Casey M. Holliday

Home

Research Interests

Vertebrate Functional Morphology & Evolution

 

Dinosaurs Had Thick Articular Cartilage

Holliday CM, Ridgely RC, Seldmayr JC, & Witmer LM. Cartilaginous Epiphyses in Extant Archosaurs and Their Implications for Reconstructing Limb Function in Dinosaurs PLOS ONE 5(9): 15p.

Relevant links:

Download the paper HERE at PLoS ONe

Download the supplemental data HERE at PLoS ONE

Visit the additional media HERE including a longer narrative, old photos, and the 2001 SVP presentation.

Please visit the WitmerLab's Pick & Scalpel Blog for additional information.

Visit Mizzou's Press Release Page HERE

Common Language Summary

Dinosaur Articular Cartilage: Hyaline cartilage is a soft tissue vital to the construction and healthy function of vertebrate limb joints. Not only is cartilage responsible for mediating bone growth during an animal’s early years, but it also provides the thin layer of lubricating articular cartilage on the joint’s surface. Even in elephants, the largest terrestrial mammals living today, this layer of articular cartilage is only about 2 mm thick, and being largely without blood vessels, it relies on diffusion to feed the cartilage cells during movement. However the surfaces of many dinosaur bones lack bony condyles necessary for making a knee, for example, the surfaces are often porous and wrinkled, indicating the presence of blood vessels, These  soft tissues necessary for joint function are stripped away during fossilization. Thus paleontologists are challenged to accurately infer posture, height, and locomotor behavior in extinct taxa like dinosaurs. Our team, originally from Ohio University, now dispersed to different schools sought to get at this problem by asking:

How much cartilage did dinosaurs have in their joints? How well can we estimate it? What significance might articular cartilages have on our interpretations of dinosaur biology?

Using data from the living relatives of dinosaurs, crocodilians and birds, this study concludes that dinosaurs built their limbs differently than mammals, relying more on cartilage than bone to not only lubricate their joints but also to actually form the articulating condyles and processes that unite and stabilize the knees, elbows, and other limb joints. The bony ends of long bones of dinosaurs indicate that blood vessels supplied these cartilages throughout the animal’s growth, thus enabling these cartilage caps to remain far larger than those found in mammals.

We developed a metric, the cartilage correction factor (CCF) to estimate the amount of cartilage on the ends of long bones. For example applying an Alligator CCF (10%) to Brachiosaurus altithorax, which has a 6ft long femur and about a 4ft long tibia, would add about 1ft of extra cartilage onto the total length of the elements. Adding 1ft extra to the height of a fossil taxon, like the 42ft tall Brachiosaurus, may seem trivial; however distributed evenly on all four joint surfaces results in cartilage caps that are 3 inches thick. That’s really thick cartilage!  

We hope this new metric, the CCF, aids paleontologists with their estimates of height by decreasing the amount of error involved in these reconstructions. However, even though we’re losing length and breadth of these elements upon the loss of cartilage, condyles and other articular structures,  the most critical features that account for the fit, or congruency of the joints, and therefore posture are lost. Because posture is difficult to estimate, ranges of motion and eventually estimates of speed and locomotor behavior suffer because of the error associated with articulating, or misarticulating these elements. That said, this is not meant to dissuade paleontologists from studying posture and locomotion, but merely to give them more an anatomical leg to stand on.

Illustration of Brachiosaurus altithorax showing height differences applying Alligator-like Cartilage Correction Factors to the limb elements. Based on the epiphyseal vasculature giving the rugose, wrinkled texture in many dinosaurs, we suggest these fossil taxa may have had even more cartilage than alligators do. Human skeleton is approximately 6ft high. Modified line drawing of Brachiosaurus skeleton used with permission from MJ Wedel.

Modified photo of Brachiosaurus cast on display at O'Hare International Airport, Chicago, IL. Cartilage-caps reconstructed to highlight the missing articular condyles.

Funding for this project was provided by National Science Foundation (NSF) DDIG 0407735 (to L.M.W and C.M.H.) and NSF IBN-9601174, IBN-0343744, IOB-0517257 (to L.M.W.) as well as Ohio University Departments of Biological and Biomedical Sciences, Ohio University College of Osteopathic Medicine, and University of Missouri Department of Pathology and Anatomical Sciences.

