Post on 20-Jan-2016
Fossils & Evolution—Brachiopoda 1
Brachiopods—Stuff to know
• Bold font terms in text
• Classification and stratigraphic ranges of Classes and Orders
• Be able to identify correct Order for any given specimen (not necessary to identify genera)
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Living brachiopods
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Brachiopoda—Phylum overview
• Solitary (but individuals often live in clusters)• Bivalved, with each valve being bilaterally
symmetrical• Marine; mostly shallow marine (100–200m), but
can occur in depths >2000m• Attached by pedicle or unattached; some
infaunal• Filter feeders
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Brachiopoda—Phylum overview
• Possibly share a common ancestor with bryozoans (both groups possess a lophophore)
• Stratigraphic range is Early Cambrian to Recent• Peak diversity in Ordovician, Devonian,
Permian• Major reduction coincident with end-Permian
mass extinction• Mesozoic peak diversity in Jurassic
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Brachiopod diversity
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Classification
O rde r Lingu lidaE a rly C am b ria n-R e ce n t
C lass Ina rticu la tam o stly p ho sph a tica rt icu la tion a bse n t
E a rly C am b ria n-R e ce n t
O rde r O rth idaE a rly C am b ria n -P e rm ian
O rde r Strophom en idaO rd o v ic ia n -T ria ss ic
O rde r P en tam eridaM id d le C a m bria n -D evo n ian
O rde r Rhynchone llidaO rd o vic ia n -R e ce n t
O rde r Sp ir ife r idaO rd o v ic ian -Ju ra ss ic
O rder T e reb ratu lidaE a rly D e vo n ia n -R e ce n t
C lass A rticu la taca lc it ic
a rt icu la tio n by tee th a n d so cke tsE a rly C am b ria n-R e ce n t
Phylum BrachiopodaE a rly C am b ria n-R e ce n t
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Brachiopod morphology• Ventral valve (a.k.a. “pedicle valve”)
– Lower or bottom valve
• Dorsal valve (a.k.a. “brachial valve”)– Upper or top valve
• Foramen = pedicle opening (largely or entirely in pedicle valve)
• Anterior = end of shell opposite foramen• Posterior = end of shell containing foramen• Commissure = line along which two valves meet• Hinge = articulation mechanism
– Teeth in pedicle valve; sockets in brachial valve
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Brachiopod morphology
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Hinge, teethand sockets
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Brachiopod morphology
• Shells may be highly ornamented– Growth lines (concentric)– Ribs (radial)– Fold (major raised area)– Sulcus (major depressed area)– Spines (sometimes extensions of growth
lamellae; sometimes discrete structures)
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Shell ornamentation
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Features of the posterior region (pedicle and hinge region)
• Pedicle opening– Delthyrium = triagular opening in pedicle
valve– Notothyrium = smaller opening in brachial
valve– Interarea = planar or curved surface between
“beak” and hingeline• Ventral interarea• Dorsal interarea
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Posterior region
“beak”
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Posterior region (cont.)
Among articulate forms,those with a hinge lineare strophic; thosewithout are astrophic
astrohpic
strophic
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Internal features
• Body cavity houses major organs in posterior region of shell
• Mantle cavity in anterior region of shell is mostly open space
• Lophophore = ciliated, arm-like structure that serves for respiration and food gathering
• Pedicle = muscular stalk for attachment to external objects or substrate
• Adductor and diductor muscles
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Internal soft anatomy
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Musculature(valves tend toclose and stayclosed upondeath)
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Lophophore
• Usually a two-part structure, with each half (brachium; plural brachia) leading to the mouth
• May be complexly looped or coiled
• May be supported by a mineralized structure—spiralium (plural spiralia) or brachidium (plural brachidia)
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Lophophore types
brachia
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Lophophore supports
spiralia spiralialoopedbrachidia
loopedbrachidia
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Class Inarticulata
• Lingula ia an example of a “living fossil”
• Relatively low diversity since Ordovician time
• Infaunal, with long fleshy pedicle
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Inarticulate brachiopods(Lingula et al.)
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Order Orthida Strophic; unequally biconvex valves; usually with well-developed delthyrium/notothyrium openings in interareas
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Order Strophomenida Strophic; convex ventral valve/concave dorsal valve
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Order Strophomenida Strophic; convex ventral valve/concave dorsal valve
(Suborder Productina)
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Order Pentamerida Strophic or astrophic; strongly biconvex with incurved
beaks; open delthyrium with spoon-shaped structure (“spondylium”)
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Order RhynchonellidaAstrophic; biconvex shell with dorsal fold and ventral sulcus
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Order Spiriferida Variable shell form; spiralia supports for lophophore
(Suborder Spiriferina)
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Order Spiriferida Variable shell form; spiralia supports for lophophore
(Suborder Atrypina)
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Order Spiriferida Variable shell form; spiralia supports for lophophore
(Suborder Athyrina)
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Order Terebratulida Astrophic (rarely strophic); biconvex shell; loop supports for
lophophore
Cererithyris(Jurassic)