Developmental Biology III

November 25, 2011

Evolution of morphology

Tamura K, Nomura N, Seki R, Yonei-Tamura S, Yokoyama H
Embryological evidence identifies wing digits in birds as digits 1, 2, and 3.
Science 331: 753-757, 2011

Before you read this paper

What's the matter with the digit identities of bird wing? Participants to this class may have this question. It is indeed a big matter for developmental biology and paleontology.

For many years, there has been considerable controversy regarding bird wing digit identity. Embryological evidence has suggested that these digits represent digits 2, 3, and 4 in the pentadactyl ground state, whereas the fossil record supports a pattern of posterior digit reduction in the theropod ancestors of birds and predicts the bird digits to represent digits 1, 2, and 3. This study examined the developmental mechanism of the posterior-most (third) digit in the chick wing and found that this digit was not developmentally comparable to digit 4 in the chick hindlimb but should instead be defined as digit 3. These findings reconcile developmental patterns with comparative morphological data, and resolve the long disputation regarding the phylogenic relationships between birds and their dinosaur ancestors. A following paper would help you to take a glance at the long debate about the identities of avian hand digits.