Belongs within: Ornithurae.
Contains: Struthio, Apteryx, Aepyornithidae, Casuariidae, Dinornithiformes, Tinamidae.
The Palaeognathae are a clade of birds found primarily on the southern continents, including the ratites and tinamous. Members of this clade are united by the lack of fusion between the maxillar process of the nasal bone and the maxillary bone, as well as the flat dorsal surface and presence of a pair of furrows on the ventral surface of the mandibular symphysis (Mayr 2009). Representatives include the Rheidae, rheas, ostrich-like birds native to South America.
The Lithornithidae are chicken- to turkey-sized birds known from the Palaeocene and Lower and Middle Eocene. They had a palaeognathous palatal structure, but are distinguished from other palaeognaths by the presence of a well-developed hallux, and from other palaeognaths except tinamous in retaining the ability to fly. Being thus defined by plesiomorphic characters, lithornithids may be paraphyletic with respect to other palaeognaths (Mayr 2005).
A frustrating giant bird
Published 1 June 2007
Eremopezus is known from leg bones from the upper Eocene of the Fayum of Egypt. The most recent review is by Rasmussen et al. (2001), but it was first described in 1904. Lambrecht later divided the then-available material into two genera, Eremopezus Andrews 1904 and Stromeria Lambrecht 1929, but there is little significant difference between material assigned to the two and they are now regarded as synonymous.
Being a giant landbird, Eremopezus was originally thought to be related to modern giant landbirds, the ratites. Ratites are a group of flightless birds distributed between the southern continents—the ostrich (Africa), rheas (South America), emu, cassowaries (Australia), moa and kiwis (New Zealand). Arguments have run back and forth about whether the ratites are monophyletic, or have arisen independently from different ancestors. Recent molecular phylogenies have been pretty much unanimous that the ratites are indeed monophyletic and, together with the flighted tinamous (Tinamidae), are the sister group to the remaining modern birds. On the basis of a prominent ridge on the tarsometatarsus, Lambrecht (1933) suggested that Eremopezus was related to the elephant birds (Aepyornithidae) of Madagascar.
The problem is that this is simply not very significant evidence, as pointed out by Rasmussen et al. (2001). Large flightless birds show a great deal of similarity in the form of the leg bones, due to similar functional requirements. The flightless carnivorous bird Diatryma has hindlimb bones indistinguishable from those of ratites, despite being more closely related to the modern Anseriformes (ducks and geese). Rasmussen et al. concluded that Eremopezus could not be reliably associated with any other known group of birds.
To add to this, Eremopezus showed a number of distinct features all of its own. It appears to have been a fairly lightly-built bird, but slightly larger than a cassowary or rhea. The distal end of the tarsometatarsus is markedly flattened dorsoventrally, and the trochleae (and hence the toes) are quite widely splayed (an attachment scar indicating the presence of a hallux—the rear-pointing toe—is present, but this was probably small as an adaptation for terrestriality). The trochleae on either side have relatively light grooves, suggesting that the toes were quite mobile. The modern birds with the most similar morphologies are Sagittarius serpentarius (secretarybird) and Balaeniceps rex (shoebill). Both these birds use their feet for manipulation—Sagittarius is a ground predator that catches prey with its feet whereas Balaeniceps uses its feet to grasp floating vegetation in swampy habitats. The Fayum of the Eocene also appears to have been a quite swampy habitat but the appeal of a gigantic secretarybird is not to be denied. In the meantime, we simply have to wait on further remains to turn up before we can say more on the subject.
Systematics of Palaeognathae
<==Palaeognathae (see below for synonymy)
|--StruthioniformesKF-V21
| |--+--StruthioWD17
| | `--Palaeotis Lambrecht 1928H86, M02 [PalaeotididaeM05]
| | `--*P. weigelti Lambrecht 1928 (see below for synonymy)M02
| `--+--+--+--ApteryxPB15
| | | `--AepyornithidaeML14
| | `--+--CasuariidaeWD17
| | `--+--DinornithiformesWD17
| | `--TinamidaeWD17
| `--Rheidae [Opisthodactylidae, Rheiformes]PB15
| | i. s.: Opisthodactylus patagonicus Ameghino 1891AH03
| | Heterorhea dabbeni Rovereto 1914U93
