[Gorjus]

. . the part of its brain dedicated to smell was huge

How can they possibly know this?

Know, as in absolute certainty? I'd say they can't. However, all vertebrate brains are arranged pretty much the same way. Corresponding areas of the brain, from the frontal lobes to the brain stem, control the same sort of things. There are distinct areas that govern sight, smell, hearing, touch, etc.

The relative size of the various parts of the brain, which can be determined with some accuracy by looking at the brain cavity in fossilized skulls, gives a pretty good idea on how well a particular capability was developed.

That's what the statement is - that the part of the brain dedicated to smell was huge - but there is usually corroborating evidence as well. Large nostrils with extensive tissue to absorb smells versus small eyes with a poor resolution capability, for example, can confirm the evidence of the brain cavity itself, and all those are determinable from fossilized remains.

As the saying goes, "The race is not always to the swift, nor the victory to the strong - but that's the way to bet."

[Junior]

Don't forget the presence of large numbers of — the word escapes me, but they are bone sheets that increased the olfactory surface area.