Factual error: When the beast itself moves, it bounds, but the sound effects make it sound as though the beast is running.
Factual error: In the book by Douglas Preston and Lincoln Child, the monster has been in the museum's subbasement for around seven years, making the lair filled with either partially or fully decomposed skeletons completely plausible. However, in the movie they change the duration to only six weeks. The lair they find in the movie with tons of skeletons doesn't connect with the time it took for them to become that decomposed.
Factual error: When D'Agosta and Hollingsworth are in the Santos Morales, they find blood on the walls and floor which is not only dry but also red. Dry blood is brown.
Factual error: When Margo and Lieutenant D'agosta walk into a lab, Margo asks one of the techs what the "soup" is, to which the tech responds Rhinoceros Megarhinos. No such species exists.
Answer: While the size is never explicitly stated, the creature does seem to be somewhat larger than a tiger and approaching the size of a horse when the scene needs it to be. Perhaps its size changes as it eats and needs sustenance?
Erik M.