139-7 A hypersegmented Kylinxia-like Arthropod from the middle Cambrian Marjum Formation (Utah): Insights into arthropod early Evolution and Phylogeny

Session: Evolution of Life in the Cambrian Seas: Biotic, Biogeochemical, and Sedimentological Contexts, Part II

Presenting Author:

Authors:

Abstract:

The lower Cambrian arthropod Kylinxia zhangi is widely regarded as bridging a key morphological gap in the arthropod stem lineage between radiodonts and deuteropods. It was originally described as combining five eyes (as in Opabinia), radiodont-like raptorial frontal appendages, and an arthrodized body composed of a four-segmented head, a long articulated anterior trunk (25 segments), a five-segmented non-articulated posterior trunk (“pygidium”), and a trilobed tail fan. A recent revision, however, proposed a more deuteropod-like morphology, with a six-segmented head and only three eyes.

We report the discovery of a Kylinxia-like arthropod in the middle Cambrian Marjum Lagerstätte in western Utah. Shared features with the Chinese taxon include a large anteromedian eye flanked by smaller lateral eyes, upward-directed radiodont-like frontal appendages, and a body divided into a six-segmented head, a multisegmented articulated anterior trunk, and a short non-articulated posterior trunk bearing caudal outgrowths. This rare Marjum arthropod differs from Kylinxia in having spiniform (rather than triangular) endites on the frontal appendages, spine-like (rather than flap-like) caudal outgrowths, and a much higher number of articulated trunk segments (>60 vs. 25 or 26). It also possesses complex digestive glands reminiscent of leanchoiliid megacheirans. The implications of this significant finding for the phylogenetic placement of Kylinxia and the evolutionary history of arthropods are discussed.

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

doi: 10.1130/abs/2025AM-8018

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.