|
Pigs, Peccaries and
Hippos Status Survey and Action Plan (1993) Chapter 3 The Afro-tropical Hippopotamuses - Hippopotamidae Hippopotamus and Hexaprotodon 3.1 Taxonomy and Description Peter Grubb Introduction The hippos, Family Hippopotamidae, are separated
from all other suiformes in the Superfamily Anthracotheroidea. All Holocene
or Recent hippos belong to two genera, Hexaprotodon
(= Choeropsis) and Hippopotamus. Only one species of each
of these are usually recognized, but three more species became extinct within
the Holocene on Madagascar (Stuenes, 1989; Faure & Guerin, 1990). The two
living and three recently extinct forms may be described as follows: The Pygmy Hippopotamus (Hexaprotodon liberiensis) The West African pygmy hippo has usually been
referred to the genus Choeropsis
but Coryndon (1977) has shown that it is essentially one of the
hexaprotodonts - more generalized hippos, previously thought to be completely
extinct. In spite of differences between this animal and the hexaprotodonts
in the number of teeth, Coryndon believed they should no longer be placed in
separate genera. Although it is much smaller than the common hippo,
the pygmy species has relatively longer limbs. It also has a proportionally
smaller, narrower head with the orbits not raised above the skull roof. There
are 38 teeth, as against 42-44 in the larger species, owing to differences in
the numbers of incisors. Dorst & Dandelot (1970) give the weight as 270
kg and the shoulder height as 80cm. There are two subspecies. The nominate race, H. l. liberiensis occurs in Guinea,
Sierra Leone, Liberia and Ivory Coast. In the Ivory Coast it has been
recorded as far east as between the Sasandra and Bandama Rivers (Dekeyser,
1954) but recently Bosman & Hall-Martin (1989) reported it from the
Azagny National Park in the southeast corner of the country. Whether it
naturally occurs there or has been introduced is not clear. The second
subspecies, H. l. heslopi, is known
only from the Niger Delta east to the vicinity of the Cross River in Nigeria
(Corbet, 1969). It differs from the nominate subspecies in skull proportions.
It may be extinct, but Oates (in litt.) reports that residents in the Niger
Delta still know of the species, and possibly it still survives. The Common Hippopotamus (Hippopotamus
amphibius) The characteristic features of this species are well
known: its great bulk and short limbs; its huge head with nostrils, eyes and
ears placed on top; and its broad snout and enormous gape. Weight is
1,100-2,600 kg, shoulder height 140-160 cm (Dorst & Dandelot, 1970). No serious attempt has been made in recent years to
assess geographic variation in the species. The supposed subspecies have been
listed below (from Lydekker, 1915) but unless more specimens are examined and
from a wider area, it is impossible to say whether diagnostic skull
characters are any more than peculiarities of particular specimens. 1. H. a. amphibius: skull with moderate
preorbital constriction, convex upper surface, long mandibular symphysis and
relatively large cheek teeth. Said to occur in Egypt (where it is now
extinct) south to Sudan, northern Zaire and Ethiopia, and west to Gambia;
also Tanzania and Mozambique. Populations in the Nile Delta and on the lower
Nile were geographically isolated from other hippos (Kock, 1970) and may have
represented distinguishable subspecies. If this is the case, the Delta
population should bear the subspecific name amphibius and the naming of other populations will have to be
re-appraised. 2. H. a. tschadensis: similar to nominate
race but with orbits more prominent. Distinguished from H. a. capensis by much shorter and wider facial region and
more forward direction of orbits. Range: Chad and Nigeria. Synonymised with H. a. amphibius by Haltenorth (1963). 3. H. a. kiboko: skull with very broad
nasals, relatively small rostral constriction, and great elevation of orbits
and occipital crest above deeply hollowed interorbital region. Orbits more
nearly circular than in H. a. capensis
and more prominent than in H. a. constrictus
- which also differs by greater rostral constriction and shorter mandibular
symphysis (see below). Also said to differ in color and hairiness of ears and
tail! Range: Kenya and Somalia. 4. H. a. constrictus: skull lighter than
in typical race with preorbital constriction deeper, upper surface more
flattened, muzzle less expanded, mandibular symphysis shorter and cheek teeth
smaller. Range: Angola, southern Zaire and Namibia. Synonymised with H. a. capensis by Ellerman et al. (1953). 5. H. a. capensis (syn. australis): skull still more flattened
than in H. a. tschadensis, so that
width of orbit is greater than height. Range: Zambia south to South Africa. Extinct
Malagasy Hippopotamuses Stuenes (1989) showed that two kinds of dwarf
hippopotamuses (Hippopotamus lemerlei
and H. madagascariensis) survived
late into the Quaternary on Madagascar, and Faure & Guerin (1990) have
described another and larger species, H.
