Red Kangaroo

After a blogging hiatus over the summer, The Eatles are back at it, telling the world about the fascinating animals they're consuming. Several years ago, the Organ Lab was fortunate to obtain a nearly adult, male red kangaroo (Macropus rufus) from our contacts at Grant's Farm in St. Louis, MO. After spending a considerable amount of time in a chest freezer in the Organ Lab, this summer with the help of IUSM Anatomy Education graduate students Jessica Byram and Naomi Schmalz, we began a systematic dissection and description of the lower limb musculature. Our plan is to get these descriptions published in a peer-reviewed journal. When we do, we will update this post with a link to the paper. In the meantime, it is worth pointing out a few reasons that kangaroo anatomy and biology is interesting.

Kangaroo foot skeleton

www.gutenberg.org

Red kangaroos are the world's largest marsupial mammal. When a baby kangaroo, or joey, is born, it is not fully developed; instead, the cherry-sized newborn climbs its mothers fur until it reaches an external pouch - a marsupium - on the front of her body where it can continue to develop while nursing for the next several months. This is where we get the term "marsupial". 

Red kangaroos live in the deserts and open grasslands of Australia, and they gather in groups called mobs. They are members of the Macropodidae family, of which all genera in the family have skeletons that are highly specialized for jumping. The forelimbs are usually small and are used for slow movements on all four limbs or for handling food. The hindlimbs, however, are elongated and the foot has no big toe (hallux, digit 1). The loss of the hallux is a direct result of specialization for running or hopping, which requires more reliance on the fourth toe, which bears the largest proportion of force while in contact with the ground. Therefore, kangaroos become functionally two-toed during locomotion (digits 4 and 5 bear the load), especially during rapid (bipedal) locomotion. The running and hopping ability of large kangaroos like the red kangaroo is outstanding. On level ground, kangaroos can reach speeds of close to 70 kilometers per hour, and individual leaps can cover distances of nearly 14 meters and heights of 3.5 meters. The tail serves an important rudder function to help steer the kangaroo at high speeds.

Male red kangaroos are solidly built with strong musculature attached to their robust skeletons. When competing for mates, males often lean backward on their large tails and fight each other with their hindlimbs. Females are smaller than their male counterparts and often have a blue-tinted pelage (fur), which is why they are often referred to colloquially as "Blue Fliers".

Contributed by Jason Organ, PhD.

For information about red kangaroos, see these papers:

McCarthy, M. (1996). Red Kangaroo (Macropus rufus) Dynamics: Effects of Rainfall, Density Dependence, Harvesting and Environmental Stochasticity The Journal of Applied Ecology, 33 (1) DOI: 10.2307/2405014 

Sharman, G., Frith, H., & Calaby, J. (1964). Growth of the pouch young, tooth eruption and age determination in the Red Kangaroo, Megaleia rufa CSIRO Wildlife Research, 9 (1) DOI: 10.1071/CWR9640020 

Sonnabend, D., & Young, A. (2009). Comparative anatomy of the rotator cuff Journal of Bone and Joint Surgery - British Volume, 91-B (12), 1632-1637 DOI: 10.1302/0301-620X.91B12.22370