ZLY 304 (AGNATHA & GNATHOSTOMATA) EVOLUTION OF FISH TAXONOMY OF FISH BASIC ORGANIZATION & MODE OF LIFE OF FISH

EVOLUTION OF FISH

Fish like creatures evolve 480 mya.

Origin of Chordates Early Cambrianperiod - first vertebrates appeared in the ocean eg: Myllokumingia respiratory gills formed by pharyngeal gill slits about 8 gill openings located in a set of pouches Myllokumingia

Class - Ostracoderms First fishes Torpedo-shaped , Small (12-35cm), jawless, finless Shelled = ostraco / skin = derm polygonal plates around the head and gills  head shield important group during the Silurian and Devonian periods filter feeders Eg Conodonts & Lamprey

Class -Ostracoderms

Conodonts Late Cambrian Eel like, 1-40 cm in length They had a notochord, cranium, myomeres, fin rays, and large eyes No gills, but since they’re little , gas exchange could occur through skin

Lamprey - Petromyzontiformes long, cylindrical bodies cartilage skeletons no paired fins jawless free-swimming predators on other fish Extanct groups Hagfish ex; Mixini Lampreys classified in a group called the agnatha (no jaws) or the cyclostomata (round mouth) HAGFISH

Hagfish - Myxini have a partial cranium (skull), but no vertebrae. Cartilage skeleton No jaws

Lamprey - Petromyzontiformes LAMPREYS

Lamprey - Petromyzontiformes Lampreys have a sucker-like mouth that lacks a jaw. They are living since late Devonian

Gnathostomata – jawed fish Middle Silurian - fish with jaws and teeth were evolved Jaws - adapted from the front elements of the gills teeth – adapted from bony scales near the skin of the mouth paired fins - swimming abilities were enhanced explored more diverse habitats and food Four groups Placodermi (extinct) Acanthodii (extinct) Chondrychthyes (extant - sharks, rays and chimaeras) Osteichthyes (extant - more highly evolved bony fishes)

Placodermi Pelvic fin Pectoral fin

Placodermi Carnivores Silurian to Devonian armored with heavy plates separate head and trunk portions linked by a hinge Had strong jaws paired pectoral and pelvic fins balance and to maneuver facilitate predation Extinction event that happen in the Devonian eradicated Placoderms as well as Ostracoderms

Acanthodians stout spines (acanthi =spine) anterior to their well developed fins 6 pairs of ventro-lateral fins in adition to pectorals and pelvic fins heterocercal tail Slim body, SMALL SCALES, big mouths Initially marine but then mostly freshwater Existed from the Late Ordovician to Early Permian

Chondrichthyes Devonian period (416-360 mya) – sharks appeared Eg; Xenacanthus a freshwater shark bottom dweller robust fins heavily calcified skeleton appeared in the Devonian and died out in the Triassic (250-200 mya).

Ironing board shark Stethacanthus sp. 37-45 MYA

Chrondrichthyes Current 1200 Spp of Chrondrichthyes are TWO CLASSES HOLOCEPHALI – EG; Chimera, Ratfish & Elephantfish ELASMOBRANCHII – Sharks, Skates & Rays Lateral line from the head to the tail first appeared in sharks and rays – helped locate prey in total darkness Cartilage skeleton predators & harmless mollusk eaters keep swimming because they have no swim bladder

TWO FORMS OF SHARKS two distinct forms of sharks: the pelagic and benthic forms. pelagic sharks - move constantly through the water & rely on this movement to pass water across the gills for respiration benthic sharks - sit on the bottom & take in water through a pair of holes at the top of their head called spiracles for respiration

TWO MAIN CLASSES OF CHONDRICTHYES CLASS 1 - HOLOCEPHALI upper jaw fused to the braincase and a operculum covering the gill slits. 35 spp. Spiracle absent Instead of teeth, they have hard grinding plates. Teeth are plate-like - non-deciduous Cartilaginous lacks a true stomach. They usually feed on small benthic creatures. feeding on hard shelled invertebrates.

HOLOCEPHALI Live In Groups In Deep Waters ( 80 -2,600 M). Chimaera Live In Groups In Deep Waters ( 80 -2,600 M). About 30-35 Odd Looking Species. Chimera Or The Ghost Sharks, Ratfish Elephantfish Placoid Scales, Large Eyes, Males Claspers All Are Oviparous - Laying Eggs That Hatch Outside The Mother's Body Spiral valve present oil filled liver is present Ratfish

ELASMOBRANCHS The most successful class of cartilaginous fish sharks, skates and rays five pairs of gill slits, two small openings on the sides of their heads called as SPIRACLES HETEROCERCAL tail.

