P aterimitra pyramidalis from S outh A ustralia: scleritome, shell structure and evolution of a lower C ambrian stem group brachiopod

The tommotiid P aterimitra pyramidalis Laurie, 1986, is redescribed based on well‐preserved material from the lower C ambrian W ilkawillina, W irrapowie and A jax limestones of the F linders R anges, S outh A ustralia. The material shows that the scleritome of P aterimitra pyramidalis includes three sclerite morphotypes (S1, S2 and L). Detailed shell microstructure studies show striking similarities with both the paterinid brachiopod A skepasma toddense and the tommotiid E ccentrotheca helenia , which strengthens the suggested evolutionary link between tommotiids and brachiopods. Based on the partly articulated specimens and similarities in shell microstructure and sclerite morphology with E ccentrotheca , P aterimitra pyramidalis is reconstructed as a tube‐dwelling, epifaunal, sessile, filter‐feeder with an organic pedicle‐like attachment structure. The proposed reconstruction of the scleritome comprises a basal unit composed of one S1 and one S2 sclerite, as well as an unresolved number of L sclerites lining a coniform tubular structure.