Please add your source as I’m recreating the park and want it to be as accurate as possible. I’ve added concepts such as Plesiosaur Pond too. The wiki has been helpful, but just incase there’s canon I’m missing.

JWE launched with 42 dinosaurs in total ( 37 base game +5 Deluxe dinosaurs ).
Later they released the Fallen Kingdom update that added 6 free dinosaurs.
Everything that would come later would be Dlc except the Nasutoceratops.
Right now the roster has 68 prehistoric creatures.
JWE2's steam page confirmed more than 75 species at launch. I firmly believe they will include all the first game's dinosaurs, but in a way that scales with the dlcs you own.
In other words, they will have all the free dinosaurs from JWE1 along with completely new ones ( mostly marine and flying reptiles ), and it could be a lot !
Then you could have extra dinosaurs depending on the dlcs you own from the first game.
IF you know the TW:Warhammer trilogy, you could understand how dlcs worked and transferred from the first game to the second, then to the upcoming third one.
I personally don't have a problem if they reuse certain models or animations, as long as they enhance them and include more to enrich the game.

Anyway, Frontier needs to address the issue of non compatible dlcs in JWE1, for example the Claire's Sanctuary dlc introduced paleo-botany, but you couldn't access it with the Return of Jurassic Park dlc.
Game1 and Game2 need to be linked, not just in narrative campaigns, but in the content we bought and spent so much on.

Note that this is all but mere speculation, don't take my words for granted.
Hope you enjoyed the read, be safe !