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Home , Australopithecine, Australopithecus, Paranthropus, Paranthropus robustus

Totem: The University of Western Ontario Journal of

Volume 13 | Issue 1 Article 11

6-21-2011 The Robust : Evidence for the Amy Rotman The University of Western Ontario

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Recommended Citation Rotman, Amy (2005) "The Robust Australopithecines: Evidence for the genus Paranthropus," Totem: The University of Western Ontario Journal of Anthropology: Vol. 13: Iss. 1, Article 11. Available at: http://ir.lib.uwo.ca/totem/vol13/iss1/11

This Article is brought to you for free and open access by Scholarship@Western. It has been accepted for inclusion in Totem: The nivU ersity of Western Ontario Journal of Anthropology by an authorized administrator of Scholarship@Western. For more information, please contact [email protected]. The Robust Australopithecines: Evidence for the genus Paranthropus

Keywords robust australopithecines, Paranthropus, morphological, trait analysis

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This article is available in Totem: The nivU ersity of Western Ontario Journal of Anthropology: http://ir.lib.uwo.ca/totem/vol13/iss1/ 11 Rotman: The Robust Australopithecines: Evidence for the genus Paranthropus

with the KNM- WT 17000 as the initial specimen through whom the Paranthropines evolved. Through a trait analysis, a paradigm analysis, and an ecological and taxonomic discussion I will be able to better interpret the fossil record of the robust australopithecines. Through the examination of the concepts of traits, paradigm, and ecology and , it will be argued that the differences between the robust australopithecines and the gracile australopithecines is great enough to warrant the use of the genus name Paranthropus in dealing with the robust , specifying that they are in fact a separate from the Australopithecines and later .

Trait Analysis The chronology of early phylogeny is wrought with differing interpretations as to the exact sequence of evolution. Of great concern is the determination of which species is considered the last common ancestor of the Paranthropus lineage and of the Homo lineage, if we do concede to the generic splitting of the two forms. The position taken in this paper is that the Paranthropus and Homo diverged approximately 3-2.5 million (MY) ago from a common ancestor of afarensis (Chamberlain 1991:141). The Robust Australopithecines: A trait analysis is required in order to Evidence for the genus Paranthropus gain an understanding of general morphological differences and similarities among the early hominids. Broadly speaking, the cranial and dental traits of the Paranthropines suggest specializations that relate to heavy chewing- Of great debate among anthropologists most likely of coarse, tough, fibrous plant foods over the past few decades is the identity of the (Foley 1995:84). The earliest evidence of the "robust" australopithecines and if this group divergence into the Paranthropine lineage was warrants a separate genus name, Paranthropus, marked by the appearance of the fossil KNM- to distinguish them from the "gracile" WT 17000, otherwise known at the "Black australopithecines. The first robust Skull." Found in deposits in West Turkana, to be discovered was found by Kenya, KNM- WT 17000 (from here on named in 1949 in and was Paranthropus aethiopicus), was initially named . Since then assigned to the species Paranthropus boisei, however, debate has raged on concerning the based on several of its robust features, such as validity of the species name Paranthropus. A the extremely large size of the palate and the variety of models have been presented to account teeth (namely the molars and ), the for various interpretations of the fossil materials build of the infraorbital and nasal areas, and its of the robust australopithecines. This paper will dish-shaped midface with forwardly positioned focus on two polar extreme views of taxonomy: zygomatic bones (Klein 1999:213). It will later one that consolidates all hominid species into a be demonstrated that this initial taxonomic single lineage, and another that allows for the naming is misleading, and therefore the splitting of hominid branches into two distinct taxonomic name Paranthropus aethiopicus is genera. A critical examination will be used for this specimen. It is widely undertaken in this paper, dealing specifically acknowledged that amongst the robust group of

