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''Crax'' is a genus of
curassow Curassows are one of the three major groups of cracid birds. They comprise the largest-bodied species of the cracid family. Three of the four genera are restricted to tropical South America; a single species of ''Crax'' ranges north to Mexico. ...
s in the order Galliformes, a clade of large, heavy-bodied, ground-feeding birds. They are known from tropical South America with one species, the
great curassow The great curassow (''Crax rubra'') is a large, pheasant-like bird from the Neotropical rainforests, its range extending from eastern Mexico, through Central America to western Colombia and northwestern Ecuador. Male birds are black with curly cr ...
, ranging northwards through Central America as far as Mexico. The curassows in this genus are noted for their sexual dimorphism; males are more boldly coloured than females and have facial ornamentation such as knobs and wattles. They are also characterised by curly crests and contrastingly-coloured crissums (the area around the
cloaca In animal anatomy, a cloaca ( ), plural cloacae ( or ), is the posterior orifice that serves as the only opening for the digestive, reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles and birds, a ...
). ''Crax'' curassows probably originated as a distinct lineage during the
Late Miocene The Late Miocene (also known as Upper Miocene) is a sub-epoch of the Miocene epoch (geology), Epoch made up of two faunal stage, stages. The Tortonian and Messinian stages comprise the Late Miocene sub-epoch, which lasted from 11.63 Ma (million ye ...
. During the
Messinian The Messinian is in the geologic timescale the last age or uppermost stage of the Miocene. It spans the time between 7.246 ± 0.005 Ma and 5.333 ± 0.005 Ma (million years ago). It follows the Tortonian and is followed by the Zanclean, the first ...
, the ancestral Crax split into two lineages separated by the
Colombian Andes The Andean region, located in central Colombia, is the most populated natural region of Colombia. With many mountains, the Andes contain most of the country's urban centers.Cordillera de Mérida The Cordillera de Mérida is a series of mountain ranges, or massif, in northwestern Venezuela. The Cordillera de Mérida is a northeastern extension of the Andes Mountains and the most important branch of the Venezuelan Andes. The ranges run south ...
which uplifted at that time. The northern lineage radiated into the great, blue-billed, and yellow-knobbed curassows, while the four southern species evolved as they became separated by the uplifting of various mountain ranges.


Characteristics

The variety of male bill ornament shapes and colors is typical for this genus, as is a curly crest and a contrasting white or rufous crissum. ''Crax'' species, even distantly related, readily
hybridize Hybridization (or hybridisation) may refer to: *Hybridization (biology), the process of combining different varieties of organisms to create a hybrid *Orbital hybridization, in chemistry, the mixing of atomic orbitals into new hybrid orbitals *Nu ...
, with fertile offspring theoretically possible in all possible mating combinations


Taxonomy

The genus ''Crax'' was introduced in 1758 by the Swedish naturalist Carl Linnaeus in the tenth edition of his ''
Systema Naturae ' (originally in Latin written ' with the ligature æ) is one of the major works of the Swedish botanist, zoologist and physician Carl Linnaeus (1707–1778) and introduced the Linnaean taxonomy. Although the system, now known as binomial nomen ...
''. The genus name may be based on the Ancient Greek κρας, ''kras'' meaning "head". The type species was designated as the
great curassow The great curassow (''Crax rubra'') is a large, pheasant-like bird from the Neotropical rainforests, its range extending from eastern Mexico, through Central America to western Colombia and northwestern Ecuador. Male birds are black with curly cr ...
(''Crax rubra'') in 1897 by the American ornithologist Robert Ridgway.


Species

The genus contains 7 species: This genus forms one of the two major lineages of curassows. It is distinguishable from its relatives by its pronounced sexual dimorphism (with the exception of the black curassow). In other genera sexual dimorphism is rarely exhibited or of minor appearance ('' Nothocrax'' and '' Pauxi''), or manifest by size only ('' Mitu'').


