Combating Water Loss

Another key to the survival and continuance of early tetrapods was the adaptation of ways to avoid water loss and the effects of dry air. If there were no fossil evidence available for the earliest land animals, paleontologists might imagine that a successful biological scheme would have been to retain the tough outer covering of dermal scales found in these animals' fish ancestors. Curiously, the fossil record disputes this imagined scheme. Remains of the earliest tetrapods show that they were only partially covered with scales, usually on their bellies and probably as a way to protect themselves from scrapes and abrasions while crawling on the ground. The dorsal, or top, side of these earliest tetrapods was not protected by a hard outer covering and probably was more like the soft, moist skin of modern amphibians. While later tetrapods did indeed develop semipermeable skin and even scales to protect against water loss, the earliest tetrapods probably lived their lives in and out of shallow waters and also benefited from a highly humid, moist atmosphere that slowed the effects of desiccation.

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