Elephant birds are members of the extinct ratite family Aepyornithidae, made up of large to enormous flightless birds that once lived on the island of Madagascar. They became extinct, perhaps around 1000–1200 AD, probably as a result of human activity. Elephant birds comprised the genera Mullerornis, Vorombe and Aepyornis. While they were in close geographical proximity to the ostrich, their closest living relatives are kiwi (found only in New Zealand), suggesting that ratites did not diversify by vicariance during the breakup of Gondwana but instead evolved from ancestors that dispersed more recently by flying.
|Aepyornis maximus skeleton and egg|
In September 2018, scientists determined that Vorombe titan reached weights of 730 kg (1,600 lb) and stood 3 m (9.8 ft) tall, making it the world's largest (heaviest) bird, slightly larger than the much older Dromornis stirtoni.
Elephant birds have been extinct since at least the 17th century. Étienne de Flacourt, a French governor of Madagascar in the 1640s and 1650s, mentions an ostrich-like bird said to inhabit unpopulated regions, though it is unclear whether he was repeating folk tales passed on from generations earlier. In 1659, Flacourt wrote of the "vouropatra – a large bird which haunts the Ampatres and lays eggs like the ostriches; so that the people of these places may not take it, it seeks the most lonely places." Marco Polo also mentioned hearing stories of very large birds during his journey to the East during the late 13th century. These accounts are today believed to describe elephant birds.
Between 1830 and 1840 European travelers in Madagascar saw giant eggs and egg shells. English observers were more willing to believe the accounts of giant birds and eggs because they knew of the moa in New Zealand. In 1851 the French Academy of Sciences received three eggs and some bone fragments. In some cases the eggs have a length up to 34 cm (13 in), the largest type of bird egg ever found. The egg weighed about 10 kg (22 lb). The egg volume is about 160 times greater than that of a chicken egg.
Aepyornis is believed to have been more than 3 m (9.8 ft) tall and weighed perhaps in the range of 350 to 500 kg (770 to 1,100 lb). In September 2018, scientists reported that Vorombe titan reached weights of 730 kg (1,600 lb), and based on a fragmentary femur, possibly up to 860 kg (1,900 lb), making it the world's largest bird. Only the much older species Dromornis stirtoni from Australia rivals it in size among known fossil birds. In the same report, the upper weight limits for A. maximus and D. stirtoni were revised to 540 and 730 kg, respectively.
Up to ten or eleven species in the genus Aepyornis have been described, but the validity of many have been disputed, with numerous authors treating them all in just one species, A. maximus. Up to three species have been described in Mullerornis. But recent work by Hansford & Turvey 2018 has restricted the number of aepyornithid species to four, with two in Aepyornis, one in Mullerornis, and one in Vorombe.
- Order Aepyornithiformes Newton 1884 [Aepyornithes Newton 1884]
- Family Aepyornithidae (Bonaparte 1853) [Aepyornithinae Bonaparte 1853]
- Genus Aepyornis Geoffroy Saint-Hilaire 1850
- Genus Mullerornis Milne-Edwards & Grandidier 1894
- Mullerornis modestus (Milne-Edwards & Grandidier 1869) Hansford & Turvey 2018 (Betsile/robust elephant-bird)
- Genus Vorombe Hansford & Turvey 2018
- Vorombe titan (Andrews 1894) Hansford & Turvey 2018
- Family Aepyornithidae (Bonaparte 1853) [Aepyornithinae Bonaparte 1853]
Several ratites outside of Madagascar have been posited as "aepyornithid"-like and could potentially make this clade considerably more speciose. These include Eremopezus from the Eocene of North Africa, unnamed Canary Island remains and several Neogene taxa in Eurasia.
