Enantiornithes: Wikis

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Enantiornithines
Fossil range: EarlyLate Cretaceous, 136–65 Ma
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Iberomesornis
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
(unranked): Ornithothoraces
Subclass: Enantiornithes
Walker, 1981
Orders

see text

Enantiornithes is an extinct group of primitive birds. They were the most abundant and diverse avialans of the Mesozoic. Almost all retained teeth and clawed hands, like other primitive birds. Enantiornithines are thought to have left no living descendants. See protobirds.

A consensus of scientific analyses indicates that Enantiornithes is one of two major sister groups of derived birds. The other group is the Ornithurae, which includes all living birds as a subset. This means that Enantiornithines are a successful branch of bird evolution, but one that diversified entirely separately from the lineage leading to modern birds.[1] This consensus has never been universally accepted and is being challenged by new studies, so that it is possible that enantiornithines may actually represent successive outgroups on the lineage leading to modern birds.[2] See Apsaravis.

Most researchers place Enantiornithines in Aves, but those that use the more restrictive definition of Aves put them lower in the Avialae. Enantiornithines were more advanced than Archaeopteryx or Confuciusornis, but in several respects more primitive than all living birds (Neornithes), perhaps following an intermediate evolutionary path. Due to the primitive features, some early studies placed Enantiornithes with Archaeopteryx in the clade Sauriurae, but only a few researchers still do.

Over 40 species of Enantiornithines have been named, but some names represent only single bones, so it is likely that not all are valid. They have been found in both inland and marine sediments, suggesting that they were an ecologically diverse group. Enantiornithine fossils appear to include waders, swimmers, fish-catchers, and hook-beaked raptors. The smallest are described as sparrow-sized, but some were much larger, such as Avisaurus which had an estimated wingspan of 1.2 meters (4 ft). Enantiornithine birds went extinct at the K-T boundary, along with hesperornithine birds and all other non-avian dinosaurs, and many other life forms.

Contents

Etymology

"Enantiornithes" means "opposite birds", from Ancient Greek einantios (ἐνάντιος) "opposite" + ornithes (όρνιθες) "birds" . This term was coined by Cyril Walker in his landmark paper which established the group.[3] Walker did not give a formal treatment of his etymology, and left it unclear what feature or features are "opposite". Elsewhere in his paper, however, Walker did state his real reason for using the term "opposite":

"Perhaps the most fundamental and characteristic difference between the Enantiornithes and all other birds is in the nature of the articulation between the scapula [...] and the coracoid, where the 'normal' condition is completely reversed."[3]

This refers to an anatomical feature - the articulation of the shoulder bones – which has a concave-convex configuration that is the inverse of that of modern birds. Specifically, in Enantiornithes, the scapular facet of the coracoid is a convex knob and the coracoidal facet of the scapula is a concave dish-shaped excavation to receive it. In neornithes the scapular facet of the coracoid is a round pit, which receives the coracoidal tubercle of the scapula[4] - compare the human glenohumeral joint, where the scapula has a similar excavation, but to receive the humerus as the coracoid is absent in mammals.

Walker's ambiguity on his reason for naming the group led to some confusion about this matter among later researchers. For example, Alan Feduccia stated in 1996:

"The birds are so named because, among many distinctive features, there is a unique formation of the triosseal canal and the metatarsals are fused proximally to distally, the opposite of that in modern birds"[5]

Feduccia's point about the tarsometatarsus is correct, but Walker did not use this reasoning in his original paper. Walker never described the fusion of the tarsometatarsus as opposite, but rather as "Only partial". Also, it is not certain that enantiornithines had triosseal canals, since no fossil preserves this feature.[1]

Discovery

The first enantiornithines to be discovered were incorrectly referred to modern bird groups. They were first recognized as a distinct lineage by C. A. Walker, in 1981, based on some partial remains from the late Cretaceous period of what is now Argentina. Since the 1990s, more complete enantiornithines were discovered and it was demonstrated that a few previously described birds (e.g. Iberomesornis, Cathayornis/Sinornis) had enantiornithine features.

