Palaeognathae
Paleognaths | |
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Palaeognathae biodiversity.
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Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Aves |
Infraclass: | Palaeognathae Pycraft, 1900 |
Orders | |
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Palaeognathae (
There are three extinct groups that are undisputed members of Palaeognathae: the
The word Paleognath is derived from the ancient Greek for 'old jaws' in reference to the skeletal anatomy of the
Origin and evolution
No unambiguously paleognathous fossil birds are known until the
One study of molecular and paleontological data found that modern bird orders, including the paleognathous ones, began diverging from one another in the Early Cretaceous.[10] Benton (2005) summarized this and other molecular studies as implying that paleognaths should have arisen 110 to 120 million years ago in the Early Cretaceous. He points out, however, that there is no fossil record until 70 million years ago, leaving a 45 million year gap. He asks whether the paleognath fossils will be found one day, or whether the estimated rates of molecular evolution are too slow, and that bird evolution actually accelerated during an adaptive radiation after the Cretaceous–Paleogene boundary (K–Pg boundary).[11]
Other authors questioned the monophyly of the Palaeognathae on various grounds, suggesting that they could be a hodgepodge of unrelated birds that have come to be grouped together because they are coincidentally flightless. Unrelated birds might have developed ratite-like anatomies multiple times around the world through convergent evolution. McDowell (1948) asserted that the similarities in the palate anatomy of paleognaths might actually be neoteny, or retained embryonic features. He noted that there were other features of the skull, such as the retention of sutures into adulthood, that were like those of juvenile birds. Thus, perhaps the characteristic palate was actually a frozen stage that many carinate bird embryos passed through during development. The retention of early developmental stages, then, may have been a mechanism by which various birds became flightless and came to look similar to one another.[12]
Hope (2002) reviewed all known bird fossils from the Mesozoic looking for evidence of the origin of the evolutionary radiation of the
Vegavis is a fossil bird from the Maastrichtian stage of Late Cretaceous Antarctica. Vegavis is most closely related to true ducks. Because virtually all phylogenetic analyses predict that ducks diverged after paleognaths, this is evidence that paleognaths had already arisen well before that time.[14]
An exceptionally preserved specimen of the extinct flying paleognathe
Mysterious large eggs from the Pliocene of Lanzarote in the Canary Islands have been attributed to ratites.[15]
An ambitious genomic analysis of the living birds was performed in 2007, and it contradicted Leonard et al. (2005). It found that tinamous are not primitive within the paleognaths, but among the most advanced. This requires multiple events of flightlessness within the paleognaths and partially refutes the Gondwana vicariance hypothesis (see below). The study looked at DNA sequences from 19 loci in 169 species. It recovered evidence that the paleognaths are one natural group (
A related study addressed the issue of paleognath phylogeny exclusively. It used molecular analysis and looked at twenty unlinked nuclear genes. This study concluded that there were at least three events of flightlessness that produced the different ratite orders, that the similarities between the ratite orders are partly due to
Beginning in 2010, DNA analysis studies have shown that tinamous are the sister group to extinct moa of New Zealand.[2][4][18][19]
A 2020 molecular study of all bird orders found paleognaths and neognaths to have diverged in the Late Cretaceous or earlier, before 70 million years ago. However, all modern paleognath orders only originated in the latest Paleocene and afterwards, with ostriches diverging in the latest Paleocene, rheas in the early Eocene, kiwis (and presumably elephant birds) very shortly after in the early Eocene, and finally Casuariiformes and tinamous (and presumably moas) diverging from one another in the mid-Eocene.[20]
History of classifications
In the history of biology there have been many competing taxonomies of the birds now included in the Palaeognathae. The topic has been studied by Dubois (1891), Sharpe (1891), Shufeldt (1904), Sibley and Ahlquist (1972, 1981) and Cracraft (1981).
Merrem (1813) is often credited with classifying the paleognaths together, and he coined the taxon "Ratitae" (see above). However, Linnaeus (1758) placed cassowaries, emus, ostriches, and rheas together in Struthio. Lesson (1831) added the kiwis to the Ratitae. Parker (1864) reported the similarities of the palates of the tinamous and ratites, but Huxley (1867) is more widely credited with this insight. Huxley still placed the tinamous with the Carinatae of Merrem because of their keeled sterna, and thought that they were most closely related to the Galliformes.
