Chapter 7—Key concepts and terms:

1. Chapter 7—Key concepts and terms: • Adaptive landscape • Convergence / divergence • Theoretical morphology • Morphospace • Functional morphologic analysis Fossils & Evolution - Ch. 7

2. Outline • Concept of adaptive landscape • Theoretical morphology • Functional morphologic analysis Fossils & Evolution - Ch. 7

3. “Adaptationist” view of functional morphology • Assumption: morphology is adaptive: i.e., morphologic features are present in an organism because they are useful to the organism • Functionally neutral features may exist, but they are probably rare Fossils & Evolution - Ch. 7

4. “Adaptive Landscape” • For any array of morphologic characters, certain character-states or combinations of character-states are more adaptive (advantageous to the organism) than others • Adaptive landscape (for two characters) • Peaks = character combinations that are highly advantageous (optimal morphology) • In reality, adaptive landscape is multidimensional Fossils & Evolution - Ch. 7

5. “Adaptive Landscape” • On an “adaptive landscape” map, a single individual plots as a point and a population plots as an area • Within any population, some individuals will possess character combinations that are higher up the adaptive peak than others • Over time, because of natural selection, the population will climb the adaptive peak • Different adaptive routes lead to convergence and divergence • There can be no route from peak to peak involving a path through an adaptive valley Fossils & Evolution - Ch. 7

6. Adaptive landscape concept from Wright (1932) Fossils & Evolution - Ch. 7

7. Example: Coiling in cephalopods adjacent whorls not in contact Fossils & Evolution - Ch. 7

8. Frequency distribution of coiling types (405 genera of ammonoids) “Adaptive peak”— optimal coiling geometry 90% of measured taxa fall within outer contour Fossils & Evolution - Ch. 7

9. Adaptive landscape (cont.) • Question: Does evolution cease when a population reaches an adaptive peak? • Answer: No! • Adaptive landscape is constantly changing!!! (environmental change, introduction of new predators/prey, competitors, disease, etc.) Fossils & Evolution - Ch. 7

10. Theoretical morphology • Loosely defined as the study of morphospace and the preferential occupancy of certain regions • Example: shell geometry in coiled invertebrates (gastropods, cephalopods, bivalves, brachiopods) Fossils & Evolution - Ch. 7

11. Theoretical morphology • Morphospace = the total spectrum of all morphologies that could possibly exist • Most morphospace is unoccupied and has never been occupied • Only a relatively few basic morphologies have actually evolved, and these “designs” have been used by large numbers of taxa Fossils & Evolution - Ch. 7

12. Shell geometry in coiled invertebrates • Coiled shells can be thought of as a tapered cone that is coiled about an axis • Geometry of the cone can be described by four attributes • Cross-sectional shape of the cone • Rate of expansion of the cone • Tightness of the coil • Whorl translation Fossils & Evolution - Ch. 7

13. Coiling attributes 1. Shape of cone (circular) 3. Tightness of coil r1 2. Rate of expansion (R2 = 2 × R1) r2 4. Translation Fossils & Evolution - Ch. 7

14. Translation of the whorls low translation high translation Fossils & Evolution - Ch. 7

15. Computer-simulatedgastropod shell Fossils & Evolution - Ch. 7

16. Morphospace of coiled shells: A = gastropods;B = cephalopods; C = bivalves; D = brachiopods Fossils & Evolution - Ch. 7

17. Coiled shell morphospace • Note that: • Most morphospace is vacant • Four evolutionary groups occupy mostly non-overlapping regions of the block • Four evolutionary groups have different functional and environmental requirements, therefore four different adaptive peaks! Fossils & Evolution - Ch. 7

18. Functional morphologic analysis • Structures in fossils are most commonly interpreted by comparison with similar structures in living animals • Homologous structures have a common evolutionary origin (but not necessarily the same function) • e.g., fore-limbs in tetrapods • Analogous structures have the same function (but not the same evolutionary origin) • e.g., wings in birds and flies Fossils & Evolution - Ch. 7

19. Functional morphologic analysis • Example: Vision in trilobites • Through natural selection, trilobite eye lenses became optimized to eliminate spherical aberration (“aplanatic” lens) • Moreover, calcite in each lens is oriented with optical axis perpendicular to visual surface (to eliminate birefringence) Fossils & Evolution - Ch. 7

20. Fossils & Evolution - Ch. 7

21. Spherical aberration negative s.a. perfect lens (all rays focused on a single point) zero s.a. imperfect lens positive s.a. Fossils & Evolution - Ch. 7

22. Functional morphology of trilobite lenses actual trilobite lenses optimum aplanatic lens Fossils & Evolution - Ch. 7

23. Functional morphology of trilobite lenses Estimation of visual field allows interpretations of life orientation and other aspects of functional morphology in trilobites Fossils & Evolution - Ch. 7

24. Functional morphologic analysis: Example: Flight in pterosaurs • Pterosaurs had wingspans of 7 meters up to 15 meters (larger than any bird) • A bird with a 7-meter wingspan would weigh 100 kg, but Pteranodon weighed only 15 kg • Therefore, Pteranodon was thought to have lacked the musculature necessary for powered flight • It was interpreted as a glider Fossils & Evolution - Ch. 7

25. Pteranodon (old reconstruction) Fossils & Evolution - Ch. 7

26. Functional analysis in Pteranodon • Wind tunnel experiments suggested that Pteranodon had a lower optimal flying speed than extant large birds or man-made gliders • Less energy required for take-off • Easy to glide and soar Fossils & Evolution - Ch. 7

27. Flying speed vs. sinking rate (estimates from wind tunnel experiments with old reconstruction) Fossils & Evolution - Ch. 7

28. New reconstruction and new interpretation of flight • Pterosaurs fit all criteria of fliers and none of gliders! • Down-and-forward flight stroke (as in birds and bats) • Inferred from structural features of sternum and shoulder girdle • Recovery stroke similar to that in birds • Wing membrane supported and controlled by a system of stiff fibers oriented like the main structural elements in birds and bats Fossils & Evolution - Ch. 7

29. Fossils & Evolution - Ch. 7

30. Fossils & Evolution - Ch. 7

31. 1: shape if wing not connected to leg 2: shape if wing connected to knee 3: shape if wing connected to ankle Fossils & Evolution - Ch. 7

32. New reconstruction& new interpretationof flight wingspan2 wing area (narrow wings) Small pterosaurs (if wing not connected to leg) Small pterosaurs (if wing connected to ankle) weight wing area Fossils & Evolution - Ch. 7 (broad wings)

33. Functional analysis in saber-toothed cats • Saber-toothed carnivores have evolved independently at least four times • What is function of large canine teeth? • No living animal occupies ecologic niche of saber-toothed cats • How did saber-toothed cats kill prey? • Attack to the back (like lions)? • Throat slashing? • Ambush, then attack to abdomen (like monitor lizard)? Fossils & Evolution - Ch. 7

34. Saber-toothed cats • Smilodon (extinct 10,000 ybp) was about 1 foot shorter than a modern lion, but twice as heavy • Smilodon had a bobtail, not a long balancing tail Fossils & Evolution - Ch. 7

35. Fossils & Evolution - Ch. 7

36. Saber-toothed cat • Gape as much as 95° • Bite force not as great as in modern big cats • Canines relatively dull • Upper and lower canines designed to shear against one another • Probably killed by a slashing bite to abdomen Fossils & Evolution - Ch. 7