| Summary: | The brain of cetaceans is very large in both absolute and relative size and possesses an extremely convoluted cortex. The understanding of how the brain of these mammals fully adapted to an aquatic life is organized is important to shed light on the processes that shaped the evolution of the mammalian brain in general, including humans. Three cortical regions, the anterior cingulate (ACC), anterior insular (AI), and frontopolar cortices (FPC) have been shown to be involved in high-level cognitive function in primates and thus, the understanding of their structural organization in cetaceans is particularly meaningful given the wide evidence of their cognitive abilities. Cytoarchitecture, chemoarchitecture based on the distribution of the calcium binding (CaBP) protein calretinin, glia/neuron ratio, and neuronal specializations were assessed in the ACC, AI, and FPC of a series of cetaceans representative of the main families such as the bottlenose dolphin (Tursiops truncatus, Odontoceti, Delphinidae), Risso’s dolphin (Grampus griseus, Odontoceti, Delphinidae), harbor porpoise (Phocoena phocoena, Odontoceti, Phocoenidae), killer whale, (Orcinus orca, Odontoceti, Delphinidae), beluga whale (Delphinapterus leucas, Odontoceti, Monodontidae), sperm whale (Physeter macrocephalus, Odontoceti, Physeteridae), pigmy sperm whale (Kogia simus, Odontoceti, Kogiidae), Amazon river dolphin (Inia geoffrensis, Odontoceti, Iniidae), minke whale (Balaenoptera acutorostrata, Mysticeti, Balaenopteridae), and humpback whale (Megaptera novaeangliae, Mysticeti, Balaenopteridae). Other species including the pigmy hippopotamus (Hexaprotodon liberiensis, Cetartiodactyla, Hippopotamidae), Florida manatee (Trichecus manatus latirostris, Sirenia, Trichechidae), Atlantic walrus (Odobenus rosmarus rosmarus, Carnivora, Odobenidae), African savannah elephant (Loxodonta africana, Proboscidea, Elephantidae), black rhinoceros (Diceros bicornis, Perissodactyla, Rhinocerotidae), rock hyrax (Procavia capensis, Hyracoidea, Procavidae), lowland streaked ...
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