Ecomorphological characterization of the quadrate and the mandible in the impact blow in woodpeckers (Picidae)

Here we analyzed the quadrate articulations with the braincase and the caudal shape of the mandible in order to determine their involvement with the impact blow of woodpecker’s drilling habits. The skulls of 29 specimens of picids belonging to the subfamilies Picinae and Picumninae were examined, and a specimen of Colaptes campestris (Picinae) was dissected. It was found that the quadrate has a double articulation in its caudal portion with its inner part articulating with the basioccipital and exoccipital processes and the lateral part with the suprameatic process of the squamous. These processes are markedly developed in Picinae, the most specialized woodpeckers in the production of cavities, but not in Jynginae, who do not drill holes in the trees, but use existing holes. These features are not present in Picumninae, which are also able to drill, but have other characteristics that allow them to bore cavities in trees without their skull being damaged. In its articulation’s facet with the medial condyle of the quadrate the mandible of the Picinae and Picumninae did not present a caudal limit as it happens in other birds, forming below this facet there is a transverse flat surface where fibers of the mandibular depressor muscle are inserted . These results suggest that both the processes and their articulations with the quadrate bone, as well as the shape of the mandible, may have an important role in the absorption of the impact on the woodpeckers.