Which dinosaur (all of the megareptiles included) was the biggest, in terms of weight and volume (I’m assuming dinosaurs are in general of ~equal density)? You can divide it into sea and land creatures, if you like.
AFAIK, it’s generally accepted to be Argentinosaurus huinculensis.
Yep…that’d be the one although pieces of something as yet to be named have been found that suggest an animal some 25 feet longer than Argentinosaurus.
The one that gets all the lady dinos, obviously. 