title: Physiological implications of the abnormal absence of the parietal foramen in a late Permian cynodont (Therapsida).
abstract: 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.
authors.affiliation: Evolutionary Studies Institute (ESI), School of Geosciences, University of the Witwatersrand, Braamfontein, 2050, Johannesburg, South Africa. amlc80@hotmail.fr.|School of Anatomical Sciences, University of the Witwatersrand, 7 York Road, Parktown, 2193, Johannesburg, South Africa. amlc80@hotmail.fr.
authors.forename: Julien
authors.initials: J
authors.lastname: Benoit
authors.affiliation: Evolutionary Studies Institute (ESI), School of Geosciences, University of the Witwatersrand, Braamfontein, 2050, Johannesburg, South Africa.
authors.forename: Fernando
authors.initials: F
authors.lastname: Abdala
authors.affiliation: Evolutionary Studies Institute (ESI), School of Geosciences, University of the Witwatersrand, Braamfontein, 2050, Johannesburg, South Africa.
authors.forename: Marc J
authors.initials: MJ
authors.lastname: Van den Brandt
authors.affiliation: School of Anatomical Sciences, University of the Witwatersrand, 7 York Road, Parktown, 2193, Johannesburg, South Africa.
authors.forename: Paul R
authors.initials: PR
authors.lastname: Manger
authors.affiliation: Evolutionary Studies Institute (ESI), School of Geosciences, University of the Witwatersrand, Braamfontein, 2050, Johannesburg, South Africa.|School for Geosciences, University of the Witwatersrand, Braamfontein, 2050, Johannesburg, South Africa.
authors.forename: Bruce S
authors.initials: BS
authors.lastname: Rubidge
mesh_terms: D000818:Animals; D005580:Fossils / Q000033:anatomy & histology*; D008116:Lizards / Q000033:anatomy & histology* / Q000502:physiology; D010870:Pineal Gland / Q000033:anatomy & histology; D012044:Regression Analysis; D013019:South Africa; D014057:Tomography, X-Ray Computed
keywords: Cynodontia; Paleoneurology; Parietal foramen; Pineal; Therapsida; Thermoregulation