Supplementary Material for: A Memory Already like an Elephant's? The Advanced Brain Morphology of the Last Common Ancestor of Afrotheria (Mammalia)

Virtually reconstructed and natural endocranial casts are used in the study of brain evolution through geological time. We here present work investigating the paleoneurological evolution of afrotherian mammals. Using microCT-generated endocasts we show that, with the exception of the subfamilies Macroscelidinae and Tenrecoidea, most Afroinsectiphilia display a more or less gyrencephalic and ventrally expanded neopallium, two derived features that are unexpected for these insectivore-grade afrotherians. This implies that the endocranial cast morphology at the root of the afrotherian clade may have been more advanced than previously thought. The reconstructed endocranial morphology of the Afrotheria's last common ancestor reaches the level of complexity of some early Cenozoic archaic ungulates. Our result gives support to the hypothesis of an ungulate-like ancestral body plan for Afrotheria. It also implies that the a priori ‘primitive' suite of traits evident in the brain of Afroinsectivora, especially in the tenrecs, may have been secondarily acquired. Implications on the overestimation of the divergence age of Afrotheria are discussed.

虚拟重建与天然颅内模（endocranial casts）被广泛应用于地质时间尺度下的脑演化研究。本研究开展了针对非洲兽总目（Afrotheria）哺乳动物古神经演化的探究工作。本研究利用显微CT（microCT）重建的颅内模开展分析，结果显示：除象鼩亚科（Macroscelidinae）与马岛猬总科（Tenrecoidea）外，多数非洲食虫类群（Afroinsectiphilia）的新皮层（neopallium）均呈现出不同程度的沟回化与腹侧扩张特征——这两类衍生性状，对于这类食虫类等级的非洲兽类而言实属意料之外。这表明非洲兽总目演化支基部的颅内模形态，可能比此前学界的认知更为先进。非洲兽总目最近共同祖先的重建颅内模形态，其复杂度已达到部分新生代早期古有蹄类的水平。本研究结果支持"非洲兽总目祖先具有类有蹄类躯体构型"这一假说。同时这也意味着，非洲食虫类群（尤其是马岛猬类（tenrecs））大脑中原本被先验认为的"原始"性状组合，实际上可能是次生获得的。本研究还探讨了其对非洲兽总目分化年代被高估这一问题的启示意义。