of local extinction and subsequent repopulation over shorter timescales may pass unnoticed in the fossil record, and lineages may appear uninterrupted. Instead, greater morphological variation within a species may be observed, which may be misinterpreted as reflecting a speciation event, or ecophenotypic variation. Combining data from genetic studies and palaeontology may provide further clues as to how faunal dispersals within Africa shaped the morphological variation in the fossil record, and how to best interpret such differences

Nyctereutes terblanchei: The raccoon dog that never was

Fossils of the raccoon dog (genus Nyctereutes) are particularly rare in the African PlioPleistocene record, whilst the sole living representative, Nyctereutes procyonoides, is found in eastern Asia and parts of Europe. In southern Africa, only one fossil species of raccoon dog has been identiied – Nyctereutes terblanchei. N. terblanchei is recognised from a handful of Plio-Pleistocene sites in South Africa: Kromdraai, Kromdraai–Coopers and Sterkfontein in Gauteng, as well as Elandsfontein in the Western Cape Province. The validity of this species identiication was questioned on the basis of the rarity of southern African fossils assigned to Nyctereutes, that is, fewer than 10 specimens have been identified as Nyctereutes. This study examined this fossil sample of the raccoon dog from the Gauteng sites and compared dental and cranial metrics of the fossil with samples of modern canids and published data. Morphological traits used to distinguish Nyctereutes, such as the pronounced subangular lobe on the mandible and the relatively large size of the lower molars, were observed to be variable in all samples. Analysis showed that the size of the dentition of the southern African fossil samples was larger than that of living raccoon dogs, but fell well within the range of that of African jackals. These results suggest that fossil Nyctereutes cannot be distinguished from other canid species based on metric data alone, and may only be diagnosable using combinations of non-metric traits of the dentition and skull. However, based on the degree of morphological variability of the traits used to diagnose Nyctereutes, as well as the rarity of this genus in the African fossil record, these fossils are more likely to belong to a species of jackal or fox

Temporal variation in Plio- Pleistocene Antidorcas (Mammalia: Bovidae) horncores: the case from Bolt's Farm and why size matters

Morphological differences in samples of fossil (Antidorcas recki) and modern (A. marsupialis) springbok horncores suggest that the ancestral species shows less sexual dimorphism than is observed in the horn dimensions of modern springbok. This pattern may prove useful when evaluating fossil springbok specimens in South African Plio-Pleistocene faunal assemblages. Undated Antidorcas craniodental specimens from Pit 3, Bolt's Farm (Cradle of Humankind, Gauteng, South Africa) have previously been referred to A. recki by Cooke.l However, comparison with numerous other springbok samples suggests that these specimens are more likely to represent male and female fossils of the extant species, A. marsupialis. This re-evaluation adds weight to the fossil evidence implying that the modern form of springbok is a southern African endemic species which first appeared around 1.5-1.0 million years ago in Swartkrans Member 1. Bolt's Farm Pit 3 fossils are inferred to be of a similar age

Sterkfontein at 75: review of paleoenvironments, fauna, dating and archaeology from the hominin site of Sterkfontein (Gauteng Province, South Africa).

Seventy-five years after Robert Broom’s discovery of the first adult Australopithecus in 1936, the Sterkfontein Caves (Gauteng Province, South Africa) remains one of the richest and most informative fossil hominin sites in the world. The deposits record hominin and African mammal evolution from roughly 2.6 million years (Ma) until the Upper Pleistocene. Earlier excavation efforts focused on the Member 4 australopithecine-bearing breccia and the Member 5 stone tool-bearing breccias of Oldowan and Early Acheulean age. Ronald J. Clarke’s 1997 programme of understanding the cave deposits as a whole led to the discovery of the near-complete StW 573 Australopithecus skeleton in the Member 2 deposit of the Silberberg Grotto, and the exploration of lesser known deposits such as the Jacovec Cavern, Name Chamber and the Lincoln Cave. Our aim is to produce a cogent synthesis of the environments, palaeodietary information, fauna and stone artefacts as recorded in the Sterkfontein sequence. We begin with an overview of the site and early accounts of the interpretations of the site-formation processes, after which we discuss each Member in turn and summarize the various types of evidence published so far. Finally, we review the most pertinent debates about the site, including the ages of Sterkfontein Member 2 and 4, and the types of habitats represented at the site through time

Variability in Plio-Pleistocene climates, habitats, and ungulate biomass in southern Africa

Vrba, and deMenocal and Bloemendal have emphasised the importance of climatic change, particularly temperature, in the context of evolution on the African continent within the past 5 million years. There is no doubt that long-term changes in climate would have affected African habitats, which in turn would have affected the distribution and abundance of populations of various mammalian taxa, including ungulates and hominids. In this study we explore relationships between oxygen isotope ratios (as determined from Shackleton's analysis of foraminifera from deep-sea cores), and estimates of ungulate biomass as determined from faunal assemblages from Plio-Pleistocene sites in southern Africa, using an approach outlined previously. We go further to assess temporal variability in ungulate biomass in terms of changes in habitat, gene pools and hominid evolutio

