Researchers in support of this model have suggested that "Archaeopteryx" possessed skeletal features similar to those of modern birds. The first such feature to be noted was the supposed similarity between the foot of "Archaeopteryx" and that of modern perching birds. The hallux, or modified of the first digit of the foot, was long thought to have pointed posterior to the remaining digits, as in perching birds. Therefore, researchers once concluded that "Archaeopteryx" used the hallux as a balancing mechanism on tree limbs. However, study of the Thermopolis specimen of "Archeopteryx", which has the most complete foot of any known, showed that the hallux was not in fact reversed, limiting the creature's ability to perch on branches and implying a terrestrial or trunk-climbing lifestyle.