Dunno, but since they weren't compared to horses, but it did list 6 feet long, let's go with the latter.
Int is animal (1-2).
Ability scores of similar Medium critters:
Ambush Drake: Str 16, Dex 15, Con 18, Int 7, Wis 10, Cha 9
Fumarandi: Str 15, Dex 11, Con 13, Int 4, Wis 13, Cha 12
Retchenbeast: Str 15, Dex 9, Con 16, Int 4, Wis 11, Cha 10
Mardallond: Str 15, Dex 12, Con 15, Int 4, Wis 14, Cha 11
Trilligarg: Str 15, Dex 12, Con 15, Int 4, Wis 14, Cha 11
Stone Drake: Str 17, Dex 15, Con 19, Int 14, Wis 12, Cha 14
Since they rely on their Spit, I'd err on the higher end of Dex. They had 3+3 HD, so decent Con, too. Nothing screams super-strong to me, so we could lean to the low end (15).