Pigs, Peccaries and Hippos Status Survey and Action Plan (1993)

Chapter 4

The Afrotropical Suids:

Potamochoerus, Hylochoerus and Phacochoerus

4.1 Taxonomy and Description

Peter Grubb

Introduction

The recent African suids have been reviewed by Haltenorth (1963), Ansell (1972), and Groves (1981). The present contribution is based on the literature and on a study of museum specimens. There is a need to examine more museum material, especially unreported accessions, in the hope of reaching more definitive conclusions concerning systematics and distribution.

The pigs of tropical Africa are the survivors of a lineage, which radiated considerably during the Tertiary (Cook & Wilkinson, 1978; Harris & White, 1979), without ever attaining a species-diversity sufficient to rival that of the African bovid ruminants. One genus (Potamochoerus) still retains a relatively conservative morphology and is superficially similar to Sus in many features. The other two (Hylochoerus and Phacochoerus) are much more specialized. Potamochoerus includes two species: the red river hog (P. porcus) occurring in the rain-forest block, extending into gallery forests, and the bushpig (P. larvatus) distributed through both the Southern Savanna and the highland forests and forest galleries of eastern Africa and Ethiopia. The single species of Hylochoerus, the forest hog (H. meinertzhageni), has a discontinuous distribution in the main forest blocks but also extends far beyond them in some gallery forests and in upland forests of East Africa. Phacochoerus species, the warthogs, are savanna pigs, which nevertheless have a wide ecological tolerance, ranging from mesic habitats into more arid zones (southern Sahara, Somali, and Southwest Arid Zones). A common and widespread species of warthog (P. africanus) is replaced in the Somali Arid (and formerly on the Southwest Arid/southwest Cape border) by a more specialized form - a separate species, the Cape or desert warthog (P. aethiopicus). Thus 5 species (and at least 12 subspecies - see below) of 3 genera of Afrotropical suids are recognized in this account:

1. The red river hog, Potamochoerus porcus (0 ssp.)

2. The bushpig, Potamochoerus larvatus (3 + ? ssp.)

3. The forest hog, Hylochoerus meinertzhageni (3 ssp.)

4. The common warthog, Phacochoerus africanus (4 ssp.)

5. The desert warthog, Phacochoerus aethiopicus (2 ssp.)

The Genus Potamochoerus

The Red River Hog and the Bushpig

The two species of 'bush pigs', the red river hog (P. porcus) and the bushpig (P. larvatus), are not unlike the Eurasian wild pig (Sus scrofa) in proportions, but are generally smaller, shorter limbed, and with different pelage. In boars there is an exostosis on each side of the snout, absent in all other living pigs, which extends laterally towards a hypertrophied apophysis on the canine sheath, these two bony knobs supporting a single large external cutaneous wart on each side of the snout, yet allowing the tendons of the nasal disc to tunnel through to their muscular origins. There are no infraorbital warts or swellings, as in the other Afrotropical genera. Compared with Sus, the skull is less elevated in the occipital region and the rostrum is less elongated. There are other differences in form and proportions, which suggest that Potamochoerus is not particularly close to Sus phylogenetically. The molars have thick enamel and are brachyodont and relatively simple.

Too many subspecific taxa of Potamochoerus have been recognized yet no convincing evidence has emerged to show that bushpig and red river hog intergrade or hybridize. As they are also clearly distinct morphologically, they are treated here as two separate species.

The Red River Hog (Potamochoerus porcus)

On average, this is the smallest African pig. Available measurements for greatest skull length (from occipital crest to tip of premaxillae) are 269-378 mm for adult females, and 327-405 mm for adult males. It is also quite the most brightly and strikingly colored of all wild pigs. The predominant color is bright russet orange with a white dorsal line starting behind the head, the hairs of which are only slightly longer than those of the flanks. The head is marked by a contrasting mask - black, with whitish muzzle, spectacles round the eyes, and cheek whiskers. The pinna is elongated with a long terminal tuft of hair. The pelage on the snout and most of the face is bristly but on the forehead and the whole of the rest of the body it is short, soft and dense. There are scattered long bristles along the flanks.

Museum specimens were examined from Guinea Bissau, Sierra Leone, Liberia, Ivory Coast, Ghana, Togo, Nigeria, Cameroon, Bioko (?), Rio Muni, Gabon, Congo and Zaire (now Democratic Republic of Congo). The record from Bioko is based on teeth picked up in the field (Tervuren Museum), which have yet to be critically studied. The River Hog is also reliably recorded from Senegal, Guinea, Benin and the Central African Republic. There are no authentic records of this species in the present restricted sense from Sudan. It ranges from the main forest block into the Niokola Koba Park in Senegal (Dupuy, 1969), as far as the Pandam Game Reserve in Nigeria (Happold, 1987), and into the southern part of the Manova-Gounda Saint Floris Park, northern C.A.R. (Fay, in litt.), and may penetrate the savanna along gallery forest in the other countries.

