Propuesta

1.6.1 Scope of the study - limitations

1.6.1.1 Access to specimens

In order to compare teeth from several presumed species of African Plio-Pleistocene hominin fossil teeth, uniformity of “inputs” to the analyses was paramount: occlusal images of specimens of lower first molars to a similar scale and format were required. To ensure such, original data was personally collected using identical photographic protocols on each occasion from several museums and collections in South Africa, Tanzania and Kenya. Additional data were collected for extant species from Belgium and South Africa. Access to specimens was limited in certain cases due to limitations imposed by permits (Nairobi), availability of personnel to allow access (Arusha) and due to limited numbers of usable, well-identified specimens in the collection itself (Nairobi, Dar es Salaam; Tervuren: Pan paniscus, notably). Numerous specimens were photographed, but even with digital enhancement, many were too damaged to include in the analyses.

1.6.1.2 Inclusion of original photographs of all holotypes (or proxies) –

selection of M1 as common molar to all holotypes

A large part of the study involved the development of a landmark placement model for the shape analyses conducted on the teeth. Since all six molar types in the upper and lower dental arcades would require potentially different landmark placement sites for their analysis, thus requiring separate analyses for each tooth type, the most prevalent type of molar tooth was chosen for the study. Lower first molars were not only the

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most common molar tooth found present in the specimens photographed around the world, but all the mandibles representing holotype specimens from fossil species that were able to be included for study (all from original photographs) contained at least one lower first molar. (See 3.1 below for additional discussion on the rationale for limiting the study to lower first molars).

1.6.1.3 Limitations of mandibular molars with respect to cranial

comparisons

It is recognised that a selected sample of lower first molars from the African Plio- Pleistocene fossil record will not provide enough information to be able to test hypotheses unequivocally, regarding inter- and intra-species variability. However, since holotypes or proxies for holotypes for all seven fossil species included in the study were able to be photographed from the original specimens, the remaining specimens in the study can certainly be compared to the holotype and to other specimens in the same species groups, so that in certain cases, anomalies (specimens that fail to group with the holotype or with others in the species group that do group in the same general area as the holotype) can be identified and highlighted for further examination. It is not within the scope of this study to include equivalent extant and fossil cranial metrics for

comparative purposes. In the case of the extant species, ranges of shape and size variability in the crania of certain species do not necessarily predict what the range of shape and size variability of lower first molars would be for that same species. For the fossil analyses, many of the specimens used for this study consist only of mandibular remains, with no full cranial data available for comparison with these specific

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1.6.1.4 Selection of a limited array of analytical methods to confirm results

Rather than conduct one single type of analysis on the specimens included in the study, it was decided to select a number of analytical techniques in order to test as

independently as possible the robustness of the results: species groupings and overlaps that might become apparent; anomalous specimens, failing to group with their

presumed species. It is stressed that this study is exploratory in nature, with small sample sizes. Due to this limitation and to considerations of length of the dissertation, each analysis tended to be carried out at a fairly basic level and additional in-depth statistical tests were not able to be considered in each instance. However, despite these limitations, the data were sufficient to confirm basic patterns of variability within extant species, and from these, the fossil sample could be assessed for species variability and potential anomalies.

1.6.1.5 Exploratory nature of the study, leading to future research

This study may be viewed as being exploratory in nature. Future research can be conducted on other molar types (e.g. maxillary molars), using other analytical techniques again (such as Euclidian distance matrix-based analyses) to compare the results obtained via the methodologies applied here. In doing so, additional specimens of extant species’ molars and those of the African Plio-Pleistocene hominin fossil record (including OH 5, the holotype for Paranthropus boisei, which has maxillary but not mandibular dentition) can be included in the study to reinforce the conclusions made. In future studies, and once sample sizes of both extant and fossil specimens can be increased, additional statistical tests should be carried out on each of the analyses conducted to add robustness to the results.

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1.6.2 Primary aims of the study, approaches used to achieve these aims

The primary aims of the study as discussed in 1.2 above together with some of the specific approaches used to address these are summarised in Table 1.1:

Table 1.1 Summary of primary aims, with approaches applied to achieve the

aims.

Aim Solution

Identification of diagnostic features of lower first

molars Comparative study conducted on fossil lower first molars based on personal observation and on

literature review Recognition of the most significant diagnostic

features of lower first molars quantitatively based on landmark placements so that each feature is correctly emphasised for purposes of the analysis

Consideration of different models of landmark placements to emphasise each diagnostic trait. Testing of the final model chosen to distinguish between known biological species (extant species); application of the same model and the same analyses to fossil molars; comparison of patterns of results between extant species and fossil species. Further testing of the model using different analytical methodologies to confirm results from the other methodologies. Grouping of species numerically in terms of

variability within and between species Landmark model to be optimised by applying “shape only” and “shape and size” analyses to

provide the best resolution between species groupings; statistical probabilistic methods to be applied to determine probabilities of

conspecificity. Application of additional morphometric

techniques to test whether there is harmony between their results

Apply not one but several analytical techniques and compare the results. Repeated confirmations of trends and of anomalies would add robustness to the results.

Assessment of any identifiable trends over time and/or geographical distance in hominin tooth morphology

Analyse shape data and size-shape data to see if trends appear over time and over geographical distance.

Detection of sexual dimorphism in the molars of extant species and comparison of these patterns in the molars of fossil species

Analyse linear and size-shape data to see if similar trends appear in both extant species and fossil species.

Correctness of the classifications of certain fossil molars from specimens currently attributed to particular species

Within the limitations of the particular specimens included in the study, check for anomalous specimens that fail repeatedly to group with their presumed species group, no matter which methodology is applied to the data Reasonability of ranges of variability within

taxonomic groupings of hominin fossils Acknowledging that this study analyses only lower first molars, compare the ranges of

variability observed within and between extant species to inform an analysis of the expected ranges of variability seen within and between the presumed species groups from the African Plio- Pleistocene period

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1.6.3 Working hypotheses

The working hypotheses to be tested were as follows:

- HSQ: “Status Quo Hypothesis”: all African Plio-Pleistocene first molar specimens discovered to date, including holotypes, are correctly classified into their current taxa; - H0: The observed degree of variability in first molar shape and size within extant species is so narrow in range that when the same parameters are applied to samples of African Plio-Pleistocene fossil hominin dental specimens discovered to date, the latter should be recognisable as discrete species;

- H1: At least some of the African Plio-Pleistocene specimens currently attributed to certain species of Homo, Paranthropus or Australopithecus may have been misclassified.; - H2: The observed degree of variability in first molar shape and size within extant species is so wide in range that when the same parameters are applied to specimens attributed to currently-accepted species groups in the African Plio-Pleistocene period, this would result in all species of that period being subsumed into one species;

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CHAPTER TWO – BACKGROUND TO THE MORPHOMETRIC STUDY: DIAGNOSTIC MORPHOLOGY OF SURFACE ENAMEL FEATURES OF LOWER FIRST MOLARS OF AFRICAN PLIO-PLEISTOCENE HOMININ SPECIMENS