Genus is not that important.

Well, pardon the cruddy .JPG quality, didn't have other copy of the file.

Anyway, simplified Tyrannosauridae. As you can see, both cladograms are identical, except for the genera used in binomial naming: One makes all genera monotypic, the other uses a broader definition; but, at the end, as long as it isn't paraphyletic, either result works.

Those are man-made cathegories to group populations of individual animals; species is not a real thing when you take geological time into account, much less ANY other taxonomical rank. One has to remember Linnaeus' ideas are not quite compatible with our modern "Evolution and Genetics" biology.