Science Marches On: Research since the documentary was made has revealed that there is no evidence for Coelophysis being a cannibal. The "babies" found in their gut were probably just smaller reptiles they had eaten.
The Swarm: At the end of the episode it gangs up to kill a dying Postosuchus.
Science Marches On: The cynodonts shown are based on the discovery of two cynodont-like teeth from the Chinle Formation. However, detailed examination has found that these teeth cannot be confidently assigned to cynodonts.
The species chosen to represent the obsolete basal synapsids of the past.
Butt Monkey: Representing all the species that can't survive the Triassic, and basically serves the episode simply as prey item for Postosuchus and Coelophysis.
The main large predator of the time period. A quasi-crocodilian creature.
Adaptation Expansion: The cause of the Postosuchus' injury is never clearly explained; the narrator only said it was injured during its last hunt. In the book, however, it is stated the Postosuchus fights a Plateosaurus and was defeated and injured by it. Furthermore, it tries to give one last fight against the Coelophysis pack and manage to kill one before succumbing to its wound.
Alas, Poor Villain: Technically it is no villain and just a predator, but its death nonetheless is one of the most depressing scenes in the series.
The main antagonist of the episode, and the largest predator in the episode.
A Day in the Limelight : A young Allosaurus named Big Al becomes the main character of the series special The Ballad of Big Al.
Art Evolution: The Allosaurus model gets better in the special The Ballad of Big Al.
Bad Ass: It certainly is, considering it hunts some of the biggest animals on the planet
Cool Versus Awesome: The climax featuring it battling the Diplodocus, Later in the special Ballad of the Big Al, a pack of Allosaurus hunts a herd of Diplodocus making it the biggest Crowning Moment Of Awesome of the entire series.
Downer Ending: In the special, Big Al the young Allosaurus dies of starvation and injury.
Death by Irony: It dies because of its one own massive size after it gets stranded, and later eaten by a group of Eustreptospondylus (note that it kills one of them in beginning of the episode).
Downer Ending: Its death at the end of the episode is just as depressing as the death of the Postosuchus in the first episode.
The Dreaded: It's the most feared creature of its environment, and the most powerful carnivore featured in the entire series. The series also contributed the fame and semi-mythical reputation earned by the Liopleurodon later in popular culture.
Rule of Cool: Liopleurodon isn't known from remains as large as the animal depicted in the show.
Sea Monster: Is actually depicted more or less as this.
Villain Protagonist: It's arguably the actual main character of the episode, and is the more memorable than the Ophtalmosaurus. However, it is averted by the fact that it's just a predator rather than actually evil.
The main protagonist of the episode, a large pterosaur.
Babies Ever After: Implied in the book (and the documentary, albeit in a "blink-and-you-miss-it" sense) to show that his journey may not have been completely pointless:
Despite this ignominious end, the old male was a success. In his 40 years of life he probably sired several thousand offspring and it is likely that some of them were on this beach, competing and succeeding where he finally failed.
Bad Ass Grandpa/Cool Old Guy: He flew halfway across the world and cheated death multiple times all because his sex drive was too much for him to ignore. The trip pretty much killed him, but you have to admit that doing something like that must have taken a lot of stamina.
Bloodier and Gorier: His death is considerably more bloody and violent in the book (simply put, the rival males more or less try to tear him apart every time he attempts to land).
Death by Sex: Inverted; he never gets the chance to mate and then he dies.
The Determinator: He would've stopped at nothing to get to his mating grounds. And later, even when he's driven away and then slowly dying of starvation and heat stress, he's still calling for females to mate with him. He fails, but still. Possibly justified since he's being driven by instinct.
Early-Bird Cameo: The specimen the improbably giant size estimates were based on didn't get scientifically described until 2012.
Rule of Cool: The producers chose the largest possible size estimate for this pterosaur to use in the show for this reason. In reality, a wingspan of 8 meters is more likely even for the large specimen the estimates were based on.
Additionally, the narrator claims that the Ornithocheirus has to keep his fur dry at all times. It is now known that ornithocheirid pterosaurs were not only adequate swimmers, but also quite capable of launching from the water if they needed to.
Ptero Soarer: More so than most other depicted pterosaurs because it's proportions are utterly screwed, it's crest has weird ridges on it that make it look like some sort of fish fin, and it lives on the beach, eating fish, when even back then the idea that they were terrestrial omnivores with possible frugivore leanings was the most common interpretation.
Science Marches On: Enantiornithines did not have tail fans like modern birds do, instead having two long feathers (most of the time). In addition, all known enantiornithine nests (and phylogenetic bracketing) suggest they were ground nesters.
