Black Pearl

While I didn't choose poorly, I did not go with what was intended for the "dark rum" based on the color of the cocktail in my source or the second site I found the recipe.

The second link actually provides more insight by listing the rum they used. When I made mine I suspected a black blended type rum was intended and considered going with Worthy Park 109, Coruba, or Gosling's Black Seal (all available in my home bar). Instead I went with a blend of Appleton Estate Signature Blend (which counts as a dark rum sometimes, because color based rum classifications are terrible), Smith and Cross (because I love adding some of that funk to everything), and El Dorado 8 Year which is much darker and closer to what I had suspected was intended.

The Thrilist link says "classic tiki drink", but I cannot find anything referencing an actual origin or any true classic tiki bar menus listing it. I'm not saying it's not a classic, but so far I have not found any truly classic references and Fernet Branca has definitely seen a sort of modern revival among bartenders and cocktail nerds.