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Roger Weller, geology instructor
by Todd Nehem
The Brachiopod is one
of best invertebrate fossils found on our planet that helps us determine
stratigraphic correlation. They are also valuable for age determination because
they can be found throughout the geological time table, except Pre-Cambrian
rocks. The brachiopods have a wide diversity of morphologic features and
richness of materials offered for study of evolution. The brachiopods are
extraordinarily abundant (common) and their shells are well-preserved in the
Paleozoic and Mesozoic deposits and rock formations like limestone. Brachiopods
are marine invertebrates in which the soft parts are enclosed by two deposits of
shell, called valves. This is the reason they are often mistaken for bivalves
and they superficially resemble the bivalve Mollusks called Pelecypods, better
known as clams. Brachiopod or Pelecypod? The brachiopods have been mistaken for
Pelecypods/clams by the average fossil collector, but there is a major
difference between the two invertebrates. One of the differences is in the
shells, the brachiopods shells are not identical as were the clams shells are.
The shells of brachiopods are composed mainly of calcium phosphate, calcium
carbonate, and chitin or some combination of these materials.
They are actually quite different from clams in their anatomy, and they are not
closely related to mollusks at all. In fact they belong to a (possibly
group known as the
because they feed by using a fringe of tentacles known as the
lophophore. These tentacles sweep microscopic
food particles in the water into the creature's mouth. Most species of
brachiopods are attached to the substrate by a muscular stalk, known as the
pedicle. There is however still a
free-floating larval stage.
The brachiopods showed up in the Paleozoic period some 520 million years ago. “Brachiopods have an extensive fossil record, first appearing in rocks dating back to the early part of the Cambrian Period, about 525 million years ago. They were extremely abundant during the Paleozoic Era, reaching their highest diversity roughly 400 million years ago, during the Devonian Period. At the end of the Paleozoic, however, they were decimated in the mass extinction that marks the end of the Permian Period, about 250 million years ago. This event, known as the Permian-Triassic mass extinction, may have killed more than 90 percent of all living species. It was the largest of all extinction events (larger than the major extinction at the end of the Cretaceous that killed off the dinosaurs)” (Brosius).
Summary of Classification: Main Divisions of Brachiopods
Brachiopoda (phylum), bilaterally symmetrical inequivalve marine bivalves, especially characterized by possessing a food apparatus called lophophore. Lower Cambrian-Recent.
Inarticulata (class), valves unhinged, lacking teeth and sockets, the shell is generally chitinophosphatic. Lower Cambrian-Recent.
Atremata (order), opening for pedicle shared by both valves. Lower Cambrian-Recent.
Lingulacea (suborder), chitinophosphatic shell thickened at posterior edge, trough apex of pedicle valve. Lower Cambrian-Recent. “Lingulate brachiopods are also among the oldest of all brachiopods, and the most morphologically conservative, having lasted since the Cambrian with very little change in shape. The preserved specimen of a living lingulate shown here, Lingula, shows the typical tongue-shaped shell (hence the name Lingulata, from the Latin word for "tongue") with a long stalk, or pedicle, with which the animal burrows into sandy or muddy sediments. These are the only brachiopods to support a minor commercial fishery”(U.C. Berkley).
Trimerellacea (suborder), calareous shell with muscle areas on platforms. Middle Ordovician-Upper Silurian.
Neotremata (order), opening for pedicle confined to pedicle valve or lacking. Lower Cambrian-Recent.
Paterinacea (suborder), apex of pedicle valve at posterior extremity, homeodeltidium present. Lower and Middle Cambrian.
Siphonotretacea (suborder), like Paterinacea but lacking a homeodeltidium, pedicle aperture at apex or in front of it. Lower Cambrian-Middle Ordovician.
Acrotertacea (suborder), apex of pedicle valve generally in front of posterior extremity, homeodeltidium lacking. Lower Cambrian-Upper Ordovician.
Discinacea (suborder), pedicle aperture slitlike, brachial valve conical. Middle Ordovician-Recent.
Caniacea (suborder), calcareous shell, pedicle valve generally attached by cementation, brachial valve conical. Middle Ordovician-Recent.
Articulata (class), valves hinged, calcareous, generally bearing well-defined teeth and sockets. Lower Cambrian-Recent.
Paleotremata (order), lack well-developed teeth and sockets. Lower Cambrian.
Orthida (order), sub-circular to semielliptical, generally biconvex shells with radial ribs, having brachiophores and simple or lobate cardinal process. Lower Cambrian-Upper Permian.
Orthacea (suborder), shell impunctate. Lower Cambrian-Lower Devonian.
Dalmanellacea (suborder), shell punctate. Middle Ordovician-Upper Permian.
Terebratulida (order), shell punctate, hinge line very short, bear a looped brachidium. Upper Silurian-Recent. Terebratulids first appear as fossils in the Devonian, as shown in the fossil range chart for brachiopods. Our representative terebratulid shown above is Oleneothyris, which lived during the Eocene. Terebratulids are responsible for the name of "lamp shells" for brachiopods; their shells resemble ancient oil lamps, with the pedicle foramen resembling a wick.
Pentamerida (order), biconvex impunctate shells having a short hinge line, open delthyrium, and generally a well-defined spondylium (the aberrant genus Enantiosphen has a loop). Middle Cambrian-Upper Devonian.
Syntrophiacea (suborder), generally smooth shells, muscle scars in brachial valve not enclosed by crural lamellae. Middle Cambrian-Lower Devonian.
Pentameracea (suborder), smooth or plicate shells, muscle scars in brachial valve enclosed by crural lamellae. Upper Ordovician-Upper Devonian.
Triplesiida (order), biconvex impunctate shells having a moderately short hinge line, forked cardinal process, and flat deltidium. Middle Ordovician-Middle Silurian.
Rhynchonellida (order), biconvex, generally strongly plicate shells having a very short hinge line and prominent beaks. Middle Ordovician-Recent. Their hinges come to a point, a condition paleontologist’s call non-strophic. They are often ridged. The commisure, the line between the two valves or shells, is zigzagged, as can be seen in the somewhat unusual asymmetric rhynchonellid Rhactorhynchia. The earliest fossil rhynchonellids are from the Ordovician period. During the Mesozoic Era, rhynchonellids were the most abundant brachiopods. A few species still exist today.
Rhynchonellacea (suborder), shell impunctate. Middle Ordovician-Recent
Also known as lamp shell Brachiopoda.
Attached to Group
Rhynchoporacea (suborder), shell punctate. Mississippian-Permian.
Strophomenida (order), pseudopunctate shells having a wide hinge line, one valve generally concave, surface costate. Lower Ordovician-Recent. The Strophomenida were the largest order of brachiopods, with about 400 genera. They were also by far the most morphologically diverse group, and included some very unusual forms, as well as more "normal" forms like those pictured above. Strophomenida first appeared in the Ordovician and persisted until the middle Jurassic. Strophomenida may be identified by their supra-apically located pedicle foramen, at least in young shells. Adult Strophomenida lacked an open pedicle foramen, and usually lived attached to the bottom or to other objects by the pedicle valve. One group of Strophomenida, the productids, are characterized by very long spines extending from the shell. These are thought to have functioned as a sort of "snowshoe," supporting and stabilizing the organism on soft mud. Other Strophomenida were attached to the bottom by a cone-shaped pedicle valve, with the upper valve covering the cone like a pot lid. The unusual brachiopod Prorichthofenia from the Permian of Texas is one of these unusual conical forms. This shape is convergent on that of other attached organisms, such as Paleozoic rugose corals and living scleractinian corals, and it is though that, like corals, some Strophomenida bore photosynthetic algae inside their tissues that helped to supply them with food (Williams).
Strophomenacea (suborder), interarea well developed on one or both valves, with deltidium and chilidium; pedicle foramen very minute or lacking. Lower Ordovician-Recent.
Productacea (suborder), interarea reduced or lacking, spines along posterior margin or distributed over shell surface. Upper Ordovician-Upper Permian.
Spiriferida (order), shells containing a spiral brachidium. Middle Ordovician-Jurassic. Spiriferida are easy to identify. They often have an extended hinge line so wide they look winged. Other prominent characters are the fold and the sulcus that you can see in the middle of the Spiriferida shown here. The feature that gives the Spiriferida their name ("spiral-bearers") is the internal support for the lophophore; this support, which is often preserved in fossils, is a thin strip of calcareous material that is typically coiled tightly within the shell.
Paraspirifer bownocki, from the Devonian of Ohio, is shown here. The gold color is actually pyrite (fool's gold) that was precipitated on the inside of the shell after burial.
Atrypacea (suborder), impunctate shells mostly having a very short hinge line and spiralia not directed toward cardinal extremities. Middle Ordovician-Lower Mississippian.
Spiriferacea (suborder), impunctate shells mostly having an extended hinge line, surface marked by costae or plicea, and spiralia directed toward cardinal extremities. Middle Silurian-Jurassic.
Rostrospiracea (suborder), impunctate shells having a short hinge line and lacking costae or plicea. Middle Silurian-Jurassic.
Punctospiracea (suborder), punctuate shells containing a spiral brachidium. Upper Silurian-Jurassic.
Learn more about Brachiopoda and their Anatomy.
A turn-of-the-century chart of brachiopod anatomy, created by the German anatomist Rudolph Lockhart, is available from the Marine Biological Laboratory at Woods Hole, Massachusetts.
Unlike their cousins the
bryozoans, brachiopods are
solitary, and never form colonies. They are limited to marine environments,
although some inarticulate brachiopods like Lingula tolerate brackish
water. During the early to mid Paleozoic Lingulids lived in association with
armored jawless fish (Ostracoderms) in marginal marine environments.
If you have been lucky enough to
actually see a living brachiopod,
it was a representative of this group; Terebratulids are the most abundant brachiopods today, Happy Hunting.
References and Links to Brachiopoda
"Brachiopod Fossils", Ohio History Central, July 1, 2005, http://www.ohiohistorycentral.org/entry.php?rec=1337
Brosius, Liz. Kansas Geological Survey. illustration by Jennifer Sims, Kansas Geological Survey; photographs by John Charlton, Kansas Geological Survey.
Moore, C. Raymond, Cecil G. Lalicker and Alfred G. Fischer. Invertebrate Fossils. New York: McGraw-Hill, 1959.
Twenhofel, H. William and Robert R. Shrock. Invertebrate Paleontology. New York: McGraw-Hill, 1935.
Sandy, M. R., and Schwimmer, B. A., 1996. "Phylum Brachiopoda," in Fossils of Ohio, edited by R. M. Feldmann and Merrianne Hackathorn. Ohio Division of Geological Survey Bulletin 70, p. 210-243.
Sokiran, EV (2002), Frasnian–Famennian extinction and recovery of rhynchonellid brachiopods from the East European Platform. Acta Pal. Pol. 47: 339–354. http://www.palaeos.com/Invertebrates/Lophotrochozoa/Brachiopoda/E0A0E0Brachiopoda.htm#Inarticulates
Weller, Roger. Cochise College Geology Professor. 2009.
Williams, A. Treatise on Invertebrate Paleontology. Part H, Volume 1: Brachiopoda. Geological Society of America and University of Kansas Press. 1965 (Orthida, Strophomenida, picture)