Pteranodon
Pteranodon (; from Greek πτερόν ( pteron, "wing") and ἀνόδων (anodon, "toothless") is a genus of pterosaur that included some of the largest known flying reptiles, with wingspans over 8 meters (26 feet). They lived during the late Cretaceous geological period of North America in present-day Kansas, Alabama, Nebraska, Wyoming, and South Dakota. More fossil specimens of "Pteranodon" have been found than any other pterosaur, with about 1,200 specimens known to science, many of them well preserved with nearly complete skulls and articulated skeletons. It was an important part of the animal community in the Western Interior Seaway.
Hyracodon
It was a lightly built, pony-like mammal of about 1.5 m (5 ft) long. "Hyracodon"'s skull was large in comparison to the rest of the body. "Hyracodon's" dentition resembled that of later rhinoceroses, but it was a much smaller animal and differed very little in appearance from the primitive horses of which it was a contemporary (32–26 million years ago). It had a short, broad snout and its long, slender limbs had three digits.
Like the primitive horses, hyracodonts inhabited open forests and wooded steppes and turned from browsing foliage to grazing grass. They died out without leaving any descendants and they mark the end of the phylogenetic branch of hornless, running rhinoceroses.