Fitting fossils together to assemble massive dinosaur skeletons is certainly no small feat. Fleshing one out—inside and out—from tooth to tail is an even more challenging undertaking, especially when the subject is an 18-meter-long sauropod.

Experts in animal nutrition, sports medicine, biomechanics and materials science joined paleontologists to re-create a full-sized model of Mamenchisaurus that spans an exhibit hall at the American Museum of Natural History in New York City. As the main, towering attraction in a new sauropod exhibit that opens to the public Saturday, April 16, this long-necked plant eater illustrates much of what scientists have learned about these colossal creatures in recent decades.

The group of dinosaurs, still characterized by the now-discarded prototype of Brontosaurus, is quite diverse, with some members reaching more than 46 meters in length and others growing to only a fraction of that size.

The proverbial elephant in the room (made only more clear by the large sauropod in the room) was: Why haven't land animals gotten this big since the great KT extinction, 65.5 million years ago? Comparing sauropods with modern animals can help to get to the bottom of this conundrum.

"Evolution works in an additive fashion," explained Martin Sander, who is visiting from the University of Bonn in Germany and helped oversee the exhibit. "It always takes what's there, so a lot of key factors were present when these animals, evolutionarily, were dog sized—and then they started growing. The same thing happens with mammals. They also started out very small. But they made a few mistakes, which eventually limited their body size to a lower limit than you would get in dinosaurs."

What were some of the early errors our ancestors made? Having live young—and chewing their food, Sander said. One thing the superlong necks of sauropods were good for was digesting food along the way, so they didn't have to build up bulky chewing muscles that would weigh down their small heads.

Scientific American attended a preview of the exhibit and learned more about how scientists are piecing together the lives of these long-gone, gigantic animals.