Another example of insular dwarfism among the dinosaurs, and a handy option for a dinosaur encounter thats not yet another massive bitey thing. I do quit like the smaller dinosaurs, and I think having a wider range of such critters in your arsenal is handy.
You might consider populating a whole island or island chain on the Hollow World with an island dinosaurian ecology...
Struthiosaurus
by Cab Davidson
Stat Struthiosaurus AC: 0 HD: 3+3 Movement Rate: 90’(30’) Attacks: 1 tail swipe Damage: 1d6 Number Appearing: 0 (1d8) Save As: F2 Morale: 6 Treasure Type: Nil Intelligence: 1 Alignment: Neutral XP Value: 65 Struthiosaurus is a primitive, small, heavily armoured species of ankylosaurid dinosaur found on certain islands. It is rarely longer than 8’, and around 3' tall at the shoulder. While an inoffensive herbivore it will defend itself if cornered by swiping with a wickedly spiked tail. Its armoured and spiked provides significant protection, and any creature attacking using natural weapons (claws and bite) must make a save vs. death ray or take 1d4 damage from the spikes.