3 major groups of living fish
cyclostomes, chrondichthyes, Osteichthyes
Cyclostomes
Jawless fish
Myxini (hagfishes) ~ 70 species
NO: vertebrae, paired fins,
jaws, or scales
Petromyzontida (lampreys) ~ 38 spp
have simple vertebrae
no jaws, paired fins, scales
Chondrichthyes
(cartilaginous fishes) ~ 1000 spp
* Elasmobranchii
– Sharks (403)
– Skates & rays (534)
* Holocephali (chimaeras) (33)
– OWN the top predator niche
Osteichthyes
(bony fishes) ~ 34,000 + spp
* Sarcopterygii (lobe-finned fishes) (8)
* Actinopterygii (ray-finned fishes) (34,000 +)
where are fish found
41% freshwater – why so many?
* 1% diadromous
* 58% saltwater
– 44% in shallow water near continents
– 1% lighted open ocean (epipelagic)
– 5% unlighted open ocean (deepwater pelagic)
– 7% ocean bottom (deepwater benthic)
* Highest diversity in the tropics
conservation
Note that ~ 86% of all fish species are found
on or near continents
– Potential for human impacts
* Freshwater fishes: 20-35% extinct or declining
– 35% of 1000 North American species
* Marine fishes: ~ 5% extinct or declining (est)
– most exploited species overfished
– ecological/economic extinction
Systematics
Basis of any taxonomic discipline
* Classification system of hierarchically
arranged names
– Reflects current evolutionary hypotheses about
relationships among taxa
– Can (and do) change as we learn more
* Natural classification
– Based on evolutionary relationships
– Allows predictions based on group membership
* Example: Family Centrarchidae
taxonomy
Describing, naming, arranging into system of
classification, devising ID keys
Systematics
Focuses on determining relationships among
species or higher taxa
Approaches to classification
Cladistics (phylogenetic systematics)
– Basis of modern systematics (Hennig, 1950)
– Two types of characters:
* apomorphies (derived)
* plesiomorphies (ancestral)
– synapomorphies – shared derived characters
– autapomorphies – define single taxa
Common body forms
Elongate, moderate, deep, rounded, compressed slightly, compressed strongly, depressed deeply
Morphology: caudal fin types
A. heterocercal – vertebral column extends into
upper lobe (sharks, sturgeon)
B. protocercal – undifferentiated (lampreys, eels)
C. homocercal – most bony fishes
– Forked, rounded, truncate, lunate, etc.
D. diphycercal – lungfish, coelocanth
Inferring ecology from morphology
- rover-predator
- lie-in-wait (fast-start) predator
- surface-oriented fish
- bottom rover
- bottom clinger
- deep-bodied fish
- eel-like fish
Fish locomotion: using fins
- oscillation of pectoral fins
– wrasses, surfperch, most deep-bodied fishes
at times - oscillation of median fins (eg, dorsal
and anal)
– ocean sunfish, porcupinefish - undulation of pectoral fins
– skates and rays - undulation of dorsal or anal fins
– bowfin, knifefishes
mouth
inferior, subterminal, terminal, supraterminal, superior
scale types
placoid – toothlike, with enamel
& dentine layers
– Chondrichthyes
– rough surface improves
hydrodynamics
– origin of chondrichthyan (& all
vertebrate) teeth
* cosmoid – bone & cosmine
– lungfishes & coelocanths
– from fusion of placoid scales
– highly modified in recent
lungfishes
ganoid – bone & ganoine
– platelike, non-overlapping
– Articulate with ball-and-socket
joint
– Found in primitive
actinopterygians (bowfin,
gars, paddlefish, sturgeons)
cycloid
– Trout, minnows, herring
– smooth margin
* ctenoid
– spiny-finned teleosts
– toothed margin improves
hydrodynamics
conodonts
Class Conodonta
* late-Cambrian to late
Triassic
– earlier “protoconodonts”
not chordates
* abundant tooth-like
fossils
– ‘conodont elements’
– biostratigraphy
* soft body not found
until 1980s
Ostracoderms
= “shell-skinned”
* not a clade! Paraphyletic …
* late Cambrian to late Devonian
* bony shield over head/thorax - endodermal bone
* small (to ~ 30cm)
* many with hypocercal tail
– reverse heterocercal
* Four distinct superclasses
– Pteraspidomorphi
– Anaspidomorphi
– Theolodonti
– Osteostracomorphi
* likely sister taxon to jawed vertebrates
* generally benthic, poor swimmers
* likely deposit feeders, but w/ muscular feeding pump
* a few deep-bodied forms (C) used water column
Types of jaw suspension
- Autostylic – mandible not
supported by hyoid arch
– lungfishes, tetrapods,
(holocephalans) - Amphistylic – mandible
partly supported by hyoid
arch
– primitive sharks - Hyostylic – mandible mainly
supported by hyoid arch - most chondrichthians
and all actinopterygians
Placoderms
- presumed most primitive jawed fishes
- possible ancestor to chondrichthyans
- BUT, appear later in fossil record than
Acanthodians - late Silurian – early Carboniferous
– ecological replacement by Chondrichthyes?
“plate-skinned” - ornamented, bony plates over anterior body
- diverse and successful!
– 25-30 families
– 200 genera - d/v compressed
– benthic - some very large
– Dunkleosteus to 6m
Acanthodians
Acanthodians – “spiny sharks”
* oldest jawed vertebrates – before Placoderms
– late Ordovician to early Permian
* NOT closely related to sharks
* now considered the earliest bony fishes
* share with bony fishes:
– operculum
– branchiostegal rays
– three otoliths
* stout median and paired spines
* multiple paired fins in some (fin-fold theory?)
* mostly small (20cm to 2.5m)
* streamlined – water column feeders
* diverse: 9 families, ~ 60 genera
SC Holocephali
- upper jaw fused to cranium
– autostylic suspension
– (holostylic – a version of
autostylic) - teeth as continual growing
plates
– anterior bladelike, rear
crushing - operculum covers 4 gill slits
- separate anal & urogenital
openings - tenaculae
- mostly scaleless
- long pointed tail
- oviparous, few eggs, long development
- adult size 60-200 cm
- benthic, moderate depths (80-2600m)
- main food = hard-shelled inverts
- swimming
– body undulations
– pectoral fin flapping
Osteichthyes
- appeared 425 mya during the Silurian
- probably evolved initially in freshwater
- dominant by 380 mya (mid-Devonian)
- Ostracoderms had just died out
- Acanthodians, placoderms, elasmobranchs
were radiating at the same time
– so origins of bony fishes unclear
coelacanth
- large size (to 2m L)
- lobed fins (which?)
- diphycercal tail
- scales – thick, bony, ± cosmoid
- hollow spines (coel – acanth)
- gular plate
- occipital joint
- autostylic jaw suspension
- fat-filled swim bladder
- spiral valve intestine
- osmoregulation – concentrate urea
- nocturnal
- moderately deep
– 100-400m - congregate in caves
in daytime
– possible limiting
factor - feed drifting, in
‘head-down’ position
