Evolution in the Fossil Record and Molecular Clocks

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GE 031 THE FOSSIL RECORD, Lecture 8 October 15,
2007
Evolution in the Fossil Record and Molecular
Clocks Protostomes /Deuterostomes Knowing
your head from your tail Fossil
Embryos Reading the Relationships of Life
Cladistics and Molecular Clocks
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What is an animal?

• Animals are multicellular heterotrophs with no
  cell walls..

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What is an animal?

• Heterotrophs carnivores, herbivores,
  detritivores
• Multicellular
• Have no cell walls
• Can actively move
• Most reproduce sexually
• Have unique development, with blastula stage
• Most possess unique tissues
• Are very diverse in form and habitat

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Blastula
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Blastula
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Bengtson Zhao, 1997
Olivooides multisulcatus Early Cambrian, 525
Ma, Shaanxi Province, China
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Peterson, 2007
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Protostoma
Porifera
Spiralia
Lophotrochozoa
Deutorostomata
Demospongia
Calcispongia
Platyzoa
Annelida
Mollusca
Ecdysozoa
Cnidaria
Only 6 of 60 phyla shown!
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Porifera

• are aquatic
• named for their thousands of pores
• lack symmetry
• have no tissues or organs
• typical cell choanocyte
• take many forms - fans, cups, crusts, and tubes
• range in size from a few mm wide to more than 1
  meter tall

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Porifera has 10,000 described species!
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Demospongiae
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Demospongiae
spicules
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Demospongiae hexactinellid Euplectella sp.
spicules
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Demospongiae
Wapkia grandis
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Demospongiae
Choia carteri
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Demospongiae
Choia carteri
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Demospongiae
Hazelia sp.
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Demospongiae
hexactinellid
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Calcispongiae
Laosciadia sp.
Leucetta losangelensis
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Calcispongiae
Eiffelia sp.
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Archaeocyatha
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Archaeocyatha
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stromatoporoids
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Parazoa vs. Eumetazoa
Protostoma
Porifera
Spiralia
Lophotrochozoa
Deutorostomata
Demospongia
Calcispongia
Platyzoa
Annelida
Mollusca
Ecdysozoa
Cnidaria
Bilateral Symmetry
Tissues
Multicellularity
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Cnidaria jellyfish, sea anemones, hydras,
corals..

• nearly all marine
• radially symmetrical animals
• form tissues and organs
• stinging cells nematocysts
• discharge their stings if the undulipodia are
  mechanically
• or chemically stimulated.

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Medusa form
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Cnidaria Class Anthozoa (anemones, corals,
etc.) Class Scyphozoa (jellyfish) Class Cubozoa
(box jellies) Class Hydrozoa (Hydra etc.)
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Cnidaria (9,500 described species)
An anemone Class Anthozoa, Subclass
Hexacorallia, Order Actiniara
A Gorgonian, Gorgonia Class Anthozoa, Subclass
Octocorallia, Order Gorgonacea
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Cnidaria (9,500 described species)
The common coral Acropora, or 'Stag's Horn' 
Class Anthozoa, Subclass Hexacorallia, Order
Scleractinia
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Class Anthozoa, Subclass Alcyonaria, Order
Pennatulacea
Ptilosarcus gurneyi
Thaumaptilon walcotti
Charniodiscus arboreus
Recent, British Columbia
Middle Cambrian, British Columbia
Vendian, South Australia
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Mackenzia costalis
Xianguangia sinica
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Class Anthozoa, order Actiniaria
Cnidopus japonicus
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Class Cubozoa, Family Carybdeidae Carybdea
marsupialis (Box Jelly)
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Cnidaria (9,500 described species)
Hydra Class Hydrozoa Order Hydroida
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Cnidaria (9,500 described species)
Aequoria Class Hydrozoa Order Siphonophora
A jellyfish, Cyanea, Class Scyphozoa, Subclass
Discomedusae, Order Semaeostomeae
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http//www.imagequest3d.com/cgi-bin/ImageFolio3/im
ageFolio.cgi?directaquatic/cnidaria/hydrozoaimg
Aequoria. Class Hydrozoa Order Siphanophorae
Physalia physalis Class Hydrozoa, Order
Siphonophora
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Parazoa vs. Eumetazoa
Protostoma
Porifera
Spiralia
Lophotrochozoa
Deutorostomata
Demospongia
Calcispongia
Platyzoa
Annelida
Mollusca
Ecdysozoa
Cnidaria
Bilateral Symmetry
Tissues
Multicellularity
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(all triploblast)
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Parazoa vs. Eumetazoa
Protostoma
Porifera
Spiralia
Lophotrochozoa
Deutorostomata
Demospongia
Calcispongia
Platyzoa
Annelida
Mollusca
Ecdysozoa
Cnidaria
Bilateral Symmetry Triloblasty, Coelom
Tissues
Multicellularity
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Parazoa vs. Eumetazoa
Protostoma
Porifera
Spiralia
Lophotrochozoa
Deutorostomata
Demospongia
Calcispongia
Platyzoa
Annelida
Mollusca
Ecdysozoa
Cnidaria
Protostome
Deutorostome
Bilateral Symmetry Triloblasty, Coelom
Tissues
, amphiblasty
Multicellularity
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Parazoa(Platyhelminthes) The Flatworms

