Decided to add onto my original post (spoiler above) and talk about a few more dinosaurs that I think could get a TLC pass. This will be a combination of my own ideas and some other ideas found in the thread (I've been enjoying reading through people's ideas)
Araneo - Starting off with a creature that gets very little love, the Spider. I believe, with the addition of Aberration, the spider should get a natural Zip Line it can plate for itself and rider. This would work like the normal Zip Line but may degrade overtime.
Archaeopteryx - I think, instead of holding it over your head and looking kind of silly, it should hang onto your back until you need to use it as a 'parachute'. I think it'd just look better.
Argentavis - New Model. Honestly, I like how it looks in the Dossier, but the in game model isn't that great and this old bird could use a very nice TLC pass.
Bronto - I don't see this dino much, as I've not seen much of a use for it (for myself, playing solo), but a small pass I'd like to see is some kind of saddle update that puts a small saddle higher on the neck to give the 'driver' a better view and not have the weird massive saddle it currently has, also adding this to the platform saddle. (I'm not sure I explained this very well...)
Carno - This lovely little derp deserves some TLC, I think it could get the Rhino's charge mechanic with extra knock back as it speeds up, also a nice new model. (I think most Theropods deserve a slight update to their stances)
Dilophosaur - While I like the Jurassic Park Reference, even in that movie that wasn't the full size (and I mean in the universe of Jurassic Park, that wasn't an adult Dilo) so I think a larger Dilo would be nice, retain the frill and spit attack, but make it big enough to ride at least, maybe? Maybe even make it a sexual dimorphism thing where one is bigger than the other.
Diplodocus - I think it should get two attacks, retain the normal head push and add an actual tail whip that does damage.
Direwolf - Legs definitely need fur, and I'd like to see the face a little less snarly, but otherwise excellent.
Leopleurodon - PLEASE make a -normal- version that does not have the 'magic' ability so that we can tame them and have them. Also, possibly reduce Megalodon spawns a little and let the Leos be a bit more common for the 'medium water dino' spot.
Megaloceros - I believe, at least for the females, an 'armor' should be introduced to give them a use. It wouldn't give them a lot of use, but people would look a lot cooler with the lance on it. Also, the model could be made a bit more majestic in my opinion, bring their head up slightly and make it look like they're somewhat puffing up their chests.
Onyc - Give them a hanging stance so they can hang onto either roofs or have a special perch you can set right under a roof to let them hang on, it must be stressful having to fly 24/7... poor little guys.
Pachy - These guys really need some TLC, I mean, they're practically useless. Again, like the Carno, they should get a charge attack but instead of more damage (Rhino) or more pushback (suggested Carno) it'd add more torpor the longer you'd been charging. Also, I believe they should get a size boost. Make them more menacing that way.
Parasaur - I'd like to see these guys get a 'Whistle Boost' ability that would increase the range of all whistles from the rider.
Ptera - I think it should get a slight TLC pass, make it look a bit nicer.
Scorpion - Let it grab smaller creatures, Dodo size about, and carry them around.
Quetz - Have them stand tall, like in their dossier, when not equipped with a platform saddle, otherwise giving them the platform makes them 'lie down'.
Raptor - I think they could be remodeled to be more like the cover art, or like the art from someone in this very post (This nice art from Promilie)
Sarcosuchus - Like others have said in this thread, this guy needs a TLC pass.
Spinosaurus - In my original post I said that I'd like to see it gain the same ability as Iguanodons, as in letting them switch between Quadrupedal movement and Bipedal movement. In Quadrupedal mode it'd probably run a bit faster and do a little less damage and in Bipedal it'd be a little slower but do more damage.
Terror bird - I think they need to stand a little taller, be a bit more proud of being the TERROR Bird.
Triceratops - They could probably use with a slight size increase.
Thus concludes my silly comment. Hope everything was clear enough and that my ideas weren't too outlandish for everyone.