Taphonomy ofIsisfordia duncanispecimens from the Lower Cretaceous (upper Albian) portion of the Winton Formation, Isisford, central-west Queensland

Caitlin E Syme,Steven W Salisbury

doi:10.1098/rsos.171651

Abstract

Taphonomic analysis of fossil material can benefit from including the results of actualistic decay experiments. This is crucial in determining the autochthony or allochthony of fossils of juvenile and adult Isisfordia duncani, a basal eusuchian from the Lower Cretaceous (upper Albian) distal-fluvial-deltaic lower Winton Formation near Isisford. The taphonomic characteristics of the I. duncani fossils were documented using a combination of traditional taphonomic analysis alongside already published actualistic decay data from juvenile Crocodylus porosus carcasses. We found that the I. duncani holotype, paratypes and referred specimens show little signs of weathering and no signs of abrasion. Disarticulated skeletal elements are often found in close proximity to the rest of the otherwise articulated skeleton. The isolated and disarticulated skeletal elements identified, commonly cranial, maxillary and mandibular elements, are typical of lag deposits. The holotype QM F36211 and paratype QM F34642 were classified as autochthonous, and the remaining I. duncani paratypes and referred specimens are parautochthonous. We propose that I. duncani inhabited upper and lower delta plains near the Eromanga Sea in life. Their carcasses were buried in sediment-laden floodwaters in delta plain overbank and distributary channel deposits. Future studies should refer to I. duncani as a brackish water tolerant species.

Highlights

Fossil remains of crocodyliforms, non-avian dinosaurs and osteichthyans encased in calcite-cemented sandstone concretions2018 The Authors
Based on the associated nature of the fossil skeletal elements, along with most fossils occurring in discrete concretionary bodies we were able to assign bone fragments and whole bones to individual I. duncani specimens
Portions of articulated skeletal units are often found truncating the edges of concretions: for example, the right forelimb and rostral portion of the skull of the I. duncani holotype QM F36211; the left femora, right femora and tibia/fibula of QM F58795; and the vertebral column of QM F58794

Summary

Introduction

Non-avian dinosaurs and osteichthyans encased in calcite-cemented sandstone concretions2018 The Authors. Detailed outcrop and core-based sedimentological and stratigraphic investigations of the Winton Formation at Isisford indicate that these remains were deposited in a fluvial to tidally influenced upper and/or lower delta plain proximal to the Eromanga Sea [6,7]. Whether these crocodyliform fossils represent animals that died and were buried in the same environment (autochthonous) or instead are carcasses that were transported from another environment (parautochthonous or allochthonous) (sensu Kidwell et al [8]) has not yet been ascertained. We propose that taphonomic analysis is required to clarify whether I. duncani inhabited this brackish water setting in life

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