I have been unable to differentiate any geographic variation from individual variation in this species and hence recognize no subspecies. (Synonyms: albifrons, albinuchalis, mawambicus, penicillatus, pictus, ubangensis).

The Bushpig (Potamochoerus larvatus)

In this species, the face is also bristly but bristly pelage extends from the head over the whole body. The bristly body hairs are very long and relatively sparse and they are particularly elongated along the back so as to form a well differentiated dorsal crest, which begins far forward, between the ears. The long bristles give the live animal a shaggy, crested appearance, very different from the trim, short-coated aspect of the river hog. The pinna of the bushpig is not so elongated, though it is still tufted. The head is never 'masked', though it contrasts in color with the body. Body color is variable between ages, individuals, sexes and populations, with polymorphism-polymorphism in some places. Too many subspecies have been recognized. The principle systematic division within the species is between the white-faced animals of eastern Africa and the remaining populations of both southern Africa and Madagascar, not between races of Africa and races of Madagascar (see later text). The following three (mainland) subspecies are recognized provisionally.

1. White-faced Bushpig, Potamochoerus larvatus hassama (synonyms: daemonis, intermedius, keniae, arrhenii).

In this subspecies, adult males are usually black or almost wholly 'blond' (off-white). Subadult males and females have blackish markings on the face and the upper parts reddish, but they are sometimes wholly black also. In cranial dimensions, the white-faced bushpig is similar to the red river hog (skull length 327-353 mm in females, 341-377 mm in males) but the temporal ridges are usually more pinched-in and the braincase is never as convex and inflated. I have seen specimens from Ethiopia, southern Sudan (both west and east of the Nile), eastern Zaire (now Democratic Republic of Congo), Rwanda, Burundi, Uganda, Kenya and northern Tanzania. The white-faced bushpig is an animal of elevated country, occurring in forest and other habitats with dense vegetation on nearly all the high ground of eastern Africa from the Virunga Mountains to Kilimanjaro and the Ethiopian highlands. It is not yet possible to identify any pattern of geographic variation over this wide area. Appreciation that only one subspecies occurs in these highlands has been hampered in the past by the considerable variation between specimens and the shortage of adequate comparative material.

2. Somali Bushpig, Potamochoerus larvatus somaliensis

These bushpig occur along the course of the Tana, Juba and Scebeli Rivers in northeast Kenya and Somalia (Funaioli & Simonetta, 1966). A Somali subspecies was differentiated by de Beaux (1924) on the basis of a single, small broken skull. I have seen two relatively small skulls from northern East Africa, a female from Kidori on the Tana River, Kenya, and a male from the southern Juba River, Somalia (greatest length 337 and 334 mm respectively). Neither of these specimens is fully adult for the hindmost cusps of the cheek teeth are not yet in wear. Even so, they are rather small for P. l. koiropotamus and more within the size range of P. l. hassama. Until more specimens can be examined and the pelage described, it is not certain whether this nominal subspecies should be synonymised with hassama. We might perhaps expect a subspecific difference because hassama tends to occur in a different kind of habitat and because the Somali populations are likely to be in contact with P. l. koiropotamus but geographically isolated from P. l. hassama. Relatively small skulls of boars from coastal southern Tanzania (334-367 mm in length) might indicate integration between somaliensis (= hassama?) and koiropotamus, but the scarcity of specimens makes this a speculative proposition.

3. Southern Bushpig, Potamochoerus larvatus koiropotamus (synonyms: capensis, cottoni, johnstoni,

maschona, nyasae, congicus).

Typically, this subspecies never has the black-and-white polymorphism pattern so characteristic of male hassama. The face is predominantly gray with a broad blackish band over the muzzle. Sometimes the whole of the body pelage is blackish or 'blond' at least in boars, but usually the upper parts of the body are russet or brown, grading into the darker tint of belly and limbs. In dimensions, this is a larger animal than any other member of the genus and the largest specimens have very prognathous skulls (skull length 367-415 mm in males, excluding some small skulls from eastern Tanzania mentioned above; 345-395 mm in females). I have seen specimens from Zaire (lower Zaire River, left bank; and Katanga), Tanzania (north at least to Kilosa), Malawi, Zambia, Zimbabwe, Mozambique, Angola and South Africa. It is reliably recorded from Botswana and probably occurs in the Caprivi Strip, Namibia, and in Swaziland. However, the species appears to be absent from an area between Durban in Natal and East London in Cape Province, South Africa (see Stuart and Stuart, 1988), leaving an isolated in southern Cape Province (Fig. ///). This distributional hiatus may be natural, though there seems to be no comment in the literature. Some southern Cape animals have a strikingly white face (Plate ///), but not all museum specimens are like this, including the holotype. As little material has been available for study, it would be premature to treat the southern Cape animals as a valid subspecies. If in the future this proved to be justifiable, these pigs would retain the name P. l. koiropotamus while bushpigs from Natal northwards would have to be called P. l. nyasae.