Enantiornithines have been found in North America, South America, Europe, Asia, and Australia. Known fossils attributable to this group are exclusively Cretaceous and it is believed that enantiornithines became extinct at the same time as their non-avian dinosaur relatives. One biogeographic study in the 1990s suggested that the distribution of enantiornithines implies a Middle Jurassic origin for the clade, but this theory has not been widely accepted by paleoornithologists; a Late Jurassic/Early Cretaceous origin is more in line with the fossil record. The earliest known enantiornithines are from the Early Cretaceous) of Spain (e.g. Noguerornis, a basal genus) and China (e.g. Eoenantiornis, a more derived genus) and the latest from the Late Cretaceous of North and South America (e.g. Avisaurus). The widespread occurrence suggests that the Enantiornithes were able to cross oceans on their own power; they are the first bird lineage with a global distribution. Some might thus even have been migratory, but given the markedly warmer climate of the Mesozoic and the fact that the known Enantiornithes are regions that were subtropical if not tropical at that time, it seems hardly likely that at least the known diversity of these birds contains long-distance migrants.

Enantiornithine fossils

This specimen, unlike the holotype, lacks well-preserved feathers

Many enantiornithine fossils were found in fragmentary states, and some taxa are known only from a single bone. Particularly exquisite specimens that are complete, in full articulation and with soft tissue preservation are known from Las Hoyas in Cuenca (Spain) and the Yixian Formation in Liaoning (PRC). Eoalulavis was found to have the remains of exoskeletons of aquatic crustaceans preserved in its digestive tract.[6]

Another interesting find from Las Hoyas was reported by Sanz et al. in 2001. The fossil includes the remains of four hatchling enantiornithine skeletons of three different species. They are substantially complete, very tightly associated, and show surface pitting of the bones that indicates partial digestion. The authors concluded that this association was a regurgitated pellet and, from the details of the digestion and the size, that the hatchlings were swallowed whole by a pterosaur or small theropod dinosaur. This was the first evidence that Mesozoic birds were prey animals, and that some Mesozoic ornithodires regurgitated pellets like owls do today.[7]

Zhang and Zhou in 2004 described an enantiornithine fossil with wing-like feather tufts on its legs,[8] similar to Archaeopteryx. Leg feathers are also reminiscent of the four-winged dinosaur Microraptor, however, in the enantiornithine differ from the feathers are shorter, more disorganized (do not clearly form a wing) and only extend down to the ankle rather than along the foot. Considered together, these not too closely-related animals suggest that auxiliary leg feathers may have been a recurring feature in the evolution and refinement of flight in theropods.

Clarke et al. (2006) surveyed all enantiornithine fossils then known and concluded that none had preserved tail feathers that formed a lift - generating fan, as in modern birds. They found that all birds outside of the ornithurae with preserved tail feathers had only short coverts or elongated paired tail plumes. Thus, they suggested that the development of the pygostyle in enantiornithes must have been a function of tail shortening, not the development of a modern tail feather anatomy. An ornithurine bird, Yixianornis, was reported by the authors as the earliest bird with a fan of tail feathers.[9]

In 2009, an enantiornithine called Shanweiniao was reported with a preserved fan of tail feathers.[10]

An unnamed bird, tentatively referred to Enantiornithes, was reported from Cenomanian Lebanon. It preserves corpuscles of amber among the fossilized bones. The authors suggest that this animal may have fed on tree sap, much like modern sapsuckers and other birds. The sap would have fossilized and become amber. This is also the first reported bird from the paleocontinent of northern Gondwana. [11 ]

Life history

Described enantiornithine fossils include eggs,[12][13] embryos,[14] and hatchlings.[15] An enantiornithine embryo, still curled in its egg, has been reported from the Yixian Formation.[16] Together with the hatchlings assigned to Gobipteryx,[17] these finds demonstrate that enantiornithine hatchlings had the skeletal ossification, well-developed wing feathers and the large brain which correlate with precocial or superprecocial patterns of development in birds of today. Thus, at least some enantiornithine birds probably hatched from the egg substantially developed and ready to run, forage, and possibly even fly in a just a few days. This, together with the fact that the most ancient lineages of modern birds - paleognaths and Galloanserae - are precocial, suggests that the precocial condition is plesiomorphic and was common among Cretaceous birds.

Analyses of enantiornithine bone histology have been conducted to determine the growth rates of the animals. One recent study of Concornis bones shows a growth pattern different from modern birds: Although growth was rapid for some weeks after hatching - probably until fledging - this fairly small species did not reach adult size for a long time, probably several years.[18] Another study supports that growth to adult size was slow, as it is in living precocial birds.[6] Altricial birds on the other hand are known to reach adult size quickly thanks to lavish parental feeding. Still other analyses[19] have interpreted the bone histology to indicate that enantiornithines may not have had fully avian endothermy, instead having an intermediate metabolic rate.

