Fish History

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Fish History Classification

• Chapter 11

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Part I Early Fishes

• Ostracoderms and Placoderms

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Refresher of geologic time scale

• Paleozoic Era 570 - 240 million years before
  present (mybp)
• Cambrian 570 - 505 mybp
• Ordovician 505 - 438 mybp
• Silurian 438 - 408 mybp
• Devonian 408 - 360 mybp
• Carboniferous 360 - 290 mybp
• Permian 290 - 240 mybp

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Refresher of geologic time scale

• Mesozoic Era 240 - 63 mybp
• Triassic 240 - 205 mybp
• Jurassic 205 - 138 mybp
• Cretaceous 138 - 63 mybp
• Cenozoic Era 63 mybp - present
• Paleogene 63 - 24 mybp
• Neogene 24 mybp - present

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Ostracoderms - earliest vertebrates in fossil
record

• Originated in late Cambrian Period (gt 500 mybp) -
  but first record is from Ordovician
• Were abundant and diverse through the Ordovician
  and Silurian Periods (approx. 100 million years)
• Became extinct by the late Devonian Period
  (approx. 380 - 400 mybp)

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What group preceded Ostracoderms?

• Earliest vertebrates probably like modern
  Cephalochordates (Amphioxus)
• Bilateral symmetry
• Free-swimming (perhaps neotonous larva)
• with cephalic sensory structures
• with branchial gill apparatus
• without bone, jaws or paired fins

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Traits of Ostracoderms

• Boney armor - first record of bone in fossils -
  protection from predators
• Internal skeleton - made of cartilage
• Heterocercal tail
• Lacked true jaws - were pump-filter feeders
• Lacked paired fins - weak swimmers
• Benthic habitat
• Small size - none longer than 15 cm

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Ostracoderm classification

• Two classes
• Class Pteraspidomorphi (diplorhina two nares
• they literally had two separate olfactory bulbs
  in the brain.
• those with a different shell, i.e. dermal armor

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Ostracoderm classification

• Class Cephalaspidomorphi (single nostril)
• jawless fish

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Success of Ostracoderms

• First use of bone
• for protection, not support
• possibly used as auxiliary supply of Calcium?
• Use of filter feeding to exploit common and
  abundant food source plankton and suspended
  organic matter

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Limitations of Ostracoderms

• Habitat limitations
• restricted to benthos
• weak swimmers due to heavy armor
• weight
• inflexibility
• Food limitations
• no jaws - restricted to plankton, suspended
  organics - slow growth

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Fate of Ostracoderms

• Extinct within 100 million years - by late
  Devonian
• Lineage debated...
• possibly lampreys (Petromyzontiformes)
• possibly Chondrichthyes
• possibly Osteichthyes

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Placoderms - earliest gnathostomes

• Originated after the Ostracoderms
• Originated in Silurian Period (440 mybp)
• Abundant and Diverse in Devonian Period
• Extinguished in Carboniferous Period (350 mybp)

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Two key traits account for Placoderm success

• True jaws
• opened new realm of food sources - larger prey
  items vs. filter-feeding - allowed faster growth
  to larger sizes
• Paired fins
• coevolved with acquisition of jaws
• greater control of movement
• more effective pursuit and capture of prey

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Additional traits first appeared in Placoderms

• Bony dermal plates (produced by dermal cells)
  with three layers
• enamel layer - outer surface - hard shiny
• spongy layer - large vacuoles
• lamellar layer - layered strata with flat
  vacuoles
• Bony internal skeleton

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Traits shared with Ostracoderms

• Negatively buoyant (due to heavy plates)
• Occupied benthic and near-benthic habitats
  (epi-benthic)
• Dorsoventrally depressed (common among benthic
  fishes)
• Strictly marine

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Differences from Ostracoderms

• Placoderms reached much greater sizes
• up to 10 m (33 feet) in length
• why? - food source, mobility
• Placoderms had slightly lighter and more flexible
  (articulated) armor

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Success of Placoderms

• Diversity
• greater than any other group of fishes present in
  Devonian
• seven orders within single class
• Duration
• 440 - 350 mybp

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Fate of Placoderms

• Probably evolutionary dead-end
• Plesiomorphies with Chondrichthyes
  Osteichthyes jaws, paired fins, internal
  skeleton - suggest common ancestor
• Apomorphies armor, jaw structure, depressed form
  - suggest they are NOT ancestral to
  Chondrichthyes Osteichthyes

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Part IIClassification Specifics
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Taxonomy The theory and practice of describing,
naming, and classifying organisms. Systematics
The classification of living organisms into
hierarchical series of groups emphasizing their
phylogenetic interrelationships. Nomenclature
The system of scientific names applied to taxa.
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Why is Classification Important?

• Communication
• Prediction

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Why is Classification Important?

• Communication
• - apply consistent names to organisms
• - Genus and species name for each organism is
  unique
• - same name used everywhere
• - important in keeping track of losses of
  biodiversity
• - know which and how many species at certain
  time
• to how severe the loss is in the present
• - Western United States water habitats altered

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Why is Classification Important?

