Introduction
The cheetah ( Acinonyx jubatus) is the fastest land animal with a widely quoted speed of 71 miles per hour or 32ms-1 however time trials under controlled circumstances show that the top speed is somewhere around 29ms-1 or 64 miles per hour (Sharpp, 1997). The Cheetah is uniquely adapted for speed and very few other land mammals can boast of such physiological specializations. Cheetah is a member of the group Felidae and they are unique in many ways. To start with, the African cheetah is the only species in the genus Acinonyx. Out of the 37 species in the cat family, cheetah stands out because of its unique physiology, behaviour and social structure. Some of the unique attributes of the cheetah include, long slender legs, enhanced cardiovascular and adrenal capabilities, specialized semiretractible claws and a unique musculature (O’brien, Roelke, & Marker, 1985). Studies have shown that the cheetah is a prime example of over specialization; an animal that is purely built for speed and has reached pinnacle of evolution in terms of speed and manoeuvrability. But what is the reason behind its unmatched speed and agility. The answer probably lies in the evolutionary forces that affected its surroundings and left a mark in its physiology.
Why is the cheetah so fast?
- Predator-prey interactions have been known to be one of the most important deciding factors that affect evolutionary stable strategies (Hilborn, Pettorelli, Orme, & Durant, 2012).
- Cheetahs are morphologically and physiologically adapted to hunt at high speeds (West et al., 2013; a M. Wilson et al., 2013). They usually go for small to medium sized preys.
- A fast animal can easily hunt down slow-moving prey. However, with higher velocity chases, acute turn angles can increase chances of injury and lead to failure.
- Most of Cheetah hunt failures are attributed to overheating and exhaustion.
Characteristics of a successful hunt can reveal the evolutionary strategies behind the speed of cheetah
- All chases were brief lasting not more than 59 seconds and the longest duration was 23s at an acceleration of 13.9ms-1 (J. Wilson, Mills, & Wilson, 2013).
- Researchers found that angular velocity during the last 5s of the chase was significantly greater during successful hunts (J. Wilson et al., 2013).
- Vectorial dynamic body acceleration was the highest during last 8s of a successful chase at 1.71±1.10g (J. Wilson et al., 2013).
- There was a significant relationship between cheetah identity, hunt success and time.
- In a separate study the hunt success of cheetah was attributed to the prey size ( small to medium) and a higher success in chases and stalks (Hilborn et al., 2012)
Greyhound and cheetah; a case of convergent evolution
- A comparison with the anatomy of greyhound provides useful insights to the speed of cheetah (P. E. Hudson, Corr, & Wilson, 2012)
- Galloping of cheetah is characterised by the flexing of the back along with swift swinging of the limbs.
- Although the anatomy of cheetah and grey hound ins almost the same, there is no documented reason why (P. Hudson & Corr, 2011) there is a disparity in their top speeds 17ms-1(greyhound) and 29ms-1(P. E. Hudson et al., 2012)
- The three major limits to the running speed of humans are peak limb force, minimum achievable swing and muscle power and the same principles can be attributed to the cheetah (P. E. Hudson et al., 2012)
- The longer leg and back of the cheetah could be one of the determinants that increase the stride length. Coupled with this, the cheetah’s ability to reduce swing times compared to the greyhound could be contributing to the higher acceleration.
- The semi-retractile claws of the cheetah provide the necessary grip required by the animals to maintain the acceleration (P. E. Hudson et al., 2011).
- Increased stride frequency of the cheetah could also be one of the deciding factors behind its high top speed (P. Hudson & Corr, 2011).
- The forelimb anatomy of the cheetah can give some important information about the top speed of cheetah. (P. E. Hudson et al., 2011)
- The long fibred SV muscles in the front leg of cheetah enables scapula translation along the rib cage. This results in a longer stride lengths (Hudson et al., 2011)
- The digital flexor muscles and the extensor digitorum communis of the cheetah are heavier than greyhound, these muscles flex the digits and provide the necessary traction for highspeed-maneuvers (Hudson et al., 2011).
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