Misplaced Pages

#777222

60-556: Ostriches are large flightless birds . Two living species are recognised, the common ostrich , native to large areas of sub-Saharan Africa , and the Somali ostrich , native to the Horn of Africa . They are the heaviest and largest living birds, with adult common ostriches weighing anywhere between 63.5 and 145 kilograms and laying the largest eggs of any living land animal. With the ability to run at 70 km/h (43.5 mph), they are

120-864: A claimed territory selected for large size and cursoriality in Tertiary ancestors of ratites. Temperate rainforests dried out throughout the Miocene and transformed into semiarid deserts, causing habitats to be widely spread across the growingly disparate landmasses. Cursoriality was an economic means of traveling long distances to acquire food that was usually low-lying vegetation, more easily accessed by walking. Traces of these events are reflected in ratite distribution throughout semiarid grasslands and deserts today. Gigantism and flightlessness in birds are almost exclusively correlated due to islands lacking mammalian or reptilian predators and competition. However, ratites occupy environments that are mostly occupied by

180-620: A developing divergent tectonic plate boundary where the African plate is in the process of splitting into two tectonic plates, called the Somali plate and the Nubian plate , at a rate of 6–7 mm (0.24–0.28 in) per year. The rift system consists of three microplates, the Victoria microplate to the north, and the Rovuma and Lwandle microplates to the south. The Victoria microplate

240-412: A diverse number of mammals. It is thought that they first originated through allopatric speciation caused by breakup of the supercontinent Gondwana . However, later evidence suggests this hypothesis first proposed by Joel Cracraft in 1974 is incorrect. Rather ratites arrived in their respective locations via a flighted ancestor and lost the ability to fly multiple times within the lineage. Gigantism

300-414: A feedback with one another, controlled by oblique rifting conditions. According to this theory, lithospheric thinning generates volcanic activity, further increasing magmatic processes such as intrusions and numerous small plumes. These processes further thin the lithosphere in saturated areas, making the thinning lithosphere behave like a mid-ocean ridge . According to marine geologist Kathleen Crane ,

360-402: A greater extreme, the terror birds (and their relatives the bathornithids ), eogruids , geranoidids , gastornithiforms , and dromornithids (all extinct) all evolved similar body shapes – long legs, long necks and big heads – but none of them were closely related. Furthermore, they also share traits of being giant, flightless birds with vestigial wings, long legs, and long necks with some of

420-502: A limited number of times per year. High parental involvement denotes the necessity for choosing a reliable mate. In a climatically stable habitat providing year-round food supply, a male's claimed territory signals to females the abundance of resources readily available to her and her offspring. Male size also indicates his protective abilities. Similar to the emperor penguin, male ratites incubate and protect their offspring anywhere between 85 and 92 days while females feed. They can go up to

480-466: A more efficient use of energy in adulthood. The name "ratite" comes from the Latin ratis , raft, a vessel with no keel . Their flat sternum is distinct from the typical sternum of flighted birds because it lacks a keel, like a raft. This structure is the place where flight muscles attach and thus allow for powered flight. However, ratite anatomy presents other primitive characters meant for flight, such as

540-649: A number of active and dormant volcanoes, among them: Mount Kilimanjaro , Mount Kenya , Mount Longonot , Menengai Crater, Mount Karisimbi , Mount Nyiragongo , Mount Meru and Mount Elgon , as well as the Crater Highlands in Tanzania. Although most of these mountains lie outside of the rift valley, the EAR created them. Notable active examples of EAR volcanism include Erta Ale , Dalaffilla (also called Gabuli, Alu-Dalafilla), and Ol Doinyo Lengai . Erta Ale

600-554: A parachute apparatus to help the bird slow down. Wings are hypothesized to have played a role in sexual selection in early ancestral ratites and were thus maintained. This can be seen today in both the rheas and ostriches. These ratites utilize their wings extensively for courtship and displays to other males. Sexual selection also influences the maintenance of large body size, which discourages flight. The large size of ratites leads to greater access to mates and higher reproductive success . Ratites and tinamous are monogamous and mate only

660-401: A pre-Cambrian weakness in the crust, a suture zone of multiple cratons , displacement along large boundary faults, and the development of deep asymmetric basins. The second stage of rifting was characterized by the deactivation of large boundary faults, the development of internal fault segments, and the concentration of magmatic activity towards the rifts. Today, the narrow rift segments of

