Tag Archives: endocasts

Language and endocasts

Since brain does not fossilize, brain endocast (i.e., replica of the inner surface of the braincase, Figure 1) constitutes the only direct evidence for reconstructing hominin brain evolution (Holloway, 1978; Holloway et al., 2004a). In this context, paleoneurology has suffered from strong limitations due to the fragmentary nature of the fossil record and the absence of any information regarding subcortical elements in extinct taxa. Additionally, variation in brain shape and organization (and in the corresponding endocast) is technically difficult to capture, as stated by Bruner (2017a, p. 64): “[…] the smooth and blurred geometry of the brain, its complex and complicated mechanisms, and its noticeable individual variability make any research associated with its morphology very entangled and difficult to develop within fixed methodological approaches.” An emblematic example might be the reluctance of paleoneurologists to consider the sulcal imprints visible on the endocranial surface because of the substantial uncertainties in describing such features in fossil specimens and related debates (e.g., the lunate sulcus in the Taung child’s endocast; Falk, 1980a, 2009, 2014; Holloway, 1981a; Holloway et al., 2004b). In 1987, Tobias even came to the conclusion that “The recognition of specific cerebral gyri and sulci from their impressions on an endocast is a taxing, often subjective and even invidious undertaking which arouses much argumentation” (p. 748) …

[keep on reading this Opinion Article by Amélie Beaudet in Frontiers in Human Neuroscience, published in a special issue dedicated to Language, skull, and brain]


Hyena paleoneurology

hyenasA series of works by Sharleen T. Sakai’s group have correlated the proportions of the anterior endocranial region with social behaviour in hyenas. They found that in spotted hyenas (Crocuta crocuta), males have relatively larger anterior cerebrum than females. The relative volume of the anterior endocranial region is also significantly larger in this species when compared to other extant species of hyenas. The spotted hyenas are the most gregarious species, living in large clans, where females are dominant and philopatric, and males disperse and must adapt to the hierarchic system of a new clan. The anterior region of the hyena’s brain comprises mostly the frontal cortex, which mediates social behaviour. The authors hypothesize, in the light of the social brain hypothesis, that the development of the frontal region in this species, and particularly in males, might have been enhanced by the need for a larger behavioural flexibility in their complex social environment. More recently, Joan Madurell-Malapeira and his colleagues compared the endocasts of two extinct spotted hyenas (C. spelaea and C. ultima) with those of extant species. The fossil specimens have similar morphology to that of C. crocuta, but less developed anterior portion of their endocranium. The authors therefore propose this feature to be an autapomorphy of C. crocuta. Consequently, the social and foraging behaviour of these fossil species are presumably less specialized, and this might contradict some speculations about competition between hyenas and humans during Pleistocene.

Sofia Pedro

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

Maba and Buia

Maba and Buia 2016

Two new endocasts on AJPA:
Maba (Asia, 300-130 ky) and Buia (Africa, 1 My).

Notoungulata endocasts

Dozo and Martínez 2016Notoungulata is an extinct order of ungulates, endemic from South America. It has two main suborders: Toxodontia, including the large-bodied ungulates, and Typotheria. Researchers from Argentina have described the endocasts from two species of Notohippids, a family from the South American Oligocene that is included in the Toxodontia group. The endocasts from Rynchippus equinus and Eurygenium latirostris were virtually reconstructed from CT scans and compared to other fossil and extant ungulates. Both endocasts were similar in size and in their overall shape, proportions and sulci morphology. They fitted into the general “design” of the Toxodontia endocasts, which have the most complex surface within the Notoungulates, with pronounced telencephalic flexure, a developed Sylvian sulcus, and a bulging temporal lobe. These features are also similar to those displayed by the rabbit-like Typotheria group, although Notohippids had larger frontal region. In contrast, extinct and extant ungulates display a different endocast morphology, without prominent Sylvian and temporal regions. According to the authors, functional interpretations for the expansion of the frontal region and the Sylvian and temporal areas in the Notohippids can suggest an increase in the snout sensitivity and an auditory specialization, respectively.

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