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Figure 1

From: Skeletal plasticity in response to embryonic muscular activity underlies the development and evolution of the perching digit of birds

Figure 1

Major transformations of Mt1 in the evolution of avian opposable hallux.

(a) Basal dinosaur exhibit the Mt1 (grey arrow) articulated to distal tarsals (Herrerasaurus); (b) Mt1 of basal tetanurans had lost its proximal epiphysis and articulated to Mt2 (Allosaurus); (c) Basal birds had the Mt1 articulated to the distal Mt2 (Archaeopteryx); (d) Most extant birds exhibit the hallux opposed to other toes, as observed in late chicken embryo (HH44); (e) Detail showing hallux inverted orientation.

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