• ribbon shaped and soft bodied
• have a mouth but no anus
• are acoelomates no mesodermal coelom
• least complex animals with heads
• but more complex than Cnidarians
• they are bilaterally symmetrical
• have organs composed of tissues and organized
  into systems.

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http//tolweb.org/tree/phylogeny.html
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Ecdysozoa
Ecdysozoans have a three-layered cuticle composed
of organic material, which is periodically molted
as the animal grows. This process is called
ecdysis and gives the group its name.
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Ecdysozoa
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Ecdysozoa
Scalidophora (288 species) Priapulida (16
species) Kinorhyncha (150 species) Loricifera
(122 species) Nematoda (20,000
species) Nematomorpha (320 species) Panarthropoda
(6,181,000-10,193,000 species Onychophora (200
species) Tardigrada (1,000 species) Arthropoda
(6,180,000-10,192,000 species)
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Other Pseudocoelomates (Aschelminths) Rotifera
Gastrotricha Kinorhyncha Acanthocephala
Cycliophora Loricifera Chaetognatha Nematomorp
ha Priapulida
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Nematoda the round worms

• Free-living nematodes slender and cylindrical
• Parasitic nematodes a variety of shapes
• lack both segmentation and cilia (except in
  sensory organs)
• they lack circular muscles and have
  longitudinal muscles, so they move by bending or
  flipping
• fixed cell number

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Nematomorpha (horse hair worms)
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Maotianshania cylindrica from Chengjiang
Nematomorpha
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Nematomorph from Orsten-type deposit
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Phylum Priapulida (Phallus Worms, 16 described
species)
Priapulid worm, Priapulus caudatus Family
Priapulidea
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Phylum Priapulida
Ottoia prolifica Burgess Shale,
515 Ma
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Palaeopriapulites
Palaeopriapulites
Priapulus caudatus
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Chaetognatha (arrow worms)
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Chaetognatha from Chegjiang
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Arthropoda insects, spiders, crabs

• distinguished by having segmented bodies and
  segmented appendages.
• body usually has 2-3 distinct parts - a cephalum
  (head), a thorax (chest), and an abdomen
• hardened external skeleton (exoskeleton), made
  of chitin.
• many metamorphose the egg develops into a
  larval form that differs from the sexually mature
  adult.

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http//tolweb.org/tree/phylogeny.html
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Sidneyia
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Marrella
Waptia
Naraoia
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Ercaicunia multinodosa
Canadaspis sp
Misszhouia (Naraoia) longicaudata
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Lophotrochozoa
Nemertea Phoronida Bryozoa Entoprocta Brachiopoda
Sipuncula Echiura Mollusca Annelida
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Mollusca clams, snails, squid..

• soft-bodied
• most have an internal or an external shell
• have a mantle a fold in the body wall that
  lines the shell and secretes the calcium
  carbonate of which the shell is made.
• have a radula, a hard strap made of chitin that
  is used to gather food by boring or scraping.
• live in aquatic or moist environments.

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Body fossil
Radula
Odontogriphus
Jean-Bernard Caron Et al., 2006
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Jean-Bernard Caron Et al., 2006
Odontogriphus
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Caudofoveata? Aplacophora ?Polyplacophora ?Monopla
cophora Bivalvia Scaphopoda Gastropoda Cephalopoda
http//tolweb.org/tree/phylogeny.html
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Annelida the true worms

• distinguished by ringlike external segments
• these coincide with internal partitions
  containing digestive and reproductive organs
  repeated in tandem.
• many develop from free-swimming ciliated larvae
  known as trochophores.

