1 / 36

Transitional Fossils

Transitional Fossils. Evidence for Evolution Seminar Talline Martins and Heidi Hillhouse 02-14-06. Outline. Introduction to transitional fossils Case studies Vascular plant evolution Tetrapod evolution Limitations Arguments against transitional fossils. Defining the issue.

Download Presentation

Transitional Fossils

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Transitional Fossils Evidence for Evolution Seminar Talline Martins and Heidi Hillhouse 02-14-06

  2. Outline • Introduction to transitional fossils • Case studies • Vascular plant evolution • Tetrapod evolution • Limitations • Arguments against transitional fossils

  3. Defining the issue • A transitional fossil may be defined as a fossil which exhibits traits common to both ancestral and derived groups. This is especially important when groups are sharply differentiated.(Freeman and Herron 2001)

  4. Defining the issue • A transitional fossil may be defined as a fossil which exhibits traits common to both ancestral and derived groups. This is especially important when groups are sharply differentiated. (Freeman and Herron 2001) • Transitional fossils are often used to test theories of species development. These theories include broad shifts in habitat use (aquatic to terrestrial organisms) or shifts in physical characteristics within a species or group of species (development of hard shells in trilobites).

  5. Dinosauria cladogram http://www.dinosauria.com/pics/clados/clado.gif

  6. Examples of Transitional Fossils • Cooksonia- emergence of vascular tissue in plants • Kalbarria brimmellae-transition from myriapods to insects • Ichthyostega- emergence of legs • Archaeopteryx- early evolution of birds • Pakicetus, Ambulocetus, Indocetus, Protocetus-land to water transition (whale) Many fossils that bridge major transitional gaps have been found

  7. Case study Evolution of vascular plants

  8. Land plant evolution • Raven (1977) predicted that adaptations should have arisen in a specific order: • Alternation of generations, dispersal of spores by erect sporophyte • Cuticle • Xylem, later reinforced by lignin • Intercellular gas spaces and epidermal pores • Stomata with guard cells (as reported in Thomas 1984)

  9. Land plant evolution • Spore development • Combination of decay resistant spore walls (suggesting the presence of sporopollenin) and tetrahedral arrangement of spores (from haploid meiotic division) is considered diagnostic for land plants • Spore fossils suggest the presence of land plants 50 million years before the first unequivocal land plant megafossils (Kendrick and Crane 1997)

  10. Land plant evolution • Xylem development • Structure of early land plants was similar to that of some green algae, but the addition of “tracheid-like” tubes demonstrates vascular plant status. • Example: “Differentially thickened” walls in Cooksonia fossils supports status as early vascular plant (Edwards et al. 1992)

  11. Vascular plant evolution • Two main branches of vascular plant development • Clubmosses • All other land plants

  12. Kendrick and Crane 1997

  13. Likely sister groups to land plants Kenrick and Crane (1997)

  14. Vascular plant evolution • Two main branches of vascular plant development • Clubmosses • All other land plants • Transitional fossils exist for both branches • For clubmosses: Rhyniopsids, including Tortilicaulis • For other land plants: Cooksonia (actually several species, some more similar to clubmosses)

  15. Cooksoniapertonii apiculispora (Non-clubmoss vascular plant lineage) Tortilicaulis offaeus (clubmoss lineage) Kendrick and Crane 1997

  16. Case study Evolution of Tetrapods

  17. lobe-finned fishes ray-finned fishes amphibians mammals reptiles birds Tetrapod evolution Backboned animals with four limbs legs

  18. How did it happen? • Paleozoic Era: late Devonian-early Carboniferous (~365-310 mya) • Crossopterygians (bony fish) • Sarcopterygian fishes (lobe-finned) • Coelacanth or lung fishes? • Where? • Shallow fresh water, tropical Euramerica

  19. Tetrapod evolution ?

  20. Some structures associated with tetrapod evolution • Limbs and digits • Ability to move on terrestrial environment • Interlocking vertebrae/connecting ribs • Provide support on land—necessary due to gravity • Ear • ability to hear on land • Lungs • Breathing

  21. Relationships among early tetrapods Long and Gordon. 2004. Physiological and Biochemical Zoology (77).

  22. Acanthostega (~360 mya) Found in 1952, eastern Greenland • Limbs: no ankles, paddle-like, 8 digits! • Skeleton: ribs too short to support weight out of the water • Lungs: present, internal gills First fossil evidence that feet did not evolve for walking! Ahlberg et al. (2005) Nature

