The Carnosaur has given rise to a debate amongst my friends, so i decided to settle the questions once and for all.
The Unit Strength chart on page 71 states the following:
"Monster: US= starting wounds"
"Ridden monster: US = Equal to monster + 1"
This gives the Carnosaur a US of 6 (5+1)
Page 74
"If a character model (including his mount) has a unit strength of 5 or more, then he can be picked out as a target regardless of the rules just given. Enemies may freely choose to either shoot at the character or the unit he has joined"
He also cannot use the "look out sir!" rule in a unit (page 75)
Also, some questions about what kind of penalty/bonus you get for shooting at him has arisen.
Since he has US >1, he does not give the usual -1 penalty for shooting at a single model (page 28)
But, since he's not a "large target" ha does not give a +1 bonus to hit, and therefore cannot see over units.
Personally i really like that they've done when they removed the "large target". You don't get +1 to hit, and you can hide him behind skirmishing skinks. And the idea of hiding him inside a unit, I just think it's lame. It looks really stupid no matter what unit you put him in...
IMO, it's better to use a skirmish screen, because if you hide him in a unit he's easier to target, and it's harder to manouver.