- The Land Before Time All Grown Up XI: Mystery of the Monsterousaurus is a 2030 theatrical animated film and in The Land Before Time All Grown Up series featuring new cast members.
A herd of dinosaurs were eating green food and drinking water when a ferocious rogue longneck named Red Foot attacks and in the bushes green eyes of a howling dinosaur appears.
In the Great Valley, Littlefoot (Eljiah Wood) and his friends Ducky (Tara Strong), Petrie (Tom Kenny), Spike (Mitchell Whitefield), Tippy (Rickey D'Shon Collins), Chomper (James Arnold Taylor) and Ruby (Grey Delisle) are so excited for the Fall Celebration as the see all the treesweet trees and they know Cera (Hayden Panettiere) is gonna be the first one to get one cause she was the one who found it and remembers that Littlefoot who found it first when the return to the Great Valley after being gone for many years and he should have gotten the first bite of the tree sweets and she teases Littlefoot for being so little the last time and Littlefoot remember that he was used by his friends to get stuff bigger then him and gets upset and leaves.
Meanwhile Mr. Thicknose gets a visit from his old friend Tilla (Queen Latifah) and Cera notice him talking to someone.
Meanwhile Littlefoot tries to reach the cliff but couldn't reach it and then at his home, he tried to get the tree stars from his tree and then mess it up and pasted out and then he had a nightmare about a longneck that looks like him with red and yellow eyes and sharp teeth and woke up after he screamed. Later, a gray two-horn (Nasutoceratops) named Nasuto (Kevin Michael Richardson) and his boys have them caused all the ttreesweet trees to lose all the treesweets, cause a monsterous longneck that's been attacked many dinosaurs in every valley and heads off to the Forest Valley where some young horned dinosaurs are and Cera takes the others to go there and they want Littlefoot to come with them.
Later, Littlefoot and his friends head off the Forest Valley and Mr. Thicknose tries to cheer up Littlefoot for saying something about something that makes him upset for being so little.
As they head for the valley Littlefoot tries to make paths but somethings are too big for him so Cera can do her own things.
When the gang arrived at the Forest Valley, they meet Mr. Kosmos, a dinosaur with lots of horns on his frilled (Kosmosceratops) who is the leader of the valley and they know who Cera is cause they heard about her father Mr. Threehorns.
When they came to a spot to see how Cera's kind do until they meet Eino, Chasma, and Styrco who know Cera is her father's daughter and Cera told them that they heard about a rouge longneck attack and then Eino, Chasma, and Styrco left to practice when a two horn named (Nasutoceratops) Tad showed and notice that Cera is Mr. Threehorn's daughter and Cera introduced him to his friends including Littlefoot when he started making fun of him and then leaves when he said to Cera friends that they can't stand a chance against the rogue longneck and Littlefoot to little to face him and Cera and the gang starts exploring her dad's home and Littlefoot starts getting upset and a mysterious white longneck like spirit starts watching them and disappeared.
Meanwhile, another horned dinosaur (Pentoceratops) named Pento warn everyone that the rogue longneck has attacked 14 dinosaurs like from a clubtail to a fast runner and notice that the herd is out in the open and send Tandy along with Trayson the Forest Valley's hero and must be careful when they ran into the rogue.
As Trayson and Tandy arrived to get the herd to safety they encountered the rogue longneck who left scratch marks on the trees like decoys and a 15th dinosaur was scratched.
Later Trayson and Tandy return with the herd, they warn Pento that they got a 15th dinosaur injured and Cera and the other arrived and meets Pento and Pento knows that she's Mr. Threehorn's daughter and female fast runner name Galla arrived and she's worried that her husband is injured for 10 days after the rogue longneck attacks and Cera wants to stop the rogue along with her friends and Pento told her it's to dangerous for her and the others and a young female no horn (Protoceratops) named Proweath heard that Cera is gonna stop the rogue with her friends and Pento allows Cera and her friends to stop the rogue.
