# Crax

Crax is a genus of curassows 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, 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 crissa (the area around the cloaca). Crax curassows probably originated as a distinct lineage during the Late Miocene. During the Messinian, the ancestral Crax split into two lineages separated by the Colombian Andes and the Cordillera de Mérida 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, 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. The genus name may be based on the Ancient Greek κρας (kras), meaning "head". The type species was designated as the great curassow (Crax rubra) in 1897 by the American ornithologist Robert Ridgway.

### Species

The genus contains 7 species:
Genus Crax – Linnaeus, 1758 – seven species :
| Common name | Scientific name and subspecies | Range | Size and ecology | IUCN status and estimated population |
| Great curassow Male Female | Crax rubra Linnaeus, 1758 Two subspecies C. r. rubra Linnaeus, 1758 C. r. griscomi Nelson, 1926 | eastern Mexico, through Central America to western Colombia and northwestern Ecuador | Size: Habitat: Diet: | VU |
| Blue-billed curassow Male Female | Crax alberti Fraser, 1852 | Colombia | Size: Habitat: Diet: | CR |
| Yellow-knobbed curassow Male Female | Crax daubentoni G.R. Gray, 1867 | Colombia and Venezuela | Size: Habitat: Diet: | NT |
| Wattled curassow Male Female | Crax globulosa Spix, 1825 | western Amazon basin in South America | Size: Habitat: Diet: | EN |
| Red-billed curassow Male Female | Crax blumenbachii Spix, 1825 | Espírito Santo, Bahia and Minas Gerais in southeastern Brazil | Size: Habitat: Diet: | EN |
| Bare-faced curassow Male Female | Crax fasciolata Spix, 1825 Three subspecies C. f. fasciolata (Spix, 1825) C. f. grayi (Ogilvie-Grant, 1893) C. f. pinima (Pelzeln, 1870) | eastern-central and southern Brazil, Paraguay, and eastern Bolivia, and extreme northeast Argentina | Size: Habitat: Diet: | VU |
| Black curassow | Crax alector Linnaeus, 1766 Two subspecies C. a. alector (Linnaeus, 1766) C. a. erythrognatha (PL Sclater and Salvin, 1877) | northern South America in Colombia, Venezuela, the Guianas and far northern Brazil. Introduced to Bahamas, Cuba, Jamaica, Haiti, Dominican Republic, Puerto Rico and Lesser Antilles | Size: Habitat: Diet: | LC |
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, 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 ancestral Crax split into two lineages which are separated by the Colombian Andes and the Cordillera de Mérida which were uplifted around that time, and the Orinoco 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, 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 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 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)