Chapter 34

1. Chapter 34 Vertebrates

2. Overview: Half a Billion Years of Backbones • Early in the Cambrian period, about 530 million years ago, an astonishing variety of animals inhabited Earth’s oceans • One type of animal gave rise to vertebrates, one of the most successful groups of animals • The animals called vertebrates get their name from vertebrae, the series of bones that make up the backbone • There are about 52,000 species of vertebrates, including the largest organisms ever to live on the Earth • Vertebrates have great disparity, a wide range of differences within the group

3. Fig. 34-1 Are humans among the descendants of this ancient organism? Myllokunmingia fengjiaoa (3 cm)

4. Fig. 34-2 Echinodermata (sister group to chordates) Cephalochordata (lancelets) ANCESTRAL DEUTERO- STOME Chordates Urochordata (tunicates) Notochord Myxini (hagfishes) Common ancestor of chordates Craniates Petromyzontida (lampreys) Head Vertebrates Chondrichthyes (sharks, rays, chimaeras) Vertebral column Actinopterygii (ray-finned fishes) Gnathostomes Jaws, mineralized skeleton Actinistia (coelacanths) Osteichthyans Lungs or lung derivatives Lobe-fins Dipnoi (lungfishes) Lobed fins Amphibia (frogs, salamanders) Tetrapods Reptilia (turtles, snakes, crocodiles, birds) Legs Amniotes Amniotic egg Mammalia (mammals) Milk

5. Concept 34.1: Chordates have a notochord and a dorsal, hollow nerve cord • Vertebrates are a subphylum within the phylum Chordata • Chordates are bilaterian animals that belong to the clade of animals known as Deuterostomia • Two groups of invertebrate deuterostomes, the urochordates and cephalochordates, are more closely related to vertebrates than to other invertebrates • 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

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

7. 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 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

8. 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 vertebrates (except vertebrates with limbs, the tetrapods) • Develop into parts of the ear, head, and neck in tetrapods Muscular, Post-Anal Tail • Chordates have a tail posterior to the anus • In many species, the tail is greatly reduced during embryonic development • The tail contains skeletal elements and muscles • It provides propelling force in many aquatic species

9. Fig. 34-4 Lancelets Cirri 2 cm Mouth Pharyngeal slits Atrium Notochord Digestive tract Atriopore Dorsal, hollow nerve cord Segmental muscles Anus Tail • Lancelets (Cephalochordata) are named for their bladelike shape • They are marine suspension feeders that retain characteristics of the chordate body plan as adults

10. Fig. 34-5 • Tunicates (Urochordata) are more closely related to other chordates than are lancelets • They are marine suspension feeders commonly called sea squirts • As an adult, a tunicate draws in water through an incurrent siphon, filtering food particles Incurrent siphon to mouth Water flow Notochord Dorsal, hollow nerve cord Excurrent siphon Tail Excurrent siphon Excurrent siphon Atrium Muscle segments Incurrent siphon Pharynx with slits Intestine Anus Stomach Intestine Tunic Atrium Esophagus Pharynx with slits Stomach An adult tunicate A tunicate larva • Tunicates most resemble chordates during their larval stage, which may last only a few minutes

11. Conceptual Summary • Vertebrates almost certainly evolved from a tadpole-lie invertebrate larva that failed to metamorphose but became sexually mature

12. 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 • Craniates have two clusters of Hox genes; lancelets and tunicates have only one cluster • One feature unique to craniates is the neural crest, a collection of cells near the dorsal margins of the closing neural tube in an embryo • Neural crest cells give rise to a variety of structures, including some of the bones and cartilage of the skull • http://www.youtube.com/watch?v=00xr4kzYZn4 (neural tube formation)

13. Fig. 34-7 Neural crest Neural tube Dorsal edges of neural plate Migrating neural crest cells Notochord

14. Hagfishes • The least derived surviving craniate lineage is Myxini, the hagfishes • Hagfishes have a cartilaginous skull and axial rod of cartilage derived from the notochord, but lack jaws and vertebrae Slime glands

15. Concept 34.3: Vertebrates are craniates that have a backbone • During the Cambrian period, a lineage of craniates evolved into vertebrates • Vertebrates became more efficient at capturing food and avoiding being eaten • Vertebrates underwent a second gene duplication involving the Dlx family of transcription factors • Vertebrates have the following derived characters: • Vertebrae enclosing a spinal cord • An elaborate skull • Fin rays, in the aquatic forms

16. Fig. 34-10 • Lampreys (Petromyzontida) represent the oldest living lineage of vertebrates • They are jawless vertebrates inhabiting various marine and freshwater habitats • They have cartilaginous segments surrounding the notochord and arching partly over the nerve cord

