The national parks in African countries such as Kenya, Tanzania and Zambia, to name a few, are unrivalled in the number and diversity of species of mammals that can be seen from a single point of view on a game drive. It is all too easy to be tempted to race around and take photographs rather than staying in one place to take it all in. On a visit to Kenya’s Nairobi National Park, I decided to take it slow and just look around me and take in the diversity of species I could see, especially in terms of the diversity of mammalian orders and families. Wanting to look at African mammals this way was partly driven by my thoughts on how I could structure a presentation to the commoner African mammals illustrated with photographs.

In this article, I will describe some of the mammals I saw on just one game drive and describe their evolutionary relationship to each other. In taxonomic terms, all mammals belong to the class Mammalia, which is in turn divided into 20 scientific orders. There are two orders in particular which are strongly associated with the large gatherings of mammals on the African plains. One contains many species of antelopes, and the other contains familiar mammals such as zebras and rhinoceroses.

Let me start with the easier of the two orders. The Perissodactyla, or odd-toed ungulates, comprises just three families. The horses (family Equidae), the rhinoceroses (family Rhinocerotidae), and the tapirs (family Tapiridae). The tapirs, of which there are four species, are absent from Africa, with three of the species found in Central and South America and one in Southeast Asia. There are seven species of wild horses, the descendants of a family that evolved in North America. In the last three million years, horses have spread across Eurasia and Africa. The best-known of them are the zebras, of which there are three species.

The Mountain and Grevy’s Zebras have a narrow range, whereas the Plains Zebra is distributed across East and Southern Africa and goes by a number of local names, sometimes reflecting the presence of distinct sub-species. My safari vehicle was parked not too far from a small herd of Plains Zebras, and I took the opportunity to observe some of their behaviour. To help me make sense of what I was observing, I had a copy of Richard D. Estes, ‘The Safari Companion: A Guide to Watching African Mammals, Including Hoofed Mammals, Carnivores, and Primates’. I had first come across Richard Estes’s books on a trip to the Masai Mara a few decades ago. From the bookshop at Kechwa Tembo, I purchased his ‘The Behaviour Guide to African Mammals: Including Hoofed Mammals, Carnivores, and Primates’. This book is more scientific than the Safari Companion. I remember being blown away by the wealth of animal behaviour information.

Also in the Perissodactyla are the rhinoceroses. I could make out both the white and black rhinoceroses in the distance. The white rhinoceroses are found in southern Africa, and the ones in Nairobi National Park are animals which have been translocated to protect them from poaching. Black rhinoceroses are native to East Africa but are also subject to intensive poaching. The ones I could see were also animals that had been moved here for protection. But some of the rhinoceroses have been born here, and I could see a mother and a young one. The rhinoceroses here are free-living, and their behaviour is wild. Later in the day, I was able to observe a duel between two white rhinoceroses.

The second order of mammals which are strongly associated with the African plains is the Artiodactyla (also referred to as the Cetartiodactyla). Modern taxonomy places together what were previously two separate orders: the Cetacea, which are the whales and dolphins, and the Artiodactyla, the even-toed ungulates. The modern taxonomic grouping demonstrates that whales and dolphins developed from four-legged ungulates. The whales and dolphins belong to thirteen families, all of which are entirely aquatic. The Artiodactyla includes another ten families of terrestrial even-hooved ungulates, some of which can be seen in the park.

One of the families is the Hippopotamidae, with two species. Of the two, the Common Hippopotamus can be seen in a number of African countries. I saw one at a waterhole in the park. The hippopotamuses do provide a hint of how a four-legged ungulate could take to the water to feed and, over millions of years, evolve into a totally aquatic mammal. Another mammal family that hints at aquatic possibilities are the Chevrotains in the family Tragulidae. Many years ago, in Horton Plains National Park in Sri Lanka, I photographed one swimming underwater to escape from a brown mongoose. Nine of the ten species of Chevrotains are found in Asia, with only the Water Chevrotain found in Africa, but it is absent from Kenya. In South Asia, the chevrotains are often referred to as mouse-deer. However, they are not deer, which are in the family Cervidae. Deer are widespread in Eurasia and the Americas, but they are almost absent from Africa, with only the red deer being present in North Africa.

The various kinds of antelopes, bushbucks, gazelles, etc. which are found in Africa are superficially similar to deer (or cervids). But these horned mammals are in a different family, the Bovidae, known as the Hollow-horned Ruminants. The Bovidae are split into two subfamilies: the Bovinae, which is divided into three tribes, and the Subfamily the Antilopinae, which is divided into nine tribes. The Bovinae includes species such as the Water Buffalo, and the Antilopinae includes antelopes. From where I was parked, I had members of both subfamilies in view.

The subfamily Bovinae comprises three tribes with 40 species. The tribe Bovini includes the Asian Water Buffalo and the Cape Buffalo (also known as the African Buffalo). Both species are aggressive and dangerous where they occur. A Cape Buffalo walked past my vehicle and looked disarmingly docile. The tribe Boselaphini has two species confined to Asia. The third tribe, Tragelaphini, included species such as the Lesser Kudu, which is seen elsewhere in Kenya.

The subfamily Antilopini is very large, with 279 species in 8 tribes. On my game drive, I saw species from 4 tribes. The familiar Common Impala (tribe Aepycerotini), Thomson’s Gazelle (tribe Antilopini), the Blue (or Common) Wildebeest (tribe Alcelaphini), and the Southern Mountain Reedbuck (tribe Redunicini). But I was not sure if some of the species I saw had been introduced to the park.

On the boundary of the park, I also saw a common warthog, which is in the pig family, the Suidae. Although I did not see them on a game drive, at the Maasai Lodge we were staying at on the boundary of the park, I had close views of Bush Hyraxes, which are in the order Hyracoidea with a single family, the Procaviidae. These small rodent-like mammals are closely related to elephants. Also more easily seen visiting home gardens on the park boundary were primates (Order Primates), including the Yellow Baboon and Vervet Monkey. Inside the park, I also saw a blue monkey. The primate order is quite diverse, with 19 families. However, all of the primates I saw in and around Nairobi National Park are in the family Cercopithecidae known as the Old World Monkeys.

Much as I was thrilled to see so much mammalian diversity, as with many visitors, I have to confess the highlight was seeing the best-known carnivore in the world. We saw two lionesses on the game drive. They were relaxing in partial shade, lying down most of the time, but from time to time they would sit up and look around. Lions are in the family Felidae, the cats, which are one of 16 families in the Order Carnivora. A carnivoran is a member of the order Carnivora and has a narrower and more specific meaning in zoological nomenclature in comparison to the general expression of being a carnivore, which is to be an animal that eats meat.

With the Carnivorans (Order Carnivora), I had altogether seen five mammalian orders in and around Nairobi National Park. Within those five orders, I had seen mammal species from many families, illustrating how rich and diverse the mammalian fauna is in the plains of Africa.