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Why does the fourth toe carry most of a kangaroo’s weight?
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kangaroo
A group of red kangaroos (Macropus rufus) using their powerful hind legs and feet to hop.
The kangaroo's fourth toe carries most of its weight because it is the primary structural component of the animal's long, narrow hind foot, which is specialized for locomotion via hopping and leaping.1
While each hind foot possesses four toes, the second and third toes are united and vestigial—a condition known as syndactyly—leaving the large fourth toe to bear the load during the kangaroo's bipedal saltatory movement. This adaptation supports the kangaroo as it lands on its hind feet and maintains a relatively straight back throughout the phases of its jump.12