Here is a list with a few suggestions I posted on Reddit, which combines both my personal ideas as well as input from other users:
Araneo
Ability to climb on most surfaces, similar to megalania ability, but without stamina drain
Ability to shoot a thread working as a temporary zip-line or grappling hook
Ability to set sticky traps
Megalodon
Ability to grab players and smaller creatures in the mouth, similar to megalosaurus ability, but underwater
Ability to grab players off of their mounts
Ability to jump out of the water and catch anything near the surface, or people on exposed rafts
Ability to detect enemies and their status, similar to abilities used by parasaurs and dire wolves, but underwater
Ability to inflict bleed damage
Upon making a target bleed, wild megalodons may come to aid a tamed megalodon without immediately becoming hostile
Tracking wheel, similar to moschops harvest wheel, but with a targetable detection ability that expands in range with increased levels
Carnotaurus
Ability to use their horns to damage stone structures
Sabertooth
Increased movement speed
Ability to sneak up on players and smaller creatures, and then pounce on them from behind
During a pounce, an ability to suffocate players and smaller creatures (this would give the oxygen stat a new purpose)
Ability to inflict bleed damage
Titanoboa
Constrictor ability
During constriction, an ability to suffocate the victim (this would give the oxygen stat a new purpose)
Infrared vision ability, similar to the snow owl ability
Carbonemys
Ability to take cover in shell, similar to doedicurus ability
Resistance to cnidaria stun effect and temporary immunity
Diplodocus
Ability to use a tail swipe and inflict damage if health drops below a certain point, for example 50%
Lymantria
Ability to climb on most surfaces, similar to megalania ability, but without stamina drain
Ability to shoot a thread working as a temporary zip-line or grappling hook
Ability to continuously produce silk
Mammoth
Increased health
Increased carry weight
Pack bonus
Trumpet ability to scare smaller creatures, similar to parasaur ability
Ability to use trunk and tusks to carry players and small creatures
Ability to use trunk and tusks to pick up old structures or structures belonging to other tribes
Kairuku
Immune to cnidaria stun
Achatina
Ability to produce achatina paste by simply feeding it berries
Pelagornis
Ability to harvest prime fish meat
Barrel roll spin ability dealing high damage, similar to pteranodon barrel roll, but only usable underwater
Toggleable soar ability enabling flight for extended periods of time at the cost of maneuverability
Pulmonoscorpius
Greatly buff the torpor in it's sting attack against wild animals, making it a viable option for knockout tames
Pincers are able to harvest prime meat
Pincers can grab and hold onto smaller creatures
Sting attack can be used while holding a creature
This is by no means a completed list. If you have any additional ideas, feel free to suggest them.
Most of these points are separate suggestions. They don't necessarily need to come in a bundle.