laloumena. H. lemerlei occurred
on the island at least until 980 + 200 yrs. B. P., but neither the H. madagascariensis or H. laloumena material has been dated,
though both are believed to be Holocene in age. The latter species is known
only from a lower jaw and limb bones obtained near Mananjary on the east
coast. It was largest of the three species but was not as big as H.
amphibius, which it otherwise appears to have resembled closely. H. lemerlei was somewhat larger than H. madagascariensis and differed from
it in that the skulls of adults were markedly (presumably sexually) dimorphic
in size. These two smaller hippos also appear to have differed in their
ecology. Like H. laloumena, H. lemerlei (Plate ///) resembled a
small H. amphibius and probably had
similar habits. Its remains have been found mostly in the coastal lowlands. H. madagascariensis was a more
terrestrial species, subfossils of which have been located in the central
highlands. Recently, Harris (1991) has reassessed the systematics of the two
smaller hippos and concluded that the more terrestrial species, madagascariensis, should be placed in
the genus Hexaprotodon. Inferences
to be drawn are firstly that each of the surviving species of hippos had
close relatives on Madagascar, and secondly that Madagascar had been
colonized three times by hippopotamuses! Early human colonization of
Madagascar, which occurred c. 1,500 yrs BP, is implicated in their
extinction, though climatic change may also have been a factor. References Bosman, P. and Hall-Martin, A. 1989. Elephants of
Africa. New Holland, London. Corbet, G. B.
1969. The taxonomic status of the pygmy hippopotamus Choeropsis liberiensis, from the Niger Delta. J. Zool. 158:
387-394. Coryndon, S. C.
1977. The taxonomy and nomenclature of the Hippopotamidae (Mammalia,
Artiodactyla) and a description of two new fossil species. Proc. K.
Nederlandse Akad. Wetensch. Ser. B. 80: 61-88. Dekeyser, P. L.
1954. L'hippopotame nain. Notes afr. 63: 91-92. Dorst, J. and
Dandelot, P. 1970. A Field Guide to the Larger Mammals of Africa. Collins,
London. Ellerman, J.
R., Morrison-Scott, T. C. S. and Hayman, R. W. 1953. Southern African Mammals
1758 to 1951: A Reclassification. British Museum, London. Faure, M. and
Guerin, C. 1990. Hippopotamus laloumena
nov. sp., la troisième éspece d'hippopotame holocene de Madagascar.
Comptes Rendus de l'Academie des Sciences, Serie 11, 310: 1299-1305. Haltenorth, T.
1963. Die Klassifikation der Säugetiere Artiodactyla 1(18). Handb. Zool.
8(32): 1-167. Harris, J. M.
1991. Family Hippopotamidae. Pp. 31-85, in Koobi Fora Research Project. Vol.
3. The Fossil Ungulates: Geology, Fossil Artiodactyls and Palaeoenvironments.
Clarendon Press, Oxford: xvi + 384 pp. Kock, D. 1970.
Die Verbreitungsgeschichte des Flusspferdes, Hippopotamus amphibius Linne, 1758, im unteren Nilgebiet.
Saugetierk. Mitt. 18: 12-25. Lydekker, R.
1915. Catalogue of the Ungulate Mammals in the British Museum (Natural
History). Vol. 5. British Museum, London. Stuenes, S.
1989. Taxonomy, habits and relationships of the sub-fossil Madagascan
hippopotamuses Hippopotamus lemerlei
and H. madagascariensis. J. Vert.
Paleontol. 9: 241-268. |
|
Next: Chapter 3.2 – The
Common Hippopotamus |