@snekkes
Isn't T-rex the genus? We don't call female cats felis and felicia.
It was a joke about missing words, and the difference between grammatical gender and sex, and so on.
First of all, in the binomial classification system, the first word denotes the genus, and the second word is the species.
Let's take cats: Felis catus. Felis, variant nominative singular spelling of feles, -is, feminine third declension noun, Latin word for cat. All of the small ones (e.g. the black-footed cat, Scottish wildcats) are the genus Felis, but only the domesticated species is catus (catus= Latin adjective- clever; cattus=late Latin noun for cat).
No-one's worrying over the grammatical gender of either Felis or catus, because
a) there is nothing that sex-specific about any of the words used for its binomial classification and;
b) crucially no-one is going around talking about how their female Felis catus will only eat Sheba food. 
Cats are found the world over so every culture that values cats will have local words for them that predate Linnaeus's classification system, and local words for male cats, female cats and cute little baby cats.
I would say the English tend to call male cats boy cats or tomcats, especially unneutered males, and unneutered females are girl cats, or queens. And babies are kittens! There's simply no frustrating or amusing gap in vocabulary.
Now let's go back to the tyrannosaurs.
Tyrannosaurus is the genus (it's Greek origin and formulated to express tyrant lizard or terrible lizard, IIRC - I don't have a Greek dictionary or any knowledge of Greek beyond what I've picked up from children's books on paleontology!), and the species name is rex. But rex is Latin for king! (Rex, regis, third declension masculine noun)
And what with tyrannosaurs not being an everyday pet (thank the Maker!), we don't have a lay term for the species, never mind words for male tyrannosaurs, female tyrannosaurs or baby tyrannosaurs. So we're having to use the scientific term to talk about them. That's not necessarily a problem, because it's quite a fun word to say, but it does mean we are explicitly referring to all of this thankfully extinct species as male! Which seems somewhat implausible. Then again, maybe that's why they're all extinct... (Hmm, can I get a grant to investigate this?)
Which is just a little daft, when you notice it. So yes, why not call any female one Tyrannosaurus regina (regina= Latin for queen), at least in jest? It's a solution to that irksome gap.