| |--Diogenornis fragilis Alvarenga 1983ML14, M09
| `--+--Pterocnemia pennataML14
| `--Rhea Brisson 1760B94
| |--R. americana Linnaeus 1758PB96
| `--R. pennataBKB15
`--Lithornithidae [Eoaves, Lithornithidae, Lithornithiformes]WD17
|--Pseudocrypturus Houde 1988M07
| `--P. cercanaxius Houde 1988M09
|--Pediorallus Harrison & Walker 1977M05
| `--*P. barbarae Harrison & Walker 1977M02
|--Promusophaga Harrison & Walker 1977M05
| `--*P. meini Harrison & Walker 1977M02
|--Fissuravis Mayr 2007M07
| `--*F. weigelti Mayr 2007M07
`--Lithornis Owen 1840M07
| i. s.: *L. vulturinus Owen 1840 [incl. Promusophaga magnifica Harrison & Walker 1977]M02
| L. celetius Houde 1988M09
| L. hookeri (Harrison 1984)M09 [=Pediorallus hookeriM02]
| L. nasi (Harrison 1984)M09 [=Pediorallus nasiM02]
|--L. promiscuus Houde 1988WD17, M09
`--+--L. plebius Houde 1988WD17, M09
`--Paracathartes Harrison 1979WD17, M07
`--P. howardae (Harrison 1979)M09
Palaeognathae incertae sedis:
Remiornis Lemoine 1881M02 [RemiornithidaeM07, Remiornithiformes]
`--*R. heberti Lemoine 1881M02
Eleutherornithidae [Eleutherornithini]U93
|--Eleutherornis Schaub 1940M02
| `--*E. helveticus Schaub 1940M02
`--Proceriavis Harrison & Walker 1979U93, M02
`--*P. maritini Harrison & Walker 1979M02
Eremopezus Andrews 1904ML14, RS01 [Eremopezidae, Eremopezithes]
`--*E. eocaenus Andrews 1904 [incl. Stromeria fajumensis Lambrecht 1929, S. fayumensis]RS01
Stromeria Lambrecht 1929U93
Inorganic: Rhea americana minilorientalis Okamura 1987O87
Palaeognathae [Apteryges, Apterygimorphae, Brevipennes, Palaeognathiformes, Panpalaeognathae, Panratitae, Ratitae, Ratiti, Struthiones, Struthioni, Struthionimorphae, Struthionoidea, Timamomorphae]
*Palaeotis weigelti Lambrecht 1928 [incl. Paleogrus geiseltalensis Lambrecht 1935, Ornitocnemus geiseltalensis]M02
*Type species of generic name indicated
References
[AH03] Alvarenga, H. M. F., & E. Höfling. 2003. Systematic revision of the Phorusrhacidae (Aves: Ralliformes). Papéis Avulsos de Zoologia 43 (4): 55–91.
[B94] Bock, W. J. 1994. History and nomenclature of avian family-group names. Bulletin of the American Museum of Natural History 222: 1–281.
[BKB15] Burleigh, J. G., R. T. Kimball & E. L. Braun. 2015. Building the avian tree of life using a large-scale, sparse supermatrix. Molecular Phylogenetics and Evolution 84: 53–63.
[H86] Houde, P. 1986. Ostrich ancestors found in the Northern Hemisphere suggest new hypothesis of ratite origins. Nature 324: 563–565.
[KF-V21] Kuhl, H., C. Frankl-Vilches, A. Bakker, G. Mayr, G. Nikolaus, S. T. Boerno, S. Klages, B. Timmermann & M. Gahr. 2021. An unbiased molecular approach using 3′-UTRs resolves the avian family-level tree of life. Molecular Biology and Evolution 38 (1): 108–127.
[M05] Mayr, G. 2005. The Paleogene fossil record of birds in Europe. Biological Reviews 80: 515–542.
[M07] Mayr, G. 2007. The birds from the Paleocene fissure filling of Walbeck (Germany). Journal of Vertebrate Paleontology 27 (2): 394-408.
[M09] Mayr, G. 2009. Paleogene Fossil Birds. Springer.
[ML14] Mitchell, K. J., B. Llamas, J. Soubrier, N. J. Rawlence, T. H. Worthy, J. Wood, M. S. Y. Lee & A. Cooper. 2014. Ancient DNA reveals elephant birds and kiwi are sister taxa and clarifies ratite bird evolution. Science 344 (6186): 898–900.
[M02] Mlíkovský, J. 2002. Cenozoic Birds of the World. Part 1: Europe. Ninox Press: Praha.
[O87] Okamura, C. 1987. New facts: Homo and all Vertebrata were born simultaneously in the former Paleozoic in Japan. Original Report of the Okamura Fossil Laboratory 15: 347–573.
[PB96] Palma, R. L., & S. C. Barker. 1996. Phthiraptera. In: Wells, A. (ed.) Zoological Catalogue of Australia vol. 26. Psocoptera, Phthiraptera, Thysanoptera pp. 81–247. CSIRO Publishing: Melbourne.
[PB15] Prum, R. O., J. S. Berv, A. Dornburg, D. J. Field, J. P. Townsend, E. M. Lemmon & A. R. Lemmon. 2015. A comprehensive phylogeny of birds (Aves) using targeted next-generation DNA sequencing. Nature 526: 569–573.
[RS01] Rasmussen, D. T., E. L. Simons, F. Hertel & A. Judd. 2001. Hindlimb of a giant terrestrial bird from the Upper Eocene, Fayum, Egypt. Palaeontology 44 (2): 325–337.
[U93] Unwin, D. M. 1993. Aves. In: Benton, M. J. (ed.) The Fossil Record 2 pp. 717–737. Chapman & Hall: London.
[WD17] Worthy, T. H., F. J. Degrange, W. D. Handley & M. S. Y. Lee. 2017. The evolution of giant flightless birds and novel phylogenetic relationships for extinct fowl (Aves, Galloanseres). Royal Society Open Science 4: 170975.