Struthioniformes is an order of birds with only a single extant family, Struthionidae, containing the ostriches. Several other extinct families are known, spanning across the Northern Hemisphere, from the Early
Eocene
The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...
to the early
Pliocene
The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58flightless forms like the Paleotidae, Geranoididae, Eogruidae and Ergilornithidae, the latter two thought to be closely related to Struthionidae.
Evolutionary history
According to Mayr and Zelenkov (2021), all Struthioniformes are united by the following characters: "a very long and narrow tarsometatarsus with short trochleae for the second and fourth toes, a tubercle next to the pons supratendineus on the distal end of the tibiotarsus, as well as a shortening of all non-ungual
phalanges
The phalanges (: phalanx ) are digit (anatomy), digital bones in the hands and foot, feet of most vertebrates. In primates, the Thumb, thumbs and Hallux, big toes have two phalanges while the other Digit (anatomy), digits have three phalanges. ...
of the fourth toe except for the proximal one" All known members of the group are thought to have been flightless. Struthioniformes were widely distributed in the Northern Hemisphere during the
Eocene
The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...
, including Paleotididae from Europe, and Geranoididae from North America, and Eogruidae and Ergilornithidae in Asia. The discovery of ''Lumbreornis'', belonging to either Paleotididae or Geranoididae, suggests that Struthiorniformes probably also inhabited South America during the Eocene. Ergilornthidae would persist in Asia into the Early
Pliocene
The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58Struthionidae likely originated from Asia. Ostriches first appeared in Africa during the early Miocene, around 21 million years ago, before dispersing into Eurasia during the late Miocene, beginning around 12 million years ago.