Comparative Anatomy Vertebrate Phylogeny: Fishes

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Comparative AnatomyVertebrate Phylogeny Fishes
Kardong Chapter s 2 3 Part 4
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Vertebrate Classification
Figure 4.1a

• Geological Eras of early vertebrates
• Paleozoic (oldest) see figure 4.1b
• Mesozoic
• Cenozoic

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Figure 4.1b.
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Cambrian Period

• Ostracoderms- first vertebrates, bony skin
• Class Agnatha- jawless fish
• No paired fins
• Bony exoskeleton with
• dermal armor
• Ex hagfish and lampreys
• Jawed fish evolved from Ostracoderms in Silurian
  period

(a)
(b)
Figure 4.2. (a) ostracoderm, (b) ostracoderm,
and (c) lamprey.
(c)
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Chordate Origins Lower to Higher Organisms

• Echinoderm ancestor (deuterostomes) gave rise to
  vertebrates
• Deuterostomes- blastopore gives rise to anus
• Protostomes- blastopore gives rise to mouth

Figure 4.3. (above) protostomes and (b)
deuterostomes.
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Gnathostomes Placoderms

• Class Placodermi
• Jawed and paired fins
• Bony dermal exoskeleton armored fish
• 1st jaws were large
• Jawed fishes gave rise to all other fishes
• Age of fishes- Devonian Period

Figure 4.4. Armored fish.
Figure 4.5. Mandibular (ma) and hyoid (hy)
arches develop in gnathostomes into
palatoquadrate (pq) and Meckels (Mc) cartilages
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Fish Evolution
(a)
(b)
Figure 4.6. (a) jawless fish, (b) early jawed
fish, and (c) modern jawed fish.
(c)
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Placoderms

• Anadromous- fish move to freshwater to breed
• Catadromous- fish move from freshwater to breed
• Hypothesized function of bone to provide
  calcium for muscle contraction

Figure 4.7. Craniates through geological time
(Book figure 3.1).
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Cartilagenous Fishes

• Chondrichthyes
• Cartilaginous skeleton
• Bone remains in scales - placoid scales
• Teeth are modified scales
• Ex elasmobranchs (sharks, rays skates,) and
  the holocephalans (chimaeras-ratfishes)

Figure 4.8. Basking shark-second largest fish.
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Elasmobranchii vs Holocephali
Figure 4.9. (Book figure 3.13).
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Tail Type

• Heterocercal- vertebral axis curves upward two
  asymmetrical lobes (dorsal portion larger)
• More primitive, some bony fish
• Ex sharks
• Homocercal- symmetrical dorsal and ventral lobes
• Most common
• Ex perch
• Diphycercal- spear shaped
• Ex lungfish, crossopterygians

Figure 4.10. Tail types.
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Class Osteichthyes

• Subclass Actinopterygii (ray-finned)
• Chondrostei- most primitive heterocercal tail
• Ex sturgeon, paddlefish, Polypterus
• Holostei- dominant in past heterocercal tail
• Ex gar, bowfin
• Teleostei- dominant today homocercal tail
• Majority of all fish

Figure 4.11. Venomous lionfish (actinopterygian).
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Figure 4.12.

• Evolutionary relationship of vertebrates with
  jaws (Gnathostomata) to those with bony skeleton
  (Osteichthyes)

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Class Osteichthyes (cont.)

• Subclass Sarcopterygii (fleshy or lobe finned)
• 3 genera of lungfish are found on 3 separate
  continents
• Continental Drift
• Torpidity- inactivity hibernation
• Aestivation- burrow through dry season
• Order Dipnoi
• Order Crossospterygii

Figure 4.13. Aestivation fish burrows into mud
until rain returns. (see Box Figure 1, p . 101).
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Early Sarcopterygians
Figure 4.14. Early Devonian fishes, including
the newly described Tiktaalik (an intermediate
link between fishes and land vertebrates). (Book
figure 3.20.).
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Order Crossopterygii

• Living fossil fish
• Species thought to be extinct until coelacanth
  (Latimeria) discovered.
• Found off coast of South Africa in 1938
• May be a separate species discovered off
  Indonesia in 1999

Figure 3.15. Global locations of coelacanth
discoveries.
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Coelacanth
Figure 3.16. Coelacanth in Indian Ocean.
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Coelacanth
Figure 4.17. Coelacanth.
Figure 4.18. Africas Sundaytimes-political
humor.
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Figure 4.19. Labyrinthodont (primitive tetrapod).

• Crossopterygiians (lobe-finned fish) gave rise
  to labyrinthodonts (early tetrapods)
• in Devonian Period

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Linking Morphology

• Limbs
• Vertebrae
• Girdles similar
• Fins skeletal composition exhibits homology with
  early tetrapods
• Amphibian diversity during Carboniferous period
• Toward reptiles, Anura, Caudata, and Apoda.

Figure 4.20.
Figure 4.21.
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More Linking Evidence

• Skulls flattened with homologous bones
• A chiridium muscular limb with well-defined
  joints and digits
• Parietal foramen
• Crossopterygian skull shows place for third eye
• Third (pineal) eye visible in young reptiles
  (e.g., tautara)
• Tooth structure
• Labyrinthodont tooth

Figure 4.22. Crossopterygian skull.
Figure 4.23. Grooved tooth.
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Lissamphibia Modern Amphibians

• Apoda - caecilians
• Long and slim segmented rings
• Dermal bones (scales) embedded in annuli

Figure 4.24. Caecilian showing annular body
rings.