FISHby Rheabelle E. Palajos

Ichthyology – study of fishes• The fishes are group of distantly related gill-breathing aquatic

vertebrates with fins.• They are the most ancient and the most diverse of the

monophyletic subphylum Vertebrata within the phylum Chordata.~27,300 living species known

• Fishes developed the appropriate physiological adaptations that enabled them to invade every conceivable type of aquatic habitat. (marine: 58%; freshwater:41%; or both, 1%)

*Catadromous-born in saltwater, spend most of their lives in freshwater, and return to the saltwater to reproduce.

*Anadromous- born in freshwater, moving from freshwater to salt water, and then returning to reproduce.

They diversified during the Devonian period which is also termed as the “Age of Fishes”.

-Most marine fishes live along coasts of landmasses (<200m deep).

-Most freshwater fishes live in rivers and streams rather than lakes and ponds. On a geological time scale, freshwater lakes are temporary.

-Most fishes (freshwater and marine) live in warmer environments.

General Anatomy

Reproduction:At least three modes of reproduction—heterosexual (dioecious) ,

hermaphroditic (External and internal self-fertilization) , and parthenogenetic (unfertilized eggs develop into embryos) --are found in fishes.

Classification:– Phylum Chordata• Subphylum Cephalochordata • Subphylum Vertebrata

– Superclass Agnatha• Class Ostracodermi• Class Myxini• Class Cephalaspidomorphi

– Superclass Gnathostomata • Class Acanthodii • Class Placodermi• Class Chondrichythes• Class Osteichthyes

• Subclass Sarcopterygii –• Subclass Actinopterygii

• Infraclass Chondrostei• Infraclass Neopterygii

Superclass Agnatha - “Jawless” vertebrates including:Class Ostracodermi (“Shelled Skin”) (EXTINCT) - Jawless

fish with bony armor, cartilage skeleton, heterocercal tail, and flattened body. Most < 15 cm long, bottom fish that sucked food from mud. Lacked paired fins. ( first fossil: Ordovician E: end of Devonian)

Class Myxini - Hagfish - Slimey, eel-like fish.Class Cephalaspidomorphi - Lampreys

Superclass Gnathostomata- Vertebrates with jaws including:•Class Acanthodii- First jawed fishes (jaw from first gill arch), bony skeleton, two rows of paired fins on the underside. They have stout ornamented spines in front of all fins. Less than 20 cm long•Class Placodermi (“Plate Skin”) (EXTINCT) - Bony plates in skin, paired fins, flattened bodies, bottom predators, some 6 m or more. (Dominated during late Devonian period and completely died out during the lower Carboniferous period)•Class Chondrichythes- cartilaginous fishes (sharks, skates, rays).

First fossil: Silurian Period marine deposits•Class Osteichthyes (Bony fish) - Most of our present day fish are here. Characterized by: Lungs (or swim bladder), bony scales.

First fossil: Lower Devonian Period freshwater deposits

Class chondrichytes ( Cartilaginous fishes) 2 evolutionary lines

a. Elasmobranchii ( sharks and rays)-cladosilachian (saltwater)-xenacanth (freshwater)-hybodont (ancestors of modern sharks

skates and rays)b. Holocephalic (chimaeras)

-strange group of bottom dwellers

Class Osteichythes (Bony fish):Subclass Sarcopterygii - Lobe-finned - Fins have bony, leg-like supports

5 Infraclasses:a. Actinista (coelecanthimorpha)b. Dipnomorpha (lungfishes)c. Osteolepimorpha (osteolepids)- int. between the fish

and amphibian.d. Porolepimorphae. Rhizodontimorpha

Class Osteichthyes (Bony fish):Subclass Actinopterygii - Ray-finned fish.

Infraclass Chondrostei - Have heterocercal tail and includes sturgeons and paddlefish.

Infraclass Neopterygii - Most present day fish are in this group. Have homocercal tail, swim bladder reduced in size and serves as a device for adjusting buoyancy, highly maneuverable fins, huge variety of body shapes.

TaphonomyWhile fish remains are common in some archaeological contexts, they

tend to be rare relative to the mammal remains in most sites.Significant taphonomic factors that influence fish remains:1.Those that alter the morphological or physical and chemical characteristics, or completeness of bones

-mineralized cartilage does not preserve well; within bony fishes some bones are more resistant to deterioration and modification than others.

”carcasses of different species of fish do not naturally decay in the same way despite almost equal external conditions”

“the ratio of the size of the body cavity to the mass of the body determines the mode of decay”

-fish bone rarely preserves in acidic sediments, whereas sediments that are neutral or basic are conducive to fish bone survival

-coarse sediments can abrade fish remains 2.Those that affect the spatial distribution of bones

-the degree of disarticulation is an indication of how decomposed fish carcasses were prior to burial; the greater the disarticulation, the longer the carcasses were exposed to bacterial action while underwater but on the surface of the lake bottom or seafloor.

Geological Importance1. They are important sediment makers.2. They may contribute information about limnology,

community composition, life history, mortality, depositional environment, and preservation.

3. Modern fish faunas and associated organisms provide taxonomic, ecological, or functional analogues for interpretation of ancient limiting factors and behaviors.

4. Interpretation of fossil skeletal patterns of disarticulation, disorientation, and displacement allows the possibility of determining temperature and depth of lakes, inferring types of lake stratification (if any) and seasons and causes of death, and of estimating oxygen conditions and something of chemistry and rate of sedimentation.

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