Jeholornis

Jeholornis (meaning 'Jehol bird') is a genus of avialans that lived between approximately 122 and 120 million years ago during the early Cretaceous Period in China. Fossil Jeholornis were first discovered in the Jiufotang Formation in Hebei Province, China (in what was previously Rehe Province, also known as Jehol—hence the name) and additional specimens have been found in the older Yixian Formation. Jeholornis had long tails and few small teeth, and were approximately the size of turkeys, making them among the largest avialans known until the Late Cretaceous. Their diet included seeds of cycads, Ginkgo or similar plants. Jeholornis were relatively large, primitive avialans, with a maximum adult length of up to 80 cm (2.6 ft). Their skulls were short and high, similar to other primitive avialans like Epidexipteryx and to early oviraptorosaurs like Incisivosaurus. The lower jaws were short, stout, and curved downward, possibly an adaptation for eating seeds. Jeholornis prima lacked teeth in their upper jaws, and had only three small teeth in their lower jaws, while J. palmapenis had a few teeth in the middle of the upper jaw (maxilla) but none in the front (premaxilla). The upper teeth of J. 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. 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 in J. prima and J. palmapenis but not in J. curvipes. Their fingers were short compared to those of Archaeopteryx and also more robust. The lower legs were not particularly long, indicating that these animals were not specialized runners. The first toe, or hallux, which is reversed in modern birds and used to perch in trees, was only partially reversed in both Jeholornis species, pointing inward and slightly backward. The halluces of Jeholornis were short, but their claw was more strongly curved than those of the other toes. Unlike deinonychosaurs and some other Mesozoic avialans, the claw of the second toe was not enlarged relative to the other claws. Their tail anatomy was more like those of dromaeosaurids than Archaeopteryx, with more strongly interlocking vertebrae, and though they had a similar number of tail vertebrae (between 20 and 24) those of Jeholornis were much longer overall than those of Archaeopteryx. The only well-preserved tail feathers come from the type specimen of J. palmapenis. A study by Erickson in 2009 has shown that Jeholornis (along with Archaeopteryx) had relatively slow ontogenic development, i.e. they grew very slowly, compared to most modern birds, which grow very quickly. The living kiwi birds however, have slow development, and it has been speculated that Jeholornis could have had a metabolism similar to these. 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 the flight feathers were asymmetrical (and therefore aerodynamic, as in modern flying birds) and up to 21 centimeters long, longer than the forearm and hand combined. The exact number of flight feathers cannot be determined from known specimens, however, as the preservation is too poor. The tails of several specimens preserve a fan of feathers (rectrices) at the tip, shorter than those on the forelimbs. The feather fan is similar to those of Microraptor and Caudipteryx, being restricted to the tip of the tail, unlike those of Archaeopteryx and Similicaudipteryx which have rectrices extending down much of the tail length. 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. Jeholornis contains at least three species: the type species, Jeholornis prima (named in reference to the Jehol group of fossil beds where it was found, and the primitive appearance of the tail) and two referred species, Jeholornis palmapenis described by Jingmai O'Connor and colleagues in 2012, and Jeholornis curvipes, described by Lefèvre and colleagues in 2014. The name J. palmapenis translates to 'palm tail' in reference to the unusual arrangement of its tail feathers, while the name J. curvipes means 'curved foot' due to a distinctive bend in the bones just above the ankle (metatarsus).