SECTION 10

#1732781022778

720-408: A result of selective breeding ; the birds were bred to grow massive breast meat that weighs too much for the bird's wings to support in flight. Flightlessness has evolved in many different birds independently, demonstrating repeated convergent evolution. There were families of flightless birds, such as the now-extinct Phorusrhacidae , that evolved to be powerful terrestrial predators. Taking this to

780-416: A week without eating and survive only off fat stores. The emu has been documented fasting for as long as 56 days. If no continued pressures warrant the energy expenditure to maintain the structures of flight, selection will tend towards these other traits. In penguins , wing structure is maintained for use in locomotion underwater. Penguins evolved their wing structure to become more efficient underwater at

840-469: A west-facing scarp (east-plunging arch) along the southern half of its length that rises to 2,300 m (7,500 ft) above the sea floor. Its movement is concurrent with the EAR. Over time, many theories have tried to clarify the evolution of the East African Rift. In 1972 it was proposed that the EAR was not caused by tectonic activity, but rather by differences in crustal density. Since

900-795: Is a basaltic shield volcano in the Afar Region of northeastern Ethiopia, active continuously since at least 1967, with a summit lava lake documented since at least 1906. The 2008 eruption of Dalafilla, its only documented activity since the start of the Holocene , is the largest recorded eruption in Ethiopian history. Ol Doinyo Lengai is currently the only active natrocarbonatite volcano on Earth. Its magma contains almost no silica; typical lava flows have viscosities of less than 100 Pa⋅s, comparable to olive oil at 26 °C (79 °F). EAR-related volcanic structures with dated activity since

960-447: Is a suitable tool to investigate Earth's subsurface structures deeper than the crust. It is an inverse problem technique that models which are the velocities of the inner Earth that reproduce the seismographic data recorded all around the world. Recent improvements of tomographic Earth models of P wave and S wave velocities suggest that a superplume upwelling from the lower mantle at the northeastern EAR feeds plumes of smaller scale into

1020-552: Is another product that is made using ostrich fat. Ostriches are of the genus Struthio in the order Struthioniformes , part of the infra-class Palaeognathae , a diverse group of flightless birds also known as ratites that includes the emus , rheas , cassowaries , kiwis and the extinct elephant birds and moas . The common ostrich was historically native to the Arabian Peninsula , and ostriches were present across Asia as far east as China and Mongolia during

1080-531: Is contentious and in need of revision pending more good material. The species are: Flightless Many domesticated birds, such as the domestic chicken and domestic duck , have lost the ability to fly for extended periods, although their ancestral species, the red junglefowl and mallard , respectively, are capable of extended flight. A few particularly bred birds, such as the Broad Breasted White turkey , have become totally flightless as

1140-578: Is generally cool and strong. Many cratons are found throughout the EAR, such as the Tanzania and Kaapvaal cratons . The cratons are thick, and have survived for billions of years with little tectonic activity. They are characterized by greenstone belts , tonalites , and other high-grade metamorphic lithologies. The cratons are of significant importance in terms of mineral resources , with major deposits of gold, antimony, iron, chromium and nickel. A large volume of continental flood basalts erupted during

1200-416: Is likely because penguins have well-developed pectoral muscles for hunting and diving in the water. For ground-feeding birds, a cursorial lifestyle is more economical and allows for easier access to dietary requirements. Flying birds have different wing and feather structures that make flying easier, while flightless birds' wing structures are well adapted to their environment and activities, such as diving in

1260-411: Is not a requirement for flightlessness. The kiwi do not exhibit gigantism, along with tinamous , even though they coexisted with the moa and rheas that both exhibit gigantism. This could be the result of different ancestral flighted birds arrival or because of competitive exclusion. The first flightless bird to arrive in each environment utilized the large flightless herbivore or omnivore niche, forcing

SECTION 20

#1732781022778

1320-431: Is often why flightlessness coincides with body mass. By reducing large pectoral muscles that require a significant amount of overall metabolic energy, ratites decrease their basal metabolic rate and conserve energy. A study looking at the basal rates of birds found a significant correlation between low basal rate and pectoral muscle mass in kiwis. On the contrary, flightless penguins exhibit an intermediate basal rate. This

1380-780: Is rotating anti-clockwise with respect to the African plate. Its rotation is caused by the configuration of mechanically weaker and stronger lithospheric regions in the EARS. Many of the African Great Lakes lie within the Rift Valley. A series of distinct rift basins, the East African Rift System extends over thousands of kilometers. North of the Afar triple junction, the rift follows two paths: west to

1440-491: Is that until the arrival of humans roughly a thousand years ago, there were no large mammalian land predators in New Zealand; the main predators of flightless birds were larger birds. Ratites belong to the superorder Palaeognathae , which include the volant tinamou , and are believed to have evolved flightlessness independently multiple times within their own group. Some birds evolved flightlessness in response to

