Natural History of Sharks, Skates, and Rays Early Chondrichthyes MARE 380 Dr. Turner

1. Natural History of Sharks, Skates, and Rays Early Chondrichthyes MARE 380 Dr. Turner

2. Defining Elasmobranchs What kind of Thyes?...Chondrichthyes What kind of Fish?...Cartilagenous Fish What kind of Brates?...Vertebrates… What kind of Dates?...Chordates…

3. Phylum Chordata 3 subphylum: Subphylum Tunicata – tunicates, sea squirts Subphylum Cephalochordata – lancelets Subphylum Vertebrata (Crainiata) – fishes, amphibians, reptiles, birds, mammals

4. Subphylum Tunicata – Sessile, feeding – Mobile, non-feeding 4 chordate traits: Dorsal hollow nerve chord, notochord, pharyngeal gill slits, post anal tail

5. Subphylum Cephalochordata 4 chordate traits: Dorsal hollow nerve chord, notochord, pharyngeal gill slits, post anal tail

6. Who did the what now? “Well, whenever I'm confused, I just check my underwear. It holds the answer to all the important questions.” – Grandpa Simpson Neoteny is the retention of juvenile traits in an adult Specifically, paedomorphosis is the developmental process by which these changes take place

7. Subphylum Vertebrata “Crainiata” Characteristics that distinguish vertebrates: Extensive skull Backbone - a dorsal row of hollow skeletal elements (vertebrae) whichenclose and protect nerve (spinal) cord

9. Fishes “I wish, I wish I did not kill that fish” – Homer Simpson • Simplest & oldest of all living vertebrates • Sharks (400-500 MYBP) • Most abundant vertebrates (by # & species) • ~29,500 living spp of fishes (>482 families) • 58% Marine; 1% diadromousfish travel • between salt & fresh water

10. Fishes Class Agnatha (jawless fish) Subclass Myxinodea (hagfish) Subclass Petromyzontida (lamprey) Infraphylum Gnathostomata (jawed fish-cart) Class Chondrichthyes (cartilaginous fish) Class Osteichthyes (jawed fish-bony) Subclass Actinopterygii (ray-finned fish) Subclass Sarcopterygii (lobe-finned fish)

12. Class Agnatha Subclass Myxinodea (hagfish) - Cartilage skull - Lack jaws & vertebrae - All Marine (30 spp.) - Scavengers - Produce slime

13. Class Agnatha Subclass Petromyzontida (lamprey) - Cartilage skull - Lack jaws & vertebrae - Freshwater & Marine (35 spp.) - Parasites – attach to host - Rasping tongue - Some diadromous

14. Infraphylum Gnathostomata Class Chondrichthyes (sharks, skates, rays, ratfish) - Cartilage skeleton (jaws & vertebrae) - Marine & few FW (750 sp.) - Traces of bone in scales & teeth - Buoyancy via liver – squaline oil - Spiral valve – corkscrew intestine SA:V ratio; compact - Internal fertilization of eggs - Claspers – modified pelvic fins ♂ Placoid scales

15. Infraphylum Gnathostomata Class Chondrichthyes (sharks, skates, rays, ratfish) Skates differ from Rays: Skates have a more muscular tail, two dorsal fins & often a caudal fin, lay eggs Skates & Rays differ from Sharks: Enlarged pectoral fins that attach to side of head, no anal fin, ventral gill openings, dorsal eyes & spiracles Ratfishes (Chimaeras): Possess an operculum or gill cover over gill slits, adults have no scales, ♂ clasper on head

16. Shark Ray Skate Ratfish

17. Early Vertebrates Earliest vertebrates - early Cambrian 530 mybp (million years before present).. Early relatives of agnathans (jawless fishes) first 500+ mybp

18. Early Fishes

19. Early Fishes 1. Ordovician (505-438 mybp) 2. Silurian (438-408) 3. Devonian (408-360) 4. Carboniferous (360-290) 5. Permian (290-240) 6. Triassic (240-205) 7. Jurassic (205-138) 8. Cretaceous (138-63) 9. Cenozoic (63-24) 10. Quaternary (24-0) A. Hemicycapsis, B. Pterapsis, C. Cyathapsis, D. Drepanapsis, E. Coccosteus, F. Helodus, G. Cladoselache, H. Raja, I. Chimaera

20. Early Fishes Conodonts – (550 mybp) – known from small (<2mm) teeth found in fossil deposits Large eyes and eel-like bodies, notochord Closer to jawed fishes than lamprey & hagfishes

21. Early Fishes Hagfishes - (Subclass Myxinodea)– (550 mybp?) – marine, jawless, eel-like fishes; scavengers Single nostril, rudimentary eyes, ventral mouth, tongue with rows of keratinized teeth

22. Early Fishes Lampreys – (Subclass Petromyzontida) – anadromous or freshwater, lawless, eel-like fishes Predatory & non-predatory forms Keratinized teeth on buccal funnel & tongue 360 mybp

23. Early Fishes Ostracoderms – some of the earliest fishes Lack jaws, have paired fins, bony armor, cartilaginous skeleton, heterocercal tail (460 mya)

24. Early Fishes Acanthodii – “spiny sharks” – some of the oldest known jawed fishes (440 mybp) Small (<20cm), large eyes, streamlined bodies, dentine-tipped scales

25. Early Fishes Placoderms – also some of the earliest jawed fishes Heavy bony skeletons No special affinities with modern fishes 380 mybp?