Later at night, the gang tries gathering treestars for late night snacks and Littlefoot tries to get some from a tree bigger than him, but Petrie got all of them and Littlefoot gets mad at him for getting in his way and Petrie was forbidden to fly to be bigger than him and the gang are worried about Littlefoot acting that way and found a place to rest where they meet a flying furry creature (prehistoric bat) named Fanga (Maia Mitchell) and sees tiny longnecks they remember including Scatter and Lizzie and the Twins even Lizzie's father Big Daddy and they heard that they're trying to stop the rogue longneck that Big Daddy calls Red Foot and he tell them how he got that name a long time ago when he attacked his own kind he hates including the white longneck name Brighterra that gave him a scar on the right side of his face before Red Foot got blood on his foot when he scratched her and sending her down into a pit to her death before Brighterra became a spirit longneck and roams around and Littlefoot got really upset when Tippy said Red Foot's bigger than him and changed his name to Tall Tail and never wants to use that name again and out in the valley Red Foot roars under the night circle (moon) to begin his next attack tomorrow and Brighterra howls and vanished.
In the morning, the herd of clubtails (Ankylosaurs) were eating plants until Red Foot attacks them and the gang woke up and heard Red Foot has striked today and tries to track him down and Ducky tries to cheer Littlefoot up but, Littlefoot grabbed her by the neck with his tail and tell her don't call him that name anymore cause his new name is Tall Tail and the gang were shocked that Littlefoot is not being kind anymore.
As they begin the search for Red Foot, they meet Trayson who is looking for Red Foot as well along with Tandy and the others and Eino, Chasma, and Styrco arrived and see Cera and the other are on the search as well and got separate ways to find Red Foot and stop him and while doing the search Littlefoot gets mad at Ruby for bumping him off the log and the Ruby was shocked.
As the gang search in the part of the valley, Littlefoot discovered more marks on the trees and they led him straight to Red Foot and tries to get him, but Cera
As the gang enters the woods they discovered that Red Foot left scratch marks on the trees and Red Foot is near by somewhere and split up to find him and after splitting up with the others Littlefoot discovers that he found Red Foot he knows that he's the one from his sleep story and tries to get him, but Cera shows up and let Red Foot know that she and Littlefoot are right behind him and Red Foot starts attacking and knocks Littlefoot in a pit and Littlefoot tries to climb out by the edge was to big for him to reach and as Red Foot starts chasing Cera, Chomper turned around and sees Cera running and gets scratched in the nose, and Cera led Red Foot to the others and Big Daddy and the tiny longnecks starts running and hiding from him and Cera starts chasing him off by charging at him leaving mark on his right leg and the gang was surprised that Cera chased Red Foot off and when Trayson and the other horn dinosaurs showed up, Cera told them that she found Red Foot first and chased him off and as the gang were about to go, they notice that Littlefoot fell into the pit and Spike tries to get him out and after he got Littlefoot out of the pit, Littlefoot gets mad at him telling him her didn't need any help and the gang was shocked that Littlefoot is still in the bad mood, and the Brighterra, who saw what happen disappeared.
As the gang were drinking water, Pento arrived and heard that Cera chased off Red Foot and tells her well done and all the dinosaurs wants to hear how she face him and Cera told everyone that she was the first one who found him before anyone did and said that her friends got scared and she led Red Foot into a trap so she can wound him
When the gang were resting, a young threehorn (Torosaurus) named Toro appeared out of nowhere and want to fight Cera and the fight between him and Cera came to an end as his big brother named Tenro stopped him and tells him that Mr Kosmo wants all the dinosaurs to attend and Cera and the gang are able to attend.
As the gang attended to the center of the valley, they see Mr. Kosmo who was surprised that Cera chased off Red Foot and Mr. Kosmo checks with Tad to see how the dinosaurs are getting along, and a threehorn (Bravoceratops) name Bravoliski inform him that all the dinosaurs are helping together and none of them are hurt and a very old twohorn (Nasutoceratops) named Mr. Nammer who is always making sure everyone is getting along together and Tad was not surprise that he's always the lucky one until she saw Cera. and hears that she scared off Red Foot and the dinosaurs are surprised that she here and want to hear how she face him and Tad makes fun of Littlefoot again when he changed his name to Tall Tail and Proweath was able to tell Mr. Kosmos on him but, Tad won't let her.
Outside of the valley, Red Foot, who got wounded by Cera eats more of the plants that made him go rouge and cause him to be very dangerous.
