User:Luxquine/sandbox/Enantiornithes Feathers Draft
Description
Many fossils of Enantiornithes are very fragmentary, and some species are only known from a piece of a single bone. Almost all specimens that are complete, in full articulation, and with soft tissue preservation are known from
Enantiornithes appear to have included waders, swimmers, granivores, insectivores, fishers, and raptors. The vast majority of Enantiornithes were small, between the size of a
Skull
Given their wide range of habitats and diets, the skulls of Enantiornithes varied considerably between species. Skulls of Enantiornithes combined a unique suite of primitive and advanced features. As in more primitive avialans like
Wing
As a very large group of birds, the Enantiornithes displayed a high diversity of different body plans based on differences in ecology and feeding, reflected in an equal diversity of wing forms, many paralleling adaptions to different lifestyles seen in modern birds. In general, the wings of Enantiornithes were advanced compared to more primitive avialans like Archaeopteryx, and displayed some features related to flight similar to those found in the lineage leading to modern birds, the
Several wings with preserved feathers have been found preserved in Burmese amber. These are the first complete Mesozoic dinosaur remains preserved this way (a few isolated feathers are otherwise known, unassigned to any species), and one of the most exquisitely preserved dinosaurian fossils known.[18] The preserved wings show variations in feather pigment and prove that Enantiornithes had fully modern feathers, including barbs, barbules, and hooklets, and a modern arrangement of wing feather including long flight feathers, short coverts, a large alula and an undercoat of down.[3]
One fossil of Enantiornithes shows wing-like feather tufts on its legs, similar to Archaeopteryx. The leg feathers are also reminiscent of the four-winged dinosaur Microraptor, however differ by the feathers being shorter, more disorganized (they do not clearly form a wing) and only extend down to the ankle rather than along the foot.[19]
Tail
Clarke et al. (2006) surveyed all fossils of Enantiornithes then known and concluded that none had preserved tail feathers that formed a lift-generating fan, as in modern birds. They found that all avialans outside of Euornithes (the clade they referred to as Ornithurae) with preserved tail feathers had only short coverts or elongated paired tail plumes. 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. These scientists suggested that a fan of tail feathers and the associated musculature needed to control them, known as the rectrical bulb, evolved alongside a short, triangular pygostyle, like the ones in modern birds, rather than the long, rod- or dagger-shaped pygostyles in more primitive avialans like the Enantiornithes. Instead of a feather fan, most Enantiornithes had a pair of long specialized pinfeathers similar to those of the extinct Confuciusornis and certain extant birds-of-paradise.[20]
However, further discoveries showed that at least among basal Enantiornithes, tail anatomy was more complex than previously thought. One genus, Shanweiniao, was initially interpreted as having at least four long tail feathers that overlapped each other[21] and might have formed a lift-generating surface similar to the tail fans of Euronithes,[22] though a later study indicates that Shanweiniao was more likely to have rachis-dominated tail feathers similar to feathers present in Paraprotopteryx.[23] Chiappeavis, a primitive pengornithid, had a fan of tail feathers similar to that of more primitive avialans like Sapeornis, suggesting that this might have been the ancestral condition, with pinfeathers being a feature evolved several times in early avialans for display purposes.[23] Another species of Enantiornithes, Feitianius, also had an elaborate fan of tail feathers. More importantly, soft tissue preserved around the tail was interpreted as the remains of a rectrical bulb, suggesting that this feature was not in fact restricted to species with modern-looking pygostyles, but might have evolved much earlier than previously thought and been present in many Enantiornithes.[24] At least one genus of Enantiornithes, Cruralispennia, had a modern-looking pygostyle but lacked a tail fan.[25]
Biology
Diet
Given the wide diversity of skull shape among Enantiornithes, many different dietary specializations must have been present among the group. Some, like Shenqiornis, had large, robust jaws suitable for eating hard-shelled invertebrates. In Longipterygidae, the snouts were long and thin with teeth restricted to the tip of the jaws, and they were likely mud-probers (small-toothed species) and fishers (large-toothed species). The short, blunt teeth of Pengornis were likely used to feed on soft-bodied arthropods.[14] The strongly hooked talons of Bohaiornithidae suggest that they were predators of small to medium-sized vertebrates, but their robust teeth instead suggest a diet of hard-shelled animals.[26]
A few specimens preserve actual stomach contents. Unfortunately, none of these preserve the skull, so direct correlation between their known diet and snout/tooth shape cannot be made.
A study on paravian digestive systems indicates that known Enantiornithes lacked a crop and a gizzard, didn't use gastroliths and didn't eject pellets. This is considered at odds with the high diversity of diets that their different teeth and skull shapes imply,[30] though some modern birds have lost the gizzard and rely solely on strong stomachal acids.[31] An example was discovered with what was suspected to be gastroliths in the what would have been the fossil's stomach, re-opening the discussion of the use of gastroliths by Enantiornithes. X-ray and scanning microscope inspection of the rocks determined that they were actually chalcedony crystals, and not gastroliths.[32]
Predation
A fossil from Spain reported by Sanz et al. in 2001 included the remains of four hatchling skeletons of three different species of Enantiornithes. 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
Life history
Known fossils of Enantiornithes include
Together with hatchling specimens of the Mongolian
Analyses of Enantiornithes bone histology have been conducted to determine the growth rates of these animals. A 2006 study of
Evidence of colonial nesting has been found in Enantiornithes, in sediments from the
A 2020 study on a juvenile's feathers further stresses the ontological similarities to modern megapodes, but cautions several differences such as the arboreal nature of most Enantiornithes as opposed to the terrestrial lifestyle of megapodes.[49]
It has been speculated that superprecociality in Enantiornithes might have prevented them from developing specialised toe arrangements seen in modern birds like zygodactyly.[50]
Although the vast majority of histology studies and known remains of Enantiornithes point to supreprecociality being the norm, one specimen, MPCM-LH-26189, seems to represent an altricial juvenile, implying that like modern birds Enantiornithes explored multiple reproductive strategies.[51]
Flight
Because many Enantiornithes lacked complex tails and possessed radically different wing anatomy compared to modern birds, they have been the subject of several studies testing their flight capabilities.
