the mostoverbearing and aggressively pushy leader of the entire of a gendersaurus clan, usually in a big city. A gendersaurus rex is often the most masculine and the most ill-fated shemale in any major city, where they like to gang up on straight cisgendered folks. Not to mention they keep their sex slaves captive (watch out, they will steal ur boyfriends!).
straight girl: hey, have u heard about this new shemale in town?
tomgirl: oh yeah, girlfriend. she should probably be the new gendersaurus rex in L.A.
describes a shemale that is very very tall and/or heavyset (i.e. giant hands, large ass fake tits, adam's apple thats bigger than their balls, etc). Usually, a gendersaurus has an aggresive (and frequently) a bitchy manner.
real girl 1: *sees a gendersaurus walking down the street* AHHHHH!!!! LOOK OUT!!! ITS A GENDERBEAST!