University of Missouri Press Release

 

Dinosaurs Significantly Taller than Previously Thought, MU Researcher Finds

MU, Ohio University study finds that thicker cartilage may have added more than one foot of height;

Discovery also has implications for posture and speed of the animals

COLUMBIA, Mo.– It might seem obvious that a dinosaur’s leg bone connects to the hip bone, but what came between the bones has been less obvious. Now, researchers at the University of Missouri and Ohio University have found that dinosaurs had thick layers of cartilage in their joints, which means they may have been considerably taller than previously thought. The study is being published this week in the journal PLoS-ONE (Public Library of Science).

“Our study of the limbs of modern-day relatives of dinosaurs shows that dinosaurs were significantly taller than original estimates,” said Casey Holliday, lead author of the study and an anatomy professor in the MU School of Medicine. “The ends of many dinosaurs’ long bones, which include leg bones such as the femur or tibia, are rounded and rough and lack major articulating structures like condyles, which are bony projections. This indicated that very thick cartilages formed these structures, and therefore the joints themselves, and would have added significant height to certain dinosaurs. This study offers new data into how and why reptiles, and mammals, such as humans, build their joints with such different amounts of bone and cartilage.”

Holliday and Lawrence Witmer, a professor of anatomy at the Ohio University College of Osteopathic Medicine, conducted research on ostriches and alligators, the closest, modern-day relatives of dinosaurs, and then studied the fossilized limbs of different dinosaurs including Tyrannosaurus rex, Allosaurus, Brachiosaurus and Triceratops. The team determined that the lengths of alligators’ and ostriches’ limbs included between 6 and 10 percent cartilage.

Using a “cartilage correction factor,” Holliday determined that many theropod dinosaurs, such as Tyrannosaurus, were only modestly taller whereas ornthischian  and sauropod dinosaurs, such as Triceratops and Brachiosaurus, may have been 10 percent taller or more. For example, Brachiosaurus, previously thought to be 42 feet tall, may actually have been more than a foot taller with the additional joint cartilages.

“This study is significant because it shows that bones can’t always speak for themselves,” Witmer said. “To understand how dinosaurs moved, we need to analyze the bones as they were inside their bodies, including their cartilage. The dinosaur bones mounted in museums don’t accurately reflect what the animals actually had in their bodies in life because the cartilage caps were lost along with the other soft tissues. Knowing how much cartilage was lost allows us to better restore the structure of a living dinosaur bone, which then allows us to better understand how dinosaurs moved and lived”

Understanding the structures of the soft tissues in dinosaurs might also have implications for their speed and posture. While an increase in limb length typically means a taller dinosaur, it could also mean a faster or slower animal, depending on how it affects the skeleton, Holliday said. This finding could have major implications on how scientists currently understand dinosaur anatomy.

Dinosaur bones are different than the bones of mammals, including humans. Mammals have small protrusions at the end of each bone that help it connect with another bone at a joint, like two puzzle pieces. The bones are linked by a very thin layer of cartilage, which provides padding in the joint, but often wears down leading to painful conditions like arthritis. Comparatively, dinosaur bones have rounded ends and no obvious way to connect one bone to another. Soft tissue structures like cartilage and muscles leave marks on bones, which enable paleontologists to make sophisticated determinations about a dinosaur’s physical attributes.

Alligators have smooth, rounded bones while young ostriches have rough surfaces on their bones that mark where blood vessels feed large cartilaginous structures in the joints. Both characteristics are similar to dinosaur bones.

Holliday’s team dissected the alligator and ostrich bones and made casts of the bones with cartilage. The team then removed the cartilage and compared the bones to the casts. The bones without the cartilage were 4 to 10 percent smaller. From the evidence, Holliday and his research team concluded that certain dinosaurs had a significant amount of cartilage, and thus, were taller than original estimates. In the future, Holliday hopes to collaborate with MU veterinarians to study how and why different vertebrates build their joints with different proportions of cartilage and bone.

Holliday and Witmer led a research team that included Ryan Ridgely from Ohio University and Jayc Sedlmayr from Louisiana State University. The National Science Foundation and Ohio University provided funding for this research. PLoS-ONE is an open-access and free journal available online at: www.plosone.org