not that they ever had any reason to suffer from an inferiority complex, but Casey Holliday is giving dinosaurs a new reason to stand tall.
Holliday, a University of Missouri professor of anatomy, and his colleagues at Ohio University have discovered that at least some dinosaurs, Brachiosaurus and Triceratops, for example, were actually about a foot taller than the previously accepted estimates.
The reason has to do with the joints of these ancient animals’ limbs. They weren’t built like those of humans or other arthritis-prone modern-day mammals. Instead, dinosaur joints were buffered by massive amounts of cartilage, enough to make any weekend athlete with a bum knee envious.
Holliday’s influential work already is giving other scientists second thoughts about how dinosaurs walked and ran. And it may even hold some modern-day medical implications.
Dinosaur cartilage may have healed better than our own, he says, and probably didn’t wear out with years of use, as ours often does: “That’s kind of a big deal. These animals were able to escape the constraints of cartilage that we have.”
Holliday is part of a post-Jurassic Park generation of dinosaur experts who are putting flesh on the fossilized bones that have long told what we know about these gargantuan creatures.
“He is one of a rare breed of innovative paleontologists willing to get their hands dirty with both sand and blood,” says Matthew Vickaryous, a biologist at the University of Guelph in Toronto. “Casey is a master of the dissection table. Similarly, he is a skilled fossil preparer. He seems to be equally at home with a pin vice or a scalpel. He is keen to understand how structures are organized and function by exploring them in minute detail. And unlike many colleagues, who seem all too willing to unquestionably accept the literature at face value, Casey seeks to confirm the observations of others and learn for himself first hand.”
Dinosaur study used to be the sole province of paleontologists schooled in geology. Scientists like Holliday, with backgrounds in biology, are changing that, challenging long-held assumptions about dinosaurs. “Geologists didn’t always know what was going on inside animals,” Holliday says.
New technology, such as sophisticated computer software and the kinds of three-dimensional scanners used by hospitals, are helping them figure out dinosaurs’ posture and how they moved. The opening of China to paleontologists, meanwhile, has been bringing a steady supply of new fossil discoveries.
holliday grew up in Melbourne Beach on Florida’s east coast. As a child, he watched the loggerhead turtles come to shore to lay their eggs in the sand.
Holliday saw Jurassic Park while he was in high school. The 1993 Steven Spielberg movie was a formative experience for many young dinosaur researchers, though Holliday traces his own interest in old bones to a physical anthropology course he took as an undergraduate at the University of Florida. By his junior year, he was in a graduate level class on evolution and working at the Florida Museum of Natural History. “I got lucky and never turned back,” he says.
After graduating from college in 1997, Holliday spent a couple of years working for Chicago’s Field Museum on its famous Tyrannosaurus rex, Sue, cutting her fossil tail, hind legs and shoulder blades out of rock. Oddly enough, the job wasn’t in the Windy City but at Disney World’s Animal Kingdom in Orlando, part of a living display of paleontologists at work. “People would bang on the glass, ‘Is that real?’” he recalls. “After work, we could go to [Animal Kingdom’s] Africa and get a beer.”
Following his Disney stint, Holliday began graduate studies at Ohio University. There he worked with researchers who were reconstructing the anatomy of dinosaurs. One of them was Lawrence Witmer, Holliday’s mentor at Ohio University and collaborator on the cartilage study and other research. During a recent interview, Witmer recalled his former student as “an innovative scholar.”
“He was one of those graduate students that everyone knew was going to be an important scientist, a player. My goal was mostly not to ‘wreck him,’ that is, to let him emerge as the innovative scholar that he was,” he says. “And he’s emerged as one of the world leaders in the study of the evolution of feeding systems in dinosaurs, birds, and their reptilian kin.”
After receiving his doctorate in ecology and evolutionary biology, Holliday joined the faculty of Marshall University in West Virginia in 2007. Two years later, he moved to MU’s School of Medicine, where he teaches anatomy.
“That’s what gets me hired at places like this,” Holliday says. “A lot of paleontologists are teaching our next generation of healers. We’re really anatomists at heart, looking at how things are put together.”
At MU, the bulk of Holliday’s work has focused on how bones in the skulls of modern and ancient animals work together. By studying the anatomy of joints and muscles, he seeks to determine how animals chewed and what they ate.
It’s more complicated than you might think. And there’s plenty of variety. Among mammals, turtles and crocodilians — crocodiles and alligators — only the jaw joint moves; the rest of the bones in the skull are fused together by sutures. That evolutionary development occurred about 220 million years ago. But birds, dinosaurs and fish all have other mobile joints in their skulls. Such flexibility offers them some distinct advantages. Snakes can stretch their head joints to swallow entire animals. Parrots have a flexible joint at the top of the bill that they use for climbing and husking seeds. There is, however, a trade-off. Animals with flexible joints in their heads lose some force when biting. Locked joints, such as those in mammals, allow animals to grind food, bite prey and defend themselves more powerfully.
One of Holliday’s current research interests involves the perplexing case of lizards, animals that appear to straddle both worlds. Lizards have head joints that look as though they ought to move, but they don’t. It appears that they recruit muscles to keep the bones rigid.
