Kangaroos are marsupials belonging to the family Macropodidae, meaning "large foot." The term "kangaroo" commonly refers to the largest species within this family, including the red kangaroo, antilopine kangaroo, eastern grey kangaroo, and western grey kangaroo. Native to Australia and New Guinea, the Australian government estimated that 42.8 million kangaroos inhabited commercial harvest areas in 2019, a decline from 53.2 million in 2013.

Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Infraclass:	Marsupialia
Order:	Diprotodontia
Suborder:	Macropodiformes
Family:	Macropodidae
Groups included
Macropus Osphranter antilopinus Osphranter rufus

Similar to the terms "wallaroo" and "wallaby," "kangaroo" represents a paraphyletic group within Macropodidae, categorized mainly by size. The largest species are termed "kangaroos," the smallest "wallabies," and intermediate-sized species "wallaroos." Additionally, tree-kangaroos, a distinct type of macropod, reside in the tropical rainforests of New Guinea, northeastern Queensland, and surrounding islands, living primarily in the tree canopy.

The general size distinctions among these groups are:

• Wallabies: Head and body length of 45–105 cm, tail length of 33–75 cm; the dwarf wallaby, the smallest macropod species, measures 46 cm and weighs 1.6 kg.
• Tree-kangaroos: Range from Lumholtz’s tree-kangaroo, with a body length of 48–65 cm, tail length of 60–74 cm, and weight of 5.9–7.2 kg, to the grizzled tree-kangaroo, which reaches 75–90 cm in length and weighs 8–15 kg.
• Wallaroos: The black wallaroo, the smaller of the two species, has a tail length of 60–70 cm and weighs 19–22 kg for males and 13 kg for females.
• Kangaroos: Large males can grow up to 2 meters tall and weigh around 90 kg.

Kangaroos have powerful hind legs, large feet adapted for leaping, a strong muscular tail for balance, and a relatively small head. Like most marsupials, female kangaroos have a pouch (marsupium) where joeys continue their postnatal development.

Their grazing habits have led to specialized teeth uncommon among mammals. The incisors crop grass close to the ground, while molars grind it efficiently. The lower jaw's two sides are not fused, allowing a wider bite. Due to the abrasive nature of grass, their molars wear down and move forward before eventually falling out and being replaced by new teeth growing at the back—a process called polyphyodonty, which is also observed in elephants and manatees.

Larger kangaroo species have adapted well to habitat changes caused by land clearing for agriculture, unlike many smaller macropods, which are now rare or endangered. Despite common misconceptions, kangaroos remain abundant in Australia.

Kangaroos, alongside koalas, are iconic symbols of Australia. They feature on the Australian coat of arms, currency, and serve as logos for well-known organizations like Qantas. The Royal Australian Air Force also uses a kangaroo emblem. Their cultural significance has led to numerous references in popular media.

Wild kangaroos are culled for their meat, leather hides, and to protect grazing land. Kangaroo meat is considered a healthier alternative to traditional meats due to its low-fat content.

Terminology

The word kangaroo originates from the Guugu Yimithirr term gangurru, which specifically refers to eastern grey kangaroos. The name was first documented as kanguru on 12 July 1770 in the diary of Sir Joseph Banks. This took place near modern-day Cooktown, along the Endeavour River, where HMS Endeavour, under the command of Lieutenant James Cook, was stranded for nearly seven weeks for repairs after sustaining damage on the Great Barrier Reef. Cook later mentioned kangaroos in his diary entry on 4 August. Guugu Yimithirr is the language spoken by the Indigenous people of that region.

A widely circulated myth suggests that the English name kangaroo originated from a misunderstanding. According to this legend, when Cook and Banks encountered the animal, they asked a local Indigenous person what it was called. The response, supposedly kangaroo, was mistakenly interpreted as the animal’s name, when in fact, it allegedly meant "I don't know" or "I don't understand." Anthropologist Walter Roth attempted to debunk this myth as early as 1898, but it gained wider recognition only in 1972 when linguist John B. Haviland confirmed that gangurru referred to a particular large, dark-colored species of kangaroo. However, during Phillip Parker King's visit to the Endeavour River region in 1819 and 1820, he reported that the local term was not kangaroo but menuah, possibly referring to a different macropod species. Similar naming confusions have occurred in history, such as with the Yucatán Peninsula.

Kangaroos are often informally called roos. Males are referred to as bucks, boomers, jacks, or old men, while females are known as does, flyers, or jills. Young kangaroos are called joeys. A group of kangaroos is collectively termed a mob, court, or troupe.

Taxonomy and Description

Extant Species

There are four living species commonly referred to as kangaroos:

• Red Kangaroo (Osphranter rufus) – The largest marsupial in existence, found in Australia’s arid and semi-arid regions, particularly in western New South Wales. A large male can reach 2 meters (6 ft 7 in) in height and weigh up to 90 kg (200 lb). While often thought to be the most abundant species, eastern greys outnumber them.
• Eastern Grey Kangaroo (Macropus giganteus) – More commonly seen than the red kangaroo due to its range across the fertile eastern regions of Australia, from Cape York Peninsula to Victoria and Tasmania. They thrive in open woodlands and are less common in heavily cleared areas.
• Western Grey Kangaroo (Macropus fuliginosus) – Slightly smaller than the eastern grey, with males weighing up to 54 kg (119 lb). It inhabits the southern coastal regions of Western and South Australia and the Murray-Darling basin. The species has a high tolerance for sodium fluoroacetate, a plant toxin, hinting at a possible origin in southwestern Australia.
• Antilopine Kangaroo (Osphranter antilopinus) – The northern counterpart of the eastern and western grey kangaroos, often called the antilopine wallaroo. Found in grassy plains and woodlands, this social species gets its name from its fur, which resembles that of an antelope. Males have enlarged nasal passages that help dissipate heat in humid climates.

