These things all live on an island where the ecosystem is dominated by dinosaurs, so none of them really get as big as, say, an elephant. Even the communal species appear in relatively small numbers, let's say 2d4, maybe 3d6 for burrowers.
d4: size
1 tiny
2 small
3 medium
4 large
d8: body type and behavior
1 rodent - solo burrowing omnivore
2 feline - solo carnivore
3 ursine (bears duh) - solo carnivore
4 lagomorph (like rabbits) - communal burrowing omnivore
5 canine - communal carnivore
6 primate - communal omnivore
7 ungulate (hoofed quadrupeds) - communal herbivore
8 chiropteran (bats) - communal omnivore
d10: covering (colors usually blend with habitat)
1 spots
2 quills
3 solid color
4 stripes
5 armadillo-like shell
6 pangolin-like scales
7 brightly colored for mating, roll again with 1d6
8 largely hairless
9 marsupial and roll again with 1d8 (yeah I know but it fits best here)
10 duck-like bill and roll again with 1d8
d12: special features
1 echolocation
2 1d4 horns or antlers
3 prehensile tail
4 prehensile snout
5 aquatic or semi-aquatic
6 absurdly long neck (headbutt attack)
7 plague carrier
8 long tusks
9 stone bite, breath, or gaze
10 sonic blast
11 shocking touch
12 speech & intelligence
I'm a little bummed out that I couldn't get the flying squirrel membrane in there but you could totally roll up a caveman by accident (3-6-8-12) so I'm calling it even.
Like the dinosaur tables I posted, if you wanted to rule out weird magic powers (for some strange reason), you could just use a d8 instead of the d12.
