The Jarrow assemblage is a Lagerstätte of Pennsylvanian tetrapods and fish preserved in the Leinster Coalfield, Ireland. Fossils from this site have an interesting taphonomy that is not observed in other Pennsylvanian coal swamp assemblages. The bone material of the Jarrow tetrapods has undergone alteration and eventual coalification – causing specimens to become poorly defined from the surrounding coal matrix. Bone alteration at Jarrow has traditionally been linked to early diagenesis. Here a multi-analytical approach, combining X-ray scanning electron microscopy, cathodoluminescence, micro-computed tomography and laser ablation quadrupole inductively coupled plasma mass spectrometry, is used to investigate the origin of alteration within the Jarrow fossil specimens. Original bone morphology is no longer present, being replaced by bituminous material and sphalerite surrounded by tabular apatite (a morphology atypical of bone apatite). Direct U-Pb dating of this recrystallised apatite provides an age of 302 ± 11.4 Ma. In recrystallised apatite, zonation in halogen elements, variably positive and negative Eu-anomalies and depletion in LREE suggest an influence of hydrothermal fluids sourced during the maturation of the Leinster Coalfield. A new taphonomic model for the Jarrow assemblage is proposed: alteration of primary fossil bone occurred primarily due to burial heating of the Leinster Coalfield caused by Variscan deformation. Bone apatite was dissolved and then recrystalised as tabular crystals in a void followed by the mineralisation of sphalerite and bituminous material within the bone giving the Jarrow assemblage fossils their unique appearance.

SEM-EDX Data

Osteoderms and a vertebra of Ophiderpeton brownriggii NMI.F16850 were mounted in epoxy resin and polished. These were then imaged using cathodoluminescence (CL) and analysed for major elements using SEM-EDX at the iCRAG laboratory, Trinity College Dublin. Analyses were carried out using a Tescan TIGER MIRA3 field emission SEM, equipped with two Oxford XMaxn 150 mm2 EDS detectors. The TIGER MIRA3 instrument utilizes the Oxford Instruments AZtec X-ray microanalysis software suite. The instrument was calibrated using appropriate mineral standards from the Smithsonian Institute (Jarosewich 2002; Jarosewich et al. 1980) following the method of Ubide et al. (2017). Analytical biases using this setup for CaO, P2O5, and F are typically < 1% (O’Sullivan et al. 2021a; Ansberque et al. 2019; Ubide et al. 2017). For elemental Cl analysis, the instrument was calibrated using natural scapolite (meionite) NMNH R6600 obtained from the Smithsonian Institute. Two quality control standards were used; a natural reference material fluorapatite, NMNH 10402 (Jarosewich et al. 1980) and scapolite BB-1 (Kendrick 2012; Kendrick et al. 2013) to verify accuracy. The observed analytical biases for Cl analyses were < 5 %. The detection limit for Cl utilizing this analytical setup is ~ 0.10 wt. %.

LA-Q-ICPMS Data

Apatite from the bone of Ophiderpeton brownriggii NMI.F16850 was also analysed by laser ablation quadrupole LA-Q-ICPMS at the iCRAG laboratory, Trinity College Dublin. The analytical setup utilized a Teledyne Photon Machines G2 laser-ablation system, comprising a 193 nm ArF excimer laser and a Helex II active two-volume ablation cell, coupled to a Thermo Scientific iCAP Qc ICPMS. Analyses were conducted using a 35 µm diameter spot. The repetition rate was 15 Hz and an energy density of 1.6 J/cm² was used. ⁴³Ca was employed as the internal standard element, used to correct for mass bias during analysis. Data reduction used the Iolite software of Paton et al. (2011). For U-Pb geochronology the data reduction scheme VizualAge_UcomPbine (Chew et al. 2014; O’Sullivan et al. 2021a) was used, which enables the use of primary standards with variable common Pb. It, in turn, is based upon the Vizual_Age data reduction scheme of Petrus and Kamber (2012).

The analytical procedure for apatite U-Pb geochronology and trace element analysis used a standard-sample bracketing procedure. The primary reference material was Madagascar apatite (ID-TIMS U-Pb concordia age of 473 ± 0.7 Ma; Chew et al. (2014) and references therein). The secondary reference materials for U-Pb geochronology were Durango apatite (206Pb/238U age of 32.72 ± 0.07 Ma; Paul et al. 2021) and McClure Mountain apatite (weighted mean apatite 207Pb/235U age of 523.51 ± 2.09 Ma; Schoene and Bowring 2006). For trace element analysis NIST612 was the primary standard employed, with Durango fluorapatite and McClure Mountain fluorapatite (values from Chew et al. 2016) employed as the secondary reference materials. U-Pb isotopes and trace elements were acquired simultaneously. In total, the analysed masses were: ⁴³Ca; ⁵¹V; ⁵⁵Mn; ⁸⁸Sr; ⁸⁹Y; ¹³⁷Ba; ¹³⁹La; ¹⁴⁰Ce; ¹⁴¹Pr; ¹⁴⁶Nd; ¹⁴⁷Sm; ¹⁵³Eu; ¹⁵⁷Gd; ¹⁵⁹Tb; ¹⁶³Dy; ¹⁶⁵Ho; ¹⁶⁶Er; ¹⁶⁹Tm; ¹⁷²Yb; ¹⁷⁵Lu; ²⁰²Hg; ²⁰⁴Pb; ²⁰⁶Pb; ²⁰⁷Pb; ²⁰⁸Pb; ²³²Th; and ²³⁸U. Some elements were analysed only to detect inclusions in the laser spot; for example, V was measured to check the raw signal for the presence of pyrite inclusions within the analysed apatite.

CT Data

CT Data was obtained of NMI.F14879 Ophiderpeton brownriggii at the XTM Facility, Palaeobiology Research Group, University of Bristol using a Nikon XTH 225 ST. The specimens were scanned with the following parameters: kV225, µA with a 10mm Cu filter. 3D models were rendered using SPIERS.

Files are either .xlsx, .csv, .tif or .stl. The former three can be read on most computers. .stl files can be viewed in most 3D viewing softwares including the freeware SPIERSview (https://spiers-software.org/)