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Investigating the effect of endocranial volume on cranial shape in platyrrhines and the relevance of this relationship to interpretations of the fossil record
Author(s) -
HalenarPrice Lauren,
Tallman Melissa
Publication year - 2019
Publication title -
american journal of physical anthropology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.146
H-Index - 119
eISSN - 1096-8644
pISSN - 0002-9483
DOI - 10.1002/ajpa.23804
Subject(s) - encephalization , crania , endocast , skull , biology , brain size , extant taxon , heteroptera , primate , anatomy , zoology , evolutionary biology , paleontology , medicine , magnetic resonance imaging , radiology
Objectives Fossils have been linked to Alouatta based on shared cranial morphology and small brain size. However, the relationship between endocranial volume and cranial shape is unclear; it is possible that any platyrrhine with a small brain may exhibit “ Alouatta ‐like” features due to being “de‐encephalized.” We test two hypotheses: (a) there are aspects of cranial shape related to encephalization common to all platyrrhines; (b) it is these cranial traits that unite the small‐brained “ Alouatta ‐like” fossils. Materials and methods Three‐dimensional cranial shape and endocranial volume (ECV) were measured on 350+ extant platyrrhine crania, Cartelles, Paralouatta , and Antillothrix . Encephalization quotient (EQ) was calculated using regressions of ECV on cranial centroid size. Multivariate regressions were performed using the shape coordinates and EQ and shape changes associated with EQ were visualized. Cranial shape was predicted for a hypothetical primate with an EQ matching the fossils and this shape was compared to the Alouatta mean. Results There is a significant proportion of cranial shape variation explained by EQ in some taxa. The aspects of shape that are correlated with EQ are shared by several taxa and some have parallel regression vectors, but there is no overall pattern of shape change common to all platyrrhines. However, all taxa look more similar to Alouatta when their EQ is decreased, particularly Pithecia . Discussion Given that a decrease in encephalization can cause a more Alouatta ‐like cranial shape in many extant platyrrhines, it should not be automatically assumed that Alouatta ‐like cranial traits in a small‐brained fossil are evidence of a phylogenetic link to the alouattin clade.