American alligator ultrasound and microCT

Unlike the majority of sauropsids, which breathe primarily through costal and abdominal muscle contractions, extant crocodilians have evolved the hepatic piston pump, a unique ventilatory mechanism powered by the diaphragmaticus muscle. This muscle attaches to the pelvis and the liver, pulling the liver and viscera caudally during inspiration and lowering pressure in the pleuroperitoneal cavity, helping to inflate the lungs. It has been hypothesized that the hepatic piston pump is coupled to modifications in the axial skeleton that result in a smooth interior thoracic ceiling, facilitating craniocaudal translation of the viscera during ventilation. We assess this using ultrasound video to visualize the hepatic-piston apparatus in breathing sub-adult and adult individuals (n = 7) of the American alligator (Alligator mississippiensis). The magnitude of displacement of the liver was calculated by measuring the distance between the most cranial and most caudal positions of the liver during ...