The female mammoth wounded by primitive human hunters in "A Mammoth Undertaking". Despite this she accepts to befriend modern human Nigel and follows him in the modern-day park.
Another example is the same mammoth being accepted by the African elephants' matriarch after risking to "die for loneliness" due to refusing to eat any food.
That example is even cooler when reading the behind the scenes about it. They made a giant puppet of a mammoth head, then animated it in front of the elephant. They weren't sure how she'd react, but to their surprise the elephant interacted with it and welcomed it as it would for a real elephant.
Nigel's Microraptor befriending his pet macaw.
Near the end of "Saving the Sabretooth", the last two Ornithomimus eggs hatch, and the babies imprint on Bob.