Thanks to a tip from A Few Good Cats, I can send you to a great Shorpy find from around 1910: Orange, Virginia's Woodberry School baseball team, plus their mascot pups! Can you spot them? The funny thing is, the Woodberry School's mascot is now the tiger.
Of course I started thinking about other dog mascots, but what I actually found first (such is the wonder of the internet) was William Windsor of the 1st Battalion of the Royal Welsh (infantry, British Army). Although that's not strictly fair, as he wasn't a mascot but an actual ranking Lance Corporal of the regiment when he retired this year at the ripe age of about 9. Which isn't bad for a goat. Want to see The Mail Online's super-cool pictorial essay of his retirement procession? Yes you do. And check out that silver plaque of appreciation on his headdress. Just a little something from HM The Queen.