Description
Jeholornis were relatively large, primitive birds, 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 both 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. 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 birds, 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. This specimen shows that the
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.
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