Additionally, around 50 smaller macropods, closely related to kangaroos, belong to the Macropodidae family.

Evolutionary History

Kangaroos and other macropods share a common ancestor with the Phalangeridae (possums) from the Middle Miocene. These ancestors were arboreal, living in dense forests that once covered Australia. As the climate dried from the Late Miocene to the Pleistocene, forests receded, and grasslands expanded, driving macropods to evolve larger bodies and foregut fermentation to digest tough grasses.

The earliest kangaroo relatives, Balbaridae and Bulungamayinae, became extinct in the Late Miocene (5–10 million years ago). Fossils of Ganguroo and Wanburoo suggest early adaptations to bipedal hopping, with modified ankle joints restricting lateral movement. Modern grey kangaroo and wallaroo relatives appeared in the Pliocene, while the red kangaroo is the most recent species, emerging in the Pleistocene (1–2 million years ago).

Kangaroos in Western Discovery

The first kangaroo observed by Europeans was shot by John Gore, an officer aboard HMS Endeavour, in 1770. Its skin and skull were sent to England, where taxidermists—unfamiliar with the species—stuffed and displayed it as a curiosity. For many 18th-century Britons, the first depiction of a kangaroo came from a painting by George Stubbs.

Comparison with Wallabies

Kangaroos and wallabies belong to the Macropodidae family and often the same genera, but kangaroos are specifically the four largest species. "Wallaby" is an informal term for smaller macropods that are neither kangaroos nor wallaroos.

Biology and Behaviour

Locomotion

Kangaroos are the only large mammals that primarily use bipedal hopping for locomotion. A red kangaroo hops comfortably at 20–25 km/h (12–16 mph) but can reach 70 km/h (43 mph) over short distances. They can sustain speeds of 40 km/h (25 mph) for nearly 2 km (1.2 mi). Their powerful gastrocnemius muscles propel them forward, while elastic 

tendons store and release 70% of potential energy.

At slow speeds, kangaroos use pentapedal locomotion, employing their tail as a tripod with their forelimbs while moving their hind feet forward. Both pentapedal walking and fast hopping are energy-intensive, but hopping at moderate speeds (above 15 km/h or 9.3 mph) is highly efficient compared to running animals of similar size.

Diet

Kangaroos have single-chambered stomachs, unlike ruminants such as cattle, which have four compartments. They sometimes regurgitate food, chew it as cud, and swallow it again, though less frequently than ruminants.

• Eastern grey kangaroos are primarily grazers, consuming various grasses.
• Red kangaroos incorporate a significant amount of shrubs into their diet.
• Smaller macropods also feed on hypogeal fungi.

Kangaroos are mostly nocturnal and crepuscular, resting in the shade during the day and foraging at night and in the early morning.

Methane-Free Digestion

Despite their plant-based diet, kangaroos produce almost no methane, unlike ruminants such as cattle. Instead, their gut bacteria convert hydrogen into acetate, which provides additional energy. Scientists are investigating whether these bacteria could be transferred to livestock to reduce methane emissions, as methane has 23 times the greenhouse gas effect of carbon dioxide per molecule.

Social and Sexual Behavior

Kangaroos live in groups called mobs, courts, or troupes, which provide protection. Social interactions include nose-touching and sniffing for recognition and bonding. Males compete for access to females through ritualized fights, often engaging in "boxing" by balancing on their tails and kicking. Larger males tend to dominate reproductive opportunities, using consort pairing to secure mates.

Predators and Defense

Natural predators of kangaroos include the now-extinct thylacine, marsupial lion, and Megalania. Today, dingoes, foxes, feral cats, and dogs pose threats. Kangaroos are strong swimmers and may drown predators or use their powerful hind legs to defend themselves.

Adaptations

Kangaroos have specialized adaptations for survival in Australia's harsh climate, including embryonic diapause, allowing females to pause embryo development during droughts. Their hind legs store elastic energy, making hopping an efficient mode of travel. The tail functions as a third leg, aiding movement. Kangaroos also exhibit synchronized breathing and hopping to conserve energy.

Reproduction and Life Cycle

A newborn joey is underdeveloped at birth and climbs into the mother's pouch for nourishment. Joeys stay in the pouch for about nine months and continue nursing up to 18 months. Females can simultaneously produce different types of milk for joeys at different stages.

Interaction with Humans

Kangaroos have been essential to Aboriginal Australians for food, tools, and cultural traditions. Since European settlement, their populations have increased due to deforestation and reduced predator numbers, leading to management efforts and culling. While usually non-aggressive, rare kangaroo attacks on humans have been reported, sometimes linked to extreme thirst or hunger.

Kangaroos and Vehicles

Collisions with kangaroos are common in Australia, leading to fatalities and vehicle damage. Road signs and "roo bars" help reduce accidents. Injured kangaroos and surviving joeys are often rescued and rehabilitated by wildlife organizations.

Symbolism and Culture

The kangaroo is a national symbol of Australia, appearing on the coat of arms, currency, and the Australian Made logo. It is also a common subject in art, branding, and popular culture.

Kangaroos remain an iconic species, adapting well to environmental changes while maintaining a complex social structure.