Fish History & Classification

Chapter 11http://main.nbii.gov/portal/community/Communities/Geographic_Perspectives/Mid-Atlantic/Featured_Projects/EKey_-_Electronic_Key_for_Identifying_Freshwater_Fishes/

Part I: Early Fishes

Ostracoderms and Placoderms

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

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

What happened when?

• Notice where major

evolutionary events

occured.

• Ancestors of fish did

not happen spontaneously.

• Continuous development

was (is) working on each

taxonomic group all

the time.

Ostracoderms (shell-skins) - earliest vertebrates in fossil record

• Originated in late Cambrian Period? (> 500 mybp) - 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)

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

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

Ostracoderm classification

• Two classes: – Class Pteraspidomorphi (sp. diplorhina = “two

nares”) – they literally had two separate olfactory bulbs

in the brain.– those with a different shell, i.e. dermal armor

Ostracoderm classification

– Class Cephalaspidomorphi (“single nostril”)– jawless fish

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

Limitations (failures) of Ostracoderms

• Habitat limitations– restricted to benthos (no kiddin’!?!)– weak swimmers due to heavy armor

• weight

• inflexibility

• Food limitations– no jaws - restricted to plankton, suspended

organics - slow growth

Fate of Ostracoderms*

• Extinct within 100 million years - by late Devonian• Lineage debated...

– possibly lampreys (Petromyzontiformes)– possibly Chondrichthyes– possibly Osteichthyes

How good were they?

• Ostracoderms were key to vertebrate evolution!• Gave rise to jawed vertebrates!• Jaw evoluation considered as the single "greatest

development in vertebrate evolution“

(Romer (1962)

I know I like mine....

Placoderms - earliest gnathostomes(jawed vertebrates)• Originated after the

Ostracoderms:– Originated in Silurian

Period (440 mybp)– Abundant and

Diverse in Devonian Period

– Extinguished in Carboniferous Period (350 mybp)

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

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

Traits shared with Ostracoderms

• Negatively buoyant (due to heavy plates)

• Occupied benthic and near-benthic habitats (epi-benthic)

• Dorsoventrally depressed (flat)--common among benthic fishes

• Strictly marine

Differences from Ostracoderms

• Placoderms reached larger sizes– up to 10 m (33 feet) in length– why? - food source, mobility

• Placoderms had slightly

lighter and more flexible

(articulated) armor

Success of Placoderms

• Diversity:– greater than any other group of fishes present in

Devonian– seven orders within single class

• Duration:– 440 - 350 mybp

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

Part II:Classification Specifics

REM:

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.

Why is Classification Important?

• Communication- “Okay...I get that...”

• Prediction- “Don’t get that...”

• CommunicationCommunication

- apply - apply consistentconsistent names to organisms names to organisms

- Genus and species name for each organism is - Genus and species name for each organism is uniqueunique

- same name used everywhere - same name used everywhere

- important in keeping track of losses of - important in keeping track of losses of biodiversitybiodiversity

- know which and how many species at certain time- know which and how many species at certain time

to how severe the loss is in the present (management)to how severe the loss is in the present (management)

- Ex. Western United States = water habitats altered- Ex. Western United States = water habitats altered

Why is Classification Important?

Why is Classification Important?

Why is Classification Important?

• PredictionPrediction

- reflects evolutionary history- reflects evolutionary history

- members of a group will - members of a group will share a more common share a more common

ancestorancestor with each other than with members of with each other than with members of

other groupsother groups

- will have inherited - will have inherited similar traitssimilar traits

- use shared history to infer that - use shared history to infer that closely relatedclosely related

speciesspecies share similar traits share similar traits

Suborder Anabantoidei- GouramiesGouramies

- possess apparatus that allows extraction of O- possess apparatus that allows extraction of O22

gulped air. (labyrinth organ)gulped air. (labyrinth organ)- BettaBetta

- systematically classified as gouramies - systematically classified as gouramies

- possess apparatus?....yep!- possess apparatus?....yep!

- able to live in low O- able to live in low O22 environments environments

Why is Classification Important?• Prediction (cont.)Prediction (cont.)

- environment- environment- can impose an adaptive regime on species that- can impose an adaptive regime on species that live therelive there

- results in shared features of unrelated species- results in shared features of unrelated species

-Gars and pikes-Gars and pikes

- similar body form due to ecological - similar body form due to ecological nicheniche

Phylum -- ChordataPhylum -- ChordataSubphylum VertebrataSuperclass GnathostomataGrade Teleostomi

Class -- OsteichthyesClass -- OsteichthyesSubclass -- ActinopterygiiInfraclass -- NeopterygiiDivision -- Teleostei

Order -- PerciformesOrder -- PerciformesFamily -- CentrarchidaeFamily -- CentrarchidaeGenus -- Genus -- MicropterusMicropterusSpecies -- Species -- salmoidessalmoides

Taxonomic Categories

- Current system based exclusively on Current system based exclusively on shared shared common ancestrycommon ancestry

- All categories that taxonomists apply to fish areAll categories that taxonomists apply to fish are artificial (descriptive) except for artificial (descriptive) except for one…species

-Species is a real entity (biological)…other is a real entity (biological)…other categories are artificial assemblagescategories are artificial assemblages

- most biologists believe that species are - most biologists believe that species are real entities that exist in nature.real entities that exist in nature.

Taxonomic Categories

Biological SpeciesBiological Species : A group of actually (or potentially) : A group of actually (or potentially) interbreeding natural populations genetically isolated interbreeding natural populations genetically isolated from other such groups by one or more reproductive from other such groups by one or more reproductive isolating mechanisms. isolating mechanisms.

Biological Species Concept (Mayr 1940)

What is a species?

- most commonly applied species conceptmost commonly applied species concept

- Some associated problems- Some associated problems

Problem:Problem:

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

What is a species?

- random genetic changesrandom genetic changes

- differences in the selective environmentdifferences in the selective environment

- Anagenesis: change in a species over time: change in a species over time-- - species exist as a single population and whole species species exist as a single population and whole species will change over time and not branch off into will change over time and not branch off into multiple discrete species.multiple discrete species.

Why are there so many species?

- formation of multiple species from a single formation of multiple species from a single ancestral species is due to ancestral species is due to isolation of the population into of the population into distinct populations or gene pools.distinct populations or gene pools.

Why?- each population undergoes anagenesis and - each population undergoes anagenesis and eventually individual populations are distincteventually individual populations are distinct enough to be recognized as separate species. enough to be recognized as separate species.

Why are there so many species?

What causes isolation?What causes isolation?- - vicariant event: a geological or climactic event: a geological or climactic event

- - Isthmus of Panama = the most studied = the most studied -- around 3.5 mya-- around 3.5 mya -- tropical Atlantic separated from tropical Pacific-- tropical Atlantic separated from tropical Pacific

Allopatric speciation: single species diverge into two speciesAllopatric speciation: single species diverge into two species in separate geographic locationsin separate geographic locations

(squirrels/mountains)(squirrels/mountains)

Why are there so many species?

Why are there so many species?

- Sometimes populations of closely related species will Sometimes populations of closely related species will coexist in an environment.coexist in an environment.

- Genetic independence achieved through prematingGenetic independence achieved through premating and postmating reproductive isolating mechanismsand postmating reproductive isolating mechanisms

Why are there so many species?

- Postmating- - hybrid sterilityhybrid sterility

- - inviabilityinviability

Why is hybridization rampant among fish?- external fertilization- external fertilization- eggs and sperm drift in the proximity of gametes from- eggs and sperm drift in the proximity of gametes from a different speciesa different species

Avoidance:Avoidance:

- sexual selection: partners choose appropriate mates- sexual selection: partners choose appropriate mates- males are brightly colored to attract females- males are brightly colored to attract females

Why are there so many species?

- Premating

- sexual selection: partners choose appropriate mates- sexual selection: partners choose appropriate mates- males are brightly colored to attract females- males are brightly colored to attract females- males especially colorful in genera that have a large- males especially colorful in genera that have a large number of coexisting speciesnumber of coexisting species

-Ecological differencesEcological differences- limits degree of competitionlimits degree of competition

- food preference, timing and location of spawningfood preference, timing and location of spawning

African Cichlids

North American Darters

Linnaean Classification

S p ec ies 1 S p ec ies 2 S p ec ies 3

G en u s 1

S p ec ies 1 S p ec ies 2 S p ec ies 3

G en u s 2

S p ec ies 1 S p ec ies 2

G en u s 3

F am ily

-Rules of NomenclatureRules of Nomenclature

- still named the same waystill named the same way as Linnaeus and Artedi did in 1758as Linnaeus and Artedi did in 1758- genus name is always capitalizedgenus name is always capitalized- species name is lower casespecies name is lower case- oldest valid name sticks with the speciesoldest valid name sticks with the species- genus names are unique among all biotagenus names are unique among all biota- species names are unique within a genusspecies names are unique within a genus

- International Code of Zoological Nomenclature- American Fisheries Society (US)

Linnaean Classification

Phylogenetic ClassificationGenus 1 Genus 2Genus 3

Species 1Species 1

Species 1Species 2Species 3Species 2 Species 2Species 3

- CladisticsCladistics- lumps together groups that are assumed to share a lumps together groups that are assumed to share a common ancestor.common ancestor.

- Clade: group that contains an ancestor and all of itsClade: group that contains an ancestor and all of its descendents.descendents.

- - Guidelines defining clade from Willi Hennig (bug man)Guidelines defining clade from Willi Hennig (bug man)- shared - shared derivedderived characters characters

-derived character: is different from some primitivederived character: is different from some primitive- common ancestor.common ancestor.

Phylogenetic Classification

Character State: Gas BladderPhysostomous Physoclistous

TermsTerms-- homologoushomologous: characters that are alike in state due : characters that are alike in state due

to to shared common ancestryshared common ancestry

- - homoplasyhomoplasy: characters that are alike in state for : characters that are alike in state for otherother

reasonsreasons- - independent originindependent origin: a trait can evolve: a trait can evolve

independently in two different lineagesindependently in two different lineagese.g., countercurrent heat exchangers in e.g., countercurrent heat exchangers in mako sharks and tuna.mako sharks and tuna.

Phylogenetic Classification

TermsTerms- - homoplasyhomoplasy (cont.) (cont.)

- - reversionreversion: a character may revert to a more : a character may revert to a more primitive state.primitive state. e.g., some eels lack scales and paired e.g., some eels lack scales and paired

finsfins like primitive agnathans. Ancestorslike primitive agnathans. Ancestors of eels possessed scales and paired of eels possessed scales and paired

fins,fins, but were lost, thus reverting to thebut were lost, thus reverting to the more primitive state.more primitive state.

Phylogenetic Classification