Blog Assignment: Comparative Anatomy - Part 3
Plantigrade, Digitigrade, and Unguligrade
Going back to the first post in this series where I talked about mammals I skipped over something big. The shape of the limbs differs greatly among the mammals I used as examples of homologous structures. While the overall skeletal structure shares all the same elements (phalanges, metatarsals, and tarsals) how these elements are arranged sets them apart.
Plantigrade locomotion is the form we humans are more familiar with. The metatarsals and phalanges are placed flat on the ground, walking with the heel hitting the ground first and the toes following. This method of moving is shared with bears, wolverines, skunks, mice, rabbits, kangaroos, and racoons. Most of these animals use their forelimbs to grab and hold things, so having flat feet to keep their balance is essential.
Digitigrade locomotion is how dogs and cats get around, among other animals. Digitigrade animals walk on the phalanges, leaving the metatarsals to make up part of the leg. It’s the equivalent of humans walking on the flat part of our fingers but not the palm of our hands. Digitigrade animals can move very fast and very quietly.
Unguligrade locomotion is probably the most unusual form of movement. Ungulates walk on the very tip of the toes, with the number of toes varying between animals. Odd-toed Ungulates will have 1, 3, or 5 toes, and Even-toed Ungulates will have 2 or 4. The very tip of the toe is covered in a hard nail, what we refer to as a hoof, with the back of the toe having a fatty cushion to help distribute weight and force. Whales and dolphins are included in this group despite not having feet because they evolved from hooved carnivores. They’re the only example of carnivores in the ungulate group (pigs being omnivores and everything else being herbivorous).
Knowing these differences in locomotion can help concept artists create variation in their creatures and show a clear distinction between beast of burden (most often ungulates) and a potential enemy with sharp claws.