Hippos
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Dwarf Hippo ( Choeropsis liberiensis ) |
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| Hippopotamidae | ||||||||||||
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The hippopotamuses (Hippopotamidae) are a family of mammals . They include two living species, the (large) hippopotamus and the pygmy hippopotamus . There are cumbersome built, nearly hairless animals that feed on plants and in Africa the southern Sahara are located. Both species are endangered in their population due to hunting and habitat destruction . Traditionally they are categorized as the ungulates , but their closest living relatives are the whales . Despite their name, they are not closely related to the horses .
features
Hippos have a heavy, barrel-shaped body supported by four short, stocky legs. The legs each end in four toes, each covered with a hoof-like nail. The pygmy hippopotamus has narrower feet with less webbed feet; it can spread its toes wider than the big hippopotamus. The mostly brownish or black colored skin is hairless except for the bristles on the face and tail. The skin is exposed to the risk of dehydration on land, which is why the skin glands of these animals secrete a reddish liquid that serves as protection from the sun's rays and - at least in the case of the hippopotamus - also has an antibiotic effect. Because of this reddish liquid, it was previously wrongly assumed that hippos would “sweat blood”. The large hippopotamus, with a head trunk length of up to 5 meters and a weight of sometimes up to 4000 kilograms, is significantly larger and heavier than the pygmy hippopotamus, which only reaches 1.75 meters head trunk length and 270 kilograms.
The head of the hippopotamus sits on a short neck, the skull is large and characterized by an elongated facial skull, while the cranial cavity is comparatively small. The muzzle region of the large hippopotamus is very wide and conspicuously shaped due to the canine fan . The eyes, nostrils and ears of both species are attached high up on the head, so that the animals only have to lift their heads out of the water a little to be able to see or breathe. Ears and nostrils can be closed as an adaptation to the partially water-dwelling way of life.
| Tooth formula | I. | C. | P | M. | |
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| 38-42 | = | 2-3 | 1 | 4th | 3 |
| 1-3 | 1 | 4th | 3 | ||
The incisors and canines are developed like a tusk and grow throughout life. The incisors are rounded and far apart. Pygmy hippos usually only have one pair of lower incisors, whereas large hippos have two or three. The upper incisors are smaller and grow downwards, the lower ones are longer and stand forward. The lower canines are the largest teeth and grow up and out. Four premolars and three molars are formed per half of the jaw . Hippos have a total of 38 to 42 teeth and the following tooth formula results.
Hippos have a multi-chambered stomach that is convergent to that of ruminants . This has two blind bags in which the food is broken down by microorganisms. But they won't chew again.
distribution and habitat
Today, hippos are only found in sub- Saharan Africa. The pygmy hippopotamus is restricted to West Africa, the large hippopotamus also occurs in the eastern and southern parts of the continent. The range of both species, however, has been greatly reduced and fragmented by human influence. They also occurred in the lower reaches of the Nile until the 19th century, and in Madagascar until a few hundred years ago . Even in the Pleistocene there were hippos in Europe and Asia, dwarf forms persisted on some Mediterranean islands until the beginning of the Holocene .
Hippos always live near bodies of water, such as rivers and lakes, but large hippos are more strongly attached to water. Pygmy hippos are mostly found in forests and swamp regions, whereas large hippos need open grassy areas as pastureland.
Way of life
Hippos are crepuscular or nocturnal animals. During the day they either rest in or near the water, at night they search for food. In doing so, they create trails or aisles through the undergrowth in order to move faster. Hippos are herbivores, while the large hippopotamus mainly eats grass, the pygmy hippopotamus also eats leaves, shoots, fruits and the like. The incisors and canines have no function in feeding, the sharp edges of the lips are used for this.
Male hippos try to establish a territory that overlaps that of several females and to reproduce with them. Large hippos often form groups of 10 to 15 animals, primarily females with their young, and more rarely bachelor groups. Pygmy hippos, on the other hand, are more solitary. However, the only stable bond in hippos is that between the mother and the young. Pygmy hippos usually avoid each other, with large hippos there can also be violent tusks between two males.
Reproduction
In the case of large hippos, many births occur in the wettest months; in pygmy hippos, no seasonality is known. The gestation period is short at six to eight months compared to body size, and a single young animal is usually born in the water. This is weaned after six to eight months and is sexually mature after several years. Hippos in human care can live to be over 50 years old, in the wild a maximum age of 30 to 40 years is assumed for large hippos.