Pycraft (1900) presented a major advance when he coined the term Palaeognathae. He rejected the Ratitae-Carinatae classification that separated tinamous and ratites. He reasoned that a keelless, or "ratite", sternum could easily evolve in unrelated birds that independently became flightless. He also recognized that the ratites were secondarily flightless. His subdivisions were based on the characters of the palatal skeleton and other organ systems. He established seven roughly modern orders of living and fossil paleognaths (Casuarii, Struthiones, Rheae, Dinornithes, Aepyornithes, Apteryges, and Crypturi – the latter his term for tinamous, after the Tinamou genus Crypturellus).
The Palaeognathae are usually considered a
Cladistics
Palaeognathae |
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Cladogram based on Mitchell (2014)[4] with some clade names after Yuri et al. (2013)[22]
Cloutier, A. et al. (2019) in their molecular study places ostriches as the basal lineage with the rhea as the next most basal.[23]
An alternative phylogeny was found by Kuhl, H. et al. (2020). In this treatment, all members of Palaeognathae are classified in Struthioniformes, but they are still shown as distinct orders here.[20]
Palaeognathae |
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Other studies have suggested that the relationships between the four main groups of non-ostrich palaeognaths (Casuariiformes, Rheiformes, Apteryformes+Aepyornithformes and Tinamiformes+Dinornithformes) are an effective polytomy, with only slightly more support for Novaeratitae over the alternative hypotheses of Apterygiformes+Aepyornithformes being more closely related to Rheiformes or to Tinamiformes+Dinornithformes.[24]
Description
Paleognaths are named for a characteristic, complex architecture of the bones in the bony palate. Cracraft (1974) defined it with five characters.
- The vomer is large and articulates with the premaxillae and maxillopalatines anteriorly. Posteriorly the vomer fuses to the ventral surface of the pterygoid, and the palatines fuse to the ventral surface of this pterygovomer articulation.
- The pterygoid prevents the palatine from articulating medially with the basisphenoid.
- The palatine and pterygoid fuse into a rigid joint.
- The articulation on the pterygoid for the basipterygoid process of the basicranium is located near the articulation between the pterygoid and quadrate.
- The pterygoid–quadrate articulation is complex and includes the orbital process of the quadrate.[25]
Paleognaths share similar pelvis anatomy. There is a large, open
Paleognaths share a pattern of grooves in the horny covering of the bill. This covering is called the
In paleognaths, the male incubates the eggs. The male may include in his nest the eggs of one female or more than one. He may also have eggs deposited in his nest by females that did not breed with him, in cases of
The
Tinamous have a very long, keeled, breastbone with an unusual three-pronged shape. This bone, the
Tinamou feathers look like those of volant birds in that they have a rachis and two vanes. The structure of tinamou feathers is unique, however, in that they have barbs that remain joined at their tips. Thus the parallel barbs are separated only by slits between them.[29] Tinamous have uropygial glands.
Ratite birds are strictly flightless and their anatomy reflects specializations for terrestrial life. The term "
Paleognaths as a whole tend to have proportionally small brains, and are among the living birds with the most limited cognitive abilities. Kiwis are exceptional, however, and have large brains comparable to those of
Sizes
Living members of Palaeognathae range from 6 inches (15 cm) to 9 feet (2.7 m) and weight can be from .09 to 345 pounds (0.0–156.5 kg).[26] Ostriches are the largest struthioniforms (members of the order Struthioniformes), with long legs and neck. They range in height from 5.7 to 9 feet (1.7–2.7 m) and weigh from 139 to 345 pounds (63–156 kg).[26] They have loose-feathered wings. Males have black and white feathers while the female has grayish brown feathers. They are unique among birds in that they retain only the third and fourth toe on each foot. Ostrich wings have claws, or unguals, on the first and second fingers (and, in some individuals, also on the third). Ostriches differ from other paleognaths in that they have a reduced vomer bone of the skull.[citation needed]
Emus are 6 to 7.5 feet (1.8–2.3 m) in height and weigh 75 to 110 pounds (34–50 kg).[26] They have short wings and the adults have brown feathers.
Rheas are 3 to 4.6 feet (91–140 cm) and weigh 33 to 88 pounds (15–40 kg).[26] Their feathers are gray or spotted brown and white. They have large wings but no tail feathers. They have no clavicles.
Cassowaries are 3.5 to 5.6 feet (1.1–1.7 m) in height and weigh 30 to 130 pounds (14–59 kg).[26] They have rudimentary wings with black feathers and six stiff, porcupine-like, quills in the place of their primary and secondary feathers.
Kiwis are the smallest of ratites, ranging in height from 14 to 22 inches (36–56 cm) and weight 2.6 to 8.6 pounds (1.2–3.9 kg).[26] They have shaggy brown feathers.
