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) at the new treesweet tree where they get ready to have some treesweets for the Fall Celebration and they know Cera (Hayden Panettiere) is gonna be the first one to get one and she teases Littlefoot for being so little the last time and Littlefoot gets upset and leaves.
Meanwhile Mr. Thicknose gets a visit from his old friend Terra (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 the tree run out of treesweets cause a monsterous longneck who 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 Littlefoot and his friends arrived at the Forest Valley, they meet Mr. Kosmos the 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.
Back at The Cave Chomper, Ruby, and the others heard what Horin was saying when they know that he and his siblings and friends were using them to get all the attention from Mr. Kosmos and everyone so they got mad at them and quit and they're no longer friends with Cera who is the reason why Littlefoot ran away and walked out on them.
When Cera , Horin and the others tried to find Chomper and the others they ran into Mr.Kosmos and Mr.Kosmos was so mad at Horin for using his guests after what Hornberto said and no choice but to put him and his siblings and friends but Cera on punishment forever and told them to march themselves right home and told them not to leave there and not to patrol ever.
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
Justin Long as Horin
Bruno Mars as Hornberto
Orlando Brown as Styraco (Styracosaurus)
as Chasmi (Chasmosaurus)
as Einio (Einiosaurus)
as Pyana ( Protoceratops)
as Rif (Protoceratops)
Idris Elba as Pento (Pentoceratops)
Nate Torrence as Centro (Centroceratops)
Littlefoot change his name to Tall Tail
(Littlefoot walking outside feeling upset)
Littlefoot: I do not like being little! (Sigh) It's not fair. I don't like when someone who makes fun of me. I can't take it anymore. I don't like my name anymore. So I'm gonna change it forever. No more Littlefoot. For now on, my new name will be Tall Tail, and that's it.
(No Longer Friends with Threehorns Anymore)
(Chomper walking to Horin and the others for what they did for ignoring Littlefoot and for making him run away and listen what they are saying.)
Horin: Listen guys we got to try to get rid of Red Foot if we ever gonna patrol like everyone and Chomper and the others are the only oneside who help us we'll need all their skills they have.
Hornberto: You're right, brother we'll need Chomper's sniff to track him down and Spike and Tippy's spiky tails and Ruby's speed and while they tired him out......
Cera: And that's when I bump him once and for all and everyone will thank you guys and everyone back in the Great Valley will thank me.
(Chomper shocked and angryly walked to the others)
Chomper: Guys, did you hear what Cera and her siblings and friends were saying about us?
Ruby: No. What were they saying about us?
Chomper: I'll tell you what they were saying. They been using us the whole time!
Ducky: (GASP) How could they?!
Petrie: All this time, they been using our skills?
Spike: That explains why everyone has been ignoring us!
Tippy: And that's why they ignored Littlefoot when change his name to Tall Tail before he ran away!
Ruby: I don't believe it! Cera lied to us when she led us here!
Horin: Hey, guys. Let's go and search for Red Foot and get rid him.
Chomper: Don't you know what happened to Tall Tail?
Horin: No, and where is he anyway?
Chomper: I'll tell you what happened to him. He ran away because of you!
Horin: Me? I didn't know.
Chomper: Of course you didn't know! He's gone, thanks to you!
Ducky: That's right!
Cera: Ducky, who are you gonna believe? My brother, or this Sharptooth?
Ducky: That sharptooth is our friend!
Cera: Friend?! Well this sharptooth lost his friend who hatched him.
Chomper: Oh, really? Well, tell me something ms Threehorn Girl, why do you always get in his way all the time?
Horin: Guys forget about this we got work to do we'll find Tall Tail later now let's go.
Chomper: That does it! The only reason you ignored Tall Tail, cause you keep paying attention to me, and the others expect Tall Tail, cause you don't see him like he's to little.
Ducky: Well, I agree with you, Chomper.
Horna: Ducky, I don't believe you thrusting him.
Spike: Are you calling my sister and liar?!
