Nutcracker Man’s Position in Human Evolution
It is generally agreed that OH5’s ancestor was the East African hominin Australopithecus aethiopicus. The species had no future descendants and was an evolutionary dead end (Wood).
However, there is some continued debate over their relationship to their fellow robust australopithecine- Australopithecus robustus. A. robustus is younger (dating to 1.8mya), though less derived and has only been found in South Africa. This has lead some to believe that the 2 species evolved independently of one another (Wood). If this was the case, A. robustus is thought to have evolved from a fellow South African hominin- A. africanus, while A. boisei descended separately from A. aethiopicus (Wood). Under this hypothesis, the morphological similarities between the two are thought to be homoplasies (Wood).
The alternative hypothesis is that both A. boisei and A. robustus descended from a single last common ancestor- A. aethiopicus (Wood). This solves the issue of homoplasy by assuming that their similarities were shared homologous traits, but does not account for the chronological and geographic complications (Why did A. boisei appear more derived but actually predate A. robustus?) (Wood).
The Specimen within the Species
OH5 was the first fossil of A./P. boisei to be found and is considered the type specimen of the species (Leakey). Like other specimens found at Omo, Koobi Fora, West Turkana, Konso, Chesowanja and Peninj- OH 5 has the unique combination of (Wood):
- Massive, wide and flat face
- With a larger brow ridge, heavier mandible and more anteriorly placed sagittal crest than A. aethiopicus or A. robustus
- A less prognathic face than A. aethiopicus
- Megadont postcanine dentition (huge molars and premolars) with thick dental enamel
- With more of a parabolically shaped dental arcade and larger postcanines than A. aethiopicus
- With a median maxillary torus not observed in A. robustus
- Endocranial volume of approximately 450-500cc
- Larger than A. aethiopicus
Nutcracker Man exhibits all of these traits and is a good specimen within his species.
Is A./P. boisei a “good” species?
There is adequate morphological and phylogenetic data to differentiate A./P. boisei as a separate and valid species from A./P. robustus (Wood). This relies primarily on dental differences between the two (such as the presence of a median maxillary torus in A./P. boisei) as well as their geographical separation. Less emphasis is placed on chronospecies classifications of “more” or “less” evolved (Wood). The differences are morphological and phylogenetic and not dependent on the passage of time.
The relationship with A. aethiopicus is a bit more complex and related to chronology . Some researchers have looked at the differences between the two (including differences in the shape of the premolar cusps and differing heights of the mandibular symphysis and corpus) and determined 2.3 mya to be the cut off between “early” and “late” stage Australopithecus/Paranthropus species in East Africa (Wood). This is consistent with the chronospecies concept in which A. boisei and A. aethiopicus make up an evolving lineage of robusts (Wood).
Questions for the Future
- I think it would be interesting to explore the specie’s extinction and the last moments of their lineage. Was it more environmental factors or competion with other hominins that led to their demise? Was there any interaction (even interbreeding) with other hominins of the area- including Homo habilis (who was found at the same site as OH5) and Homo rudolfensis. Were their powerful masticatory muscles and massive cheek teeth partially to blame (in preventing more flexibility in diet)? What was it about them that decreased survival/reproduction (at least in relation to other hominins)?
- I also think it would be interesting to further explore their possible tool use. Was Leakey right in initially identifying OH5 as the early tool user? If so, how was the species using them? Was it different than what is seen in modern-day chimps and primates OR even different from other hominin tool users? Was their use a consequence of acculturation with others (mimicking other tool users they interacted with) or was it an independent behavior?
- I also think it would be interesting to look further into their diet. Our text mentions the Sr/Ca isotope studies that were conducted on A. robustus. This found that they were at least occasional meat eaters because their strontium levels were so low. Did Nutcracker Man and his species share these diet behaviors? Were they also partially scavenging/eating meat?
Works Cited
Derrico F, Backwell LR. 2003. Possible Evidence of Bone Tool Shaping by Swartkrans Early Hominids. Journal of Archaeological Science 30:1559–1576.
Leakey LSB. 1959. A New Fossil Skull From Olduvai. Nature 184:491–493.
Wood B, Constantino P. 2007. Paranthropus boisei: Fifty years of evidence and analysis. American Journal of Physical Anthropology 134:106–132.
