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Late Permian cynodont fossil missing parietal foramen ("third eye")
A new paper:
Julien Benoit , Fernando Abdala, Marc J. Van den Brandt, Paul R.
Manger & Bruce S. Rubidge (2015)
Physiological implications of the abnormal absence of the parietal
foramen in a late Permian cynodont (Therapsida).
The Science of Nature 102:69
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.