Sterkfontein Member 2 paleoenvironment

Pickering and colleagues (2004) examine the fauna from Sterkfontein Member 2, coming to the following conclusion:

In summary, the mammalian fauna from Member 2 indicates a paleohabitat that was probably typified by rolling, rock-littered and brush- and scrub-covered hills (suitable for caracals and Makapania, and also commonly exploited by papionins). The valley bottom might have retained standing water year-round, and perhaps supported a tree line or restricted riverine forest, fringed by open woodland or grassland -- a setting appropriate for Alcelaphini, the abundant monkeys, and ambush predators, such as leopards (292).

The authors find this paleoenvironmental reconstruction to be basically similar to other contemporary hominid sites, such as Kanapoi (Wynn 2000), as well as the fauna from the Jacovec cavern. All of these contrast with earlier hominid sites, which were predominantly closed woodlands (WoldeGabriel et al. 2001; Pickford and Senut 2001). Indeed, WoldeGabriel and colleagues (2001:177) conclude that:

The demonstration that the earliest hominids consistently derive from strata bearing indicators of wooded environments may explain their rarity at some sites. It therefore seems increasingly likely that early hominids did not frequent open habitats until after 4.4 Myr. Before that, they may have been confined to woodland and forest habitats.

The final conclusion of Pickering and colleagues (2004) is about the relative abundance of hominid fossils, which are much rarer in the overall composition of the fauna than at sites like Kanapoi. They consider that this relative absence of hominids may either result from a relative scarcity of hominids in the environment, or instead from taphonomic biases that may have led hominids to be underrepresented in Member 2 in particular. They point out that the Member 2 hominids are relatively unaffected by carnivores, with an absence of toothmarks or other indicators of predation. This contrasts with the hominid fossils from the open-air sites in East Africa, where marks from carnivores and other predators are common In their view, the hominids mainly got into the deposit by walking in and dying. This is not as common as carnivores carrying in prey to eat it, but both recent papionins and hominids are known to enter caves -- in the case of the baboons, apparently because caves are cool places to escape the sun. They do not evaluate whether predation may have been higher in Member 4, but are apparently open to the possibility that differences in the taphonomy are mainly consequences of differences in hominid behavior.

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References:

Barrett L, Gaynor D, Rendall D, Mitchell D, Henzi SP. 2004. Habitual cave use and thermoregulation in chacma baboons (Papio hamadryas ursinus). J Hum Evol 46:215-222.

Leakey MG, Feibel CS, McDougall I, Ward C, Walker A. 1998. New specimens and confirmation of an early age for Australopithecus anamensis. Nature 393:62-66.

Pickering TR, Clarke RJ, Heaton JL. 2004. The context of Stw 573, an early hominid skull and skeleton from Sterkfontein Member 2: Taphonomy and paleoenvironment. J Hum Evol 46:279-297.

Pickford M, Senut B. 2001. The geological and faunal context of Late Miocene hominid remains from Lukeino, Kenya. C R Acad Sci Paris Sciences de la Terre et des planetes 332:145-152.

Ward CV, Leakey MG, Walker A. 2001. Morphology of Australopithecus anamensis from Kanapoi and Allia Bay, Kenya. J Hum Evol 41:255-368.

WoldeGabriel G, Haile-Selassie Y, Renne PR, Hart WK, Ambrose SH, Asfaw B, Heisken G, White TD. 2001. Geology and paleontology of the late Miocene Middle Awash Valley, Afar Rift, Ethiopia. Nature 412:175-178.

Wynn JG. 2000. Paleosols, stable carbon isotopes, and paleoenvironmental interpretation of Kanapoi, northern Kenya. J Hum Evol 39:411-432.