Evolution and Diversity of Fishes: Primitive Fishes

1. Lecture 6 Evolution and Diversity of Fishes: Primitive Fishes

2. Kingdom Animalia Phylum Chordata • Chordata • Originated b/w 600 - 580 mya • Bilateral symmetry • Notochord • Dorsal tubular nerve cord • Pharyngeal pouches • Postanal tail • Segmented muscles—? • Ventral heart • Complete digestive system

3. Kingdom Animalia Phylum Chordata Subphylum Urochordata • Urochordata • Originated 550 mya • Bilateral symmetry • Notochord • Dorsal tubular nerve cord • Pharyngeal pouches • Postanal tail • Segmented muscles • Ventral heart • Complete digestive system Tunicates

4. Kingdom Animalia Phylum Chordata Subphylum Urochordata Tunicates

5. Kingdom Animalia Phylum Chordata Subphylum Urochordata Subph. Craniata • The first fishes • Originated ~540 mya • Lineages now extinct • Chordate traits for whole • life-cycle • Fish-like form—median fins • Developed head with eyes • < 5 cm long Tunicates First fishes

6. Kingdom Animalia Phylum Chordata Subphylum Urochordata Subph. Craniata • Craniata • Originated ~540 mya • 60,000+ species • Well developed head • More advanced organ • systems • 2+ chambered heart • Hemoglobin Tunicates First fishes

7. Kingdom Animalia Phylum Chordata Subph. Urochordata Subph. Craniata SuperclassMyxinomorphi Hagfishes Tunicates First fishes

8. SuperclassMyxinomorphi—Hagfishes • Non-vertebrate • 70 species • Marine scavengers • A fish??? • Scaleless • Eyeless • Secondarily lost • Osmoconformers • No true teeth • Made of keratin, on tongue Barbels Nostril

9. Hagfishes—fun facts http://www.youtube.com/watch?v=tKTRv3hx1s0 • Ventilation • Water enters nostril  exits through up to 16 gill openings • Also obtain oxygen through skin • Inner ear—one semicircular canal • 3-chambered heart • Three additional auxiliary hearts—single chambered • No stomach • High starvation tolerance—1 year Knot tying to rasp prey

10. Hagfishes—fun facts • Slime glands—secondarily derived • Protection • Predators • When feeding inside • carcasses http://www.youtube.com/watch?v=Bb2EOP3ohnE http://video.nationalgeographic.com/video/news/animals-news/new-zealand-hagfish-slime-vin/ Large eggs—up to 2 inches No larval stage

11. Kingdom Animalia Phylum Chordata Subph. Urochordata Subph. Craniata Supercl. Myxinomorphi Supercl. Petromyzontomorphi Supercl. Gnathostomata 530 mya 38 living species (18 are parasitic) Mostly cool water Hagfishes Tunicates First fishes Lampreys

12. SuperclassPetromyzontomorphi—Lampreys Similarities with hagfish • No true vertebrae • Notochord • No scales • Cartilaginous skeleton • Jawless • Keratin teeth on tongue • Single nostril

13. SuperclassPetromyzontomorphi—Lampreys New adaptations • Functional eyes • Dorsal fin • 2 semicircular canals • More advanced organs • Osmoregulation • One heart—5x blood pressure • Spiral valve •  fecundity • Neuromasts

14. Parasitic Lampreys • Buccal chamber used to create negative pressure • Saliva contains anticoagulants • Host often dies • Invasive in Great Lakes Oral disc with “teeth”

15. SuperclassPetromyzontomorphi—Lampreys • Gill pores not connected to pharynx • Ventilation achieved by expanding contracting chambers • Why is this adaptive? • Olfactory chamber with single opening • Up to 85 chromosome pairs

16. Lamprey life-cycle • Anadromous • Semelparous— • Nest building • Ammocoetes—larval form • Blind, toothless, filter-feeders • Live up to 7 years; > 5 inches • Up to 30 per m2 • Role of olfaction— • Metamorphosis—

17. Extinct jawless fishes No extant fishes link lampreys to elasmobranchs • Extensive fossil record of jawless fishes fills the gap • True bone & vertebrae, teeth, two nostrils, lateral line, paired fins

18. Kingdom Animalia Phylum Chordata Subph. Urochordata Subph. Craniata Supercl. Myxinomorphi Supercl. Petromyzontomorphi Superclass Gnathostomata Hagfishes Tunicates First Fishes Lampreys

19. Evolution of Jaws were one of the most important adaptations for vertebrates— Jaws arose from modification of gill arches

20. SuperclassGnathostomata Class Placodermi • Placoderms • Now extinct • Jaws • Paired fins with skeletal support • 3 semicircular canals Placoderms

21. Placoderms—plate-skin • Very successful and diverse—440  350 mybp • All trophic niches • Herbivores, planktivores (25’ long), predators • Color vision • Viviparous • Claspers !!!

