I have netflix, and every once in a while I happen upon a movie that I forgot I had placed in my instant queue. This happened last week and for two hours I watched a program about mammals. I love animals, so I thought the entire thing was just awesome, but I especially loved the beginning about mammals that still have their reptilian roots. There are only two mammals in the world that still lay eggs (as opposed to having live-births, like us humans for example). These are the Echidna and the Platypus. While both are interesting, I think the Platypus just looks a whole lot cooler.
Quick and dirty deal: The Platypus has a duck-bill, webbed feet, and a beaver-like tail. The first time a pelt was brought to Europe, people thought it was a hoax. It is the only member of its family and genus (talking in scientific terms here) and the males of the species are also somewhat venomous, with the ability to kill smaller animals and seriously incapacitate a human.
The males are larger than the females, but they all range between 15 and 24 inches long. They live exclusively in Tasmania and Eastern Australia, and can live to be 17 years old in captivity. They have been found as old as 11 in the wild. They are excellent swimmers and along with their fellow Monotremes (egg-laying mammals), use electrolocation to find food in the water, because they close their eyes.
A ton of interesting information can be found on the wikipedia article. Especially interesting are the bits about their sex chromosomes and the debate over "platypuses" or "platypi". They are luckily not considered an endangered species, because of the efforts to protect such a unique animal, and their tendency to remain aloof.
Platypus Wiki Info