1500-677: The Albertine Rift , and farther south, the valley of Lake Malawi . The rift also continues offshore from the coast of Mozambique along the Kerimba and Lacerda grabens , which are joined by the Davie Ridge, a 2,200 km-long (1,400 mi) relic fracture zone that cuts across the West Somali basin, straddling the boundary between Tanzania and Mozambique. The Davie Ridge ranges between 30–120 km (19–75 mi) wide, with

1560-558: The Ethiopian Highlands and the Kenya Highlands are hotspots of higher rainfall amid the semi-arid to arid lowlands of East Africa. Lakes which form within the rift, including Lake Victoria , have a large effect on regional climate. They are a source of water vapour, and also lead to the formation of lake breeze systems , which affect weather across large areas of East Africa. The east to west river valleys within

1620-600: The Holocene (no more than 11,000 years ago). Extinct species are indicated with a cross (†). A number of species suspected, but not confirmed to be flightless, are also included here. Longer-extinct groups of flightless birds include the Cretaceous patagopterygiformes , hesperornithids , the Cenozoic phorusrhacids ("terror birds") and related bathornithids , the unrelated eogruids , geranoidids , gastornithiforms , and dromornithids (mihirungs or "demon ducks"), and

1680-501: The Late Pleistocene and possibly into the Holocene . The genus Struthio was first described by Carl Linnaeus in 1758. The genus was used by Linnaeus and other early taxonomists to include the emu , rhea , and cassowary , until they each were placed in their own genera. The Somali ostrich ( Struthio molybdophanes ) has recently become recognized as a separate species by most authorities, while others are still reviewing

1740-641: The Oligocene , with the majority of the volcanism coinciding with the opening of the Red Sea and the Gulf of Aden approximately 30 Ma. The composition of the volcanics are a continuum of ultra-alkaline to tholeiitic and felsic rocks. It has been suggested that the diversity of the compositions could be partially explained by different mantle source regions. The EAR also cuts through old sedimentary rocks deposited in ancient basins. The East African Rift Zone includes

1800-837: The Red Sea Rift and east to the Aden Ridge in the Gulf of Aden . Southward from the Afar triple junction , the EAR consists of two main branches. The Eastern Rift Valley (also known as Gregory Rift ) includes the Main Ethiopian Rift , runs southward from the Afar triple junction, and continues south as the Kenyan Rift Valley, then transects Congo DR , Uganda , Rwanda , Burundi , Zambia , Tanzania , Malawi and Mozambique . The Western Rift Valley includes

1860-512: The plotopterids . East African Rift The East African Rift ( EAR ) or East African Rift System ( EARS ) is an active continental rift zone in East Africa . The EAR began developing around the onset of the Miocene , 22–25 million years ago. It was formerly considered to be part of a larger Great Rift Valley that extended north to Asia Minor . A narrow zone, the rift is

Ostrich - Misplaced Pages Continue

1920-482: The upper mantle . Parallel to geological and geophysical measures (e.g. isotope ratios and seismic velocities) it is constructive to test hypotheses on computer based geodynamical models. A 3D numerical geodynamic model of the plume-crust coupling was capable of reproducing the lateral asymmetry of the EAR around the Tanzania craton . Numerical modeling of plume-induced continental break-up shows two distinct stages, crustal rifting followed by lithospheric breakup, and

1980-459: The 1990s, evidence has been found in favor of mantle plumes beneath the EAR. Others proposed an African superplume causing mantle deformation. Although the effects of deep-rooted mantle plumes are an important hypothesis, their location and dynamics are poorly understood, and a matter of active research. The question is still debated. The most recent and accepted view is the theory put forth in 2009: that magmatism and plate tectonics have

2040-488: The African fossil species is comparatively straightforward, many Asian species of ostrich have been described from fragmentary remains, and their interrelationships and how they relate to the African ostriches are confusing. In India, Mongolia and China , ostriches are known to have become extinct only around, or even after, the end of the last ice age ; images of ostriches have been found prehistoric Chinese pottery and petroglyphs . Today, ostriches are only found natively in

2100-472: The East African Rift system form zones of localized strain. These rifts are the result of the actions of numerous normal faults which are typical of all tectonic rift zones. As aforementioned, voluminous magmatism and continental flood basalts characterize some of the rift segments, while other segments, such as the Western branch, have only very small volumes of volcanic rock. The African continental crust