26. Placoderms Most likely sister group to the combined lineages of Acanthodii, Chondrichthyes, and Osteichthyes; share: 1) jaws with common structure 2) Two pairs of paired fins w/ bony girdles 3) three semicircular canals in inner ear

27. Early Fishes Osteichthyes – bony fishes – loosely defined group Defined by common structures and lack of characters that define chondrichthyes 420 mybp

28. Early Fishes Chondrichthyes – What are they Doctor? Sharks, rays, & skates… But that’s not important right now…

29. Early Cartilagenous Fishes Chondrichthyan fishes most successful measured by historical endurance; ability to survive extinctions Defined by cartilagenous skeleton mineralized by calcifications (tesserae) and modification of mixopterygia (claspers) in ♂

30. Early Cartilagenous Fishes Two sister taxa: Elasmobranchii (sharks, rays, skates) & Holocephali (chimeras)

31. Evidence of Early Chondrichthyans Easier group to define than bony fishes: 1) only approximately 850 species 2) fossil groups are poorly known

32. Evidence of Early Chondrichthyans Scales & spines from early chond. Identified in Lower Silurian (430 mybp) to Devonian (350 mybp) Difficult to nail down due to similar morphology among scales & spines of thelodonts & acanthodians (spiny sharks) at this time

33. Evidence of Early Elasmobranchii True sharks - appeared in middle Devonian (350 mybp); Rays appeared during Jurassic (200 mybp) Few well preserved specimens; difficult to piece together evolution Two early forms: cladoselachian & xenacanth sharks

34. Evidence of Early Elasmobranchii Two early forms: Cladoselachian Xenacanth (350 mybp)

35. Order Cladoselachiformes Lacked: claspers, an elongate skull, amphistylic jaw suspension, no anal fin, Had: triangular, paired fins, multicusped teeth Predator in marine systems

36. Jaws…Then & Now Devonian shark: Snout typically short and rounded; jaws longish and located at the front of the head Modern sharks: Snout typically longish and pointed; jaws shorter and located underneath the head

37. Jaws…Then & Now Long jaws are structurally weaker than short ones and less able to produce a powerful bite Early sharks may have plucked prey from the bottom or with forceps-like delicacy

38. Jaws…Then & Now

39. Order Xenacanthiformes Had: 2 anal fins, tail diphycercal (pointed) Predator in freshwater systems

40. Order Hybodontiformes Ancestral to modern sharks Appeared during Permian (260 mybp) Fed on large, active invertebrates – first with large, sharp teeth

41. Order Chimaeriformes Appeared during Devonian (350 mybp) with Elasmobranchs Modern forms during Jurassic (170 mybp)

42. Modern Cartilagenous Fishes Monophyletic group Common origin – distinct from bony fishes

43. Modern Cartilagenous Fishes Beyond cartilage have several traits in common…. 1. Simple box-like cranium 2. Upper jaws (palatoquadrate cartilage) not fused to cranium; lower jaw is a single element (Meckel’s cartilage) 3. 4-7 internal & external gill openings 4. Vertebral column is notochord; becomes supported by calcified vertebrae

44. Modern Cartilagenous Fishes 5. Pectoral & pelvic fins are supported internally by a girdle skeleton; externally by rays (lepidotrichia) of flexible connective tissue 6. Basal skeleton on ♂ anal fins – claspers (paired copulatory organs) 7. Most have covering of small placoid scales (dermal denticles)

45. Modern Cartilagenous Fishes

46. S-U-C-C-E-S-S Success due to adaptive characteristics: 1) buoyancy 2) respiration 3) external covering 4) feeding 5) movement 6) sensory systems 7) osmoregulation 8) reproduction

47. Buoyancy -no swimbladder -combination of methods to reduce density Cartilage less dense than bone (1.1 vs 2.0) Large, oil-filled liver (0.8) (water 1.0) Hydrodynamic lift from heterocercal tail & pectoral fins

48. Respiration 3 basic means of respiration 1) Two-pump system (like teleosts) – pump O2 water across gills in slow-moving, bottom oriented sharks 2) Ram ventilation – push water across gills during swimming; fast-moving sharks 3) Spiracles – used to bring water across gills; small round opening precede gills on lateral sides of head – on top of head in rays – almost absent in pelagic sharks

49. Spiracle small round opening precede gills on lateral sides of head

50. External Covering All have placoid scales Rays – few rows on back; sometimes modified into spines Sharks – skin overlapping into lightweight, protective coat fast-swimming sharks have channels between scales to minimize turbulence