Hi Sherry!
Congratulations on getting one out of two of your reservations. If you are really hoping for T-Rex, I would keep checking back as reservations do get cancelled all the time. My family always visits Animal Kingdom on the first day of our vacation, with the shorter hours it gives us a chance to enjoy a nice relaxing meal on our first day. I agree that T-Rex is a fabulous way to bookend your day at Animal Kingdom, but my number one suggestion is Boma at Animal Kingdom Lodge.
Boma, in my opinion, is an excellent value for your Disney dollars. African inspired cuisine includes various meats,salads and some very yummy desserts served buffet style. It also gives you another chance to check out another one of Disney's beautiful deluxe resorts. The grounds at Animal Kingdom Lodge are absolutely stunning and you might even catch a trainer tutorial while you wait for your reservation. The resort is located close to Animal Kingdom, just be aware you will have to transfer buses when returning to your resort.
Rainforest Cafe located at Animal Kingdom would also be another good option and most certainly goes really well with the theme of the day. Very similar to T-Rex, this restaurant is always a hit with my children who love to watch the animals in action during the thunderstorms.
I hope that your reservations work out for you, please let me know if you need anymore help planning your upcoming vacation!
Best Wishes!
Mandy