Forget Anastasia and Christian. Nothing says Valentine’s Day like dinosaur porn. What’s not to like? It’s so much more fun than Fifty Shades, more sex-positive – and much pervier. With short stories including Taken by the T-Rex, Ravished by Triceratops and In the Velociraptor’s Nest, it takes dinomania to a whole new level, while also possibly answering the question “why did dinosaurs become extinct”? (Interspecies confusion.)

Why go to all the bother of taming the monster inside Christian Grey when – since it’s all imaginary anyway – you could get it on with an actual monster? It’s part of a larger genre of “monster erotica”, which also includes girl-on-centaur, girl-on-satyr and guy-on-pterodactyl action (in Pterodactyl Turned Me Gay, a title surely beloved of the Christian right and containing the immortal line: “I was covered from head to toe with the pterodactyl cum”). Dino erotica sits comfortably in the context of Greek mythology, where interspecies mingling was quite the thing. And don’t forget that EL James’s work began its life as fan fiction for Twilight, which was girl-on-vampire. Monsters, all.

Shaggy love … monster romance in pop culture goes all the way back to King Kong. Photograph: Everett Collection/Rex

With a heavy reliance on plots depicting independent and resourceful warrior women in rabbit-skin bikinis, grunting cavemen with ineffectual spears and oversized scaly creatures softened by feminine allure, it is pop culture central. References include the sexy lizards of V, King Kong, Godzilla, One Million Years BC, the supermodel-style aliens of the remade Battlestar Galactica, the stealthy reptilification of the crew of the Starship Enterprise and Benedict Cumberbatch as Smaug.

Plots are usually variations on: dinosaur creates perilous situation for pre-modern community; perilous situation is resolved by plucky athletic girl making out with the dinosaur. (Although The Raptor and the Warrior, intriguingly, features a battle, followed by a description of the warrior-princess doinking her tame velociraptor steed afterwards, as a way of winding down, you see.)

The mistresses of the genre are Christie Sims and Alara Branwen (both aliases), who say they came up with the idea while at college in Texas. They also say, for the record, that T rex is sexually frustrated because his arms are too short to reach between his legs. Other writers coming up fast including Pippa Pout and Hunter Fox.

So, aside from being a hoot, what is the special attraction of dinosaur porn? Media and cultural studies professor Clarissa Smith, an editor of the publication Porn Studies, says: “There are a number of pleasures potentially on offer here – the fact that this is really fantasy. Even if there is evidence that dinosaurs existed, we don’t know masses about them, and they have mythological qualities. The idea of having sex with one is outside the realms of possibility. It’s a bit like ‘magic’, where all rules become suspended, and for that reason it may well allow … for kinds of imaginative risk-taking impossible in more standard couplings.”

Smith suggests that an element of fear and the permission to think about non-human sexual pleasures may help explain interest in the genre. “I think this is perhaps the appeal of monsters – that it is the very impossibility of such scenarios that are fascinating and arousing, allowing the possibility of joining in with the game of imagining such outrageous couplings with other people.”

Those inclined to write it all off as a marginal fetish should think again, she says: “It’s not that unusual, actually … Picasso also sketched activities involving women, fish and mythical beasts.”