Department of Anatomy, New York Institute of Technology College of Osteopathic Medicine, Old Westbury, NY, USA.
Center for Biomedical Innovation, New York Institute of Technology College of Osteopathic Medicine, Old Westbury, NY, USA.
Proc Biol Sci. 2022 May 25;289(1975):20220245. doi: 10.1098/rspb.2022.0245. Epub 2022 May 18.
No vertebrate, living or extinct, is known to have possessed an odd number of limbs. Despite this 'forbidden phenotype', gaits that use odd numbers of limbs (e.g. tripedalism or pentapedalism) have evolved in both avian and mammalian lineages. Tripedal locomotion is commonly employed by parrots during climbing, who use their beaks as an additional support. However, it is unclear whether the beak functions simply as a stabilizing hook, or as a propulsive limb. Here, we present data on kinetics of tripedal climbing in six rosy-faced lovebirds (). Our findings demonstrate that parrots use cyclical tripedal gaits when climbing and the beak and hindlimbs generate comparable propulsive and tangential substrate reaction forces and power. Propulsive and tangential forces generated by the beak are of magnitudes equal to or greater than those forces generated by the forelimbs of humans and non-human primates during vertical climbing. We conclude that the feeding apparatus and neck flexors of parrots have been co-opted to function biomechanically as a propulsive third limb during vertical climbing. We hypothesize that this exaptation required substantive alterations to the neuromuscular system including enhanced force-generating capabilities of the neck flexors and modifications to locomotor central pattern generators.
已知没有任何脊椎动物，无论是现存的还是已灭绝的，拥有奇数数量的肢体。尽管存在这种“被禁止的表型”，但鸟类和哺乳动物的谱系中都进化出了使用奇数数量肢体的步态（例如三足步态或五足步态）。三足运动在鹦鹉攀爬时经常被使用，它们用喙作为额外的支撑。然而，目前尚不清楚喙的作用是简单地作为稳定钩，还是作为推进肢体。在这里，我们提供了关于六种玫瑰脸爱情鸟（）三足攀爬运动学的数据。我们的发现表明，鹦鹉在攀爬时使用周期性的三足步态，喙和后肢产生相当的推进和切向基质反作用力和功率。喙产生的推进力和切向力的大小与人类和非人类灵长类动物在垂直攀爬时前肢产生的力相等或更大。我们得出的结论是，鹦鹉的进食器官和颈部屈肌已被协同作用，在垂直攀爬时作为一个推进的第三肢体发挥生物力学功能。我们假设这种适应需要对神经系统进行实质性的改变，包括增强颈部屈肌的产生力的能力和对运动中枢模式发生器的修改。
