CRONETTE BIRD CODE
The color code is the same as in the Fig. 4. (B) Linear measurements on the phalanges, calculated from the 3D landmarks. Ungual phalanx: base – middle of the ventral face and – middle of the dorsal face – top of the tubercle – apex of the phalanx. For all the toes, all the phalanges except the ungual were measured in the same way: base – middle of the ventral face and middle of the dorsal face head of the phalanx – lateral point and – medial point. Digits II, III IV: lateral and medial point. Digit I: on the proximal end, proximal and dorsal points and on the middle of the distal side of the trochlea, lateral and medial points dorsally.
Measurements: (A) 3D schematic representation of the 3D landmarks on the specimens: Distal metatarsus. In all cases, the functional result is the same tool, a pincer-like foot.įeet functional morphology grasping osteology. The second pattern is unique for the clade and under muscle-morphogenetic control. The first pattern is convergent and common among tetrapods and follows rules of skeletal development.
In the two other cases (heterodactyl and zygodactyl) that have two toes that point backward, the hallux is rather small in contrast to the other backward-pointing toe, which is enlarged. Moreover, a proximo-distal gradient in phalanx size is observed depending on the degree of terrestriality. In the anisodactyl foot, the hallux is the only backward-oriented toe and is enlarged in climbing species and reduced in terrestrial ones. Our data on the proportions of the phalanges analyzed in a phylogenetic context show that two different morphological patterns exist that depend mainly on habitat and toe orientation. In birds, foot morphology is highly variable, with different orientations of the toes, making it a good model for the study of the role of functional, developmental, and phylogenetic constraints in the evolution of phenotypic diversity.
This is especially true for bipedal and arboreal species living in a complex three-dimensional environment that likely induces strong selection on foot morphology. The feet are the only contact between the body and the substrate in limbed animals and as such they provide a crucial interface between the animal and its environment.
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