Uh, would it not make MORE sense to WEIGH the reindeer, polar bears, giraffes and elephants? and then calculate the skeletal ratios and apply that to dinosaurs? This approach seems to mean that all dinosaurs would have to look like Twiggy!
That's how they did it. Take a modern skeleton, determine the minimum wrap volume, take known body density figures, that gives a minimum body weight for the animal. But actual measured animals in the natural state weigh in at 20% more than this.
Do the same for a dino skeleton to get the minimum weight. Now assume wild dinos were more like modern animals than roly-poly butterballs, so use the same 20% addition to get natural weight.