Bimaturism in extinct and extant primates

Extended male growth such as that seen in orangutans and mandrills is interpreted as a form of risk aversion. Species that occupy unstable environments extend their growth periods to distribute the metabolic demands of growth. Frugivores are more likely to extend growth periods because of the seasonality and unpredictability of fruiting times, whereas folivores are more likely to have higher growth rates for shorter periods of time due to the reliability and abundance of foliage. Likewise, males of taxa with extended maturation times are not in direct competition with the dominant or alpha males until they are physically able to challenge them. The growing male’s juvenile appearance is seen as less threatening by the dominant males. The hypothesis suggesting P. robustus achieved its high levels of cranial sexual dimorphism through bimaturism via extended male growth is unlikely given the inferred diet of Paranthropus spp. The most likely explanation is Paranthropus spp. achieved sexual dimorphism through other heterochronic processes or through a combination of those processes. As in gorillas, the high levels of sexual dimorphism in Paranthropus spp. are likely to be the result of the heterochronic change known as female progenesis, in which the Paranthropus females may have ended growth earlier than males who continue growing. Our hypothesis is that the ontogenic and heterochronic basis of gorilla sexual dimorphism is a plausible mechanism to explain the inferred sexual dimorphism in Paranthropus spp.

Author

• Mitchell, Taylor

Language

• en

Keyword

• Hominins
• Bimaturism
• Progenesis
• Paranthropus
• Hypermorphosis
• Heterochrony

Date created

• 2025

Type of Work

• Master's Thesis

License

• All rights reserved

Rights statement

• In Copyright

GW Unit

• Anthropology

Degree

• M.S.

Advisor

• Barr, W Andrew
• Wood, Bernard A

Persistent URL

•  https://scholarspace.library.gwu.edu/etd/rj4305559