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The highly conserved nature of this system suggests that even aquatic Osteichthyes have some need for a surfactant system, which may seem strange as there is no gas underwater.
In Lampreys, this mechanism takes the form of a "cough", where the lamprey shakes its body to allow water flow across its gills.
Presumably, the tracks were made by animals walking along the bottoms of shallow bodies of water.
The specific aquatic ancestors of the tetrapods, and the process by which land colonization occurred, remain unclear, and are areas of active research and debate among palaeontologists at present.
The lung/swim bladder originated as an outgrowth of the gut, forming a gas-filled bladder above the digestive system. The heavy scale armour of the early bony fishes would certainly weigh the animals down.
In its primitive form, the air bladder was open to the alimentary canal, a condition called physostome and still found in many fish. In cartilaginous fishes, lacking a swim bladder, the open sea sharks need to swim constantly to avoid sinking into the depths, the pectoral fins providing lift.
The cartilaginous fishes do not have such an anchoring for the pectoral fins.
This allowed for a movable joint at the base of the fins in the early bony fishes, and would later function in a weight bearing structure in tetrapods.In cartilaginous fishes and teleosts, the heart lies low in the body and pumps blood forward through the ventral aorta, which splits up in a series of paired aortic arches, each corresponding to a gill arch.The aortic arches then merge above the gills to form a dorsal aorta supplying the body with oxygenated [email protected] Hi Guys an Sonia living in Ghana and working. I would like to meet single men who are serious minded, responsible, matured,trustworthy,warmhearted and kind to people.We can start dating and who knows, it will lead to something else! Disclaimer: This is a free online dating website trial for Asklovedr.In lungfishes, bowfin and bichirs, the swim bladder is supplied with blood by paired pulmonary arteries branching off from the hindmost (6th) aortic arch.