A History of Fishes
Where did they come from?
Evolutionary History
 Fish have adapted to a wide range of
environmental parameters
•
•
•
•
•
Temperatures
pH
O2 Concentrations
Salinity
Depths
A History of Fishes
-1.8°C - 40°C
4 - 10
0 - Saturation
0 - 90
0 - 7000m
2
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
A History of Fishes
3
Evolutionary History
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)
A History of Fishes
6
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
A History of Fishes
7
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)
A History of Fishes
8
Placoderms
A History of Fishes
9
Chondrichthyes
This group
is important
 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
A History of Fishes
10
Chondrichthyes
 Two distinct evolutionary lines
• Elasmobranchii
o Sharks, skates, and rays
• Holocephali
o Ratfishes and chimaeras
A History of Fishes
11
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
A History of Fishes
12
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
A History of Fishes
13
Actinopterygii (Ray-fined fishes)
 Chondrostei
• Sturgeons, and
paddlefishes
A History of Fishes
14
Actinopterygii (Ray-fined fishes)
 Neopterygii
• Remaining
23,000+bony
fishes
A History of Fishes
15
Osteichthyes Lineage
Neopterygii
Evolutionary Review
Ostracoderms - primitive jawless fishes
•No living representatives, possible relatives include hagfish and lamprey
Placoderms - first jawed fishes
Chondrichthyes - cartilaginous fishes
•No apparent descendants
Holocephali - ratfishes
Elasmobranchii -sharks,
skates, & rays
Sarcopterygii - lobe-finned fishes
•Present day lungfishes and coelcanth
Osteichthyes bony fishes
A History of Fishes
Actinopterygii - ray-fined
fishes
Chondrostei - sturgeons &
paddlefishes
Neopterygii remaining bony fishes
17
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
A History of Fishes
18
Physical Properties of
Water
 Water is 800x denser than air!
 Water is incompressible
 Water is a universal solvent
A History of Fishes
19
Have you hugged your
Ichthyologist?
 Ichthyology - study of fishes
• Describing new taxa
• Understanding evolutionary relationships
o Taxonomy and systematics
• Ecology, physiology, and behavior
A History of Fishes
20
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
A History of Fishes
21
Species Names
 Each spp. is assigned a unique two part
scientific name
• Longnose Dace Rhinichthys cataractae
(Valenciennes 1842)
• Names are usually descriptive in some way
o Rhinichthys - nose-fish
o cataractae - the fast water in which it lives
A History of Fishes
22
A History of Fishes
23