And of course, LBTlover, we can't forget about LBT 3 where Cera's father forbid her to EVER play with Littlefoot again because he was "a bad influence".
I really think you hit the nail on the head with how close we've got here.
However, I think one "different species couple" is closer, if only slightly.
Let's look at the concept of Ducky and Petrie, shall we?

First off, we can not argue just how close Ducky was to Petrie right from the start. Just from the name she showed interest in the little flyer. ("Petrie, huh? Funny name!") In a later scene when Littlefoot asked Petrie to fly up to the top of a tree to get some food, he responded in a scared manner and Ducky comforted him. Then when Petrie accomplished getting all the green food down, Ducky kissed him as her thanks. Finally, from the same original LBT movie, we have the big Sharptooth fight. By the end, Petrie is seemingly sacrificed. Ducky then cries tears of sorrow for him... only to have him come climbing up the cliff and nearly hug him to death with joy.

From there, I can't remember much from her side until LBT 4 where Petrie showed he was scared when they were about to travel through the mists. Ducky noticed he was scared and comforted him. ("Do not be afraid, Petrie, I am here.")
When the two reunited after Ducky was kidnapped in LBT 7, the two hugged one another.
In the latest sequal, Ducky shows concern for Petrie with how he was being treated by his siblings.
Now, with Petrie's side, it's more of the scenes where he comes to her rescue. The Sharptooth fight in the original LBT and LBT 2. LBT 4 holds a bit more there. Not only does he try to save Ducky from Itchy, but he also shows the most concern for when it was believed the hard impact of hitting the water had killed her. He even bravily stands up to Dil when Ducky is lying there motionless on Dil's mouth. He then tries to save her when Dil tosses her up in the air only to barely miss in grabbing her. (You have to play the scene in slow-motion to notice it.) Then after all the danger was gone, Petrie swooped down and carried her to safety.
Petrie is the one who is most concerned about her when she gets kidnapped in LBT 7.
All of these cute scenes have shown that the two really care about one another, and from the start have had a bond more powerful than friendship. There's something there between them, but they probably know they can't engage in those feelings because they're different species. If only they were the same, then maybe something interesting could develop.

So, I believe Ducky&Petrie is closer than Littlefoot&Cera, if only slightly.

What do you say?