Biological Relationships Between the Red River Hog and the Bushpig

These two species are allopatric and their ranges are contiguous in some places. Sympatry may also occur in some areas, but this has yet to be confirmed. Along the lower Zaire River, below Kinshasa in Zaire (now Democratic Republic of Congo), for example, the two species are separated only by this river - the smaller P. porcus occurring on the right bank and the large P. l. koiropotamus (synonym: congicus) on the left (Angolan) side. The two populations are morphologically quite distinct with no indication of gene flow between them. A similar situation obtains around the Sudan-Zaire border, where museum specimens of P. porcus have been obtained close to the Sudan border in Zaire and a male P. l. hassama has been obtained nearby on the Sudan side, but no intermediates between these are known. In the Rift highlands of Zaire (now Democratic Republic of Congo), Rwanda and Burundi, the two species appear to be ecologically/altitudinally separated, with museum specimens from the mountain slopes all being P. l hassama, while those from lowland forest are P. porcus. No intermediate specimens are known and the two species have not been recorded from the same locality, but they appear to come very close to each other.

In Uganda, only P. l. hassama, the white-faced bushpig, is known from museum specimens, though Ghiglieri et al. (1982) observed wild pigs of the genus Potamochoerus in the Kibale Forest which they thought were intermediates between 'P. porcus koiropotamus' (i.e. P. larvatus hassama) and 'P. porcus porcus' because their polymorphism variation seemed to span the whole range exhibited by these taxa. However, they did not demonstrate that this variation is atypical for P. l. hassama - which shows all the polymorphism varieties that they observed. Since no special resemblances to P. porcus were reported in face pattern, type of pelage or ear shape, evidence of genetic introgression by this species cannot be said to have been established. It is possible that P. porcus has made a narrow penetration of Uganda between the Rift mountains by crossing the Semliki River, and it may have hybridized with P. larvatus in the Kibale Forest, but more convincing evidence is needed.

Kingdon (1979) also assumed that introgression had occurred between the red river hog and the bushpig, because he thought that East Africa populations of Potamochoerus show features intermediate between the two taxa, a view that is not accepted here. Lönnberg's (1910) so-called intermediate species, P. intermedius, from an unspecified locality in Uganda, is not intermediate at all but falls within the range of variation of P. l. hassama. De Beaux (1924) had already established that it was a representative of P. larvatus.

Bushpigs on Madagascar

It is widely appreciated that the bushpig is a newcomer to the Malagasy fauna. It is present on Mayotte in the Comoros (Benson, 1960) as well as on Madagascar itself. Whilst no tradition or cultural practice appears to have been described in the zoological literature which could provide a clue as to how bushpigs were brought to the region, Simoons (1953) has cited references to the semi-domestication or at least taming of Potamochoerus along the northern edge of its range, and even its alleged later carriage to South America and to England (also see Vercammen et al., this vol.). It may be argued that since the Malagasy bushpigs did not diverge naturally but only after human interference, they should be regarded as synonymous with the mainland P. l koiropotamus, which they resemble most closely; and any scientific names bestowed upon these feral populations should not be given currency. However, the mainland and island populations can be distinguished morphologically, so it would be premature to synonymise them when so little is known about their differentiation. To do so would also raise problems of nomenclature, in that the earliest name for the insular pigs - larvatus - has priority over the name koiropotamus and its rejection would flout the Rules of Zoological Nomenclature. Moreover, the unspoken consensus is to accept names based on populations which became feral in early historic, if not prehistoric, times. The deer Cervus timorensis (which was almost certainly introduced to Timor) provides a parallel example.

To complicate matters further, it is necessary to recognize two subspecies of Malagasy bushpigs, whose status can be settled only when further specimens become available. These subspecies are:

4. Malagasy Bushpig, Potamochoerus larvatus larvatus (synonyms: edwardsi, madagascariensis)

Lönnberg (1910) believed that this name applied to a West Malagasy race. He had examined the skull of an adult male from northwest Madagascar which was much smaller than any other specimen of the species ever recorded, but which otherwise resembled Cuvier's illustration of a skull in the original description of the species. Lönnberg surmised that the drier and harsher environment of West Madagascar would support a smaller-sized animal than the moister zone of eastern Madagascar and, indeed, the skulls of eastern specimens are larger (nominal subspecies hova) than Lönnberg's single specimen. Lönnberg had been informed that the Malagasy people distinguished two kinds of wild pig, a darker and a redder sort, and he matched this concept with his two-subspecies hypothesis. Specimens examined from western Madagascar are juveniles, so Lönnberg's views on coloration cannot be verified. His conclusions rest upon a single animal whose external appearance is not known, and we still do not know whether the bushpig of western Madagascar is really a small-sized form or whether Lönnberg was misled by an exceptional individual and all Malagasy bushpigs belong to a single subspecies.

5. East Malagasy Bushpig, Potamochoerus larvatus hova

The eastern Malagasy race, possibly valid as a subspecies, is known by both skins and skulls. With a gray head, black muzzle, russet upper parts and dark under parts, it cannot easily be separated from P. l. koiropotamus except in its smaller dimensions (skull length 359 mm in one female, 356 and 368 mm in two males) but available photographs suggest a sleeker animal with shorter hair.

