The sixth sense in mammalian forerunners: Variability of the parietal foramen and the evolution of the pineal eye in South African Permo-Triassic eutheriodont therapsids
The sixth sense in mammalian forerunners: Variability of the parietal foramen and the evolution of the pineal eye in South African Permo-Triassic eutheriodont therapsids
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DOI：
10.4202/app.00219.2015
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发表时间：
2016-12-01
影响因子：
1.8
通讯作者：
Rubidge, Bruce S.
中科院分区：
文献类型：
--
作者：
Benoit, Julien;Abdala, Fernando;Rubidge, Bruce S.
在一些现存的外温动物中，第三眼（或松果体眼）是一个感光器官，位于颅顶中线的顶骨孔内。松果体眼将有关暴露于阳光的信息发送到松果体复合体，松果体复合体是大脑中专门用于调节体温、生殖同步和生物节律的区域。顶骨孔在哺乳动物中是不存在的，但在大多数哺乳动物的最近灭绝的亲属中存在，兽孔目。一项广泛的调查的发生和大小的顶骨孔在不同的南非therapsid类群表明，随着时间的推移，顶骨孔往往，在一个收敛的方式，变得更小，更频繁地缺席在eutherocephalians（Akidnognathiidae，Whaitsiidae，和Baurioidea）和non-pellaliform eucynodonts。在后者中，Probainognathia是唯一一个完全丧失顶骨孔的物种，它是导致顶骨孔的谱系。这些结果提示松果体感光功能的逐渐和收敛性丧失和第三眼的退化。考虑到松果体器官在外温动物中实现微调温度调节的作用（即，虽然在哺乳动物祖先中，顶骨孔的逐渐消失可能与哺乳动物祖先从中温代谢向高代谢率（内温性）的转变有关，但在卡鲁地层序列中，顶骨孔随时间的推移而逐渐消失。眼睛中含有黑视素的视网膜神经节细胞的出现取代了松果体眼的感光作用，也可能伴随着松果体眼的丧失。
In some extant ectotherms, the third eye (or pineal eye) is a photosensitive organ located in the parietal foramen on the midline of the skull roof. The pineal eye sends information regarding exposure to sunlight to the pineal complex, a region of the brain devoted to the regulation of body temperature, reproductive synchrony, and biological rhythms. The parietal foramen is absent in mammals but present in most of the closest extinct relatives of mammals, the Therapsida. A broad ranging survey of the occurrence and size of the parietal foramen in different South African therapsid taxa demonstrates that through time the parietal foramen tends, in a convergent manner, to become smaller and is absent more frequently in eutherocephalians (Akidnognathiidae, Whaitsiidae, and Baurioidea) and non-mammaliaform eucynodonts. Among the latter, the Probainognathia, the lineage leading to mammaliaforms, are the only one to achieve the complete loss of the parietal foramen. These results suggest a gradual and convergent loss of the photoreceptive function of the pineal organ and degeneration of the third eye. Given the role of the pineal organ to achieve fine-tuned thermoregulation in ectotherms (i.e., "cold-blooded" vertebrates), the gradual loss of the parietal foramen through time in the Karoo stratigraphic succession may be correlated with the transition from a mesothermic metabolism to a high metabolic rate (endothermy) in mammalian ancestry. The appearance in the eye of melanopsin-containing retinal ganglion cells replacing the photoreceptive role of the pineal eye could also have accompanied its loss.