5/3/15. Vertebrate Evolution Traces a Long and Diverse History. Construction of Complex Chordate Bodies Begins on a Stiffening Scaffold

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1 Construction of Complex Chordate Bodies Begins on a Stiffening Scaffold Chordata is the most advanced animal phylum. All chordates have, at some time during development, a notochord. Both invertebrate and vertebrate chordates are represented in ocean environments. In some chordates the notochord is lost during development. These are the invertebrate chordates. Most chordates (about 95%) retain the notochord in some form. These are the vertebrate chordates. Chordates Phylum Chordata: notochord and dorsal nerve chord at some point in life cycle. Invertebrate chordates: Subphylum Urochordata: sea squirts, salps and larvaceans (jelly-like critters) Subphylum Cephalochordata: lancelets (fish-like but without vertebrae Vertebrate Evolution Traces a Long and Diverse History One proposed family tree for the vertebrates and their relatives, the invertebrate chordates. 1

2 Vertebrates - Top of the Food Web Subphylum Vertebrata: Dorsal nerve cord developed into spinal cord protected by vertebrae. Ø Vertebrates consist of the most complex, large, fast, and conspicuous organisms [including humans]. Significance of Class Agnatha This is the class of the jawless fish. Species include lampreys and hagfish. Organisms in this class are significant - they may represent the ancestor of bony fish/ sharks. Lampreys The long, eel-like fish drinking the blood of this lake trout is one of nearly fifty species of lampreys, a group of jawless fishes found in temperate rivers and coastal seas. 2

3 Hagfish Hagfish enter both living and dead fish, feeding on the insides. While having no ability to enter through skin, they may enter through openings such as the mouth, gills or anus. hagfish.html Characteristics of Sharks and Rays Class Chondrichthyes includes sharks, rays and their close relatives. Sharks and rays have jaws, lack a swim bladder, and have cartilaginous skeletons. Ø Sharks have an excellent sense of smell (can detect diluted blood). Ø Sharks have a conveyor belt of multiple rows of teeth They swing into place as old teeth wear out and fall away. Sharks and rays have electroreception to assist with predation. Sharks and rays have organs called ampullae of Lorenzini - visible pits near their snouts. The ampullae of Lorenzini detect electrical currents generated by living organisms. 3

4 Reproduction Most sharks/rays fertilize their eggs internally. Male deposits sperm in female via a pair of copulatory organs called claspers located at the base of the pelvic fins. The female lays egg cases in which juveniles develop for up to six months at which time one or more sharks or rays emerge. A few shark species are ovoviviparous the eggs hatch within the mother s body (e.g., whale shark). They give birth to live young rather than release egg cases. whaledolphintrust.co.uk The largest fish in the ocean. Shark size ranges from hand-sized [pygmy shark] to the whale shark the largest fish in the ocean. Whale sharks can reach 14 meters (46 feet). Basking sharks can reach 10 meters (33 feet). Megamouth sharks can reach 6 meters (20 feet). All three are filter feeders - consume plankton and small fish. Megamouth N.E. Megalodon Megamouth is a rare shark that feeds on plankton. Maximum size about ft long. Megalodon (big teeth) was the ancestor of the Great white shark. It was a predator and probably measured more than 50 feet long. It probably preyed on whales. 4

5 Basic Shark Anatomy Most sharks have long slender bodies: use their pectoral fins for loft and steering; swim by undulating their muscular bodies and sweeping their caudal fin from side to side. Why do sharks get a bad rap? Remember selachophobia??? How many shark attacks on humans? On average, fewer than 10 per year In Florida, from , there were 523 shark attacks, 8 fatal; compared to 438 lightning fatalities ( relarisk.htm). Humans kill tens of thousands of sharks every year Shark fins are cut off for soup and sharks then left to die, unable to swim. 5

6 According to the American Film Institute, Jaws ranks among the fifty greatest movies of all time and the second- greatest thriller ever (Behind Alfred Hitchcock s Psycho). Rays Pectoral fins have evolved into wings Tail evolved into defensive whip in some species; with a venomous spine in stingrays. The manta is the largest of all rays. Like the whale shark, manta rays are plankton feeders. Manta wingspans may exceed 8 meters (26 feet) Superclass Osteichthyes Comprises the Familiar Bony Fishes About 90% of all living fishes are contained within the osteichthyan order Teleostei, which contains the cod, tuna, halibut, goldfish, and other familiar species. Some of the diversity exhibited by teleost (bony) fishes. Note: not all drawn to the same scale. 6

7 Bony Fish (superclass Osteichthyes) How are bony fish different from sharks? Skeletons made of bone Most have a swim bladder and scales Most reproduce externally - large numbers of offspring with few expected to survive to maturity Fishes Are Well Adapted to Their Environment Challenges of living in a marine environment Movement, shape and propulsion - fish must be able to move through water, which is 1,000 times denser and 100 times more viscous than air Depth control - fish tissue is usually denser than the surrounding water, so fish must have a system to keep from sinking Gas exchange - the problem of extracting oxygen from water Osmotic considerations - fish need to maintain proper salt levels in their bodies Feeding and defense - competitive pressure among a large number of fish resulted in the evolution of a wide variety of feeding habits Shape matters to swimmers Turbulence and drag. At the same speed, with the same frontal area, shape (a) will have about 15 times as much drag as shape (c). Shape (b) shows only a small improvement in drag over the disk. 7

8 Pelagic (open ocean) fish and demersal reef fish Open ocean fish are fast swimming, torpedo shaped fish (e.g., tuna) Reef fish adapt diverse strategies that include concealment and camouflage and therefore more color. Bony Fish (superclass Osteichthyes; class Actinopterygii), basic anatomy: Ø Most control buoyancy by adding or releasing gas to/from their swim bladder. They control the swim bladders with oxygen gas exchanged to and from blood circulation. This allows many species to hover nearly motionless in midwater. Gas Exchange Is Accomplished through Gills Cutaway of a mackerel, showing the gills (a). Broad arrows in (b) and (c) indicate the flow of water over the gill membranes of a single gill arch. Small arrows in (c) indicate the direction of blood flow through the capillaries of the gill filament in a direction opposite to that of the incoming water. This mechanism is called countercurrent flow. 8

9 Successful Fishes Quickly Adapt to Their Osmotic Circumstances Osmoregulation in freshwater and marine fishes. Clupeiformes - order of fish that includes anchovies, sardines, herrings: small fish important prey for penguins, birds, seals, us. Credit: OAR/National Undersea Research Program (NURP) Other important fish for human consumption? 9