The first species of Struthio appear during the Miocene epoch, though various Paleocene, Eocene, and Oligocene fossils may also belong to the family.[4][5] Ostriches are classified in the ratite group of birds, all extant species of which are flightless, including the kiwis, emus, and rheas. Traditionally, the order Struthioniformes contained all the ratites. However, recent genetic analysis has found that the group is not monophyletic, as it is paraphyletic with respect to the tinamous, so the ostriches are usually classified as the only members of the order,[6][7] though the IUCN uses a broader classification and includes all "ratites" and tinamous in Struthioniformes.[8]
Evolution
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 the late Eocene to early Pliocene of Asia. It is therefore most likely that Struthionidae originated in Asia.[9] The oldest records of Struthionidae, belonging to the genus Struthio, are from the Early Miocene of Africa, around 21 million years old. Struthio dispersed into and became widespread in Eurasia during the late middle-Late Miocene epoch beginning around 12 million years ago. Pachystruthio from the Late Pliocene of Eurasia contains some of the largest bird species ever with some species likely weighing up to 450 kilograms (990lb).[10]
While the relationship of the African fossil species is comparatively straightforward, many Asian species of ostriches have been described from fragmentary remains, and their interrelationships and how they relate to the African ostriches are confusing. In 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 there on prehistoric pottery and petroglyphs.[11][12][13]
Distribution and habitat
Today ostriches are only found natively in 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.[14] 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 the Somali ostrich, but they are kept from interbreeding by behavioral and ecological differences.[15] 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.[16] Escaped common ostriches in Australia have established feral populations.[17]
Taxonomy
In 2019, the species S. pannonicus, S. dmanisensis (the giant ostrich), and S. transcaucasicus were transferred to the genus Pachystruthio.[18]
Order Struthioniformes Latham 1790 (ostriches)
Family Struthionidae Vigors 1825
Genus †Pachystruthio (Kretzoi 1954) (Late Pliocene – Pleistocene)
Genus Struthio Linnaeus 1758 (Early Miocene – Recent)
Zelenkov, N. V.; Lavrov, A. V.; Startsev, D. B.; Vislobokova, I. A.; Lopatin, A. V. (2019). "A giant early Pleistocene bird from eastern Europe: unexpected component of terrestrial faunas at the time of early Homo arrival". Journal of Vertebrate Paleontology. 39 (2): e1605521. Bibcode:2019JVPal..39E5521Z. doi:10.1080/02724634.2019.1605521. S2CID198384367.
Buffetaut, E.; Angst, D. (November 2014). "Stratigraphic distribution of large flightless birds in the Palaeogene of Europe and its palaeobiological and palaeogeographical implications". Earth-Science Reviews. 138: 394–408. doi:10.1016/j.earscirev.2014.07.001.
Agnolin et al, Unexpected diversity of ratites (Aves, Palaeognathae) in the early Cenozoic of South America: palaeobiogeographical implications Article in Alcheringa An Australasian Journal of Palaeontology · July 2016 DOI: 10.1080/03115518.2016.1184898
Yuri, T. (2013) Parsimony and model-based analyses of indels in avian nuclear genes reveal congruent and incongruent phylogenetic signals. Biology, 2:419–44.
Janz, Lisa; etal. (2009). "Dating North Asian surface assemblages with ostrich eggshell: implications for palaeoecology and extirpation". Journal of Archaeological Science. 36 (9): 1982–1989. Bibcode:2009JArSc..36.1982J. doi:10.1016/j.jas.2009.05.012.
Zelenkov, N. V.; Lavrov, A. V.; Startsev, D. B.; Vislobokova, I. A.; Lopatin, A. V. (2019). "A giant early Pleistocene bird from eastern Europe: unexpected component of terrestrial faunas at the time of early Homo arrival". Journal of Vertebrate Paleontology. 39 (2): e1605521. Bibcode:2019JVPal..39E5521Z. doi:10.1080/02724634.2019.1605521. S2CID198384367.
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