• have bristles composed of chitin used for
  locomotion or
• other functions, such as anchoring the worms in
  their burrows.

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Annelida
Class Polychaeta ?Class Clitellata Oligochaeta -
earthworms, etc Acanthobdellida Branchiobdelli
da Hirudinea - leeches ?Class Myzostomida -
crinoid parasites ?Class Archiannelida -
polyphyletic
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Phylum Annelida (True Worms, 12,000 described
species)
Polychaete worm, Pontodora sp. FamilyProtodrilidae
, Order Phyllodocida, Class Polychaeta
Polychaete worm, Poeobius meseres Family
Poeobiidae, Order Poeobiida, Class Polychaeta
Polychaete worm, Harmothoe anilopes Family
Polynoidae, Order Aphroditoidea, Class Polychaeta
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Phylum Annelida
Feather Duster Worm, Schizobranchia
insignis Family Sabellidae, Order
Sabellida, Class Polychaeta
Earthworm, Lumbricus terrestris Family
Lumbricidae, Order Lumbriculida, Subclass
Oligochaeta, Class Clitellata
Bloodworm, Tubifex tubifex Family
Tubificidae, Order Haplotaxida, Subclass
Oligochaeta, Class Clitellata
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Phylum Annelida
African Leech, Limnatis africana, Family
Hirudinidae, Order Arhynchobellae, Subclass
Hirudinoidea Class Clitellata
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Phylum Annelida
Canadia spinosa
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Phylum Annelida
Burgessochaeta
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Parazoa vs. Eumetazoa
Protostoma
Porifera
Spiralia
Lophotrochozoa
Deutorostomata
Demospongia
Calcispongia
Platyzoa
Annelida
Mollusca
Ecdysozoa
Cnidaria
Protostome
Deutorostome
Bilateral Symmetry Triloblasty, Coelom
Tissues
, amphiblasty
Multicellularity
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Deuterostomes
Chordata
Echinodermata
Notochord Segmentation
Protostoma
Calcium carbonate endoskeleton Radial
symmetry Water vascular system
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Echinodermata starfish, sea urchins

• have tube feet controlled by a water vascular
  system
• calcium carbonate endoskeleton
• adults radially symmetrical!
• exclusively marine
• able to regenerate body parts

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Echinodermata (6,000 described species)
The Pink Star, Pisaster brevenspinus Class
Asteroidea
The Edible Sea Urchin, Tripneustes
ventricosus Class Echinoidea
Deep Sea Stalked Crinoid, Metacrinus
rotundus Class Crinoidea
The Brown Sea Cucumber, Stichopus mollis Class
Holothuroidea
The Common Brittle Star, Ophiothrix
fragilis Class Ophiuridea
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Echinodermata
Echmatocrinus
Eldonia
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Echinodermata
Cotyledion tylodes
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Hemichordata (90 described species)
The Acorn Worm, Saccoglossus bromophenolosus Class
Enteroptneusta
Pterobranch, Cephamodiscus gracilis Class
Pterobranchia
Graptolite, Didymograptus vacillans (Ordovician,
Sweden) Class Graptolithina
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Hemichordata Yunnanozoon lividum
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Yunnanozoon lividum
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Deuterostomes
Chordata
Echinodermata
Notochord Segmentation
Protostoma
Calcium carbonate endoskeleton Radial
symmetry Water vascular system
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Chordates sea squirts, lancelets, and
vertebrates

• our own phylum!!
• have a dorsal nerve cord and notochord
• a tail at some life stage
• the best known of all the animals
• includes mammals, birds, reptiles, amphibians,
  and fish
• 45,000 species

