Jeholornis
| Jeholornis | ||||||||||||
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Fossil plate with Jeholornis sinensis |
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| Lower Cretaceous Period | ||||||||||||
| 110 million years | ||||||||||||
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| Jeholornis | ||||||||||||
| Zhou & Zhang , 2002 | ||||||||||||
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Jeholornis ( Syn. : Shenzhouraptor ) was a primitive bird genus whose fossils in the Cretaceous Jehol group , one as fossil deposit known rock sequence in the northeast China provincial Liaoning were discovered. The nomenclature of the taxon is controversial because two scientific descriptions were published almost at the same time,namingthe same taxon differently.
In addition to Archeopteryx and Rahonavis , Jeholornis was one of the few members of the group of birds close to origin that had a long bony tail without any signs of pygostyle . With up to 27 caudal vertebrae, the tail was even longer than that of all known specimens of the primeval bird Archeopteryx , whose tail consisted of a maximum of 23 vertebrae. Zhou and Zhang (2003) assume that the ancestor of all birds also had at least 27 tails. Jeholornis' caudal spine resembles that of dromaeosaurid deinonychosaurs , a bird-like group of theropod dinosaurs, in one other property : the vertebral bodies were framed by elongated lateral and ventral vertebral processes that stiffened the tail.
On the other hand, Jeholornis shows a more modern anatomy than the geologically older Archeopteryx . In contrast to the very pronounced dentition of the primitive bird, Jeholornis only had three very small teeth in the lower jaw . Presumably in adaptation to eating seeds, both the upper and lower jaws are shorter and more robust. In the expression of the pelvic spine (the sacrum s) takes jeholornis an intermediate position between Archeopteryx and the higher birds one: Compared to the five un -fused pelvic vertebrae ( Sakralia ) that the sacrum of Archeopteryx developed form, and seven or more fused pelvic vertebrae in higher In birds like Confuciusornis , Jeholornis had six pelvic vertebrae that were fused together.
In contrast to Archeopteryx , which presumably lacked a bony sternum , the sternum of Jeholornis appears advanced: It was elongated and equipped with perforated lateral trabecular extensions. Jeholornis was better adapted to flapping flight than the primeval bird : the shoulder joint pit was more backward, the raven bones elongated like struts and the metacarpal bones I and II fused close to the body to form a carpometacarpus . The ratio between the lengths of the front and rear limbs, which in Jeholornis was more in favor of the front limbs , also speaks in favor of better flight ability . Jeholornis' hand, on the other hand, was smaller and more robust than that of Archeopteryx .
In two copies of Jeholornis there are also impressions of the tail feathers - similar to the feathered theropods Caudipteryx and Microraptor , the tail ends in a fan of feathers. Impressions of the wings are also preserved; they prove that Jeholornis had the asymmetrical flight feathers necessary for active flyers.
As in Archeopteryx and a number of theropod dinosaurs, many vertebrae of Jeholornis show pneumatic foramina, which shows that the ancestors of the birds already had a complex breathing system - apparently there were air sacs connected to the lungs , their evaginations (diverticula) including the vertebrae and others Bones filled (pneumatized). In addition, Jeholornis has the earliest phylogenetic evidence of a collarbone air sac - the openings in the sternum processes suggest its presence.
Jeholornis is one of the few Mesozoic birds whose diet there is direct evidence: In the abdomen of a specimen, numerous impressions of round to oval plant seeds can be seen. The fossilized stomach contents show Jeholornis as a grain-eating bird in accordance with the beak morphology.
See also
- Jehol group , Jiufotang formation , Archeopteryx , Confuciusornis , bird skeleton , air sac (bird) , paleornithology
literature
- Zhonghe Zhou : The origin and early evolution of birds: discoveries, disputes and perspectives from fossil evidence. In: The natural sciences . Vol. 91, No. 10, 2004, pp. 455-471, doi : 10.1007 / s00114-004-0570-4 .
- Zhonghe Zhou, Fucheng Zhang: A long-tailed, seed-eating bird from the Early Cretaceous of China. In: Nature . Vol. 418, No. 6896, 2002, pp. 405-409, doi : 10.1038 / nature00930 .
- Zhonghe Zhou, Fucheng Zhang: Jeholornis compared to Archeopteryx, with a new understanding of the earliest avian evolution. In: The natural sciences. Vol. 90, No. 5, 2003, pp. 220-225, doi : 10.1007 / s00114-003-0416-5 .