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early hominids, robusticity of traits increased WT 17000 (that were previously believed to through chronological history. Therefore, it is specifically tie it to Paranthropus boisei) were noted that Paranthropus robustus and actually chronologically primitive traits that are Paranthropus boisei were markedly more robust shared with the last common ancestor, than the earlier Australopithecines in many of Australopithecus afarensis. As well, thirteen out their features. Whether these two specimens of sixteen derived characteristics that were were simply geographic variants of one another common between KNM-WT 17000 and or they reflected a greater taxonomic distinction Paranthropus boisei were revealed to be present is currently under debate. However, these in other Australopithecine (Kimbel et at. contemporaneous species did share an 1988:260). Based on these re-analyses, Kimbel extraordinary number of characteristics. It is in et al. (1988) show that there were only three their masticatory apparatus where the description characters used in Walker's analysis which 'robust' applies. While their and canines directly link KNM- WT 17000 with were relatively small, their teeth were Paranthropus boisei. With this in , I can greatly expanded -- as noted in the fact that their argue that the fossil KNM- WT 17000 is deciduous and permanent premolars were almost morphologically dissimilar to Paranthropus fully molarized (Klein 1999:215). As compared boisei and therefore, it must be understood as a to the more gracile australopithecines, whose separate species, one that was intermediate teeth do not show such extreme changes in size, between the early australopithecines and the the robusts' teeth are said to be indicative of a later, more robust paranthropines. Kimbel et more specialized dietary adaptation. at.'s (1988) re-analysis of the character traits of In terms of skull morphology, the robust KNM- WT 17000 deals with thirty-two traits. Of group of early hominids is in direct contrast with these, twelve are primitive to Australopithecus both the earlier, gracile australopithecines, as afarensis, six are derived traits shown to be well as with the larger-brained early hominids, shared with all later hominids (including beginning with , who existed Australopithecus africanus, Paranthropus contemporaneously with them. The robust robustus, Paranthropus boisei, and to a small species' dish-shaped faces were characterized by extent early Homo), an additional twelve were very powerfully built zygomatic arches which derived and shared with only the paranthropines, arise far forward on the (Klein and only two were shown to be derived and 1999:215). Their were very thick and shared exclusively with Paranthropus boisei deep, with tall and broad ascending rami which (Kimbel et al. 1988:261). arise much more laterally and inferiorly than In the above re-analysis, the those found in Australopithecus afarensis (Klein characteristics analyzed demonstrated the 1999:215). These traits, along with their affiliation of KNM -WT 17000 to the other early anteriorly placed sagittal crests, reflect a much hominids. The primitive traits demonstrated greater emphasis on the temporalis muscle and KNM-WT 17000's derivation from the earlier other bones, which suggests an increased Australopithecus afarensis. These features also specialization in mastication. Homo specimens ruled out Australopithecus africanus as the last are seen to be lacking in the dental common ancestor for the Paranthropines and the specializations noted in the paranthropines, as early Homos. The primitive characters shared by they have much smaller and more parabolic jaws. KNM- WT 17000 and Australopithecus afarensis They have more even sized (generalized) teeth were not demonstrated in the Australopithecus and much longer and larger brain cases which africanus fossils, therefore to include them at the stand at around 600-700 cc (Foley 1995:84). In beginning of the lineage of the Paranthropines addition to this, Homo faces are small and much would imply an extraordinary amount of less prognathous than those found in the character reversals. The remaining derived paranthropines (Foley 1995:84). features shared in common with KNM-WT When Walker initially assigned KNM- 17000 and the Paranthropines implies that they WT 17000 to Paranthropus boisei, the forty are all part of the same phylogeny, evolving from features used to show their close affmity actually Australopithecus afarensis (in whom these provide us with misleading interpretations. In a features were not demonstrated). Those derived more recent analysis of the same material traits also exhibited in Australopithecus conducted by Kimbel, White and Johanson africanus are understood to be parallelisms. (1988), it was shown that sixteen of the forty A phylogenetic hypothesis to best character states that were displayed by KNM- demonstrate the affmity of these early hominids,

