The original kobolds were earth-spirits that made miners sick, like poison-coated caltrops in tunnels. The little spiky stones were named after the earth-spirits; and mineral cobalt can be found as sharp boot-penetrating crystals usually coated in mercury.
Since their traps are found in mines, the first kobolds were gnomes with candles on their hats, much like World of Warcraft kobolds.
D&D first edition (aka Advanced D&D) gave us scaly dogs
D&D second edition went ratmen
D&D third edition went into halfling-lizardmen, and 4th and 5th edition continued this trend.
Ryoko Kui, who writes+draws Dungeon Meshi, prefers her kobolds to be cainine
