Tag Archives: birds

Brain shape and encephalization in birds

marugan-lobon-et-al-2016Encephalization quotients (EQ) have been extensively used to characterize brain evolution, but this univariate metric only includes information on relative size. Marugán-Lobón and his colleagues recently analysed the association between endocranial shape changes and EQ by applying geometric morphometrics to a sample of modern bird endocasts. A Principal Component Analysis accounting for phylogenetic history showed that the bird endocasts varied essentially in the relative expansion of the forebrain and in the degree of flexion of the braincase. The distribution of the specimens in the morphospace has a phylogenetic structure, with morphological affinity between close evolutionary clades, particularly the landbirds, which display larger forebrains. Size explains 10% of the shape variation. EQ accounts for changes in relative forebrain expansion, with larger EQs associated with larger forebrains. A second study was computed correcting for phylogeny, i.e. computing regression analyses on the phylogenetic independent contrasts of shape and size against EQ. When allometric and phylogenetic signals were removed, shape variation was mostly associated with the degree of flexion of the endocasts, and EQ was not significantly correlated with these morphological changes. The authors conclude that, excluding the general effect of size, EQ does not explain shape differences among birds’ endocasts. Therefore, other factors are probably responsible for brain variation in birds.

Sofia Pedro


Parrots brain

Carril et al 2015A team of researchers from Argentina has recently studied the endocranial morphology of Neotropical parrots. They reconstructed the endocasts from several species and conducted a morphological analysis to evaluate the previously proposed evolutionary history of these taxa. Their investigation supplies three main findings. First, these birds have higher than expected brain volumes for their body mass, and the authors suggest this might be associated with the evolution of cognitive abilities or their versatile behaviour. Second, two different morphotypes were distinguished according to the maximum width of the hemispheres: a more quadrangular or walnut-shaped brain and a more rounded brain shape. A reconstruction of the ancestral morphology is similar to the more rounded type. However, as the distribution of the two types across the species is heterogeneous, the authors hypothesize the walnut type might be the primitive for all the parrots, and the rounded type primitive for the Neotropical parrots.

Sofia Pedro