Blackbucks (Antilope cervicapra) and Pronghorns (Antilocapra americana) live thousands of miles apart – the former in South Asia, the latter in North America. They share similarities in terms of body structure (built for speed over long distances) and habitat (open country with an abundance of grass and forb). Both belong to the infraorder Pecora, hoofed mammals that include the great majority of large to medium-sized terrestrial herbivores (equipped with four-chambered stomachs to process plant matter). Pecora is derived from the Latin pecus which means ‘horned livestock’. That is where the similarity ends.
Blackbucks are strikingly handsome creatures, the males standing out with their black coats and contrasting white underparts. Long, corkscrew-like horns add to the majestic appearance. Females, juvenile males and young ones are drab in comparison. Members of the Bovidae (cattle) family, they are the only representatives of the genus Antilope, whose closest relatives are the true gazelles of the genus Gazella. The Pronghorn of North America is a distant relative, being the only survivor of the Antilocapridae family, which occupied ecological niches corresponding to those of Old World bovids. Unlike the Bovidae, the Antilocapridae were confined to the North American continent.
Pronghorns are marked out by their distinct coats (reddish brown with white patches on the face, throat, belly and rump), manes (short haired) and horns (lyre shaped structures that grow from a bony core). The horns are used for sparring between males and have a keratinous covering that is shed annually. It is these appendages that set them apart from bovids (cattle) and cervids (deer). Their closest relatives are the Giraffidae (Giraffes and the Okapi of Africa). Unlike their massive cousins across the Atlantic, Pronghorns evolved for mobility. This is what makes them look like antelopes.
Blackbucks weigh up to 57 kg while Pronghorns can reach 65. Both are fleet of foot, clocking up maximum speeds of 80 and 88 kph respectively. That makes them among the fastest terrestrial creatures on the earth. In fact, over long distances they can easily outdo the Cheetah (Acinocnyx jubatus) whose top speed of 110 kph lasts for no more than 20 seconds. We know that the Cheetah hunted Blackbucks for millennia, before being driven to extinction. The intense competition between predator and prey made these antelopes one of the fastest creatures of South Asia. What explains the Pronghorn’s blinding speed (88 kph) and unbelievable endurance (56 kph for 6 km)?
Evolutionary biology has the concept of parallel evolution. This refers to the development of similar traits (in this case, high speed over long distances) in species from related but distinct lineages (the Bovidae and Antilocapridae families). The final piece of the puzzle is the creature whose hunting skills drove the Pronghorn to such extremes of physical performance. In my previous post, I had mentioned the Cheetah’s relationship to the Puma (Puma concolor) and Jaguarundi (Puma yagouaroundi) of the Americas. It is a close but long extinct relative of the latter two that made the Pronghorn the second fastest sprinter on terra firma. Known as the American Cheetah, Miracinonyx trumani was also a member of the tribe Acinonychini.
The Cheetah was the first to separate from them (4.9 million years ago), followed by the Jaguarundi (4 million years ago). The common ancestor of the American Cheetah and Puma was more like the latter in build (robust) and nature (ambush hunter). Miracinonyx diverged 3 million years ago, evolving a short face, large nasal cavities and long limbs to take down prey on the open plains. A successful predator, it roamed North America for 2.5 million years, disappearing at the end of the Ice Age. At 95 kg (to its Old World counterpart’s sprightly 72 kg), it must have been a formidable threat; formidable enough to drive Pronghorn evolution. In a final twist, the Old World Cheetah of South Asia suffered the same fate as its American cousin, leaving behind prey faster than necessitated by far slower hunters.
Image Attribution: The image above, sourced from Wikimedia Commons shows a landscape painting, ‘Prong Horned Antelope’ (c. 1865), by the German-born American artist Albert Bierstadt. Bierstadt was famous for his portraits of the 19th century American West, an era when the United States began expanding across the continent at a rapid pace, taking over lands previously untouched by European settlements and industry. The painting is preserved in the National Museum of Wildlife Art, Jackson Hole, Wyoming (USA).