I had the Fast biter and Leaf eater idea too. Five Fast Biters would find a Club Tail egg that survived a rockslide (parents and other eggs dead). They would hatch the egg, not knowing what it was, and eventually found that it was a Club Tail.
As the Club Tail was only a baby, they couldn't bring themselves to eat her as she was just a newly hatched baby, they named her Leafie (because she ate leaves) and hid her for years.
Eventually, they encountered Littlefoot and Co. who came to their home of Hunter Valley and eventually got him and the others to take her to the Great Valley to live so she wouldn't have to hide the rest of her life. They do promise to visit her often.
As for Chomper, I sent him away after it appeared that Red Claw was defeated. The Valley didn't have time to panic when he started taking down fish and even Tickle Fuzzies. He wasn't starving, but was overly hungry and had vowed that he'd never hunt a Flattooth due to having been saved by one (see film V).
However, after coming to the Great Valley sometime after his 20th Star Day (when he comes of age), the Great Valley lets him in for a while but eventually their hatred of all things fanged gets them to say he'll have to leave the following morning.
Littlefoot has a big blowout with the Great Valley leadership and acts most disrespectfully, though, of course, Littlefoot is right, over this, getting the Council to warn him to behave.
Littlefoot, Chomper, and Chomper's girlfriend Andromeda (seems like a plausible name for someone Chomper will eventually marry), plan to sneak Chomper's sweetheart in through a secret entrance, have her stay the night, have Littlefoot bring the adults to her the next morning,show that Chomper is nice and has trained others to be nice and that they should let him in.
(The Great Valley's secret is that Longnecks took it over and killed the T-Rexes that lived in it, or loads of them, not that the Sharpteeth didn't return the favor during the attack, and there was a nasty feud between the two that ended, at least from open war, when the Meanest Ever Sharptooth, who was sent as an assassin, was killed.
What's ironic about Chomper is that the expelled Sharpteeth had a prophecy that the first T-Rex to hatch in the Great Valley would be the one who would "wipe out the leadership of the Great Valley and put things back the way they should be.". However, Chomper has no interest in doing that.
However, an evil scheming villain, who appears to be a handsome Leaf Eater, but is really a Bothtooth who has caused the deaths of tons of people in the Mysterious Beyond, is panicky as Chomper found out his secret and he realizes that Chomper is the first Sharptooth that he's not going to be able to persuade to be silent.
Well, he wakes up on the Far Walkers who came to the Great Valley due to the mess he was making in the Mysterious Beyond. It happened to be the Old One.
She encountered Chomper's sweetheart, and, having been around for ages, was alive during the time of the Longneck conquest of the Great Valley, and has it in for descendants of those Sharpteeth, of which Chomper's lover is one.
She is about to kill Androemda but Chomper intervenes and accidentlaly slices her open with his claws. Smelling blood and being so enraged at her behavior, he nearly bites into her, but is stopped by both Littleofot and Andromeda crying out for him to stop.
Sadly, he was seen and had to bolt. Littlefoot helped him get away, for which Littlefoot was later given lifetime banishment for.
After looking like the hero, the villain takes over the Great Valley.
In the end though, the villain is exposed and defeated and Chomper helps save the Valley for Red Claw, the Old One's death was chalked up to accident on Chomper's part and murder on the part of the villain.
The Great Valley learns that it's not what someone looks like but who they are that is important. Also, Chomper finds some interesting things to hunt (i.e. Bothteeth, minus Fast Runners, and Egg Stealers, minus Strut.)
Also, Littlefoot is let back in and made the new leader of Ali's herd and he marries Ali. Chomper and his now mate Andromeda are allowed to stay permanently as a reward for helping out the Great Valley when loads of lives would have been lost had they not helped.