The Genus Hylochoerus

The Forest Hog

Pigs of this genus belong to the single extant species, H. meinertzhageni - the so-called 'giant' forest hog. However, they overlap in size with Potamochoerus species and, contrary to the impression created in some popular accounts, the lowland races are not much larger than the red river hog and not as large as the largest bushpigs. Only the East African forest hogs are giants. Pigs of this genus are always coal-black in polymorphism when adult. Piglets are said to be plain colored (Dorst & Dandelot, 1970) and a piglet less than 10 weeks old from the Virunga National Park lacked any sign of stripes (d'Huart, in litt.), but specimens in the Natural History Museum, London, are dark brown with light brown stripes. The pelage is wholly bristly, the bristles much stouter than in Potamochoerus larvatus. The ears are not tufted and the nasal disc is very broad. There are no tusk apophyses and no rostral warts, but in boars the zygoma is thickened and pneumatised, supporting large infraorbital renoid swellings. The dentition is far more specialized than in Potamochoerus and hypsodont, with enamel pillars supported by cementum, which wears through to the dentine soon after eruption. The anterior cheek teeth tend to be lost during maturation. The structure of the skull and the facial musculature are adapted to a folivorous rather than an omnivorous diet (Ewer, 1970). The skull is broad in comparison with that of Potamochoerus and the tusks of the boars flare out, for their tips are not abraded through wear by the lower canines.

Recent reviews (Haltenorth, 1963; Ansell, 1972) recognized three subspecies of forest hog: ivoriensis, rimator and nominate meinertzhageni (synonyms: ituriensis, gigliolii, schultzi), though ivoriensis has been included as a synonym within rimator by Kuhn (1965). Other authors have remarked on the distinctiveness of ivoriensis or on the differences between ituriensis and meinertzhageni. Having examined available museum specimens, I concluded that it is indeed possible to recognize three subspecies (though not with the synonymy given above) each of which is associated with a distinctive region or environment.

1. West African Forest Hog, Hylochoerus meinertzhageni ivoriensis

This subspecies does not differ significantly from the next in dimensions (skull length in mm 333-372 for females, 355-397 for males), but the shape of the skull is distinctive and unlike that of other subspecies.

Specimens from Liberia, Ivory Coast and Ghana have been examined, and it has been reliably recorded from Guinea (Prunier, 1946). Records from Guinea Bissau (De Sa e Melo Cristino, 1958) are not sufficiently detailed to be acceptable (Ansell, 1972) and the same must be said for Baudenon's (1958) claim that it occurs in Togo.

2. Congo Forest Hog, Hylochoerus meinertzhageni rimator (synonyms: ituriensis, gigliolii).

Specimens from Cameroon, Congo and Zaire (now Democratic Republic of Congo) have been examined, and this subspecies has been reliably recorded from the highland forest on the Cameroon border of Nigeria (Hall, 1976; Happold, 1987; Dowsett and Dowsett-Lemaire, 1989), the Central African Republic, Gabon and southern Sudan west of the Nile. This Sudan population is almost certainly continuous with those of Zaire and C.A.R. In the C.A.R. it is now known to range well north of the main forest block (Fay, in litt.). The Nigerian population may be an isolated one. At the same time, the Forest Hog is absent from lowland forest in Nigeria, western Cameroon and western and southern Gabon. In Zaire it is absent from most of the forests south of the Congo (Zaire) River and Schouteden's (1945) evidence that it occurs here has never been supported by specimens.

Complete skulls have been examined from Cameroon, Congo and Zaire north of the Zaire River only, subspecific identity of populations in other countries or regions being inferred. There is some geographic variation in size, specimens from the western part of the range being on average smaller than those from further east. Greatest length of skull in mm is 330-377 (females) and 341-388 (males) for Cameroon and Congo, but 331-391 (females) and 362-404 (males) for Zaire (mostly in the east). The samples from which these measurements were obtained are widely separated geographically but cannot be differentiated subspecifically, so the nominal Ituri subspecies ituriensis is synomised with rimator, originally described from Cameroon.

3. Giant Forest Hog, Hylochoerus meinertzhageni meinertzhageni (synonym: schultzi).

Only this, the nominate subspecies, deserves the epithet 'giant'. Greatest skull length in mm is 381-427 (females) and 410-461 (males). It resembles the subspecies rimator in the shape of the skull, but differs not only in its great size, but also in the size of the tusks, at least in boars, which flare widely. The cheek teeth are also different in that the cementum is developed at the expense of the enamel pillars, which are therefore more widely separated.

I have seen specimens from eastern Zaire (Albertine Rift Highlands only), Uganda and Kenya and fragmentary esteological material from Ethiopia. Intergradation between the lowland forest rimator and this very large highland race presumably occurs along the foothills of the Rift Highlands. The species is reliably recorded from Rwanda and northern Tanzania, and from east of the Nile in the Imatong Mountains, Sudan (Cotton, 1936). From their dimensions (d'Huart 1978, and in litt.), specimens from Virunga and Kahuzi are also of this nominate race. It is also said to occur in Burundi, but d'Huart (1978) was not satisfied that this is the case. It has not yet been shown that the populations in Ethiopia, Sudan and Tanzania represent the nominate race.