2160-614: The Somali Jet) in the western Indian Ocean . The Somali Jet supplies water vapour for the high rainfall during the Indian Monsoon and is responsible for roughly half the global cross-equatorial atmospheric mass flux in the lower-branch of Hadley Circulation . The Rift Valley in East Africa has been a rich source of hominid fossils that allow the study of human evolution. The rapidly eroding highlands quickly filled

2220-642: The Somali ostrich, but they are kept from interbreeding by behavioral and ecological differences. The Arabian ostriches in Asia Minor and Arabia were hunted to extinction by the middle of the 20th century, and in Israel attempts to introduce North African ostriches to fill their ecological role have failed. Escaped common ostriches in Australia have established feral populations. In 2008, S. linxiaensis

2280-413: The ability to fly. They are, however, weak fliers and are incapable of traveling long distances by air. Although selection pressure for flight was largely absent, the wing structure has not been lost except in the New Zealand moas. Ostriches are the fastest running birds in the world and emus have been documented running 50 km/h. At these high speeds, wings are necessary for balance and serving as

2340-404: The absence of predators, for example on oceanic islands . Incongruences between ratite phylogeny and Gondwana geological history indicate the presence of ratites in their current locations is the result of a secondary invasion by flying birds. It remains possible that the most recent common ancestor of ratites was flightless and the tinamou regained the ability to fly. However, it is believed that

2400-453: The cost of their efficiency in the air. The only known species of flightless bird in which wings completely disappeared was the gigantic, herbivorous moa of New Zealand , hunted to extinction by humans by the 15th century. In moa, the entire pectoral girdle is reduced to a paired scapulocoracoid , which is the size of a finger. Many flightless birds are extinct ; this list shows species that are either still extant or became extinct in

2460-786: The evidence. Struthionidae is a member of the Struthioniformes , a group of paleognath birds which first appeared during the Early Eocene , and includes a variety of flightless forms which were present across the Northern Hemisphere (Europe, Asia and North America) during the Eocene epoch. The closest relatives of Struthionidae within the Struthioniformes are the Ergilornithidae , known from

Ostrich - Misplaced Pages Continue

2520-473: The evolution of flightlessness hypothesized intraspecific competition selected for a reduced individual energy expenditure, which is achieved by the loss of flight. Some flightless varieties of island birds are closely related to flying varieties, implying flight is a significant biological cost . Flight is the most costly type of locomotion exemplified in the natural world. The energy expenditure required for flight increases proportionally with body size, which

2580-575: The fastest birds on land. They are farmed worldwide, with significant industries in the Philippines and in Namibia . South Africa produces about 70% of global ostrich products, with the industry largely centered around the town of Oudtshoorn . Ostrich leather is a lucrative commodity, and the large feathers are used as plumes for the decoration of ceremonial headgear. Ostrich eggs and meat have been used by humans for millennia. Ostrich oil

2640-402: The fusion of wing elements, a cerebellar structure, the presence of a pygostyle for tail feathers, and an alula on the wing. These morphological traits suggest some affinities to volant groups. Palaeognathes were one of the first colonizers of novel niches and were free to increase in abundance until the population was limited by food and territory. A study looking at energy conservation and

2700-512: The late Eocene to early Pliocene of Asia. It is therefore most likely that Struthionidae originated in Asia. The earliest fossils of the genus Struthio are from the early Miocene ~21 million years ago of Namibia in Africa, so it is proposed that genus is of African origin. By the middle to late Miocene (5–13 mya) they had spread to and become widespread across Eurasia. While the relationship of

2760-510: The later arrivals to remain smaller. In environments where flightless birds are not present, it is possible that after the K/T Boundary there were no niches for them to fill. They were pushed out by other herbivorous mammals . New Zealand had more species of flightless birds (including the kiwi , several species of penguins , the takahē , the weka , the moa, and several other extinct species ) than any other such location. One reason

2820-475: The loss of flight is an easier transition for birds than the loss and regain of flight, which has never been documented in avian history. Moreover, tinamou nesting within flightless ratites indicates ancestral ratites were volant and multiple losses of flight occurred independently throughout the lineage. This indicates that the distinctive flightless nature of ratites is the result of convergent evolution. Two key differences between flying and flightless birds are

2880-430: The ocean. Species with certain characteristics are more likely to evolve flightlessness. For example, species that already have shorter wings are more likely to lose flight ability. Some species will evolve flatter wings so that they move more efficiently underwater at the cost of their flight. Additionally, birds that undergo simultaneous wing molt, in which they replace all of the feathers in their wings at once during