The next day, Mr. Kosmos wishes everyone good luck as they track down Red Foot and during the search, Fanga tell the gang how she came to the valley without her family and Littlefoot discovered more marks on the trees and they led him straight to Red Foot and tries to get him, before did it again when she bump him down a cliff into the water and Cera kept her friends back as she chased off Red Foot.
Later Cera was about to begin her speech to everyone and Tad appeared telling her friends that she's way better than them and laughs at Littlefoot for being to little, and Cera tells that she managed to scare off Red Foot before anyone could, and Littlefoot relies that all this brings back memories of his youth and when he got older and knows that Cera has been using him the whole time, and Cera promise everyone that she will save her father's home.
After Cera finished her speech to everyone, Littlefoot gets mad at her for using him after he found Red Foot before she did like she did back in the Great Valley and calls her a liar and he been keep secrets from her when he had a sleep story about him getting killed by Red Foot and he didn't tell her cause she might get in his way like she always do and quits and leaves the Forest Valley and never wants to see her ever again and doesn't want to be found or be bother by her or anyone again and thanks to Cera who got her friends into terrible messes, the gang get really mad at her for making them jealous and look like losers and losing Littlefoot who's not himself anymore, and breaks up with her telling her that they're no longer friends with her anymore and leaves the valley leaving her to do problems without their help, and the tiny longnecks also leaves as well and Cera got sad that Littlefoot and doesn't like her anymore.
At a river Chomper and the gang are outcast from their home cause they'll get lost if they can't find their way back without Littlefoot and encountered to Longneck Swimmers (Elasmosaurus) who are really mad that Ducky took their eggs by mistake.
Later back in the Forest Valley, Cera who's really sad that Littlefoot never wants to see her again and saw Mr. Kosmo who was heading to a meeting and told him that she lied to him and said that Littlefoot found Red Foot first before she did after changing his name to Tall Tail and she missed the old Littlefoot and Mr. Kosmo was glad that she told him and he told her in the valley they don't make fun of dinosaurs no matter how big or small. And Tandy who heard what Cera said finds out that Tall Tail is Littlefoot.
Later, the twins encountered Red Foot and were about to be scratched, but Red Foot discovered some tracks that came from Littlefoot and begins to track him down and kill him.
While being sad that she lost the old Littlefoot and her friends, Cera discovered a part of her dad's home where she meets 3 young female threehorns who are her long lost sisters she lost over the past years.
Meanwhile, Littlefoot, who is still very angry that he can't reach things that bigger and higher and fell down into a pit, and in the forest, and a path that's leads to the Mysterious Beyond was open and a pack of Fast Biters (Dromeosaurus) matches in to the valley.
Later, Chomper and the others were about to find Littlefoot by looking for his tracks but then encountered the fast biters that got in and attack them and they fight back with the help from the Tiny Longnecks and just when the fast biters were about to get them they smelled something coming their way and runs back to the path they came in and it was Red Foot and Red Foot was looking for Littlefoot and then attack Chomper and the Gang.
Back in the Forest Valley, Tandy tells Trayson and the others that Tall Tail is really Littlefoot when he change his name and Tad overheard her what she was saying and Centro warns them about Chomper and the others are fighting Red Foot but Tad say that is Cera's business, and Tandy and the other along went out to help them.
Back in the forest outside the Valley, Spike and Tippy got wounded by Red Foot so was Petrie and Ducky and Ruby who got scratched after weaking him, and Chomper who bravely stands up for his friends and when Tandy and everyone found them they were too late and sees Chomper fighting Red Foot and weaked him by biting and scratching him but Red Foot scratched him in the mouth and hit him with his tail and then continues his search for Littlefoot.
Back in the valley, Cera heard that her friends were injured by Red Foot and was on his way to kill Littlefoot like Big Daddy said Red Foot hunts those he hasn't before and tries to save Littlefoot before it was to late.
At the pit Littlefoot tries his best to get out but keeps coming down and gets really upset for being to little and he meets Brighterra and then tries to climb out and was about to slide down but, grabbed the branch with his teeth and continues to climb until he was able to get to the top and then saw Red Foot who found him and starts chasing him and started roaring so loud allowing Cera and the others know that he found Littlefoot, and Tad thinks he's looking for Cera but Mr. Nammer told him Red Foot's not cause it something to do with those tracks that came from Littlefoot.
