The film follows a Tyrannosaurus rex named Heart who was raised by a Maiasaura. Realizing he was different, he ventures out to find where he belongs. One day, Heart finds a baby Ankylosaurus who mistakes him for his father, accepting "umasou ((you) look delicious)" as his actual name. Originally intending to eat him, Heart comes to be genuinely concerned for Umasou's wellbeing as a familial bond develops between the two.
There is also a series of five-minute shorts lasting 20 episodes with every five episodes being an adaption of a book, all of them staring a male Tyrannosaurus rex which is most likely not the same dinosaur. The first story is about the protagonist's relationship with Umasou. The second one is about the protagonist's relationship with an unnamed Elasmosaurus (named Pero Pero in the film). The third story is about the protagonist, Heart. The fourth story is about the protagonist's relationship with 5 baby Ankylosaurus and their relationship with each other. The third one is the only one of the 4 stories where the protagonist is named. The film is essentially a combination of the first three stories retold with unaddressed issues being bought up (like how a Tyrannosaurus needs to eat meat to live).
A second film was released in July 2015.
A third film was originally supposed to be released in Early Summer of 2020 in Japan but had been postponed due to the COVID-19 Pandemic. It opened in Japanese theatres on December 10, 2021.
On December 13th, 2021, Discotek Media announced that they licensed both movies and the TV series, with a Blu-Ray release set for spring 2022.
For similar carnivore/herbivore antics, see One Stormy Night.
The film contains the following tropes:
- Actionized Adaptation: The original story was a series of storybooks being read by a female narrator. The movie gives Heart and other Tyrannosaurus rexes some fight scenes.
- Actor Allusion: Kappei Yamaguchi plays a Jerk with a Heart of Gold outcast from his mother and father's respective species, but loves loves his mother despite the circumstances of his birth.
- Anger Born of Worry: Heart experiences this when looking for Umasou whom is out of sight (Umasou was trying to get berries for him), and interrogates a pair of raptors before finding him. His yelling at leaving without his supervision is very understandable.
- Adopt the Food: Heart initially intended to eat Umasou, and even makes a half-hearted attempt to do so after waking up from a nightmare about having eaten his adopted mother and brother. Ultimately, he realizes he can't go through with it and raises the baby Ankylosaurus as an adopted son, training him to defend himself against predators.
- Animal Jingoism: The opening features Troodon raiding the Maiasaura nesting grounds. And then there's the battle between the Tyrannosaurus pack and the Triceratops.
- Anti-Villain: One-eyed Baku is the leader of the Big Jaws and a Worthy Opponent to the protagonist. He's frequently shown being respectful towards Heart and once saved the land from "gluttonous long necks from the south", but when Heart and the Big Jaws start fighting each other, Baku is forced to take action against him.
- Anxiety Dreams: Heart has them throughout the movie. They're pretty screwed up.
- Archnemesis Dad: Baku is this to Heart towards the end of the movie.
- Artistic License – Paleontology: It's meant to be an entertaining movie, not a biologically accurate one. For instance, Maiasaura and Tyrannosaurus rex were separated by more than eight million years, with Daspletosaurus being the contemporary tyrannosaur of Maiasaura's day.
- Award-Bait Song: "Kimi to Irou Jikan no Naka De." It's even particularly Disney-esque, instead of anime-esque.
- Big Brother Instinct: Light was born a few seconds before Heart and took care of his little brother when they were children, even going so far as to try and protect Heart with his own body when they were attacked by Gonza. After he's grown up, he seems to be this as well to his other three younger siblings born from a different brood of eggs.
- Bittersweet Ending:
- While the volcano eruption doesn't harm anyone, Heart can't really stay with his mother and siblings. He continues to live with Umasou, mostly alone.
- This is actually happier than the book, where Umasou ends up going back to his real parents because Heart can't guarantee his safety.
- Call a Rabbit a "Smeerp": "Big Jaw" for Tyrannosaurus, "Hard Shell" for Ankylosaurus, "Three Horn" for Triceratops, and "Big Jaw of the sea" for mosasaurs. Strangely, Giganotosaurus are referred to as "Gluttonous Long Necks from the south".
- Cartoon Creature: The tree-climbing creature that warns Heart and Light about the Big Jaws, which resembles a reptilian sloth with horns and chameleon-like eyes. Other unknown creatures include a trio of what appear to be reptilian goats, and a flock of scavenging pterosaurs that resemble vultures.
