110-405: The hippopotamus ( Hippopotamus amphibius ) ( / ˌ h ɪ p ə ˈ p ɒ t ə m ə s / ; pl. : hippopotamuses ; often shortened to hippo ( pl. : hippos ), further qualified as the common hippopotamus , Nile hippopotamus , or river hippopotamus , is a large semiaquatic mammal native to sub-Saharan Africa . It is one of only two extant species in the family Hippopotamidae ,
220-429: A US$ 73 million exhibit to house three adult hippos, featuring a 250,000 L (55,000 imp gal; 66,000 US gal) tank. Modern hippo enclosures also have a complex filtration system for the animal's waste, an underwater viewing area for the visitors, and glass that may be up to 9 cm (3.5 in) thick and capable of holding water under pressures of 31 kPa (4.5 psi). In Egyptian mythology ,
330-630: A ballerina hippo dancing to the opera La Gioconda . The film Hugo the Hippo is set in Tanzania and involves the title character trying to escape being slaughtered with the help of local children. The Madagascar films feature a hippo named Gloria . Hippos even inspired a popular board game, Hungry Hungry Hippos . Semiaquatic In biology , being semi-aquatic refers to various macro organisms that live regularly in both aquatic and terrestrial environments . When referring to animals ,
440-472: A constant rate. These " molecular clocks ", however, are fallible, and provide only approximate timing: for example, they are not sufficiently precise and reliable for estimating when the groups that feature in the Cambrian explosion first evolved, and estimates produced by different techniques may vary by a factor of two. Organisms are only rarely preserved as fossils in the best of circumstances, and only
550-617: A factor in their eventual extinction. Isolated individual Malagasy hippos may have survived in remote pockets; in 1976, villagers described a living animal called the kilopilopitsofy , which may have been a Malagasy hippo. Hippopotamus gorgops from the Early Pleistocene to the early Middle Pleistocene of Africa and West Asia grew considerably larger than the living hippopotamus, with an estimated body mass of over 4,000 kg (8,800 lb). Hippopotamus antiquus ranged throughout Europe, extending as far north as Britain during
660-426: A fraction of such fossils have been discovered. This is illustrated by the fact that the number of species known through the fossil record is less than 5% of the number of known living species, suggesting that the number of species known through fossils must be far less than 1% of all the species that have ever lived. Because of the specialized and rare circumstances required for a biological structure to fossilize, only
770-454: A great distance across South Africa . The hippo is considered to be extremely aggressive and has frequently been reported charging and attacking boats. Small boats can easily be capsized by hippos and passengers can be injured or killed by the animals, or drown in the water. In one 2014 case in Niger , a boat was capsized by a hippo and 13 people were killed. Hippos will often raid farm crops if
880-499: A hierarchical classification system still in use today. Darwin and his contemporaries first linked the hierarchical structure of the tree of life with the then very sparse fossil record. Darwin eloquently described a process of descent with modification, or evolution, whereby organisms either adapt to natural and changing environmental pressures, or they perish. When Darwin wrote On the Origin of Species by Means of Natural Selection, or
990-418: A high-pitched squeal followed by a deeper, resonant call. The animals can recognise the calls of other individuals. Hippos are more likely to react to the wheeze honks of strangers than to those they are more familiar with. When threatened or alarmed, they produce exhalations, and fighting bulls will bellow loudly. Hippos are recorded to produce clicks underwater which may have echolocative properties. They have
1100-513: A long snout. Their skeletal structures are graviportal , adapted to carrying their enormous weight, and their dense bones and low centre of gravity allows them to sink and move along the bottom of the water. Hippopotamuses have small legs (relative to other megafauna ) because the water in which they live reduces the weight burden. The toes are webbed and the pelvis rests at an angle of 45 degrees. Though chubby-looking, hippos have little fat. The eyes, ears, and nostrils of hippos are placed high on
1210-876: A marked population expansion during or after the Pleistocene , attributed to an increase in water bodies at the end of the era. These findings have important conservation implications, as hippo populations across the continent are currently threatened by loss of access to fresh water. Hippos are also subject to unregulated hunting and poaching . The species is included in Appendix II of the Convention on International Trade in Endangered Species (CITES) meaning international export/import (including in parts and derivatives) requires CITES documentation to be obtained and presented to border authorities. As of 2017,
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#17327900921441320-418: A mid-Ordovician age. Such index fossils must be distinctive, be globally distributed and occupy a short time range to be useful. Misleading results are produced if the index fossils are incorrectly dated. Stratigraphy and biostratigraphy can in general provide only relative dating ( A was before B ), which is often sufficient for studying evolution. However, this is difficult for some time periods, because of
1430-536: A mutation first appeared. Phylogenetics and paleontology work together in the clarification of science's still dim view of the appearance of life and its evolution. Niles Eldredge 's study of the Phacops trilobite genus supported the hypothesis that modifications to the arrangement of the trilobite's eye lenses proceeded by fits and starts over millions of years during the Devonian . Eldredge's interpretation of
1540-570: A portion of the deceased organism, usually that portion that was partially mineralized during life, such as the bones and teeth of vertebrates , or the chitinous or calcareous exoskeletons of invertebrates . Fossils may also consist of the marks left behind by the organism while it was alive, such as animal tracks or feces ( coprolites ). These types of fossil are called trace fossils or ichnofossils , as opposed to body fossils . Some fossils are biochemical and are called chemofossils or biosignatures . Gathering fossils dates at least to