17. Concept 34.4: Gnathostomes are vertebrates that have jaws • Today, jawed vertebrates, or gnathostomes, outnumber jawless vertebrates • Gnathostomes have jaws that might have evolved from skeletal supports of the pharyngeal slits • Other characters common to gnathostomes: • An additional duplication of Hox genes • An enlarged forebrain associated with enhanced smell and vision • In aquatic gnathostomes, the lateral line system, which is sensitive to vibrations

18. Lateral Line System

19. Fig. 34-13-3 Concept 34.4: Gnathostomes are vertebrates that have jaws Gill slits Cranium Mouth Skeletal rods The skeleton of the jaws and their supports may have evolved from two pairs of skeletal rods (red and green) located between gills slits near the mouth. Pairs of rods anterior to those that formed the jaws were either lost or incorporated into the cranium or jaws.

20. Chondrichthyans (Sharks, Rays, and Their Relatives) • Chondrichthyans (Chondrichthyes) have a skeleton composed primarily of cartilage • The cartilaginous skeleton evolved secondarily from an ancestral mineralized skeleton • Swim in primative vertebrate fashion (sinious) • Gills open separately to environment • The largest and most diverse group of chondrichthyans includes the sharks, rays, and skates • http://www.metacafe.com/watch/336740/great_white_shark_video/ (great white shark eating a seal)

21. Fig. 34-15a Pelvic fins Pectoral fins (a) Blacktip reef shark (Carcharhinus melanopterus)

22. Most sharks • Have a streamlined body and are swift swimmers • Are carnivores • Have a short digestive tract; a ridge called the spiral valveincreases the digestive surface area • Have acute senses • Shark eggs are fertilized internally but embryos can develop in different ways: • Oviparous: eggs hatch outside the mother’s body • Ovoviviparous: the embryo develops within the uterus and is nourished by the egg yolk • Viviparous: the embryo develops within the uterus and is nourished through a yolk sac placenta from the mother’s blood • The reproductive tract, excretory system, and digestive tract empty into a common cloaca

23. Fig. 34-15b (b) Southern stingray (Dasyatis americana)

24. Fig. 34-15c (c) Spotted ratfish (Hydrolagus colliei)

25. Ray-Finned Fishes and Lobe-Fins • The vast majority of vertebrates belong to a clade of gnathostomes called Osteichthyes • Osteichthyes includes the bony fish and tetrapods • Nearly all living osteichthyans have a bony endoskeleton • Aquatic osteichthyans are the vertebrates we informally call fishes • Most fishes breathe by drawing water over gills protected by an operculum • Fishes control their buoyancy with an air sac known as a swim bladder

26. Fig. 34-16 Swim bladder Dorsal fin Adipose fin (characteristic of trout) Caudal fin Spinal cord Brain Nostril Anal fin Cut edge of operculum Lateral line Liver Gills Anus Gonad Heart Stomach Urinary bladder Pelvic fin Kidney Intestine

27. Ray-Finned Fishes • Class Actinopterygii, the ray-finned fishes, includes nearly all the familiar aquatic osteichthyans • The fins, supported mainly by long, flexible rays, are modified for maneuvering, defense, and other functions • http://www.youtube.com/watch?v=cKP53sB0itI (clown fish and sea anemone) • http://www.youtube.com/watch?v=iaoLxR9FTwk&feature=related (seahorse giving birth)

28. Fig. 34-18 • The lobe-fins (Sarcopterygii) have muscular pelvic and pectoral fins which can be used to “walk” underwater across the substrate • Three lineages survive and include coelacanths, lungfishes, and tetrapods

29. Conceptual Summary: • These two classes of jawed fish also have two pairs of lagteral fins which allow fishes to balance and maneuver and were important in the evolution of paired limbs

30. Concept 34.5: Tetrapods are gnathostomes that have limbs • 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 • The transition to land depended on solving probloems such as dehydration, lack of buoyant support, fertilization • Tetrapods have some specific adaptations: • Four limbs, and feet with digits • Ears for detecting airborne sounds • In one lineage of lobe-fins, the fins became progressively more limb-like while the rest of the body retained adaptations for aquatic life • For example, Acanthostegalived in Greenland 365 million years ago

31. Fig. 34-19 Bones supporting gills Tetrapod limb skeleton

32. Amphibians: Frogs, Salamanders, Toads, Newts • Amphibians (class Amphibia) are represented by about 6,150 species of organisms in three orders • Amphibian means “both ways of life,” referring to the metamorphosis of an aquatic larva into a terrestrial adult • Amphibians require water for external fertilization and external embryonic development • No amnion • Excretes ammonia (by product of the breakdown of proteins & nucleic acids • Thin skinned – gas exchange through skin • First vertebrate with true tongue

33. Fig. 34-21 (a) Order Urodela (b) Order Anura (c) Order Apoda

34. Fig. 34-22 (a) Tadpole (b) During metamorphosis (c) Mating adults

35. This frog incubates her eggs in a pouch of skin, helping to protect the eggs from predators. When the eggs hatch, the female deposits the tadpoles in water where they begin life on their own.

