All creatures from summon monster spells.

[NegInfinity]

As far as I can tell, all creatures from summon monster spells, have absolutely identical stats (for a specific spell level).

It is possible to summon tiny creatures with absolutely ridiculous scores, like a bat with 31 strength, for example. Then there's ability to summon rabbit of Caernbbannog. The stats remain the same regardless of creature type, so apparently popup menu only affect their visual representation and not actual abilities.

It is sorta hilarious at first, but as far as I can tell it is either a bug or oversight.

There's a good explanation of how monster leveling is supposed to work here:
http://www.giantitp.com/forums/showthre ... r-Handbook