Mesozoic life wrap-up

1. Mesozoic life wrap-up Plants, dinosaurs, birds, and mammals

2. Plants are: • Seedless plants (vascular and nonvascular) • Many divisions • Important in Paleozoic: Ferns, Sphenopsids, Lycophytes • Gymnosperms: ‘naked seeds’ • Angiosperms: ‘seeds in a vessel’ Paleozoic: Lycopods grew to giant forests! Two Sphenophytes

3. Geologic sequence • Nonvascular plants (eg Cooksonia + friends) • Vascular seedless • Example: Lycophytes, Sphenopsids • Giant Lycopod trees in Paleozoic; now small • Horsetails are modern remnant of major Paleo. Sphenops • Evolution of seeds! Spermatophytes • Gymnosperms: late Paleozoic • Angiosperms: mid-Cretaceous (late Mesozoic)

4. Angiosperms are special because: • Insect-polinated instead of wind polinated • Insect relationship allows for new means of plant diversification: evolve to match a specific bug • Animal-dispersed via fruits • Encase seeds bribing animals to disperse • Animal and insect relationships allow more rapid dispersion + more remote existence • Seed comes with its own early nutrition inside

5. The Diversification of Reptiles • Reptile diversification began • during the Mississippian Period • with the evolution of the first animals to lay amniotic eggs • From this basic stock of so-called stem reptiles • all other reptiles, as well as birds and mammals, evolved

6. Reptiles and Birds • Relationships among fossil and living reptiles and birds

7. First Dinosaurs • Evolved from archosaurs (reptiles) • Late Triassic • Small, only 3 ft long • Major characteristics • Can walk fully upright - bipedal • Special hip and ankle structure

8. Archosaurs and the Origin of Dinosaurs • Reptiles known as archosaurs • archo meaning "ruling" and sauros meaning "lizard” • include crocodiles, pterosaurs (flying reptiles), dinosaurs, and the ancestors of birds • Including such diverse animals • in a single group implies • that they share a common ancestor • and indeed they possess several characteristics that unite them

9. Dinosaurs Orders • All dinosaurs possess • a number of shared characteristics, • yet differ enough for us to recognize two distinct orders • the Saurischia • and Ornithischia • A distinctive pelvic structure characterizes each order • 3 bones in pelvis: illium, ischium, and pubis • Saurischian: pubis points down • Orinischian: pubis points back

10. Distinctive Pelvic Structure • Saurischian dinosaurs • have a lizardlike pelvis • and are thus called lizard-hipped dinosaurs • Ornithischians • have a birdlike pelvis • and are called bird-hipped dinosaurs • Convergent evolution • ‘birdlike’ pelvic structure reinvented in Saurischian descendents (avian dinosaurs = birds)

11. Hip Structure MSN encarta

12. Saurischian Dinosaurs • The saurischians, • include two distinct groups • known as theropods and sauropods • All theropods • were carnivorous bipeds • ranging in size from tiny Compsognathus • to giants such as Tyrannosaurus • and similar species • that might have weighed • as much as 7 or 8 metric tons

13. Dinosaur Cladogram • Cladogram showing dinosaur relationships • showing Pelvises of ornithischians and saurischians • Among the several subgroups of dinosaurs • theropods were carnivores • all others were herbivores

14. Therapods www.enchantedlearning.com/subjects/dinosaurs/dinoclassification/Saurischian.html

15. Sauropods www.enchantedlearning.com/subjects/dinosaurs/dinoclassification/Saurischian.html

16. Dinosaur Cladogram

17. Small Theropod Dinosaur • Compsognathus weighed only 2 or 3 kg • Bones found within its ribcage indicate it ate lizards

18. Tyrannosaurus • The skull of Tyrannosaurus, • another theropod, • measured more than 1 m long

19. Sauropods • Included among the sauropods • are the truly giant, quadrupedal herbivorous dinosaurs • Apatosaurus, Diplodocus, and Brachiosaurus, the largest known land-animals of any kind • Brachiosaurus, • a giant even by sauropod standards, • weighed as much as 75 metric tons, • partial remains indicate that even larger sauropods may have existed

20. Dinosaur Cladogram

21. Ornithischians • “Bird-hipped” dinos • Herbivorous dinos (eg. stegosaurus) • Did not lead to birds! (Birds evolved from carnivorous dinos with saurischian hip)

22. Warm-Blooded Dinosaurs? • Were dinosaurs endotherms • warm-blooded : generates internal heat to maintain body temperature • like today's mammals and birds, • or were they ectotherms • cold-blooded: relies on the environment + behavior to regulate body temperature • as are all of today's reptiles? • At some point between dinosaur and bird, became endothermic. When?

23. Evidence for Endothermy: Large Brain • Brain size correlates with endothermy in modern mammals and reptiles • Some dinosaurs had more brain per body than modern reptiles • Problems: how to measure brain size? Value of correlative data?