1650-400: A richly diverse assembly of early multicellular eukaryotes . The fossil record and faunal succession form the basis of the science of biostratigraphy or determining the age of rocks based on embedded fossils. For the first 150 years of geology , biostratigraphy and superposition were the only means for determining the relative age of rocks. The geologic time scale was developed based on
1760-448: A small percentage of life-forms can be expected to be represented in discoveries, and each discovery represents only a snapshot of the process of evolution. The transition itself can only be illustrated and corroborated by transitional fossils, which will never demonstrate an exact half-way point. The fossil record is strongly biased toward organisms with hard-parts, leaving most groups of soft-bodied organisms with little to no role. It
1870-431: A variety of plants if presented with them in captivity, but their diet in nature consists almost entirely of grass, with only minimal consumption of aquatic plants. Hippos spend most of the day in water to stay cool and hydrated. Just before night begins, they leave the water to forage on land. A hippo will travel 3–5 km (1.9–3.1 mi) per night, eating around 40 kg (88 lb) of grass. By dawn, they are back in
1980-855: Is Lu the Hippo, from the Ellie Schiller Homosassa Springs Wildlife State Park . As of 2024, he is 64 years old. Hippopotamus amphibius arrived in Europe around 560–460,000 years ago, during the Middle Pleistocene. The distribution of Hippopotamus amphibius in Europe during the Pleistocene was largely confined to Southern Europe, including the Iberian Peninsula, Italy, and Greece, but extended into northwestern Europe, including Great Britain (as far north as North Yorkshire ),
2090-449: Is a notable example of how knowledge encoded by the fossil record continues to contribute otherwise unattainable information on the emergence and development of life on Earth. For example, the research suggests Markuelia has closest affinity to priapulid worms, and is adjacent to the evolutionary branching of Priapulida , Nematoda and Arthropoda . Despite significant advances in uncovering and identifying paleontological specimens, it
2200-606: Is an example of mutualism , in which the hippo benefits from the cleaning while the fish receive food. Hippo defecation creates allochthonous deposits of organic matter along the river beds. These deposits have an unclear ecological function. A 2015 study concluded hippo dung provides nutrients from terrestrial material for fish and aquatic invertebrates, while a 2018 study found that their dung can be toxic to aquatic life in large quantities, due to absorption of dissolved oxygen in water bodies. The parasitic monogenean flatworm Oculotrema hippopotami infests hippopotamus eyes, mainly
2310-412: Is any preserved remains, impression, or trace of any once-living thing from a past geological age . Examples include bones , shells , exoskeletons , stone imprints of animals or microbes , objects preserved in amber , hair , petrified wood and DNA remnants. The totality of fossils is known as the fossil record . Though the fossil record is incomplete, numerous studies have demonstrated that there
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#17327900921442420-521: Is around 1,480 kg (3,260 lb) for bulls and 1,365 kg (3,009 lb) for cows. Exceptionally large males have been recorded reaching 2,660 kg (5,860 lb). Male hippos appear to continue growing throughout their lives, while females reach maximum weight at around age 25. It is 2.90 to 5.05 m (9 ft 6 in to 16 ft 7 in) long, including a tail of about 35 to 56 cm (14 to 22 in) in length and 1.30 to 1.65 m (4 ft 3 in to 5 ft 5 in) tall at
2530-579: Is attributed to the disruptions caused by the Second Congo War . The poachers are believed to be Mai-Mai rebels, underpaid Congolese soldiers, and local militia groups. Reasons for poaching include the belief hippos are harmful to society, as well as financial gain. As of 2016, the Virunga hippo population appears to have increased again, possibly due to better protection from park rangers, who have worked with local fishermen. The sale of hippo meat
2640-411: Is capable of running 30 km/h (19 mph) over short distances. Hippos inhabit rivers, lakes, and mangrove swamps. Territorial bulls each preside over a stretch of water and a group of five to thirty cows and calves. Mating and birth both occur in the water. During the day, hippos remain cool by staying in water or mud, emerging at dusk to graze on grasses. While hippos rest near each other in
2750-468: Is common among small mammals such as rodents). Calves no longer need to suckle when they are a year old. Hippos coexist alongside a variety of large predators in their habitats. Nile crocodiles , lions , and spotted hyenas are known to prey on young hippos. Beyond these, adult hippos are not usually preyed upon by other animals due to their aggression and size. Cases where large lion prides have successfully preyed on adult hippos have been reported, but it
2860-538: Is enough information available to give a good understanding of the pattern of diversification of life on Earth. In addition, the record can predict and fill gaps such as the discovery of Tiktaalik in the arctic of Canada . Paleontology includes the study of fossils: their age, method of formation, and evolutionary significance. Specimens are usually considered to be fossils if they are over 10,000 years old. The oldest fossils are around 3.48 billion years to 4.1 billion years old. The observation in
2970-479: Is generally accepted that the fossil record is vastly incomplete. Approaches for measuring the completeness of the fossil record have been developed for numerous subsets of species, including those grouped taxonomically, temporally, environmentally/geographically, or in sum. This encompasses the subfield of taphonomy and the study of biases in the paleontological record. Paleontology seeks to map out how life evolved across geologic time. A substantial hurdle
3080-804: Is generally rare. Lions occasionally prey on adults at Gorongosa National Park and calves are sometimes taken at Virunga. Crocodiles are frequent targets of hippo aggression, probably because they often inhabit the same riparian habitats; crocodiles may be either aggressively displaced or killed by hippos. In turn, very large Nile crocodiles have been observed preying occasionally on calves, "half-grown" hippos, and possibly also adult female hippos. Groups of crocodiles have also been observed finishing off still-living male hippos that were previously injured in mating battles with other males. Hippos occasionally visit cleaning stations in order to be cleaned of parasites by certain species of fishes. They signal their readiness for this service by opening their mouths wide. This
