Why did armored Sauropods evolve?

[andrewsaurus rex]

Sauropods with armour on their backs puzzle me.  Why did they evolve?  They were so tall that most predators couldn't reach their backs and were more likely to go after their legs and flanks, which were generally unarmoured.   Was the armour more for show than defense?

[stargatedalek]

No predator that could only reach the flanks was attacking a sauropod. That is just suicide.

Predators would have targeted young animals (which there would have been a lot of). So the armor most likely just carried over into adulthood.

That or it was used in intraspecific combat with other sauropods.

[Cretaceous Crab]

They were so tall that most predators couldn't reach their backs.

No predator that could only reach the flanks was attacking a sauropod.

No predator we know of. Probably a Longshot but there may be some titanic carnivore we haven't discovered yet that could take on an adult titanosaur.

[andrewsaurus rex]

yes I was wondering about that.....something yet undiscovered.   As I said in the other thread I started, there must have been some keystone predator keeping the sauropod populations in check.

[Dusty Wren]

You don't need a huge predator to keep a sauropod population in check, though. Smaller predators that prey on young sauropods and keep them from reaching adulthood are more than enough. Especially since, if I'm remembering this correctly, sauropods aren't known for providing parental care.

[andrewsaurus rex]

right, that's a good point. 

[GojiraGuy1954]

They were so tall that most predators couldn't reach their backs.

No predator that could only reach the flanks was attacking a sauropod.

No predator we know of. Probably a Longshot but there may be some titanic carnivore we haven't discovered yet that could take on an adult titanosaur.

No

[irimali]

I remember reading (sorry that I can't recall where off the top of my head) that sauropod osteoderms may have been more densely packed on the backs of babies and juveniles, and then became more spaced out as the animals grew.  Not sure if there was direct evidence or it was a hypothesis.  I believe there was evidence that adults were regularly absorbing and redepositing bone within their osteoderms, so adults may have hung on to them more as a calcium reservoir than for protection.   

[Halichoeres]

Yeah, a calcium reservoir would be particularly useful to an egg-layer with pneumatized bone. The original function of bone in primitive fishes was probably mineral storage, but it turned out later to be useful as armor and muscle anchor.