Exploring Vertebrates: Characteristics and Evolution

1. Chapter 34 Vertebrates

2. There are about 52,000 species of vertebrates, including the largest organisms ever to live on the Earth

3. Derived Characters of Chordates • All chordates share a set of derived characters • Some species have some of these traits only during embryonic development • Four key characters of chordates: • Notochord • Dorsal, hollow nerve cord • Pharyngeal slits or clefts • Muscular, post-anal tail

4. LE 34-3 Dorsal, hollow nerve cord Muscle segments Brain Notochord Mouth Anus Pharyngeal slits or clefts Muscular, post-anal tail

5. Notochord • The notochord is a longitudinal, flexible rod between the digestive tube and nerve cord • It provides skeletal support throughout most of the length of a chordate • In most vertebrates, a more complex, jointed skeleton develops, and the adult retains only remnants of the embryonic notochord

6. Dorsal, Hollow Nerve Cord • The nerve cord of a chordate embryo develops from a plate of ectoderm that rolls into a tube dorsal to the notochord • The nerve cord develops into the central nervous system: the brain and the spinal cord

7. Pharyngeal Slits or Clefts • In most chordates, grooves in the pharynx called pharyngeal clefts develop into slits that open to the outside of the body • Functions of pharyngeal slits: • Suspension-feeding structures in many invertebrate chordates • Gas exchange in aquatic vertebrates • Develop into parts of the ear, head, and neck in terrestrial vertebrates

8. Muscular, Post-Anal Tail • Chordates have a tail posterior to the anus • In many species, the tail is lost during embryonic development • The tail contains skeletal elements and muscles • It provides propelling force in many aquatic species

9. Concept 34.2: Craniates are chordates that have a head • The origin of a head opened up a completely new way of feeding for chordates: active predation • Craniates share some characteristics: a skull, brain, eyes, and other sensory organs

10. Derived Characters of Vertebrates • Vertebrates have the following derived characters: • Vertebrae enclosing a spinal cord • An elaborate skull • Fin rays, in aquatic forms

11. Fishes breathe by drawing water over gills in chambers covered by a bony flap called the operculum

12. Lobe-Fins • The lobe-fins, class Sarcopterygii, have muscular and pectoral fins • They include coelacanths, lungfishes, and tetrapods

13. Concept 34.5: Tetrapods are gnathostomes that have limbs and feet • One of the most significant events in vertebrate history was when the fins of some lobe-fins evolved into the limbs and feet of tetrapods

14. Derived Characters of Tetrapods • Tetrapods have some specific adaptations: • Four limbs and feet with digits • Ears for detecting airborne sounds

15. Amphibians • Class Amphibia is represented by about 4,800 species of organisms • Most amphibians have moist skin that complements the lungs in gas exchange

16. Order Anura includes frogs and toads, which lack tails

17. Amphibian means “two lives,” referring to the metamorphosis of an aquatic larva into a terrestrial adult

18. LE 34-22a The male grasps the female, stimulating her to release eggs. The eggs are laid and fertilized in water. They have a jelly coat but lack a shell and would desiccate in air.

19. LE 34-22c During metamorphosis, the gills and tail are resorbed, and walking legs develop.

20. LE 34-24 Extraembryonic membranes Amnion Chorion Allantois Yolk sac Embryo Amniotic cavity with amniotic fluid Yolk (nutrients) Shell Albumen

21. Reptiles • The reptile clade includes the tuatara, lizards, snakes, turtles, crocodilians, birds, and the extinct dinosaurs. Reptiles have scales that create a waterproof barrier. They lay shelled eggs on land

22. Most reptiles are ectothermic, absorbing external heat as the main source of body heat • Birds are endothermic, capable of keeping the body warm through metabolism

23. The other major living lineage of lepidosaurs are the squamates, the lizards and snakes • Lizards are the most numerous and diverse reptiles, apart from birds Video: Galápagos Marine Iguana

24. Snakes are legless lepidosaurs that evolved from lizards Video: Snake Ritual Wrestling

25. Turtles • Turtles are the most distinctive group of reptiles alive today • Some turtles have adapted to deserts and others live entirely in ponds and rivers • All turtles have a boxlike shell made of upper and lower shields that are fused to the vertebrae, clavicles, and ribs Video: Galápagos Tortoise

26. LE 34-28 Finger 1 Bone structure Palm Wing Finger 2 Finger 3 Forearm Wrist Shaft Shaft Vane Barb Barbule Hook Feather structure

27. The Origin of Birds • Birds probably descended from theropods, a group of small, carnivorous dinosaurs • By 150 million years ago, feathered theropods had evolved into birds • Archaeopteryx remains the oldest bird known

28. LE 34-29 Wing claw Toothed beak Airfoil wing with contour feathers Long tail with many vertebrae

29. LE 34-30a Emu. This ratite lives in Australia

30. Derived Characters of Mammals • Mammary glands, which produce milk, are a distinctively mammalian character • Hair is another mammalian characteristic • Mammals generally have a larger brain than other vertebrates of equivalent size

31. Monotremes • Monotremes are a small group of egg-laying mammals consisting of echidnas and the platypus

32. Marsupials • Marsupials include opossums, kangaroos, and koalas • A marsupial is born very early in its development • It completes its embryonic development while nursing in a maternal pouch called a marsupium

33. LE 34-34a A young brushtail possum. The young of marsupials are born very early in their development. They finish their growth while nursing from a nipple (in their mother’s pouch in most species).

34. LE 34-34b Long-nosed bandicoot. Most bandicoots are diggers and burrowers that eat mainly insects but also some small vertebrates and plant material. Their rear-opening pouch helps protect the young from dirt as the mother digs. Other marsupials, such as kangaroos, have a pouch that opens to the front.

35. In Australia, convergent evolution has resulted in a diversity of marsupials that resemble eutherians in other parts of the world

36. LE 34-35 Eutherian mammals Marsupial mammals Plantigale Deer mouse Mole Marsupial mole Flying squirrel Sugar glider Wombat Woodchuck Wolverine Tasmanian devil Patagonian cavy Kangaroo

37. Eutherians (Placental Mammals) • Compared with marsupials, eutherians have a longer period of pregnancy • Young eutherians complete their embryonic development within a uterus, joined to the mother by the placenta • The living orders of eutherians originated in the late Cretaceous period