Evolution

''Crax'' curassows probably originated as a distinct lineage during the Tortonian (Late Miocene), some 10-9
mya Mya may refer to: Brands and product names * Mya (program), an intelligent personal assistant created by Motorola * Mya (TV channel), an Italian Television channel * Midwest Young Artists, a comprehensive youth music program Codes * Burmese ...
, in the western or northwestern Amazonas basin, as indicated by mt and nDNA sequence data calibrated against geological events (Pereira & Baker 2004, Pereira ''et al.'' 2002). Some 6 mya during the
Messinian The Messinian is in the geologic timescale the last age or uppermost stage of the Miocene. It spans the time between 7.246 ± 0.005 Ma and 5.333 ± 0.005 Ma (million years ago). It follows the Tortonian and is followed by the Zanclean, the first ...
, the ancestral ''Crax'' split into two lineages which are separated by the
Colombia Colombia (, ; ), officially the Republic of Colombia, is a country in South America with insular regions in North America—near Nicaragua's Caribbean coast—as well as in the Pacific Ocean. The Colombian mainland is bordered by the Car ...
n Andes and the
Cordillera de Mérida The Cordillera de Mérida is a series of mountain ranges, or massif, in northwestern Venezuela. The Cordillera de Mérida is a northeastern extension of the Andes Mountains and the most important branch of the Venezuelan Andes. The ranges run south ...
which were uplifted around that time, and the
Orinoco The Orinoco () is one of the longest rivers in South America at . Its drainage basin, sometimes known as the Orinoquia, covers , with 76.3 percent of it in Venezuela and the remainder in Colombia. It is the fourth largest river in the wor ...
which consequently assumed its present-day basin. The northern lineage quite soon thereafter radiated into the ancestors of the great, blue-billed, and yellow-knobbed curassows, which were isolated from each other by the uplift of the northern Cordillera Occidental, and the
Serranía del Perijá The Serranía del Perijá, Cordillera de Perijá or Sierra de Perijá is a mountain range, an extension of the eastern Andean branch ( Cordillera Oriental), in northern South America, between Colombia and Venezuela Venezuela (; ), offici ...
, respectively; it is fairly certain that these lineages were well distinct by the end of the Miocene. (Pereira & Baker 2004) The evolution of the 4 southern species was somewhat more complex. In the Messinian, about 6–5.5 mya, the ancestors of the wattled curassow became isolated in the western Amazonas basin. With increasing aridification of southeastern Brazil, the ancestors of the red-billed curassow found refuge in the mountain ranges between the
Brazilian Highlands The Brazilian Highlands or Brazilian Plateau ( pt, Planalto Brasileiro) are an extensive geographical region, covering most of the eastern, southern and central portions of Brazil, in all approximately half of the country's land area, or some 4,5 ...
and the Atlantic during the mid- Zanclean, some 4.5-4 mya. The divergence between the bare-faced and black curassow lineages apparently took place around the Uquian
Ensenadan The Ensenadan age is a period of geologic time (1.2–0.8 Ma) within the Early Pleistocene epoch of the Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the ...
boundary, some 1.5 mya. This which coincides with one or several period(s) of elevated sea levels during which the lower Amazonas basin was a brackish lagoon which offered little curassow habitat. Their present ranges are consequently still separated by the Amazonas river. (Pereira & Baker 2004)


References


Sources

*Pereira, Sérgio Luiz & Baker, Allan J. (2004): Vicariant speciation of curassows (Aves, Cracidae): a hypothesis based on mitochondrial DNA phylogeny. ''
Auk An auk or alcid is a bird of the family Alcidae in the order Charadriiformes. The alcid family includes the murres, guillemots, auklets, puffins, and murrelets. The word "auk" is derived from Icelandic ''álka'', from Old Norse ''alka'' (a ...
'' 121(3): 682–694. nglish with Spanish abstract DOI:10.1642/0004-8038(2004)121 682:VSOCAC.0.CO;2HTML abstractHTML fulltext without images
*Pereira, Sérgio Luiz; Baker, Allan J.& Wajntal, Anita (2002): Combined nuclear and mitochondrial DNA sequences resolve generic relationships within the Cracidae (Galliformes, Aves). ''Systematic Biology'' 51(6): 946–958. PDF fulltext
{{Taxonbar, from=Q869569 Curassows Bird genera Extant Tortonian first appearances