Hominoid Cranial Evolution


Extant hominoid cranial variability, although marked, represents only a remnant of a temporally and geographically expansive evolutionary history. Attempts to reconstruct the evolutionary processes that have played a role in the morphological divergence of this superfamily have been complicated by a sparse hominoid fossil record, and ambiguity related to phylogenetic relationships. Moreover, morphological variation in the cranium is influenced by a complex combination of functional, developmental and architectural constraints, complicating our ability to tease apart specific evolutionary pressures. However, due to advances in the field of evolutionary quantitative genetics, recent studies of extant hominoid taxa have reconstructed the potential evolutionary processes that have generated cranial diversity. Collectively, these studies have shown that directional selection, although identified in the evolutionary path to hominins, was not the major driving force behind this divergence. Rather, it is a combination of genetic drift and stabilising selection that characterises the evolution of the hominoid cranium.

Key Concepts

  • Morphological diversity in the hominoid cranium is extensive.
  • Cranial diversity is influenced by evolutionary, developmental, functional, structural forces and constraints.
  • Extant hominoids are a small fraction of all hominoids that have ever lived.
  • The hominoid fossil record is fragmentary and phylogenetic relationships are ambiguous.
  • Quantitative genetic analyses indicate a combination of evolutionary processes have shaped the hominoid cranium.

Keywords: apes; basicranial flexion; morphological constraint; natural selection; genetic drift; morphological variability; evolutionary processes

Figure 1. (a) Phylogenetic tree of the Hominoidea with branch length estimates scaled by substitution rates/site × 104. Data were taken primarily from Perelman et al. with the exception of the taxa and branches highlighted in green and pink which are approximations based on the information given in Carbone et al. and Nater et al. . (b) An alternative model of the Pongo lineage from Nater et al. showing P. tapanuliensis as a direct descendant of the ancestor of all Pongo. This scenario depicts an early split between the lineages leading to P. abelii and P. tapanuliensis, with a later split leading to P. pygmaeus. Tree redrawn based on Figure . Schroeder and von Cramon‐Taubadel . Reporoduced with permission of John Wiley & Sons.
Figure 2. An illustration of extant hominoid cranial diversity. Courtesy of Noreen von Cramon‐Taubadel.
Figure 3. Phylogenetic tree of the Hominoidea with branches coloured according to the specific evolutionary processes identified in Schroeder and von Cramon‐Taubadel . Red indicates directional selection; blue indicates genetic drift; yellow indicates stabilising selection; dashed light blue lines indicate branches along which there is some evidence for genetic drift instead of stabilising selection. Black branches indicate instances where no data were available. Tree redrawn based on Figure . Schroeder and von Cramon‐Taubadel . Reporoduced with permission of John Wiley & Sons.


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Schroeder, Lauren, and von Cramon‐Taubadel, Noreen(Mar 2020) Hominoid Cranial Evolution. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0028134]