There’s two jokes in there. The primary one is that the implication is that back in “cave man” days the only two occupations were hunter and gatherer, yet it’s being introduced how more modern meetings would be now that there are a plethora of job options.

The second is a bit more of an in joke to another comment that mentions the pointy end of a stegosaurus is called a “Thagomizer” after the late Thag Simmons, most likely of this comic.

The reason a lot of people know about the second comic is scientists actually didn’t have a name for the pointy part and labeled it the Thagomizer after the comic.