53-550: Mullerornis modestus is an extinct species of elephant bird , and the only member of the genus Mullerornis . The genus is named after Georges Muller, a French explorer, who was killed in 1892 by hostile members of the Sakalava people . Mullerornis is smaller than the more well-known Aepyornis , with a still substantial body mass of approximately 80 kilograms (180 lb). A bone possibly belonging to Mullerornis has been radiocarbon dated to about 1260 BP , suggesting that
106-520: A molecular clock analysis estimating the split around 27 million years ago. Molecular dating estimates that the divergence between Aepyornithidae and Mullerornithidae occurred approximately 30 Ma, close to the Eocene-Oligocene boundary, a period of marked global cooling and faunal turnover in the Northern Hemisphere. Up to 10 or 11 species in the genus Aepyornis have been described, but
159-417: A large (~48%) grazing component to their diets, similar to that of the living Rhea americana , while the other species ( A. maximus , Mullerornis modestus ) were probably browsers . It has been suggested that Aepyornis straightened its legs and brought its torso into an erect position in order to browse higher vegetation. Some rainforest fruits with thick, highly sculptured endocarps , such as that of
212-548: A length of approximately 26–40 centimetres (10–16 in) and a width of 19–25 centimetres (7.5–9.8 in). The largest Aepyornis eggs are on average 3.3 mm ( 1 ⁄ 8 in) thick, with an estimated weight of approximately 10.5 kilograms (23 lb). Eggs of Mullerornis were much smaller, estimated to be only 1.1 mm ( 3 ⁄ 64 in) thick, with a weight of about 0.86 kilograms (1.9 lb). The large size of elephant bird eggs means that they would have required substantial amounts of calcium, which
265-482: A long history of coexistence between elephant birds and humans; however, these conclusions conflict with more commonly accepted evidence of a much shorter history of human presence on the island and remain controversial. The oldest securely dated evidence for humans on Madagascar dates to the mid-first millennium AD. A 2021 study suggested that elephant birds, along with the Malagasy hippopotamus species, became extinct in
318-598: A result of human activity. Elephant birds comprised three species, one in the genus Mullerornis , and two in Aepyornis . Aepyornis maximus is possibly the largest bird to have ever lived, with their eggs being the largest known for any amniote . Elephant birds are palaeognaths (whose flightless representatives are often known as ratites ), and their closest living relatives are kiwi (found only in New Zealand), suggesting that ratites did not diversify by vicariance during
371-495: 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. hildebrandti , suggesting that the former occupied forested habitats where the sense of smell is more useful while the latter occupied open habitats. A 2022 isotope analysis study suggested that some specimens of Aepyornis hildebrandti were mixed feeders that had
424-529: Is driven by the strong westerly winds in the latitudes of the Southern Ocean. In latitudes where there are continents, winds blowing on light surface water can simply pile up light water against these continents. But in the Southern Ocean, the momentum imparted to the surface waters cannot be offset in this way. There are different theories on how the Circumpolar Current balances the momentum imparted by
477-428: Is known from an intact egg, around 80–90% of the way through incubation before it died. This skeleton shows that even at this early ontogenetic stage that the skeleton was robust, much more so than comparable hatchling ostriches or rheas, which may suggest that hatchlings were precocial . The eggs of Aepyornis are the largest known for any amniote , and have a volume of around 5.6–13 litres (12–27 US pt),
530-455: Is little evidence of human hunting of elephant birds. Humans may have utilized elephant bird eggs. Introduced diseases ( hyperdisease ) have been proposed as a cause of extinction, but the plausibility for this is weakened due to the evidence of centuries of overlap between humans and elephant birds on Madagascar. Antarctic Circumpolar Current Antarctic Circumpolar Current ( ACC ) is an ocean current that flows clockwise (as seen from
583-644: Is mostly due to the prevailing westerly winds . Jack London 's story "Make Westing" and the circumstances preceding the mutiny on the Bounty poignantly illustrate the difficulty it caused for mariners seeking to round Cape Horn westbound on the clipper ship route from New York to California. The eastbound clipper route , which is the fastest sailing route around the world, follows the ACC around three continental capes – Cape Agulhas (Africa), South East Cape (Australia), and Cape Horn (South America). The current creates