3190-484: Is illegal, but black-market sales are difficult for Virunga National Park officers to track. Hippo meat is highly valued in some areas of central Africa and the teeth may be used as a replacement for elephant ivory. A population of hippos exists in Colombia , descended from captive individuals that escaped from Pablo Escobar 's estate after his death in 1993. Their numbers grew to 100 by the 2020s and ecologists believe
3300-402: Is mostly purplish-grey or blue-black, but brownish-pink on the underside and around the eyes and ears. Their skin secretes a natural, red-coloured sunscreen substance that is sometimes referred to as "blood sweat" but is neither blood nor sweat. This secretion is initially colourless and turns red-orange within minutes, eventually becoming brown. Two highly acidic pigments have been identified in
3410-487: Is powered by huge masseter and digastric muscles which give them large, droopy cheeks. The jaw hinge allows the animal to open its mouth at almost 180°. A folded orbicularis oris muscle allows the hippo to attain an extreme gape without tearing any tissue. On the lower jaw, the incisors and canines grow continuously, the former reaching 40 cm (16 in), while the latter can grow to up to 50 cm (20 in). The lower canines are sharpened through contact with
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3520-438: Is replete with the mollusks , the vertebrates , the echinoderms , the brachiopods and some groups of arthropods . Fossil sites with exceptional preservation—sometimes including preserved soft tissues—are known as Lagerstätten —German for "storage places". These formations may have resulted from carcass burial in an anoxic environment with minimal bacteria, thus slowing decomposition. Lagerstätten span geological time from
3630-470: Is the difficulty of working out fossil ages. Beds that preserve fossils typically lack the radioactive elements needed for radiometric dating . This technique is our only means of giving rocks greater than about 50 million years old an absolute age, and can be accurate to within 0.5% or better. Although radiometric dating requires careful laboratory work, its basic principle is simple: the rates at which various radioactive elements decay are known, and so
3740-623: Is the genus Kenyapotamus , which lived in Africa from 15 to 9 million years ago . Hippopotamid species would spread across Africa and Eurasia, including the modern pygmy hippo. From 7.5 to 1.8 million years ago , a possible ancestor to the modern hippo, Archaeopotamus , lived in Africa and the Middle East. The oldest records of the genus Hippopotamus date to the Pliocene (5.3–2.6 million years ago). The oldest unambiguous records of
3850-413: Is the science of deciphering the "layer-cake" that is the sedimentary record. Rocks normally form relatively horizontal layers, with each layer younger than the one underneath it. If a fossil is found between two layers whose ages are known, the fossil's age is claimed to lie between the two known ages. Because rock sequences are not continuous, but may be broken up by faults or periods of erosion , it
3960-728: Is typically 40 to 50 years. Donna the Hippo was one of the oldest living hippos in captivity. She lived at the Mesker Park Zoo in Evansville, Indiana , in the US until her death in 2012 at the age of 61. The oldest hippo ever recorded was called Bertha; she had lived in the Manila Zoo in the Philippines since it first opened in 1959. When she died in 2017, her age was estimated to be 65. The oldest living hippopotamus in captivity
4070-467: Is very difficult to match up rock beds that are not directly adjacent. However, fossils of species that survived for a relatively short time can be used to match isolated rocks: this technique is called biostratigraphy . For instance, the conodont Eoplacognathus pseudoplanus has a short range in the Middle Ordovician period. If rocks of unknown age have traces of E. pseudoplanus , they have
4180-596: The Bouri Formation and dated to around 160,000 years ago. 4,000–5,000 year art showing hippos being hunted have been found in the Tassili n'Ajjer Mountains of the central Sahara near Djanet . The ancient Egyptians recognised the hippo as ferocious, and representations on the tombs of nobles show humans hunting them. The hippo was also known to the Greeks and Romans . The Greek historian Herodotus described
4290-801: The Cambrian period to the present . Worldwide, some of the best examples of near-perfect fossilization are the Cambrian Maotianshan Shales and Burgess Shale , the Devonian Hunsrück Slates , the Jurassic Solnhofen Limestone , and the Carboniferous Mazon Creek localities. A fossil is said to be recrystallized when the original skeletal compounds are still present but in a different crystal form, such as from aragonite to calcite . Replacement occurs when
4400-558: The Early and Middle Pleistocene epochs, before being replaced by the modern H. amphibius in Europe during the latter part of the Middle Pleistocene. The Pleistocene also saw a number of dwarf species evolve on several Mediterranean islands, including Crete ( Hippopotamus creutzburgi ), Cyprus (the Cyprus dwarf hippopotamus , Hippopotamus minor ), Malta ( Hippopotamus melitensis ), and Sicily ( Hippopotamus pentlandi ). Of these,
4510-745: The IUCN Red List drawn up by the International Union for Conservation of Nature (IUCN) lists the species as vulnerable , with a stable population estimated between 115,000 and 130,000 animals. The hippo population has declined most dramatically in the Democratic Republic of the Congo. By 2005, the population in Virunga National Park had dropped to 800 or 900 from around 29,000 in the mid-1970s. This decline
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4620-586: The Phacops fossil record was that the aftermaths of the lens changes, but not the rapidly occurring evolutionary process, were fossilized. This and other data led Stephen Jay Gould and Niles Eldredge to publish their seminal paper on punctuated equilibrium in 1971. Synchrotron X-ray tomographic analysis of early Cambrian bilaterian embryonic microfossils yielded new insights of metazoan evolution at its earliest stages. The tomography technique provides previously unattainable three-dimensional resolution at
