According to Wikipedia, the class Mammalia has 29 orders (e.g. Carnivora), 156 families (e.g. Ursidae), 1258 Genera (e.g. Ursus), and nearly 6000 species (e.g. Polar Bear). Some orders like Chiroptera (bats) and Rodentia are very large with many families, genera, and species. Some are really small like Orycteropodidae, which has only one species – the aardvark. Humans are in the order Primates, of which there are quite a few families and genera. Almost all of them live in tropical or subtropical areas and almost all of them have small populations, many of them endangered. The exception of course is humans who is the only species remaining of the genus homo. The other genera in the great ape family hominidae – gorillas, orangutans, chimpanzees, and bonobos – are all in big trouble.
I think most people would attribute the incomparable success of humans to their resilience, intelligence, and ingenuity. However, another important factor could be their bottomless capacity for intentional cruelty. Although there seems to be a decline in violence throughout history as documented in Steven Pinker’s recent book, there are still no shortages of examples. Take a listen to this recent Econtalk podcast with Mike Munger on how the South rationalized slavery. It could very well be that what made modern humans dominate earth and wipe out all the other homo species along the way was not that they were more intelligent but that they were more cruel and rapacious. Neanderthals and Denisovans may have been happy sitting around the campfire after a hunt, while humans needed to raid every nearby tribe and kill them.