Dome-headed, small-brained island mammal from the Late Cretaceous of Romania
Dome-headed, small-brained island mammal from the Late Cretaceous of Romania
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DOI：
10.1073/pnas.1801143115
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发表时间：
2018-05-08
影响因子：
11.1
通讯作者：
Norell, Mark A.
中科院分区：
文献类型：
--
作者：
Csiki-Sava, Zoltan;Vremir, Matyas;Norell, Mark A.
岛屿效应是一种众所周知的进化现象，与大陆近亲相比，孤立于资源有限环境中的海岛物种经常改变它们的大小、解剖和行为。这在现代和新生代哺乳动物中得到了很好的记录，但尚不清楚更古老、更原始的中生代哺乳动物是否以类似的方式对岛屿栖息地做出反应。我们描述了一个相当完整和保存完好的kogaionid骨骼，这是白垩纪居住在岛屿上的多瘤哺乳动物的一种神秘的辐射，以前以零碎的化石为代表。这具骨架来自罗马尼亚最新的白垩纪，属于一个以前未被报道的属和物种，具有几个异常特征，包括一个自动变形的穹顶头骨和任何高级哺乳动物中相对于身体大小最小的大脑之一，但它仍然保留着扩大的嗅球和副丘脑用于感觉处理。根据与更新的岛屿哺乳动物的相似之处，我们将这些不寻常的神经感觉特征解释为与岛屿效应有关。这表明，适应岛屿环境的能力在哺乳动物历史的早期就已经形成，在兽类哺乳动物出现之前，具有与岛屿相关的修改的哺乳动物是众所周知的矮化恐龙动物群的关键组成部分。此外，该标本表明，大脑尺寸的缩小与感觉敏锐度的提高有关，但没有明显的身体大小变化，这是哺乳动物孤岛效应的一种新表现。
The island effect is a well-known evolutionary phenomenon, in which island-dwelling species isolated in a resource-limited environment often modify their size, anatomy, and behaviors compared with mainland relatives. This has been well documented in modern and Cenozoic mammals, but it remains unclear whether older, more primitive Mesozoic mammals responded in similar ways to island habitats. We describe a reasonably complete and well-preserved skeleton of a kogaionid, an enigmatic radiation of Cretaceous island-dwelling multituberculate mammals previously represented by fragmentary fossils. This skeleton, from the latest Cretaceous of Romania, belongs to a previously unreported genus and species that possesses several aberrant features, including an autapomorphically domed skull and one of the smallest brains relative to body size of any advanced mammaliaform, which nonetheless retains enlarged olfactory bulbs and paraflocculi for sensory processing. Drawing on parallels with more recent island mammals, we interpret these unusual neurosensory features as related to the island effect. This indicates that the ability to adapt to insular environments developed early in mammalian history, before the advent of therian mammals, and mammals with insular-related modifications were key components of well-known dwarfed dinosaur faunas. Furthermore, the specimen suggests that brain size reduction, in association with heightened sensory acuity but without marked body size change, is a novel expression of the island effect in mammals.