The Ediacaran origin of Ecdysozoa: integrating fossil and phylogenomic data

Ecdysozoans (Phyla Arthropoda, Kinorhyncha, Loricifera, Nematoda, Nematomorpha, Onychophora, Priapulida, Tardigrada) are invertebrates bearing a tough, periodically moulted cuticle that predisposes them to exceptional preservation. dominate the oldest exceptionally preserved bilaterian animal biotas in early mid-Cambrian ( c. 520–508 Ma), with possible trace fossils latest Ediacaran (<556 Ma). The fossil record of Ecdysozoa is among best understood major clades and believed document their origins evolutionary history well. Strikingly, however, molecular clock analyses have implied considerably deeper Precambrian origin for Ecdysozoa, much older than earliest fossils. Here, using an improved set calibrations, we performed Bayesian estimate time-tree sampling all eight phyla first time. Our results recover Scalidophora as sister group Nematoida + Panarthropoda (= Cryptovermes nov.) suggest divergence occurred at least 23 myr before potential ecdysozoan This finding impervious use plausible phylogenies, prior distributions, rate models matrix partitioning strategies. Arthropods exhibit more precision less incongruence between fossil- clock-based estimates clade ages other phyla. Supplementary material: Full methodologies used appendix calibration points available https://doi.org/10.6084/m9.figshare.c.5811381 Thematic collection: article part Advances Cambrian Explosion collection at: https://www.lyellcollection.org/cc/advances-cambrian-explosion