How did kangaroos evolve to hop?

For a agelong time, biomechanics experts believed that giant, extinct kangaroos were simply excessively dense to hop. While the largest modern kangaroos measurement astir 90 kg, their prehistoric relatives were overmuch larger and weighed much than 250 kg. And scientists antecedently calculated that if you took the anatomy of a modern kangaroo and scaled it up to that weight, the forces generated by hopping would drawback their ankle tendons and fracture their bones.

However, a January 22 study has challenged this limit: by looking astatine the fossils alternatively than relying lone connected mathematical scaling from modern kangaroos, researchers person recovered that kangaroo ancestors didn’t conscionable turn larger: they besides evolved a antithetic skeletal operation to grip the immense weight.

The survey identified 2 large adaptations that made hopping mechanically imaginable for these giants. First, their weight-bearing ft bones, the 4th metatarsals, were importantly shorter and thicker than those of modern kangaroos. This compact signifier made the bones much resistant to bending forces, preventing fractures upon landing. Second, their bottommost bones, called calcanea, were overmuch wider, providing a ample area  for the gastrocnemius tendon to attach. This suggested the animals possessed heavy tendons susceptible of withstanding the tensions required to assistance their bodies.

There was 1 trade-off, however. While the adaptations allowed them to hop without injury, the giants apt sacrificed velocity and vigor efficiency. Unlike modern kangaroos that bounce efficiently implicit agelong distances, the extinct giants astir apt hopped lone for short, high-power bursts, possibly to flight predators.