 The first specimen , AMNH 5240 , was discovered in 1911 by Barnum Brown in Red Deer River , Alberta , Canada , and secured by him in the Fall of 1912 . As well as an almost complete skeleton , the find was notable because impressions of much of the creature 's skin had also survived . The specimen came from the <unk> River Group of the province . The left or underside of the skeleton was preserved in <unk> clay , making it difficult to expose the skin . The skeleton was articulated , and only missing about the last 0 @.@ 61 metres ( 2 @.@ 0 ft ) of the tail and the forelimbs . Both <unk> and <unk> are preserved in position , but the rest of the forelimbs are gone , except for phalanges and pieces of <unk> , <unk> and radii . Apparently the remaining forelimbs were weathered or eroded away . <unk> of the integument were preserved covering over a large part of the skeletons outlining , and shows the form of the body . Another specimen , AMNH <unk> , was found in 1914 by Brown and Peter <unk> . Both specimens are now housed in the American Museum of Natural History in their original death poses . 
