title: Endocranial morphology of Palaeocene Plesiadapis tricuspidens and evolution of the early primate brain.
abstract: Expansion of the brain is a key feature of primate evolution. The fossil record, although incomplete, allows a partial reconstruction of changes in primate brain size and morphology through time. Palaeogene plesiadapoids, closest relatives of Euprimates (or crown-group primates), are crucial for understanding early evolution of the primate brain. However, brain morphology of this group remains poorly documented, and major questions remain regarding the initial phase of euprimate brain evolution. Micro-CT investigation of the endocranial morphology of Plesiadapis tricuspidens from the Late Palaeocene of Europe--the most complete plesiadapoid cranium known--shows that plesiadapoids retained a very small and simple brain. Plesiadapis has midbrain exposure, and minimal encephalization and neocorticalization, making it comparable with that of stem rodents and lagomorphs. However, Plesiadapis shares a domed neocortex and downwardly shifted olfactory-bulb axis with Euprimates. If accepted phylogenetic relationships are correct, then this implies that the euprimate brain underwent drastic reorganization during the Palaeocene, and some changes in brain structure preceded brain size increase and neocortex expansion during evolution of the primate brain.
authors.affiliation: Institut des Sciences de l'Evolution (ISEM UMR 5554), Université Montpellier 2, , CC 064, Place Eugène Bataillon, 34270 Montpellier Cedex 05, France, Muséum national d'Histoire naturelle, UMR 7207 CR2P CNRS/MNHN/UPMC, , 8 rue Buffon, CP 38, 75231 Paris Cedex 05, France, Museum of Paleontology, The University of Michigan, , Ann Arbor, MI 48109-1079, USA, O.D. Earth & History of life, Royal Belgian Institute of Natural History, , 29 rue Vautier, 1000 Brussels, Belgium.
authors.forename: Maeva J
authors.initials: MJ
authors.lastname: Orliac
authors.forename: Sandrine
authors.initials: S
authors.lastname: Ladevèze
authors.forename: Philip D
authors.initials: PD
authors.lastname: Gingerich
authors.forename: Renaud
authors.initials: R
authors.lastname: Lebrun
authors.forename: Thierry
authors.initials: T
authors.lastname: Smith
mesh_terms: D000818:Animals; D005075:Biological Evolution; D001921:Brain / Q000033:anatomy & histology*; D005060:Europe; D005580:Fossils; D011323:Primates / Q000033:anatomy & histology*; D012886:Skull / Q000033:anatomy & histology*; D055114:X-Ray Microtomography
keywords: computed tomography; endocast; euprimates; plesiadapiforms; vertebrate palaeontology