Frilla: Okay, this has gone far enough. After everything you guys did for us, we let you guys help us.
Ruby: Oh, yeah, so you can show off to everyone who ignore us and payed a attention to Cera? You guys used to be good to us, but now, you're just a couple of threehorns who didn't like Tall Tail like your father who is dead!
Cera: (GASP) How could you say that about my dad?!
Ducky: Well, your dad was always so grumpy to everyone back in the Great Valley!
Petrie: Your father always making up rules like he so bossy all the time, and that upsets us, and we don't like being upset!
Spike: That's right.
Ducky: Your dad always blames everything on everyone in the Great Valley like Tall Tail,his grandparents, Doc, Mr.Thicknose and all of us us!
Petrie: Plus, he's chased off my uncle Pterano after he saved Ducky after she was kidnapped when we were little!
Chomper: When I was little, he made fun of my arms for being so little!
Ruby: And don't him anyway. I'mean glad he's dead!
Tippy: Oh, and worst, it's his fault Spike and I were forbidden to play with each other, cause he had that fight with my leader and we almost got in trouble when he didn't want to share with my herd like everyone back in the Great Valley!
Cera: You guys are really starting to upset me.
Chomper: You know what, she doesn't belong with us anymore. She belongs to her long lost siblings!
Spike: And why are still hanging out with her? We forbid ourselves.
Tippy: You hear that, Cera? We forbid ourselves to hang out with you, and your siblings!
Ducky: And hears one last thing: Sharptooth, Swimmers, Flyers, Spiketails, Fast Runners and Longnecks are no longer friends with Threehorns anymore!
Ruby: Come on, guys. We are leaving this valley.
Chomper: Away from these threehorns!
Spike: Hold up. Tip and I forgot to Horin something for his father did.
Tippy: Yeah. Shall we?
(SPIKE SHAKE HIS HEAD)
(SPIKE AND TIPPY SWING THEIRSKILLS AT HORIN AND HORIN GOT HURT AND CERA HER SIBLINGS GASP)
Chomper: Now, let's go.
(CHOMPER AND THE OTHERS ANGRYLY LEAVE)
Littlefoot Doesn't like Threehorns Anymore
(Littlefoot (Tall Tail) trying to reach to treestars but couldn't get one, and Cera found him and talk to him.)
Cera: There you are I've been looking for you.
Littlefoot: what do you want?
Cera; What do I want? You know how long I was looking for you.
Littlefoot: Why were you looking for me? should be off tracking that rouge longneck, Red Foot?
Cera: No, cause I can't do this by myself cause it's your fault Chomper, Ruby and the others have quit and left the Forest Valley cause they think my brother, Horin and my siblings and their friends have been using them.
Littlefoot: Why was that brother of yours using my herd for?
Cera: Look, never mind that. You're coming back to help me track down Red Foot.
Littlefoot: No. I'm done. I'm not helping anymore, cause everyone will ignore me like they ignore Chomper and the others.
Cera: You don't even have a choice! You're gonna help me get rid of the rogue, and that's that!
(Littlefoot turned around and Yelled.)
Littlefoot: No! No, no, no, no, no, no, no! I'm not helping you anymore, understand?! It's always been about you! Everyone knows who you are, who you're related to, and I don't like it!
Cera: Don't you dare talk to me that way!
Littlefoot: I don't care! And I don't like you anymore! The reasons I don't like you cause you're a lousy, grumpy, cranky, grouchy and a tempered Threehorn like you father who's not here anymore cause he's dead! And you always care for no one, but yourself! And what you did is get the first tree sweet off the tree I found and teased me like you did last time when we were little before I met the tiny longneck, and It was you're fault I had them take the blame and it was you're fault that Ducky, Petrie and Spike were mad at me!
Cera: Littlefoot, how dare you---
Littlefoot: And don't call me Littlefoot anymore! I'm done with that name! I never wanna use it anymore! This has gone to far! I don't like threehorns anymore! I don't like your father, your brother and your other siblings, and most of all I don't you anymore! So go away and get lost you fat headed horn face!
