There’s a reason that towering mammals the likes of King Kong are resigned to fiction. Our aching bones can only take so much weight before they start crumbling under the pressure. But if that’s the case, then why were dinosaurs able to reach such phenomenal heights? According to a new study, the answer isn’t so much about the bones themselves as it is the soft, squishy joints they lay between.
The scientists leading the new study published in PLOS ONE measured the ends of bones in both mammals and dinosaurs as well as their descendants to see how joint and bone shape changes as size increases.
As mammals grow, our bones become progressively rounder at the ends to be able to support the increase in weight while minimising pressure as much as possible. Reptiles and birds, however, (as well as the dinosaurs that came before them) have bones that grow wider and flatter as more weight is added to the frame. So considering that these two very different shapes are both meant to sustain more weight, the joints and cartilage that connect them must also work differently.
For humans and other mammals, as the bones become rounder the connecting cartilage continues to stretch thin and tight across the bones surface. Because the soft, connective cartilage is close-fitting and maleable, our weight is able to distribute more evenly. The wider, flatter bones of reptiles, however, solve the problem by packing as many layers of the stuff as they can — which as it turns out, is a much more efficient method. According to Matthew Bonnan from the Richard Stockton College of New Jersey and one of the lead authors on the study:
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.
Of course, these gelatinous joint fillings weren’t the only thing letting dinos tower over the rest of the prehistoric world. The lighter, hollow bones favoured by reptiles also meant that larger frames didn’t require as much support as our own solid bricks for bones. This does, however, at least begin to explain why dinosaurs were able to reach such larger than (modern) life proportions.
Still, as pillowy and bouncy as their joints may be, everything has its limits. You know, like extinction-event comets. [Live Science]