Aepyornis maximus is commonly known as the 'elephant bird', a term that apparently originated from Marco Polo's account of the rukh in 1298, although he was apparently referring to an eagle-like bird strong enough to "seize an elephant with its talons". Sightings of eggs of elephant birds by sailors (e.g. text on the Fra Mauro map of 1467–69, if not attributable to ostriches) could also have been erroneously attributed to a giant raptor from Madagascar. The legend of the roc could also have originated from sightings of such a giant subfossil eagle related to the African crowned eagle, which has been described in the genus Stephanoaetus from Madagascar, being large enough to carry off large primates; today, lemurs still retain a fear of aerial predators such as these. Another might be the perception of ratites retaining neotenic features and thus being mistaken for enormous chicks of a presumably more massive bird.
Taxonomy and biogeographyEdit
Like the ostrich, rhea, cassowary, emu, kiwi and extinct moa, Mullerornis and Aepyornis were ratites; they could not fly, and their breast bones had no keel. Because Madagascar and Africa separated before the ratite lineage arose, Aepyornis has been thought to have dispersed and become flightless and gigantic in situ.
More recently, it has been deduced from DNA sequence comparisons that the closest living relatives of elephant birds are New Zealand kiwi, though they are not particularly closely related, being estimated to have diverged from each other 54 million years ago. Elephant birds are actually part of the mid-Cenozoic Australian ratite radiation; their ancestors flew across the Indian Ocean well after Gondwana broke apart. The existence of possible flying palaeognaths in the Miocene such as Proapteryx further supports the view that ratites did not diversify in response to vicariance. Gondwana broke apart in the Cretaceous and their phylogenetic tree does not match the process of continental drift. Madagascar has a notoriously poor Cenozoic terrestrial fossil record, with essentially no fossils between the end of the Cretaceous (Maevarano Formation) and the Late Pleistocene. Molecular clock estimates from complete mitochondrial genomes obtained from Aepyornis eggshells suggest that Aepyornis and Mullerornis diverged from each other during the mid Oligocene around 27 million years ago, suggesting elephant birds must have been present on Madagascar before this time.
Claims of findings of "aepyornithid" egg remains on the eastern Canary Islands, if valid, would represent a major biogeographical enigma. These islands are not thought to have been connected to mainland Africa when elephant birds were alive. There is no indication that elephant birds evolved outside Madagascar, and today, the Canary Island eggshells are considered to belong to extinct North African birds that may not have been ratites (possibly Eremopezus/Psammornis, or even Pelagornithidae, prehistoric seabirds of immense size). Various "aepyornithid-like" eggs and bones occur in Paleogene and Miocene deposits in Africa and Europe.
Two whole eggs have been found in dune deposits in southern Western Australia, one in the 1930s (the Scott River egg) and one in 1992 (the Cervantes egg); both have been identified as Aepyornis maximus rather than Genyornis. It is hypothesized that the eggs floated from Madagascar to Australia on the Antarctic Circumpolar Current. Evidence supporting this is the finding of two fresh penguin eggs that washed ashore on Western Australia but originated in the Kerguelen Islands, and an ostrich egg found floating in the Timor Sea in the early 1990s.
Examination of brain endocasts has shown that both A. maximus and A. hildebrandi had greatly reduced optic lobes, similar to those of their closest living relatives, the kiwis, and consistent with a similar nocturnal lifestyle. The optic lobes of Mullerornis were also reduced, but to a lesser degree, suggestive of a nocturnal or crepuscular lifestyle. A. maximus had relatively larger olfactory bulbs than A. hildebrandi, suggesting that the former occupied forested habitats where the sense of smell is more useful while the latter occupied open habitats.
Because there is no rainforest fossil record in Madagascar, it is not known for certain if there were species adapted to dense forest dwelling, like the cassowary in Australia and New Guinea today. However, some rainforest fruits with thick, highly sculptured endocarps, such as that of the currently undispersed and highly threatened forest coconut palm Voanioala gerardii, may have been adapted for passage through ratite guts, and the fruit of some palm species are indeed dark bluish purple (e.g. Ravenea louvelii and Satranala decussilvae), just like many cassowary-dispersed fruits.