SKATES pelvic fin divided into two lobes  stocky tail w/o stinging spine  enlarged, thorn-like scales ('bucklers') along the midline of back males have rows of enlarged scales near the eyes and wingtips RAYS one-lobed pelvic fin  whip-like tail, usually with stinging spine  no bucklers along back or tail 

TEETH Most vertebrate have teeth that are locked into sockets in their jaws The teeth of cartilaginous fish are simply attached to the jaw by fleshy tissue

SHARK SENSES AND SEX normal five senses smell/taste is extremely good. LATERAL LINE present Ampullae of Lorenzini located in their snouts. They are connected by pores to their surroundings. These organs can detect electrical impulses. Theoretically they could detect the electric field produced by a 12 volt battery being dropped into the middle of the Atlantic Ocean. Internal fertilization OVIPAROUS, meaning that laying leathery eggs (mermaid’s purses) OVIVIVIPAROUS meaning that the eggs hatch inside the mother and the young are born live.

Class - Osteichthyes Consists of all the bony fish = 30000 species Tilapia and catfish Jaws present & have paired fins Heterocercal caudle fin Gas filled airbladder Single gill slit on each side - Operculum protect the gills Skin is protected by scales external fertilization of egg have sharp eyesight Mucous glands and embedded dermal scales are present in the skin

Class Osteichthyes two sub-classes: Sarcopterygii - LOBE FINNED FISH with lobed, fleshy fins muscular fins supported by bones lungfishes and lobefins Actinopterygii - RAY FINNED FISH thin, flexible skeleton rays the higher bony fishes

Sarcopterygii - LOBED-FINNED FISHES End of Devonian - sea levels dropped at the end of the life became difficult for fishes some fish developed fins that were stiff, rounded and well muscled. Those who had rounded well muscled fins are now called as lobed finned fishes, and as SARCOPTERYGII in Latin. fleshy fins supported by central bones, homologous to the bones in your arms and legs. These fins underwent modification, becoming the limbs of amphibians and their evolutionary descendants such as lizards, canaries, dinosaurs, and humans.

Sarcopterygii - LOBED-FINNED FISHES This group includes six species of lungfishes and one species of coelacanth that has muscular fins with large, jointed bones attaching the fins to the body. The lungfish are a small group found mostly in freshwater stagnant water or ponds that dry up in Africa, South America, and Australia. Current thinking agrees that one of these lobe-finned fishes adapted to moving on the land and was the ancestral amphibian. Although the rest are long extinct are, few Lobed -finned fish still living in the sea such as THE COELACANTH

Sarcopterygii - LOBED-FINNED FISHES COELACANTHS were thought to have become extinct 70 million years ago 1938 -off Madagascar more than 200 have been captured since 1938. Several other populations of coelocanth have now been found, but large numbers being caught are threatening this relic species. Their lobed fins can move alternately, like a walking land animal. They live in deep water and feed near the seabed.

Subphylum - Vertebrata Kingdom - Animalia Phylum - Chordata Subphylum - Vertebrata Super class - Pisces Class - Agnatha jawless fish (50 sp) Hagfish Lampreys Class –Chrondrichthyes cartilaginous fish (600 sp) Sharks Skates Rays Class- Osteichthyes bony fish (30000 sp) 2 sub classes Lungfish, Eels, Carps, Lizardfish, Silversides & Salmon Sub class - Sarcopterygii Lung fish and lobed fin fishes lobed, fleshy fins muscular fins supported by bones Sub class - Actinopterygii ray finned fish thin, flexible skeleton rays the higher bony fishes 21 orders

TELEOST VARIETY Although most teleost fish are fusiform (torpedo) - shaped not all are Seadragon – its shape helps to camouflage it amongst seaweeds

TELEOST VARIETY Sargassum fish

TELEOST VARIETY Sunfish – extremely flattened – swims like a manta ray on its side Marlin – has a long spike (modified upper jaw) that they use for attacking prey and defiance

TELEOST VARIETY Flatfish – effectively a teleost fish on their sides They are born looking like normal fish - but one of their eyes migrates to the other side of the body Some have chromatophores – pigment cells that allow quick camouflaging of animals

TELEOST VARIETY Some teleosts have extra large pectoral and pelvic fins When trying to avoid predators flying fish extend their fins and fly for 10s of meters over the sea surface