We present the first description of the endocranial cast of the small raoellid artiodactyl Indohyus indirae. Raoellidae are sister group to Cetacea and the new morphological observations allow for outlining some of the early steps of the evolutionary history of the cetacean brain. The combination of primitive artiodactyl features and typical cetacean characters is unique about the Indohyus endocast. The fact that it presents the symplesiomorphic brain pattern observed in earliest Artiodactyla indicates that the cetacean brain derives from a very simple, plesiomorphic brain, with simple neocortical folding pattern, widely exposed midbrain, and concurrent small neocortex expansion. On the other hand, the Indohyus endocast shows characters that also occur in early cetaceans. These include modifications of the olfactory tract with narrow, elongated olfactory bulbs and peduncles, accompanied by a posterior location of the braincase in the cranium. The derived endocranial cast features of Indohyus mainly reflect changes in cranial architecture and these are most probably associated with modifications of the masticatory apparatus and a shift in diet. Indohyus meninges were very thin like in most terrestrial artiodactyls and it had no extensive rostral or lateral retia mirabilia. It however shows a branching pattern of ramification of intraosseous blood sinuses above the cerebellum that might represent the initial development of the caudal venous rete mirabile that would have colonized the endocranial cavity later on, in early archaeocetes.

我们目前的小raoellid偶蹄动物的endocranial投的首次描述印多霍斯indirae。Raoellidae是鲸类的姊妹群，新的形态学观察结果概述了鲸类脑进化史的一些早期步骤。的原始偶蹄动物功能和典型鲸类字符的组合是关于独特印多霍斯endocast。它呈现出最早在Artiodactyla中观察到的全形大脑模式的事实表明，鲸类大脑起源于一个非常简单的全形大脑，具有简单的新皮层折叠模式，广泛暴露的中脑和并发的小新皮层扩张。另一方面，Indohyus内播显示的字符也出现在早期的鲸类动物中。这些措施包括用狭窄，细长的嗅球和花梗修饰嗅觉通道，并在颅骨中放置大脑箱的后部位置。的派生endocranial铸造设有印多霍斯主要体现在颅架构的变化和这些是最可能与咀嚼装置的修改和饮食的移位相关联。印度支那脑膜非常薄，就像大多数陆生动植物一样，它没有广泛的延髓或侧生尿道反射。然而，它显示了小脑上方骨内血窦分支的分支模式，这可能代表了尾静脉静脉网状奇迹的最初发展，而后者后来将在早期的考古古迹中定居在颅内腔中。