Kangaroos are marsupials , the only kind of mammal that grows their young in pouches. Kangaroos are restricted to Australia, and marsupials to Australia and the Americas. They are not found anywhere else in the world.
Kangaroos evolved around 15 million years ago (Meredith et al., 2009). Scientists believed they started out in trees and moved onto grasslands. There are four main groups. The oldest are tree kangaroos, which did not shift down from the trees. The other three groups are classified based on size. Wallabies are the smallest, kangaroos are the biggest, and wallaroos are somewhere in between.
“Kangaroo” comes from the aboriginal Guugu Yimidhirr name: ganguruu (Gangurru, 2021). In 1770, James Cook landed on the shores of Australia, broken and battered after his ordeal with the Great Barrier Reef. Immediately after they landed, the crew was faced with what was probably the oddest animal they had ever seen. A giant, upright rabbit-looking creature, which hopped to move around. If that wasn’t odd enough, this strange ganguruu grew its young in pouches.
All kangaroos are herbivores, specialized for eating grass. They use pointed incisors to pluck grass, and molars to grind it down and eat it. Grass is abrasive, so kangaroo teeth are replaced throughout their lifetime (Stan, 2015).
Kangaroos eat grass, but what eats kangaroos?
Most kangaroo species are too large to be eaten by anything when they are fully grown. When they are young joeys, they may be eaten by dingoes. Before it went extinct, the Tasmanian tiger was thought to be an important predator for kangaroos.
The need for speed: Why do kangaroos hop?
Have you ever tried running a hopping race? Or just getting from one room to another on one foot? It isn’t terribly easy, is it? So why would hopping evolve?
Kangaroos are not the only animals that hop on two legs (McGowan & Collins, 2018), but they are certainly the largest ones. All hopping animals have short forelimbs (arms) and long tails. In kangaroos, the tail takes so much of the weight that it acts like a third leg. The tail is also heavy enough to balance the forward motion of the hopping.
Moving on two limbs instead of four is also more energy efficient. In a dry continent like Australia, covering huge ranges is critical. Resources can be scarce and located very far apart.
Although the scientific debate is ongoing, bipedal hopping might also allow kangaroos to move faster than if they moved on four limbs. The red kangaroo is the largest kangaroo, and can reach a speed of 72 km/h (45 miles per hour)! The eastern gray kangaroo can reach speeds of 65 km/h (40 mph) (Government of Victoria).
The unique evolution and history of kangaroos make them some of the most fascinating creatures to study. They are the largest hopping mammals, and the largest marsupials. Arid Australia is one of the hardest environments to survive in. Kangaroos not only survive, but do it with style!
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Glossary
Marsupial: A mammal which completes fetal development in an external pouch
References
Gangurru: Aboriginal Kangaroo Facts | Welcome To Country. (2021, January 9). https://www.welcometocountry.org/gangurru-aboriginal-kangaroo-facts/
ktmoelle. (2020, August 20). Kangaroo Evolution [Text]. https://askabiologist.asu.edu/kangaroo-evolution
McGowan, C. P., & Collins, C. E. (2018). Why do mammals hop? Understanding the ecology, biomechanics and evolution of bipedal hopping. Journal of Experimental Biology, 221(12), jeb161661. https://doi.org/10.1242/jeb.161661
Meredith, R. W., Westerman, M., Springer, M. S., Meredith, R. W., Westerman, M., & Springer, M. S. (2009). A phylogeny and timescale for the living genera of kangaroos and kin (Macropodiformes: Marsupialia) based on nuclear DNA sequences. Australian Journal of Zoology, 56(6), 395–410. https://doi.org/10.1071/ZO08044
Phillips, M. J., Haouchar, D., Pratt, R. C., Gibb, G. C., & Bunce, M. (2013). Inferring Kangaroo Phylogeny from Incongruent Nuclear and Mitochondrial Genes. PLOS ONE, 8(2), e57745. https://doi.org/10.1071/ZO08044
Stan, F. (2015). Gross anatomy of digestive system in Eastern grey kangaroo (Macropodidae family). Lucrari Stiintifice – Universitatea de Stiinte Agricole a Banatului Timisoara, Medicina Veterinara, 48(1), 173–182.
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