58-6 Fossils Bridge Late Triassic Gap in the Non-Marine Vertebrate Paleocommunity Record and Pose New Questions about the End-Triassic Extinction

Session: Future Leaders in Paleontology

Presenting Author:

Ben Kligman

Authors:

Kligman, Ben Thomas¹, Whatley, Robin L.², Ramezani, Jahandar³, Marsh, Adam D⁴, Lyson, Tyler Ranse⁵, Fitch, Adam J⁶, Parker, William⁷, Behrensmeyer, Anna K.⁸

(1) Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC, USA, (2) Columbia College Chicago, Chicago, IL, USA, (3) Massachusetts Institute of Technology, Cambridge, MA, USA, (4) Petrified Forest National Park, Petrified Forest, Arizona, USA, (5) Denver Museum of Nature and Science, Denver, CO, USA, (6) Field Museum, Chicago, Illinois, USA, (7) Petrified Forest National Park, Petrified Forest Natl Pk, AZ, USA, (8) National Museum of Natural History, Smithsonian Institution, Washington, DC, USA,

Abstract:

Despite abundant evidence indicating a mass extinction in marine life at the end-Triassic (~201.4 million years ago, =Ma), gaps in the non-marine record of temporally-constrained vertebrate bonebeds in the ~12 Ma preceding the end-Triassic obscure the timing and nature of extinction in continental vertebrate communities across this interval. A new Late Triassic vertebrate assemblage from the Owl Rock Member of the Chinle Formation in Petrified Forest National Park, Arizona, USA, from fluvial deposits with a high-precision U-Pb zircon age of 209.187 ± 0.083 Ma partially fills this gap.

Sedimentological and taphonomic analyses of the PFV 393 bonebed demonstrate that it was deposited over a short period of time and sampled a limited area, indicating that the fauna represents a contemporaneous paleocommunity. The fossil assemblage consists of three-dimensionally preserved, delicate, and small skeletal elements of known and new taxa including Hybodontiformes, actinopterygians, actinistians, metoposaurids, salientians, synapsids, lepidosaurs, testudinatans, trilophosaurids, Vancleavea campi, a doswelliid, Revueltosaurus sp., loricatans, phytosaurs, and a new species of pterosaur. The presence of vertebrate lineages endemic to the Triassic, including some of the globally-latest occurrences of metoposaurids, trilophosaurids, Vancleavea, and Doswelliids, highlights their persistence in a mesic, fluvial paleocommunity through a prolonged interval of regional warming and aridification. These lineages co-existed with frogs, lepidosaurs, turtles, and pterosaurs - all key elements of post-Triassic Mesozoic communities.  This shows for the first time that their ecological association occurred well before the end-Triassic extinction. The presence of archaic and modern lineages in the same community captures a major transition in Phanerozoic land-vertebrate faunas, possibly driven (at least on the regional scale) by the northward drift of Laurentia from humid equatorial conditions into more arid subtropical latitudes.  

Whether extinction of the archaic fauna was gradual over the 7 million year gap following the PFV 393 bonebed or concentrated at the end of the Triassic remains unknown. Discovery of new evidence for paleocommunities as well as new radioisotopic dates on known assemblages will be essential to establish the tempo and mode of faunal change on land across this pivotal transition in Earth’s history.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7384

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