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Pigs, Peccaries and
Hippos Status Survey and Action Plan (1993) Chapter 1 THE SUBORDER SUIFORMES Colin P. Groves and Peter Grubb Pigs and babirusa, peccaries and hippopotamuses
belong to the mammalian Order Artiodactyla, the even-toed ungulates, of which
there are three major lineages or clades - the Suiformes, Tylopoda and Pecora
- each ranked as a suborder. Of these, the Suiformes are the only
non-ruminants. The Tylopoda are the camels and llamas, and the Pecora are the
deer, giraffes, cattle, goats, antelopes and their relatives. In many ways,
the Suiformes are the most primitive of the three. The stomach is less
complex than in ruminants, many teeth are present and they are low-crowned
and bunodont, the unguligrade condition of the limbs is less advanced and, in
one family, the females make nests! These are generalizations, which indicate
the primitive nature of some suiform artiodactyls, but they do not apply to
all of them. Within the Suiformes there are three living
Families: Hippopotamidae (hippopotamuses), Dicotylidae (peccaries) and Suidae
(pigs). The first is separated into a Superfamily Anthracotheroidea together
with fossil relatives, while the others are assigned to the Suoidea (Simpson,
1945), a classification that may need modification in future. Hippopotamidae Holocene or Recent hippos belong to two genera, Hexaprotodon (including Choeropsis according to Coryndon,
1977) and Hippopotamus, each with
one surviving and one and two (respectively) recently extinct species
(Steunes, 1989; Faure & Guerin, 1990; Harris 1991). The two genera can be
traced back to the late Miocene as separate entities, while the family itself
separated from its ancestors (anthracotheres?) about 11 million years ago.
Hippos are distinguished among the Suiformes by several features: the lack of
the snout disc, the arrangement of limb muscles, the weak development of
hooves with the lateral digits reaching the ground, the naked glandular skin,
the specialized stomach morphology and the amphibious habit. Dicotylidae Pigs and peccaries agree in having a remarkable
organ adapted to rooting in the soil - the snout disc or rhinarium. The tip
of the snout is flattened and supported by cartilage, a tough pad for pushing
into even quite hard ground. The upper edge of the disc is at right angles,
or even at an acute angle to the top of the snout, so that loosened soil is
most easily pushed aside by an upward motion of the head. The lower edge runs
without a break into the mucous membrane of the mouth. The nostrils are
centered in the disc where they are well placed to detect potentially edible
items but can be closed so that soil does not enter the nasal passages. The
snout is moved by special muscles located just in front of the eyes, so that
fine rooting movements are possible. The three species of living peccaries are assigned
to the genera Tayassu and Catagonus. C. wagneri was only recognized as an extant species in 1975
(Wetzel, 1977) - an amazing discovery - but was first described from late
Pleistocene sub-fossil deposits in the 1930's. Peccaries are now confined to
the New World, but the family has not always been so restricted in
distribution. Their earliest representatives occur in the Oligocene of
Europe, and up until the Middle Miocene (Chinji Formation of India) they
still inhabited Eurasia. Peccaries survived into the late Pleistocene in
areas of North America and South America where they are now absent (mainly
the genera Platygonus, Catagonus and Mylohyus). Recently a peccary was thought to have turned up in
the Pliocene of South Africa (Hendey, 1976), but it has now been shown to be
a new species of dwarf pig (Pickford, 1988). Nevertheless, true peccaries
occurred in the Miocene of Africa (Pickford, 1986). Pickford's research has also revealed closer links
between hippopotamuses and peccaries than have previously been acknowledged.
Both groups have specialized digestive tracts and adaptations for a very wide
gape (Herring, 1975). In both, the upper canine points down while the lower
one points up and, when the mouth is closed, fits into a notch formed by the
bony sheath of the upper canine root. Pickford also noted that in both
groups, the upper canine is round in section with a deep posterior open
groove (rather than rounded-triangular without indentation as in true pigs),
that there is little or no sexual dimorphism in canine development and that
there are close similarities in the cuspidation of the cheek teeth in
primitive hippos and peccaries. Peccaries differ from pigs in other and more
advanced features, including the very short tail, which has no more than
seven vertebrae; the presence of a scent gland on the back just in front of
the sacral region; and the cursorial specializations of the hind foot.