Later Littlefoot was still running from Red Foot and heads stright to the crevasse and got unconscious when he tripped and Red Foot was about to kill him but then was stopped by the young horn dinosaurs and took all them down, and heads straight for Littlefoot so he can kill him, but Cera arrived to stop him in order to save her friend and knocks him down, and Red Foot gets really mad when she gave him to many wounds he doesn't like and scratched Cera really bad and knocking her unconscious.
After taking out Cera, Red Foot goes for Littlefoot so he can kill him but notice that he's vanished and then Littlefoot attack from behind and the fight between Littlefoot and Red Foot goes on when Littlefoot goes for Red Foot's foot and breaks it with his tail so Red Foot can't scratch him and was able to beat him by using his tail to knock him off the cliff into the crevasse and Red Foot was gone forever.
The gang woke up from being unconscious sees what Littlefoot did and Mr. Kosmos appeared and found out what happen to Red Foot and Trayson told him that Littlefoot defeated him and everyone thanks him, but Tad said that Cera was supposed to beat Red Foot, not Littlefoot cause Littlefoot hurt her feelings and stole her chance to stop the rogue, but Toro told Tad that Littlefoot saved all their lives and all the valleys and all the dinosaurs that live and thanks him and his friends for doing it for them in places and and the twins told Tad that he's right and they knew that he teared the herd apart by making them jealous of Cera, and Littlefoot gets mad at Tad for making fun of him and his name and size and Mr. Kosmos gets mad at Tad for what he did to Littlefoot and the others for having them turn against Cera and thanks the gang for weaking Red Foot long enough for Littlefoot to save all the dinosaurs and his kind and told Chomper that his kind will be so jealous that he stood up to Red Foot as they got scared and Mr. Nammer are surprised that Littlefoot was okay cause they knew who he was and Mr. Kosmos replace Tad with Mr. Nammer as The new Attended Leader and Mr. Nammer tell him that Tad has caused enough trouble for everyone and he is not to set one foot in their valley again or in other valleys and Tad was banished from the Forest Valley by Mr. Kosmos, and loses his horns when Littlefoot breaks them off his head and was exiled to the Mysterious Beyond.
As they return to the valley, Cera's sisters punished her for all the trouble she did, and made the gang laugh and Littlefoot starts smiling and and laughing again as he return to his old self again and they and their new friend Fanga, and the tiny longneck begin to head home and want Cera's sisters to come with them, but Cera' s sister said they can't cause they belong in their father's home and say goodbye to Cera as Cera goes with her friends back to the Great Valley.
As the gang return to the Great Valley, the encountered Brighterra who followed them, and vanish in front of them and starts having the fall celebration and Littlefoot became the first one to get a treesweet even through he was the one who found the trees and welcomes home the tiny longneck and Fanga the first flying furry creature in the valley, and at the end, Brighterra starts howling after Red Foot was defeated and will always watches.
Elijah Wood as Littlefoot
Hayden Panettiere as Cera
Tara Strong as Ducky
Tom Kenny as Petrie
Mitchell Whitfield as Spike
Rickey D'Shon Collins as Tippy
James Arnold Taylor as Chomper
Grey Delisle as Ruby
Dorian Hardwood as Mr. Thicknose
Queen Latifah as Tilla (Pachyrhinosaurus)
Kevin Michael Richardson as Nausto (Naustosaurus)/ Big Daddy
Cree Summer as Lizzie
Leigh Kelly as Skitter
Ashley Rose Orr as Dusty
Nika Futterman as Rocky
Cedrick Yarbrough as Mr.Kosmos (Kosmosceratops)
Idris Elba as Pento (Pentoceratops)
Nate Torrence as Centro (Centroceratops)
Maia Mitchell as Fanga (Prehistoric Fruit Bat)
Sarah Hyland as Cera's sibling 1
Madison Pettis as Cera's sibling 2
Maisie Klompus as Cera's sibling 3
Octavia Spencer as Galla (Gallaminus)
Different Lands by Shakira (Music of Littlefoot and his friends heading for the Forest Valley).
Faster I can Fly by Maia Mitchell
I Have no Friends by Hayden Panttiere (Music of Cera being sad after Littlefoot quits and the other quit).