Portrayals of these creatures generally show them with four short legs, large horns on their heads, and a long tail, usually with a saw-toothed backbone. It has been said that all mythology is based upon some reality. In this case I believe that the belief in Unktehi and similar creatures originated with observations of mammoth and mastodon fossils. Spring runoff erosion of riverbanks would occasionally have exposed the gigantic bones and skulls of these giant elephantids and, with no modern analog for the creature, the people would have figured out the best answer they could to them. In this case they assumed that they were found on the riverbank because they had lived in the river. Similarly, Inuit and other northern peoples usually believe that mammoth bones come from giant creatures which live underground because they find them weathering from the earth. In many of these beliefs the light of the sun is believed to be deadly to the creatures because by the time that they emerge to the light of day they only exist as bones or other remains. The abnormally large size of the bones on the riverbank would prove the gigantic size of the creatures. I believe that the idea of huge horns on their heads come from the tusks of the mammoths. Native American observers had no animal analog for the front-projecting tusks of an elephantid, instead they would assume that they projected upward like the horns of a bison, but immeasurably larger. Simply turn the mammoth skull upside down and there you have it, an immense skull with gigantic horns that stick up from the creature’s head.
Although called giant horned water serpents these creatures are usually portrayed as having short legs. Presumably, like the Sisiutl (see link below) that I posted about on May 1, 2010, they could grow legs whenever they wished. I believe that the myths of Unktehi and Uncegila represent the Native American’s creative solution to the questions raised by the giant fossils, and that portrayals of these myths provide the imagery in their art, including the rock art.