2940-671: The onset of the Holocene include approximately 50 in Ethiopia, 17 in Kenya , and 9 in Tanzania . The EAR is the largest seismically active rift system on Earth today. The majority of earthquakes occur near the Afar Depression, with the largest typically occurring along or near major border faults. Seismic events in the past century are estimated to have reached a maximum moment magnitude of 7.0. The seismicity trends parallel to

3000-642: The ratites, although they are not related. Divergences and losses of flight within ratite lineage occurred right after the K-Pg extinction event wiped out all non-avian dinosaurs and large vertebrates 66 million years ago. The immediate evacuation of niches following the mass extinction provided opportunities for Palaeognathes to distribute and occupy novel environments. New ecological influences selectively pressured different taxa to converge on flightless modes of existence by altering them morphologically and behaviorally. The successful acquisition and protection of

3060-488: The rift could eventually cause eastern Africa to separate from the mainland, although this potential event could take tens of millions of years. Studies that contribute to the broader understanding on the evolution of rifts can be grouped into the techniques of isotope geochemistry, seismic tomography and geodynamical modeling. The varying geochemical signatures of a suite of Ethiopian lavas suggest multiple plume sources: at least one of deep mantle origin, and one from within

SECTION 50

#1732781022778

3120-691: The rift system, including the Turkana Channel in northern Kenya and the Zambezi river valley, concentrate low-level easterly winds and accelerate them towards Central Africa . This leaves East Africa drier than it otherwise would be, and also supports the high rainfall in the Congo Basin rainforest . The formation of the east–west valleys could in turn be important for the aridification of East Africa over millions of years. The barrier presented by EARS concentrates monsoonal winds (known as

3180-451: The rift system, with a shallow focal depth of 12–15 km (7.5–9.3 mi) beneath the rift axis. Further away from the rift axis, focal depths can be below 30 km (19 mi). Focal mechanism solutions strike NE and frequently demonstrate normal dip-slip faulting, although left-lateral motion is also observed. The East African Rift system affects regional, continental and even global climate. Regions of higher elevation, including

3240-513: The smaller wing bones of flightless birds and the absent (or greatly reduced) keel on their breastbone, which anchors muscles needed for wing movement. Adapting to a cursorial lifestyle causes two inverse morphological changes to occur in the skeleto-muscular system: the pectoral apparatus used to power flight is paedorphically reduced while peramorphosis leads to enlargement of the pelvic girdle for running. Repeated selection for cursorial traits across ratites suggests these adaptions comprise

3300-411: The subcontinental lithosphere. In accordance, a 2014 study compares the geochemical signature of rare earth isotopes from xenoliths and lava samples collected in the EAR. The results corroborate the coexistence of a superplume "common to the entire rift" with another mantle material source being either of subcontinental type or of mid-ocean ridge type. The geophysical method of seismic tomography

3360-464: The upwelling between stages of an upper mantle plume. Prior to the rift's formation, enormous continental flood basalts erupted, uplifting the Ethiopian , Somali, and East African plateaus. The first stage of rifting of the EAR was characterized by rift localization and magmatism along the entire rift zone. Periods of extension alternated with relative inactivity. There was also the reactivation of

3420-455: The valley with sediments, creating a favorable environment for the preservation of remains. The bones of several hominid ancestors of modern humans have been found here, including those of " Lucy ", a partial australopithecine skeleton discovered by anthropologist Donald Johanson dating back over 3 million years. Richard and Mary Leakey have also done significant work in this region. In 2008, two other hominid ancestors were discovered here:

3480-570: The wild in Africa , where they occur in a range of open arid and semi-arid habitats such as savannas and the Sahel , both north and south of the equatorial forest zone. The Somali ostrich occurs in the Horn of Africa , having evolved isolated from the common ostrich by the geographic barrier of the East African Rift . In some areas, the common ostrich's Masai subspecies occurs alongside

3540-575: The year, are more likely to evolve flight loss. A number of bird species appear to be in the process of losing their powers of flight to various extents. These include the Zapata rail of Cuba , the Okinawa rail of Japan , and the Laysan duck of Hawaii . All of these birds show adaptations common to flightlessness, and evolved recently from fully flighted ancestors, but have not yet completely given up

3600-409: Was transferred to the genus Orientornis . Three additional species, S. pannonicus , S. dmanisensis , and S. transcaucasicus , were transferred to the genus Pachystruthio in 2019. Several additional fossil forms are ichnotaxa (that is, classified according to the organism's trace fossils such as footprints rather than its body) and their association with those described from distinctive bones

#777222