The Rock Hyrax

Procavia capensis, commonly known as the rock hyrax, are actually the closest living relative to elephants! They belong to the class Mammalia, the order Hyracoidea, and the family Procaviidae.

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Range and Habitat: The rock hyrax can be found in East Africa and the Middle East. They live in areas with large rocks and boulders such as mountain cliffs and outcrops. They are very adaptable and can live in dry savanna or in rain forest areas as long as they have small crevices or cavities to hide from predators in. These rocks also allow for hyraxes to bask on them when it is cold (3,4). 


Physical Description: Rock hyraxes are small creatures that range in size from 30cm-58cm. They are covered in brown fur with a light tan underbelly. They have longer hairs that stick out from the body called guard hairs which help the hyrax feel its way around. They have short legs, rounded ears, no tail, and two large incisor teeth that look like mini tusks. They have rubber-like soles on their feet which provide them traction on the rocks. They have a scent gland on its back that can be black, yellow, or orange. This scent gland allows them to communicate with other hyraxes (3,4). 

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Physiology: Hyraxes physiology is very unique compared to other mammals. They have a complex digestive system which contains one large cecum and a pair of ceca on the colon. These ceca break down most of the food particles because the stomach has limited microbials to ferment the food. Because of this, their digestive system retains food particles longer than other mammals. This was determined by a study that gave hyraxes and other mammal species fluid markers to see how long it takes to go through their digestive system. Most species had excreted at least 80% of the marker after 24 hours, but hyraxes had only excreted 5% (6). Besides a slow metabolism, hyraxes also employ both methods of thermoregulation because they have poor thermoregulatory capabilities. They can maintain an internal body temperature, but when it gets somewhat cold they need to sun themselves. They will also leave the safety of their shelter if they are too hot or cold (1). However; during water shortages, the hyrax can tolerate a larger range of temperatures without activating heat production or cooling mechanisms. Also during water shortages, hyraxes can recycle urea. The recycled urea forms ammonia which can then be used to form amino acids and break down food particles in the hindgut (5). 

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Behavior: The rock hyrax lives in colonies of 2-50 individuals. They are diurnal animals, but can sometimes be active at night. They bask during the day, but will stay in their shelter if it is raining or too hot. They are omnivores and eat grasses, shrubs, fruits, leaves, insects, and small lizards. When eating, the head male will keep a lookout in a nearby tree. If he spots a predator, he will make a sharp bark to warn the others to hide. The hyrax has many different calls, but typically you can hear them grunt to warn others to stay away, whistle to indicate that they are happy, bark to alert other hyraxes that a predator is nearby, and mew to indicate to the others their location (4). The hyrax breeding season takes place from August to November.  Female hyraxes have a gestation period of 7-8 months and give birth to 1-4 young. The pups are well-developed immediately after birth and look like miniature adult hyraxes. The pups suckle for three months, but can eat solid foods within the first month of being born. They can also move about very easily after just a day. They become sexually mature at 16-17 months of age and can live up to 11 years (3).

Evolutionary History: Before DNA evidence, scientists thought that hyraxes were more closely related to rodents. However; we now know that hyraxes are the closest living relative to elephants. There is a common ancestor that existed about 60 million years ago that connects hyraxes and elephants. Elephants and hyraxes share many morphological features such as similar shaped bones, tusks, hoof-like toenails, and similar amino acids. They also have their lungs attached to their rib-cage and both do not have a gallbladder (2). Mitochondrial DNA evidence has also supported this relationship. In addition to DNA evidence, there is fossil evidence to conclude that elephants and hyraxes are related. About 23-54 million years ago, a large, ancient hyrax species called Titanohyrax walked the Earth. Titanohyrax skull was 30cm in length compared to the modern hyrax skull which is 12cm in length. It is estimated that Titanohyrax weighed approximately 800kg. The large size of Titanohyrax gives scientists more evidence to conclude that hyraxes and elephants are related. Unlike the elephants though, hyraxes did not stay the same size as their ancestors. It is thought that the ancient hyraxes could not compete with ungulates for food and water which is why they died and the smaller species survived (7).

References: 

1. Feldhamer, George A., Lee C. Drickamer, Stephen Vessey, and Joseph Merritt. Mammalogy: Adaptation, Diversity, Ecology. 3rd ed. Baltimore: Johns Hopkins UP, 2007. 376-378. Print 
2. Gross, Amanda. "The Hyrax and the Elephant: Distant Cousins." 11 Apr. 2014. Web. 7 Dec. 2014. http://www.critters360.com/index.php/the-hyrax-and-the-elephant-distant-cousins-39289/
3. "Rock Hyrax (Procavia Capensis)." Rock Hyrax Videos, Photos and Facts. 14 Mar. 2011. Web. 7 Dec. 2014. http://www.arkive.org/rock-hyrax/procavia-capensis/
4. "Rock Hyrax." (Procavia Capensis). Web. 7 Dec. 2014. http://a-z-animals.com/animals/rock-hyrax-/
5. Rubsamen, K., I. Hume, and W. Engelhardt. "Physiology of the Rock Hyrax." ScienceDirect, 2 Oct. 1981. Web. 7 Dec. 2014. http://ac.els-cdn.com/0300962982902195/1-s2.0-0300962982902195-main.pdf?_tid=7cde009c-7444-11e4-9332-00000aacb362&acdnat=1416880003_340137b0d392a166ba1b9cdf80da4b82
6. Stevens, C. E. Comparative Physiology of the Vertebrate Digestive System. Cambridge [Cambridgeshire]: Cambridge UP, 1988. Print.
7. Wade, Aaron. "Hyracoidea (Hyraxes) Investigative Report." Hyraxes. 1 Jan. 2008. Web. 7 Dec. 2014. http://tolweb.org/treehouses/?treehouse_id=4741