Classification

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Phylogeny

Enantiornithes is the sister group to Ornithurae or Ornithuromorpha depending on the taxonomic authority, and together they could form a clade called Ornithothoraces. Most phylogenetic studies have recovered Enantiornithes as a monophyletic group distinct from the modern birds and their closest relatives. The 2002 phylogenetic analysis by Clarke and Norell, though, reduced the number of enantiornithine autapomorphies to just four.[2] This raises the possibility that the discovery of new fossils could unite Enantiornithes and the birds closer to living species into one clade. If this proves to be true, then Enantiornithes is a paraphyletic taxon and thus phylogenetically invalid. All enantiornithines would then be united in the next larger clade Ornithothoraces instead, and called "ornithothoracines". (see Apsaravis for more on the possible invalidation of Enantiornithes)

On the other hand, Confuciusornis might be closer to Enantiornithes than to living birds rather than about equally distinct from both, which in turn would render the Ornithothoraces meaningless too. In that case, the Pygostylia would apply, but that taxon, too, is ill-defined. Altogether, the radiation of the early truly avian lineages (as opposed to "dinobirds" like Archaeopteryx or Dalianraptor) presents a highly confusing picture at present, and while the apparent deep divergence between Enantiornithes and Neornithes seems real, the relationships of these two and other Cretaceous groups like Hesperornithes or Liaoningornithiformes is not well resolved.

Enantiornithine systematics are also highly provisional. The version used here, although based on many sources, is only tentative, and in need of revision in light of abundant new fossil discoveries. What appears fairly certain by now[20] is that there were subdivisions within Enantiornithes possibly including some minor basal lineages in addition to the more apomorphic Euenantiornithes. The latter may be a clade or an evolutionary grade (and hence are also of questionable validity). The details of the interrelationship of all these lineages, indeed the validity of most, is disputed, although the Avisauridae, for one example, seem likely to constitute a valid group. Phylogenetic taxonomists have hitherto been very reluctant, and justifiably so, to suggest delimitations of enantiornithine clades.[21]

Taxonomy

Subclass Enantiornithes[22][23][24][25][26][27]

Sometimes included in the Enantiornithes are the following taxa:

  • Aberratiodontus (Early Cretaceous) - euenantiornithine (own order)?
  • Dalingheornis (Yixian Early Cretaceous of Dawangzhangzi, China)
  • Longipteryx (Early Cretaceous) - euenantiornithine (own order or family)?
  • Paraprotopteryx (Yixian Early Cretaceous of Fengning, China)
  • Shanweiniao (Yixian Early Cretaceous of China) - same group as Longipteryx?
  • Wyleyia (Early Cretaceous) - basal?
  • Nanantius (Early -? Late Cretaceous) - enantiornithiform?
  • Abavornis (Late Cretaceous) - euenantiornithine?
  • Catenoleimus (Late Cretaceous)
  • Explorornis (Late Cretaceous) - euenantiornithine?
  • Horezmavis (Late Cretaceous of Kyzyl Kum, Uzbekistan) - gobipterygiform?
  • Gargantuavis (Late Cretaceous)
  • Incolornis (Late Cretaceous) - euenantiornithine?
  • Patagopteryx (Late Cretaceous)
  • Family Zhyraornithidae - enantiornithiform?

The three taxa "Jibeinia", "Vescornis", and "Hebeiornis", may be synonyms. (See the three articles for details on the confusion). If so, "Jibeinia" was published in 1997[36], "Vescornis"was described in 2004[37], and "Hebeiornis"was published in 1999 but it may not have been an adequate description[38]. Therefore, if the three names truly do describe the same Genus, the senior synonym of the three would be "Jibeinia". Unfortunately, Dr. Hou reported the holotype of Jibeinia lost in 2001.[36]

The Late Cretaceous taxon "Cerebavis" is based on an endocranial cast and while this is not diagnostic, it is different from modern birds and as far as can be told from Ornithurae in general.

