New research supports that the trabecular bone structure found in a variety of dinosaurs is the key to supporting their massive weight.
A multidisciplinary team that includes paleontologists, with mechanical and biomedical engineers have revealed the unique bone structure, different from those found in birds or mammals, in dinosaurs like hadrosaurs, or the duck-billed dinosaurs, and other species.
"The structure of the trabecular, or spongy bone that forms in the interior of bones we studied is unique within dinosaurs," said paleontologist Tony Fiorillo from the Southern Methodist University. Fiorillo explained that similar to those seen in ham or steak bones, trabecular bone tissues surround the porous inner part of the dinosaur bones.
The Trabecular Bone Structure's Load Bearing Capacity
The study, published in the website for PLOS ONE, notes that while the bone strength and biomechanics for dinosaurs have been examined in previous studies, the relationship between their trabecular bone structure and mechanical behavior is not yet investigated.
To conduct their inquiries, the researchers examined bone samples from dinosaurs, specifically the distal femur and proximal tibia - bones found in the leg and thighs - with the species' body mass ranging from 23 to 8,000 kilograms. They conducted micro-computed tomography (uCT) scanning and allometric scaling, revealing how the trabecular bone architecture related to the dinosaurs' body mass.
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The researchers found out that for mammals and birds, there is no definite link between their body mass and their respective trabecular bone volume fraction. It goes against the common preconception that more massive animals require stiffer bone structures.
To explain the trabecular bone structure in massive animals such as dinosaurs, the researchers proposed the adaptation to accommodate the large gravitational load and minimize bone mass by keeping a constant bone volume fraction.
"Unlike in mammals and birds, the trabecular bone does not increase in thickness as the body size of dinosaurs increase," Fiorillo explains. In dinosaurs, the spongy bone becomes denser, instead of growing denser. Without this adaptive mechanism, the skeletal structure to support the hadrosaur will be so heavy that the movement becomes be difficult.
Implications of Trabecular Bone Mechanics
"Understanding the mechanics of the trabecular architecture of dinosaurs may help us better understand the design of other lightweight and dense structures," said lead author Trevor Aguirre, Ph.D., also a graduate of Mechanical Engineering from Colorado State University.
To provide an idea of these bone structures' mechanical behavior, the team used finite element modeling. Models have revealed that the trabecular bone architecture in plesiomorphic therapods—ancient dinosaurs with hollow bones and three toes—somehow resembles those of modern humans instead of birds. It suggests similar biomechanics to modern humans.
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The study notes that it was impossible to analyze the mechanical properties of the fossilized bone samples, such as those from the mammoth, where the dinosaur bones were compared. Therefore, they used the mechanical properties from human trabecular bones in their finite element models.
To have an idea of how large hadrosaurus can get, here is a size comparison video from the Dinosaur Fights Youtube channel:
