Evolution of brachiopods

[3] Under this hypothesis, the Phoronid worms share a similar evolutionary history; molecular data also appear to indicate their membership of Brachiopoda.

[4] Under the Brachiopod Fold Hypothesis, the "dorsal" and "ventral" valves would in fact represent an anterior and posterior shell.

[6] Moreover, the dorsal and ventral valves of Lingula do not display the Hox gene expression patterns that would be expected if they were ancestrally 'anterior' and 'posterior'.

[8] Continuing research in the current century has brought on a new exciting perspective on the affinities of tommotiids: they are now being regarded as stem-group brachiopods.

[9] A later publication (Holmer et al. 2008) asserted that Micrina was a bivalved animal not unlike a brachiopod, having only two armor plates in life.

Unlike the traditional view of them being slug-like animals comparable to Halkieria, the articulated exoskeleton suggest that they were sessile filter feeders,[1][11] just like the brachiopods and their sister-group phoronids.

[13][14] The oldest known brachiopod is Aldanotreta sunnaginensis from the lowest Tommotian Stage, early Cambrian of the Siberia was confidently identified as a paterinid linguliforms.

[15] This mosaic of traits lead to a repeated suggestion of the possibility that paterinates[16][15](or at least a few of them[13]) could be very early diverging members separate from the lingulates.

During the Ordovician and Silurian periods, brachiopods became adapted to life in most marine environments and became particularly numerous in shallow water habitats, in some cases forming whole banks in much the same way as bivalves (such as mussels) do today.