New Information on the Development of the Hominid Cranium is Revealed by Paleoanthropologists
A morphometric method using traditional anthropometric variables reveals heterochronies and allometries in the evolution of the human cranium.
According to recent research that was just published in the journal PeerJ, human evolution is the only one that has ever combined a rise in brain size with the development of a progressively more juvenile skull shape. Four hominid craniums from specimens of Australopithecus anamensis, A. prometheus, Homo naledi, and H. longi were included in the sample. The study also includes samples of young great apes from contemporary species.
Additionally, this research introduces a novel method for interpreting hominization in terms of embryonic development, which refers to variations in the timing of the developmental processes' beginning or ending as well as variations in their rhythm between an ancestral species and a derived species. Based of this; one of the authors' initial findings was that Australopithecus and members of the genus Homo share with Great Apes; a negative expansion of the neurocranium, the cranial vault that gauges brain development. They discovered that the neurocranium develops more slowly than the other parts of the skull. However, a positive rate was discovered in the splanchnocranium; during development, the face's dimensions, which are correlated with the size of the teeth, increase more quickly.
In other words, larger craniums exhibit larger relative sizes in the face and smaller sizes in the cranial vault. Although australopithecines' cranial evolution during development followed the same scaling as apes', a series of lateral transpositions also happened in humans. The Homo genus's developmental trajectory took a new turn at this point, with adults retaining the traits of the infant crania of the ancestor species. These modifications involved a paedomorphic process known as "juvenilization" of cranial dimensions, which allowed for more advanced brain development in our evolutionary lineage than in other animals.
Finally, this study showed that, while belonging to a relatively recent species in the fossil record of human evolution—less than 300,000 years—Homo naledi's cranium has proportions that are comparable to those of the Homo habilis, the species's ancestors who date back more than 2 million years.
Juan Antonio Pérez-Claros et al, Heterochronies and allometries in the evolution of the hominid cranium: a morphometric approach using classical anthropometric variables, PeerJ (2022). DOI: 10.7717/peerj.13991