Science Marches On: The evidence that female Tyrannosaurus were larger than the males is circumstantial at best. The discovery of the large feathered tyrannosauroid Yutyrannus also suggests even large coelurosaurs were feathered.
Bad Ass : They are one of the biggest land carnivore of it's time and without doubt one of the fiercest.
Cool Versus Awesome: Their confrontation with the entelodonts. Hell, its so awesome, that it was actually the cover for the DVD release of Walking With Beasts. It seems as if it was the main point of the episode, and the indricotheres where just Supporting Protagonists.
Meaningful Name : Hyaenodon literally means "Hyena's tooth" though technically it doesn't related to Hyenas.
What an Idiot : It tries to defend it's prey from the entelodonts in a rather desperate act (pooping on it) in order to hide it's smell. Doesn't work at all. As weird as it is though it was based on a real life fossil evidence.
WHOSLAUGHINGNOW : One showned chasing a lone Entelodont in the middle of the rain. It's not clear if it's the same Hyaenodon who got chased away by the entelodonts earlier.
A large relative to pigs, a scavenger in Mongolia.
Always a Bigger Fish: One if them is chased by an Hyaenodon, but it seems that the two are equals, given a group of entelodonts were seen driving a Hyaenodon away earlier.
Bad Ass : They deserve their title "Hogs from hell" indeed.
Lovable Coward: Is easily scared off the the australopithecines, despite them not having a chance of hurting them.
Smilodon (sabre-toothed cat)
A large carnivore, and the main protagonist of the episode.
Artistic License - Paleontology: Their behavior, which was bluntly copied from extant African lions. Most notably, the females are seen chasing down Macrauchenia, being able to do sharp turns while running. Smilodon was an ambush predator that could only run in short bursts of speed; its short tail would have made it very unbalanced in a high speed chase.
Bad Ass : As expected from the biggest, baddest cat that ever lived. Those saber tooth is rather fragile though. Special mention goes to Half-Tooth
Bad Ass Crew : The pride/pack is the most efficient killing machine in the plain of it's era. However it later zig-zagged due to the fact it doesn't do much to defend their youngs from the brothers and quickly runs away without giving a fight after seeing it's new leader killed by the Megatherium.
An European lion, adapted to the snowy environment.
Artistic License - Paleontology: They reused the Dinofelis model for the lion, recoloring it white, resulting in an anatomically inaccurate cave lion with small saber teeth (which they actually lacked).
A Giant Spider, and the largest that ever lived. Note that this was probably the most severe case of Science Marches On on behalf of the producers: They based this creature on the fossils of a creature called Megarachne, but late in production, it was found that this was actually sea scorpion. The name of the spider in the show was changed to Mesothelae (a group of basal spiders), and they decided to leave it in, though evidence for such a creature doesn't exist.
A giant dragonfly and a secondary predator of the segment.
Always a Bigger Fish: Steals the Petrolacosaurus from the Mesothelae spider. Then gets its eaten by the Proterogyrinus during the storm.
Bad Ass : As the Narrator puts it they are "the Queen of the sky" of the carboniferous era
Big Badass Bird of Prey: While it's not an actual bird of prey (having been alive before birds of any kind even came into existence), its behavior is quite a bit like some sort of hawk. A case of Truth in Television, as dragonflies in modern times are aerial hunters.
Heroic BSOD: He goes into this after Scowler leaves him for dead, even welcoming the scavengers coming in to eat him. But Alex tells him to live or die for something worth dying for like Bulldust did, giving him the resolve to rejoin the herd.
Idiot Hero: Was this at the beginning. Begins to shape up after Scowler nearly loses the herd in an icy lake.
Toothy Bird: Although somewhat realistic, since many similar birds had teeth and all, Alex's design is seemingly more oriented towards cartoony bird appearences, having a "beak" with teeth instead of the feathered snout of known enantiornithe snouts.
What the Hell, Hero?: He couldn't believe it when Patchi tells him to let him die, so he scolds him and says that if he's going to die...then he should die for something worth living for (his love for Juniper).
Kick the Son of a Bitch: Him attacking Scowler and nearly killing him at the climax of the film can be seen as this, especially considering how the latter had just left his own brother to die in a ditch.
Predators Are Mean: Subverted. He is never depicted evil or malicious, but rather just hungry and wanting to feed his pack.
An older Pachyrhinosaurus and the leader of his herd. He's also Patchi and Scowler's father.
Big Damn Heroes: He saves his sons from Gorgon before the latter could eat them...but at the cost of his life.