4730-569: The Renaissance . Leonardo da Vinci concurred with Aristotle's view that fossils were the remains of ancient life. For example, Leonardo noticed discrepancies with the biblical flood narrative as an explanation for fossil origins: If the Deluge had carried the shells for distances of three and four hundred miles from the sea it would have carried them mixed with various other natural objects all heaped up together; but even at such distances from
4840-602: The Song dynasty during the 11th century, who kept a specific seashell fossil with his own poem engraved on it. In his Dream Pool Essays published in 1088, Song dynasty Chinese scholar-official Shen Kuo hypothesized that marine fossils found in a geological stratum of mountains located hundreds of miles from the Pacific Ocean was evidence that a prehistoric seashore had once existed there and shifted over centuries of time . His observation of petrified bamboos in
4950-432: The fossil record , show their closest living relatives are cetaceans ( whales , dolphins , and porpoises ). The common ancestor of hippos and whales branched off from Ruminantia and the rest of the even-toed ungulates; the cetacean and hippo lineages split soon afterwards. Tylopoda Suina Ruminantia Hippopotamidae Cetacea The most recent theory of
5060-402: The law of superposition ) preserved different assemblages of fossils, and that these assemblages succeeded one another in a regular and determinable order. He observed that rocks from distant locations could be correlated based on the fossils they contained. He termed this the principle of faunal succession . This principle became one of Darwin's chief pieces of evidence that biological evolution
5170-403: The thunderbird . There is no such direct mythological connection known from prehistoric Africa, but there is considerable evidence of tribes there excavating and moving fossils to ceremonial sites, apparently treating them with some reverence. In Japan, fossil shark teeth were associated with the mythical tengu , thought to be the razor-sharp claws of the creature, documented some time after
5280-749: The wet season . Male hippos always have mobile spermatozoa and can breed year-round. After becoming pregnant, a female hippo will typically not begin ovulation again for 17 months. Hippos mate in the water, with the cow remaining under the surface, her head emerging periodically to draw breath. Cows give birth in seclusion and return within 10 to 14 days. Calves are born on land or shallow water weighing on average 50 kg (110 lb) and at an average length of around 127 cm (50 in). The female lies on her side when nursing, which can occur underwater or on land. The young are carried on their mothers' backs in deep water. Mother hippos are very protective of their young, not allowing others to get too close. One cow
5390-453: The 16th century. Roman naturalist Pliny the Elder wrote of " tongue stones ", which he called glossopetra . These were fossil shark teeth, thought by some classical cultures to look like the tongues of people or snakes. He also wrote about the horns of Ammon , which are fossil ammonites , whence the group of shelled octopus-cousins ultimately draws its modern name. Pliny also makes one of
5500-739: The 19th century that certain fossils were associated with certain rock strata led to the recognition of a geological timescale and the relative ages of different fossils. The development of radiometric dating techniques in the early 20th century allowed scientists to quantitatively measure the absolute ages of rocks and the fossils they host. There are many processes that lead to fossilization , including permineralization , casts and molds, authigenic mineralization , replacement and recrystallization, adpression, carbonization , and bioimmuration. Fossils vary in size from one- micrometre (1 μm) bacteria to dinosaurs and trees, many meters long and weighing many tons. A fossil normally preserves only
5610-413: The 8th century AD. In medieval China, the fossil bones of ancient mammals including Homo erectus were often mistaken for " dragon bones" and used as medicine and aphrodisiacs . In addition, some of these fossil bones are collected as "art" by scholars, who left scripts on various artifacts, indicating the time they were added to a collection. One good example is the famous scholar Huang Tingjian of
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#17327900921445720-456: The Cyprus dwarf hippo survived until the end of the Pleistocene or early Holocene. Evidence from the archaeological site Aetokremnos continues to cause debate on whether or not the species was driven to extinction or even encountered by humans. The hippopotamus is a megaherbivore and is exceeded in size among land animals only by elephants and some rhinoceros species. The mean adult weight
5830-948: The Elder , in his time, the best location in Egypt for capturing this animal was in the Saite nome ; the animal could still be found along the Damietta branch of the Nile after the Arab Conquest in 639. Reports of the slaughter of the last hippo in Natal Province were made at the end of the 19th century. Hippos are still found in the rivers and lakes of the northern Democratic Republic of the Congo , Uganda , Tanzania , and Kenya , north through to Ethiopia , Somalia , and Sudan , west to The Gambia , and south to South Africa . Genetic evidence suggests common hippos in Africa experienced
5940-773: The Netherlands, and western Germany during interglacial periods, such as the Last Interglacial (130–115,000 years ago). The youngest records of the species in Europe are from the Late Pleistocene of Greece, dating to around 40–30,000 years ago. Archaeological evidence exists of its presence in the Levant , dating to less than 3,000 years ago. The species was common in Egypt 's Nile region during antiquity , but it has since been driven out. According to Pliny
6050-615: The Preservation of Favoured Races in the Struggle for Life , the oldest animal fossils were those from the Cambrian Period, now known to be about 540 million years old. He worried about the absence of older fossils because of the implications on the validity of his theories, but he expressed hope that such fossils would be found, noting that: "only a small portion of the world is known with accuracy." Darwin also pondered