22. Placoderms—extinction • Late-Devonian (360 mya) mass extinction event • Multiple extinction pulses occurred over several million years • 70% of species • Some major jawless groups also went extinct • Widespread anoxia • Modern fishes outcompeted remaining placoderms • Placoderm limitations • Sluggish • No replacement teeth • Subject to breakage and wear • Jaws still primitive

23. SuperclassGnathostomata Class Placodermi Class Chondrichthyes • Chondrichthyes • (cartilaginous fishes) • Liver for buoyancy • Spiral valve (or similar) • 970 extant species • Considered “primitive” • …….but Subclass Elasmobranchii Subclass Holocephali Placoderms Rays Sharks Chimaeras

24. Chondrichthyes—fossil record • Most evolutionary lineages are extinct • Extant groups a fraction of historic diversity • 320 mya around half of fishes

25. Subclass Holocephali—Chimaeras • Originated ~370 mya • 3 families and 33+ extant species • 12 extinct orders • Extant families over 100 million years old

26. Subclass Holocephali—Chimaeras • Upper jaw fused to cranium • Teeth crushing/cutting plates • Grow continuously • Operculum • No spiracle • Oviparous—large eggs • Mostly scaleless • Poisonous dorsal spine

27. Subclass Elasmobranchii—Sharks & Rays • First shark-like fish—420 mya • Extant species: 403 sharks; 534 skates & rays

28. Subclass Elasmobranchii—Jaws • Inferior mouth allows for more muscle attachment • Stronger jaws • Upper teeth connect to palatoquadrate cartilage • Free from cranium • Jaws close rapidly • Upper jaws adapted for slicing in some

29. Subclass Elasmobranchii—Jaws • Rays use palatoquadrate to manipulate prey • Teeth replacement in all sharks • Replacement varies by species—2 days  1 month

30. Internal fertilization—elasmobranchs • Skates and some sharks are oviparous • Rays and a majority of sharks are viviparous • Give birth to developed young • Ancestral condition • Claspers—Modified pelvic fins

31. Internal fertilization—elasmobranchs Viviparous sharks • Gestation period varies 3 months  3 years • Typically < 1 year • Relatively long rest period (~1 year) • Clutch size varies 2  100+ • Typically < 10 • Embryo develops in uterus • Nourished by yolk sac • Oophagy— • Placenta—

32. Internal fertilization—elasmobranchs Oviparous sharks • All nourishment from yolk sac • Average of 60 eggs/year • Keratin shell • Egg stage ranges from 3 weeks  15 months Mermaid Purses

33. SuperclassGnathostomata Class Placodermi Class Chondrichthyes Class Sarcopterygii Subclass Elasmobranchii Subclass Holocephali Lungfish Placoderms Coelacanth Rays Sharks Chimaeras Tetrapods

34. Class Sarcopterygii Subclass: Coelacanth • Originated 400 mya • Most extinct by 60 mya • Living species found 1938 • Two highly endangered species known http://channel.nationalgeographic.com/wild/videos/finding-the-coelacanth/ Tetrapods Lungfish Coelacanth

35. Coelacanth • Lobed fins • Swim bladder—fat filled, for buoyancy • Secondarily modified • Spiral valve • No nasal-pharyngeal connection • Otoliths • Viviparous • Gestation > 1 year Rostral organ

36. Coelacanth • Cosmoid scales—fusion of placoid scales • Restricted to areas of recent-steep lava flows • Paired fins move like tetrapod legs • Feed by suction

37. Class Actinopterygii Class Sarcopterygii Actinopterygii—ray finned fishes Originated 380 mya • Body muscle moves rays Tetrapods Lungfish Coelacanth

38. Class Actinopterygii Class Sarcopterygii SublassChondrostei Chondrostei 27 extant species Much diversity has been lost Relic species, but extant forms highly derived Tetrapods Lungfish Coelacanth Sturgeons

39. Sturgeons • Primitive larval stage • Cartilaginous skeleton—secondarily derived • Spiral valve • Plates—ganoid scales • Swim bladder • Feeding mode—

40. Sturgeons—at risk species • Perhaps the most at-risk group for extinction • Caviar  up to $2500/pound • Beluga over $4000 • Female gonads up to 25% body weight • At. sturgeon harvest > 6 million lbs. annually in 1890 Beluga—largest freshwater fish over 25 feet, 2600 pounds, 110 years

41. Sturgeons—at risk species • Spawn in freshwater—rivers (gravel bottom) • Many species anadromous • Siltation • Dams • High age at maturity • Up to 30 years old • Females don’t spawn yearly • Low natural mortality of adults

42. Sturgeons—at risk species • Close to 50 sturgeon populations endangered • Many have been extirpated • Poaching adults and bycatch of juveniles hinder recovery Alabama sturgeon—described in 1990

43. Originate 250 mya Class Actinopterygii Class Sarcopterygii SublassNeopterygii SublassChondrostei Teleosts Order Lepisosteiformes Tetrapods Lungfish Coelacanth Gars Sturgeons

44. Gars • Seven species in one family • North and Central America • Fresh & brackish water • Often low O2 • Highly vascularizedphysostomous swim bladder • http://news.cornell.edu/stories/2013/02/ct-scans-help-answer-question-fish-lung-evolution Alligator Gar up to 300 lbs.

45. Gars • Bony skeleton • Ganoid Scales • Abbreviated heterocercal tail • More complex fin swimming • Eggs are toxic Can be very important predators 22 day larva Cartilage—blue Bone—red