References

  1. ^ a b Chiappe & Walker, 2002
  2. ^ a b Clarke, J.A. and Norell, M.A. (2002): The Morphology and Phylogenetic Position of Apsaravis ukhaana from the Late Cretaceous of Mongolia. American Museum Novitates 3387: 1-46. PDF fulltext
  3. ^ a b Walker, C.A. (1981): New subclass of birds from the Cretaceous of South America. Nature 292: 51-53. {DOI|10.1038/292051a0}} (HTML abstract)
  4. ^ Hope, S. (2002): The Mesozoic record of Neornithes (modern birds). In: Chiappe, L.M. and Witmer, L.M. (eds.): Mesozoic Birds: Above the Heads of Dinosaurs: 339-388. University of California Press, Berkeley. ISBN 0520200942
  5. ^ Feduccia, A. (1996): The Origin and Evolution of Birds. Yale University Press, New Haven. ISBN 0-300-06460-8
  6. ^ a b Sanz, J.L., Chiappe, L.M. and Buscalioni, Á.D. (1995). The Osteology of Concornis lacustris (Aves: Enantiornithes) from the Lower Creataceous of Spain and a reexamination of its phylogenetic relationships. American Museum Novitates 3133: 1-23. PDF fultlext
  7. ^ Sanz, Jose L., Chiappe, Luis M., Fernandez-Jalvo, Yolanda, Ortega, Francisco, Sanches-Chillon, Begona, Poyato-Ariza, Francisco, Perez-Moreno, Bernardino P. (2001) "A Cretaceous Pellet" Nature 409:98-99 22 February 2001
  8. ^ Zhang, F. and Zhou, Z. (2004): Leg feathers in an Early Cretaceous bird. Nature 431(7011): 925. doi:10.1038/431925a (HTML abstract)
  9. ^ Clarke, Julia A., Zhou, Zhonghe, Zhang, Fucheng. (2006) "Insight into the evolution of avian flight from a new clade of Early Cretaceous ornithurines from China and the morphology of Yixianornis grabaui" "Journal of Anatomy" 208:287-308.
  10. ^ Jingmai K. O’connor, Xuri Wang, Luis M. Chiappe, Chunling Gao, Qingjin Meng,Xiaodong Cheng, And Jinyuan Liu (2009). "Phylogenetic support for a specialized clade of Cretaceous enantiornithine birds with information from a new species" Journal of Vertebrate Paleontology 29(1):188–204, March 2009# 2009 by the Society of Vertebrate Paleontology
  11. ^ Della Vecchia, F.B., Chiappe, L.M. "FIRST AVIAN SKELETON FROM THE MESOZOIC OF NORTHERN GONDWANA" Journal of Vertebrate Paleontology 22(4):856–860, December 2002.
  12. ^ Mikhailov, 1991
  13. ^ Mikhailov, 1996
  14. ^ Elżanowski, 1981
  15. ^ Sanz, J.L., Chiappe, L.M., Pérez-Moreno, B.P., Moratalla, J.J., Hernández-Carrasquilla, F., Buscalioni, Á.D., Ortega, F., Poyato-Ariza, F.J., Rasskin-Gutman, D. and Martínez-Delclós, X. (1997): A Nestling Bird from the Lower Cretaceous of Spain: Implications for Avian Skull and Neck Evolution. Science 276(5318): 1543-1546. doi:10.1126/science.276.5318.1543 PDF fulltext
  16. ^ Zhou, Z. and Zhang, F. (2004) A Precocial Avian Embryo from the Lower Cretaceous of China. Science 306(5696): 653. doi:10.1126/science.1100000 Supporting Online Material
  17. ^ Elżanowski (1995)
  18. ^ Cambra-Moo, O., Delgado Buscalioni, Á.D., Cubo, J., Castanet, J., Loth, M.-M., de Margerie, E., and de Ricqlès, A. (2006): Histological observations of Enantiornithine bone (Saurischia, Aves) from the Lower Cretaceous of Las Hoyas (Spain). C. R. Palevol 5(5): 685–691. doi:10.1016/j.crpv.2005.12.018 PDF fulltext
  19. ^ E.g. Chiappe (1995)
  20. ^ Chiappe (2002)
  21. ^ Sereno, P.C. (2005): TaxonSearch: Stem Archosauria. Version 1.0, 2005-NOV- 7. Retrieved 2006-OCT-02.
  22. ^ Chiappe, L.M. (1992): Enantiornithine (Aves) tarsometatarsi and the avian affinites of the Cretaceous Avisauridae. J. Vertebr. Paleontol. 12(3): 344-350.
  23. ^ Chiappe, L.M. and Calvo, J.M. (1994): Neuquenornis volans, a new Late Cretaceous bird (Enantiornithes: Avisauridae) from Patagonia, Argentina. J. Vertebr. Paleontol. 14(2): 230-246. HTML abstract
  24. ^ Kurochkin, E. (1996): A new enantiornithid of the Mongolian Late Cretaceous, and a general appraisal of the Infraclass Enantiornithes (Aves). Paleontological Institute, Moscow.
