Panthera atrox controversy

This used to be called the American lion. Now some people think that it is a giant jaguar rather than a lion. It is a mystery to be solved.

I hadn't heard it was believed to be a jaguar. It has always been a lion to me (either a subspecies of the living P. leo or a species in its own right). A 2009 paper which looked into the mitochondrial DNA of the various extant and extinct lions show that it is a lion: http://www.uni-mainz.de/FB/Biologie/Anthropologie/MolA/Download/Barnett et al. 2009.pdf