24. Evidence for Endothermy: Insulation • More compelling evidence for theropod endothermy • comes from their probable relationship to birds • recent discoveries in China of dinosaurs with feathers or a feather-like covering • Today, only endotherms have hair, fur, or feathers for insulation

25. Evidence for Endothermy: • Dinosaurs present at high latitudes • Problem: Cretaceous Interior Seaway • Predator/prey relationship • Endotherms eat more therefore an ecosystem can support fewer of them • Fossil record suggests many herbivores, fewer carnivores

26. Evidence for Endothermy: dominance over mammals • Endotherms can move fast for long periods of time • Ectotherms can only do short bursts • Other possible explanations for dinosaurian head start over mammals?

27. Triassic Extinction

28. Triassic Extinction • Hit mammals hard • Dinosaurs not as affected • Possible cause: • Pangaea fragmentation lead to volcanic CO2 release • CO2 greenhouse? • Evidence: plant fossils show fewer stomates: pores to admit CO2

29. Mammal ancestry, Paleozoic • Therapsids --> Cynodonts • mammals • Thecodontians • Stem reptiles • Plesiosaurs • Icthyosaurs • Archosaurs • Other reptiles

30. Mammals • Mammals have hair, make milk, have 3 ear bones, and are warm-blooded • Marsupials and placentals give birth to live babies • Monotremes lay leathery eggs • Some have very short pregnancies and carry immature babies in pouches (all marsupials and some monotremes) Tree of life Web Project http://tolweb.org/tree/phylogeny.html

31. Mammals • Evolved from cynodonts in Late Triassic • Strong fossil record of transition: • Bone structure (jaw and ear) • Many types of teeth • Only 2 sets of teeth • Teeth meet for grinding • Skin instead of scales • Remained mouse-sized for 150 m.y.

32. First Mammals www.gridclub.com/fact_gadget/1001/nature/land_mammals/314.html

33. Birds evolved in the Jurassic • Archaeopteryx • Feathers and wings • No bill • Reptilian backbone

34. Archaeopteryx’s Feathers • Not clear if Archaeopteryx could fly or only glide • Did feathers evolve: • For flight • For insulation • For display • Maybe another example of evolutionary opportunism • Feathered, non-flying theropods found in China

35. K/T Boundary Extinction Review • Greatest mass extinction took place at the end of the Paleozoic Era • K/T extinction has attracted more attention because it affected dinosaurs http://www.lpl.arizona.edu/SIC/impact_cratering/Chicxulub/totaldiversity.jpg

36. K/T Boundary Extinction • N America suffered most • Also going on: seas cooling, receding globally • Many animals in decline before K/T boundary • Mammals, birds, turtles, crocodiles, lizards, snakes and amphibians survived

37. K/T Boundary http://www.mhhe.com/earthsci/geology/mcconnell/gti/metaphor.htm

38. What did Earth look like 65 Ma?

39. What caused the K/T extinction? • One proposal has become popular since 1980 • based on a discovery in Italy • 2.5-cm-thick clay layer at the Cretaceous-Tertiary boundary with a remarkably high concentration of iridium • Worldwide iridium layer now known

40. Cretaceous-Tertiary Boundary • K/T boundary site in Italy • 2.5-cm-thick clay layer shows high concentration of iridium

41. Boundary Clay • Closeup view of the boundary clay in the Raton Basin, New Mexico

42. Boundary Clay • Deep sea core • Recovered by Joides Resolution in 1997 http://www.usssp-iodp.org/Education/poster.html http://www.nmnh.si.edu/paleo/blast/k_t_boundary.htm

43. Iridium Anomaly • Significance of the iridium anomaly • iridium is rare in crustal rocks • found in much higher concentrations in some meteorites • May also result from expoure to supernovas (but supernovas also create isotopic anomalies not present at K/T) • Accordingly, some investigators propose • meteorite impact explains the anomaly • meteorite perhaps 10 km in diameter • impact set in motion a chain of events leading to extinctions

44. Boundary Sites • North American Cretaceous-Tertiary boundary sites also contain • soot • shock-metamorphosed quartz grains http://wwwdsa.uqac.ca/~mhiggins/MIAC/chicxulub.htm

45. Meteorite Impact Crater • Centered on Chicxulub on the Yucatán Peninsula of Mexico • Discovered in 1950’s, interpreted to be volcanic

46. Chicxulub Crater www.ig.utexas.edu – GAIL CHRISTESON

47. Chicxulub Crater Palaeo.gly.bris.ac.uk/Communication/Hanks/Fig6.html

48. Chicxulub Crater http://wwwdsa.uqac.ca/~mhiggins/MIAC/chicxulub.htm

49. Chicxulub Crater http://www.lpl.arizona.edu/SIC/impact_cratering/Chicxulubprpage/Chicxulub_drilling_hires.jpg

50. Impact Site • Centered on the town of Chicxulub, Yucatan Peninsula of Mexico • The 180-km diameter structure lies beneath layers of sedimentary rock and appears to be the right age