| Jeholornis | |
|---|---|
 | |
| Fossil specimen of a juvenileJ. prima (IVPP V13550),Paleozoological Museum of China | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Clade: | Avialae |
| Order: | †Jeholornithiformes |
| Family: | †Jeholornithidae |
| Genus: | †Jeholornis Zhou & Zhang, 2002 |
| Type species | |
| †Jeholornis prima Zhou & Zhang, 2002 | |
| Other species | |
| Synonyms | |
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Jeholornis (meaning "Jehol bird") is agenus ofavialandinosaurs that lived between approximately 122 and 120 million years ago during the earlyCretaceous Period inChina. FossilJeholornis were first discovered in theJiufotang Formation inHebei Province, China (in what was previouslyRehe Province, also known as Jehol—hence the name) and additional specimens have been found in the olderYixian Formation.[1]
Jeholornis had longtails and few smallteeth, and were approximately the size ofturkeys,[2] making them among the largestavialans known until the Late Cretaceous. Their diet included seeds ofcycads,Ginkgo orsimilar plants.
Jeholornis were relatively large,basal avialans, with a maximum adult length of up to 75 cm (2.5 ft) and an estimated weight of 2.27-9.1 kg (5-20 lbs).[2] Another estimation listed it at 85 cm (2.6 ft) and 780 gr (1.72 lbs).[3] Their skulls were short and high, similar to basal paravians likeEpidexipteryx and to earlyoviraptorosaurs likeIncisivosaurus. The lower jaws were short, stout, and curved downward, possibly an adaptation for eating seeds.[4]Jeholornis prima lacked teeth in their upper jaws, and had only three small teeth in their lower jaws,[5] whileJ. palmapenis had a few teeth in the middle of the upper jaw (maxilla) but none in the front (premaxilla). The upper teeth ofJ. palmapenis seem to have been angled slightly forward as in some other basal avialans. The teeth in all three species were small, blunt and peg-like with no serrations.[4]
Their arms were robust and longer than the legs, with relatively well-developed shoulder girdles indicating strong wing musculature. The wishbone (furcula) was U-shaped inJ. prima andJ. palmapenis but not inJ. curvipes. Their fingers were short compared to those ofArchaeopteryx and also more robust. The lower legs were not particularly long, indicating that these animals were not specialized runners.[4] The first toe, orhallux, which is reversed in modern birds and used to perch in trees, was only partially reversed in bothJeholornis species, pointing inward and slightly backward. The halluces ofJeholornis were short, but their claw was more strongly curved than those of the other toes. Unlikedeinonychosaurs and some otherMesozoic avialans, the claw of the second toe was not enlarged relative to the other claws.[4] Their tail anatomy was more like those ofdromaeosaurids thanArchaeopteryx, with more strongly interlocking vertebrae, and though they had a similar number of tail vertebrae (between 20 and 24) those ofJeholornis were much longer overall than those ofArchaeopteryx.[5] The only well-preserved tail feathers come from the type specimen ofJ. palmapenis.
