placodes

Placodes (depicted above), like neural crest cells, are multipotent cells unique to vertebrates. Placodes are ectodermal in origin and can either be neurogenic or non-neurogenic. Neurogenic placodes give rise to nervous or sensory cranial structures. Non-neurogenic placodes, such as epidermal placodes, give rise to hair follicles, teeth, and feathers.

Photo Credit: Dr Mark Hill, UNSW Embryology

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Scales, Feathers and Hair Have a Common Ancestor

by NICHOLAS ST. FLEUR

Reptiles have scales. Birds have feathers. Mammals have hair.
How did we get them?

For a long time scientists thought the spikes, plumage and fur characteristic of these groups originated independently of each other. But a study published Friday suggests that they all evolved from a common ancestor some 320 million years ago.

This ancient reptilian creature — which gave rise to dinosaurs, birds and mammals — is thought to have been covered in scale-like structures. What that creature looked like is not exactly known, but the scales on its skin developed from structures called placodes — tiny bumps of thick tissue found on the surface of developing embryos.

Scientists had previously found placodes on the embryos of birds and mammals, where they develop into feathers and hairs, but had never found the spots on a reptilian embryo before. The apparent lack of placodes in present-day reptiles fueled controversy about how these features first formed…

(read more: NY Times)

photographs by Nicolas Di-Poï & Michel C. Milinkovitch