Symbiosis with Red Claw
There seems to be a symbiotic relationship between Red Claw, Screech and Thud as Ruby has once said "Where ever Screech & Thud are, Red Claw is never far behind" and in at least one episode, The Hidden Canyon, the Fast Biters actually led Red Claw to a breach in the wall protecting the Great Valley from Sharpteeth. In later episodes, Screech and Thud have been seen hunting without Red Claw.
How or why they hunt together is unknown, though it could do with simple symbiosis: Screech & Thud use their smarts, small size and greater agility to access places Red Claw can't get to when hunting and flush out prey while Red Claw's brute strength and ferocity protects them from being attacked or eaten themselves and guarantees them an easy meal.
Nonetheless, it is almost impossible for Littlefoot and his friends to encounter one without encountering all three and at full strength. They make an incredible, not to mention lethal, team of carnivores.
- Screech and Thud may be siblings, though this was not confirmed over the course of the series.
- A Utahraptor that resembles Screech appears in the episode The Spooky Nighttime Adventure.
- A noticeable error its that Screech and Thud have two fingers, despite the fact that real life dromaeosaurs sport three. This is somewhat remedied with the discovery of the dinosaur Balaur bondoc, a stem-bird with two fingers on its hands and two sickle-claws on its feet.
- In Escape From The Mysterious Beyond, Thud seems to overhear and understand what Chomper and Ducky say to each other. When Ducky says "I hope they get here soon", Thud responds with "Your friends aren't coming back, little biter." This seems to imply that Thud is capable of understanding, though not speaking, leaf-eater.
- Thud calls Chomper 'little biter', which may be a term designated for young or small Sharpteeth.