Download Chapter 1 Preservation and the fossil record

Chordates
Echinoderms
Molluscs
Segmented worms
Bryozoans
Arthropods
Cnidarians
Sponges
Brachiopods
Deuterostomes (anus
forms before mouth)
Coelomates (true body cavity)
Animals with nerve and muscle cells
Fossils &animals
Evolution—Cnidaria
Multicellular
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Cnidarians—Stuff to know
• All bold font morphologic terms in text
• Classification and stratigraphic ranges of
paleontologically important groups
• Skeletal mineralogy
• Septal insertion patterns in rugosans and
scleractinians
• Hermatypic vs. ahermatypic ecology
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Cnidarians—Be able to identify:
• Order Scleractinia
– Genus Diploria; Genus Montastrea;
Genus Dichocoenia
• Order Rugosa
– Genus Hexagonaria; Genus Pachyphyllum
• Order Tabulata
– Genus Favosites; Genus Halysites;
Genus Aulopora
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Cnidaria—Phylum overview
• Colonial and solitary invertebrates
• Examples include hydroids, jellyfish, sea anemones, corals
• Two body layers (ectoderm and endoderm) separated by
middle, non-cellular (“jelly”) layer (mesogleoa)
• No coelom (no true body cavity)
• No organs
• Primary radial symmetry
• Possess specialized stinging structures (nematocysts)
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Cnidaria—Phylum overview
(cont.)
• Body is a polyp (mouth up) or medusa
(mouth down)
• Digestive system is a central mouth that
leads to a digestive cavity (enteron)
• Mouth may be surrounded by tentacles
• Muscle cells and nerve cells facilitate
simple movements
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Basic body forms
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Cnidaria—Phylum overview
(cont.)
• Skeleton may be absent, internal, or
external
– If present, organic or calcareous
•
•
•
•
Aquatic (fresh and marine)
Suspension feeders
Sessile, planktonic, or nektonic
Stratigraphic range is Late Proterozoic
(Ediacaran) to Recent
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Classification
• Class Hydrozoa (“hydroids,” unimportant as
fossils)
• Class Scyphozoa (jellyfish, unimportant as
fossils)
• Class Anthozoa (true corals and others)
– Exclusively marine
– Polyp stage only; no medusa
– Free-swimming larvae
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Cnidaria classification
Phylum Cnidaria
Class Hydrozoa
(unimportant)
Class Scyphozoa
(unimportant)
Class Anthozoa
(corals et al.)
Subclass Octocorallia
(relatively unimportant)
Subclass Zoantharia
Order Tabulata
(tabulates)
Early Ordovician-Permian
Order Rugosa
(rugose)
Middle Ordovician-Permian
Order Scleractinia
(modern corals)
Middle Triassic-Recent
Note: Permian scleractinian-like
forms are now known
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Skeletal morphology
• Coral skeletons are external and calcareous
– Aragonite or calcite
• Skeleton is secreted by the epidermis at the base
of the polyp
• Skeleton consists of basal plate, radial septa, and
outer wall (theca)
• As skeleton grows upward, new basal plates may
be added
– Tabulae (transverse plates)
– Dissepiments (smaller, curved plates)
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Polyp and
skeleton
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Skeletal morphology (cont.)
• Polyp occupies the calice, the part of the skeleton
above the last-formed tabula or dissepiments
• Skeleton of one coral (solitary or colonial) is a
corallum
• Skeleton of one polyp in a colony is a corallite
• Skeletal tissue between corallites in a colony is
coenosteum
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Skeletal morphology (cont.)
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Skeletal morphology (cont.)
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Skeletal morphology (cont.)
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Septal insertion
• Tabulates lack septa or possess only minor
septa
• Order of septal insertion is the most
important aspect of classification in the
rugose corals and scleractinians
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Septal insertion in Rugose corals
• First six septa are “protosepta”
– Stage 1: cardinal and counter septa
– Stage 2: alar septa (on either side of cardinal septum)
– Stage 3: counterlateral septa (on either side of counter
septum)
• All subsequent septa (metasepta) are added on
either side of cardinal septum and on counter side
of alar septa
• Septa cluster into four quadrants  hence,
“Tetracorals”
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Septal insertion in Rugose corals
Six protosepta
x = cardinal sector
y = alar sector
Fossulae = gaps between
sectors 18
Fossils & Evolution—Cnidaria
Septal insertion in scleractinians
• Stage 1: six protosepta
• Stages 2 and higher: metasepta added in
the center of spaces between existing septa
– Metasepta added in groups of 6, 12, 24, 48, etc.
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Septal insertion in scleractinians
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Coral evolution
• Among the common corals, tabulates (Early
Ordovician-Permian) were first to originate
• Rugose corals (Middle Ordovician-Permian)
might have evolved from tabulates or they might
have a separate ancestor
• Scleractinians might have evolved from rugosans
(?), or from a naked sea anemone
–
–
–
–
Permian “scleractinian-like” forms are known
Late Paleozoic aragonitic rugosans are known
No Early Triassic corals are known
Pattern of septal insertion is quite different in rugosans
and scleractinians
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Coral
evolution
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Coral ecology and reefs
• Hermatypic = reef corals that possess
zooxanthellae (symbiotic algae)
– Shallow, tropical water (25–29°C; < 90 m depth)
– Rapid skeletal growth
– Oligotrophic (low nutrient) environments
• Ahermatypic = non-reef corals without
zooxanthellae
– Wide environmental range (all latitudes)
– Up to 6000 m depth; down to 1°C temp
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