Tinamous range in size from 8 to 21 inches (20–53 cm) and weigh 1.4 to 5 pounds (640–2,270 g).[26]
Locomotion
Many of the larger ratite birds have extremely long legs and the largest living bird, the ostrich, can run at speeds over 35 mph (60 km/h). Emus have long, strong legs and can run up to 30 mph (48 km/h). Cassowaries and rheas show a similar likeness in agility and some extinct forms may have reached speeds of 45 mph (75 km/h).[citation needed]
Biogeography
Today, the ratites are largely restricted to the Southern Hemisphere, though across the Cenozoic they were also present in
There are two theories regarding the evolution of paleognaths. According to the Gondwana vicariance hypothesis, the paleognaths evolved once, from one ancestor, on Gondwana during the Cretaceous, and then rode on the daughter landmasses that became today's southern continents. This hypothesis is supported most strongly by molecular clock studies, but it is weakened by the lack of any Cretaceous or southern fossil paleognaths, as well as the early radiation of paleognaths in Laurasian landmasses. According to the Tertiary radiation hypothesis,[a] they evolved after the Cretaceous–Paleogene extinction event from multiple flying ancestors on multiple continents around the world. This hypothesis is supported by molecular phylogeny studies and matches the fossil record, but it is weakened by morphological phylogenetic studies. Both hypotheses have been supported and challenged by many studies by many authors.[5]
A 2016 study of both genetic and morphological divergence concludes that the group had a Laurasian origin.[9]
Gondwana vicariance hypothesis
Cracraft (2001) gave a comprehensive review to the data and strongly supported the Gondwana vicariance hypothesis with phylogenetic evidence and historical biogeography. He cites molecular clock studies that show a basal divergence date for neornithes being around 100 Mya. He credits the authors of the molecular clock studies with the observation that the lack of southern paleognath fossils may correspond to the relatively scarce southern Cretaceous deposits, and the relative lack of paleontological field work in the southern hemisphere. Moreover, Cracraft synthesizes the morphological and molecular studies, noting conflicts between the two, and finds that the bulk of the evidence favors paleognath monophyly. He also notes that not only the ratites, but other basal groups of neognathous birds, show trans-Antarctic distribution, as would be expected if the paleognaths and neognaths had diverged in Gondwana.[32]
Geological analyses have suggested that
Ultimately, the earliest recorded paleognaths are flying, presumably plesiomorphic
Tertiary radiation hypothesis[a]
Houde demonstrated that the
Relationship to humans
The human lineage evolved in Africa in
Today, ratites such as the ostrich are farmed and sometimes even kept as pets. Ratites play a large role in human culture; they are farmed, eaten, raced, protected, and kept in zoos.
See also
- Flightless bird
- List of fossil bird genera
- List of Late Quaternary prehistoric bird species
- List of recently extinct bird species
References
- ^ a b This designation has as a part of it a term, 'Tertiary', that is now discouraged as a formal geochronological unit by the International Commission on Stratigraphy.[31]
Footnotes
- ^ Wetmore, A. (1960). "A Classification for Birds of the World". Smithsonian Miscellaneous Collections. 139. Washington D.C.: Smithsonian Institution: 1–37.
- ^ PMID 24825849.
- ^ Clements, J. C. et al. (2010)
- ^ S2CID 206555952.
- ^ a b Houde, P. T. (1988)
- ^ a b Leonard, L. et al. (2005)
- ^ ISBN 978-3-540-89627-2 – via Google Books.
- ^ a b A lithornithid (Aves: Palaeognathae) from the Paleocene (Tiffanian) of southern California
- ^ PMID 27989673.
- ^ Cooper, Alan & Penny, David (1997)
- ^ Benton, Michael J. (2005)
- ^ McDowell, Sam (1948)
- ISBN 0-520-20094-2.
- ^ Clarke, J. A. et al. (2005)
- ^ Sánchez Marco, Antonio (2010). "New Data and an Overview of the Past Avifaunasfrom the Canary Islands". Ardeola: International Journal of Ornithology. 57 (1): 13–40.
- S2CID 6472805.
- ^ PMID 18765814.
- PMID 20525622.
- PMID 21596537.
- ^ PMID 32781465.
- ^ "The IUCN Red List of Threatened Species". IUCN Red List of Threatened Species. Retrieved 9 May 2020.
- PMID 24832669.
- PMID 31135914.
- PMID 37227001.
- ^ Cracraft, Joel (1974)
- ^ ISBN 0 7876 5784 0.
- ^ Eyton, T.C. (1867)
- ^ a b Feduccia, Alan (1996)
- ^ Davies, S. J. J. F. (2002)
- S2CID 31628714.
- ISBN 978-0-521-78142-8.
