The lion (Panthera leo) has long been know as the king of the jungle. It is the second largest cat, with males weighing in at 250 kg (550 lbs) and about 2 m (6 ft) in length. However, this is nothing compared to the ancient American lion, the largest lions ever to have existed at 300 kg (660 lbs) and 2.5 m (8 ft).
Most people know about the superb hunting skills that the lionesses practice, and that the males basically do nothing but defend their pride from other male lions. Lions are the only cat to have sexual dimorphism, as the males have a distinctive mane. Some relatively recent research had some interesting things to say about the mane, in terms of selection and possible purpose. They found that males with darker longer manes were more likely to win male competitions, and be successful at mating. So, males may be able to size up their competition by comparing manes. But, males with darker manes had more difficulties in hotter weather conditions, to the extreme that their sperm can be come deformed. Of course, there is the idea that having a handicap to over come means that you are very healthy, and would make a good mate (think peacock tails). The original study can be found here.