One or more of the characters is a Time Lord.
Specifically, Holly is the Rani. In the episode "Elsewhen", Holly encounters a blonde woman apparently in her twenties who calls herself "Rani", who turns out to be Holly's older self come back in time to help her. Rani admits that she can time travel at will and understands the technology of the Land. Given that the pylons of the Land display TARDIS-like properties, it seems reasonably plausible that at least one is a TARDIS, and the future Holly used it to escape the Land to Gallifrey where she, like Ace would have in the original series, became a Time Lady. How she then went from girl hero to Mad Scientist (and from blonde to a brunette) can probably be attributed to a bad series of regenerations.- Blandings the Repairman from Season 3 is a funny little man with old fashioned clothes and mannerisms and a British accent who comes from a mysterious Sufficiently Advanced civilization with time doorway technology. It seems entirely possible he was intended as an homage to Doctor Who.
The Sleestaks did not evolve naturally
They were constructed, just like the rest of the Land, by the ancient humanoids seen in "The Musician." Then the ancient humanoids went about transplanting prehistoric life, including the Dinosaurs and the Pakuni, from different time periods on Earth to the Land. Maybe the goal was to test whether an intelligently designed species could compete against naturally evolved predators. The Sleestak God is a Great Old One
...making the series an adjunct to the Cthulhu Mythos. The depiction of the Sleestak God as an unseen, but apparently massively large, insatiably hungry mass deep within a network of caves and attended by a race of brutal, mindless servants is rather Lovecraftian. Some fan theories have linked it to Tsathoggua, a creation of Clark Ashton Smith for his Hyperborean stories within the mythos Shared Universe, who fits most of the above descriptions quite well, with the exception that its cult is said to be hairy and ape-like, while the Sleestak clearly aren't. But who's going to tell it that it can't have more than one cult?- Word of God says that the Sleestak God was supposed to end up being a Running Gag. It would be akin to the Monty Python vorpal bunny. It was actually the "Sleestak queen," the egg-laying female. It made a great deal more noise than its actual mass would indicate, though it'd still be vicious and predatory. This doesn't actually contradict the theory, though - nothing saying Great Old Ones have to be big, and the description matches up with Shub Niggurath.
Holly becomes Ranee because of the Pylon sent to Earth in "Hurricane."
In "Hurricane," a time doorway is opened leading to Earth twenty years in the future. Not only does an astronaut briefly visit the Land, but a whole Pylon gets sucked through the portal to Earth. Assuming the Marshalls get home in "The Circle," this pylon could very well be how adult Holly learns to operate them, paying a visit to her younger self in "Elsewhen." The dinosaurs were imported from an alternate Earth, not ours
The dinosaurs drag their tails, Dopey's egg was enormous, Big Alice is too big for an allosaurus, and Grumpy's muzzle is much too broad. Clearly, they're from another world entirely. Season 3 takes place in the alternate Land of the Lost shown in "Split Personality"
The differences between the lands could explain how Chaka could suddenly speak English so much better. It also conveniently ties in with the popular idea of placing "Circle" at the end of Season 2. Perhaps the original Marshalls made it home and season 3 was simply about a different group (whose Rick made it home).