Hippos and people
Both species of hippopotamus living today are endangered. The reasons for this are, on the one hand, the hunting for their meat, their skin and - in the case of the large hippopotamus - their teeth, which have been processed into ivory . In addition, there has recently been the loss of their habitat due to conversion into agricultural land. The fact that the distribution areas of these animals are partly in countries affected by wars and conflicts and that effective protection is therefore not possible plays a further role. The ranges of both species have decreased and become severely fragmented, and a further decline in populations is feared. The total population of the pygmy hippopotamus is estimated at 3000 animals, the species is considered endangered . For the large hippopotamus, estimates amount to 125,000 to 148,000 animals, this species is listed as endangered ( vulnerable ). There are six zoos in Germany that keep hippos (as of 2019).
Systematics
External system
By the end of the 20th century, the flow horses were undoubtedly the Paarhufern assigned (Artiodactyla). Due to the low-crowned shape of their molars and the structure of the stomach , which is very similar to that of the umbilical pigs , they formed, together with real pigs and umbilical pigs, the subordination of the pig-like or non-ruminant (Suina or Nonruminantia). The umbilical pigs in particular were considered close relatives of the hippos.
Since the 1990s, systematic studies have been started using molecular biology . The attempt is made to obtain genetic information by sequencing the DNA and RNA and to compare it with the data of other living beings in order to determine the degree of relationship based on the degree of similarity. These studies came to the surprising conclusion that the ungulates are paraphyletic with respect to the whales , that is, that some ungulates are more closely related to the whales than the rest of their group. In fact, the hippos turned out to be the closest living relatives of the whales, this was confirmed, among other things, by casein genes , SINEs , fibrinogen sequences, cytochrome and rRNA sequences, IRBP and vWF gene sequences, adrenoreceptors and apolipoproteins . In one of these studies, Claudine Montgelard, Francois M. Catzeflis and Emmanuel Douzery first proposed the name Cetartiodactyla for the new taxon from cloven-hoofed and whales in 1997 , which is composed of the scientific names of whales (Cetacea) and artiodactyla. At the beginning of the 21st century, fossil remains of primitive representatives of the whales ( Pakicetus ) were found, which have the pair-hoofed structure of the ankle bone and thus confirm the close relationship.
Morphological studies were also carried out to support the molecular biological evidence of the close relationship between hippos and whales. Similarities could be found in the arrangement of the cusps of the molars , in the structure of the metatarsals and in the skull , which support a sister group relationship between these two taxa. Whether the most noticeable commonality, the loss of the fur and the sebum glands , is a common characteristic or an independently developed adaptation to the aquatic way of life is controversial.
The problem is that the oldest whale species lived in the early Eocene (around 53 million years ago), while the oldest known hippopotamus only lived in the Miocene (around 15 million years ago). Since the common ancestor of whales and hippos must have lived before the first whales, there is a 40 million year gap in the fossil history of hippos. In view of the comparatively good fossil find rate of the ungulates it seems unlikely that there are no remains of any ancestor of the hippopotamus. Research therefore focused on the Anthracotheriidae , a group of cloven-hoofed ungulates that was widespread from the Eocene to the Miocene and that was described as "hippopotamus" when it was discovered in the 19th century. A study from 2005 showed that the youngest representatives of the Anthracotheriidae have strong similarities with the hippos. Accordingly, a possible scenario is that the whales and the Anthracotheriidae descend from a common ancestor and the hippos evolved from the Anthracotheriidae. In 2015 the genus Epirigenys was described on the basis of lower jaw and tooth finds from northern Kenya, the age of which is around 30 million years. Within the Anthracotheriiden, the genus represents the closest relatives of the hippopotamuses in terms of phylogeny and stands opposite them as sister groups . Evidence from Epirigenys in eastern Africa suggests that the hippos may have evolved on the continent. According to this, the ancestors of today's hippos are descended from immigrants who reached Africa in the Lower Miocene (around 23 million years ago) before the land bridge to Eurasia was built .
The suspected lineages within the Cetartiodactyla can be shown in the following cladogram:
| Cetartiodactyla (ungulates and whales) |
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Internal system
As mentioned above, the hippos are a geologically young group that first appeared in the Miocene around 15 million years ago. The oldest known representative is Kenyapotamus from the Middle Miocene from Africa. In the late Miocene, the group was already spread over Africa and Eurasia, but the hippos never came to the New World .
The genus Archaeopotamus is known from Africa and the Middle East , while the genus Hexaprotodon is known from Asia , although it is disputed whether the pygmy hippopotamus that is still alive today should be classified in this genus or in its own genus Choeropsis . An investigation by Jean-Renaud Boisserie suggests the second solution.
