Noninvasive computed tomography (CT) scanning techniques performed on the high-quality preserved holotypes of Mendozahippus fierensis (grouped within the paraphyletic ‘Notohippidae’) and Gualta cuyana (Leontiniidae) allowed a thorough description of both endocasts, not only associated with the brain but also with closely related endocranial spaces, which proved to be highly diagnostic among Notoungulata and relevant from a paleobiological perspective. The specimens come from Quebrada Fiera (Mendoza, Argentina), an upper Oligocene locality extensively studied, especially during the last decade. Regarding brain endocast proportions and neocortical complexity, M. fierensis shows morphological affinities to coeval ‘notohippids,’ whereas G. cuyana resembles Leontinia gaudryi. An acute olfaction is inferred from the large olfactory bulbs and piriform lobes. Conversely, evidence concerning the development (and implications) of some necortical areas (i.e., somatosensory cortex and auditory cortex) were inconclusive. The encephalization quotients are around those previously reported for ‘notohippids’ and Toxodontidae Nesodontinae, and slightly lower than in Typotheria (except for Mesotheriidae). Other endocranial traits previously unexplored (such as the transverse diploic communication between the temporal sinuses in M. fierensis and the large temporal sinuses inferred for G. cuyana) show that there is relevant variability within Toxodontia that deserves further research. Extending similar approaches to early diverging taxa will certainly contribute to a better understanding of the morphological evolution of the brain, special sense organs, and associated blood circulation pattern in toxodontians and notoungulates in general.

对高质量保存的Mendozahippus fierensis（分组在“共生” Notohippidae”内）和Gualta cuyana（Leontiniidae）的高质量完整型进行的无创计算机断层扫描（CT）扫描技术可以对这两种内cast物进行详尽的描述，不仅与大脑有关，而且与脑内有关具有紧密相关的颅内间隙，这在Notoungulata中被证明是高度诊断性的，并且从古生物学的角度来看是相关的。这些标本来自Quebrada Fiera（阿根廷门多萨），这是渐新世上层地区，经过广泛研究，尤其是在最近十年中。关于脑内投射的比例和新皮质的复杂性，Fierensis表现出对同代“ notohippids”的形态亲和力，而G. cuyana类似于Leontinia gaudryi。从大的嗅球和梨状叶推断出急性嗅觉。相反，有关某些皮质区域（即体感皮层和听觉皮层）发育（和影响）的证据尚无定论。脑化商大约是以前报道的“线虫类”和弓形虫科的齿状商，并且比伤寒属（Typotheria）略低（除Mesotheriidae外）。其他endocranial性状前所未见的（如在时间鼻窦之间的横向障通信M. fierensis和大颞鼻窦推断为G. cuyana）表明弓形虫内存在相关的变异性，值得进一步研究。将相似的方法扩展到早期发散的分类单元肯定会有助于更好地理解弓形虫和一般非弓形虫的大脑，特殊感觉器官以及相关的血液循环模式的形态演变。