The Brain of Ardipithecus

Ardipithecus was a hominin species that lived between 4.4 and 5.7 million years ago. In this video we will examine all research related to it's brain size, brain shape and brain function.

Sahelanthropus Tchadensis is a hominin species that is based on the fossil remains of a various skeletal bones and teeth, but only a single skull. A word of caution: Since only a single skull is available any conclusions we draw from these analyses are tentative.

Two subspecies are identified: Ardipithecus ramidus and Ardipithecus kadabba, both found in Ethiopia by the research group of Yohannes Haile-Selassie. The fossils show an early hominin, likely of the human ancestoral line. But where this species exactly fits is uncertain.

Ardipithecus brain has features that resemble those of Sahelanthropus tchadensis, such as a narrow post orbital region. This implies that the frontal cortex did not yet develop as in later australopithecines. Furthermore, the back of the brain, i.e. visual cortex and cerebellum, is flexed, which is not seen in any other species. It suggests early adaptations to upright posture.

But there are clear differences in brain morphology between Ardi and Toumai. Particularly, the elongated shape of Sahelanthropus brain is not shared by Ardipithecus. Rather the brain shape of Ardipithecus rather resembles that of Australopithecus africanus. So could there be a link there? Maybe, but other features suggest that a direct link between Australopithecus and Ardipithecus is not obvious.

Time stamps:
0:00 Who was Ardipithecus?
1:39 Comparing brains of Ardipithecus and Sahelanthropus
5:57 Comparing brains of Ardipithecus and Australopithecines
8:12 Where does Ardipithecus fit in the ancestoral tree?

References/resources:
Boccia, M., Nemmi, F., & Guariglia, C. (2014). Neuropsychology of environmental navigation in humans: review and meta-analysis of FMRI studies in healthy participants. Neuropsychology review, 24(2), 236–251. https://doi.org/10.1007/s11065-014-92...

Cerling, T. E., Levin, N. E., Quade, J., et al. (2010). Comment on the paleoenvironment of Ardipithecus ramidus. Science, 328(5982), 1105. https://doi.org/10.1126/science.1185274

Kimbel, W. H., Suwa, G., Asfaw, B., et al. (2014). Ardipithecus ramidus and the evolution of the human cranial base. PNAS, 111(3), 948–953. https://doi.org/10.1073/pnas.1322639111

Kozma, E. E., Webb, N. M., Harcourt-Smith, W., et al. (2018). Hip extensor mechanics and the evolution of walking and climbing capabilities in humans, apes, and fossil hominins. PNAS, 115(16), 4134–4139. https://doi.org/10.1073/pnas.1715120115

Lovejoy, C. O., Suwa, G., Simpson, et al. (2009). The great divides: Ardipithecus ramidus reveals the postcrania of our last common ancestors with African apes. Science, 326(5949), 100–106.

Mongle, C. S., Strait, D. S., & Grine, F. E. (2019). Expanded character sampling underscores phylogenetic stability of Ardipithecus ramidus as a basal hominin. J Human Evol, 131, 28–39. https://doi.org/10.1016/j.jhevol.2019...

Prang T. C. (2019). The African ape-like foot of Ardipithecus ramidus and its implications for the origin of bipedalism. eLife, 8, e44433. https://doi.org/10.7554/eLife.44433

Sarmiento E. E. (2010). Comment on the paleobiology and classification of Ardipithecus ramidus. Science, 328(5982), 1105. https://doi.org/10.1126/science.1184148

Simpson, S. W., Levin, N. E., Quade, J., et al. (2019). Ardipithecus ramidus postcrania from the Gona Project area, Afar Regional State, Ethiopia. J Human Evol, 129, 1–45. https://doi.org/10.1016/j.jhevol.2018...

Suwa, G., Asfaw, B., Kono, R. T., et al. (2009). The Ardipithecus ramidus skull and its implications for hominid origins. Science, 326(5949), .

Suwa, G., Sasaki, T., Semaw, S., et al. (2021). Canine sexual dimorphism in Ardipithecus ramidus was nearly human-like. PNAS, 118(49), e2116630118. https://doi.org/10.1073/pnas.2116630118

White, T. D., Asfaw, B., Beyene, Y., et al. (2009). Ardipithecus ramidus and the paleobiology of early hominids. Science, 326(5949), 75–86. https://doi.org/10.1126/science.1175802

White, T. D., Lovejoy, C. O., Asfaw, B., et al. (2015). Neither chimpanzee nor human, Ardipithecus reveals the surprising ancestry of both. PNAS, 112(16), 4877–4884. https://doi.org/10.1073/pnas.1403659111

Narrated by: Miles Wischnewski

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