Yes, titanopterans were a thing. And yes, gigatitan is one of them. But no, there were not teratitans (well, that we know of...) nor anything larger.
There have been bigger insects than gigatitan. But for the triassic its an extraordinary creature, and its various resemblances with both mantises and grasshopers (it would have been unable to leap, but there's good evidence it could chirp) are fascinating examples of convergent evolution.
Anyway, how can you not take the name 'gigatitan' and not want to make teratitans and petatitans for a game? It just leaps off the page, doesn't it? Teratitans are intended as being a foe you might encounter a lot of in a 1940's pulp story. Petatitan is the big creature looming over a town in a 1950's style monster movie, whereas of course the alluded to exatitan is like something straight out of a 1960's Toho studios Godzilla film. You would anticipate a party can't beat it, but they may be able to find its one weakness or outwit it to save the day.
Titanopteran
by Cab Davidson
| Titanopteran | |||
| Stat | Giga | Tera | Peta |
| AC: | 2 | -3 | -6 |
| HD | ½* | 4* | 32* |
| Move (walking) | 30’ (10’) | 60’ (20’) | 90’(30’) |
| Move (flying) | 120’(40’) | 240’(80’) | 360’(120’) |
| Attacks | 2+1 | 2+1 | 2+1 |
| Damage | d2/d2+d4 | d6/d6+d12 | 3d8/3d8/8d8 |
| Number Appearing: | 0 (1d4) | 0 (1d2) | 0 (1) |
| Save As: | NM | F2 | F16 |
| Morale: | 11 | 11 | 11 |
| Treasure Type: | Nil | V | J+K+L |
| Intelligence: | 0 | 1 | 2 |
| Alignment: | Neutral | Neutral | Neutral |
| XP Value: | 6 | 100 | 10000 |
Titanopterans are huge insects somewhat resembling winged mantis, but being rather bulkier, and on a vast scale. While typically found in lost world areas, when eggs escape in to other regions they are a considerable nuisance. They are built somewhat blockier, bulkier than modern preying mantis, but their prime means of attack, being ambush, is the same. They take on the primary colours and patterns of the habitats in which they are found – in jungles they are dappled green and brown, in plains they are typically green, etc. They can remain motionless for hours, even days, and can often (1-4 on 1d6) surprise foes if hunting by this means.
They attack with horribly bladed forelimbs that are covered with backward pointing prongs. Any creature smaller than them is brought to the mouthparts and bitten if both claws hit, and if they are smaller than their foes then titanopteran lifts itself up to the foe to bite after hitting with both claws.
Gigatitans are around 30” long, with wingspans of around 40”. They typically attack prey no larger than chickens, but if hungry will try to kill and eat almost anything. Teratitans are roughly ogre sized, being able to take prey up to the size of small giants. Whereas petatitans are enormous, typically being around three times the size of an elephant, and are capable of posing as if mighty trees or rock walls to hunt massive prey.
Rumours persist of exatitans and zettatitans, colossal insects preying on the gargantuan creatures of lost world regions, but these rumours are unconfirmed. Theoretically an exatitan would have 8 times the hit dice of a petatitan (256HD) and be a considerable threat to kraken, behemoths and others among the largest known megafauna. The fabled zettatitan would theoretically be capable of hunting down larger living asteroids.