New evidence suggests pyroclastic flows are responsible for the remarkable preservation of the Jehol biota

Abstract

The lower Cretaceous Yixian and Jiufotang formations contain numerous exceptionally wellpreserved invertebrate, vertebrate and plant fossils that comprise the Jehol Biota. Freshwater and terrestrial fossils of the biota usually occur together within some horizons and have been interpreted as deposits of mass mortality events. The nature of the events and the mechanisms behind the exceptional preservation of the fossils, however, are poorly understood. Here, after examining and analysing sediments and residual fossils from several key horizons, we postulate that the causal events were mainly phreatomagmatic eruptions. Pyroclastic density currents were probably responsible for the major causalities and for transporting the bulk of the terrestrial vertebrates from different habitats, such as lizards, birds, non-avian dinosaurs and mammals, into lacustrine environments for burial. Terrestrial vertebrate carcasses transported by and sealed within the pyroclastic flows were clearly preserved as exceptional fossils through this process.

Cellular preservation of musculoskeletal specializations in the Cretaceous bird Confuciusornis

“…The exceptional preservation was enabled by taphonomic processes of charcoalification of carcasses by a hot pyroclastic density flow13. Photomicrography, backscatter scanning electron microscopy (BSEM), computed tomography (CT) scanning, X-ray microdiffraction and energy dispersive X-ray spectroscopy (EDX) analyses of the surrounding sediments and long bone mineralizations were described in a prior study13.…”

“…The exceptional preservation was enabled by taphonomic processes of charcoalification of carcasses by a hot pyroclastic density flow13. Photomicrography, backscatter scanning electron microscopy (BSEM), computed tomography (CT) scanning, X-ray microdiffraction and energy dispersive X-ray spectroscopy (EDX) analyses of the surrounding sediments and long bone mineralizations were described in a prior study13. The specimen bears a suite of morphological characteristics that are diagnostic of Confuciusornis , such as a straight femoral shaft, ball-shaped femoral head with a distinct capital fossa, straight tibiotarsus, proximally fused and very short tarsometatarsus, slit between metatarsal III and IV proximally, metatarsal I attached distally to the lateral side of metatarsal II, slender and splint-shaped metatarsal V, and highly recurved claws with horny sheaths141516 (Supplementary Fig.…”

“…1f,g). Scanning electron microscopy-based energy-dispersive X-ray analysis shows that the tissues comprise mainly carbonaceous materials13 (Supplementary Fig. 2).…”

Histologic Examination of an Assemblage of Psittacosaurus (Dinosauria: Ceratopsia) Juveniles From the Yixian Formation (Liaoning, China)

“…Jiang et al () hypothesized that the Lujiatun animals were caught in pyroclastic flows resulting in the excellent preservation of fossils from the Lujiatun beds. This hypothesis was supported by the fact that a number of animals from the Lujiatun beds that Jiang et al () examined histologically had modifications to their periosteal surface as a result of burning including pits, cracking, and elimination of microstructure close to the periosteal surface (see supplemental figure 20 of Jiang et al, ). On the basis of the previous evidence, Hedrick et al () could not refute the hypothesis that DMNH D2156 was preserved in a pyroclastic flow, but preferred a lahar or fluvial flow due to mineralogical indicators.…”

The Vertebrate Integument Volume 2

“…A recent study of Sinosauropteryx IVPP V12415 provides the most graphic evidence from the Cretaceous (~130 MYA) of a violent end to an animal during a volcanic eruption (Lingham-Soliar 2014a), believed to have generally resulted in the widespread destruction of the Jehol biota (Jiang et al 2014). It compares with relatively recent human and animal victims of a similar fate, i.e., from a volcanic catastrophe in the ancient Roman cities of Pompeii and Herculaneum.…”