The role of landscapes in shaping hominin habitats in Africa

Here I briefly review palaeoenvironmental evidence from sites repeatedly used by hominins in eastern and southern Africa, such as Sterkfontein (Cradle of Humankind, Gauteng, South Africa). Common ‘mosaic’ habitat reconstructions involve the presence of a lake or river setting, with a combination of forest or woodland with savannah grasslands in close spatial proximity. The Tectonic Landscape Model [Bailey et al. pp. 257-280 & Reynolds, et al., pp. 281-298 (JHE 60, 2011)], is a new hominin habitat model which explains why certain sites appeared to have been repeatedly used by our ancestors over millions of years. Specific geomorphological processes, such as tectonic faulting, would have created complex topography and thereby encouraged heterogeneous habitats to form, and sustained such features through time. The Plio-Pleistocene is characterised by several key climatic transitions that would have presented unique challenges for hominins and other fauna. Therefore, a more complete appreciation of how geomorphological processes affect landscapes, surface water and vegetation is critical to the characterisation of the hominin niche and also of the strategies employed by our ancestors to adapt to past climatic changes. Furthermore, the use of complex topography by hominins may explain aspects of their postcranial anatomy, diets and possible routes that they may have used to disperse to other regions. Keywords: geomorphology, endemism, speciation, human evolution, Africa, Plio-Pleistocene

Footprints and human evolution: Homeostasis in foot function?

Human, and hominin tracks, occur infrequently within the geological record as rare acts of sedimentary preservation. They have the potential, however, to reveal important information about the locomotion of our ancestors, especially when the tracks pertain to different hominin species. The number of known track sites is small and in making inter-species comparisons, one has to work with small track populations that are often from different depositional settings, thereby complicating our interpretations of them. Here we review several key track sites of palaeoanthropological significance across one of the most important evolutionary transitions (Australopithecus to Homo) which involved the development of anatomy and physiology better-suited to endurance running and walking. The sites include the oldest known hominin track site at Laetoli (3.66 Ma; Tanzania) and those at Ileret (1.5 Ma; Kenya). Tracks from both sites are compared with modern tracks made by habitually unshod individuals using a whole-foot analysis. We conclude that, contrary to some authors, foot function has remained relatively unchanged, perhaps experiencing evolutionary homeostasis, for the last 3.66 Ma. These data suggest that the evolutionary development of modern biomechanical locomotion pre-dates the earliest human tracks and also the transition from the genus Australopithecus to Homo

Environmental hydro-refugia demonstrated by vegetation vigour in the Okavango Delta, Botswana

Climate shifts at decadal scales can have environmental consequences, and therefore, identifying areas that act as environmental refugia is valuable in understanding future climate variability. Here we illustrate how, given appropriate geohydrology, a rift basin and its catchment can buffer vegetation response to climate signals on decadal time-scales, therefore exerting strong local environmental control. We use time-series data derived from Normalised Difference Vegetation Index (NDVI) residuals that record vegetation vigour, extracted from a decadal span of MODIS images, to demonstrate hydrogeological buffering. While this has been described previously it has never been demonstrated via remote sensing and results in relative stability in vegetation vigour inside the delta, compared to that outside. As such the Delta acts as a regional hydro-refugium. This provides insight, not only to the potential impact of future climate in the region, but also demonstrates why similar basins are attractive to fauna, including our ancestors, in regions like eastern Africa. Although vertebrate evolution operates on time scales longer than decades, the sensitivity of rift wetlands to climate change has been stressed by some authors, and this work demonstrates another example of the unique properties that such basins can afford, given the right hydrological conditions

Modelling the role of groundwater hydro-refugia in East African hominin evolution and dispersal.

Water is a fundamental resource, yet its spatiotemporal availability in East Africa is poorly understood. This is the area where most hominin first occurrences are located, and consequently the potential role of water in hominin evolution and dispersal remains unresolved. Here, we show that hundreds of springs currently distributed across East Africa could function as persistent groundwater hydro-refugia through orbital-scale climate cycles. Groundwater buffers climate variability according to spatially variable groundwater response times determined by geology and topography. Using an agent-based model, grounded on the present day landscape, we show that groundwater availability would have been critical to supporting isolated networks of hydro-refugia during dry periods when potable surface water was scarce. This may have facilitated unexpected variations in isolation and dispersal of hominin populations in the past. Our results therefore provide a new environmental framework in which to understand how patterns of taxonomic diversity in hominins may have developed

Soft-sediment deformation below mammoth tracks at White Sands National Monument (New Mexico) with implications for biomechanical inferences from tracks

Implicit in any biomechanical analysis of tracks (footprints), whatever the animal, is the assumption that depth distribution within the track reflects the applied plantar pressure in some way. Here we describe sub-track deformation structures produced by Proboscidea (probably Mammuthus columbi) at White Sands National Monument (WHSA) in New Mexico. Patterns of sub-surface deformation are consistent with the plantar pressure data for modern Proboscidea, but do not reflect track morphology. Our work cautions against overinterpreting track topology of any large animal, including extinct animals such as sauropods, in terms of their biomechanics unless the subsurface stratigraphy and associated variation in shear strength is known