Aladar (voice of D.B. SWEENEY) is a three-ton iguanodon who, through a series of mishaps, came to be adopted and raised by a family of lemurs headed by patriarch Yar (voice of OSSIE DAVIS) and matriarch Plio (voice of ALFRE WOODARD). Although he's obviously much different than his primate siblings, including Zini (voice of MAX CASELLA) and Suri (voice of HAYDEN PANETTIERE), and hasn't grown up with any of his own kind, Aladar is a happy and carefree dinosaur.
That is, until a horrific meteorite storm arrives and destroys their home island. Forced to flee and swim to safety, Aladar and his family find nothing but desolate and ravaged lands filled with hungry carnivores such as raptors and the terrifying and much larger carnotaurs.
Luck prevails for the small family as they encounter a large herd of disparate herbivorous dinosaurs migrating toward the safety of a reportedly paradisiacal nesting ground. Unfortunately, the tribe is led by Kron (voice of SAMUEL E. WRIGHT), a dictator-like iguanodon who, with the aid of his right-hand dinosaur, Bruton (voice of PETER SIRAGUSA), pushes the herd to its limits as they try to reach those grounds as quickly as possible.
The much smaller Aladar immediately clashes with Kron, especially when the leader seems not to care about the old or tired stragglers including Baylene (voice of JOAN PLOWRIGHT), a "dainty" brachiosaur, and Eema (voice of DELLA REESE), a slow moving styrachosaur. As Aladar tries to keep them caught up with the rest of the herd, he meets and eventually befriends Kron's gentler sister, Neera (voice of JULIANNA MARGULIES). With many miles and long days ahead of them, and despite repeated encounters with the various carnivores, the herd tries to complete their journey.