6160-566: The Proterozoic and deeper still in the Archean is only "recounted by microscopic fossils and subtle chemical signals." Molecular biologists, using phylogenetics , can compare protein amino acid or nucleotide sequence homology (i.e., similarity) to evaluate taxonomy and evolutionary distances among organisms, with limited statistical confidence. The study of fossils, on the other hand, can more specifically pinpoint when and in what organism
6270-682: The Yoruba. Hippo masks were also used in Nyau funerary rituals of the Chewa of Southern Africa. According to Robert Baden-Powell , Zulu warriors referred to hippos in war chants. The Behemoth from the Book of Job , 40:15–24 is thought to be based on the hippo. Hippos have been the subjects of various African folktales . According to a San story, when the Creator assigned each animal its place in nature,
6380-411: The animal's skin from cracking if it stays out of water too long. The testes of the males do not fully descend and a scrotum is not present. In addition, the penis retracts into the body when not erect . The genitals of the female hippos are unusual in that the vagina is ridged and the vulval vestibule has two large, protruding diverticula . Both of these have an unknown function. A hippo's lifespan
6490-413: The beach, indicating the fossils were once living animals. He had previously explained them in terms of vaporous exhalations , which Persian polymath Avicenna modified into the theory of petrifying fluids ( succus lapidificatus ). Recognition of fossil seashells as originating in the sea was built upon in the 14th century by Albert of Saxony , and accepted in some form by most naturalists by
6600-661: The beginning of recorded history. The fossils themselves are referred to as the fossil record. The fossil record was one of the early sources of data underlying the study of evolution and continues to be relevant to the history of life on Earth . Paleontologists examine the fossil record to understand the process of evolution and the way particular species have evolved. Fossils have been visible and common throughout most of natural history, and so documented human interaction with them goes back as far as recorded history, or earlier. There are many examples of paleolithic stone knives in Europe, with fossil echinoderms set precisely at
6710-483: The closest living relatives of the hippopotamids are cetaceans ( whales , dolphins , porpoises , etc.), from which they diverged about 55 million years ago. Hippos are recognisable for their barrel-shaped torsos, wide-opening mouths with large canine tusks, nearly hairless bodies, pillar-like legs, and large size: adults average 1,500 kg (3,300 lb) for bulls (males) and 1,300 kg (2,900 lb) for cows (females). Despite its stocky shape and short legs, it
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#17327900921446820-422: The completely aquatic cetaceans . The other branch became the anthracotheres , a large family of four-legged beasts, the earliest of which in the late Eocene would have resembled skinny hippos with comparatively smaller, narrower heads. All branches of the anthracotheres, except that which evolved into Hippopotamidae , became extinct during the Pliocene , leaving no descendants. A rough evolutionary lineage of
6930-670: The deity Sopdu , the Morning Star, equivalent of Venus in Roman mythology. Fossils appear to have directly contributed to the mythology of many civilizations, including the ancient Greeks. Classical Greek historian Herodotos wrote of an area near Hyperborea where gryphons protected golden treasure. There was indeed gold mining in that approximate region , where beaked Protoceratops skulls were common as fossils. A later Greek scholar, Aristotle , eventually realized that fossil seashells from rocks were similar to those found on
7040-607: The described morphological differences were small enough that they could have resulted from simple variation in nonrepresentative samples. A study examining mitochondrial DNA from skin biopsies taken from 13 sampling locations found "low, but significant, genetic differentiation" among H. a. amphibius , H. a. capensis , and H. a. kiboko . Neither H. a. tschadensis nor H. a. constrictus have been tested. Until 1909, naturalists classified hippos together with pigs based on molar patterns. Several lines of evidence, first from blood proteins, then from molecular systematics , DNA and
7150-466: The dry northern climate zone of what is now Yan'an , Shaanxi province, China, led him to advance early ideas of gradual climate change due to bamboo naturally growing in wetter climate areas. In medieval Christendom , fossilized sea creatures on mountainsides were seen as proof of the biblical deluge of Noah's Ark . After observing the existence of seashells in mountains, the ancient Greek philosopher Xenophanes (c. 570 – 478 BC) speculated that
7260-415: The earlier known references to toadstones , thought until the 18th century to be a magical cure for poison originating in the heads of toads, but which are fossil teeth from Lepidotes , a Cretaceous ray-finned fish. The Plains tribes of North America are thought to have similarly associated fossils, such as the many intact pterosaur fossils naturally exposed in the region, with their own mythology of
7370-550: The earliest known stromatolites are over 3.4 billion years old. The fossil record is life's evolutionary epic that unfolded over four billion years as environmental conditions and genetic potential interacted in accordance with natural selection. The Virtual Fossil Museum Paleontology has joined with evolutionary biology to share the interdisciplinary task of outlining the tree of life, which inevitably leads backwards in time to Precambrian microscopic life when cell structure and functions evolved. Earth's deep time in
7480-464: The earth during earthquake and subsidences, and petrifies whatever comes into contact with it. As a matter of fact, the petrifaction of the bodies of plants and animals is not more extraordinary than the transformation of waters. From the 13th century to the present day, scholars pointed out that the fossil skulls of Deinotherium giganteum , found in Crete and Greece, might have been interpreted as being
7590-478: The existence of a world previous to ours, destroyed by some kind of catastrophe. Interest in fossils, and geology more generally, expanded during the early nineteenth century. In Britain, Mary Anning 's discoveries of fossils, including the first complete ichthyosaur and a complete plesiosaurus skeleton, sparked both public and scholarly interest. Early naturalists well understood the similarities and differences of living species leading Linnaeus to develop
