I think the idea of the Great Valley dinosaurs finding allies in displaced sharpteeth and other dinosaurs is a good one. Your story has already featured groups of dinosaurs not affiliated with either valley (the spikethumbs from the Land of Mists, the egg stealers in Chapter 20, and the swimmers with bows and arrows); you could introduce some new ones that the GV could recruit to help them fight.
Another idea I had was that when the GV inhabitants attempt to retake their home, some of the dinosaurs from Styracus’s herd could change sides and fight with them (if they deem that the GV dinosaurs have a good chance of succeeding in their endeavor based on the fighting forces they have mustered). As you showed with Blackjack the clubtail in the last chapter, some of Styracus’s followers are displeased with the war. I would imagine that the first priorities of such characters would be to keep their new home, and if sticking with Styracus and Excidium meant that they would be defeated and kicked out of it, would prefer to fight with, or surrender, to the other side. (Does any of that make sense?

)
The two Big Water Swimmers and Mo were gliding through the glassy water of the ocean.
You refer to the plesiosaurs as both “Big Water Swimmers” and “Aquatic Longnecks” in this chapter. My opinion is that “Aquatic Longneck” (or “Water Longneck”, or “Swimming Longneck”; I tend to think of “aquatic” as being a bit too fancy a word for LBT) ought to be used when referring specifically to the plesiosaurs, while “Big Water Swimmer” could be used for any marine reptile, such as Mo.
Almost as the words left his mouth, he mentally slapped himself.
Should be “as soon as”.
"I take it that you were successful?" Pterano asked.
"We were. But not without casualties, Rytho, Ed, Sorna, Isla, Nublar and Cirrus did not make it off the island," Deimos said sadly.
Not necessarily a mistake, but Pterano and the others who stayed on High Tree Island do not know who Sorna, Isla, Nublar and Cirrus are. It might make sense if Deimos mentioned that they were a group of fast runners native to the island who had helped them. (This is probably the least significant issue I am highlighting in this review, and it wouldn’t matter much if you ignored it.)
"Elsie, I mean to ask you this a while ago but, who's the other Aquatic Longneck with you?" Littlefoot asked.
Should be “meant”.
Styracus, Stoneclaw, Flamewing, Icthy, Dil Saber, Theta, Hasta and a single Reborn and a single Diamond were gathered around the burned out remains of a campfire.
You’re missing a comma between the two underlined names. Also, considering that Stoneclaw and Flamewing are both Reborn, it makes things a little confusing when you say that there is “a single Reborn” with them. The solution I’d suggest is to list Stoneclaw and Flamewing’s names, followed by “another Reborn”. Here’s an example of how the sentence could be rewritten:
Styracus, Icthy, Dil, Saber, Theta, Hasta, Stoneclaw, Flamewing, another Reborn, and a single Diamond were gathered around the burned out remains of a campfire.
"There are apparently no weapons and no patrols that we can see in Berry Valley and -," Ozzie said before Sierra cut him off.
The hyphen indicating the interruption should be a dash, and there should be no comma.
There, Styracus stood, flanked by Stoneclaw and another Reborn, this one was a sickleclaw with metallic silver skin and strange metallic claws.
Since you mentioned earlier that there was another Reborn present, perhaps this should be changed to “the other”. Also, the word “was” is not necessary.
Stoneclaw seethed at Styracus's diplomatic approach but he figured that something would go wrong and he will get to kill.
Should be “would”.
"What's the matter, afraid," he said mockingly.
There should be a question mark at the end of Theta’s line.
He was standing next to half of a Yellowbelly and behind him were the remains of several Yellowbellies, spread out over many square feet of bloody ground/
Obviously you meant to type a period here. One of the few typos I’ve seen involving a punctuation mark.

"Let's see if we can keep a few of those Yellowbellies as food," Saber said, "After all, we have three sharpteeth to feed."
"Saber, perhaps you are not aware of this but we Reborn do not need food," the silver sickleclaw said.
"Okay, make that three sharpteeth and one Sharpbeak."
If I understand correctly, the sharpteeth in the group are Saber, Stoneclaw, the Reborn sickleclaw, and the Diamond sickleclaw. Unless Saber is discounting himself, shouldn’t his initial statement be “four sharpteeth”? And if the Reborn do not need to eat, his revised statement should be “two sharpteeth, one sharpbeak, and one bellydragger”.
I found the scene with the yellow bellies to be rather disturbing myself.

They certainly weren’t my favorite dinosaurs in the LBT series, but I wouldn’t have wished this on them. (Perhaps I am unusual in this regard.) Not that it can be helped, but even they knew well enough to run from the
Baryonyx in LBT XIII. It seems strange that they didn’t just do the same here. (Just my opinion.)
By the way, congratulations on becoming an Ultimate LBT Fan, Serris.
