While many well-conceived studies have been conducted on unidirectional suction flow systems, both in fishes and larval salamanders, our biomechanical knowledge on bidirectional systems, although used by a great variety of aquatic tetrapods, is lagging behind. Metamorphosed amphibians and other tetrapods with reduced gills and closed gill slits evolved a bidirectional suction flow system where the inflowing water is first stored in the expanded pharyngo-esophageal cavity and then slowly released through the slightly opened mouth again.
Obviously, such a unidirectional suction flow is restricted to animals with gills and gill slits, such as fishes or larval amphibians. Such an expansion causes the prey and surrounding water to accelerate into the gaping mouth, and the engulfed water is then expelled through the gill slits. Most suction feeding fish species use a fast motion of the hyoid and abduction of the gill cover as the main contributor to suction generation by oropharyngeal expansion. The widespread use of suction feeding among aquatic vertebrates proves that it is a very effective way to capture a wide range of prey. Owing to the incompressibility of water, this expansion causes prey and surrounding water to be drawn into the open mouth, a behaviour referred to as suction feeding.
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We hypothesize that this modified way of generating suction is primitive for salamanders, and that this behaviour could have played an important role in the evolution of terrestrial life in vertebrates by releasing mechanical constraints on the hyobranchial system.Ī key component of aquatic prey capture in most vertebrates is an explosive expansion of the oropharyngeal cavity by a series of coordinated movements of head parts. Computational fluid dynamics simulations, based on three-dimensional morphology and kinematical data from high-speed videos, indicate that the viscerocranial elements mainly serve to accommodate the water that was given a sufficient anterior-to-posterior impulse beforehand by powerful jaw separation. davidianus uses an alternative suction mechanism that mainly relies on accelerating water by separating the ‘plates’ formed by the long and broad upper and lower jaw surfaces. Compared with fish and previously studied amphibians, A. Here, we study the cranial morphology, as well as kinematic and hydrodynamic aspects related to prey capture in the Chinese giant salamander ( Andrias davidianus). Unfortunately, little is known about the interplay between jaws and hyobranchial motions to generate bidirectional suction flows. Such a shift can still be observed during metamorphosis of salamanders, although many adult salamanders retain their aquatic lifestyle and feed by high-performance suction. During the evolutionary transition from fish to tetrapods, a shift from uni- to bidirectional suction feeding systems followed a reduction in the gill apparatus.