The Genus Phacochoerus

The Common Warthog and the 'Desert' Warthog

The warthogs differ in proportions from the other Afrotropical suids. They are more unguligrade and have a proportionally huge head. The skull is very strongly modified from the Sus-Potamochoerus form. The ascending process of the mandible is elongated; the maxilla is considerably deepened, accommodating enlarged, very hypsodont molars; the zygomatic arch is much deepened as well and the orbits are displaced postero-dorsally relative to the rostrum so that they rise above the drastically shortened braincase. Except for the wide spreading canine sheaths, the skull has become triangular in dorsal outline, broad at the back, narrowing towards the front. The lower tusks do not wear down the tips of the upper tusks, which are long and curved. The tusks of sows are relatively large in proportion to those of boars, compared with the condition in the other Afrotropical genera. The cheek teeth are even more specialized than those of Hylochoerus. They are far more hypsodont and the enamel pillars are more numerous, narrower and closely packed together. The full number of cheek teeth is quoted as 22 but usually many of these are absent from mature animals. The pelage is coarse and very sparse, except for a prominent dorsal crest of long bristles. In young animals especially there is often a fringe of white hairs on the cheeks. Both genal and rostral warts are present, the latter unsupported by bony excrescences.

Nowadays all scientific and popular accounts dealing with the existing African fauna recognize only a single species of warthog, though paleontologists have long recognized that there are two Holocene species from Africa. These species are very well defined and they were almost universally recognized as distinct in the zoological literature for over 140 years. Clearly there is a need for a full presentation of the evidence for the two-species theory, which amounts to a reappraisal of the genus, and this will be done elsewhere. In the meantime a summary of some of the relevant information appertaining to the two species recognized here will be given below.

Common Warthog (Phacochoerus africanus)

This species is very widespread, occurring in all nations, which extend into the Northern Savanna or the Southern Savanna and the bordering arid zones. I have examined museum material from Mauritania, Senegal, Guinea Bissau, Sierra Leone, Ivory Coast, Ghana, Mali, Burkina Faso, Niger, Nigeria, Cameroon, Chad, Sudan, Ethiopia (including Eritrea), Zaire (now Democratic Republic of Congo), Rwanda, Burundi, Uganda, Kenya, Somalia, Tanzania, Malawi, Zambia, Zimbabwe, Mozambique, Angola, Namibia, Botswana, Swaziland and South Africa. The species is reliably known also from Gambia, Guinea, Togo, Benin and C.A.R. The following names would be available if subspecies were to be recognized: africanus (Senegal), fossor (Chad), bufo (Sudan), aeliani (Eritrea), centralis (eastern Zaire), massaicus (Tanzania), sundevallii (Natal) and shortridgei (Namibia).

Systematic studies of the common warthog have been based almost entirely on skulls, as the sparsely-haired skins are rarely preserved and almost nothing is known about variation of the pelage. There is much variation in the form of the skull but very few biologists have studied warthog skulls to determine geographic variation in the species. Lönnberg (1908, 1909) tried to identify variation in proportions, but his samples were so small that he did not always successfully differentiate individual variation and geographic variation. Hollister (1924) later demonstrated that massaicus must be a synonym of aeliani, though it now seems that he might have been wrong, and Hill (1942) could not distinguish Botswana specimens referred to shortridgei from animals from north-east Zaire, East Africa, Zululand and Transvaal (by implication, centralis, massaicus, sundevallii and shortridgei would be synonyms of aeliani). Lundholm (ms. quoted by Ansell 1972 and Meester et al., 1986) regarded shortridgei as a synonym of sundevallii. Schwarz (1920) on the other hand was satisfied that the subspecies fossor, which he had named, could be differentiated from bufo.

Preliminary analysis of skull measurements indicates the following. West African skulls are very large, with relatively long post-orbital length. Specimens from the Sahel are smaller and may grade into the Eritrean population, with narrow intertemporal width but still with relatively long postorbital length. Central African populations also have very large skulls, but with shorter postorbital length. Kenya specimens are similar but smaller, and Southern African warthogs are smaller still, with narrow intertemporal width and short postorbital length. The analyses of ranges of means values of such cranial parameters (adult males only; from many small samples obtained from museum specimens and Hollister, 1924), therefore provide a basis for the definition of subspecies, but it becomes much more difficult to identify putative subspecies when the variance of samples is taken into account (Grubb, unpubl.). However, samples from the following areas are sufficiently differentiated in at least one measurement to be regarded as subspecifically distinct: Senegal/ Eritrea; Senegal/Kenya; Kenya/Eritrea; Eritrea/ Somalia; Natal/Malawi; Natal/Senegal. But relatively substantial samples from Zambia, Katanga, Kivu-Rutshuru and Kenya cannot be separated from each other or from Malawi or Natal.

