Endocranial volumes of primate species: scaling analyses using a comprehensive and reliable data set

Abstract

We present a compilation of endocranial volumes (ECV) for 176 non-human primate species, based on individual data collected from 3813 museum specimens, at least 88% being wild-caught. In combination with body mass data from wild individuals, strong correlations between endocranial volume and body mass within taxonomic groups were found. Errors attributable to different techniques for measuring cranial capacity were negligible and unbiased. The overall slopes for regressions of log ECV on log body mass in primates are 0.773 for least-squares regression and 0.793 for reduced major axis regression. The leastsquares slope is reduced to 0.565 when independent contrasts are substituted for species means (branch lengths from molecular studies). A common slope of 0.646 is obtained with logged species means when grade shifts between major groups are taken into account using ANCOVA. In addition to providing a comprehensive and reliable database for comparative analyses of primate brain size, we show that the scaling relationship between brain mass and ECV does not differ significantly from isometry in primates. We also demonstrate that ECV does not differ substantially between captive and wild samples of the same species. ECV may be a more reliable indicator of brain size than brain mass, because considerably larger samples can be collected to better represent the full range of intraspecific variation. We also provide support for the maternal energy hypothesis by showing that BMR and gestation period are both positively correlated with brain size in primates, after controlling for the influence of body mass and potential effects of phylogenetic relatedness.

Internal carotid arterial canal size and scaling in Euarchonta: Re-assessing implications for arterial patency and phylogenetic relationships in early fossil primates

“…For extant taxa, the majority of values for both body mass and endocranial volume were taken from supplementary files of Isler et al (2008). For non-primate euarchontans, we reference Stephan et al (1981), Pirlot and Kamiya (1982) and Tacutu et al (2013).…”

“…Figure 5. Morphospace of stapedial and promontorial canal area using endocranial volume to control for absolute size A, Against endocranial volumes that represent within species, sex-specific means (data from Isler et al, 2008), we plot both the natural log of promontorial canal cross sectional area (blue dots) and stapedial canal area (red dots) for individuals. We take the regression line relating promontorial canal area to endocranial volume in taxa with a patent promontorial artery (Table 2, equation #7) as the most meaningful line of subtraction for both canal areas.…”

“…These relationships suggest strong negative allometry, as an isometric slope of an area to volume is 0.666. Given the lack of direct data on ossicle scaling we further tested the idea that negative allometry of ossicle size restricts stapedial artery reliance with a dataset from Coleman and Boyer (2011), adding data on endocranial volume from Isler et al (2008) (SOM Table S7) and using the Bininda-Emmonds et al (2007) tree (SOM Part II, tree #5). Using the same phylogenetic generalized least squares regression methods and software as in other analyses of this study, we found that the area of the stapes footplate (as a proxy for the potential area of the obturator foramen that passes the stapedial artery) does indeed scale with strong negative allometry to both body mass and endocranial volume: 0.30e0.31, respectively (where isometry would be 0.66) (SOM Part VI).…”

Primate brains, the ‘island rule’ and the evolution of Homo floresiensis

“…Isler et al (2008) suggest sample size 159 has a more important effect on parameter estimation than data quality so it is likely the size of 160 the dataset is the most limiting factor of this study. 161…”

Preliminary notes on a newly discovered skull of the extinct monkey Antillothrix from Hispaniola and the origin of the Greater Antillean monkeys

“…As noted by Rosenberger (1979), cebines have unusually narrow interorbital regions, dorsoventrally narrow zygomatic arches, shallow glenoid fossae, and weak postglenoid processes. The cebine brain is disproportionally large for a platyrrhine (Isler et al, 2008) and the neocortex is expanded over the olfactory bulbs. The outer table of the frontal conforms to the profile of the neocortex (Kay and Fleagle, 2010).…”