7700-462: The god Set takes the form of a red hippopotamus and fights Horus for control of the land, but is defeated. The goddess Tawaret is depicted as a pregnant woman with a hippo head, representing fierce maternal love. The Ijaw people of the Niger Delta wore masks of aquatic animals like the hippo when practising their water spirit cults, and hippo ivory was used in the divination rituals of
7810-601: The ground) when they move fast enough. Hippos are reported to reach 30 km/h (19 mph) but this has not been confirmed. They are incapable of jumping but can walk up steep banks. The hippopotamus sleeps with both hemispheres of the brain resting, as in all land mammals, and usually sleeps on land or in water with the nostrils exposed. Despite this, it may be capable of sleeping while submerged, intermittently surfacing to breathe without waking. They appear to transition between different phases of sleep more quickly than other mammals. Because of their size and their habit of taking
7920-519: The hand grip, dating back to Homo heidelbergensis and Neanderthals . These ancient peoples also drilled holes through the center of those round fossil shells, apparently using them as beads for necklaces. The ancient Egyptians gathered fossils of species that resembled the bones of modern species they worshipped. The god Set was associated with the hippopotamus , therefore fossilized bones of hippo-like species were kept in that deity's temples. Five-rayed fossil sea urchin shells were associated with
8030-640: The hippo can thus be traced from Eocene and Oligocene species: from Anthracotherium and Elomeryx to the Miocene species Merycopotamus and Libycosaurus and finally the very latest anthracotheres in the Pliocene . These groups lived across Eurasia and Africa. The discovery of Epirigenys in East Africa, which was likely a descent of Asian anthracotheres and a sister taxon to Hippopotamidae, suggests that hippo ancestors entered Africa from Asia around 35 million years ago . An early hippopotamid
8140-682: The hippo had to jump into a nearby pool. The hippo lost most of his hair and was too embarrassed to leave the water. Hippopotamuses were rarely depicted in European art during the Renaissance and Baroque periods, due to less access to specimens by Europeans. One notable exception is Peter Paul Rubens ' The Hippopotamus and Crocodile Hunt (1615–1616). Ever since Obaysch inspired the "Hippopotamus Polka", hippos have been popular animals in Western culture for their rotund appearance, which many consider comical. The Disney film Fantasia featured
8250-529: The hippo in The Histories (written circa 440 BC) and the Roman naturalist Pliny the Elder wrote about the hippo in his encyclopedia Naturalis Historia (written circa 77 AD). The Yoruba people called the hippo erinmi , which means "elephant of the water". Some individual hippos have achieved international fame. Huberta became a celebrity during the Great Depression for trekking
8360-404: The hippos wanted to live in the water, but were refused out of fear they might eat all the fish. After begging and pleading, the hippos were finally allowed to live in the water on the condition they would eat grass instead of fish, and fling their dung so it can be inspected for fish bones. In a Ndebele tale, the hippo originally had long, beautiful hair, but it was set on fire by a jealous hare and
8470-535: The limits of fossilization. Fossils of two enigmatic bilaterians, the worm-like Markuelia and a putative, primitive protostome , Pseudooides , provide a peek at germ layer embryonic development. These 543-million-year-old embryos support the emergence of some aspects of arthropod development earlier than previously thought in the late Proterozoic. The preserved embryos from China and Siberia underwent rapid diagenetic phosphatization resulting in exquisite preservation, including cell structures. This research
8580-560: The modern H. amphibius date to the Middle Pleistocene , though there are possible Early Pleistocene records. Three species of Malagasy hippopotamus became extinct during the Holocene on Madagascar , the last of them within the past 1,000 years. The Malagasy hippos were smaller than the modern hippo, a likely result of the process of insular dwarfism . Fossil evidence indicates many Malagasy hippos were hunted by humans,
8690-494: The nictitating membrane. It is the only monogenean species (which normally live on fish) documented to live on a mammal. Cut marks on bones of H. amphibius found at Bolomor Cave , a site in Spain preserving fossils dating from 230,000 to 120,000 years ago, provides evidence for Neanderthal butchery of hippopotamuses. The earliest evidence of modern human interaction with hippos comes from butchery cut marks on hippo bones found at
8800-577: The opportunity arises, and humans may come into conflict with them on these occasions. These encounters can be fatal to either humans or hippos. According to the Ptolemaic historian Manetho , the pharaoh Menes was carried off and then killed by a hippopotamus. Hippos have long been popular zoo animals. The first record of hippos taken into captivity for display is dated to 3500 BC in Hierakonpolis, Egypt. The first zoo hippo in modern history
8910-528: The origins of Hippopotamidae suggests hippos and whales shared a common semiaquatic ancestor that branched off from other artiodactyls around 60 million years ago . This hypothesised ancestral group likely split into two branches again around 54 million years ago . One branch would evolve into cetaceans , possibly beginning about 52 million years ago , with the protowhale Pakicetus and other early whale ancestors collectively known as Archaeoceti . This group eventually underwent aquatic adaptation into
9020-404: The other being the pygmy hippopotamus ( Choeropsis liberiensis or Hexaprotodon liberiensis ). Its name comes from the ancient Greek for "river horse" ( ἱπποπόταμος ). After elephants and rhinoceroses , the hippopotamus is the next largest land mammal . It is also the largest extant land artiodactyl . Despite their physical resemblance to pigs and other terrestrial even-toed ungulates,
