The latest encrinurid trilobites from the Lower Devonian of Xinjiang, Northwest China

Encrinurids are common in Ordovician and Silurian strata but whether they survived into the Early Devonian is still controversial. This paper documents the encrinurid Batocara sp. near the Silurian-Devonian boundary in western Junggar, Xinjiang. The highest horizon of Batocara sp. is located above the first appearance datum of the Devonian conodont Caudicriodus, confirming that encrinurids may cross the Silurian-Devonian boundary. The presence of Caudicriodus angustoides bidentatus, Zieglerodina planilingu and plate-type loboliths of scyphocrinoids above the highest horizon of Batocara sp. indicates that encrinurids here extend only into the lower part of the first conodont zone of the Lochkovian (i.e., Caudicriodus hesperius Biozone). Encrinurids are widely distributed and easily recognized, and unlike graptolites and conodonts are not controlled by lithofacies. Therefore, it might be possible to use the highest horizon of encrinurids as indicator fossils to identify the approximate position of the Silurian-Devonian boundary in areas or sections where graptolites and conodonts are not present, and at least in northwest China.

Automated summary

This study documents the fossil of the encrinurid-like organism Batocara sp. near the Silurian-Devonian boundary in western Junggar, Xinjiang. The presence of Batocara sp. above the first appearance of the Devonian conodont Caudicriodus suggests that encrinurids may have survived into the Early Devonian. The study also suggests that the highest horizon of encrinurids can be used as indicator fossils to identify the Silurian-Devonian boundary in areas without graptolites and conodonts.