Figure 6
From: Developmental mechanisms underlying webbed foot morphological diversity in waterbirds
Scenario of webbed foot evolution in birds. The lobate feet observed in the common coot and little grebe were probably created through distinct developmental processes. The lobate foot of the common coot may have evolved through proliferation of interdigital tissue cells that express Gremlin1 along the toes in an anisodactyl-footed ancestor. On the other hand, the little grebe’s locate foot may have arisen by loss of Gremlin1 expression at the centre of the interdigital tissues of a palmate-footed ancestor. Although Gremlin1 is expressed in all St. 31 interdigital tissues in the totipalmate-footed great cormorant, its expression disappears in the centre of the interdigital tissues at St. 33. This suggests that the webbing of the great cormorant may have arisen through a distinct developmental mechanism, where BMP signaling plays a fundamental role.