A study byGregory M. Erickson in 2009 has shown thatJeholornis (along withArchaeopteryx) had relatively slowontogenic development, i.e. they grew very slowly, compared to most modern birds, which grow very quickly. The livingkiwi birds however, have slow development, and it has been speculated thatJeholornis could have had ametabolism similar to these.[6]
Feather traces from the wing have only been identified in two specimens, LPM 0193 (J. prima) and (SDM 20090109.1 (J. palmapenis). The first specimen shows that theflight feathers were asymmetrical (and therefore aerodynamic, as in modern flying birds) and up to 21 centimeters long, longer than the forearm and hand combined.[7] The exact number of flight feathers cannot be determined from known specimens, however, as the preservation is too poor.[5]
The tails of several specimens preserve a fan of feathers (rectrices) at the tip, shorter than those on the forelimbs.[7] The feather fan is similar to those ofMicroraptor andCaudipteryx, being restricted to the tip of the tail, unlike those ofArchaeopteryx andSimilicaudipteryx which have rectrices extending down much of the tail length.[5] In at least one species,Jeholornis palmapenis, there were 11 tail feathers. The feathers were short and pointed, and arched away from the body of the tail, so that the entire array of tail feathers resembled a palm frond. The tail feathers did not overlap, and so could not have formed a lift-generating surface, so the tail was probably used mainly for display.[4]
Jeholornis contains at least threespecies: thetype species,Jeholornis prima (named in reference to theJehol group of fossil beds where it was found, and the primitive appearance of the tail)[8] and two referred species,Jeholornis palmapenis described byJingmai O'Connor and colleagues in 2012, andJeholornis curvipes, described by Ulysse Lefèvre and colleagues in 2014.[9] The nameJ. palmapenis translates to "palm tail" in reference to the unusual arrangement of its tail feathers,[4] while the nameJ. curvipes means "curved foot" due to a distinctive bend in the bones just above the ankle (metatarsus).[9]
Zhonghe Zhou and Fucheng Zhang classifiedJeholornis in a new family,Jeholornithidae, of which it is thetype genus, and the orderJeholornithiformes.[10] Nophylogenetic definitions for these groups were provided by Zhou and Zhang, but a topological definition was provided in 2020 by Wang and colleagues where Jeholornithiformes was defined as "the most inclusive clade containingJe. prima but excluding the extant birds".[11]
The results of a phylogenetic analysis of all valid jeholornithiform species considered by Wang and colleagues is shown below:
| Avialae |
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Over 100 specimens ofJeholornis have been found,[12] though only seven have been formally described. Thetype specimen is in the collection of theInstitute of Vertebrate Paleontology and Paleoanthropology in Beijing. It is cataloged as IVPP V13274, and was reported in the journalNature in 2002. A second specimen is in the collection of theLiaoning Provincial Museum of Paleontology, and is catalogued as LPM 0193 it was reported as a new species,Shenzhouraptor sinensis, in the journalThe Geological Bulletin of China in 2002, but is likely a junior synonym ofJeholornis prima.[9] Two more specimens were later accessioned by the IVPP as V13550 and V13553 and they were reported in the journalNaturwissenschaften in 2003. A fifth specimen, SDM 20090109, was described in 2012 and made the type specimen of the speciesJ. palmapenis. A sixth specimen, STM2-51, was reported in 2013 and preserved round structures in the body cavity which were interpreted as ovaries.[13] A seventh specimen, YFGP-yb2, was described in 2014 and made the type specimen of a third species,J. curvipes.[9]
The non-pygostylian avialanJixiangornis orientalis was considered a possible synonym ofJeholornis prima.[14][15] However, aphylogenetic analysis performed in 2014 found that it may actually be more closely related to short-tailed avialans (Pygostylia) than toJeholornis.[9]
Shenzhouraptor sinensis (the name of which is derived from "Shenzhou", an ancient name for China, and "raptor", Latin for "violent plunderer"[7]) was described in the July 2002 issue ofGeological Bulletin of China by Ji et al., the same month asJeholornis was described by Zhou and Zhang. Two of the diagnostic characteristics which could have distinguishedShenzhouraptor fromJeholornis were its smaller size and the absence of teeth, which may be attributed to age and preservational bias. The other major difference was a different number ofcaudalvertebrae, though Zhou and Zhang showed in 2003 that the specimen was missing several of the proximal caudals.[16]
