since beastmen were never much of an interest of mine, i'm not sure if they even use domesticated animals. the Warhammer wiki certainly implies they don't. but perhaps Lustrian beastmen include members that are more/less altered (depending on your opinion as to how beastmen originate) and thus include some that are indistinguishable from the regular animals until you get right up close. interestingly Toxodon wasn't related to Rhinos. it was one of those convergent evolution situations. the Notoungulata was a distinctly south american linage that diverged from the rest of the ungulates 57 some million years before. and a more modern reconstruction: