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.
Phylum
Brachiopoda Taxonomy |
Subphylum |
Class |
Order |
Extinct |
Linguiliformea
|
Lingulata
|
Linguilida |
no |
Siphonotretida |
Devonian |
Acrotretida |
Ordovician |
Paterinata |
Paterinida |
no |
Craniformea
|
Craniforma
|
Craniida |
no |
Craniopsida |
Carboniferous |
Trimerellida |
Silurian |
Rhychonelliformea
|
Chileata
|
Chileida |
Cambrian |
Dictyonellidina |
Permian |
Obolellata |
Obolellida |
Cambrian |
Kutorginata |
Kutorginida |
Cambrian |
Strophomenata
|
Orthotetidina |
Permian |
Triplesiidina |
Silurian |
Billingselloidea |
Ordovician |
Clitambonitidina |
Ordivician |
Strophomenida |
Carboniferous |
Productida |
Permian |
Rhynchonellata
|
Protorthida |
Cambrian |
Orthida |
Carboniferous |
Pentamerida |
Devonian |
Rhynchonellida |
no |
Atrypida |
Devonian |
Spiriferida |
Jurassic |
Thecideida |
no |
Athyridida |
Cretaceous |
Terebratulida |
no |
|