(Cera was shocked and Littlefoot turn around away from her and Cera sniff and the her tears come out.)
Cera: How could you say that to me? (SNIFF SNIFF) You're not the same Littlefoot I know anymore....(SNIFF AND CRYING)
(Cera runs away crying while Littlefoot stays angry.)
(Cera is still running and then stop while crying.)
Cera: (SNIFF) The Littlefoot I know is gone and it's all my fault. (SNIFFING AND CRYING)
(And then she walk away while crying.)
Littlefoot is Littlefoot again
Mr. Kosmos: What in Saurus Rock happen to Red Foot?
Proto: Littlefoot has beaten him. He knows how to beat Red Foot. He pretend he was dead and waited long enough to aim for his foot, cause he knew his foot would be a distraction when one of us gets scratch. You did it. You beaten that rouge.
Littlefoot: Funny, I feel more I let my herd to get hurt.
Proto: Thanks to your herd, and especially your Sharptooth friend, Chomper, who stood up to that rouge, you're a hero.
(Littlefoot was happy to smile again)
Tad: No! No, no, no! Hold it! Cera's the one who suppose to beat that rouge! Not him! He got in her way! He hurt her feelings! He's a threehorn hater! And worst of all, he'd ruined my crater!
Littlefoot: Hey, whoa, whoa, Tad! I've may have gotten mad at Cera for all of this mess she got me into, but I'm not a Threehorn hater anymore cause everyone is thanking me and my herd for what we did for them.
(Tad nodding his head)
Uh, he's right, Tad. You must have made Cera's friends jealous to much. And you're the one who tear the herd apart, not Horin. And Horin was right. You did put everyone in danger.
(Tad angryly turned his head to)
Horin:And then when me and the others came to help Cera's friends, you've knock Pento off the cliff while he was trying to save the elderly dinosaurs that were trapped in the cave in your crater!
Littlefoot: And then before I ran away and got mad at Cera, you've made fun of me cause of my name and my size and laugh at me, cause you're reason why I don't like my name anymore, cause you think it's funny!
Tad: What..wha....what are you talking about?
Mr. Kosmos: Tearing the herd apart by making friends jealous of Cera? Making fun of Littlefoot? So this is why Littlefoot didn't like his name anymore! And that explains why he doesn't like threehorns and all of us with horns anymore! I should have known you the so asame of you, Tad! No ones that jealous! And no ones that funny!#
Tad: But, but, but, but, Mr. Kosmos, sir, Littlefoot's name is to funny.
Mr. Kosmos: No it's not, it's mean! We like Littlefoot's name just the way it is and I don't like when someone like you makes fun of him! I'll deal with you later, Tad!
(Mr.Kosmos walking to Horin and apologize) Mr.Kosmos: Horin, I own you and the others an apology. You were right along.
Horin: I guess you do believe me.
Mr.Kosmos: And Littlefoot, I'm so sorry I let Tad make fun of you, and thank you for saving us. Every dinosaurs in every valleys will hear that saved all of them even your kind by getting rid of that monster.
Littlefoot: Really, Well, how about that.
Mr.Kosmos: And, Chomper, your kind will be so jealous when they hear that a brave friendly sharptooth like you stand up to that rouge.
Chomper: Wow! I guess they will be.
Music Dinosaur Like Me by Phil Collins (Music of Littlefoot and his friends heading for the Forest Valley).
It's a Valley Out There by Philip Lawrence (Music when Cera and the others did all their training expect Littlefoot who didn't do well)
There's No Way Back by Phil Collins (Music of Littlefoot quitting and giving up and running away when he didn't keep up with the others after a fight with Red Foot)
They are not Helping No more (Music of Horin and his siblings and friends but Cera who are on punishment for using Chomper and the others and leaving Littlefoot left out)
Friends No More by Trisha Yearwood(Music of Cera being sad after being yelled by Littlefoot who doesn't like threehorns anymore).