Tinamiformes Ratites (/ˈrætaɪts/) are a polyphyletic group consisting of all birds within the infraclass Palaeognathae that lack keels and cannot fly.

[4][5] The modern bird superorder Palaeognathae consists of ratites and the flighted Neotropic tinamous (compare to Neognathae).

Shorter than an emu, but heavier and solidly built, cassowaries prefer thickly vegetated tropical forest.

In New Guinea, cassowary eggs are brought back to villages and the chicks raised for eating as a much-prized delicacy, despite (or perhaps because of) the risk they pose to life and limb.

They reach up to 1.8 metres (5 ft 11 in) tall and weigh as much as 85 kilograms (187 lb)[18] South America has two species of rhea, large fast-running birds of the Pampas.

They nest in deep burrows and use a highly developed sense of smell to find small insects and grubs in the soil.

Although shorter than the tallest moa, a large A. maximus could weigh over 400 kilograms (880 lb) and stand up to 3 metres (9 ft 10 in) tall.

The longstanding story of ratite evolution was that they share a common flightless ancestor that lived in Gondwana, whose descendants were isolated from each other by continental drift, which carried them to their present locations.

Supporting this idea, some studies based on morphology, immunology and DNA sequencing reported that ratites are monophyletic.

[12][19] Cracraft's 1974 biogeographic vicariance hypothesis suggested that ancestral flightless paleognaths, the ancestors of ratites, were present and widespread in Gondwana during the Late Cretaceous.

[20] The earliest known ratite fossils date to the Paleocene epoch about 56 million years ago (e.g., Diogenornis, a possible early relative of the rhea).

Also, the Middle Eocene ratites such as Palaeotis and Remiornis from Central Europe may imply that the "out-of-Gondwana" hypothesis is oversimplified.

A 2008 study of nuclear genes shows ostriches branching first, followed by rheas and tinamous, then kiwi splitting from emus and cassowaries.

However, the elephant bird–kiwi relation appears to require dispersal across oceans by flight,[9] as apparently does the colonization of New Zealand by the moa and possibly the back-dispersal of tinamous to South America, if the latter occurred.

[28] Kiwi and tinamous are the only palaeognath lineages not to evolve gigantism, perhaps because of competitive exclusion by giant ratites already present on New Zealand and South America when they arrived or arose.

[9] The fact that New Zealand has been the only land mass to recently support two major lineages of flightless ratites may reflect the near total absence of native mammals, which allowed kiwi to occupy a mammal-like nocturnal niche.

[29] However, various other landmasses such as South America and Europe have supported multiple lineages of flightless ratites that evolved independently, undermining this competitive exclusion hypothesis.

[30] Most recently, studies on genetic and morphological divergence and fossil distribution show that paleognaths as a whole probably had an origin in the northern hemisphere.

Early Cenozoic northern hemisphere paleognaths such as Lithornis, Pseudocrypturus, Paracathartes and Palaeotis appear to be the most basal members of the clade.

[16] Loss of flight allows birds to eliminate the costs of maintaining various flight-enabling adaptations like high pectoral muscle mass, hollow bones and a light build, et cetera.

Kiwis are exceptions to this trend, and possess proportionally larger brains comparable to those of parrots and songbirds, though evidence for similar advanced cognitive skills is currently lacking.

[14] Some extinct ratites might have had odder lifestyles, such as the narrow-billed Diogenornis and Palaeotis, compared to the shorebird-like lithornithids, and could imply similar animalivorous diets.

Cassowaries and emu are polyandrous, with males incubating eggs and rearing chicks with no obvious contribution from females.

Kiwis stand out as the exception with extended monogamous reproductive strategies where either the male alone or both sexes incubate a single egg.

[43] Ratites and humans have had a long relationship starting with the use of the egg for water containers, jewelry, or other art medium.

Male ostrich feathers were popular for hats during the 18th century, which led to hunting and sharp declines in populations.

Rhea feathers are popular for dusters, and eggs and meat are used for chicken and pet feed in South America.