Koala (Phascolarctos cinereus) Fact Sheet: Physical Characteristics

*Females can be 50% smaller than males. *Size varies by latitude - smaller in north

Shaped like a teddy bear, with small compact body, short limbs, and large rounded ears
Short, dense, woolly fur

• Overall light gray, white under parts, rump dappled with white; coat color varies
• Ears fringed with white hair
• Black, leathery nose
• Hair longer on back than on belly
• Fur cushions koala when sitting on and against tree branches

Adaptations for specialized Eucalyptus diet: (Grand & Barboza 2001)

• Massive jaws
• Powerful chewing muscles
• Sharp cutting molars (Hume 1999)
  • Cusps interlock tightly; excessory cusps add extra cutting action
• Caecum (portion of large intestine) up to 2.5 m (8 ft) long for processing low-quality Eucalyptus
• Low metabolic rate - diet is nutrition-poor (Hume 1999)

Eyes with slits of pupils vertical rather then horizontal as in other marsupials (Jackson 2003)
Marsupial pouch in koala opens towards the bottom of the pouch, facing outwards (not up or back) (Australian Koala Foundation 2010):

• Strong sphincter muscle at opening keeps joey from dropping out
• When joey is older and heavier, it pulls pouch down and back when leaning out
• Wombat's pouch opens similarly (to keep dirt out when mother is digging)
• Reflects koala's evolutionary links to a shared common ancestor with wombats

Hand (Weisbecker & Sánchez-Villagra 2006):

• First two fingers opposable to other three (zygodactyly); each digit has strongly curved claw
  • Claws help koala secure a grip on bark of trees (Grand & Barboza 2001)
• Wrist bones modified from those of its terrestrial relatives

Hind foot:

• First toe opposable to other four
• Second and third toes partly fused with separate claws but one sheath of skin (syndactyly)
  • The syndactyl toes used as comb to keep fur groomed (Smith 1979a)

All toes with long, sharp claws except first digit of hind foot.

Males: 50% heavier, with wider face (Jackson 2003)

• Head broader
• Slightly curved, "Roman" nose (Lee & Martin 1988)
• Broader chin
• Smaller ears
• Large sternal gland on chest
• Bellow more frequently than females

Female: smaller, weighs less (Jackson 2003)

• Head narrower
• Straighter nose
• Chin more pointed
• Larger ears
• No sternal gland

Reasons for large body size of males (Ellis & Bercovitch 2011):

• Not for male/male competition - males rarely show physical aggression towards each other over access to females
• May be a reproductive strategy to provide extra energy reserves for a long mating season, a tactic of "endurance rivalry"
• Bellows of larger individuals may be more attractive to females

Broad, high-cusped cheek teeth for chewing fibrous leaves

• As members of diprotodont order, large incisors project forward from lower jaw
• Canines on the upper jaw but not the lower jaw (Jackson 2007; Wilson and Mittermeier 2015)
  
• After age 6, teeth become smoother and less efficient at shearing (Lanyon & Sanson 1986)

Cheek pouches (Sonntag 1921) (Tuttle 1975)
Ear region highly specialized in koalas and wombats (Szalay 1994)

• Middle ear volume for both animals is extremely large compared to other marsupials (Louys et al. 2009)
• Koalas emit low pitched bellows that are detected with these highly sensitive ears (Louys et al. 2009)

Fingerprints of koalas and humans are strikingly similar (Henneberg et al. 1997)

• Patterns of koala dermal ridges, even in their microscopic aspects, nearly identical to human
• Koala fingerprints, like those of humans, are unique for each individual

Small brain: 0.2% body weight; one of smallest in any marsupial

Highly sensitive ears help koalas detect low pitched bellows of other koalas.

Their second and third toes are partly fused and wrapped with a single sheath of skin but each toe retains a claw.

Image credit: © Epstula from Flickr. Some rights reserved.

Australian Koala Foundation (2010)
Degabriele (1980)
Ellis & Bercovitch (2011)
Grand & Barboza (2001)
Henneberg et al. (1997)
Hume (1999)
Jackson (2003)
Jackson (2007)
Lanyon & Sanson (1986)
Lee & Martin (1988)
Louys et al. (2009)
Nowak (1999)
Smith (1979a)
Sonntag (1921)
Szalay (1994)
Tuttle (1975)
Weisbecker & Sánchez-Villagra (2006)
Wilson and Mittermeier 2015