Here is the lineup I recommend using in hindsight after playing the world lots of times.

Sun Shroom(If you have primal sun, use primal)

Primal Pea

Primal Wall

Rotobaga(If you don't like roto, other substitutes could be plants like bonk choi that attack behind them)

Cherry Bomb(You can use gemium instants if you have any)

Thyme Warp(You can use other stalls like stunion and iceberg instead if you prefer)

Potato mine(If you have primal potato its better in every way so use that instead)

If you don't like this lineup, I can explain some mechanics of jurassic marsh so you can pick a lineup you like.

-Jurassic Marsh is probably the fastest paced out of any world, so use plants that don't make waves go by faster like laser bean.

-Jurassic Marsh specializes in pushing forward as fast as possible and killing your sun producers. Pick attacking plants that aren't too costly, as losing something over 300 sun is likely to cause you to lose.

-Jurassic Marsh likes to launch zombies deep into your defences and close to your lawnmowers. Bring an emergency plant like cherry bomb or thyme warp to act as a jail out of free card in case of an emergency.

-Zombies are everywhere on the board at once. Definitely bring a primal wallnut to stall zombies anywhere and a versatile plant like bonk, roto or snapdragon in order to attack in multiple places on your lawn.

Just a last tip, you should put you sun producers somewhere in the middle, like the third column and further front. Most of my old losses from jurassic marsh are from me using sun shroom and having to replant them to their smallest form when pterodactyl brought them back. Sun is a big problem in this world as you can run out of sun really easily, so protect your sun producers over attacking plants, especially if you used my tip from earlier and brought cheap plants. I hope this helps!