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Proc Natl Acad Sci U S A. 2018 Nov 6;115(45):11555-11560. doi: 10.1073/pnas.1805803115. Epub 2018 Oct 22.

Archaeorhynchus preserving significant soft tissue including probable fossilized lungs.

Author information

1
Institute of Geology and Paleontology, Linyi University, Linyi, 276000 Shandong, China.
2
Shandong Tianyu Museum of Nature, Pingyi, 273300 Shandong, China.
3
Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, 10010 Beijing, China; jingmai@ivpp.ac.cn zhouzhonghe@ivpp.ac.cn.
4
CAS Center for Excellence in Life and Paleoenvironment, 10010 Beijing, China.
5
Department of Zoology, University of Johannesburg, 2006 Johannesburg, South Africa.
6
Key Laboratory of Economic Stratigraphy and Palaeogeography, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, 21008 Nanjing, China.
7
Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, 10010 Beijing, China.

Abstract

We describe a specimen of the basal ornithuromorph Archaeorhynchus spathula from the Lower Cretaceous Jiufotang Formation with extensive soft tissue preservation. Although it is the fifth specimen to be described, unlike the others it preserves significant traces of the plumage, revealing a pintail morphology previously unrecognized among Mesozoic birds, but common in extant neornithines. In addition, this specimen preserves the probable remnants of the paired lungs, an identification supported by topographical and macro- and microscopic anatomical observations. The preserved morphology reveals a lung very similar to that of living birds. It indicates that pulmonary specializations such as exceedingly subdivided parenchyma that allow birds to achieve the oxygen acquisition capacity necessary to support powered flight were present in ornithuromorph birds 120 Mya. Among extant air breathing vertebrates, birds have structurally the most complex and functionally the most efficient respiratory system, which facilitates their highly energetically demanding form of locomotion, even in extremely oxygen-poor environments. Archaeorhynchus is commonly resolved as the most basal known ornithuromorph bird, capturing a stage of avian evolution in which skeletal indicators of respiration remain primitive yet the lung microstructure appears modern. This adds to growing evidence that many physiological modifications of soft tissue systems (e.g., digestive system and respiratory system) that characterize living birds and are key to their current success may have preceded the evolution of obvious skeletal adaptations traditionally tracked through the fossil record.

KEYWORDS:

Aves; Jehol; Ornithuromorpha; lungs; respiration

PMID:
30348768
PMCID:
PMC6233124
DOI:
10.1073/pnas.1805803115
[Indexed for MEDLINE]
Free PMC Article

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