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Phylum Chordata (50,000 described
species) Subclass Cephalochordata
Lancet, Branchiostoma lanceolatum sp.
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Phylum Chordata Subclass Cephalochordata
Lancet, Branchiostoma lanceolatum sp.
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Phylum Chordata Subphylum Cephalochordata
Pikaia gracilens Burgess Shale
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Pikaia
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Phylum Chordata Sub Phylum Cephalochordata
Cathaymyrus diadexus
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Phylum Chordata
Orange sea squirt, Pycnoclavella sp. Family
Clavelinidea, Order Apolusabranchia Superclass
Tunicata, Subphylum Urochordata
www.ambergriscaye.com/ wallpaper/page4.html
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Shu et al., 2001
Cheungkongella ancestralis
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Phylum Chordata
Orange sea squirt, Pycnoclavella sp. Family
Clavelinidea, Order Apolusabranchia Superclass
Tunicata, Subphylum Urchordata
Great White Shark, Carcharodon carcharias Family
Lamnidae, Order Lamniformes Subclass
Elasmobranchii, Subphylum Craniata
Human, Homo sapiens Family Hominidae, Order
Primates Class Mammalia, Subphylum Craniata
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Craniata
Deuterostomes with a Head
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Phylum Chordata
Myllokunmingia fengjiaoa
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Myllokunmingia fengjiaoa
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Craniata
Deuterostomes with a Head
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Phylum Chordata (50,000 described
species) Subclass Craniata
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Big Questions 1. Coelomates vs. the
Ecdysozoa. 2. Where do the lophophorates fit
in? 3. What is the sistergroup to the
Bilateria? 4. Timing of the metazoan
radiation(s).
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Molecular Systematics
Molecular systematics is a branch of systematics
that uses molecular biology techniques. The
evolutionary relationships of organisms are
studied using their DNA, RNA and protein
sequences to establish their systematic
positions. They make use of largely cladistic
methods. The methodology often assumes the
molecular clock hypothesis. Requires living or
very young fossil material but may use fossils
for calibration.
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Underlying Characteristics and Assumptions 1.
Molecular systematics is an essentially cladistic
approach. Assumes that classification must
correspond to phylogenetic descent, and that all
valid taxa must be at least paraphyletic and
preferably monophyletic. 2. Molecular systematics
often uses the molecular clock assumption that
quantitative similarity of genotype is a
sufficient measure of the recency of genetic
divergence, (which is really non-cladistic). This
assumption could be wrong if either some
relatively small genotypic modification acted to
prevent interbreeding between two groups of
organisms, or in different subgroups of the
organisms being considered, genetic modification
proceeded at different rates. 3. In animals, it
is often convenient to use mitochondrial DNA for
molecular systematic analysis.
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Molecular Clock The molecular clock (based on the
molecular clock hypothesis) is a technique uses
molecular data to determine when two species
diverged. It deduces elapsed time from the number
of differences between their DNA RNA or protein
sequences. It is sometimes called a gene
clock. It assumes that the rate of evolutionary
change of any specified protein, RNA, or DNA
molecule was approximately constant over time and
over different lineages. Calibration is required
by use of the fossil record for numerical
estimates.
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Ctenophora Brachiopoda Phoronida
Lophophorata Bryozoa Placozoa
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Ctenophora
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Xanioascus Burgess
Maotianoascus Chengjiang
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Brachiopoda
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Brachiopoda
Lingulella from Chengjiang
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Phoronida
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Bryozoa (Ectoprocta)
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Placozoa
One known species Tricoplax adherens Simplest
Known animal Two-layer body 2-3 mm across
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Coelomates vs. the Ecdysozoa where do the
Lophoporates go?
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• Main problems with Ecdysozoa
• ecdysis may not be a clear unique derived
  character for the Ecdysozoa
• annelids are also moulting animals
• other phyla excluded from the new clade (e.g. the
  gastrotrichs) carry out a gradual ecdysis by
  flaking similar to that of the polychaetes.
• some Ecdysozoa phyla have unrelated embryogeny
  and overall mophophology
• annelids have a body architecture that is more
  similar to arthropods than some of the Ecdysozoa

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What is the sistergroup to the Bilateria?
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Alternative sistergroups to the Bilateria
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Everyone else!
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Timing of the metazoan radiation(s) Would Darwin
be satisfied?
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Molecular Clock Test Case
Honeycreepers
Honeycreepers
Fruit Flies
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Amino acid data
Amino acid distance Plotted against geologic age
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Doushantuo
Chengjiang
Burgess
Peterson, 2007
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BUT !
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Timing of the metazoan radiation(s).
Blair Blair Hedges, 2004
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Molecular clock age of split
Minimum geological age of split
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Darwin would not be satisfied !