- Charles Atlas Superpower: Heart trains and practises martial arts to the extent that he's easily one of the strongest characters aside from Baku, capable of doing one-finger push-ups and leaping high enough to kick a sauropod in the head.
- Chekhov's Gun: When the land slightly gives way as Heart steps on it while looking for his mother - the same spot she later falls from.
- Also could be the focus on making his little arms stronger, when he later needs to pull his mother back up the cliff.
- Children Raise You: Heart matures by looking after Umasou.
- Cool Old Guy: Beckon, the old Tyrannosaurus. He's too old to eat solid food or even move, so he leaves Umasou alone. He's so sessile that he has berry plants growing on him.
- Curbstomp Battle: After chasing Umasou away so that he can live on his own, Heart hears his cries and goes to save him. When he sees Umasou in Gonz's mouth, he goes completely berserk and utterly destroys Gonz and his friends.
- Crystal Dragon Jesus: Somewhat. They're shown (particularly the mother) praying to the Egg Mountain.
- Death of a Thousand Cuts: Heart employs this strategy in his fight against Baku, at least before the gloves come off.
- Dramatic Irony: Heart never finds out that Baku is his biological father, even though Beckon notes the Strong Family Resemblance between them early on.
- Dumb Dinos: Averted - both herbivores and carnivores are sapient and can speak.
- Eat the Dog: Heart initially plans on doing this with Umasou, but he ends up unable to resist the cute little guy.
- Family-Unfriendly Death: Some of the violence in the film is tame; however, many of the tyrannosaurs are shown killing other dinosaurs on screen, ripping them open and devouring flesh and guts, which mostly just looks like pink bubblegum. There's little blood.
- Fluffy the Terrible:
- Funny Animal Anatomy: A Chilantaisaurus with bull horns. Even though no skull material of the carnosaur have been discovered yet, it is still pretty outlandish.
- Good Parents: Heart and Light's mother. Helps that she is a Maiasaura, whose name actually translates to "good mother lizard".
- Happily Adopted: One of the main thrusts of the movie. Heart was adopted by a plant-eater, and he adopts Umasou (another plant-eater) in turn. All of whom are pretty happy with the situation.
- Hard-Work Montage: Heart and Umasou are shown doing various types of training, including agility, headbutting, striking down trees and roaring, all to the tune of "Jump Kick, Tail Smash". Doubles as a Training Montage, since Heart is preparing Umasou to fight if something tries to eat him.
- Hate Sink: The elder Maiasaura leader shows no qualms or remorse about trying to murder the just-hatched baby T-Rex, Heart in front of it’s adopting mother and showing little regard for how cruel they’re being. They make the excuse of once it’s grown, it could kill the herd but it just shows his blatant disregard for life. When Light (Heart’s brother) and the mother Maiasaura return to the herd, he offhandedly mentions her as a “nuisance” in a rather callous manner and is rather rude to Heart when he returns as Egg Mountain erupts, telling Light not to speak to him, resulting in Heart giving him a well-deserved Death Glare.
- Herbivores Are Friendly: Just like Predators Are Mean, the film shows two sides to this. Heart's adoptive mother and brother are some of the kindest characters in the movie, and little Umasou goes out of his way to find food that both he and Heart can eat. However, almost everyone is shown to be willing to kill if it is necessary. Among a few other examples, Heart's mother tramples a Troodon to protect her eggs, and the leader of her herd nearly does the same to Heart when he's just a hatchling.
- Informed Species: The dinosaurs in this movie aren't particularly realistic-looking, to the point where it's hard to figure out what some of them are. In particular:
- A strangely demon-horned carnivore, which is supposed to be the Chilantaisaurus from the book, but just looks like some kind of demon.
- The T. rex in the film walk upright, have short rounded snouts, and have a row of spines running down their backs making them look like a bizarre cartoony Expy of Godzilla.
- Interspecies Adoption: Two generations of it! Heart is a T. rex who was adopted by a Maiasaura, and who later adopts a baby Ankylosaurus.
- Ironic Nursery Rhyme: "Big Jaw," first introduced into the film as a lullaby sung by a giant sloth mother, is about how Tyrannosaurus will hunt you down and eat you if you cry.
- Lighter and Softer: Despite its Family-Unfriendly Violence, the tone of the movie never really wavers.
- Meaningful Name: Heart is a pretty soft-hearted dinosaur, no matter how much he tries to look tough. Later in the movie, when Heart is carrying an injured Umasou in his mouth, we see the outline of Umasou in his mouth, and the shape of his heart beating in his chest.
