[Pontiac]

"The fossil ankle and ear bones of Djarthia make it clear that the Monito del Monte descends from a Djarthia-like ancestor, and so probably returned to South America from Australia before Gondwana broke up. The continents have been separated by deep ocean since about 40 million years ago."

Like the Monito del Monte, Djarthia was a little larger than a mouse

How do find the fossilized ear bones of creature the size of mouse?

Bones that size would hardly be large than the grains of sand you would be sifting through.

[Youngblood]

I’ve watched a guy at a well-known natural history museum working on the extraction of a tiny jawbone from a piece of rock under a microscope. Not work for the easily bored or distracted (or the hard of seeing), let me tell you!