Following these indications, subspecies bufo and centralis are certainly redundant and synonyms of massaicus; shortridgei is almost certainly a synonym of sundevallii. Peripherally distributed africanus, aeliani and sundevallii are distinct from each other, but they appear to link up - perhaps clinally - with other supposed subspecies. This is an interim report, and when material from critical areas is examined and larger local samples are assembled, it may prove necessary to regard this taxon as monotypic, exhibiting geographic variation of such a continuous nature that discrete subspecies cannot be identified. In the meantime, the following (four) subspecies may be recognized provisionally:

1. Northern Warthog, Phacochoerus africanus africanus

Range: Northern Savanna and Sahel region (including: Mauritania, Senegal, Guinea Bissau, Ivory Coast, Burkina Faso, Nigeria, Chad, Sudan, CAR, N. Zaire and S. Ethiopia).

2. Eritrean Warthog, Phacochoerus africanus aeliani

Range: Eritrea, Djibouti and Somalia only?

3. Central African Warthog, Phacochoerus africanus massaicus (synonyms: bufo, centralis and (?)fossor).

Range: East and Central Africa (including: Kenya, Zaire, Rwanda, Burundi, Katanga, Zambia, Malawi and Angola).

4. Southern Warthog, Phacochoerus africanus sundevallii (synonym: shortridgei).

Range: Southern Africa (including: Zimbabwe, Botswana, Namibia, Natal).

Cape and Somali Warthogs

(Phacochoerus aethiopicus)

For much of the last century and in this century also, at least among paleontologists, two species of warthog have been recognized. The Cape warthog was distinguished principally by its lack of functional incisors. The common warthog has two incisors in the upper jaw and usually six in the lower jaw. One or more may be lost, but their former presence can be identified in cleaned skulls from traces of the alveoli. Other distinguishing features of Cape warthog skulls and teeth have also been noted in the literature, but have hardly ever been reviewed and evaluated in a systematic manner. The natural distribution of the Cape warthog was never properly identified and few specimens ever became available, none after the mid-nineteenth century. The specific name of the Cape warthog is the earliest one of the genus, so when all warthogs were considered to be one species, the characteristics of the better-known common warthog became associated with the name of the less well-known species. It became the accepted view among zoologists that the Cape warthog was no more than an extinct geographic representative of the common warthog. Paleontologists on the other hand have recognized two kinds of warthog in fossil material from South Africa and have treated P. aethiopicus and P. africanus as two different species, believing that the former is now extinct (see Ewer, 1957 for an important review).

In 1909, Lönnberg noted that two male warthog skulls obtained in Somalia also lacked incisors. He created a new species, P. delamerei, on the basis of these specimens and noted other similarities with P. aethiopicus, though he was not convinced that these two taxa were immediately related to each other. Nevertheless, warthogs with a specialized incisor-less morphology and other characters were now known from South Africa and East Africa. Roosevelt & Heller (1922) noticed this discontinuous distribution between north-east and south Africa - between Somali Arid and Southwest Arid Zones - which recalls the distribution of other animals of dry environments such as the dikdik or oryx. In the interim, however, Lydekker (1915) had grouped all warthogs into one species, P. aethiopicus - the specific name properly associated with the Cape warthog. Since then, few neontologists have recognized the important divisions within the genus and there appear to be no acknowledgements in the literature of Roosevelt & Heller's (1922) perceptive observations nor of the anatomical features linking delamerei and aethiopicus which Lönnberg (1909) and Heller (1914) identified.

My own studies not only confirm differences between the common warthog and the Cape species, but that the Somali warthog and the Cape warthog are so alike that they should be regarded as conspecific. The principle features of the Cape/Somali warthog, P. aethiopicus, in comparison to the common warthog, P. africanus, are:

- the skull is relatively small, but proportionately shorter and broader;

- the front part of the zygomatic arch is thickened by internal sinuses and swollen into a spherical hollow knob just in front of the jugal-squamosal suture (in the common warthog, the zygomatic arch may be robust but it is never quite so thickened and there is no formation of a knob);

- there is never any trace of upper incisors, even in relatively young individuals, and the lower incisors, even if present, are rudimentary and non-functional (whereas the common warthog always has two upper incisors, though these may be lost in very old animals, and usually six, functional lower incisors in the adult dentition, of normal suine form);

- in the Cape warthog (but not yet confirmed in the Somali form), the large third molars are very different from those of the common species in that no roots have been formed by the time all the enamel columns have come into wear, so that the columns are able to continue growing and extend the life of the tooth; and

- in the common warthog the skull roof behind the internal nares is marked by two deep and distinct 'sphenoidal pits', not found in any other African suid, while in the Cape/Somali species, these pits have expanded enormously, disappearing as distinct entities, so as to contribute to two vaults between the pterygoids, separated by a deep vomerine ridge.

