In our world, the kongamato is a cryptid from the heart of Africa. In your world, it might be the missing link between dino/pterosaurs and dragons, an evolutionary offshoot or throwback, or just another sign that “true dragons” aren’t the only rulers of the skies, especially deep in the jungle…
Because of their great power, the kongamatos of the Yukarumbi River Delta are worshipped as heralds of the gods. To the region’s serval-spotted catfolk, they are seen as avatars of doom, used in their carvings and trail signs to represent danger and death. But to the neighboring Draconic-speaking werecrocodiles, they are demigods to be emulated. Some of crocs’ faith is so strong they receive clerical spells from worship of the kongamatos alone. And sages eager to dismiss werecrocodiles as brutes would be surprised at the number of dragon disciple sorcerers in their ranks. For their part, the kongamatos are pleased with the worship, as it sometimes yields them meals in the form of sacrifices. Thus they are prone to regard anything near their sacred altars—including nosy explorers—as offerings.
A mapping expedition to Behemoth Island, a huge land mass populated by giant beasts and monsters, is going surprisingly well. The adventurers’ miraculous gnomish submersible (miraculous in that it works) carries them to the island underwater without attracting attention. Upon arrival, it beaches itself upright, transforming into a steel tower meant to serve as a safe redoubt from which to explore. “Meant” being the operative word, because almost immediately the structure is punctured by the adamantine beaks of a pair of hungry nesting kongamatos.
Kongamatos have one advantage true dragons lack: sonic breath weapons and bites. This makes them valuable allies against fiends, almost all of whom are vulnerable to such attacks. Of the celestial races though, only the burliest chaotic azatas (bralanis with class levels or less courtly ghaeles) can stomach riding the primeval beasts. Not always able to leave their posts, they sometimes hire mortal adventurers to hire—or capture and subdue—kongamatos to serve as steeds and breeding stock.
—Pathfinder Bestiary 3 169
Don’t laugh at Behemoth Island. If Godzilla had Monster Island and Transformers had Dinobot Island, I get Behemoth Island.
Also, does anyone remember the island of Gargantua in D&D? Yeah, that was a thing.
You’ll note that I tapped into the old Dragonlance/Spelljammer stereotype of gnomes making flawed inventions. Both settings so thoroughly mined that territory that in 3.0/3.5 we seemed to avoid it reflexively. But here’s the thing: it worked. Gnomes + machines was always a great way to set them apart from dwarves (also miners), halflings (also tricksters), and even elves (also tied to nature). Take machinery away, and gnomes have a hard time finding their place. Making them practically fey was a good move on Pathfinder’s part, though I think we still need some supplements/adventures/strong gnome-centered novels to make the characterization stick.
There’s a larger point here—one maybe that I’ve made before?—about thinking about hard-to-define monsters/characters/classes when you create your own worlds. It’s never hard to make a world where elves or gnomes or thieves have a place. But try starting with the gnomes…or the druids…or the monks…or the halflings…or the half-orcs. When your world has a convincing place for them, it’s a convincing world.
(Or alternately, there is always the case to be made for leaving a race/class out. Maybe you ditch gnomes and half-orcs in favor of wayangs and hobgoblins? How does that change your assumptions about what your fantasy RPG looks like?...)