I agree with DarkHououmon. But I would also add some tidbits.
I think Litlefoot's mother was refering to the culture she was a part of - the leafeaters. Everybody sticks to their species, but the herds still live together and share the same food and water. They speak the same language. On the other hand, the critters you speak of and the sharpteeth are not a part of this culture and Littlefoot's mum may not have been thinking about them when she said that. She never mentioned the sharpteeth, after all. The sharptooth way of live is incompatible with that of the leafeaters, and many of the critters who appeared at Littlefoot's birth are probably too primitive to speak and have notions of speciesm (with the exception of pterosaurs, who appear to be a tolerant bunch throughout the whole movie).
