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Fishes. Chapter 24. Diversity. “Fish” has many usages extending beyond what are actually considered fishes today (e.g., starfish, etc.). Fishes do not form a monophyletic group. In an evolutionary sense, can be defined as all vertebrates that are not tetrapods.
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Fishes Chapter 24
Diversity • “Fish” has many usages extending beyond what are actually considered fishes today (e.g., starfish, etc.). • Fishes do not form a monophyletic group. • In an evolutionary sense, can be defined as all vertebrates that are not tetrapods. • Common ancestor of fishes is also an ancestor of land vertebrates. • Therefore in pure cladistics, would make land vertebrates “fish. • Approximately 24,600 living species. • Adapted to live in medium 800 times denser than air. • Can adjust to the salt and water balance of their environment.
Diversity • Evolution in an aquatic environment both shaped and constrained its evolution. • “Fish” refers to one or more individuals of one species. • “Fishes” refers to more than one species.
Ancestry of Fishes • Fishes have descended from an unknown free-swimming protochordate ancestor. • Agnathans including ostracoderms. • Gnathostomes derived from one group of ostracoderms. • Four groups of gnathostomes flourished during the Devonian, two survive today.
Fossils of Early Vertebrates • Armored, jawless vertebrates called ostracoderms had defensive plates of bone on their skin. • One group of ostracoderms led to the gnathostomes.
Fossils of Early Vertebrates • Placoderms, one group of early jawed fishes, died out during the Carboniferous. • Left no descendents.
Fossils of Early Vertebrates • Another group, the acanthodians, were common during the Devonian, but became extinct during the Permian. • They were distinguished by having heavy spines on all fins except the caudal (tail) fin. • Possible sister group of the bony fishes.
Fossils of Early Vertebrates • A third group of gnathostomes, the cartilaginous fishes (Class Chondrichthyes) lost the dermal armor and uses cartilage rather than bone for the skeleton. • Sharks, skates, rays, chimaeras.
Fossils of Early Vertebrates • The last group, the bony fishes, are the dominant fishes today. • Ray-finned fishes include most modern bony fishes. • Lobe-finned fishes contain few living species. • Includes sister group of tetrapods. • Lung fishes & coelacanths.
Origins of Bone and Teeth • Mineralization appears to have originated with vertebrate mouthparts. • The vertebrate endoskeleton became fully mineralized much later.
Agnathans • The least derived vertebrate lineages that still survives are class Myxini, the hagfishes and class Petromyzontida, the lampreys. • They lack: jaws, internal ossification, scales, and paired fins. • Pore-like gill openings along the side of the body.
Class Myxini - Hagfish • Entirely marine. • Feeds on annelids, molluscs, crustaceans, & dead or dying fishes. • Predators or scavengers.
Class Myxini - Hagfish • Hagfishes are jawless marine vertebrates that have a cartilaginous skull and axial rod of cartilage derived from the notochord. • They lack vertebrae.
Class Myxini - Hagfish • A hagfish can tie itself in knots to increase leverage when burrowing into a dead fish. • Produces large amounts of slime.
Class Petromyzontida - Lampreys • Lampreys(Class Petromyzontida) are found in fresh and saltwater. • Lampreys have cartilaginous segments surrounding the notochord and arching partly over the nerve cord.
Class Petromyzontida - Lampreys • All ascend freshwater streams to breed. • Marine forms are anadromous. • Freshwater forms move between lakes & streams.
Class Petromyzontida - Lampreys • Lamprey larvae are called ammocoetes. • Larvae look much like amphioxus. • Possess basic chordate characteristics in simplified form. • Suspension feeders.
Class Petromyzontida - Lampreys • Many are parasitic as adults. • Those that are not, do not feed as adults.
Derived Characters of Gnathostomes • Gnathostomes have jaws that evolved from skeletal supports of the pharyngeal slits.
Derived Characters of Gnathostomes • Other characters common to gnathostomes include: • Enhanced sensory systems, including the lateral line system. • An extensively mineralized endoskeleton. • Paired appendages.
Fossil Gnathostomes • The earliest gnathostomes in the fossil record are an extinct lineage of armored vertebrates called placoderms.
Fossil Gnathostomes • Another group of jawed vertebrates called acanthodians radiated during the Devonian period. • Closely related to the ancestors of osteichthyans (bony fishes).
Class Chondrichthyes • Members of class Chondrichthyes have a skeleton that is composed primarily of cartilage. • The cartilaginous skeleton evolved secondarily from an ancestral mineralized skeleton.
Subclass Elasmobranchii • The largest and most diverse subclass of Chondrichthyes, Elasmobranchii, includes the sharks and rays.