Metatarsals 3 and 4 are fused together into a single cannon bone except for
their distal extremities; digit 5 has completely disappeared though there is
a remnant of metatarsal 5, and in Catagonus,
but not in Tayassu, there is no
external trace of digit 2 on the hind foot. Suidae The babirusa (Babyrousa
babyrussa) of Sulawesi (formerly Celebes) and some neighboring islands in
Indonesia may have no common ancestors with the true pigs more recent than
the late Oligocene, c. 40 million years BP. Indeed, this animal is peculiar
in several respects, including its somewhat more complex stomach (Langer,
1988), the remarkable canines of the male (Groves, 1981), and the style of
combat between males, which is quite different from that of true pigs (A.
Macdonald pers. comm.). For the moment, it is retained in its own subfamily,
Babyrousinae, but its eventual assignment to a family of its own seems
possible. The true pigs of the subfamilies Suinae and
Phacochoerinae, include four living genera - Sus in Eurasia and North Africa, and Potamochoerus, Hylochoerus
and Phacochoerus (only living genus
assigned to Phacochoerinae) in the Afrotropical Region. Among these, Sus and to some extent Potamochoerus are the most generalized
of surviving suiforms in their bunodont dentition, retention of many teeth
and less specialized digestive tract and limbs. Yet all Suinae share unique
features of the canines and some have other highly specialized adaptations.
The upper canines are rounded-triangular in cross-section, larger in males
than in females, and their alveoli are directed outward and even somewhat
upward. The upper canines are abraded across their tips through honing by the
lower canines, as in peccaries or hippos (the more primitive condition, Sus and Potamochoerus), or along their anterior surfaces only, so that
they are not kept short but grow unchecked, curving outwards, backwards and
upwards (Hylochoerus, Phacochoerus and many extinct genera).
The canines in the genera just mentioned have evolved to be among the largest
of any mammals, relative to body size. In some of the same genera, but
particularly Phacochoerus,
modification of the molars for the grinding of abrasive vegetable material
has become extremely specialized. Knobs, warts or fender-like excrescences on
the skull have evolved repeatedly among true pigs (and also in the
Pleistocene American peccary Platygonus
vetus) partly in association with patterns of combat between males. The greatest radiation of pigs and the development
of the most extreme specializations occurred in Africa, so it is of some interest
to unravel the phylogeny of the group. Thenius (1970) traced the Suidae back
to the Oligocene, Palaeochoerus
being the earliest genus. Ancestors of Potamochoerus
and Sus (Propotamochoerus and Dicoryphochoerus,
respectively) were present in the Middle Siwaliks. Sus appeared in the lower Pliocene of Europe (S. minor) and Indonesia (S. stremmi). Potamochoerus is now known (White & Harris, 1977) from the
mid-Pliocene, while the Nyanzachoerus-Notochoerus
line, an offshoot of the Propotamochoerus
stem according to Thenius (1970), is known from the latest Miocene in East
Africa. Another offshoot, Kolpochoerus
(= Mesochoerus according to Cooke
& Wilkinson, 1978), first appeared in the Upper Pliocene and can be
regarded as the direct ancestor of Hylochoerus.
From quite a different stock, whose earlier representatives are as yet
unknown, comes Metridiochoerus (= Stylochoerus), known first in the
Upper Pliocene and plausibly the ancestor of Phacochoerus (White & Harris, 1977). In summary, it seems
possible that the African suid radiation was monophyletic but this has not
been fully established (though see Bender, 1992). Hylochoerus proves to be less closely related to Phacochoerus than one might conclude
from similarities in the dentition. Thenius (1970) broke the Suinae into two
subfamilies, one containing only Phacochoerus.
Until the cladistic relationships of the whole group are finalized, it may be
premature to make these divisions. References Bender, P. A.
1992. A reconsideration of the fossil suid Potamochoeroides shawi, from the Makapansgat limeworks,
Potgietersrus, Northern Transvaal. Navorsinge van die Nasionale Museum
Bloemfontein 8: 1-67. Cooke, H. B. S.
and Wilkinson, A. F. 1978. Suidae and Tayassuidae. In: V. J. Maaglio & H.
B. S. Cooke (eds), Evolution of African Mammals. Harvard University Press,
Cambridge, Massachusetts: 435-528. Coryndon, S. C.
1977. The taxonomy and nomenclature of the Hippopotamidae (Mammalia,
Artiodactyla) and a description of two new fossil species. Proc. Konink.
Nederlanadse Akad. Weten. Amsterdam B 80: 61-88. Faure, M. and
Guerin, C. 1990. Hippopotamus laloumena
nov. sp., la troisieme espece d'hippopotame Holocene de Madagascar.
Comptes Rendus de l'Academie des Sciences, Serie 11,310: 1299-1305. Groves, C. P.
