Parallel evolution of jugal structures in Devonian athyridide brachiopods

Here, we describe Sinathyris crassa gen. et sp. nov., a new early Emsian (Early Devonian) athyridide brachiopod with a double spiralium from the Guangxi Province of southern China. Unlike the majority of genera of the subfamily Helenathyridinae, which possess accessory spiral lamellae developed directly from the jugal branches, the form described here shows these lamellae arising from a distally bifurcating jugal stem. These differences suggest that the double spiralium in S. crassa might have appeared independently from the double spiralium of the helenathyridins. To test the subfamily assignment of Sinathyris gen. nov., we carried out phylogenetic analyses, which indicate that the new genus is more appropriately referred to the Didymothyridinae. The cladistic analyses of the athyridides indicate that double spiralia have developed independently among these brachiopods at least five times during their evolutionary history.