Origin of Vertebrates

1. Origin of Vertebrates 14 September 2012 Devonian Sea Karen Carr Studio, Inc.

2. Vertebrates – What are they? • Two major characteristics • Vertebrae— bony (or cartilaginous) structures that usually surround the notochord and … • Cranium— bony (or cartilaginous) structure that encases brain and … • Cephalization – anterior clustering of … • Anterior neural tube enlarged into…

3. Vertebrae Fig. 3.2

4. Vertebrates – What are they? • Neural crest cellsand epidermal placodes • Embryonic, transient, do not fossilize • Give rise to some sensory organs of the cranium (lens, olfactory mucosa, inner ear) and distinctive teeth Fig. 5.28

5. Origin of Vertebrates • Three evolutionary steps most likely • Prevertebrates • Hemichordata, Cephalochordata, Urochordata • Key features: • Agnathans (“agnathostomes”) • “without jaw mouth” • Key features: • Gnathostomes • “jaw mouth” • Key features:

6. Origin of Vertebrates Read pp. 84-86 Fig. 3.3

7. Lampreys Hagfishes Fig. 3.4

8. Hagfishes • Single median nostril • No paired fins or … • Partial cranium, but no … • Scavengers; rasps on tongue • Very few fossils • 1991 Myxinikelasiroka found • ~300 million years ago • Little change in hagfish since

9. Lampreys • Like hagfish, lamprey: • Have a single median nostril • Have no paired fins or bone • Have a limited fossil record • Unlike hagfish, lamprey: • Have true … • Display a complete braincase (cartilaginous) • Go through a larval stage (“ammocoetes”) • Larvae are passive feeders; trap food in mucus • Latent ability to produce …

10. Extinct Agnathans - Conodonts • Have characteristics of chordates: • Notochord • Dorsal nerve cord • Postanal tail • Pharyngeal slits (from impression) • Conodontelements show evidence of tissue that is derived from … • BUT! • No lower jaw (still Agnathans) • Specialized feeding apparatus

11. Conodonts Project and impale! Slice and crush! Fig. 3.7

12. Conodonts • Where do they fit? M.A. Purnell and P.C.J. Donoghue (1997) Architecture and functional morphology of the skeletal apparatus of ozarkodinidconodonts. Phil. Trans. R. Soc. Lond. B, 352: 1545-1564

14. Extinct Agnathans - Ostracoderms • Mostly small … • Absent or small … • Bony dermal armor • Cartilaginous skeleton Pteraspidomorphs – no paired fins, paired nasal openings “Other ostracoderms”– some with (non-homologous) paired fins, most single nasal opening

16. Gnathostomes • Jawed fishes • Paired pectoral and … • New Food-Gathering Technique: … • Placoderms (Plate-skinned fish) • Chondricthyes(Cartilaginous fish) • Elasmobranchii (Sharks and Rays) • Holocephali (Chimaeras) • Acanthodii (“Spiny Forms”) • Teleostsor “Osteichthyes” (Bony fish) • Sarcopterygii (lobe-finned fishes) • Actinopterygii (ray-finned fishes)

17. Gnathostomes

18. Osteichthyes • Most living vertebrates Fig. 3.15

19. Actinopterygii • Ray-finned fishes • Most diverse vertebrates – ~20,000 species!

20. Sarcopterygii • Fleshy-finned fishes • Actinistia (Coelacanths) – 2 species? • Dipnoi (Lungfishes) - ~6 species • “Rhipidistians” – Eusthenopteron Lungfish Panderichthys Coelacanth “Rhipidistians”

21. What’s the difference? Actinopterygian Sarcopterygian

22. Sarcopterygian Fins Eusthenopteron Panderichthys Tiktaalik Acanthostega H= humerus; Int = intermedium; R = radius; U = ulna; Ure = ulnare. Scale bar, 1 cm

23. Tetrapods Fig. 3.21

24. Early Tetrapods • Acanthostega – mostly aquatic • Internal gills; tail; girdles • Ichthyostega – more terrestrial • More robust limbs and girdles; tail Ichthyostega Acanthostega

25. The Move to Land • What challenges did early tetrapods face during the transition to land? • Or, what things would have to change morphologically, and why?

26. The Move to Land