A History of Fishes

Where did they come from?

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Evolutionary History Fish have adapted to a wide range of

environmental parameters• Temperatures -1.8°C - 40°C• pH 4 - 10• O2 Concentrations 0 - Saturation• Salinity 0 - 90• Depths 0 - 7000m

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Diversity and Evolution The diversity of fishes reflects their long

evolutionary history

A major challenge to ichthyologists involves unraveling the evolutionary pathways of both extant (living) and extinct taxa

Evolutionary History

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Ostracoderms Characteristics

• Lack of jaws, lack of paired fins, bony armor, and internal cartilaginous skeleton

Modern day representatives of this group include the classes Pteraspidomorphi (hagfishes) and Cephalaspidomorphi (lampreys)

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Early Jawed fishes Jaws are probably the greatest

advancement in vertebrae evolution• This allowed for an explosion in

diversity due to the different prey items that can be processed

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Placoderms Diverse group with a bizarre

appearance• Jaws, dermal body plates, internal skeleton, and

paired fins

• Some were over 2 meters in size and possessed a craniovertebral joint (increased prey size)

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Placoderms

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Chondrichthyes Arose during the early Paleozoic and

followed a very different line of evolution• Cartilaginous fishes, 2 distinct lines of

evolution, the connection between the two is poorly understood

o Since cartilage does not readily fossilize not a very good fossil record

Characteristics

This group is important

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Chondrichthyes Two distinct evolutionary lines

• ElasmobranchiioSharks, skates, and rays

• HolocephalioRatfishes and chimaeras

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Sarcopterygii (Lobe-finned fishes) Present day lungfishes and coelacanths

• This group has paired fins which actually have muscle in the fin itself

It is this class which is believed to have given rise to the amphibians

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Actinopterygii (Ray-fined fishes) The most successful of all the modern fishes Distinguished form sarcopterygians: triangular

dorsal fin, paired fins without fleshy lobes, and ray finned

As this class flourishes the previous groups decline or disappear, which may show possible ecological interactions

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Actinopterygii (Ray-fined fishes)

Chondrostei• Sturgeons, and

paddlefishes

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Actinopterygii (Ray-fined fishes)

Neopterygii• Remaining

23,000+bony fishes

Neopterygii

Osteichthyes Lineage

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Evolutionary ReviewOstracoderms - primitive jawless fishes

•No living representatives, possible relatives include hagfish and lamprey

Placoderms - first jawed fishes

•No apparent descendants

Chondrichthyes - cartilaginous fishes

Holocephali - ratfishesElasmobranchii -sharks, skates, & rays

Osteichthyes - bony fishes

Sarcopterygii - lobe-finned fishes

•Present day lungfishes and coelcanth

Actinopterygii - ray-fined fishes

Chondrostei - sturgeons & paddlefishes

Neopterygii - remaining bony fishes

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Population Distributions By volume 97% of all water on earth is

found in the worlds oceans• 58% of all fish species are marine• 41% are freshwater species• 1% move between the two habitats

Marine Habitat• 13% of marine species associate in open

water• 78% live over the continental shelf

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Physical Properties of Water Water is 800x denser than air!

Water is incompressible

Water is a universal solvent

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Have you hugged your Ichthyologist?

Ichthyology - study of fishes• Describing new taxa • Understanding evolutionary

relationshipsoTaxonomy and systematics

• Ecology, physiology, and behavior

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Nomenclature The most frustrating aspect of ichthyology

is the constant changing of scientific names

These names change for several reasons: Changes are necessary as new

information is discovered concerning evolutionary history

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Species Names Each spp. is assigned a unique two

part scientific name• Longnose Dace Rhinichthys cataractae

(Valenciennes 1842)• Names are usually descriptive in some

wayoRhinichthys - nose-fishocataractae - the fast water in which it lives

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