- Names to Run Away from Really Fast: One-Eye, or Baku, the alpha Big Jaw. Three times the size of Heart and the younger Big Jaws, he rules his pack by tooth and claw, and most of the time, Heart shies away from actually fighting him. Until the very end, when it's his Maiasaur family on the line.
- Non-Action Guy: Light, Heart's childhood friend and "brother". He is a plant eater, so he doesn't have any of the raw strength that Heart possesses, and is almost completely unremarkable.
- Overly-Long Tongue: Pero Pero the Elasmosaurus gets her name from the Japanese onomatopoeia for "lick", and fittingly has a very long tongue.
- Papa Wolf: Heart becomes increasingly protective of Umasou as the movie progresses, despite only seeing him as "tasty-looking" at first. When Gonza and the other Big Jaws try to eat Umasou, Heart flips out and attacks all of them - which leads to him being forced into exile for his crimes.
- Predation Is Natural: Baku points out that until he began hunting and eating meat, Heart was slowly starving on his diet of fruit. Heart himself explains rather bluntly that if he doesn't eat meat, he will die.
- Predators Are Mean: Played straight and subverted. The young Big Jaws are bullies, but Baku appears to be offering food and shelter to baby Heart when he thinks the latter has been orphaned, later stating that he was "skin and bones" at the time, and only exiles Heart to protect the rest of the Big Jaws. And then of course there's Heart himself who, while a competent hunter, tries his best to act mean yet fails miserably. Just like the herbivores being willing to kill in self-defense (see Herbivores Are Friendly above), the carnivores are simply hunting to survive.
- Raptor Attack: The nest-raiding Troodon from the beginning of the film. Heart also chases a pair of raptors to inquire if they've eaten Umasou.
- Ridiculously Cute Critter: Umasou. He's so cute that Heart confusedly starts talking to him as if he was his own son only a few seconds after seeing him.
- Sapient Eat Sapient: Most herbivorous and carnivorous dinosaurs, as well as other prehistoric animals, are sapient and speech-capable... not that that stops the carnivores from chowing down on the herbivores and even each other.
- Single-Stroke Battle: When Heart and Gonza face off for the last time, they lunge past each other. Heart tears a chunk of Gonza's neck out, mortally wounding him, and is himself uninjured.
- Small Parent, Huge Child: Tyrannosaurus rex Heart is quite a bit larger than his adoptive mother, a Maiasaura. In real life, Tyrannosaurus was about ten feet longer, and the animals were probably a similar weight.
- Spared by the Adaptation: Pero Pero in the book version seemingly dies from his injuries. In the anime, she's still alive and kicking even after parting ways with Heart and Umasou.
- Soundtrack Dissonance: In one of the more violent scenes in the movie, Heart beats several other Big Jaws unconscious while a nursery rhyme plays in the background.
- Stock Dinosaur Archetypes: The main dinosaurs are pretty complex; Tyrannosaurus are fearsome predators as shown with Baku and Gonza, but are also capable of being nice and affectionate, even towards herbivores, as demonstrated by the protagonist, Heart, who was raised by a Maiasaura and himself becomes a father-figure to an Ankylosaurus he names Umasou. While the Maiasauralive up to the title of Good Mother, they can also be very aggressive when it comes to egg looters and the herd leader is a rare example of a herbivore being a Hate Sink, showing condescension and hate towards Heart for simply being a carnivore despite his good nature. The other dinosaurs are more stereotypical, with predators shown as persistent and willing to raid nests and herbivores being placid unless attacked, though the narrative makes it clear they're only doing what they do in order to survive a tough world.
- Strong Family Resemblance: When Baku stops by to leave him food, Beckon notes that Heart resembles Baku when he was younger and speculates that Baku's long-lost egg may have been saved. While Baku never informs Heart of their relationship, the mother Maiasaura realizes Baku is Heart's father after he scolds her for how she raised him, then thanks her for nevertheless keeping Heart alive.
- Unnamed Parent: Heart and Light's mother.
- Unstoppable Rage: Upon seeing Umasou in Gonza's jaws, Heart went completely BERSERK and savagely attacks Gonza and his pack. By the time he's calmed down, he slaughtered his pack while Gonza is lying on his back, his teeth shattered after Heart shoved a boulder in his mouth before kneeing it
- Vegetarian Carnivore: Heart, at first. When he finds out he actually enjoys the taste of meat, he's horrified since he thought he was a herbivore.