Not sure how many of you know this, but I'm a supporter in the idea that Redclaw and Sharptooth are one and the same dinosaur. I've written an explaination for why I believe this may be so.
1. Death
The first sharptooth seems to die at the end of the first movie. However, there is never a confirmation in the movie that Sharptooth had actually died. And it is not true that sharpteeth could not swim. In the fifth movie we see the striped sharptooth swimming in the Big Water, and there was a scientific discovery that showed evidence of large theropods being able to swim. Sharptooth could have come out of the water after the kids had left and disappeared, perhaps to recover from whatever injuries he had sustained.
2. Strength
It is obvious that Redclaw does not seem as physically strong as Sharptooth, and has not displayed any feats of wonder that Sharptooth had. However, there are some explainations for this. Redclaw might be slowly succumbing to old age, becoming weaker. If Redclaw is indeed pretty old, that alone would explain his lack of "incredible feats". Another explaination could be that Redclaw is only pretending to appear weaker than Sharptooth to fool the Great Valley into thinking he could be generally easily defeated. He could use this as an advantage and attack when they least expected it, when he felt the time was right.
3. Determination
Redclaw is probably the most determined terrestial sharptooth other than the original. Just as with the original Sharptooth following Littlefoot and his friends throughout the months that it probably took to the Great Valley, Redclaw hangs relatively close to the outside of the Great Valley. How long he has been there is unknown, but it was at least one year as revealed in one of the episodes. This kind of determination has only been seen one time before with the first Sharptooth.
4. Size
Chomper once mentions that Redclaw is the "biggest and meanest sharptooth of them all", a reputation that could easily describe the first Sharptooth. This kind of reputation could link Redclaw to Sharptooth, as it does nothing to disprove that there is no real connection between the two dinosaurs.
5. Appearance
It is obvious that Redclaw looks different from Sharptooth and this could be evidence that they are two different dinosaurs. But again this can be explained. Sharptooth's original eye was damaged when Littlefoot accidentally hit him with a thorn and over time it could have changed from the original red color to a pale yellow, perhaps caused by pus and the vision in that eye could have been permanently damaged, which may also account for his lack of doing things that Sharptooth was able to do. The skin of his body could have dramatically paled due to old age or severe malnutrition, caused by not being able to hunt as effectively as he could, although he's clearly eaten well enough to sustain himself for years.
6. Teamwork
The original Sharptooth seems powerful enough to hunt on his own, and thus it would appear odd that he would need help from fastbiters. However, damaged eyesight could be why he hangs around two fastbiters. It could be a symbiotic relationship similar to Dil and Ichy. The fastbiters could be the "eyes", doing most of the searching for prey while Redclaw is their brawn, the big guy to take down the prey. Redclaw's decreased strength could be another factor in him seeking help from what look like two young fastbiters.
7. Scar
The scar seems to be on the wrong side. It would make sense for the scar to be on the side where Sharptooth had originally suffered the blow from the thorns. However the thorns didn't leave long scratches on the dinosaur's skin in anyway. The notion that the scar would be on the right side would not make sense because of this. The long scar most likely has another origin. It could have been recieved when he had been knocked into the water by Littlefoot and his friends, perhaps hitting his head on a sharp ledge down there. He also could have suffered an injury sometime later, perhaps hitting his head against a sharp rock when lunging for prey.
8. Intelligence
Redclaw does not seem to be as smart as Sharptooth and could be seen as being senial. This could be attributed to his possible old age or the lack of good nutrition. Redclaw probably is not as smart as he once was if he is indeed old. Malnutrition could have weakened not only the body but the mind as well. The original Sharptooth would have shown a decrease in intelligence as well as he had gotten older or suffered from malnutrition as well. The lack of intelligence is not a good explaination to seperate Redclaw from Sharptooth.
9. Revenge
In the first movie, Sharptooth was motivated by revenge, constantly hunting down Littlefoot and his friends even what appears to be months later. Redclaw shows similar determination in the series. His motivation could be the same as that of Sharptooth, explaining why he seems to constantly target the same kids and why he seemed to be after Ruby, her family, and Chomper. Redclaw might even be more determined than Sharptooth given that he has hung around the valley for at least one year while Sharptooth has probably only been hunting the gang for a few months. It could be that Sharptooth's lust for revenge and determination had increased after his defeat outside the valley's walls.
Possible Story:
After being struck by the boulder and pushed underneath the water, Sharptooth could have come to a short time after the young dinosaurs left the scene. Using his powerful legs, he could easily have pushed himself out of the water and crawled back onto the land. The boulder would have left some serious injuries, and he might have left the scene quickly to find a safe place to heal. His right eye would have healed, but due to pus being in there for so long, his eye could have been permanently stained a pale yellow, and the eye would hae lost some sight in it, making it harder for him to see. Without his once reliable eyesight, he is no longer able to hunt very well, and loses his strength as he becomes less able to hunt and take down large prey.
Over time, he would have started to succumb to a combination of malnutrition and old age, and the combination of the two could have caused his skin to change from a healthy black to an unhealthy pale color. He may have run into Screech and Thudd at some point and formed a symbiotic relationship where they helped each other to hunt. Screech and Thudd became the eyes while Sharptooth would be the brawn. But even with the help of Screech and Thudd, Sharptooth would continue to have problems hunting down large, nutritious prey and would continue to suffer for it. And as he got older, his strength would continue to weaken to point where he barely retains half the strength he once did. Screech and Thudd would continue to remain by his side because they still desired the protection from such a large sharptooth.
Sharptooth may have had a run-in with Chomper's parents and may have tried to attack Chomper, only to hit his head against a sharp rock and causing him to get the long scar on his left side. The cut may have caused some damage in his left eye, leaving him even less able to hunt for himself. Furious, Sharptooth could have hunted down Chomper relentlessly, which may be why Ruby was assigned to protect Chomper and why Sharptooth would have been after her family. This also explains why Sharptooth hangs near the Great Valley outside of Littlefoot and his friends being there. Sharptooth's name would have been changed to Redclaw because of one of his hand claws being permanently stained red as a result of the deep cut.
Somewhere along the lines, relatively quickly, Redclaw would have discovered Littlefoot and his friends were there along with Chomper. Knowing that the very dinosaurs he sought revenge on were there, his determination would increase to an intensity that beats the determination that he had before. He would stay near the valley for however long it takes to get his revenge on those dinosaurs, staying around for at least a year, perhaps even longer. He would start pretending to be pretty stupid and not too strong in order to fool the gang into thinking they could defeat him easily. He would not charge in like he did before because he would remember the last time he had been so foolish. Redclaw might know the original entrance of the Great Valley and perhaps is biding his time until he is certain of the right time.
Anyone have any thoughts on this?