Why are characters named Momonga named after flying squirrels? In both One Piece and in Overlord, there is a character named Momonga (in Overlord, Momonga was his earlier name, but he goes by Ainz Ooal Gown during the series).

 

「モモンガ」 (momonga) is the Japanese word for "flying squirrel" and is used for the type native to Japan, as well as for the northern flying squirrel and southern flying squirrel of North America, and for the Siberian dwarf flying squirrel (in contrast, the word 「ムササビ」 [musasabi] is used to refer to giant flying squirrels native to and outside of Japan), and the marsupial sugar glider is called 「フクロモモンガ」 (fukuro momonga).

These characters both are not particularly cute, are large in size, have small eye sockets, and do not feature a patagium (a.k.a. gliding membrane-like flap of skin or fabric stretched from their wrists to their ankles). In other words, they do not feature the best-known features of flying squirrels. Why were they named Momonga?  Is there anything about them that was intentionally derived from real-life flying squirrels?
In One Piece, the animal name is the most typical source of the character's name. You can read how the author decided the name 'Monkey' in the manga #20 Chapter 178's SBS.
The origin novel of Overlord is written on a free novel BBS Arcadia. You can read how the author decided the name 'Momonga' on the following 1st chapter (Japanese) (I'll translate just the conclusion):

※　名前でモモンガは無いですよね。
でも、普通にネットゲームをしている社会人の方なら、基本的にちょっとおちゃらけ入った名前の方が多いような気がするんですよね。私だけですかね？
口調とか、名前とか変更するときがそのうち来る予定です。
※ Momonga is a strange name.
But many working online gamers choose the strange name, I think. Just me?
I'm planning to change his tone and name.