Gnathostome Phylogeny

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Gnathostome Phylogeny
opc
nc
otc
no
pcc
tc
h
s
pq
h
m
the ancestral condition
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Gnathostome Phylogeny
Gnathostomes
Myxiniformes
Osteostracans
Anaspids
Petromyzontiformes
???
Heterostracans
ostracoderms
Vertebrates Finally!!
Ancestral craniate
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Gnathostome Phylogeny

• Gnathostomes
• jawed fishes appear in the Silurian
• neural and hemal arches-metameric
• centrum surrounds notochord-metameric
• three semicircular canals
• median fins - caudal, dorsal, anal
• heterocercal or homocercal caudal fin
• paired pectoral and pelvic fins
• appendicular skeleton
• yaw, pitch, roll

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Gnathostome Phylogeny
Chondrichthyes
Osteichthyes
Placoderms
eugnathostomes
ancestral gnathostome
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Gnathostome Phylogeny

• Placoderms - bony endoskeleton (neural and hemal
  arches, no centrum), heavy bony plates covering
  anterior body, smaller plates (tesserae?)
  covering posterior (no scales)
• Chondrichthyes - cartilaginous endoskeleton
  (centrum in addition to neural and hemal arches),
  some forms have mineralized cartilage placoid
  scales
• Osteichthyes - bony endoskeleton (centrum in
  addition to neural and hemal arches), scales but
  not placoid scales

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Gnathostome Phylogeny
placoderms
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Gnathostome Phylogeny
Dinichthyes aka Dunkleosteus
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Gnathostome Phylogeny
Dinichthyes aka Dunkleosteus
20 cm
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Gnathostome Phylogeny
Dinichthyes aka Dunkleosteus
20 cm?
300 cm?
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extinct dermal bone tesserae nuchal
gap gnathal plates rather than teeth no
spiracle palatoquadrate firmly attached to
chondrocranium musculature of mandible medial to
palatoquadrate
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Gnathostome Phylogeny

• Eugnathostomes
• centrum neural and hemal arches
• scales
• teeth
• spiracle
• no nuchal gap
• palatoquadrate loosely attached
• musculature of mandible lateral to palatoquadrate

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Gnathostome Phylogeny
Chondrichthyes
Osteichthyes
Placoderms
eugnathostomes
ancestral gnathostome
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Chondrichthyes

• The cartilaginous fishes
• Two main groups
• Holocephalians - ratfish, rabbitfish, or chimeras
  (30 species)

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Chondrichthyes

• The cartilaginous fishes
• Two main groups
• Elasmobranchs - sharks (360 species in two major
  groups), skates and rays (450 species)

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Chondrichthyes
placoid scale AKA dermal denticle homologous to
teeth?
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Chondrichthyes

• Unifying synapomorphies
• placoid scales
• ceratotrichia - cartilaginous rods that support
  the fins
• (vs. lepidotrichia in Osteichthyes)
• cartilaginous skeleton
• pelvic fins in males modified to form claspers
• internal fertilization

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Chondrichthyes

• electrosensitivity
• olfaction
• vision
• proprioception

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Chondrichthyes
dentition spiral valve
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claspers internal fertilization viviparity matrotr
ophy
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Lifestyles of the Chondrichthyes

• Skates and rays
• marine
• benthic
• enlarged pectoral fins
• dorsoventrally flattened
• scale number is reduced
• cryptically colored
• durophagous
• teeth modified as flat crushing plates
• some are large, pelagic filter feeders

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Lifestyles of the Chondrichthyes

• Sharks
• usually pelagic marine fishes
• large (often 2 m or more)
• fusiform
• countershaded
• well designed predators

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Chondrichthyes

• Sharks as predators
• locate prey in a geographic sense
• detect prey
• capture prey
• avoid injury
• ingest prey
• digest prey