Dinosaur is the name of the dominant life forms native to the Land of the Lost. Like their Earth-version counterparts, they are large reptilian-like animals that propagate by laying eggs and forming large single-species communities although a few live in isolated solitary lifestyles. There are many different species of dinosaurs indigenous to the land of the Lost, including the infamous Tyrannosaurus rex and the Brontosaurus.
Several of the species encountered by the Marshalls include a Coelophysis (many named Spot), a Tyrannosaurus rex named Grumpy, an Allosaurus named Big Alice and her son, Junior, a Triceratops named Spike, a female Brontosaurus named Emily and her baby, Dopey.
Species in this version included some Parasaurolophus (one baby named Tasha who is currently with the Porters), Tyrannosaurus Rex (one named Scarface), a Triceratops (named Princess), a Stegosaurus (named Spike - not be confused with the Triceratops from the 1970s series), an Apatosaurus and a Pteranodon.
Dinosaurs such as Grumpy the T-Rex, some Pteranodons, a Compsognathus, a female Allosaurus who looked similar to Big Alice, and some form of raptor were encountered. The word Hadrosaur is used to describe an item Will had acquired, but those dinosaurs are not seen. Co-existing with the dinosaurs are amazing creatures like Giant crabs, Bug's and the Sleestak.
- It is unrevealed if the Sleestak are evolved from intelligent humanoid dinosaurs.