Monday, October 4, 2010
WASHINGTON: Some dinosaurs may have been at least 10 percent taller than previously thought, US paleontologists said in a study that found the creatures had large amounts of cartilage.
The dinosaurs had thick layers of cartilage in their joints that may have added more than a foot (30 centimeters) to their height, according to researchers at the University of Missouri (MU) and Ohio University, who said this may have changed their speed and posture.
"Our study of the limbs of modern-day relatives of dinosaurs shows that dinosaurs were significantly taller than original estimates," said study lead author Casey Holliday, an anatomy professor at the MU School of Medicine.
She explained that many dinosaurs' long bones, such as the femur or tibia, lack major articulations and have rounded ends with rough surfaces.
"This indicated that very thick cartilages formed these structures, and therefore the joints themselves, and would have added significant height to certain dinosaurs," Holliday added.
In contrast, mammal bones have small protrusions at their ends that help them connect with other bones at a joint. The bones are then linked with a very thin layer of cartilage.
The study, which was published in the Public Library of Science's journal PLoS-ONE, shed further light on how reptiles and mammals such as humans build their joints with different amounts of cartilage and bone.
The researchers compared articulations of ostriches and alligators -- the closest living relatives to dinosaurs -- to fossilized limbs of dinosaurs like Tyrannosaurus rex and Triceratops.
They found that alligators' and ostriches' limbs included six to 10 percent cartilage.
By applying a "cartilage correction factor," Holliday found that many theropod dinosaurs, such as Tyrannosaurus, were only modestly taller, while ornthischian and sauropod dinosaurs like Triceratops and Brachiosaurus, may have been 10 percent taller or more.
Brachiosaurus, which was previously thought to be 42 feet (13 meters) tall, may actually have been more than a foot taller with the additional joint cartilages, according to the researchers.
"This study is significant because it shows that bones can't always speak for themselves," said Lawrence Witmer, a professor of anatomy at the Ohio University College of Osteopathic Medicine.
"To understand how dinosaurs moved, we need to analyze the bones as they were inside their bodies, including their cartilage."
He said dinosaur bones mounted in museums in fact do not accurately reflect the creatures' height when they were alive because the cartilage caps and other soft tissues were lost.