Why dinosaurs grew so large decoded

This April 28, 2011 photo shows a Tyrannosaurus rex dinosaur replica at the Woodland Park Zoo in Seattle.

The largest dinosaurs were able to grow to a gigantic size because they had softer, squishy joints than land mammals, a new study suggests.

Large, plant-eating dinosaurs, including sauropods, were much more common than giant land-based mammals, which were also herbivores.

The largest sauropods frequently weighed more than 30 tonnes and included massive species.

The study suggests that one reason for this disparity may lie between their bones, ISNS reported.

Researcher Matthew Bonnan from The Richard Stockton College of New Jersey and his colleagues measured the width of the ends of thigh and arm bones in mammals, dinosaurs and their descendants — modern day reptiles and birds — to see how joints changed as the animals’ size increased.

Mr. Bonnan likens cartilage to sheets of rubber stretched across the hard ends of bones to cushion them. As mammalian bones grow rounder at the edges, cartilage stretches thin and tight across their surfaces.

The close-fitted, stretchy material transfers weight evenly across the bone surfaces.

Dinosaur joints, however, appear to pack in more layers of cartilage as the animals size up, researchers said.

“More than just evenly distributing the pressure, the joint itself may be deforming a little - it’s actually squishier, increasing the force it can sustain,” said Mr. Bonnan.

Researchers said predicting the structure of dinosaur cartilage based on the bones on either side is difficult.

Many modern-day reptiles and birds have held on to these squishy joints, which lends some weight to the idea.