Subclass Elasmobranchii • Most sharks have a streamlined body and are swift swimmers. • Heterocercal tail – the upper lobe of the tail is longer than the lower. • Placoid scales. • The upper & lower jaws have a front, functional row of teeth and several developing rows growing behind as replacements.
Subclass Elasmobranchii • Spiral valve in intestine slows passage of food and increases absorptive area. • Large fatty liver aids in buoyancy.
Subclass Elasmobranchii– Acute Senses • Prey is initially detected using large olfactory organs. • Mechanorecptors in the lateral line system sense low-frequency vibrations from far away. • Vision is important at close range. • Bioelectric fields surrounding their prey can be detected using electroreceptors in the ampullae of Lorenzini on the shark’s head.
Subclass Elasmobranchii • All chondrichthyans have internal fertilization. • Oviparous species lay large yolky eggs soon after fertilization. • Some lay eggs in a capsule called a “mermaid’s purse” that often have tendrils to attach it to a some object.
Subclass Elasmobranchii • Ovoviviparous species retain developing young in the uterus while they are being nourished by the yolk.
Subclass Elasmobranchii • In viviparous species, young receive nourishment from the maternal bloodstream through a placenta, or from nutritional secretions produced by the mother. • Some receive additional nutrition by eating eggs & siblings. • Parental care ends as soon as eggs are laid or young are born.
Subclass Elasmobranchii • Skates and rays are specialized for bottom dwelling with a flattened body and enlarged pectoral fins. • Gill openings on ventral surface. • Water enters through spiracles on dorsal surface.
Subclass Elasmobranchii • Stingrays have a slender whip-like tail with one or more saw-edged spines with venom glands at the base. • Electric rays have large electric organs that can discharge high-amperage, low voltage current into the surrounding water.
Subclass Holocephali • A second subclass is composed of a few dozen species of chimaeras, or ratfishes. • Flat plates instead of teeth. • Upper jaw fused to cranium.
Osteichthyes • Osteichthyes are the bony fishes. • Bone replaces the cartilage during development. • A swim bladder is present for controlling buoyancy and respiration in some. • Not a monophyletic group.
Osteichthyes • Fishes breathe by drawing water over four or five pairs of gills located in chambers covered by a protective bony flap called the operculum.
Class Actinopterygii • Ray-finned fishes (class Actinopterygii) contain all the familiar bony fishes – more than 23,600 species.
Class Actinopterygii • The fins, supported mainly by long, flexible rays are modified for maneuvering, defense, and other functions.
Class Actinopterygii • Two main groups of ray-finned fishes. • Chondrosteans (e.g. sturgeons) have heterocercal tails and ganoid scales.
Class Actinopterygii • Neopterygians – one lineage of early neopterygians led to the modern bony fishes (teleosts). • Early type neopterygians include the bowfin and gars.
Class Actinopterygii • The major lineage of neopterygians are teleosts, the modern bony fishes. • Changes in fins increased maneuverability and speed. • Symmetrical, homocercal, tail allows increased speed.
Teleosts • Thinner, lighter cycloid and ctenoid scales replace the heavy dermal armor of primitive ray-finned fishes. Some (e.g. eels) lack scales.
Teleosts • Fins diversified for a variety of functions: camouflage, communication, complex movements, streamlining, etc.
Teleosts • The swim bladder shifted purpose from primarily respiratory to buoyancy. • Gill arches in many diversified into pharyngeal jaws for chewing, grinding, and crushing.
Class Sarcopterygii • Lobed-finned fishes (class Sarcopterygii) include 2 species of coelacanths and 6 species of lungfishes. • This group was much more abundant during the Devonian. • Rhipidistians are an extinct group of sarcopterygians that led to tetrapods.
Class Sarcopterygii • All early sarcopterygians had lungs as well as gills and a heterocercal tail. • Later sarcopterygians have a continuous flexible fin around the tail. • They have fleshy, paired lobed fins that may have been used like legs to scuttle along the bottom.
Class Sarcopterygii • Some lungfishes can live out of the water for long periods of time. • During long dry seasons, the African lungfish can burrow down into the mud and secrete lots of slime forming a hard cocoon where they will estivate until the rains return.
Class Sarcopterygii • Coelocanths arose during the Devonian and peaked (max. species) in the Mesozoic. • One genus, two species currently. • Believed to be extinct for 70 million years, rediscovered in 1938. • The second species was discovered in 1998.
Locomotion in Water • Fishes use trunk and tail musculature to propel them through the water. • Musculature is composed of zigzag bands called myomeres.
Locomotion in Water • Flexible fishes like eels use a serpentine movement. • Not very efficient for high speed. • Fast swimmers are less flexible. • Body undulations limited to caudal region.
