Physical Features of Bipedal Lizards
Researchers have concluded that bipedal motion is developed in species with already high-speed quadrupedal motion. While it is difficult to trace the phylogeny of this trait, the physical adaptations observed in species exhibiting bipedal behavior are much more apparent. Snyder and Laerm have noted that bipedal lizards also have longer hindlimbs than their strictly quadrupedal counterparts. In addition, Laerm notes that the crurotarsal joint is rotated which allows for the hindlimb to swing forward laterally. The tails of bipedal lizards also tend to be elongated, which enhances balance during bipedal motion.
An Evolutionary Spandrel
Since there are no real advantages in speed or locomotive costs to bipedalism, why is this behavior observed? Aerts et al. propose that bipedalism is an evolutionary spandrel, an analogy made famous by Gould and Lewonton.
In cathedrals, due to the construction of arches, there are unusually shaped and curved corners, or spandrels. Often these are decorated with unique and elaborate paintings that utilize the unique shape of the space. These spandrels were not created to house paintings and reliefs of unusual shapes, rather the artwork is designed to efficiently and aesthetically utilize this space. The style of artwork that adorns these spaces would not exist if the space was not there first. In a similar fashion, most researchers believe bipedalism has arisen as a consequence of certain morphological changes that have occurred first.
|Content by Juliana M. Arrighi and Mikella Procopio; Title photo by Marcel Burkhard|