Review—Evolution and Phylogeny
Lecture 6b
Determining a Phylogenetic Tree—1
• Based on shared characters (traits)
– Internal or external
• Major derived characters (synapomorphies)—
large scale relationships
– Examples: physostomus vs. physoclistous, ctenoid
scales, thoracic pelvic fins
Determining a Phylogenetic Tree—1
• Secondarily derived traits—fine scale
relationships
– Typically many traits are examined
• Meristic counts and anatomical features
Determining a Phylogenetic Tree—1
Determining a Phylogenetic Tree—2
• Fossil record often used to determine ancestral
origins of major lineages
Determining a Phylogenetic Tree—3
• Gene sequencing and DNA fingerprinting
commonly used to determine relationships
• Molecular clocks—Genes used to determine
when major branch points occur
– Technique uses specific genes known to evolve at
a constant rate
• No selection pressure
• Genetic drift
Determining a Phylogenetic Tree—3
• Molecular clocks must be calibrated—example
– Branching point for birds and mammals  310 mya
• Extensive fossil record
– Hypothesis: all mammals are equally different from
any bird species, at this gene site
Sublass
Neopterygii
Teleosts
Class Actinopterygii
Class Sarcopterygii
Sublass
Chondrostei
Order
Lepisosteiformes
Gars
Sturgeons
Tetrapods
Lungfish
Coelacanth
Primitive Fishes Phylogeny Fish-like form
Osmoregulation
True teeth
Jaws
Swim bladder
Teleosts
Teleostei
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Originated 215 mya
> 26,000 species
Adaptations of jaws, fins, swim bladder, & skeleton
All possess_____ or ______ scales, mobile maxilla
bone, & ________ caudal fin
– Scales overlap like shingles  greater flexibility
Phylogeny—teleostei
Detached maxilla,
cycloid/ctenoid
scales, homocercal tail
Leptocephalus larvae
Weberian ossicles
Physoclistous swim bladder
Cladogram—teleostei
Jaws
Protrusible premaxilla
Teleost Evolution: jaws & feeding
Premaxilla bone
Maxilla bone
Bowfin—non-teleost fish
Synapomorphy—jaw morphology #1
• Protrusible jaw
• Posterior connection of maxilla bone freed
• Swings forward
• Benefits?
Synapomorphy—jaw morphology #2
Pipette mouth—premaxillary
bone also freed
• Structure slides along
groove over skull
•
http://www.xromm.org/projects/fish-feeding
Pipette mouth advantage
• Increased suction power; more focused
Flow speed (m/s)
Gape & protrusion (mm)
– Tradeoff  gape reduction
– Ideal for small prey
• Attack speed also 
• Suction not always
produced
• LMB almost 2x
Pharyngeal teeth
• Protrusion of jaws has tradeoff
– Maxillary bone not toothed in advanced forms
• Pharyngeal teeth well developed in many teleosts
– Gill arches, tongue, bones on roof of mouth
Moray eel—pharyngeal jaws
• Eels have weak suction power
– Swallowing prey more difficult
• Modified anterior gill arches
– Project forward to draw prey in
Moray eel—pharyngeal jaws
Herbivorous teleosts
• Almost all non-teleosts are carnivorous
• Most herbivorous teleosts in freshwater or on
coral reefs
– Feed on algae or aquatic plants
– Many temperate species are omnivorous
Herbivorous teleosts
• Plants  thick cell walls made of cellulose
– How do mammals overcome this?
• Herbivores have pharyngeal mills or gizzards
• Highly acidic stomachs & long intestines
– High intake, low assimilation
Phylogeny—teleostei
Paired fin placement and function
Pectoral fins
placed higher
Pelvic fins thoracic
Synapomorphies—paired fin placement
More primitive  pectorals ventral to gills; horizontal
– Paired fins for stabilization & braking, no spines
Derived  pectorals behind gills & vertical; pelvics thoracic
– Pectorals  maneuvering & thurst
– Pelvic fins  braking & stabilization
• Defense
Paired fin adaptations—more advanced teleosts
Cladogram—teleostei
Dorsal fin
Two dorsal fins
Synapomorphy—Dorsal fin
More primitive  single, only soft-rays, less articulating
– Prevents rolling
More advanced  Two fins
– Anterior fin spinous and retractable
• Function—
– Posterior fin soft rays, articulating
• Function—
Dorsal fin adaptations—more advanced teleosts
Bone reduction occurred throughout
teleost evolution
• Vertebrate reduction— > 60 in elopomorpha 
< 30 in advanced forms
• Reduction in vertebral accessories (ribs)
• Fewer bones in skull and tail
• Scales reduced in size and thickness
Phylogeny—teleostei
Tetraodontiformes—four teeth
• Most derived and recently evolved group
– Originated 65 mya
– 360 living species—mostly marine
Tetraodontiformes
• Many bones fused or lost
• 16 vertebrae
• Premaxilla and maxillary fused
• Pelvic fins lost
• Scales modified into small spines or ossicles, or
bony plates
Tetraodontiformes
Many have adapted to previously unoccupied niches
– Diet of sponges, sea urchin, coral, jellyfish
– Some eat benthic or pelagic invertebrates
Fin swimmers—types?
Tetraodontiformes—Leatherjackets
Triggerfish and filefish—leatherjackets
• Make noise grinding teeth or drumming swim
bladder with pectoral spine-bone
• Locking dorsal spine
• Eyes move independent
Humuhumu………..
“the fish that sews with a
needle and grunts like a pig
Tetraodontiformes—Puffers
Puffers—fill stomach to puff up  3x volume
– Stomach may  volume 100x
– Causes spines to erect—diodontidae
• Freshwater species
• Viscera and eyes are toxic
– 2nd most toxic vertebrate
Fugu anyone?
Tetraodontiformes—Mola
Four species
• Mola mola  weigh > 4000 lbs.
• > 300 million eggs in larger sunfish  low ________
• Highest among vertebrates
• Much of skeleton cartilaginous—secondarily derived
• Feed on abundant jellyfish
• Common bycatch on driftnet and longline fisheries
Slender Mola
http://www.youtube.com/watch?v=U60obmWODLQ