Other differences have been described, but their validity may need further investigation. However, the characters of the incisors, cheek teeth, zygoma and sphenoid region are trenchant, discrete and functionally quite independent. There is no indication of intermediate states and no likelihood that the morphological differences merely indicate intra-population variation, particularly as one of the species is itself discontinuously distributed. One could not have better morphological evidence for the existence of two species. Furthermore they may even be sympatric in some places. The two subspecies of 'desert' warthogs may be described as follows:

Cape Warthog, Phacochoerus aethiopicus aethiopicus (extinct)

Cape warthog specimens in museums lack locality records but specimens subsequently identified as belonging to this species were obtained by Sparrman between the Sondags and Boesmans rivers, eastern Cape Province, and by Burchell on the upper Orange River, south of Hopetown, again in the eastern Cape. The full extent of the Cape warthog's former distribution remains unknown. Possibly it was restricted to the Karoo. There is no mention of this subspecies being obtained after about 1860.

Somali or Desert Warthog, Phacochoerus aethiopicus delamerei

This geographic representative of the Cape warthog is recorded from Somalia, both in the north and in Jubaland in the south, and from northern Kenya. Both this species and the common Warthog have been obtained in northern Somalia, where locality records for the common species form an enclave in the vicinity of Berbera, with sparse records of Somali warthog to the west, east and south. The two species may be parapatric or even partly sympatric and ecologically segregated in northern Somalia, but this has yet to be confirmed. Their relative geographical disposition in Kenya (or eastern Ethiopia) cannot be assessed at all in the absence of adequate specimens or information.

Somali warthog from Kenya and Jubaland are larger than those from northern Somalia and it may be necessary to describe them as a separate subspecies. Not enough specimens are available, however, to determine whether this should be done.

Areas of interest for further research on the taxonomy of Afrotropical suids

Potamochoerus:

There is a need to obtain a better understanding of the distribution of the red river hog and bushpig, especially at the edges of their respective ranges, with a view to the assessment of their genetic and ecological relationships and the factors with affect their dispersion. Further studies of the systematics of this genus, especially the nature and extent of individual and geographic variation within and between selected regions/populations of P. larvatus, are also required:

Priority Projects:

1. Field studies in selected locations along the contact zone between the two species.

These studies are needed to determine local relationships between the populations of these two species (i.e. are they parapatric or locally sympatric?, locally hybridizing or lacking any interspecific gene flow ?) and to identify the form of ecological segregation between them. Particular locations/questions requiring investigation include: a) in Sudan - is the red river hog present?; b) in Uganda - is there really hybridization in the Kibale Forest, or elsewhere, or is the red river hog absent from the country ?; and c) in eastern Zaire/Rwanda/Burundi - how is the apparent geographical segregation of the two species related to altitude and vegetation formation ?

2. Investigate aspects of the systematics, karyotype, geographical variation and distribution of the bushpig in East and South Africa.

These studies are required in order to: a) establish the form of color polymorphism in the species; b) determine whether the Taru Desert and other inhospitable areas in Kenya and Tanzania promote the geographic isolation of bushpig populations, especially between upland and coastal lowland habitats, and to establish whether a lowland coastal and riverine subspecies, somaliensis, can validly be differentiated in these countries; and c) assess the systematic position of the (now?) isolated Cape Province population with respect to the Central and East African populations (see Fig. ///).

3. Investigate the origins, systematics and ecology of the Malagasy bushpigs.

Such studies should be designed to establish: a) the nature of the geographical variation on the island and the need or otherwise to recognize one or more Malagasy subspecies; b) to define more precisely any differences in morphology between the Malagasy and mainland African populations, using modern methods of genetic analysis where possible; c) by means of anthropological/archaeological studies, to attempt to determine the way in which bushpigs were brought to Madagascar and the social/cultural context in which this occurred; and d) to investigate the ecological role of the bushpig in relation to the native fauna and flora of Madagascar.

Hylochoerus

Further studies are required on the geographical variation and distribution of this species, both generally and in selected, critical areas so as to enhance our understanding of the diversity and systematic relationships of those populations.

Priority Projects:

1. Ascertain the external appearance and variation with age and sex of the different subspecies/regional populations.

These studies, which should be undertaken by non-destructive means (namely by good quality photographic records), are needed to establish the distinctiveness of these taxa/ populations more fully in the eyes of conservationists and the public.

2. Clarify the systematics and karyotype of the species over its range.

Photographic records, as well as osteological and soft-tissue material from hunter-killed animals, should be obtained in order to determine this genetic and geographic variation and, in particular, to determine the characters of Ethiopian, Imatong (Sudan), Tanzanian and Nigerian populations so as to establish which subspecies they represent.

3. Review all available distribution records and to conduct further field investigations to ascertain whether the species occurs or occurred formerly in those localities or countries for which detailed evidence of their occurrence is still lacking (e.g. Togo; see Fig. 8).

Phacochoerus

Geographical variation and, hence, the subspecific taxonomy of the common warthog, P. africanus, is still poorly understood owing to the shortage or absence of taxonomic material from key areas over the species' range. Further, and comparative, studies of both species, particularly in arid habitats, are also required in order to clarify their systematic and ecological relationships.