1981. Ancestors for the Pigs: Taxonomy and Phylogeny of the Genus Sus. Tech.
Bull. 3, Dept. Prehistory, Research School Pacific Studies, Australian Nat.
Univ.: vii + 1-96. 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. Hendey, Q. B.
1976. Fossil peccary from the Pliocene of South Africa. Science 192: 787-789. Herring, S. W.
1975. Adaptations for gape in the hippopotamus and its relatives. Forma
Functio 8: 85-100. Langer, P.
1988. The Mammalian Herbivore Stomach - Comparative Anatomy, Function and
Evolution. Gustav Fischer, Stuttgart and New York: 136-161. Pickford, M.
1986. A revision of the Miocene Suidae and Tayassuidae (Artiodactyla,
Mammalia) of Africa. Tertiary Research 7: 1-83. Pickford, M.
1988. Un etrange suide nain du Neogene superieur de Langebaanweg (Afrique du
Sud). Ann. Paleontol. 74: 229-250. Simpson, G. G.
1945. The Principles of Classification and a Classification of Mammals. Bull.
Amer. Mus. Nat. Hist. 85: xvi + 11-350. Stuenes, S.
1989. Taxonomy, habits and relationships of the sub-fossil Madagascan
hippopotamuses Hippopotamus lemerlei
and H. madagascariensis. J. Vert.
Paleontol. 9: 241-268. Thenius, E.
1970. Zur Evolution und Verbreitungsgeschichte der Suidae (Artiodactyla,
Mammalia). S. Saugetierk. 35: 321-342. Wetzel, R. M.
1977. The Chacoan peccary Catagonus wagneri (Rusconi). Bull. Carnegie Mus.
Nat. Hist. 3: 1-36. White, T. D.
and Harris, J. M. 1977. Suid evolution and correlation of African hominid
localities. Science 198: 13-21. |
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Table 1. Taxonomy of living
and recent Suiformes Order: Artiodactyla (comprising
three suborders: Suiformes, Tylopoda and Pecora) Suborder: Suiformes (comprising
two superfamilies and three families, as follows): Superfamily: Anthracotheroidea Family: Hippopotamidae (no separate subfamilies, but two genera and two living and three recently extinct species, as follows): Genus: Hippopotamus Species: H. amphibius (5? ssp) - Common Hippo
H. laloumena - Madagascan
Hippo (extinct)
H. lemerlei - Madagascan
Dwarf Hippo (extinct)
Genus: Hexaprotodon (= Choeropsis) Species: H. liberiensis (2 + ? ssp) - Pygmy
Hippo
H. madagascariensis - Madagascan Pygmy Hippo (extinct) Superfamily: Suoidea (comprising two families, seven genera and at least fifteen species,
as follows): Family: DicotyIidae (no separate subfamilies, but two genera and three species, as
follows):
Genus: Tayassu Species: T. tajacu (? 14 ssp) -
Collared Peccary
T. pecari (c. 5 ssp) - White-lipped Peccary
Genus: Catagonus Species:
C.
wagneri (0 ssp) - Giant or Chacoan Peccary Family: Suidae (comprising
three subfamilies, five genera and <fourteen species, as follows): Subfamily: Suinae - the
'true' pigs Genus: Sus Species: S.
scrofa (c. 16 ssp) - Eurasian Wild Pig S.
salvanius (0 ssp) - Pigmy Hog S.
bucculentus - Vietnam Warty Pig (extinct ?) S.
verrucosus (2 ssp) - Javan Warty Pig S.
barbatus (3 ssp) - Bearded Pig S.
cebifrons (0 ? ssp) - Visayan Warty Pig S.
philippensis (0 ? ssp) - Philippine Warty Pig S.
celebensis (0 ? ssp) - Sulawesi Warty Pig Genus: Potamochoerus Species: P.
larvatus (5 ? ssp) - Bushpig
P. porcus (0 ssp) - Red River Hog Genus: Hylochoerus Species: H.
meinertzhageni (3 + ? ssp) - Forest Hog Subfamily: Phacochoerinae - the warthogs Genus: Phacochoerus Species: P.
aethiopicus (2 ssp, 1 extinct) - Desert Warthog
P. africanus (c. 4 ssp) - Common Warthog Subfamily: Babyrousinae - babirusa Genus: Babyrousa Species: B.
babyrussa (4 ? ssp, 1 extinct ?) - Babirusa Total: superfamilies 2, families
3, subfamilies 5, genera 9, species (provisionally) >22 (of which 3, possibly
4, are extinct), subspecies
(provisionally) >63 (of which at least 1, but possibly 3 or more, are
extinct). |
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Neotropical Tayassuids |