Occasionally subfossil eggs are found intact.[full citation needed] The National Geographic Society in Washington, D.C. holds a specimen of an Aepyornis egg which was given to Luis Marden in 1967. The specimen is intact and contains the skeleton of the unhatched bird. The Denver Museum of Nature and Science in Colorado holds two intact eggs, one of which is currently on display. Another giant Aepyornis egg is on display at the Harvard Museum of Natural History in Cambridge, Massachusetts, and a complete, unbroken egg is held at Leeds Discovery Centre in the UK. A cast of the egg is preserved at the Grant Museum of Zoology at London University.
An intact specimen is also exists in Kuleli Military High School Museum, Istanbul, Turkey.
David Attenborough owned an almost complete eggshell, dating from 600 to 700 CE, which he pieced together from fragments that were given to him while making his 1961 BBC series Zoo Quest to Madagascar. In March 2011, the BBC broadcast the 60-minute documentary Attenborough and the Giant Egg, presented by Attenborough, about his personal scientific quest to discover the secrets of the elephant bird and its egg.
There is also an intact specimen of an elephant bird's egg (contrasted with the eggs from other bird species, including a hummingbird's) on display at the Delaware Museum of Natural History, just outside Wilmington, Delaware, US, and another in the Natural History Museum, London.
The Melbourne Museum has two Aepyornis eggs. The first was acquired for £100 by Professor Frederick McCoy in June 1862, and is an intact example. In 1950 it was subjected to radiological examination, which revealed no traces of embryonic material. A second, side-blown Aepyornis egg was acquired at a later date.
In April 2018, staff at the Buffalo Museum of Science radiographed what had long been thought to be a model of an elephant bird egg. The cream-colored object, measuring 12 inches (300 mm) in length and 28 inches (710 mm) in circumference and weighing over 3 pounds (1.4 kg), was found to be a mislabeled real egg (the museum does also have such a model in its collections).
Two eggs have been discovered on the Western Australia coast, one discovered in the 1930s and another in 1992. A study concluded that the egg found at Cervantes was 2000 years old and had likely drifted across the Indian Ocean.
Relationship with humansEdit
It is widely believed that the extinction of Aepyornis was a result of human activity. The birds were initially widespread, occurring from the northern to the southern tip of Madagascar. One theory states that humans hunted the elephant birds to extinction in a very short time for such a large landmass (the blitzkrieg hypothesis). There is indeed evidence that they were hunted and their preferred habitats destroyed. Eggs may have been particularly vulnerable. 19th-century travelers saw eggshells used as bowls, and a recent archaeological study found remains of eggshells among the remains of human fires, suggesting that the eggs regularly provided meals for entire families.
The exact time period when they died out is also not certain; tales of these giant birds may have persisted for centuries in folk memory. There is archaeological evidence of Aepyornis from a radiocarbon-dated bone at 1880 ± 70 BP (approximately 120 CE) with signs of butchering, and on the basis of radiocarbon dating of shells, about 1000 BP (approximately 1000 CE).
An alternative theory is that the extinction was a secondary effect of human impact resulting from transfer of hyperdiseases from human commensals such as chickens and guineafowl. The bones of these domesticated fowl have been found in subfossil sites in the island (MacPhee and Marx, 1997: 188), such as Ambolisatra (Madagascar), where Mullerornis sp. and Aepyornis maximus have been reported. Also reported by these authors, ratite remains have been found in west and south west Madagascar, at Belo-sur-Mer (A. medius, Mullerornis rudis), Bemafandry (M. agilis) and Lamboharana (Mullerornis sp.).
Recently human tool marks have been found on elephant bird bones dating to approximately 10,000 BCE. This not only vastly extends the range of human existence on Madagascar's prehistoric past, but suggests a more complex relationship between these birds and human beings and their eventual extinction, as they apparently coexisted for a massive period of time. However, the absence so far for any evidence of human habitation in the succeeding 6000 years raises difficult questions concerning whether the early human presence might have been temporary, and/or restricted to just a portion of the island.
In art and literatureEdit
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