Several scientists have come to the conclusion thatJeholornis andShenzhouraptor are specimens of the same species. However, both names were published in print within days of each other, and there was initially controversy over which name should be considered official. The date on the article describingJeholornis was July 25, 2002.[8] The discovery ofShenzhouraptor was reported in at least one newspaper on July 23, 2002,[17] though the official paper naming the species, published in a monthly journal, did not bear a specific date of issue.[10] In 2003, Ji and colleagues madeJeholornis a junior synonym ofShenzhouraptor.[18] In 2006, Zhou and Zhang noted that the ICZN gives priority to these over monthly journals, and argued that because of thisJeholornis has priority overShenzhouraptor.[10] Most studies have since treatedJeholornis prima as the valid name for the species.[4][9]
In 2020, a publication of a new genus and species of jeholornithiform,Kompsornis longicaudus, by Wang and colleagues included a re-evaluation of the diagnostic characteristics of allJeholornis species, including the holotype ofShenzhouraptor. This examination concluded thatShenzhouraptor was a valid species distinct fromJeholornis prima and other jeholornithiforms, rejecting the suggestion that they are synonymous. A phylogenetic analysis supported this conclusion, recoveringShenzhouraptor as a less derived species outside of a clade composed ofJeholornis prima,J. curvipes andKompsornis.[11]
The type fossil ofJeholornis prima preserved over 50 round seeds in the area of thecrop, each about 8-10 millimeters wide. The seeds belong to theform genusCarpolithes, thus it is uncertain what exact lineage of plant they represent.[8] ThisJ. prima specimen, while about two times heavier than the type specimenShenzhouraptor, had three small teeth in the lower jaw, whereas no teeth were visible in the latter. Two other specimens, IVPP V13353 and the aforementioned V13550 are smaller still and most certainly immature individuals; they both have teeth. In theShenzhouraptor type, thedentary and anterior skull are poorly preserved and this makes it impossible to say whether there were any teeth.[7] The jaw is deep, the dentaries are well fused, and the teeth are reduced, and all indicate a specialized seed-feeding habit forJeholornis.[8] In 2017 it was announced, that one specimen was fossilized withgastroliths in its stomach.[19] A 2022 study by theUniversity of Oxford,england andLinyi University showed thatJeholornis prima was the earliest known fruit eating bird. This trait possibly developed when plants somewhere around 135 million years ago started developing new kinds of fruits. Some birds likeJeholornis evolved the ability to eat thefruits and a co-evolutionary relationship started about 120 million years ago. During this study, they also found thatJeholornis was not just eating the seeds but the entire fruit itself. It would have defecated un-crushedseeds helping the plant spread and grow into morefruit producingplants providing more food scorces forJeholornis.[20]
The shoulder girdles ofJeholornis were well developed and probably allowed for better flight capability than seen inArchaeopteryx. The flight apparatus of theJeholornis was overall quite similar to that ofConfuciusornis in form and function, with forelimbs longer than hindlimbs, and a short, robust hand.[5] However, like other basal (non-ornithothoracean) avialans and theropod dinosaurs, the shoulder blades ofJeholornis were oriented along the sides of the body, rather than on top of its back. This meant that the shoulder girdle was slung low, and according to a 2006 study by Phil Senter, would have allowed only for a typical dinosaurian motion of the shoulder. Primitive avialans likeArchaeopteryx,Confuciusornis, andJeholornis would not have been able to lift their arms vertically to achieve true flapping flight, though semi-powered gliding or parachuting would have been possible.[21]
Examination of the claw curvature inJeholornis suggests it may have been able to perch and may have been at least partlyarboreal, spending much of its time in trees.[8] One key adaptation of modernperching birds is the reversed, opposable first toe, or "hallux."Jeholornis was initially described as having a reversed hallux, though others cast doubt on this interpretation, noting that the reversed appearance could be an artifact of the way the fossils were crushed. Indeed, in most avialans with a reversed hallux, the foot bone where the reversed toe attaches is twisted, allowing the toe to point backward, but this feature is not found in anyJeholornis specimen. In a 2008 presentation for the conference of theSociety of Avian Paleontology and Evolution (SAPE), Zhiheng Li and Yuguang Zhang re-examined the evidence for a reversed hallux inJeholornis. They found that the hallux could appear reversed or not depending on the position the specimen was fossilized in, and that the toe bones showed intermediate adaptations between a reversed and non-reversed hallux. They concluded that the first toe ofJeholornis was generally held in reversed position, but had not yet acquired the advanced adaptations for reversal seen in more advanced perching birds.[22]
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