Aquatic Vertebrates PART I

1. VERTEBRATE ZOOLOGY (VZ Lecture06 – Spring 2012 Althoff - reference PJH Chapters 5 & 6) Aquatic VertebratesPART I SPOTTED RATFISH RATFISHES

2. __________________: The Cartilaginous Fishes • Unlike their agnathan ancestors, this line of vertebrates has had a loss of bone….but not a major “step back” as cartilage is lighter and perhaps allows for easier maneuverability • Unlike their ancestors, they have some senses and systems that have reached higher levels than some other extant vertebrates • Two major groups: Neoselachii: sharks, skates, & rays Holocephali: ratfishes

3. RATFISHES ~ 30 species

4. Evolutionary History & Specializations • Unlike today, most early Chondrichthyes were found primarily in freshwater habitats SHARKS • Bursiform: _______________________ • Progressive “changes” in _________________ • Progressive “changes” in _________________

5. CLADOSELACHE Fig. 5-1a p103 PJH

6. Caudal fin: externally symmetrical, ________________________… resembles extant sharks CLADOSELACHE Fig. 5-1a p103 PJH

7. Other features of early Chondrichthyans • Skin: few scales (still!)…around the eyes, some fins and within mouth behind teeth • These teeth-like scales had cusps of dentine covered with enamel-like substances that enveloped over a pulp core. These types of scales known as _______________ scales. • Presence of ___________ claspers of some Paleozoic sharks indicated _________ fertilization • Some groups had symmetrical, deeply forked tails—in modern day sharks, this is characteristic of fast swimming oceanic species

8. Tooth replacement: 2 “designs” Extant shark Edestoids(early chondrichthian) Fig. 5-2 p104 PJH

9. Other notes on early Chondrichthyan teeth • Several teeth in a “tooth whorl” were functional simultaneously for some species • Some had ___________ teeth…well-adapted to crushing shelled prey • Some had _____________________ for cutting and shearing

10. Anterior teeth: sharp cusps Posterior teeth: crushing surface Early Mesozoic: ELASMOBRANCHS • Further evolution of chondrichthyans impacted ____________ and ________________ systems • Prominent genus was Hybodus (Hybodont sharks) key “improvement”: _____________dentition

11. _______________ sharks 1 2 Mouth is _______, not “underslung” like extant sharks Fig. 5-3 p105 PJH

12. Hybodont Sharks: Advances in Pectoral & Pelvic Fins • More mobile than broad-based fins of Paleozoic sharks • Both pairs of fins supported on narrow stalks formed on 3 narrow, platelike basal cartilages that replaced long series of basals seen in earlier sharks • Such an arrangement allowed the fin to be rotated to a different angle as the shark swam up or down • Musculature & flex of fins also permitted curving from front to back and base to tip….________ fins, thus, could produce a) more anterior lift, b) aid in turning, and c) stabilize straight-line movement

13. 1) Reduction in the___________ 2) _________made of proteinaceous flexible fin rays that extended to margin of fin 1a 2a 1 2

14. Towards Extant Sharks: Advances in Caudal Fin design/function • Reduced hypochordal lobe • Division of radials • Addition of flexible ceratotrichia

15. Extant Sharks, Skates, & Rays: • Arose during early Triassic (Mesozoic) • Most conspicuous difference between most members of early radiations and extant sharks is the rostrum (snout) that _______________ the ventrally positioned mouth in most forms

16. Sharks Skates Rays

17. Sharks • ~ 360 species of pleurotremate elasmobranchs: sharks with gill openings on the side of the head • ~ 60 of these species are ______________ that include the dogfish (next lab D/E)…usually live in cold, deep water • ~ 280 of these species are ___________: the dominant carnivores of shallow, warm oceansex. whale shark, mackerel shark (including great white), and hammerhead sharks

18. Extant Sharks: common characteristics • Cartilaginous vertebral ________ with notochord fitting in depressions on opposing faces of adjacent vertebrae: allows flex side-to-side • Intercalary plates protect the spinal cord above and major arteries and view below the centra • Placoid scales have single cusp and single pulp cavity…reduces turbulence in flow of water next to body surface

19. Extant Sharks: advanced sensory systems • Extraordinary sensitivity of the neuromast organs and ampullae of Lorenzini (Chapter 4) to electrical potentials and _________ temperature differences: influences detection of water masses of different temps….influencing likelihood of finding prey species • Chemoreception: pick up concentrations of chemicals in concentrations as low as ________ • Vision: at low light levels is excellent. Due to ____-rich retina and cells containing crystals of guanine located in choroid layer = _________________ • __________ brain, proportionately, than most other fishes….helpful for processing sensory input

20. Extant Sharks: Jaws designed for consumption of large food items ____________ jaw suspension: allows for movably to side of the cranium ____________ jaw suspension: allows for multiple jaw positions & protrusion of upper jaw….allowing different feeding opportunities Fig. 5-5 p110 PJH

21. Nourishment of Embryos Elasmobranchs: Reproductive Strategy isbroad ranged • ___________trophy: Greek = egg + nourishment yolk supplies most of the nourishment of the embryo • ___________trophy: Greek = mother + nourishment female reproductive tract provides most of the nourishment of the embryo

22. Eggs develop outside body… Eventual “live” birth… Elasmobranchs: Reproductive Strategy • Reduction in ___________________________ • Most produce few young (2-14 vs. 2-11 million eggs for Atlantic cod) • Move from “external” to “internal” fertilization with special “grasping structures” for copulation • Biennial reproduction (probably) • Many have eggs stay and hatch in oviduct • Some exhibit ________ …. others _________