Quantification of neocortical ratios in stem primates

Long, Adam; Bloch, Jonathan I.; Silcox, Mary

doi:10.1002/ajpa.22724

Cited by 37 publications

(46 citation statements)

References 43 publications

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“…() suggested that the neocortical surface area increased through time in rodents as has been shown for primates (Long et al. ), but this increase was less intense in rodents and started later. In the context of this paper, it is of interest to compare the data from the sciurid C. wilsoni with data from primates that are roughly contemporaneous: Oligocene anthropoids.…”

Section: Discussionmentioning

confidence: 82%

“…Nevertheless, data on neocortical surface area in primates have been published, and a trend in neocortical surface area increase has been demonstrated for this group (Long et al. ). For rodents, a similar trend can be inferred based on the results of this and previous studies (Bertrand et al.…”

Section: Discussionmentioning

confidence: 99%

“…Primates and Rodentia both exhibit an increase in neocortical surface area (with caudal expansion) through time (Long et al. ; Bertrand et al. ).…”

Section: Discussionmentioning

confidence: 99%

“…Third, only one side of the neocortex (the most complete hemisphere) was selected, the superior sagittal sinus was excluded and the area of the hemisphere was doubled (NS1 × 2; following Jerison, ; Long et al. ).…”

Section: Methodsmentioning

confidence: 99%

“…This feature represents a key landmark, as it provides information on the degree of development of the neocortex (Jerison, ; Long et al. ). In lemurs, there is a relationship between the rhinal fissure and the orbitotemporal canal (Martin, ), which has also been inferred for other taxa (Novacek, ).…”

Section: Methodsmentioning

confidence: 99%

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Virtual endocast of the early Oligocene Cedromus wilsoni (Cedromurinae) and brain evolution in squirrels

2016

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Extant squirrels exhibit extensive variation in brain size and shape, but published endocranial data for living squirrels are limited, and no study has ever examined brain evolution in Sciuridae from the perspective of the fossil record to understand how this diversity emerged. We describe the first virtual endocast for a fossil sciurid, Cedromus wilsoni, which is known from a complete cranium from Wyoming (Orellan, Oligocene), and make comparisons to a diverse sample of virtual endocasts for living sciurids (N = 20). The virtual endocasts were obtained from high-resolution X-ray micro-computed tomography data. Comparisons were also made with endocasts of extinct ischyromyid rodents, the most primitive rodents known from an endocranial record, which provide the opportunity to study the neuroanatomical changes occurring near the base of Sciuridae. The encephalization quotient of C. wilsoni is higher than that of Ischyromys typus from the same epoch, and falls within the range of modern terrestrial squirrel variation, but below the range of extant scansorial, arboreal and gliding sciurids when using cheek-tooth area for the estimation of body mass. In a principal components analysis, the shape of the endocast of C. wilsoni is found to be intermediate between that of primitive fossil taxa and the modern sample. Cedromus wilsoni has a more expanded neocortical surface area, especially the caudal region of the cerebrum, compared with ischyromyid rodents. Furthermore, C. wilsoni had proportionally larger paraflocculi and a more complex cerebellar morphology compared with ischyromyid rodents. These neurological differences may be associated with improvements in vision, although it is worth noting that the size of the parts of the brain most directly involved with vision [the rostral (superior) colliculi and the primary visual cortex] cannot be directly assessed on endocasts. The changes observed could also relate to balance and limb coordination. Ultimately, the available evidence suggests that early squirrels were more agile and visually oriented animals compared with more primitive rodents, which may relate to the process of becoming arboreal. Extant sciurids have an even more expanded neocortical surface area, while exhibiting proportionally smaller paraflocculi, compared with C. wilsoni. This suggests that the neocortex may continue increasing in size in more recent sciurid rodents in relation to other factors than arboreality. Despite the fact that both Primates and Rodentia exhibit neocortical expansion through time, since the adoption of arboreality preceded major increases in the neocortex in Primates, those neurological changes may be related to different ecological factors, underlining the complexity of the inter-relationship between time and ecology in shaping the brain in even closely related clades.

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Section: Discussionmentioning

confidence: 82%

Section: Discussionmentioning

confidence: 99%

“…Primates and Rodentia both exhibit an increase in neocortical surface area (with caudal expansion) through time (Long et al. ; Bertrand et al. ).…”

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Virtual endocast of the early Oligocene Cedromus wilsoni (Cedromurinae) and brain evolution in squirrels

2016

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Endocranial morphology of Microchoerus erinaceus (Euprimates, Tarsiiformes) and early evolution of the Euprimates brain

Ramdarshan

Orliac

2015

American J Phys Anthropol

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Comparison with the endocasts of other available late Eocene primates shows that they already exhibited a variety of brain morphologies, highlighting the complex history of the external features of the primate brain, as early as the Eocene. M. erinaceus was a fruit and gum eater considered as nocturnal based on its orbit size. However, its brain showed small olfactory bulbs--smaller than in the coeval diurnal taxa Adapis parisiensis--and a neocorticalization similar to folivorous taxa. These observations contrast with patterns observed in primates today where nocturnal taxa have larger olfactory bulbs than diurnal taxa, and call into question a direct correlation between frugivory and neocorticalization increase in primates.

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Eocene Paleoecology of Adapis parisiensis (Primate, Adapidae): From Inner Ear to Lifestyle

Bernardi

Couette

2017

The Anatomical Record

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European adapids, especially Adapis parisiensis, have been extensively studied over the past two centuries, essentially for taxonomic and phylogenetic purposes. Analyses of dental, cranial, and postcranial morphology have led to various hypotheses about the diet, locomotion, and lifestyle of this fossil primate species. As the morphology of Adapis parisiensis is not directly comparable to any extant species, some interpretations are still debated. The inner ear is crucial to several functional parameters, such as auditory acuity, balance, agility, orientation, and head motion speed during locomotion. We examined the inner ear morphology of Adapis parisiensis in order to make some functional inferences, using μCT techniques to access the internal morphology without damaging the fossil specimens. We analyzed the length and shape of the cochlea, the size of the oval window, and the size and orientation of the semicircular canals of seven Adapis parisiensis crania. Results indicate that the species was more sensitive to high frequencies than low frequencies. Results for locomotion style are different, depending on the method used. Results about the coefficient of agility are in good agreement with previous studies, proposing a slow/medium slow locomotion for the fossil species. In contrast, angular velocity magnitude (AVM) results show a great range of variation in the locomotor repertory for Adapis parisiensis, probably indicating that the model used is not adapted to the study of the fossil record. A comparison to measurements of extant strepsirhines leads us to conclude that Adapis parisiensis was probably monogamous and solitary, with a small home range. Anat Rec, 300:1576-1588, 2017. © 2017 Wiley Periodicals, Inc.

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Quantification of neocortical ratios in stem primates

Cited by 37 publications

References 43 publications

Virtual endocast of the early Oligocene Cedromus wilsoni (Cedromurinae) and brain evolution in squirrels

Virtual endocast of the early Oligocene Cedromus wilsoni (Cedromurinae) and brain evolution in squirrels

Endocranial morphology of Microchoerus erinaceus (Euprimates, Tarsiiformes) and early evolution of the Euprimates brain

Eocene Paleoecology of Adapis parisiensis (Primate, Adapidae): From Inner Ear to Lifestyle

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