9130-562: The population should be eradicated, as they are breeding rapidly and are an increasing menace to humans and the environment. Attempts to control them include sterilisation and culling . Hippos are semiaquatic and require enough water to immerse in, while being close to grass. They mostly live in freshwater habitat, but can be found in estuaries . They prefer relatively still waters with gently sloping shores, though male hippos may also be found in very small numbers in more rapid waters with rocky slopes. Like most herbivores, hippos will consume
9240-545: The problems involved in matching rocks of the same age across continents . Family-tree relationships also help to narrow down the date when lineages first appeared. For instance, if fossils of B or C date to X million years ago and the calculated "family tree" says A was an ancestor of B and C, then A must have evolved earlier. It is also possible to estimate how long ago two living clades diverged, in other words approximately how long ago their last common ancestor must have lived, by assuming that DNA mutations accumulate at
9350-443: The ratio of the radioactive element to its decay products shows how long ago the radioactive element was incorporated into the rock. Radioactive elements are common only in rocks with a volcanic origin, and so the only fossil-bearing rocks that can be dated radiometrically are volcanic ash layers, which may provide termini for the intervening sediments. Consequently, palaeontologists rely on stratigraphy to date fossils. Stratigraphy
9460-462: The relative ages of rock strata as determined by the early paleontologists and stratigraphers . Since the early years of the twentieth century, absolute dating methods, such as radiometric dating (including potassium/argon , argon/argon , uranium series , and, for very recent fossils, radiocarbon dating ) have been used to verify the relative ages obtained by fossils and to provide absolute ages for many fossils. Radiometric dating has shown that
9570-599: The river ' . In English, the plural is "hippopotamuses". The modern hippopotamus and the pygmy hippopotamus are the only living members of the family Hippopotamidae. Some taxonomists place hippos and anthracotheres in the superfamily Anthracotheroidea. Hippopotamidae are classified along with other even-toed ungulates in the order Artiodactyla . Five subspecies of hippos have been described based on morphological differences in their skulls as well as differences in geographical range: The suggested subspecies above were never widely used or validated by field biologists;
9680-414: The roof of their skulls. This allows these organs to remain above the surface while the rest of the body is submerged. The nostrils and ears can close when underwater while nictitating membranes cover the eyes. The vocal folds of the hippo are more horizontally positioned, much like baleen whales. Underneath are throat tissues, where vibrations are transmitted to produce underwater calls. The hippo's jaw
9790-430: The same paths to feed, hippos can have a significant impact on the land across which they walk, keeping the land clear of vegetation and depressing the ground. Over prolonged periods, hippos can divert the paths of swamps and channels. By defecating in the water, the animals also appear to pass on microbes from their gut, affecting the biogeochemical cycle . On occasion, hippos have been filmed eating carrion , usually near
9900-429: The sea and that they were still living when the strait of Gibraltar was cut through. In the mountains of Parma and Piacenza multitudes of shells and corals with holes may be seen still sticking to the rocks.... In 1666, Nicholas Steno examined a shark, and made the association of its teeth with the "tongue stones" of ancient Greco-Roman mythology, concluding that those were not in fact the tongues of venomous snakes, but
10010-423: The sea we see the oysters all together and also the shellfish and the cuttlefish and all the other shells which congregate together, found all together dead; and the solitary shells are found apart from one another as we see them every day on the sea-shores. And we find oysters together in very large families, among which some may be seen with their shells still joined together, indicating that they were left there by
10120-454: The secretions; one red hipposudoric acid and one orange norhipposudoric acid, which inhibit the growth of disease-causing bacteria and their light-absorption profile peaks in the ultraviolet range, creating a sunscreen effect. Regardless of diet, all hippos secrete these pigments so food does not appear to be their source; rather, they may be synthesised from precursors such as the amino acid tyrosine . This natural sunscreen cannot prevent
10230-476: The shoulder, with males and females ranging 1.40 to 1.65 m (4 ft 7 in to 5 ft 5 in) and 1.30 to 1.45 m (4 ft 3 in to 4 ft 9 in) tall at the shoulder respectively. The species has a typical head–body length of 3.3–3.45 m (10.8–11.3 ft) and an average standing height of 1.4 m (4 ft 7 in) at the shoulder. Hippos have barrel-shaped bodies with short tails and legs, and an hourglass-shaped skull with
10340-586: The skulls of the Cyclopes of Greek mythology , and are possibly the origin of that Greek myth. Their skulls appear to have a single eye-hole in the front, just like their modern elephant cousins, though in fact it's actually the opening for their trunk. In Norse mythology , echinoderm shells (the round five-part button left over from a sea urchin) were associated with the god Thor , not only being incorporated in thunderstones , representations of Thor's hammer and subsequent hammer-shaped crosses as Christianity
10450-424: The smaller upper canines. The canines and incisors are used mainly for combat instead of feeding. Hippos rely on their flattened, horny lips to grasp and pull grasses which are then ground by the molars . The hippo is considered to be a pseudoruminant ; it has a complex three-chambered stomach, but does not "chew cud ". Hippo skin is 6 cm (2.4 in) thick across much of its body with little hair. The animal
10560-467: The sudden appearance of many groups (i.e. phyla ) in the oldest known Cambrian fossiliferous strata. Since Darwin's time, the fossil record has been extended to between 2.3 and 3.5 billion years. Most of these Precambrian fossils are microscopic bacteria or microfossils . However, macroscopic fossils are now known from the late Proterozoic. The Ediacara biota (also called Vendian biota) dating from 575 million years ago collectively constitutes