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taking into account the suite of character traits controversies, all data exists within a theoretical previously discussed, is that Australopithecus framework. Wolpoff explained that the fIeld of africanus is the exclusive ancestor of Homo. is almost subjective in the There are a number of derived characteristics sense that "there are neither refutation nor used to confIrm the validity of this hypothesis, proofs ... only probability statements for which including an overall reduction in pneumatization any and all observations are appropriate" of the mastoid process of the , an (Wolpoff 1976:95). In this sense, Wolpoff increase in steepness of the , and a conceded that the field of anthropology does rely mean increase in the relative length of the upper upon differing paradigms and that each occipital (Kimbel et al. 1988:263). This anthropologist's paradigm will bring a new hypothesis requires the least amount of interpretation on the old material. parallelisms and is therefore the most A difference in opinions on trait list bias parsimonious in examining early hominid is shown in the papers written by Skelton and phylogeny. Therefore, through the analysis of McHenry (1998) and in Strait and Grine (1998), character traits perfonned by Kimbel et al. which discussed early hominid phylogeny. (1988), a clear tree of phylogenetic relationships Skelton and McHenry criticize Strait and Grine's can be drawn to demonstrate that KNM- WT grouping of Paranthropus aethiopicus with 17000 (Paranthropus aethiopicus) and Paranthropus robustus and boisei to create a Australopithecus africanus diverged from monophyletic clade. Skelton and McHenry's Australopithecus afarensis several million years (1998: 109) analysis placed Paranthropus ago. The robust paranthropines evolved from the aethiopicus within the sister clade of P. fossil KNM-WT 17000, while the early homos africanus, P. robustus, P. boisei, and Homo. evolved from Australopithecus africanus in a These varied phylogenies were arrived at separate branch of evolution. because of different assumptions and procedures which relate to the effect of trait list bias. The Paradigm Analysis distinctions that are noted are due to different In understanding the phylogenetic assumptions of correlations among traits, as well relationship that is accepted in this paper, it is as an unequal representation of the functional important to be aware of how a particular complexes of traits (Skelton and McHenry paradigm can greatly affect one's analysis and 1998: 109). Although this trait list bias is agreed interpretation of the fossil record. Phylogeny is upon as causing problems in both analyses, there concerned primarily with the course of evolution is no consensus between these groups of and the branching or diverging events which take anthropologists as to how to compensate for the place. Dating and morphology of the fossil bias. record suggests that the hominid fossil record Strait and Grine (1998: 115) believe that constituted a number of distinctive evolutionary the best chance for arriving at an agreement over branching events as opposed to comprising of a early hominid phylogeny requires an open single evolutionary lineage (Foley 1995:72). discussion about characteristics and The phylogeny of the hominid lineage that I methodology. They evaluate Skelton and propose is that between 3 and 2.5 MY ago, McHenry's (1998) analysis, and in particular Australopithecus afarensis was the last common their use of functional groupings of traits. They ancestor to lead to two diverged lineages, the explain that Skelton and McHenry's separation megadontic specialists (the Paranthropines), and of the anterior dentition from the traits relating to the larger-brained generalists (Homo). However, heavy chewing does not qualify as a valid despite evidence that is continually debated functional grouping. Diet is responsible for amongst anthropologists, there is still no trends seen in both anterior and posterior consensus as to which phylogenetic framework is dentition, as well as in other masticatory features the best representative of . This of the skull, and therefore, anterior dentition is the problem of paradigm. cannot be separated from this grouping (Strait Each anthropologist brings his or her and Grine 1998: 115). In this sense, we can see own biases and worldviews into an analysis of how each group's paradigm affects the ways in the fossil record, and these are consequently which they group character traits. reflected within the hypotheses, methodology, Strait and Grine (1998) believe in and conclusions at which they arrive. As character trait lists that take into account Wolpoff (1976) discusses in a paper on the characteristics that are not only functionally theory behind paleoanthropological related, but also phylogenetically compatible

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with one another -- this is the of cladistic other , Vrba (1988) explains that the theory. They state that Skelton and McHenry robust dental and cranial morphology directly (1998) use complexes which are not reasonable reflects an adaptation for feeding on tough foods. within . The phylogenetic relationship This is best seen in the robust cranial accepted in this paper is in agreement with that characteristics: greatly thickened , of Strait and Grine (1998). Paranthropus the expansion of cheek teeth (the molars and aethiopicus is shown as being differentiated from premolars) and a reduction of the anterior Australopithecus afarensis, and early Homo (canines and incisors) teeth, as well as through its megadontic characteristics. Anterior pronounced and expanded areas of insertion for dentition morphology is directly related to heavy the immense masticatory muscles (Vrba masticatory action and is thus considered part of 1988:418). Through an analysis of these traits, it a similar functional complex as the rest of the seems clear that the robust features were an masticatory apparatus which functions to sustain adaptation to the changing ecology of the heavy chewing. environments occupied in Africa and the foods eaten by the paranthropines. An Ecological and Taxonomic Discussion An examination of another early Approximately 3-2.5 million years ago, hominid species living contemporaneously with conditions of cooling and drying arose on the Paranthropus, Homo habilis/ rudolfensis, African landscape; this was the fIrst widespread illustrates a parallel evolution in some of the North Polar glaciation. As Vrba (1988:407) features associated with this adaptation to a more explains, physical, environmental changes that open, savanna environment (Bromage and have evolutionary repercussions can arise from Schrenk 1995: 110). Many of the masticatory two sources: tectonic plate movement which is and dental adaptations seen in the cranium of relatively localized, and global climatic changes early Homo demonstrate a similar adaptation to which are widespread. The global event which tougher fruit and savanna foods. However, the occurred 2.5 million years ago initiated both Homo lineage is considered much more climatic and biotic changes within Africa. The generalized in terms of its dental traits than the result of these changing conditions was the paranthropines. The evolutionary trajectory that creation of more extensive open habitats and a Homo followed turned out to be very different change in the form of vegetation to a more from that of Paranthropus. resistant arid-tolerant variety (Bromage and It can be argued that the key variable in Schrenk 1995:110). The amount of woodland the endurance and survival of the available decreased greatly, and early hominids australopithecines and Homo was 'culture' and were forced to adapt to living in an open savanna the paranthropines were lacking in this ability for habitat. The selective pressures that arose in culture. Although the environmental pressures conjunction with the changing environmental resulted in extreme adaptations, the Homo landscape resulted in the phyletic splitting of lineage was able to further adapt to changing Australopithecus afarensis into two separate environments because of their use of 'culture' in lineages, Paranthropus and Homo (Bromage and terms of the development of more sophisticated Schrenk 1995: 110). tools. The environment provided these separate Adaptations to the environment and to genera with a series of selective challenges to coarse, fIbrous food items are noted in the fIrst which they adapted through similar means. paranthropine, Paranthropus aethiopicus. However, approximately 2 MY ago, the Throughout time, the Paranthropus lineage environment once again underwent great changes adapted itself more fully to this new open and returned to dryer and more humid habitat. As can be noted in the later conditions. Paranthropines, facial robusticity and megadonty Fossil evidence suggests that prevailed throughout the existence of the genus. Paranthropus boisei dispersed southward in The robust lineage became more specialized in Africa, and under these more moderate response to resources that were prevalent in these conditions, evolved into Paranthropus robustus more open environments. Vrba proposes a (Bromage and Schrenk 1995: 112). This is functional link between the robust cranial argued because fossil evidence suggests that morphology of the Paranthropines and the food Paranthropus robustus was a less extreme resources that were prevalent within the open, version of the "hyper-robust" Paranthropus arid environments that they occupied. Based on boisei. It can be argued that while the early an analogy of the functional morphologies of Paranthropines adapted to the cool, dry climate