Priority Projects:

1. Undertake further basic studies pertinent to the alpha-taxonomy of P. africanus using new methods or involving previously unstudied material, in order to determine whether there really are discrete subspecies.

These investigations should include the acquisition of additional taxonomic materials from selected regions, as well as photographs of adults from all different regions. The latter will enable an assessment of geographical variation in external appearance, as museum skins are too few or too distorted and misleading to provide much assistance.

2. Investigate the ecology and behaviour of both species of warthogs in arid environments.

In the light of recent studies of the common warthog, P. africanus, in mesic or relatively mesic environments, comparative studies would be of particular interest in the Sahel (for P. africanus) and the Somali Arid zone (for P. aethiopicus delamerei). In terms of its morphology and in the extent to which it has, as a pig, extensively occupied an arid habitat, the latter is the most specialized of all living suids, at least in the sense of deviating most from an ancestral form, or in relation to a more generalized taxon such as Sus. The ecological constraints impinging upon its life history must be severe indeed, bearing in mind the problems faced by warthogs in well-watered habitats, and how it is able to overcome these is of considerable scientific interest, as well as relevant to its future management.

3. Make a thorough study of the geography and comparative ecology of Phacochoerus africanus and P. aethiopicus where they are likely to be in contact.

These areas are northern Somalia, Jubaland, eastern Ethiopia and northern Kenya. These studies are needed to determine whether these species are sympatric, parapatric or whatever, and how they are ecologically segregated.

4. Investigate the distribution, variation, and population biology of the (now?) isolated northern and southern populations of the Somali warthog, P. aethiopicus delamerei, with a view to determining their relative taxonomic and conservation status and future management needs.

References

Ansell, W. R. H. 1972. Artiodactyla (excluding the genus Gazella). In: J. Meester & H. Setzer (eds.; 1971-1977): The Mammals of Africa. An Identification Manual. Smithsonian Institution Press, Washington D.C.; Part 15: pp.1-84.

Baudenon, P. 1958. Note sur le statut des ongules au Togo. Mammalia, 23: 390-393.

de Beaux, O. 1924. Beitrag zur Kenntnis der Gattung Potamochoerus Gray. Zool. Jahr. 47: 379-504.

Benson, C. W. 1960. The birds of the Comoro Islands. Ibis, 103: 5-106.

Cooke, H. B. S. and Wilkinson, A. F. 1978. Suidae and Tayassuidae. In: V. J. Maglio & H. B. S. Cooke (eds): Evolution of African Mammals. Harvard University Press, Cambridge: 435-482.

Cotton, W. B. 1936. Note on the giant forest-hog (Hylochoerus meinertzhageni). Proc. Zool. Soc. Lond. for 1936: 687-688.

De Sa e Melo Cristino, J. 1958. Statut des ongules en Guinea Portugaise. Mammalia, 22: 387-389.

D'Huart, J.-P. 1978. Ecologie de l'Hylochere (Hylochoerus meinertzhageni Thomas) au Parc National des Virunga. Exploration Parc Nat. Virunga, (2) 25: 1-156. Fondation pour favoriser les recherches scientifiques en Afrique, Brussels.

Dorst, J. and Dandelot, P. 1970. A Field Guide to the Larger Mammals of Africa. Collins, London.

Dowsett, R. J. and Dowsett-Lemaire, F. 1989. Larger mammals observed in the Gotel Mts. and on the Mambilla Plateau, eastern Nigeria. Touraco Research Report, 1: 38-41.

Dupuy, A. 1969. Contribution a l'‚tude de potamochere, Potamochoerus porcus (Linne) a Senegal. Mammalia, 33: 347-350.

Ewer, R. F. 1957. A collection of Phacochoerus aethiopicus teeth from the Kalkbank Middle Stone Age site, central Transvaal. Palaeont. Africana, 5: 5-20.

Ewer, R. F. 1970. The head of the forest hog, Hylochoerus meinertzhageni. E. Afr. Wildl. J., 8: 43-52.

Fagotto, F. 1985. Larger animals of Somalia in 1984. Environmental Conservation, 12 (3): 260-264.

Funaioli, U. and Simonetta, A. M. 1966. The mammalian fauna of the Somali Republic: status and conservation problems. Mon. zool. Ital., 75 (Supp.): 285-247.

Ghiglieri, M. P., Butynski, T. M., Struhsaker, T. T., Leland, L., Wallis, S. J. and Waser, P. 1982. Bush pig (Potamochoerus porcus) polychromatism and ecology in Kibale Forest, Uganda. Afr. J. Ecol., 20: 231-236.

Groves, C. P. 1981. Ancestors for the Pigs: Taxonomy and Phylogeny of the Genus Sus. Tech. Bull., Dept. Prehistory, Res. Sch. Pacific Studies, Australian National University, 3: 1-96.

Hall, P. 1976. Priorities for wildlife conservation in north-eastern Nigeria. Nigerian Field, 41: 99-112.

Haltenorth, T. 1963. Klassifikation der Saugetiere: Artiodactyla 1 (18). Handbuch der Zoologie, 8 (32): 1-167.