Traditionally, they have been considered inferior flyers, due to the shoulder girdle anatomy being assumed to be more primitive and unable to support a ground-based launching mechanism,
However, several studies have shown that they were efficient flyers, like modern birds, possessing a similarly complex nervous system and wing feather ligaments. Additionally, the lack of a complex tail appears to not have been very relevant for avian flight as a whole - some extinct birds like lithornids also lacked complex tail feathers but were good flyers,[54] and they appear to have been capable of a ground based launching.[55]
Due to the difference in sternal and shoulder girdle anatomy, many Enantiornithes used a flight style unlike that of any modern bird species[clarification needed], though more typical flight styles were present as well.[56]
At least Elsornis appears to have become secondarily flightless.[57]
- .
- .
- ^ PMID 27352215.
- ^ PMID 30700773.
- S2CID 213510021.
- PMID 31303484.
- ^ S2CID 84677039.
- PMID 18397240.
- S2CID 85942925.
- PMID 30479894.)
{{cite journal}}
: CS1 maint: unflagged free DOI (link - .
- ISSN 0272-4634.
- .
- ^ S2CID 86503357.
- ^ Cite error: The named reference
Pterygornis
was invoked but never defined (see the help page). - S2CID 3649504.
- .
- S2CID 88601510.
- S2CID 4322054.
- ^ PMID 16533313.
- S2CID 196607241.
- ^ PMID 24482756.)
{{cite journal}}
: CS1 maint: unflagged free DOI (link - ^ PMID 26748849.
- S2CID 85800831.
- ^ Cite error: The named reference
:1
was invoked but never defined (see the help page). - ^ Cite error: The named reference
bohaiornithidae
was invoked but never defined (see the help page). - ^ hdl:2246/3667.
- JSTOR 4524284.
- S2CID 133781513.
- .
- ^ Houston, David C.; Copsey, J. A. (1994). "Bone digestion and intestinal morphology of the Bearded Vulture". The Journal of Raptor Research. 28 (2): 73–78.
- ^ "Short Crystal: Quartz and the Fossilized Bird | GeoRarities". 2021-03-12. Retrieved 2021-05-06.
- S2CID 663531.)
{{cite journal}}
: CS1 maint: numeric names: authors list (link - ^ Mikhailov, Konstantin E. (1991). "Classification of fossil eggshells of amniotic vertebrates" (PDF). Acta Palaeontologica Polonica. 36 (2): 193–238.
- ^ Mikhailov, Konstantin E. (1996). "New Genera of Fossil Eggs from the Upper Cretaceous of Mongolia". Paleontological Journal. 30 (2): 246–8.
- ^ Elżanowski, Andrzej (1981). "Embryonic bird skeletons from the late Cretaceous of Mongolia" (PDF). Palaeontologia Polonica. 42: 147–79.
- .
- S2CID 34504916.
- ^ hdl:2246/5890.
- ^ Elżanowski, Andrzej (1995). "Cretaceous birds and avian phylogeny". Courier Forschungsinstitut Senckenberg. 181: 37–53.
- S2CID 86747842.
- S2CID 86747842.
- .
- ^ O'Connor, Jingmai K.; Wang, Min; Zheng, Xiao-Ting; Wang, Xiao-Li; Zhou, Zhong-He (2014). "The histology of two female Early Cretaceous birds" (PDF). Vertebrata PalAsiatica. 52 (1): 112–28.
- ^ Chiappe, L.M. (1995). "The phylogenetic position of the Cretaceous birds of Argentina: Enantiornithes and Patagopteryx deferrariisi". Courier Forschungsinstitut Senckenberg. 181: 55–63.
- S2CID 245082389.
- S2CID 1396792.
- PMID 23613776.
- .
- .
- PMID 30899080.
- S2CID 86007060.
- ^ Zhou, Shuang; Zhou, Zhong-He; O'Connor, Jingmai K. (2012). "A new basal beaked ornithurine bird from the Lower Cretaceous of Western Liaoning, China" (PDF). Vertebrata PalAsiatica. 50 (1): 9–24.
{{cite journal}}
: Unknown parameter|lay-date=
ignored (help); Unknown parameter|lay-source=
ignored (help); Unknown parameter|lay-url=
ignored (help) - ^ Houde, Peter W. (1988). "Paleognathous Birds from the Early Tertiary of the Northern Hemisphere". Publications of the Nuttall Ornithological Club (Cambridge Massachusetts, USA: Nuttall Ornithological Club) 22
- PMID 26440221.
- PMID 22163324.
- S2CID 85391743.