Unusual bone bed reveals a vertebrate community with pterosaurs and turtles in equatorial Pangaea before the end-Triassic extinction

Sep 29, 2026

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Temporally constrained microvertebrate bone beds are used to clarify continental-scale biotic change during the 12 million years before the end-Triassic extinction. The study reports assemblage PFV 393 from Arizona’s Owl Rock Member, dated with high-precision U-Pb zircon to 209.187 ± 0.083 Ma, about 7.6 Ma before the extinction. The preservation documents a diverse local paleocommunity containing multiple reptile and tetrapod lineages, including pterosaurs and stem-turtles, revealing persistence through environmental transition and informing dispersal and ecological coexistence patterns.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages11

Reading Time28 min

AccessFree to download

Significance

Methods and dating context

Fossil assemblage and paleoecology

RESEARCH ARTICLE EVOLUTION EARTH, ATMOSPHERIC, AND PLANETARY SCIENCES Unusual bone bed reveals a vertebrate community with pterosaurs and turtles in equatorial Pangaea before the end-Triassic extinction Ben T. Kligmana,1, Robin L. Whatleyb , Jahandar Ramezanic , Adam D. Marshd , Tyler R. Lysone , Adam J. Fitcha , William G. Parkerd , and Anna K. Behrensmeyera Affiliations are included on p. 10. Edited by Neil Shubin, The University of Chicago, Chicago, IL; received March 16, 2025; accepted May 15, 2025 Temporally constrained microvertebrate bone beds are powerful tools for understanding continent-scale biotic change. Such sites are rare globally in nonmarine settings during the 12 million years (Ma) preceding the end-Triassic extinction (ETE; ~201.5 Ma), obscuring patterns of faunal change across this interval. A vertebrate assemblage from Arizona, USA, provides unique insights into community composition and ecology prior to the ETE. PFV 393 is a macro-and microvertebrate bone bed preserved ina volcaniclastic fluvial channel-fill with a high-precision U-Pb zircon age of 209.187 ± 0.083 Ma. The fossil assemblage consists of three-dimensionally preserved, delicate, and small skeletal elements of known and new taxa that document a local paleocommunity including hybodontiformes, actinopterygians, actinistians, metoposaurids, salientians, synapsids, lepidosaurs, testudinatans, trilophosaurids, Vancleavea, doswelliids, Revueltosaurus, loricatans, phytosaurs, and pterosaurs. The new early-diverging pterosaur is one of the few Triassic pterosaurs found outside of Europe and the only one with a documented precise radioisotopic age. The testudinatan material shows the rapid dispersal of terrestrial stem-turtles across the Pangaean supercontinent in the Norian and refines temporal constraints on the origin of the turtle shell. The presence of vertebrate lineages endemic to the Triassic highlights their persistence in a mesic, fluvial paleocommunity through a prolonged phase of environmental change preceding the ETE. These lineages coexisted with frogs, lepidosaurs, turtles, and pterosaurs-all key elements of post–Triassic Mesozoic communities. The arrival of turtles and pterosaurs in west-central Pangaea therefore may have been driven by the northward drift of Laurentia from humid equatorial conditions into more arid subtropical latitudes. Triassic | end Triassic extinction | Pterosauria | Testudinata | Pangaea The ecological roles for many ofour modern terrestrial vertebrate groups evolved during Late Triassic–Early Jurassic (~237 to 174 Ma), a nearly 60 Ma time span including atransformational Earth system change—the end-Triassic extinction event [“ETE,” ~201.5 Ma; (1, 2)] . Fossils from the Colorado Plateau in southwestern North America offer some of the most informative windows into this prolonged time interval, with species-rich vertebrate bone beds providing the best evidence for past community composition (e.g., ref. 3), the origins of otherwise rare small-bodied living tetrapods such as caecilians and frogs (e.g., refs. 4 and 5) and the ecological rise of dinosaurs and their closest relatives (e.g., ref. 6). The abundance of volcanic ash suitable for U-Pb geochronology has allowed depositional history of the Triassic fossil beds ofthe Colorado Plateau to be reconstructed at exceptional resolution in the outcrop (e.g., refs. 7 and 8) and in subsurface (9). Within the overall time interval, prolonged aridification and climatic instability began ~215 Ma and continued up to the ETE (9–13), but a ~ 12 Ma global gap in macro-and microvertebrate bone beds preceding the ETE has obscured how this impacted the phylogenetic and functional composition of vertebrate communities and how individual lineages responded to environmental change. Filling this critical gap is a vertebrate assemblage from the Owl Rock Member of the upper Chinle Formation at Petrified Forest National Park (PEFO) in northeastern Arizona, with a dire

FAQs

What fossil assemblage is studied, and where was it found?

PFV 393 is a macro- and microvertebrate bone bed from the Owl Rock Member of the upper Chinle Formation in northeastern Arizona’s Petrified Forest National Park.

How old is PFV 393, and how was the age determined?

PFV 393 is dated to 209.187 ± 0.083 Ma using high-precision U-Pb zircon geochronology.

What do the fossils reveal about vertebrate communities before the end-Triassic extinction?

The assemblage shows diverse lineages, including frogs, lepidosaurs, turtles, and pterosaurs, coexisting with more archaic groups in mesic fluvial environments during a prolonged phase of environmental change.

Sep 29, 2026

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