Long-necked dinosaurs were the largest animals that ever walked on land. Moving cathedrals of sinew and bone, these plant-eating giants—called sauropods—could stretch up to 120 feet from head to tail. At their heaviest, they weighed a staggering 70 tons.
But a new study published today in Nature Communications takes a whack at sauropods' conventional origin story. A new Chinese species of sauropod named Lingwulong shenqi—the “amazing dragon of Lingwu”—directly implies that major groups of Earth's largest land animals arose some 15 million years earlier than previously thought.
The announcement comes mere weeks after another blockbuster paper in Nature Ecology and Evolution revealed that sauropods' early days were a time of evolutionary experimentation. An ancient cousin of classic sauropods named Ingentia prima—“the first giant”—arrived at an anatomical path to hugeness millions of years before the classic long-necked dinosaurs.
“I love these papers, as they are both game-changers,” says University of Edinburgh paleontologist Steve Brusatte, the author of The Rise and Fall of the Dinosaurs and a National Geographic explorer. “It's not so much that what we thought we knew about sauropods was wrong, but just that some of the key events in their evolution happened many millions of years before we used to think.”
Sauropods dominated Earth's land ecosystems for most of the age of dinosaurs, stretching from the late Triassic more than 200 million years ago to the late Cretaceous, about 90 million years ago. But they didn't start out massive; the first sauropods were bipedal pipsqueaks.
Paleontologists thought that the so-called “true sauropods” didn't accrue the adaptations necessary to become living, vegetarian skyscrapers until about 180 million years ago, during the middle Jurassic. These animals grew more or less continuously from birth, and their bodies morphed to either shed or bear more weight. Their skulls shrank and neck bones became air-filled honeycombs; their legs became stout columns.
But when and where did these crucial evolutionary steps take place? Much earlier than the middle Jurassic, it turns out.
A team led by National University of San Juan paleontologist Cecilia Apaldetti found puzzling remains of a long-necked dinosaur in Patagonia that dated to roughly 208 million years ago. The partial remains, formally named Ingentia prima, belonged an animal some 34 feet long and about ten tons—a staggering size for an animal that preceded the sauropod anatomical “toolkit.”
These older cousins of the true sauropods had stumbled onto their own way of getting massive. Unlike the later mid-Jurassic sauropods, their bones didn't smoothly grow at the same rate; instead, they grew in alternating slow and fast bursts. What's more, their limbs had more bend to them than later sauropods' column-like limbs, yet they supported the animals' weight just fine. Their neck bones also weren't as air-filled or elongated as later long-necked dinosaurs.
The find confirms that already during the late Triassic, dinosaurs started to occupy the giant-herbivore niche—and did so with a mosaic of traits.
“...Dinosaurs had an unusual ability to innovate anatomically from the beginning of their evolution,” says Apaldetti. “This allowed them to dominate and prevail in almost any terrestrial ecosystem for millions of years. This 'anatomical versatility' probably was crucial to them becoming one of the most successful vertebrates in the history of life on Earth.”
The Amazing Dragon
Just weeks after Ingentia's unveiling, a separate team of paleontologists working in China announced their discovery of Lingwulong shenqi, a 174-million-year-old type of sauropod called a diplodocoid. The find is poised to make a splash; Lingwulong was found where, and when, it was least expected.
In 2005, Chinese Academy of Sciences paleontologist Xing Xu, a National Geographic explorer, and his colleagues started digging at northwest China's Lingwu site, discovered the year before by a local farmer. In the years since, they've found eight to ten individual dinosaurs—including Lingwulong, the first dinosaur of its kind ever found in Asia.
“I realized that these discoveries might be able to fill in a blank,” says Xu, the study's lead author.
Lingwulong stands out because it helps clarify how sauropod evolution aligned with the breakup of Pangaea, Earth's primeval supercontinent. This planet-wide breakup played a huge role in how terrestrial life evolved during the age of dinosaurs. As newly formed seas separated once-connected areas, land animals couldn't fan out across them as they once did—leaving the isolated regions stewing in their own evolutionary juices.
Before Lingwulong, no diplodocoids had ever been found in eastern Asia, an absence that paleontologists surmised was a biological reality of the time. To explain the missing dinosaurs, scientists suggested that an inland sea had cut off eastern Asia from the rest of Pangaea starting about 180 million years ago. This mega-moat, it was thought, prevented diplodocoids and its cousins—the so-called neosauropods—from reaching eastern Asia.
With Lingwulong in the picture, however, scientists must now consider that neosauropods achieved widespread distribution across Pangaea before it broke up. This implies that the major branches of the sauropod family tree forked off some 15 million years earlier than previously thought.
“The discovery of our new animal...means that this isolation hypothesis has been somewhat watered down, or even placed in serious doubt,” says study co-author Paul Upchurch, a paleontologist at University College London and a National Geographic explorer. “...We propose that many of the groups that were supposedly absent in China might well have been present, but we simply do not see them there yet because of poor sampling in the fossil record rather than genuine absence.”