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Antidorcas evolution and dietary adaptations in changing palaeoenvironments in southern Africa
Lauren SewellEmail: [email protected]; Twitter: @Laurensewell2; Website: http:lauren915.wix.com/lcsewellresearchSupervised by Dr Sally Reynolds, Professor Matthew Bennett and Dr JohnStewart, Bournemouth University, United Kingdom
BACKGROUND INFORMATION
ACKNOWLEDGEMENTS:Supervisory team: Dr Sally Reynolds, Professor Matthew Bennett, Dr John Stewart, funded by Bournemouth University PhD studentship.With special thanks to PalAss for awarding a small travel grant to allow representation at this conference. Collaborators: Dr Philip Hopley, Dr Gildas MerceronInstitutions: Natural History Museum, London. National Museums Scotland, Edinburgh. Ditsong Museum, Pretoria. The University of the Witwatersrand, Johannesburg. Institutde Paléoprimatologie et Paléontologie humaine: Evolution et Paleoénvironnements- iPHEP CNRS UMR 7262- Université de Poitiers, France.
METHODS RESULTS DISCUSSION
FURTHER WORK
Morphological Measurements Measurements are used alongside visual dentallandmark assessments to identify remains tospecies and locate where species changesoccur. Dentition shows what the animal iscapable of eating but cannot be used as adietary proxy to prove what they did consume.
Geometric morphometric analysis of selectedAntidorcas australis/ marsupialis fossils tounderstand their taxonomic assignment.
Phytolith analysis of Antidorcas dentalremains from all Member of interest .
Increase sample sizes in all categories. Isotopic analysis (carbon and oxygen)MATERIALS:
REFERENCES:Permanent dental molars.Fossil materials: Antidorcas bondi, Antidorcas recki,Antidorcas australis and Antidorcas marsupialis.Supplementary species to provide grazing(Damaliscus dorcas/pygargus) and browsing(Tragelaphus strepsiceros) signals.Collections: Sterkfontein Member 4 and 5 (East,Stw53 Infill and West) Swartkrans Member 1(hanging remnant and lower bank), 2 and 3, Cradleof Humankind, Gauteng Province, South Africa.Modern materials: Antidorcas marsupialis to providelevels of anticipated intra-specific variation,Damaliscus pygargus (blesbok) to provide a knowngrazing signal and Tragelaphus strepsiceros (greaterkudu) to provide a known browsing signal.
Phytoliths are plant remains that can be preserved indental calculus. Bovids from Sterkfontein and Swartkranshave not been examined for phytoliths previously. Dentalcalculus will be scraped from fossilised dentition to beanalysed for the presence of phytoliths. Where presentthey will provide conclusive evidence of vegetation typepresent and consumed in that individual animal’slifetime.
Phytolith Analysis
Stable Isotope Analysis (Carbon and Oxygen)Vegetation consumed during dental enamel formation ispreserved and visible through isotopic analysis. Plants fixcarbon according to vegetation type, with woodlandvegetation being more depleted in carbon than tropicalgrasses. Higher carbon values are therefore indicative of agreater grazing component in the diets of herbivores.
Dental Microwear Textural Analysis (DMTA)Microscopic wear imprinted on the dental enamel facets showcase the last few meals eaten by that individual. Wear patterns are unique to the type of vegetation and the mastication process of the species consuming it. Values are produced for direction and shape of wear (Ungar et al. 2007)
Mesowear
The macro-level wear on permanent molars isassessed according to the occlusal relief of thetooth and the cusp shape.Protocol set out byFortelius and Solounias (2000).
Brink, J.S. and Lee-Thorp, J.A., 1992 The feeding niche of an extinct springbok, Antidorcas bondi(Antelopini, Bovidae), and its palaeoenvironmental meaning. South African Journal of Science. 88, 227-229.
DeMenocal, P.B., 2004. Arican climate change and faunal evolution in the Pliocene-Pleistocene. Earth andPlanetary Science Letters 220 (1), 3-24.
Fortelius, M. & Solounias, N., 2000. Functional Characterization of Ungulate Molars Using the Abrasion-Attrition Wear Gradient: A new method for reconstructing Paleodiets. American Museum Noviates 3301, 1-36.
Gentry, A.W., 1978. Bovidae. IN: Maglio, V.J. and Cooke, H.B.S. (Eds.) Evolution of African Mammals.Cambridge University Press: London.
Gentry, A.W., 1992. The subfamilies and tribes of the family Bovidae. Mammal Review 22 (1), 1-32.Hopley, P.J., Marshall, J.D., Weedon, G.P., Latham, A.G., Herries, A.I.R. and Kuykendall, K.L., 2007. Orbital
forcing and the spread of C4 grasses in the late Neogene: stable isotope evidence from South Africanspeleothems. Journal of Human Evolution 53 (5) 620-634.