- ^ Cracraft, Joel (2001)
- ^ Jones, M. (2009)
- ^ .
- S2CID 132516050.
- S2CID 42829066.
- ^ Olson, Storrs L. (1989)
- ^ Houde, Peter (1986)
- S2CID 39180646.
- ^ J. Hansford, P. C. Wright, A. Rasoamiaramanana, V. R. Pérez, L. R. Godfrey, D. Errickson, T. Thompson, S. T. Turvey, Early Holocene human presence in Madagascar evidenced by exploitation of avian megafauna. Science Advances. 4, eaat6925 (2018). https://www.science.org/doi/10.1126/sciadv.aat6925
Sources
- Clements, J.F. Schulenberg, T.S. Iliff, M.J. Sullivan, B.L. & Wood, C.L. (2010) The Clements checklist of the birds of the world: Version 6.5.
- Burnie, D. & Wilson, D. (2005) Animal: The Definitive Visual Guide to the World's Wildlife. New York, New York: DK publishing, inc.. pp. 260–265. ISBN 0-7894-7764-5.
- Clarke, G.M.; Tambussi, J.A.; Noriega, C.P.; Erickson, J.I.; Ketchum, R.A. (2005). "Definitive fossil evidence for the extant avian radiation in the Cretaceous" (PDF). Nature. 433 (7023): 305–308. S2CID 4354309.
- Leonard, L.; Dyke, G.J.; Van Tuinen, M. (2005). "A new specimen of the fossil palaeognath Lithornis from the Lower Eocene of Denmark" (PDF). American Museum Novitates (491): 1–11. S2CID 55323962.
- Davies, S.J.J.F. (2002) Ratites and Tinamous New York, NY: Oxford University Press ISBN 978-0-19-854996-3
- Cracraft, J (2001). "Avian evolution, Gondwana biogeography and the Cretaceous-Tertiary mass extinction event". Proceedings of the Royal Society of London B: Biological Sciences. 268 (1466): 459–469. PMID 11296857.
- Wyse, E. (2001) Dinosaur Encyclopedia: From Dinosaurs to the Dawn of Man. New York, New York: DK publishing, inc.. pp. 138–145. ISBN 0-7894-7935-4.
- Wexo, J, (2000) Zoobooks: Ostriches and other Ratites. Poway, California: Wildlife Education. ISBN 1-888153-57-1.
- Drenowatz, C. (1996). The Ratite Encyclopedia. Charley Elrod.
- Feduccia, A. (1996) The Origin and Evolution of Birds New Haven, CT: Yale University Press p. 420 ISBN 978-0-300-07861-9
- Sibley, C. (1993) A World Checklist of Birds. New Haven: Yale University Press. ISBN 0-300-05547-1.
- Elwood, A. (1991) Ostriches, Emus, Rheas, Kiwis, & Cassowaries. Mankato, Minnesota: Creative Education. ISBN 0-88682-338-2.
- Benton, M.J. (1990) Vertebrate Palaeontology (3rd ed.) Oxford, England: Blackwell Publishing ISBN 978-0-632-05637-8
- Olson, Storrs L. (1985): The fossil record of birds. In: Farner, D.S.; King, J.R. & Parkes, Kenneth C. (eds.): Avian Biology 8: 79-238. Academic Press, New York. Not in copyright; PDF fulltext
- Olson, S.L. (1989) Aspects of the global avifaunal dynamics during the Cenozoic. Proceedings of the 19th International Ornithological Congress (University of Ottawa Press): 2023–2029.
- Houde, P.W. (1988) Paleognathous Birds from the Early Tertiary of the Northern Hemisphere. Publications of the Nuttall Ornithological Club.
- Houde, P.W. (1986). "Ostrich ancestors found in the Northern Hemisphere suggest new hypothesis of ratite origins". Nature. 324 (6097): 563–565. S2CID 3791030.
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- Cracraft, J (1974). "Phylogeny and Evolution of the Ratite Birds". Ibis. 116 (4): 494–521. .
- McDowell, S (1948). "The bony palate of birds". The Auk. 65 (4): 520–549. JSTOR 4080603.
- Eyton, T.C. et al. (1867) Osteological Avium; or A sketch of the osteology of birds Wellington: R. Hobson
External links
- Page On the classification of Paleognaths of Animal Diversity Web
- Regional Cladogram of Paleognaths
- Evolutionary Cladogram of Paleognaths
- Avibase
- Introduction to the Palaeognathae
- Oxford Journal on the Molecular Biology and Evolution of Aves
- Paleognath Monophyly
- Ornithology and Natural History
- Avian Biotech
- Palaeognathae on the Tree of Life Web Project