Meeting Abstract
Among all vertebrates, crocodylians are thought to be unique in lacking a pineal gland. This is despite the possession of well-developed pineal glands in birds, their closest living sister group, and evidence for a pineal gland across extinct archosauriforms in the form of a pineal fossa or foramen. Crocodylians do, however, demonstrate a rhythmic melatonin cycle. Previously, we demonstrated that the crocodylian Harderian gland, as in other tetrapods including birds, forms part of a Harderian-retinal-hypothalamic axis (HaH) that rhythmically secretes melatonin along a circadian cycle. Crocodylians, as archosaurs, share with birds a similar secretory and immunological nature and a similar vascular network supplying and draining the Harderian gland. During our earlier studies we found gross and histological evidence of a follicular “pineal” gland in Alligator with pinealcytes similar in appearance to the follicular nature of the gland in basal birds. The use of iodine-enhanced micro-CT imaging has further evidenced a pineal gland in Alligator mississippiensis. We are currently conducting a more extensive analysis of this structure in other species of Crocodylia via micro-CT (Caiman crocodilus) and digitization (C. crocodilus and Crocodylus niloticus) using a digital capture station and specimens from the R. Glenn Northcutt Comparative Collection of Vertebrate Neuroanatomy and Embryology; this is part of a larger effort to create a comparative digital neuroanatomy database and atlas and demonstrates its vital use as a tool in the study of brain evolution.