Lee-Thorp, J.A., Sponheimer, M., & Luyt, J., 2007 Tracking changing environments using stable carbonisotopes in fossil tooth enamel: an example from the South African hominin sites. Journal of Human Evolution53, 595-601.
Luyt, J., 2001. Revisiting the palaeoenvironments of the South African hominid-bearing Plio Pleistocenesites: new isotopic evidence from Sterkfontein. MSc Thesis.
Potts, R., 1998. Environmental hypotheses of hominin evolution. American Journal of PhysicalAnthropology 107 (S27), 93-136.
Ungar, P.S., Merceron, G. and Scott, R.S., 2007. Dental microwear texture analysis of Varswater bovids andearly Pliocene paleoenvironments of Langebaanweg, Western Cape Province, South Africa. Journal ofMammalian Evolution, 14(3), 163-181.
Vrba, E.S., 1973. Two species of Antidorcas Sundevall at Swartkrans (Mammalia: Bovidae). Annals of theTransvaal Museum, 28(15), 287-352.
Vrba, E.S., 1974. Chronological and ecological implications of the fossil Bovidae at the Sterkfonteinaustralopithecine site. Nature. 250, 19-23.
Vrba, E. S., 1985. Environment and evolution: alternative causes of the temporal distribution ofevolutionary events. South African Journal of Science. 81, 229-236.
Springbok (genus Antidorcas) was an abundant, herbivorous antelope present in many hominin-bearing deposits in Africa. Traditional studies assert that there areno less than 4 species present throughout the temporal period of 2.8-0.8 Ma in southern Africa. Antidorcas bondi was thought to be a grazing species, part of agrazing succession, feeding on the newest shoots (Brink and Lee-Thorp 1992). The ancestral Antidorcas recki was believed to have been a predominantly browsingspecies (Luyt 2001). The extant, Antidorcas marsupialis is believed to have been a mixed feeder throughout, adapting its diet to the changing palaeovegetationconditions. The potential fourth species, Antidorcas australis, has relatively little known about its palaeoecology and its taxonomic assignment as a distinct speciesfrom Antidorcas marsupialis is debated (Vrba 1974, Gentry 1978,1992), there is the suggestion that it was a transitional form between A. recki and A. marsupialis.
Species identifications are made on visual assessment (Vrba 1973) and morphological measurements. A multi-method analysis of diet is conducted onthese Antidorcas species to understand the prevailing vegetation types present in the geographic and temporal area. The link between faunal evolution and climaticchanges is a long-standing one (e.g. Vrba 1985; Potts 1998; De Menocal 2004, Hopley et al. 2007) but remains to be resolved. The predominant pattern is one ofincreasing grasslands with marked transitions at 2.5 Ma and 1.7 Ma.
Preliminary analysis supports the idea ofincreased grassland, particularly afterc.1.7Ma (Lee-Thorp et al. 2007).
No pulses of faunal turnover are yetapparent in the dataset (dataset sample sizeenlargement is pending).
Antidorcas sp. (combined fossilspecimens of Antidorcas australis and A.marsupialis) exhibit greater variation in allmethods than that of modern Antidorcasmarsupialis. Hinting that A. australis warrantsseparate species status.
Antidorcas bondi is consistentlyshown to be a grazing species through allmethods, supporting Brink and Lee-Thorp(1992)’s finding from other sites in SouthAfrica.
Antidorcas recki is typically shownto be a browsing species through allmethods, supporting Luyt (2001).
Marked change is noted betweenSwartkrans Member 2 and 3 in increasedtooth width for Antidorcas marsupialis andAntidorcas bondi, suggesting considerableinfluencing forces, presumably these aredietary driven adaptations and thereforeindicative of changing palaeoenvironments.
Occlusal length of permanent dental molars remainsrelatively consistent through time, whereas bucco-lingualwidth increases from c.1.7 Ma in at least 2 Antidorcasspecies (A. bondi and A. marsupialis).
Antidorcas bondi consistently falls into the lower reliefcategories for mesowear, as would be typical of a grazingspecies. Fossil Antidorcas marsupialis/ australis showsgreater variation than modern A. marsupialis, withstatistical analyses showing this is not due to sexualdimorphism. Thereby hinting at the presence of 2populations with differing diets, probably of separatespecies.
Fossil A. marsupialis displays a greater browsing signalthan modern A. marsupialis. Surface complexity indicatessignificantly different diets for modern Antidorcas andthose in Sterkfontein Member 4, Member 5 (west) andSwartkrans Member 3. Suggestive of a greaterbrowse(trees and shrubs) component in the diet than inmodern samples.
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