Possible Clues:

• Old doctor drops boxes — one's very heavy!
• Metropolitan Museum mascot William is a blue one
• Semi-aquatic and extremely scary beast
• Animal with a wide yawn
• Animal whose full name comes from the Greek for "river horse"
• Zambezi wallower
• Aquatic pachyderm
• ''Hungry, hungry'' critter of a kid's game
• Pachyderm
• African wader