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and open savanna by developing more robust as outlined in the previous arguments, there is features in order to survive on the tough foods sufficient evidence to argue for the genus available, Paranthropus robustus existed in a Paranthropus, deriving from a last common much more temperate environment and thus a ancestor of Australopithecus afarensis. slight reversal in the robusticity of the skull developed. This biogeographic perspective helps us to further understand the forces that acted upon the phylogenetic splitting of the early hominids into these two very distinct groups, with Paranthropus aethiopicus leading the way for Bromage, T.G., and Schrenk, F. 1995. the more megadont Paranthropines. I argue that Biogeographic and climatic basis for a narrative ecological forces were the main pressures that of early hominid evolution. Journal of Human acted in producing these separate lineages of Evolution. 28:109-114. early hominid evolution. Chamberlain, A.T. 1991. A Chronological Concluding Notes Framework for Human Origins. World A great problem plaguing modem . 23:137-146. anthropologists concerns the placement of the robust group of early hominids within the Foley, Robert 1995. Before Humanity. evolutionary line. Although many people argue Oxford: Blackwell Publishers Ltd. for a single lineage for the evolution of the early hominids, it can be demonstrated that this is not Kimbel, W.H., White, T.D., and Johanson, D.C. necessarily a logical argument. When evaluating 1988. "Implications of KNM-WT 17000 for the whether the robust group constitutes genetic- Evolution of "Robust" Australopithecines". In level differences from the Australopithecines and Evolutionary History of the "Robust" early Homo, one must take into account general Australopithecines. Frederick E. Grine, (editor). morphological differences between fossils, the pp. 259-268. New York: Aldine de Gruyter. bias of paradigm and its influence on one's professional work, as well as ecological Klein, Richard G. 1999. The Human Career: concerns. Human Biological and Cultural Origins: 2nd In an analysis of the traits of the Edition. Chicago: The University of Chicago Paranthropus lineage in comparison to the Press. Australopithecines and early Homo, it has been demonstrated that the primitive and derived traits Skelton, R.R., and McHenry, H. 1998. Trait list allow for the genetic-level splitting of the bias and a reappraisal of early hominid Paranthropines, using Australopithecus afarensis phylogeny. Journal of Human Evolution 34: 109- as the last common ancestor. This was primarily 113 visible in the Paranthropines' unique dental and cranial specializations that relate to mastication. Strait, D.S., and Grine, F.E. 1998. Trait list bias? In an examination of the issue of paradigm, it is A reply to Skelton and McHenry. Journal of noted that every individual brings his or her own Human Evolution. 34:115-118. biases and world-views into an experiment, and therefore, we must examine all sides of an Vrba, Elisabeth. S. 1988. "Late argument and draw our own conclusions Climatic Events and Hominid Evolution". In regarding their validity. In terms of ecological Evolutionary History of the "Robust" variables, it is demonstrated that changing Australopithecines. Frederick E. Grine, (editor). environmental and climatic changes have a great pp 405-426. New York: Aldine de Gruyter. influence on the adaptation and survival of early hominids. The shifting ecology of the Plio- Wolpoff, M.H. 1976. Data and Theory in required that the early hominids Paleoanthropological Controversies. American adapt to their new environments and habitats. Anthropologist. 78:94-96. The results of these adaptations were specializations so unique to the Paranthropines as to make a genetic-level split from the Australopithecines and Homo logical. Therefore,

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