54-3 Paleobiology, morphology and evolutionary significance of the Cambrian stem-group chelicerate Molaria

Session: New Approaches to Old Fossil Collections

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Abstract:

Cambrian Burgess Shale-type localities are crucial for understanding the early evolution of animals. The exceptional preservation of soft tissues in these fossiliferous deposits facilitates detailed comparisons between entire faunas and have led to the (re)description of key species and reassessment of their paleobiogeographic distribution. The aim of this work is to revise the morphology, phylogenetic position and spatio-temporal patterns of the enigmatic Cambrian genus Molaria. First described based on the type species M. spinifera in 1912 from the middle Cambrian Burgess Shale (Canada), this taxon was last revisited in 1981 based on over 100 specimens. A second species, M. steini, was described in 2017 from the early Cambrian Sirius Passet (Greenland). Here, we redescribe the type material of M. spinifera including new details of the exoskeleton, internal organs, and appendages. We find evidence that Molaria has phylogenetic affinities with the stem lineage of Chelicerata. We also report a new Molaria species from the early Cambrian Guanshan Biota (China) that reveals detailed appendicular data thanks to micro computed tomography imaging. The spatio-temporal distribution of Molaria indicates a wide diversification and distribution over a relatively short interval (~7 Ma) during the early to mid-Cambrian. These findings mirror patterns observed in other Cambrian genera and contribute to understand the early arthropod evolution.

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

doi: 10.1130/abs/2025AM-8081

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