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#1733105172125636-570: Is reported to have opened to water circulation 33.5 million years ago (Ma). The timing of the opening of the Drake Passage, between South America and the Antarctic Peninsula, is more disputed; tectonic and sediment evidence show that it could have been open as early as pre-34 Ma, estimates of the opening of the Drake passage are between 20 and 40 Ma. The isolation of Antarctica by
689-416: Is the smallest of the elephant birds, with a body mass of around 80 kilograms (180 lb), with its skeleton much less robustly built than Aepyornis . A. hildebrandti is thought to have had a body mass of around 230–285 kilograms (507–628 lb). Estimates of the body mass of Aepyornis maximus span from around 275 kilograms (606 lb) to 700–1,000 kilograms (1,500–2,200 lb) making it one of
742-403: Is usually taken from a reservoir in the medullary bone in the femurs of female birds. Possible remnants of this tissue have been described from the femurs of A. maximus. It is widely believed that the extinction of elephant birds was a result of human activity. The birds were initially widespread, occurring from the northern to the southern tip of Madagascar . The late Holocene also witnessed
795-624: The Kerguelen Islands , and an ostrich egg found floating in the Timor Sea in the early 1990s. Like the ostrich , rhea , cassowary , emu , kiwi and extinct moa , elephant birds were ratites; they could not fly, and their breast bones had no keel . Because Madagascar and Africa separated before the ratite lineage arose, elephant birds has been thought to have dispersed and become flightless and gigantic in situ . More recently, it has been deduced from DNA sequence comparisons that
848-653: The Macquarie Ridge south of New Zealand. The ACC varies with time. Evidence of this is the Antarctic Circumpolar Wave , a periodic oscillation that affects the climate of much of the southern hemisphere. There is also the Antarctic oscillation , which involves changes in the location and strength of Antarctic winds. Trends in the Antarctic Oscillation have been hypothesized to account for an increase in
901-677: The Ross and Weddell Gyres . The ACC connects the Atlantic , Pacific , and Indian Oceans, and serves as a principal pathway of exchange among them. The current is strongly constrained by landform and bathymetric features. To trace it starting arbitrarily at South America, it flows through the Drake Passage between South America and the Antarctic Peninsula and then is split by the Scotia Arc to
954-680: The mid-ocean ridge in the Southeast Pacific. The current is accompanied by three fronts : the Subantarctic front (SAF), the Polar front (PF), and the Southern ACC front (SACC). Furthermore, the waters of the Southern Ocean are separated from the warmer and saltier subtropical waters by the subtropical front (STF). The northern boundary of the ACC is defined by the northern edge of the SAF, this being
1007-632: 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." There has been speculation, especially popular in the latter half of the 19th century, that the legendary roc from the accounts of Marco Polo was ultimately based on elephant birds, but this is disputed. Between 1830 and 1840, European travelers in Madagascar saw giant eggs and eggshells. British observers were more willing to believe
1060-692: The 1930s (the Scott River egg) and one in 1992 (the Cervantes egg); both have been identified as Aepyornis maximus rather than Genyornis newtoni , an extinct giant bird known from the Pleistocene of Australia. 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 may have originated in
1113-547: The Aepyornithiformes, with the latter placed into Mullerornithidae. Elephant birds were large sized birds (the largest reaching 3 metres (9.8 ft) tall in normal standing posture) that had vestigial wings, long legs and necks, with small heads relative to body size, which bore straight, thick conical beaks that were not hooked. The tops of elephant bird skulls display punctuated marks, which may have been attachment sites for fleshy structures or head feathers. Mullerornis
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#17331051721251166-614: The Circumpolar Current is the Antarctic Convergence , where the cold Antarctic waters meet the warmer waters of the subantarctic , creating a zone of upwelling nutrients. These nurture high levels of phytoplankton with associated copepods and krill , and resultant food chains supporting fish, whales, seals , penguins, albatrosses , and a wealth of other species . The ACC has been known to sailors for centuries; it greatly speeds up any travel from west to east, but makes sailing extremely difficult from east to west, although this
