Early Ordovician (Tremadoc) – Carboniferous (Namurian)
Strophomenida is an extinct order of stationary, epifaunal suspension feeders
Characteristics of the Order
- Pseudopunctate shell structure
- Concavoconvex to convexoconcave or even biconvex profile
- Sometimes the teeth are absent and replaced (in function) by hinge line denticles
- Wide hinge line
- Pseudo-deltidium/chilidium present
- Distinct lack of spines
Treatise on Invertebrate Paleontology, Part H, Vol. 2 (2000):
- Extended Information:
- Strophomenate brachiopods with pseudo-punctate shell structure, normally with taleolae; spines absent; shell outline normally with relatively wide hinge line, variable profile from concavoconvex to convexoconcave, also biconvex; delthyrium and notothryum variably covered by pseudo-deltidium and chilidium; some species cemented at the umbo; teeth usually present but sometimes absent and replaced in function by hinge line denticles; cardinal process bifid or trifid; mantle canal systems saccate to pinnate where seen.
- Since the revision of the supraordinal classification of the Braciopoda (Williams & others, 1996) the order Strophomenida is now much more restricted than in the previous Treatise (Moore, 1965), in which it also included the chonetids, productids, davidsonids, oldhaminids, and lyttoniids as well as the strophomenids. The order is restricted to two central superfamilies, the Strophomenoidea and the Plectambonitoidea, neither of which has an external spines (unlike the chonetidines and productidines) bot which invariably have pseudopunctate shell structure (unlike the orthotetidines). The irregular shape of the oldhaminids and lyttoniids are very different from the general bilateral symmetry of the Strophomenida. The key variables within the order are discussed under the two superfamilies below. The Strophomenoidea were derived from the Plectambonitoidea, probably in early Arenig time, and the Plectambonitoidea probably evolved from the Billingselloidea at about the Cambro-Ordovician boundary. Both the included superfamilies were abundant and diverse during Ordovician and early Silurian times, but the Plectambonitoidea dwindled as the Silurian progressed, with a small number lingering into the Eifelian. The Strophomenoidea also floursished during most of the Devonian but where badly depleted by the Frasnian-Famennian extinction, with the few remaining representatives becoming extinct near the end of the Namurian.