  23. Ichthyostega (~363 mya) Found in 1955, eastern Greenland • Limbs: strong enough to support itself, hind limbs were ‘flipper-like’, 7 digits! • Skeleton: able to support organs out of water, but no lateral movement • Lungs: present/gills First fossil evidence for non-aquatic limb use! Ahlberg et al. (2005) Nature

  24. Pederpes (354-344 mya) Found in 1971, but only described in 2002, western Scotland • Limbs: forward-facing hind feet, non-paddle-like, 5 digits! • Skeleton: resembles that of Ichthyostega • Lungs: present/gills First fossil evidence for terrestrial locomotion! Clack (2002) Nature

  25. “Limitations” of transitional fossils • Some organisms don’t fossilize well: terrestrial animals, invertebrates • Some strata do not produce many fossils • Fossils are hard to find!

  26. Arguments against transitional fossils as evidence for evolution • Some arguments can be dealt with logically • Transitional fossils are missing • Response: Only popular transitional fossils have gotten press (whale, Archaeopteryx). Others are not seen often beyond primary literature. • Punctuated equilibrium is often misunderstood with scientists agreeing with the lack of transitional forms • Response: Need to educate the public about punctuated equilibrium

  27. Arguments against transitional fossils as evidence for evolution • Some arguments can be dealt with logically • Transitional fossils are missing • Response: Only popular transitional fossils have gotten press (whale, Archaeopteryx). Others are not seen often beyond primary literature. • Punctuated equilibrium is often misunderstood with scientists agreeing with the lack of transitional forms • Response: Need to educate the public about punctuated equilibrium

  28. Arguments against transitional fossils as evidence for evolution • Reconstructions are based often on incomplete fossils Ahlberg et al. (2005) Nature

  29. Arguments against transitional fossils as evidence for evolution • Some arguments are dead ends: • The earth isn’t really that old, therefore any dating arguments are obviously invalid • Fossils were placed by the devil to lure us away from proper faith.

  30. Arguments against transitional fossils as evidence for evolution • Some arguments are dead ends: • The earth isn’t really that old, therefore any dating arguments are obviously invalid • Fossils were placed by the devil to lure us away from proper faith.

  31. Simpson tree of life

  32. References • Freeman and Herron 2001. Evolutionary analysis 2nd edition. Prentice-Hall, New Jersey. • Kenrick, P. and P. Crane, 1997. The origin and early evolution of plants on land. Nature. 389: 33-39 • Raven, J. A. 1977. The evolution of vascular land plants in relation to supracellular transport processes. Pp. 153-219. In: Woodhouse, H. W., ed. Advances in Botanical Research 5. Academic Press; New York. • Simpson based Tree of Life gi.cebitec.uni-bielefeld.de/people/boecker/ • Thomas, R. D. K. 1984. When and How did plants and animals take to the land? Paleobiology 10(1): 1-8 • The Virtual Fossil Museum http://www.fossilmuseum.net/index.htm

  33. References (cont.) • Ahlberg, P. E. and Milner, A. R. 1994. The origin and early diversification of tetrapods. Nature 368: 507-514. • Ahlberg, P. E., Clack, J. A., and Blom, H. 2005. The axial skeleton of the Devonian tetrapod Ichthyostega. Nature 437:137-140. • Clack, J. A. 2002. An early tetrapod from ‘Romer’s Gap’. Nature 418:72-76. • Clack, J. A. et al. 2003. A uniquely specialized ear in a very early tetrapod. Nature 425:65-69. • Coates, M. I. And Clack, J. A. 1991. Fish-like gills and breathing in the earliest known tetrapod. Nature 352:234-236. • Long, J.A. and Gordon, M. S. 2004. The greatest step in vertebrate history: a paleobiological review of the fish-tetrapod transition. Physiological and Biochemical Zoology 77(5):700-719.

  34. A: mechanical support/environment/structures B: probable locomotion C: respiratory structures D: water balance/osmoregulation E: sensory systems: cutaneous/visual F: probable prey-capture and feeding mechanisms G: probable mode of reproduction

More Related