Deinosuchus is very low-priority at the moment, due to already having a similar ecosystem without it. There should be tamable Quetzalcoatlus, though.
What about the Sarcosuchus then? And oh, sweet!
EDIT: Holy shit, the alamosaurus eats everything, T-rex has no chance whatsoever. Even 4 of them.
EDIT2: I made a baby
[CREATURE:SPINOSAURUS_SAWR]
[COPY_TAGS_FROM:THEROPOD_SMALLARMS_SAWR]
[APPLY_CREATURE_VARIATION:USE_TEMPLATE_SAWR:DORSAL_FIN_SAWR]
[GO_TO_START]
[DESCRIPTION:One of the most lethal natural predators ever to walk the earth. Even larger than the Tyrannosaurus. Has a large dorsal fin on its back.]
[NAME:Spinosaurus:Spinosaurus:Spinosaurus
[CASTE_NAME:Spinosaurus:Spinosaurus:Spinosaurus]
[GENERAL_CHILD_NAME:Spinosaurus chick:Spinosaurus chicks]
[CREATURE_TILE:'S':4:0:0]
[PETVALUE:800][NATURAL]
[LARGE_ROAMING]
[BIOME:GRASSLAND_TEMPERATE]
[BIOME:RIVER_TEMPERATE_FRESHWATER]
[BIOME:RIVER_TEMPERATE_BRACKISHWATER]
[FREQUENCY:5]
[CLUSTER_NUMBER:1:3]
[TRAINABLE][PET_EXOTIC]
[CARNIVORE][LARGE_PREDATOR]
[PREFSTRING:monstrous appearance]
[PREFSTRING:dagger-like teeth]
[PREFSTRING:terror-inspiring roar]
[GO_TO_END]
[CHILD:10]
[BODY_SIZE:0:0:5500]
[BODY_SIZE:3:0:55000]
[BODY_SIZE:20:0:6050000][DIFFICULTY:5]
[MAXAGE:50:70]
[HOMEOTHERM:10070]
[EGG_SIZE:500]
[CLUTCH_SIZE:5:10]
[SELECT_CASTE:ALL]
[SET_TL_GROUP:BY_CATEGORY:ALL:SKIN]
[TL_COLOR_MODIFIER:BURNT_UMBER:1:CINNAMON:1:COPPER:1:DARK_BROWN:1:DARK_PEACH:1:DARK_TAN:1:ECRU:1:PALE_BROWN:1:PALE_CHESTNUT:1:PALE_PINK:1:PEACH:1:PINK:1:RAW_UMBER:1:SEPIA:1:TAN:1:TAUPE_PALE:1:TAUPE_SANDY:1]
[TLCM_NOUN:skin:SINGULAR]
[SET_TL_GROUP:BY_CATEGORY:EYE:EYE]
[TL_COLOR_MODIFIER:BLACK:1]
[TLCM_NOUN:eyes:PLURAL]
[SELECT_MATERIAL:TOOTH]
[MULTIPLY_VALUE:10]
[SELECT_MATERIAL:LEATHER]
[MULTIPLY_VALUE:5]
[CAN_DO_INTERACTION:ROAR_SAWR]
[CDI:ADV_NAME:roar]
[CDI:USAGE_HINT:ATTACK]
[CDI:BP_REQUIRED:BY_CATEGORY:EYE]
[CDI:VERB:let loose a bloodcurdling roar:lets loose a bloodcurdling roar:NA]
[CDI:TARGET_VERB:are shaken by the Spinosaurus' roar:is shaken by the Spinosaurus' roar:NA]
[CDI:TARGET_RANGE:A:20]
[CDI:WAIT_PERIOD:8400]
I approve of everything here.
If you want to make your own Spinosaurus ecosystem, try the Kem Kem fossil beds on Wikipedia. I approve of all dinosaur mods added, as long as they fill the mission statement of Saur Fortress (they're all accurate). Spino is in the feathered group of dinosaurs, so I'd recommend copy/pasting the swamp-feather material from Baryonyx. Sarchosuchus would also be able to be here. I can't do it right now, due to procrastination and the need to do the Triassic ecosystem.
The Alamosaurus is basically Armok in dinosaur form, yeah. If you want an even match, based on weight, try having 60 rexes v. one Alamosaurus. T. rex is 5 tons, Alamosaurus is 120 tons.