A new family of Cambrian rhynchonelliformean brachiopods (Order Naukatida) with an aberrant coral-like morphology

Abstract

Tomteluva perturbata gen. et sp. nov. and Nasakia thulensis gen. et sp. nov., two new rhynchonelliformean brachiopod taxa, are described from carbonate beds from the lower middle Cambrian (Series 3, Stage 5) basinal Stephen Formation, Canada, and the upper lower Cambrian (Series 2, Stage 4) Henson Gletscher Formation, North Greenland, respectively. The two taxa are characterized by an unusual coral-like morphology typified by a high conical ventral valve with an anteriorly curved umbo and a tube-like structure inside the ventral valve, interpreted as pedicle tube. Both resemble the problematic late middle Cambrian (Drumian) species Anomalocalyx cawoodi Brock from Australia, whose systematic affiliation is controversial. Together, the three genera are interpreted as representatives of a new family of rhynchonelliformean brachiopods, the Tomteluvidae fam. nov., which is interpreted as an aberrant or derived taxon within the Order Naukatida. Convergence between the Tomteluvidae and the coralla of small solitary Cambrian coralimorphs, as well as the late Palaeozoic reef-building richthofenioid brachiopods, might indicate adaptation to a similar life habits and environments. However, their small size (length 4 mm), well-developed pedicle and perfect morphological symmetry make it more likely that tomteluvids lived attached to frondose algae or sponges, above the seafloor, in a similar fashion to the acrotretoid brachiopods with which they show a high degree of morphological convergence. Morphological features of the pedicle tube of N. thulensis suggest that the tomteluvid pedicle is homologous to that in modern rhynchonelliformean brachiopods. This is the first evidence of the pedicle type within the Naukatida and represents the oldest confirmation of a rhynchonellate pedicle.