  25. ^ Zhou, Z. and Hou, L.-H. (2002): The Discovery and Study of Mesozoic Birds in China. In: Chiappe, L.M. and Witmer, L.M. (eds.): Mesozoic Birds: Above the Heads of Dinosaurs: 160-183. ISBN 0520200942
  26. ^ Chiappe, L.M. and Walker, C.A. (2002): Skeletal morphology and systematics of the Cretaceous Euenantiornithes (Ornithothoraces: Enantiornithes). In: Chiappe, L.M. and Witmer, L.M. (eds.): Mesozoic Birds: Above the Heads of Dinosaurs: 240-267. University of California Press, Berkeley. ISBN 0520200942
  27. ^ Haaramo, M. (2006): Mikko's Phylogeny Archive: †Enantiornithes. Version of 2006-APR-03. Retrieved 2006-OCT-02.
  28. ^ Harris, J.D., Lamanna, M.C., You, H.-L., Ji, S.-A. and Ji, Q. (2006): A second enantiornithean (Aves: Ornithothoraces) wing from the Early Cretaceous Xiagou Formation near Changma, Gansu Province, People's Republic of China. Canadian Journal of Earth Sciences 43(5): 547–554. PDF fulltext
  29. ^ Buffetaut, É. (1998): First evidence of enantiornithine birds from the Upper Cretaceous of Europe: postcranial bones from Cruzy (Hérault, France). Oryctos 1: 127-130. HTML abstract
  30. ^ Buffetaut, É., Mechin, P. and Mechin-Salessy, A. (2000): An archaic bird (Enantiornithes) from the Upper Cretaceous of Provence (southern France). C. R. Acad. Sci. Paris IIA - Sciences de la Terre et des planètes 331(8): 557–561. doi:10.1016/S1251-8050(00)01451-8 (HTML abstract)
  31. ^ Lamanna, M.C., You, H.-L., Harris, J.D., Chiappe, L.M., Ji, S.-A., Lü, J.-C. and Ji, Q. (2006): A partial skeleton of an enantiornithine bird from the Early Cretaceous of northwestern China. Acta Palaeontologica Polonica 51(3): 423–434. PDF fulltext
  32. ^ Morrison, K., Dyke, G.J. and Chiappe, L.M. (2005): Cretaceous fossil birds from Hornby Island (British Columbia). Canadian Journal of Earth Sciences 42(12): 2097–2101. HTML abstract
  33. ^ a b Li, L., Hu, D.-Y., Duan, Y., Gong, E.-P. and Hou, L.-H. (2007). "Alethoalaornithidae fam. nov., a new family of enantiornithine bird from the Lower Cretaceous of western Liaoning." Acta Palaeontologica Sinica, 46(3): 365-372. (http://www.cqvip.com/qk/90074X/200703/25642898.html) [in Chinese]
  34. ^ a b Zhou, Zhonghe and Zhang, Fucheng (2007) "Mesozoic Birds of China - A Synoptic Review" Frontiers of Biology in China March 2, 2007 2(1):1-14.
  35. ^ Zhang, Fucheng., Zhou, Zhonghe (2000) "A Primitive Enantiornithine Bird and the Origin of Feathers" Science 290, 1955-1959 DOI: 10.1126/science.290.5498.1955
  36. ^ a b c Hou, Lianhai (1997) "Mesozoic Birds of China" Institute of Vertebrate Paleontology and Paleoanthropology, Beijing, China. Published by the Phoenix Valley Provincial Aviary of Taiwan. In Chinese, translated by Will Downs, Bilby Research Center, Northern Arizona University, January, 2001.
  37. ^ a b Zhang, Fucheng., Ericson, Per G.P., Zhou, Zhonghe. (2004) "Description of a new enantiornithine bird from the Early Cretaceous of Hebei, northern China" Canadian Journal of Earth Science 41: 1097 - 1107 doi: 10.1139/E04-055
  38. ^ Xu, G.L., Yang, Y.S., Deng, S.Y. (1999) First Discovery of Mesozoic Bird Fossils in Hebei Province and its Significance. Regional Geology of China 18(4):444-448

Wikispecies

Up to date as of January 23, 2010

From Wikispecies

Taxonavigation

Main Page
Cladus: Eukaryota
Supergroup: Unikonta
Cladus: Opisthokonta
Regnum: Animalia
Subregnum: Eumetazoa
Cladus: Bilateria
Cladus: Nephrozoa
Cladus: Deuterostomia
Phylum: Chordata
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Superclassis: Tetrapoda
Classis: Aves
Subclassis: †Saurornithes
Infraclassis: Ornithothoraces
Legio: Ornithurae
Cohort: Enantiornithes

Name

Enantiornithes C.A. Walker, 1981

Vernacular names

English: Enantiornithines

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