Endocranial morphology of Palaeocene<i>Plesiadapis tricuspidens</i>and evolution of the early primate brain

Orliac, Maëva J.; Ladevèze, Sandrine; Gingerich, Philip D.; Lebrun, Renaud; Smith, Thierry

doi:10.1098/rspb.2013.2792

Cited by 36 publications

(71 citation statements)

References 34 publications

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“…; Orliac et al. ; see exceptions in Table S15). The callosciurin R. laticaudatus (USNM 488511) is the only extant sciurid from our sample with a well‐defined sylvian sulcus, a somewhat surprising observation as this feature has often been considered a distinctive trait of Euprimates.…”

Section: Discussionmentioning

confidence: 97%

“…; Orliac et al. ; Ramdarshan & Orliac, ; Bertrand & Silcox, ). Consequently, it is becoming possible to better understand crucial aspects related to brain evolution in the two groups, and to look for instances of parallelism.…”

Section: Discussionmentioning

confidence: 99%

“…, , ; Orliac et al. ; Ramdarshan & Orliac, ; Bertrand & Silcox, ; Bertrand et al. ; Dozo & Martínez, ).…”

Section: Methodsunclassified

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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: 97%

Section: Discussionmentioning

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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“…Second, following Orliac et al . (), the superior sagittal sinus was excluded from the surface area (NS2). Third, we followed Jerison () and Long et al .…”

Section: Methodsmentioning

confidence: 99%

Virtual endocasts of fossil Sciuroidea: brain size reduction in the evolution of fossoriality

et al. 2018

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Aplodontia rufa (mountain beaver) is the only extant member of the Aplodontidae. The fossil record indicates that this family displayed greater taxonomic and ecological diversity in the past, and that the burrowing adaptations of Aplodontia might be derived. We describe the first virtual endocasts of A. rufa and of three fossil aplodontids: Prosciurus relictus and Pros. aff. saskatchewaensis (early Oligocene), and Mesogaulus paniensis (early Miocene). Our results show that the endocasts of early aplodontid rodents are more similar to those of early arboreal squirrels than to those of the later occurring aplodontids in terms of both relative size and morphology. The endocranial features observed in sciurids and early aplodontids, missing in later aplodontids, have been associated with better vision and the development of arboreality in squirrels. Basal Aplodontidae known from postcrania have been described as generalists with some features for arboreality, which may provide a basis for these similarities. In contrast, the relatively small endocasts of the later occurring aplodontids, which lack traits related to visual specialization, may reflect their burrowing adaptations, as they would be less reliant on visual cues. When integrated with data from the most primitive fossil rodents, the Ischyromyidae, these new data suggest that early squirrels and aplodontids diverged from more terrestrial ischyromyids to become more arboreal, with relatively larger brains showing traits for improved vision. Recent Aplodontidae with fossorial adaptations returned to a more ischyromyid‐like condition in their endocranial features. These results are consistent with previous observations that changes in locomotion are reflected in the endocranial anatomy of rodents.

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“…While preservation is not adequate to reconstruct the endocast more caudally, it is clear that D. szalayi would have had relatively large olfactory bulbs similar to those reconstructed for other plesiadapiforms including Plesiadapis (Gingerich and Gunnell, 2005;Orliac et al, 2014), Ignacius (Silcox et al, 2009), andMicrosyops (Silcox et al, 2010a). The position of the frontal relative to the maxilla is difficult to reconstruct because of distortion of the specimen, but the front of the olfactory bulbs is clearly fairly far forward, at the level of the orbit as in Ignacius, but not Microsyops or Plesiadapis, in which the endocast extends less far rostrally (Silcox et al, 2009(Silcox et al, , 2010aOrliac et al, 2014). It has been suggested that the apparently more rostral extension of the olfactory bulbs shared between I. graybullianus, dermopterans, and short-faced euprimates might be related to shortening of the face and occurred multiple times in euarchontan evolution (Silcox et al, 2010a).…”

Section: Face and Braincasementioning

confidence: 96%

Cranial anatomy of Paleogene Micromomyidae and implications for early primate evolution

Bloch

Chester

Silcox

2016

Journal of Human Evolution

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Paleogene micromomyids are small (∼10-40 g) euarchontan mammals with primate-like molars and postcrania suggestive of committed claw-climbing positional behaviors, similar to those of the extant arboreal treeshrew, Ptilocercus. Based primarily on evidence derived from dental and postcranial morphology, micromomyids have alternately been allied with plesiadapiforms, Dermoptera (colugos), or Primatomorpha (Primates + Dermoptera) within Euarchonta. Partial crania described here of Paleocene Dryomomys szalayi and Eocene Tinimomys graybulliensis from the Clarks Fork Basin of Wyoming are the first known for the family Micromomyidae. The cranium of D. szalayi exhibits a distinct, small groove near the lateral extreme of the promontorium, just medial to the fenestra vestibuli, the size of which suggests that the internal carotid artery was non-functional, as has been inferred for paromomyid and plesiadapid plesiadapiforms, but not for Eocene euprimates, carpolestids, and microsyopids. On the other hand, D. szalayi is similar to fossil euprimates and plesiadapoids in having a bullar morphology consistent with an origin that is at least partially petrosal, unlike that of paromomyids and microsyopids, although this interpretation will always be tentative in fossils that lack exhaustive ontogenetic data. Micromomyids differ from all other known plesiadapiforms in having an inflated cochlear part of the bony labyrinth and a highly pneumatized squamosal and mastoid region with associated septa. Cladistic analyses that include new cranial data, regardless of how bullar composition is coded in plesiadapiforms, fail to support either Primatomorpha or a close relationship between micromomyids and dermopterans, instead suggesting that micromomyids are among the most primitive known primates.

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Endocranial morphology of PalaeocenePlesiadapis tricuspidensand evolution of the early primate brain

Cited by 36 publications

References 34 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

Virtual endocasts of fossil Sciuroidea: brain size reduction in the evolution of fossoriality

Cranial anatomy of Paleogene Micromomyidae and implications for early primate evolution

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