Thoracic adaptations for ventilation during locomotion in humans and other mammals

Bipedal humans, like canids and some other cursorial mammals, are thought
to have been selected for endurance running, which requires the ability to
sustain aerobic metabolism over long distances by inspiring large volumes
of air for prolonged periods of time. Here we test the general hypothesis
that humans and other mammals selected for vigorous endurance activities
evolved derived thoracic features to increase ventilatory capacity. To do
so, we investigate whether humans and dogs rely on thoracic motion to
increase tidal volume during running to a greater extent than goats, a
species that was not selected for endurance locomotion. We found that
while all three species use diaphragmatic breathing to increase tidal
volume with increasing oxygen demand, humans also use both dorsoventral
and mediolateral expansions of the thorax. Dogs use increased dorsoventral
expansion of the thorax, representing an intermediate between humans and
goats. 3D analyses of joint morphology of 10 species across four mammalian
orders also show that endurance-adapted cursorial species independently
evolved more concavo-convex costovertebral joint morphologies that allow
for increased rib mobility for thoracic expansion. Evidence for similarly
derived concavo-convex costovertebral joints in Homo erectus corresponds
with other evidence for the evolution of endurance running in the genus
Homo.