inherited swim bladders that opened to the esophagus and were capable of functioning as lungs (a condition still found in lungfish and some physostome ray-finned fishes), allowing them to hunt in stagnant water or in waterways where rotting vegetation would have lowered oxygen content. The earliest forms, such as Acanthostega, had vertebrae and limbs quite unsuited to life on land. This is in contrast to the earlier view that fish had first invaded the land—either in search of prey like modern mudskippers, or to find water when the pond they lived in dried out. Early fossil tetrapods have been found in marine sediments, suggesting marine and brackish areas were their primary habitat. This is further corroborated by fossils of early labyrinthodonts being found scattered all around the world, indicating they must have spread by following the coastal lines rather than through freshwater only. The first labyrinthodonts were all large to moderately large animals, and would have suffered considerable problems on land despite their members ending in toes rather than fin-rays. While they retained gills and fish-like skulls and tails with fin rays, the early forms can readily be separated from Rhipidistan fish by the cleithrum/scapula complex being separate from the skull to form a pectoral girdle able to carry the weight of the front end of the animals. They were all carnivorous, initially eating fish and possibly going ashore to feed off washed up carrion of sea animals caught in tidal ponds, only later turning into predators of the large invertebrates of the Devonian at the waters edge. The various early forms are for convenience grouped together as Ichthyostegalia. While the body shape and proportions of the ichthyostegalians went largely unchanged throughout their evolutionary history, the limbs underwent a rapid evolution. The proto-tetrapods like from Elginerpeton and Tiktaalik had extremities ending in fin-rays with no clear fingers, primarily suited for movement in open water, but also capable of propelling the animal across sandbanks and through vegetation filled waterways. Ichthyostega and Acanthostega had paddle-like polydactyl feet with stout bony toes that also would have enabled them to drag themselves across land. The aquatic ichthyostegalians flourished in tidal channels and swampland through the remainder of the Devonian, only to disappear from the fossil record at the transition to the Carboniferous. Onto land The end of the Devonian saw the late Devonian extinction event, followed by a gap in the fossil record of