Paleontologists have found the most complete skeleton ever of a dimetrodon, the famous animal with a huge sail on its back, in Texas.  Dimetrodons are often mistaken for dinosaurs, but they in fact predated the dinos by a large number of years.  The fossil was unearthed in an ancient sinkhole which has been yielding dimetrodon bones for over 100 years, but never one so complete.  Scientists are still exposing more of the remains as of press time, and the creature has been nicknamed "Wet Willi" in honor of Samuel Williston, the paleontologist who first worked at the site.  Dimetrodons were about the size of a tiger and were the largest predator in Texas in their day, about 287 million years ago, millions of years before the first dinosaur walked the Earth.  They are classified as synapsids, a group which includes modern-day mammals, and were identified by a large fin, or sail, along their backs.  The purpose of the sail is unknown, but speculation about it has sparked many heated discussions among scientists.  It has been thought to be some sort of "radiator" which allowed the animal to take in and get rid of heat, but the most recent argument has involved the sail being able to change colors, making it useful in warding off intruders or in mating rituals.