Of all known insular mammals, hippos and elephants present the extremes of body size decrease, reducing to 4 and a mere 2% of their ancestral mainland size, respectively. Despite the numerous studies on these taxa, what happens to their relative brain size during phyletic dwarfing is not well known, and results are sometimes conflicting. For example, relative brain size increase has been noted in the Sicilian dwarf elephant, Palaeoloxodon falconeri, whereas relative brain size decrease has been postulated for Malagasy dwarf hippos. Here, I perform an analysis of brain, skull, and body size of 3 insular elephants (Palaeoloxodon "mnaidriensis," P. tiliensis, and P. falconeri) and 3 insular hippos (Hippopotamus madagascariensis, H. lemerlei, and H. minor) to address this issue and to test whether relative brain size in phyletic dwarf species can be predicted. The results presented here show that the encephalization of all insular elephants and hippos is higher than that of their continental relatives. P. falconeri in particular has an enormous encephalization increase, which has so far not been reported in any other insular mammal. Insular brain size cannot be reliably predicted using either static allometric or ontogenetic scaling models. The results of this study indicate that insular dwarf species follow brain-body allometric relationships different from the expected patterns seen for their mainland relatives.

中文翻译：

---

大象和河马的矮化期间大脑的变化。

在所有已知的岛上哺乳动物中，河马和大象的体型极端降低，分别降至其祖先大陆大小的4％和仅有2％。尽管对这些分类单元进行了大量研究，但是在系统矮化期间它们相对大脑大小发生了什么尚不为人所知，并且有时会产生矛盾。例如，在西西里的矮人象Palaeoloxodon falconeri中已经注意到相对脑大小的增加，而对于马达加斯加矮人河马则假定相对脑大小的减小。在这里，我对3头岛屿象（Palaeoloxodon“ mnaidriensis”，P。tiliensis和P. falconeri）和3头岛河马（Hippopotamus madagascariensis，H。lemerlei和H）的大脑，头骨和体型进行了分析。次要）来解决这个问题，并测试是否可以预测系统矮人物种的相对大脑大小。此处显示的结果表明，所有孤立的大象和河马的脑性都高于其大陆亲属。尤其是falconeri的脑病化大大增加，到目前为止，在任何其他岛上哺乳动物中均未见报道。使用静态异体测量或个体发育缩放模型无法可靠地预测岛状大脑的大小。这项研究的结果表明，岛屿矮人物种遵循的脑体异形关系不同于其大陆亲属的预期模式。尤其是falconeri的脑病化大大增加，迄今为止，在任何其他岛屿哺乳动物中均未见报道。使用静态异体测量或个体发育缩放模型无法可靠地预测岛状大脑的大小。这项研究的结果表明，岛屿矮人物种遵循的脑体异形关系不同于其大陆亲属的预期模式。尤其是falconeri的脑病化大大增加，迄今为止，在任何其他岛屿哺乳动物中均未见报道。使用静态异体测量或个体发育缩放模型无法可靠地预测岛状大脑的大小。这项研究的结果表明，岛屿矮人物种遵循的脑体异形关系不同于其大陆亲属的预期模式。