1219-415: The Circumpolar Current may directly transport momentum downward in the water column. This is because such flows can produce a net southward flow in the troughs and a net northward flow over the ridges without requiring any transformation of density. In practice both the thermohaline and the eddy/meander mechanisms are likely to be important. The current flows at a rate of about 4 km/h (2.5 mph) over
1272-758: 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. Complete mitochondrial genomes obtained from elephant birds eggshells suggest that Aepyornis and Mullerornis are significantly genetically divergent from each other, with
1325-711: The South Pole) from west to east around Antarctica . An alternative name for the ACC is the West Wind Drift . The ACC is the dominant circulation feature of the Southern Ocean and has a mean transport estimated at 100–150 Sverdrups (Sv, million m /s), or possibly even higher, making it the largest ocean current. The current is circumpolar due to the lack of any landmass connecting with Antarctica and this keeps warm ocean waters away from Antarctica, enabling that continent to maintain its huge ice sheet . Associated with
1378-470: The Southern Ocean, transformation of these waters into light surface waters, and a transformation of waters in the opposite direction to the north. Such theories link the magnitude of the Circumpolar Current with the global thermohaline circulation , particularly the properties of the North Atlantic. Alternatively, ocean eddies , the oceanic equivalent of atmospheric storms, or the large-scale meanders of
1431-632: The accounts of giant birds and eggs because they knew of the moa in New Zealand. In 1851 the genus Aepyornis and species A. maximus were scientifically described in a paper presented to the Paris Academy of Sciences by Isidore Geoffroy Saint-Hilaire , based on bones and eggs recently obtained from the island, which resulted in wide coverage in the popular presses of the time, particularly due to their very large eggs. Two whole eggs have been found in dune deposits in southern Western Australia , one in
1484-459: The amount of sea ice is lowest, and in August–September the sea ice is at its greatest extent. Ice levels have been monitored by satellite since 1973. Upwelling of deep water under the sea ice brings substantial amounts of nutrients. As the ice melts, the melt water provides stability and the critical depth is well below the mixing depth, which allows for a positive net primary production . As
1537-585: The animal was still extant at the end of the first millennium. Aepyornis modestus was shown by Hansford and Turvey (2018) to be a senior synonym of all nominal Mullerornis species described by Milne-Edwards and Grandidier (1894), resulting in the new combination Mullerornis modestus . Like other elephant birds and its kiwi relatives, Mullerornis probably was nocturnal based on the small size of its optic lobes, though it shows less optical lobe reduction than these other taxa, implying slightly more crepuscular habits. Isotopic evidence suggests that Mullerornis
1590-462: The breakup of Gondwana but instead convergently evolved flightlessness from ancestors that dispersed more recently by flying. Elephant birds have been extinct since at least the 17th century. Étienne de Flacourt , a French governor of Madagascar during the 1640s and 1650s, mentioned an ostrich-like bird, said to inhabit unpopulated regions, although it is unclear whether he was repeating folk tales from generations earlier. In 1659, Flacourt wrote of
1643-712: The closest living relatives of elephant birds are New Zealand kiwi , though the split between the two groups is deep, with the two lineages being estimated to have diverged from each other around 54 million years ago. Placement of Elephant birds within Palaeognathae, after: Struthionidae (ostriches) Rheidae (rheas) Tinamidae (tinamou) † Dinornithiformes (moa) Apterygidae (kiwis) † Aepyornithiformes (elephant birds) Casuariiformes (emu, cassowary) The ancestors of elephant birds are thought to have arrived in Madagascar well after Gondwana broke apart. The existence of possible flying palaeognathae in
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1696-418: The continent. Diatom production continues through the summer, and populations of krill are sustained, bringing large numbers of cetaceans , cephalopods , seals, birds, and fish to the area. Phytoplankton blooms are believed to be limited by irradiance in the austral (southern hemisphere) spring, and by biologically available iron in the summer. Much of the biology in the area occurs along the major fronts of
