Improved Divine Smite will not trigger on an unarmed strike.
The paladin in my campaign – covered in my previous question – is a minotaur. This means he could attack with his horns, to potentially trigger Improved Divine Smite.
Minotaur, Unearthed Arcana: Centaurs and Minotaurs:
Horns. Your horns are natural melee weapons, with which you’re proficient. When you hit with them, the target takes piercing damage equal to 1d6 + your Strength modifier.
Paladin, PHB page 85:
Improved Divine Smite. By 11th level, whenever you hit a creature with a melee weapon, the creature takes an extra 1d8 radiant damage.
Do natural melee weapons from racial traits trigger Improved Divine Smite?
In other words, do natural weapons count as melee weapons? Or is there some other rule that categorizes/treats natural melee weapons differently from other melee weapons?
For my campaign I'm mostly interested in the natural melee weapon from minotaurs. I'm assuming, however, the same rules would apply for other natural melee weapons gained through racial traits – e.g. a lizardfolk's Bite, tabaxi's Claw, centaur's Hoove, etc. If this assumption is wrong, please enlighten me.