Are you suggesting that dinosaurs were not part of nature? We see exactly this in nature. Not more than an hour ago I was looking at a vertebra from a Blue Whale in my Chiropractor's office. It was huge... but my Chiropractor took a model human vertebra from the similar part of the spine and showed me that they were virtually identical in shape... just differing in size.
Some people have no idea how really big these titanosaurs really were.
Mounted Argentinasaurus fossil skeleton - 114 feet long
Notice the man under its tail... now imagine muscles, tendons, and skin on that framework... and a gut and internal organs hanging down from those ribs. Also image the size of the diaphragm needed to pump the lungs. How about the muscles needed to keep that neck and tail off the ground... cantilevered out over 40 feet in each direction. Where are the attachment points on the spine for large stay muscles above the neck and tail?
The following picture is a posterior (one of the vertebra from in front of the pelvis) vertebra from a South American Titanosaur the Argentinosaurus huinculensis, next to a human for scale. The estimated weight for this sauropod was between 180-200,000 lbs.
Argentinasaurus vertebra
From the looks of the girl, I'd say she was 5'2", so the vertebra is probably a little over 4 feet tall.
Here is another set of mounted Argentinasaurus fossls... with the bones found in this instance placed in the appropriate locations.
Argentinasaurus
The posterior vertebra of the Amphicoelias fragillimus was reliably described as being 8 feet tall. Twice as tall as the vertebra pictured above.
Every other diplodocoid fossils that have been found, including ones that are complete, have posterior vertebra sizes that are proportionate to their length and proportionate to other sizes of their other bones. For example a 2 foot tall vertebra for a 40 foot long Diplodocus fossil is matched proportionately by a 3 foot tall vertebra in a 60 foot Diplodocus and all the other bones are similarly scaled up compared to the smaller animal. Paleontologists have found the same scaling between other species of sauropods. There is no reason to believe that this would be different for other sauropod dinosaurs. That would make a conservative (this is a conservative web site, you know) multiplier factor for scaling of this very similar build diplodocoid dinosaur about 1.8.
Found with the 8 foot Amphicoelias fragillimus vertebra was a 15 foot femur. Note that the Argentinasaurus' femur in the picture above is about 7-8 feet tall. imagine that fossil in the picture above TWICE as tall. This 15 foot to 8 foot Femur ratio confirms around a 2 times multiplier factor for the size of the Amphicoelias over the Argentinasaurus. Let's stick with the conservative 1.8 factor.
Assuming that the A. fragillimus was not really, really skinny, (which the width of the vertebra would seem exclude) and is actually very similar in build and body shape to all the other sauropods, the Square Cube Law should at least give us a ball-park estimate for its weight. 1.83 is 5.832. That is the multiplier factor to use to determine the volume and the mass of the larger dinosaur. If Argentinosaurus really weighs 180,000 pounds, then A. Fragillimus would weigh an absurd 1,049,760 pounds (!) That's some ball-park.
If we were to arbitrarily decide that the larger beasty were only 1/2 as wide in proportion to the Argentinosaurus (unlikely as the ribs would be the defining dimension and they connect to that 8 foot vertebra) we could perhaps knock off a good portion of that weight... maybe get it down to under 500,000 pounds... but I doubt it.