From the first dawn of life, all organic beings are found to resemble each other in descending degrees, so they can be classed in groups under groups. Charles Darwin, Origin of Species, Chapter 13

Brachiopods are marine organisms commonly called lamp shells that live on continental shelves and the upper parts of continental slopes. The soft parts of brachiopods are covered with a shell made of two valves that vary in size and chracteristics. The two valves are held together in two distinct ways that led to differentiation of brachiopods into two major groups: (1) In Articulate brachiopods, the valves are joined at the posterior end by means of teeth and sockets; and, (2) The Inarticulates, muscles join the two halves.

The brachiopods made their first unambiguous appearance in Early Cambrian, though Neoproterozoic forms are still ambiguous. Lingulids were the most common animals in Late Cambrian followed by Pentamerids. Ordovician brachiopods became more widespread in the Ordovician, as Orthids diversified into Strophomenids and Pentamenids into Rhynchonellids. Terebratulids appeared by the end of Silurian. Then began the phase of disappearance of Articulate brachipods. Many genera of Pentamerids, Strophomenids and Terebratulids disappeared in the Devonian.

After most brachiopods faced extinction in Permian, with only a few non-articulates, some Rhynchonellids, some Spiriferids and some Terebratulids continuing into the Mesozoic Era. Thereafter, brachiopods were represented only by Terebratulids and four non-articulate Orders.

The Brachiopods have left a prodigious and diverse fossil record. Compared with some 12,000 fossil species that are known, only 350 species exist today. Thus, they are much declined from their Paleozoic prominence, and yet the classification of these animals is a continuing challenge, requiring that modern genomics be used to unravel their evolutionary mysteries.