The Allosaurus got a complete visual make-over for this special. They look much different from their original appearance in the second episode of Walking with Dinosaurs (1999).
The Apatosaurus is just a recycled animation model of Diplodocus, without back-spikes and with a different coloration. Since they were very closely related, the animators didn't need to build a completely new model for Apatosaurus. Similarly, the Othnielia and Dryosaurus are slightly tweaked and recolored variations of the original hypsilophodont model.
The small herbivorous dinosaur that Al tries to catch, Othnielia, has been renamed Othnielosaurus since this special aired, since many fossils originally thought to have belonged to Othnielia had proved to be those of a different dinosaur. Othnielia is considered by some palaeontologists to be a dubious name.
In the early 2020s, new research suggested that Big Al might have been a female Allosaurus, rather than a male as proposed in this program.
The sound effects of the Allosaurus mating calls are actually chimpanzee shrieks slowed and pitched down.