1749-568: The current is credited by many researchers with causing the glaciation of Antarctica and global cooling in the Eocene epoch. Oceanic models have shown that the opening of these two passages limited polar heat convergence and caused a cooling of sea surface temperatures by several degrees; other models have shown that CO 2 levels also played a significant role in the glaciation of Antarctica. Antarctic sea ice cycles seasonally, in February–March
1802-511: The current, the Subtropical, Subantarctic, and the Antarctic Polar fronts, these are areas associated with well defined temperature changes. Size and distribution of phytoplankton are also related to fronts. Microphytoplankton (>20 μm) are found at fronts and at sea ice boundaries, while nanophytoplankton (<20 μm) are found between fronts. Studies of phytoplankton stocks in
1855-552: The currently undispersed and highly threatened forest coconut palm ( Voanioala gerardii ), may have been adapted for passage through ratite guts and consumed by elephant birds, 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, suggesting that they too may have been eaten by elephant birds. Elephant birds are suggested to have grown in periodic spurts rather than having continuous growth. An embryonic skeleton of Aepyornis
1908-762: The east, with a shallow warm branch flowing to the north in the Falkland Current and a deeper branch passing through the Arc more to the east before also turning to the north. Passing through the Indian Ocean, the current first retroflects the Agulhas Current to form the Agulhas Return Current before it is split by the Kerguelen Plateau , and then moving northward again. Deflection is also seen as it passes over
1961-494: The extinction of other Malagasy animals, including several species of Malagasy hippopotamus , two species of giant tortoise ( Aldabrachelys abrupta and Aldabrachelys grandidieri ), the giant fossa , over a dozen species of giant lemurs , the aardvark-like animal Plesiorycteropus , and the crocodile Voay . Several elephant bird bones with incisions have been dated to approximately 10,000 BC which some authors suggest are cut marks, which have been proposed as evidence of
2014-414: The front. Some research has been conducted on Antarctic phytoplankton as a carbon sink . Areas of open water left from ice melt are good areas for phytoplankton blooms. The phytoplankton takes carbon from the atmosphere during photosynthesis. As the blooms die and sink, the carbon can be stored in sediments for thousands of years. This natural carbon sink is estimated to remove 3.5 million tonnes from
2067-618: The global extra-tropical circulation at ≈ 10^4 kilometers". The current helps preserve wooden shipwrecks by preventing wood-boring " ship worms " from reaching targets such as Ernest Shackleton 's ship, the Endurance . The "State of the cryosphere" report found, that the Antarctic Circumpolar Current became weaker. By 2050 it expected to lose 20% of its strenght with "widespread impacts on ocean circulation and climate." The Weddell Sea Bottom Water has lost 30% of its volume in
2120-515: The interval 800-1050 AD (1150–900 years Before Present ), based on the timing of the latest radiocarbon dates. The timing of the youngest radiocarbon dates co-incided with major environmental alteration across Madagascar by humans changing forest into grassland, probably for cattle pastoralism , with the environmental change likely being induced by the use of fire. This reduction of forested area may have had cascade effects, like making elephant birds more likely to be encountered by hunters, though there
2173-409: The largest birds ever, alongside Dromornis stirtoni and Pachystruthio dmanisensis . Females of A. maximus are suggested to have been larger than the males, as is observed in other ratites. Examination of brain endocasts has shown that both A. maximus and A. hildebrandti had greatly reduced optic lobes , similar to those of their closest living relatives, the kiwis, and consistent with
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2226-481: The latest 32 years, and the Antarctic Bottom Water is expected to shrunk. This will impact ocean circulation, nutrients, heat content and carbon sequestration. UNESCO mentions that the report in the first time "notes a growing scientific consensus that melting Greenland and Antarctic ice sheets, among other factors, may be slowing important ocean currents at both poles, with potentially dire consequences for
