When you explore any prehistoric realms you will find Wild Ultrasaurus Eggs. When you click on a Wild Ultrasaurus Eggs you can turn it into an Ultrasaurus (which costs resources). You don’t need to have a unit there, so you can look around the prehistoric wilderness and convert any wild eggs you find.
Now you have an Ultrasaurus, it can lay Ultrasaurus Eggs (which costs resources). If your Ultrasaurus layed the egg, it’s not a wild egg and only you can get an Ultrasaurus from that egg.
An Ultrasaurus Egg will take about 48 hours to hatch into an Ultrasaurus. Different dinosaurs have different incubation times, for example a Pteradactyl is only 2 hours and a Velociraptors is 4 hours. Mostly the incubation time matches the rarity and strength of the dinosaur.
This means you can’t spam dinosaurs like you do Soldiers or Archers. You’ll need to plan that dinosaur army ahead of time.
Also eggs are fragile and can be destroyed, so you’ll need to breed your dinosaurs and keep their eggs safe.
And we are hopefully, fingers crossed, touch wood, aiming to go live this Friday.