How did sauropod dinosaurs move their heads? When they stood, were their super-long necks stretched up high to the treetops like a giraffe's? Set horizontal to the ground like a cow's? Or in some other orientation as yet unimagined?
Many scientists have pinned their understanding of sauropod neck posture and flexibility on a groundbreaking computer model, described in a 1999 study in the journal Science. But a new study, published Wednesday in the journal PLOS ONE, suggests that model doesn't convey the whole picture because it doesn't fully consider how soft tissues like cartilage and muscle -- absent from dinosaur bones but available for study in extant animals -- might have influenced flexibility.
"No one ever said, 'Let’s apply this to a living animal,'" said Matthew Cobley, a graduate student at the University of Utah and first author of the PLOS ONE study. "When we did, we saw it was totally wrong."
Cobley, who did the work as part of his master's studies at the University of Bristol in England, decided to look at ostriches to gain insight into the sauropod biology. Scientists look at living relatives of dinosaurs, including reptiles and birds, to infer information about soft tissues in dinosaurs, Cobley said. In this case, ostriches provided the best analog for the sauropods because they also have long necks. (Giraffes, another obvious candidate for study, aren't as good a fit because mammals have significantly fewer vertebrae in their necks than sauropods and birds, he added.)
Cobley obtained three female ostrich necks and used an instrument called a goniometer to measure the angles formed at joints between vertebrae as he bent the neck as far as it could go. Taking measurements on the necks with muscles and cartilage intact and after soft tissues were removed, he discovered that the necks were less flexible with the soft tissues intact.
"That demonstrates that a computer model that doesn't take soft tissues into account can't be adequate," Cobley said. "When you look at extinct animals, you have to consider soft tissue.
"If I’m not looking at how soft tissue affects flexibility," he said, "I’m not getting a idea of how flexible [the animal] is in real life."
The computer models were so widely accepted that they've influenced depictions of sauropods on popular TV shows and in museum exhibits. Cobley said his research doesn't suggest a better way to position the necks in such presentations -- rather, it reminds scientists that they don't understand everything about how dinosaurs really stood.
"We don't really know what's going on," he said.
Debating the finer points of how dinosaurs stood or moved their necks can seem like a trivial pursuit, said Mathew Wedel, a biologist at the Western University of Health Sciences in Pomona, who has also researched the question. But it's a detail of great importance to paleobiologists, who want to know how sauropods -- who thrived for some 150 million years -- lived so successfully on Earth for so long.
If scientists can understand what herbivorous creatures like Apatosaurus and Brachiosaurus were capable of doing with their long necks, they can speculate about their eating patterns and how species competed for food resources, said Wedel, who was not involved with Cobley's research.
"For more than twice the length of the whole age of mammals, these guys were ... ecologically dominant," Wedel said. "If we want to understand Mesozoic ecosystems, we have to understand what sauropods were doing."
Wedel praised Cobley for what he said was "a ton of work" coming up with methods to gauge the neck flexibility, and said he hoped that scientists would now take the process Cobley developed and apply it to study other animals such as swans, cranes, llamas, giraffes and owls to look for patterns that might help paleontologists better understand sauropod anatomy.
Wedel said he had just submitted a paper for publication that suggested that sauropod muscles would have improved flexibility -- not hampered it.
"Now I have to change it," he said with a laugh.