36. Concept 34.6: Amniotes are tetrapods that have a terrestrially adapted egg • Amniotes are a group of tetrapods whose living members are the reptiles, including birds, and mammals • Amniotes are named for the major derived character of the clade, the amniotic egg, which contains membranes that protect the embryo • The extraembryonic membranes are the amnion, chorion, yolk sac, and allantois • Amniotes have other terrestrial adaptations, such as relatively impermeable skin and the ability to use the rib cage to ventilate the lungs

37. The amniotic egg: • The embryos of reptiles and mammals form four extraembryonic membranes which is an evolutionary adaptation that protects developing embryo from drying out. • Amnion – The amnion protects the embryo in a fluid-filled cavity that cushions against mechanical shock. • Allantios – The allantois is a disposal sac for certain metabolic wasted produced by the embryo. The membrane of the allantois also functions with chorion as a respiratory organ. • Chorion – The chorion and the membrane of the allantois exchange gasses between the embryo and the air. Oxygen and carbon dioxide diffuse freely across the shell. • Yolk sac – The yolk sac contains the yolk, a stockpile of nutrients. Blood vessels in the yolk sac membrane transport nutrients from the yolk into the embryo. Other nutrients are stored in the albumen (“egg white”).

38. Fig. 34-25 Chorion Allantois Yolk sac Amnion Embryo Amniotic cavity with amniotic fluid Yolk (nutrients) Albumen Shell

39. Reptiles: Lizards, Snakes, Turtles and Crocodiles • The reptile clade includes the tuataras, lizards, snakes, turtles, crocodilians, birds, and the extinct dinosaurs • They produce live born offspring or amniotic eggs which have membranes specialized for respiration, protection and storage of waste products. Fertilization is internal, embryonic development is external • Reptiles have scales that protect and reduce water loss • They lay shelled eggs on land • Ectothermic – taking most of their heat from the environment • Early reptiles showed much more diversity in methods of locomotion, feeding habits and life histories compared with modern reptiles.

40. Fig. 34-26

41. Fig. 34-27 (a) Tuatara (Sphenodon punctatus) (b) Australian thorny devil lizard (Moloch horridus) (c) Wagler’s pit viper (Tropidolaemus wagleri) (d)Eastern box turtle (Terrapenecarolinacarolina) (e) American alligator (Alligator mississippiensis)

42. http://www.arkive.org/galapagos-marine-iguana/amblyrhynchus-cristatus/video-06c.html (galapagos marine iguana)

43. Birds • Birds are archosaurs, but almost every feature of their reptilian anatomy has undergone modification in their adaptation to flight • The major adaptation is wings with keratin feathers which provide protection, insulation, allow for flight and play a role in courtship rituals • Flight enhances hunting and scavenging, escape from terrestrial predators, and migration • Flight requires a great expenditure of energy, acute vision, and fine muscle control • Endothermic – generate heat by their metabolism • Other adaptations include lack of a urinary bladder, females with only one ovary, small gonads, and loss of teeth

44. Fig. 34-28 Finger 1 (b) Bone structure Palm (a) Wing Finger 2 Finger 3 Forearm Wrist Shaft Shaft Barb Vane Barbule Hook (c) Feather structure

45. Fig. 34-29 Toothed beak Wing claw Fossil evidence indicates that Archaeopteryx was capable of powered flight but retained many characters of nonbird dinasaurs. Airfoil wing with contour feathers Long tail with many vertebrae

46. Fig. 34-30a (a) Emu – a flightless bird

47. Fig. 34-30b (b) Mallards – Like many birds the mallard exhibits pronounced color differences between the sexes

48. Fig. 34-30c (c) Laysan albatrosses – Most birds have specific , mating behaviors, such as this courtship ritual.

49. Fig. 34-30d (d) Barn swallows – toes on their feet can lock around a branch or wire, enabling them to rest in place for long periods of time

50. Conceptual Summary • Feathers permit birds to fly while retaining other means of locomotion. They also contribute to endothermy, which has permitted birds to colonize most parts of the world.