• Communication (cont.)
• - Western United States water habitats altered

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Why is Classification Important?

• Prediction
• - reflects evolutionary history
• - members of a group will share a more common
• ancestor with each other than with members of
• other groups
• - will have inherited similar traits
• - use shared history to infer that closely
  related
• species share similar traits

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Suborder Anabantoidei

• Gouramies
• - possess apparatus that allows extraction of O2
• gulped air.
• Betta
• - systematically classified as gouramies
• - possess apparatus?
• - able to live in low O2 environements

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Why is Classification Important?

• Prediction (cont.)
• - environment
• - can impose an adaptive regime on species that
• live there
• - results in shared features of unrelated
  species
• -Gars and pikes
• - similar body form due to ecological niche

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Taxonomic Categories
Phylum -- Chordata Subphylum Vertebrata Supercla
ss Gnathostomata Grade Teleostomi Class --
Osteichthyes Subclass -- Actinopterygii Infracla
ss -- Neopterygii Division -- Teleostei Order --
Perciformes Family -- Centrarchidae Genus --
Micropterus Species -- salmoides
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Taxonomic Categories

• Current system based exclusively on shared
• common ancestry
• All categories that taxonomists apply to fish
  are
• artificial except for onespecies
• Species is a real entityother categories are
• artificial assemblages
• - most biologists believe that species are
• real entities that exist in nature.

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What is a species?
Biological Species Concept (Mayr 1940)
Biological Species A Group of actually or
potentially interbreeding natural populations
genetically isolated from other such groups by
one or more reproductive isolating mechanisms.

• most commonly applied species concept
• - Some associated problems

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What is a species?

• Problem
• hybridization
• -fish are notorious for this practice
• -hybrids are often sterile (or thought to be!
  (HSB?)
• -some are fertile and able to backcross with
• either parent

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Why are there so many species?

• random genetic changes
• differences in the selective environment
• Anagenesis change in a species over time
• - species exist as a single population and whole
  species
• will change over time and not branch off
  into
• multiple discrete species.

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Why are there so many species?

• formation of multiple species from a single
• ancestral species is due to isolation of the
  population into
• distinct populations or gene pools.
• Why?
• - each population undergoes anagenesis and
• eventually individual populations are
  distinct
• enough to be recognized as separate species.

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Why are there so many species?
What causes isolation? - vicariant event a
geological or climactic event - Isthmus of
Panama the most studied -- around 3.5
mya -- tropical Atlantic separated from
tropical Pacific Allopatric speciation single
species diverge into two species
in separate geographic
locations
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Why are there so many species?

• Sometimes populations of closely related species
  will
• coexist in an environment.
• Genetic independence achieved through premating
• and postmating reproductive isolating
  mechanisms

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Why are there so many species?

• Postmating
• - hybrid sterility
• - inviability
• Why is hybridization rampant among fish?
• - external fertilization
• - eggs and sperm drift in the proximity of
  gametes from
• a different species
• Avoidance
• - sexual selection partners choose appropriate
  mates
• - males are brightly colored to attract females

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Why are there so many species?

• Premating
• - sexual selection partners choose appropriate
  mates
• - males are brightly colored to attract females
• - males especially colorful in genera that have
  a large
• number of coexisting species
• Ecological differences
• limits degree of competition
• food preference, timing and location of spawning

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African Cichlids
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North American Darters
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Linnaean Classification
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Linnaean Classification

• Rules of Nomenclature
• still named the same way as Linnaeus and Artedi
  did in 1758
• genus name is always capitalized
• species name is lower case
• oldest valid name sticks with the species
• genus names are unique among all biota
• species names are unique within a genus
• International Code of Zoological Nomenclature
• American Fisheries Society (US)

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Phylogenetic Classification
Genus 1
Genus 2
Genus 3
Species 1
Species 3
Species 2
Species 2
Species 3
Species 2
Species 1
Species 1
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Phylogenetic Classification

• Cladistics
• lumps together groups that are assumed to share
  a
• common ancestor.
• Clade group that contains an ancestor and all
  of its
• descendents.
• - Guidelines defining clade from Willi Hennig
  (bug man)
• - shared derived characters
• derived character is different from some
  primitive
• common ancestor.

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Character State Gas Bladder
Physoclistous
Physostomous
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Phylogenetic Classification
Terms - homologous characters that are alike in
state due to shared common ancestry -
homoplasy characters that are alike in state for
other reasons - independent origin a trait
can evolve independently in two different
lineages e.g., countercurrent heat exchangers
in mako sharks and tuna.
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Phylogenetic Classification
Terms - homoplasy (cont.) - reversion a
character may revert to a more primitive
state. e.g., some eels lack scales and
paired fins like primitive agnathans.
Ancestors of eels possessed scales and
paired fins, but were lost, thus
reverting to the more primitive state.