2279-509: The most northerly water to pass through Drake Passage and therefore be circumpolar. Much of the ACC transport is carried in this front, which is defined as the latitude at which a subsurface salinity minimum or a thick layer of unstratified Subantarctic mode water first appears, allowed by temperature dominating density stratification. Still further south lies the PF, which is marked by a transition to very cold, relatively fresh, Antarctic Surface Water at
2332-461: The ocean each year. 3.5 million tonnes of carbon taken from the ocean and atmosphere is equivalent to 12.8 million tonnes of carbon dioxide. An expedition in May 2008 by 19 scientists studied the geology and biology of eight Macquarie Ridge sea mounts, as well as the Antarctic Circumpolar Current to investigate the effects of climate change of the Southern Ocean. The circumpolar current merges
2385-400: The sea ice recedes epontic algae dominate the first phase of the bloom, and a strong bloom dominate by diatoms follows the ice melt south. Another phytoplankton bloom occurs more to the north near the Antarctic Convergence , here nutrients are present from thermohaline circulation . Phytoplankton blooms are dominated by diatoms and grazed by copepods in the open ocean, and by krill closer to
2438-576: The southern sea have shown that the Antarctic Circumpolar Current is dominated by diatoms, while the Weddell Sea has abundant coccolithophorids and silicoflagellates. Surveys of the SW Indian Ocean have shown phytoplankton group variation based on their location relative to the Polar Front, with diatoms dominating South of the front, and dinoflagellates and flagellates in higher populations North of
2491-518: The surface. Here a temperature minimum is allowed by salinity dominating density stratification, due to the lower temperatures. Farther south still is the SACC, which is determined as the southernmost extent of Circumpolar deep water (temperature of about 2 °C at 400 m). This water mass flows along the shelfbreak of the western Antarctic Peninsula and thus marks the most southerly water flowing through Drake Passage and therefore circumpolar. The bulk of
2544-434: The transport is carried in the middle two fronts. The total transport of the ACC at Drake Passage is estimated to be around 135 Sv, or about 135 times the transport of all the world's rivers combined. There is a relatively small addition of flow in the Indian Ocean, with the transport south of Tasmania reaching around 147 Sv, at which point the current is probably the largest on the planet. The circumpolar current
2597-486: The transport of the Circumpolar Current over the past two decades. Published estimates of the onset of the Antarctic Circumpolar Current vary, but it is commonly considered to have started at the Eocene / Oligocene boundary. The isolation of Antarctica and formation of the ACC occurred with the openings of the Tasmanian Passage and the Drake Passage . The Tasmanian Seaway separates East Antarctica and Australia, and
2650-577: 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 . Recent work has restricted the number of elephant bird species to three, with two in Aepyornis , one in Mullerornis . All elephant birds are usually placed in the single family Aepyornithidae, but some authors suggest Aepyornis and Mullerornis should be placed in separate families within
2703-520: The waters of the Atlantic, Indian, and Pacific Oceans and carries up to 150 times the volume of water flowing in all of the world's rivers. The study found that any damage on the cold-water corals nourished by the current will have a long-lasting effect. After studying the circumpolar current it is clear that it strongly influences regional and global climate as well as underwater biodiversity. The subject has been characterized recently as "the spectral peak of
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#17331051721252756-548: The winds. The increasing eastward momentum imparted by the winds causes water parcels to drift outward from the axis of the Earth's rotation (in other words, northward) as a result of the Coriolis force . This northward Ekman transport is balanced by a southward, pressure-driven flow below the depths of the major ridge systems. Some theories connect these flows directly, implying that there is significant upwelling of dense deep waters within
2809-474: Was likely a browsing herbivore. The eggs of Mullerornis are substantially smaller than those of Aepyornis , weighting approximately 0.86 kilograms (1.9 lb), with a shell thickness of about 1.1 mm ( 3 ⁄ 64 in). Elephant bird Elephant birds are extinct flightless birds belonging to the order Aepyornithiformes that were native to the island of Madagascar . They are thought to have become extinct around 1000 AD, likely as
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