The genus Hippopotamus was rich in species and forms and is now only represented by the large hippopotamus ( H. amphibius ). H. gorgops is known from Africa and Europe , which was characterized by its raised eyes sitting on small stalks, from the Pleistocene of Europe the gigantic H. antiquus . Also in the Pleistocene, dwarf forms developed on some Mediterranean islands , which are examples of island dwarfing , these are the Cypriot ( H. minutus ), the Cretan ( H. creutzburgi ), the Maltese ( H. melitensis ) and the Sicilian pygmy hippopotamus ( H. pentlandi ) . The three Malagasy hippos , H. madagascariensis , H. lemerlei and H. laloumena, which became extinct only a few centuries ago , are also mostly included in the genus Hippopotamus (although the systematic classification of H. madagascariensis is controversial).
Sources and web links
literature
- Ronald M. Nowak: Walker's Mammals of the World . Johns Hopkins University Press, 1999 ISBN 0-8018-5789-9
- Hubert Hendrichs: Artiodactyla (Paraxonia), artifacts . In: Wilfried Westheide, Reinhard Rieger (Ed.): Special Zoology. Part 2: vertebrates or skulls . Spectrum Akademischer Verlag, Heidelberg - Berlin 2004, pp. 608–630, ISBN 3-8274-0307-3 .
Notes and individual references
- ↑ The big hippopotamus is usually called simply hippopotamus or hippopotamus. To make it easier to differentiate, the term large hippopotamus is used throughout this article for the species.
- ↑ Degree of endangerment and population estimate of both species in the IUCN Red List of Threatened Species .
- ↑ StadtZeitung Karlsruhe No. 45, November 8, 2019, p. 6.
- ↑ John Gatesy, Cheryl Hayashi, Mathew A. Cronin, Peter Arctander: Evidence from milk casein genes that cetaceans are close relatives of hippopotamid artiodactyls. In: Molecular Biology and Evolution, 13 (7): 954-963 (1996).
- ↑ M. Shimamura et al .: Molecular evidence from retroposons that whales form a clade within even-toed ungulates. in: Nature, 388: 666-670 (1997) PMID 9262399
- ↑ John Gatesy: More DNA support for a Cetacea / Hippopotamidae clade: The Blood clotting protein genes y fibrinogen. in: Molecular Biology and Evolution, 14 (5): 537-543 (1997)
- ↑ Claudine Montgelard, Francois M. Catzeflis and Emmanuel Douzery: Phylogenetic relationships of artiodactyls and cetaceans as deduced from the comparison of cytochrome b and 12S rRNA mitochondrial sequences. In: Molecular Biology and Evolution, 14 (5): 550-559 (1997). PDF
- ↑ John Gatesy, Michel Milinkovitch, Victor Waddell and Michael Stanhope: Stability of cladistic Relationships between cetaceans and Higher-Level Artiodactyl taxa. In: Systematic Biology, 48 (1): 6-20 (1999). Abstract
- ↑ Ole Madsen, Diederik Willemsen, Björn M. Ursing, Ulfur Arnason and Wilfried W. de Jong: Molecular Evolution of the Mammalian Alpha 2B Adrenergic Receptor. In: Molecular Biology and Evolution 19: 2150-2160 (2002).
- ↑ Heather Amrine-Madsen, Klaus.-P. Koepfli, Robert K. Wayne and Mark S. Springer: A new phylogenetic marker, apolipoprotein B, provides compelling evidence for eutherian relationships. In: Mol. Phylogenet. Evol. 28: 225-240 (2003). PMID 12878460
- ↑ Jonathan Geilser and Mark Uhen: Morphological Support for a close Relationship between Hippos and Whales. In: Journal of Vertebrate Paleontology 23 (4): 991-996 (2003).
- ^ JR Boisserie, F. Lihoreau, M. Brunet: The position of Hippopotamidae within Cetartiodactyla. In: Proceedings of the National Academy of Sciences . Volume 102, number 5, February 2005, pp. 1537-1541, doi: 10.1073 / pnas.0409518102 , PMID 15677331 , PMC 547867 (free full text).
- ^ Fabrice Lihoreau, Jean-Renaud Boisserie, Fredrick Kyalo Manthi and Stéphane Ducrocq: Hippos stem from the longest sequence of terrestrial cetartiodactyl evolution in Africa. Nature Communications 6, 2015 doi: 10.1038 / ncomms7264
- ↑ According to Robin Beck et al .: A higher-level MRP supertree of placental mammals. In: BMC Evol Biol. 2006; 6: 93. PMC 1654192 (free full text)
- ^ Jean-Renaud Boisserie: The phylogeny and taxonomy of Hippopotamidae (Mammalia: Artiodactyla): a review based on morphology and cladistic analysis. In: Zoological Journal of the Linnean Society 143 (2005), pp. 1–26 doi: 10.1111 / j.1096-3642.2004.00138.x