Holliday is examining lizards’ muscle spindles, sensory receptors within muscles that give the brain information it needs to determine the position of body parts. He thinks that the muscles may help lizards maintain the proper orientation of their heads as they eat. He’s hoping to find funding for research on live lizards, but he’s not sure he’ll get it. “I work in a hospital, and there’s a huge mammalian bias here,” he says. “Maybe other vertebrates that share the world with us have answers to some questions.”
Maybe even other vertebrates that came before us, such as dinosaurs.
consider the problems that lead to thousands of human knee repair and replacement operations every year. Joints like the knee in people and other mammals fit together tightly. Even as fossils, there’s little space between the bones. That’s because we have very thin layers of cartilage to keep the bones from rubbing against each other. This flexible connective tissue lacks blood vessels; its life support comes from diffusion — nutrients are sucked in and waste materials are pushed out as joints flex. But without a blood supply, our cartilage is slow to heal.
That wasn’t a problem for dinosaurs, and still isn’t for birds or crocodilians. They appear to have blood vessels feeding their cartilage, Holliday says, and it’s this generous blood supply that made it possible for dinosaurs to have thick cartilage in their limbs.
Holliday started working on questions about dinosaur limbs back in 2000, while he was a graduate student. Only recently has it become one of his main interests. “The project had to be set aside from time to time as Casey attended to ‘little’ matters like finishing his doctoral dissertation and getting employed,” Witmer says. “But he stuck with it, and took a relatively simple project and built it into a highly influential study.”
Paleontologists have always pondered why dinosaur skeletons didn’t fit together as tightly as those of mammals. The ends of their limb bones, such as femurs, were rounded and rough. They lacked projections called condyles that fit in with the adjacent bones to form joints. Some museums left gaps separating limb bones as they assembled dinosaur skeletons. “But nobody chased it down to find out what was going on,” Holliday says.
The solution to the mystery, according to Holliday, is that the dinosaurs’ joints were formed largely of cartilage, rather than bone. And, like other soft tissue, the cartilage didn’t survive to become fossilized.
Holliday and Witmer reached that conclusion after studying specimens of two modern dinosaur descendents, alligators and birds, including chickens, quail and ostriches. The alligators came from the Rockefeller State Wildlife Refuge and Game Preserve in Louisiana and the ostriches from a commercial business. After dissecting the animals, they compared casts of bones with the cartilage intact to those of the bones alone. Cartilage, they found, accounted for six to 10 percent of the lengths of the alligators’ and ostriches’ limbs.
Holliday and Witmer applied their “cartilage correction factors” to dinosaurs and figured that the limb bones of these animals were capped with about three inches of cartilage. That totaled up to more than a foot of extra height for some species.
The additional cartilage also offered an explanation for why the ends of the dinosaur bones contained grooves and pock marks: these were places that accommodated blood vessels. Holliday’s new estimates of dinosaurs’ height and leg length mean scientists will have a harder time calculating how dinosaurs walked, or how fast. “That’s kind of bad news for paleontology,” Holliday says. “It raises the bar for accuracy.”
Holliday is planning to take up that challenge himself, possibly by plotting three-dimensional computer models to see how joints move with and without larger bolsters of cartilage. And he’s putting more alligator cartilage under the microscope. He recently traveled to the Louisiana refuge to bring back a couple dozen 1- to 2-foot long alligators and parts of 12 five-foot gators. The goal is to find more evidence that the tissue is maintained by its own blood supply. Luckily, he just received an extra 6-foot chest freezer for large specimens; the single freezer he already had was full of specimens for his many projects. “I have about 10 burners going on,” he says. “But it’s pretty standard for comparative anatomists to have their fingers in a lot of pies.”
A quick tour of Holliday’s lab confirms this. It is a veritable museum of anatomical treasures. There’s a gecko — no longer as lively as the one in the TV commercials — in one jar. Another jar contains the head of a Nile monitor lizard. A third has the head of a newly hatched alligator.
A wealth of specimens spills into Holliday’s office as well. There are skulls of a turtle, an ostrich, a pronghorn antelope and a Komodo dragon. And there’s a cast of a Tyrannosaurus jaw — he took that one to his daughter Audrey’s preschool.
Holliday does a lot of outreach to school children, sharing his enthusiasm for the life sciences. He also maintains a blog, Holliday Lab at Mizzou, and an online atlas of three-dimensional images of the bones of an alligator skull taken from CT and MRI scans.
“I kind of live this,” he says. “Work’s fun. I wouldn’t be doing this if it wasn’t fun. And I’ve got a three-year-old who occupies most of my time when I’m awake.”
Audrey, the 3-year-old, seems to be following in the footsteps of her father and her mother, Dawn, an adjunct professor of biology at MU who will be leaving the University this fall to join the faculty of Westminster College in Fulton. Audrey’s a big fan, he says, of the PBS cartoon series, Dinosaur Train, to which, incidentally, Holliday gives high marks for scientific accuracy. “My daughter has turned into quite the dinosaur aficionado,” the proud father says.
And if all the discoveries about dinosaurs that Holliday and other researchers are making were to find their way into a remake of Jurrasic Park when Audrey is in high school?
“Jurrasic Park fifteen years from now would be a completely different production,” Holliday says.