Paleontologists have examined five specimens with differently preserved feathers from Sapeornis chaoyangensis, an early bird species that lived during the Early Cretaceous epoch, some 125-120 million years ago, and was part of the famous Jehol Biota.
The forelimb feathers of Sapeornis chaoyangensis specimens present different preservations. STM 15-36(A) is the specific detail of forelimb feathers marked with a red rectangle (A) in STM 15-36. Image credit: Zhao et al., doi: 10.3389/feart.2022.1020594.
The Jehol Biota is an Early Cretaceous terrestrial and freshwater ecosystem preserved in a multi-layered rock formation in northeastern China.
It is famous for stunning fossils which preserve soft tissue such as skin, organs, feathers, and fur.
“Jehol Biota provides the most informative source for understanding Mesozoic ecology,” said Dr. Yan Zhao, a researcher with the Institute of Geology and Paleontology at Linyi University.
“Better understanding of the diverse taphonomy of Jehol terrestrial vertebrates can help us finally understand more about the past and future of biological evolution.”
“An exceptionally well-preserved set of soft tissues are reported for myriad taxa from Jehol Biota, which contain irreplaceable information for understanding the early evolution of biological and ecological characteristics. We’d like to probe the factors that influence their preservation.”
In the new research, Dr. Zhao and colleagues analyzed five fossils of Sapeornis chaoyangensis from the Shandong Tianyu Museum of Natural History (STM).
All these specimens preserve a complete and articulated (fossilized with all the joints still connected) skeleton.
One of the specimens, labeled STM 15-36, preserves a complete coat of feathers in astonishing detail.
In addition, the paleontologists collected three host sediments from various sections of each specimen.
They then analyzed the sediments to determine what kind of organic material the birds were surrounded by when they were buried and how the sediments were deposited.
“STM 15-36 was associated with the coarsest sediment grain as well as the best preservation, and the surrounding organic material came mainly from terrestrial plants rather than from lake algae like the other four birds,” they said.
“The climate when STM 15-36 was deposited was warmer and wetter, and the environment it was deposited in was more anoxic, which prevented the decay of the feathers before they were fossilized.”
“There were two possible options to explain STM 15-36’s rapid burial: volcanic activity or a powerful rainstorm washing it away and burying it under other debris,” they added.
“Since fossils in pyroclastic flows don’t preserve soft tissue well, the most likely explanation is that the bird was swept away by a rainstorm and rapidly buried at the bottom of a lake, where a restricted burial environment ensured it wasn’t disturbed.”
This combination of circumstances meant that millions of years later, the beautiful plumage of Sapeornis chaoyangensis would still be preserved in stone.
“This find provides a valuable case study of the taphonomy of Jehol terrestrial vertebrates and the nature of Mesozoic ecosystems,” Dr. Zhao said.
A paper on the findings appears today in the journal Frontiers in Earth Science.
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Yan Zhao et al. 2023. Taphonomic analysis of the exceptional preservation of early bird feathers during the early Cretaceous period in Northeast China. Front. Earth Sci 10; doi: 10.3389/feart.2022.1020594
