The third eye (pineal eye), an organ responsible for regulating exposure to sunlight in extant ectotherms, is located in an opening on the dorsal surface of the skull, the parietal foramen. The parietal foramen is absent in extant mammals but often observed in basal therapsids, the stem-group to true mammals. Here, we report the absence of the parietal foramen in a specimen of Cynosaurus suppostus, a Late Permian cynodont from South Africa (SA). Comparison with Procynosuchus delaharpeae, a contemporaneous non-mammalian cynodont from SA, demonstrates that the absence of this foramen is an abnormal condition for such a basal species. Because seasonality was marked during the Late Permian in SA, it is proposed that the third eye was functionally redundant in Cynosaurus, possibly due to the acquisition of better thermoregulation or the evolution of specialized cells in the lateral eyes to compensate for the role of the third eye.
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The authors thank Dr. Jashashvili (ESI) for CT scanning and Z. Erasmus for granting the access to the Iziko Museum collections. This research was conducted with the financial support from the DST/NRF Centre of Excellence in Paleosciences, the NRF African Origins Platform, and PAST (the Paleontological Scientific Trust) and its Scatterlings projects.
Conflict of interest
The authors declare no conflict of interest.
Communicated by: Robert Reisz
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Benoit, J., Abdala, F., Van den Brandt, M.J. et al. Physiological implications of the abnormal absence of the parietal foramen in a late Permian cynodont (Therapsida). Sci Nat 102, 69 (2015) doi:10.1007/s00114-015-1321-4
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