In the game of Yu-Gi-Oh! Is there a difference between discarding a card and destroying a card from the hand?
Discarding, banishing, tributing, destroying, are all forms of 'sending' a card from one location to another. They are all forms of send, so anything that says 'when this is sent from hand to graveyard' would trigger from a discard, or destruction in hand from anything that can do that (not many do, but it can happen). However the terms themselves are in no way interchangable. Discarding a card, or tributing a card, NEVER counts as 'destroying' it. Even if they're coming from the same place, and ending up in the same place, they are two distinct game actions and a trigger condition that looks for one, will only ever accept that exact one. So, you can discard Babycerasaurus or Petiterandon for Fossil Excavation, but you are not destroying them and they will not trigger. Also note, their activation condition says 'by an effect', and that's also an important thing to remember because paying a cost is not 'part of the effect' so even if they did trigger from a discard, they could only trigger from a resolution that discards them and not a cost (this is how Dark World monsters work).