10670-451: The teeth of some long-extinct species of shark. Robert Hooke (1635–1703) included micrographs of fossils in his Micrographia and was among the first to observe fossil forams . His observations on fossils, which he stated to be the petrified remains of creatures some of which no longer existed, were published posthumously in 1705. William Smith (1769–1839) , an English canal engineer, observed that rocks of different ages (based on
10780-761: The term describes those that actively spend part of their daily time in water (in which case they can also be called amphibious ), or land animals that have spent at least one life stages (e.g. as eggs or larvae ) in aquatic environments. When referring to plants , the term describes land plants whose roots have adapted well to tolerate regular, prolonged submersion in water, as well as emergent and (occasionally) floating-leaved aquatic plants that are only partially immersed in water. Examples of semi-aquatic animals and plants are given below. Semi aquatic animals include: Semi aquatic plants include: Fossil record A fossil (from Classical Latin fossilis , lit. ' obtained by digging ' )
10890-464: The unique ability to hold their heads partially above the water and send out a cry that travels through both water and air; individuals respond both above and below water. Cows reach sexual maturity at five to six years of age and have a gestation period of eight months. A study of endocrine systems revealed cows may begin puberty at as early as three or four years. Bulls reach maturity at around 7.5 years. Both conceptions and births are highest during
11000-459: The water and grazing areas. "Yawning" serves as a threat display. When fighting, bulls use their incisors to block each other's attacks and their large canines as offensive weapons. When hippos become over-populated or a habitat shrinks, bulls sometimes attempt infanticide , but this behaviour is not common under normal conditions. The most common hippo vocalisation is the "wheeze honk", which can travel over long distances in air. This call starts as
11110-423: The water dries up. The bull has breeding access to all the cows in his territory. Younger bachelors are allowed to stay as long as they defer to him. A younger male may challenge the old bull for control of the territory. Within the pods, the hippos tend to segregate by sex and status. Bachelor males lounge near other bachelors, females with other females, and the territorial male is on his own. When hippos emerge from
11220-407: The water to graze, they do so individually. Hippos engage in "muck-spreading" which involves defecating while spinning their tails to distribute the faeces over a greater area. Muck-spreading occurs both on land and in water and its function is not well understood. It is unlikely to serve a territorial function, as the animals only establish territories in the water. They may be used as trails between
11330-537: The water, grazing is a solitary activity and hippos typically do not display territorial behaviour on land. Hippos are among the most dangerous animals in the world due to their aggressive and unpredictable nature. They are threatened by habitat loss and poaching for their meat and ivory (canine teeth). The Latin word hippopotamus is derived from the ancient Greek ἱπποπόταμος ( hippopótamos ), from ἵππος ( híppos ) ' horse ' and ποταμός ( potamós ) ' river ' , together meaning ' horse of
11440-451: The water. Despite being semiaquatic, an adult hippo is not a particularly good swimmer, nor can it float. It rarely enters deep water; when it does, the animal moves by bouncing off the bottom. An adult hippo surfaces every four to six minutes, while young need to breathe every two to three minutes. Hippos move on land by trotting , and limb movements do not change between speeds. They can reach an airborne stage (a stage when all limb are off
11550-724: The water. There are other reports of meat-eating and even cannibalism and predation . Hippos' stomach anatomy lacks adaptions to carnivory and meat-eating is likely caused by lack of nutrients or just an abnormal behaviour. It is challenging to study the interaction of bulls and cows because hippos are not sexually dimorphic , so cows and young bulls are almost indistinguishable in the field. Hippo pods fluctuate but can contain over 100 hippos. Although they lie close together, adults develop almost no social bonds. Males establish territories in water but not land, and these may range 250–500 m (820–1,640 ft) in lakes and 50–100 m (160–330 ft) in rivers. Territories are abandoned when
11660-524: The world was once inundated in a great flood that buried living creatures in drying mud. In 1027, the Persian Avicenna explained fossils' stoniness in The Book of Healing : If what is said concerning the petrifaction of animals and plants is true, the cause of this (phenomenon) is a powerful mineralizing and petrifying virtue which arises in certain stony spots, or emanates suddenly from
11770-525: Was Obaysch , who arrived at the London Zoo on 25 May 1850, where he attracted up to 10,000 visitors a day and inspired a popular song, the "Hippopotamus Polka". Hippos generally breed well in captivity; birth rates are lower than in the wild, but this can be attributed to zoos' desire to limit births, since hippos are relatively expensive to maintain. Starting in 2015, the Cincinnati Zoo built
11880-458: Was adopted, but also kept in houses to garner Thor's protection. These grew into the shepherd's crowns of English folklore, used for decoration and as good luck charms, placed by the doorway of homes and churches. In Suffolk , a different species was used as a good-luck charm by bakers, who referred to them as fairy loaves , associating them with the similarly shaped loaves of bread they baked. More scientific views of fossils emerged during
11990-408: Was real. Georges Cuvier came to believe that most if not all the animal fossils he examined were remains of extinct species. This led Cuvier to become an active proponent of the geological school of thought called catastrophism . Near the end of his 1796 paper on living and fossil elephants he said: All of these facts, consistent among themselves, and not opposed by any report, seem to me to prove
12100-411: Was recorded protecting a calf's carcass after it had died. Calves may be temporarily kept in nurseries , guarded by one or more adults, and will play amongst themselves. Like many other large mammals, hippos are described as K-strategists , in this case typically producing just one large, well-developed infant every couple of years (rather than many small, poorly developed young several times per year, as
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