Chapter 34

1. Chapter 34 Vertebrates

2. Vertebrates Get their name from vertebrae, the series of bones that make up the backbone

3. Vertebrates • There are approximately 52,000 species of vertebrates • Which include the largest organisms ever to live on the Earth. Plant-eating dinosaurs at 40,000 kg were the heaviest terrestrial animals. The Blue Whale at 100,000 kg is the biggest animal ever to have existed

4. Chordates • Chordates have a notochord and a dorsal, hollow nerve cord • Vertebrates are a subphylum of 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 invertebrates

5. Chordates Craniates Vertebrates Gnathostomes Osteichthyans Lobe-fins Tetrapods Amniotes Echinodermata(sister group to chordates) Chondrichthyes(sharks, rays, chimaeras) Cephalaspidomorphi(lampreys) Amphibia(frogs, salamanders) Cephalochordata(lancelets) Reptilia(turtles, snakes,crocodiles, birds) Actinopterygii(ray-finned fishes) Urochordata(tunicates) Actinistia(coelacanths) Dipnoi(lungfishes) Myxini(hagfishes) Mammalia(mammals) Milk Amniotic egg Legs Lobed fins Lungs or lung derivatives Jaws, mineralized skeleton Vertebral column Head Brain Notochord Ancestral deuterostome A hypothetical phylogeny of chordates

6. Dorsal,hollownerve cord Brain Notochord Musclesegments Mouth Anus Pharyngealslits or clefts Muscular,post-anal tail Derived Characters of Chordates • All chordates share a set of derived characters • Although some species possess some of these traits only during embryonic development 1. Notochord 2. Dorsal, hollow nerve cord 3.Pharyngeal slits 4. Muscular post-anal tail

7. Notochord • The notochord • Is a longitudinal, flexible rod located between the digestive tube and the nerve cord • 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

8. Dorsal, Hollow Nerve Cord • The nerve cord of a chordate embryo • Develops into the central nervous system: the brain and the spinal cord

9. 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 • These pharyngeal slits • Function as suspension-feeding structures in many invertebrate chordates • Are modified for gas exchange in aquatic vertebrates • Develop into parts of the ear, head, and neck in terrestrial vertebrates

10. Muscular, Post-Anal Tail • Chordates have a tail extending posterior to the anus • Although in many species it is lost during embryonic development • The chordate tail contains skeletal elements and muscles • And it provides much of the propelling force in many aquatic species

11. Incurrentsiphonto mouth Notochord Excurrentsiphon Dorsal, hollownerve cord Excurrent siphon Tail Excurrent siphon Atrium Musclesegments Pharynxwith numerousslits Incurrentsiphon Intestine Anus Stomach Intestine Tunic Atrium Esophagus Stomach Pharynx with slits (b) In the adult, prominent pharyngeal slits function in suspension feeding, but other chordate characters are not obvious. (a) An adult tunicate, or sea squirt, is a sessile animal (photo is approximately life-sized). (c) A tunicate larva is a free-swimming butnonfeeding “tadpole” in which all fourchief characters of chordates are evident. Tunicates (subphylum Urochordata) • Marine suspension feeders commonly called sea squirts • Tunicates most resemble chordates during their larval stage which may be as brief as a few minutes • As an adult a tunicate draws in water through an incurrent siphon, filtering food particles

12. Tentacle 2 cm Mouth Pharyngeal slits Atrium Notochord Digestive tract Atriopore Dorsal, hollownerve cord Segmentalmuscles Anus Tail Lancelets (subphylum Cephalochordata) • Named for their bladelike shape • Lancelets are marine suspension feeders that retain the characteristics of the chordate body plan as adults

13. Craniates • 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 common characteristics • A skull, brain, eyes, and other sensory organs

14. Neuraltube Neuralcrest Dorsal edgesof neural plate Ectoderm Ectoderm (a) The neural crest consists of bilateral bands of cells near the margins of the embryonic folds that form the neural tube. (b) Neural crest cells migrate todistant sites in the embryo. Migrating neuralcrest cells Notochord Neural crest • Unique to craniates, the neural crest, a collection of cells that appears near the dorsal margins of the closing neural tube in an embryo

15. (c) The cells give rise to some of the anatomical structuresunique to vertebrates, including some of the bones and cartilage of the skull. Neural crest cells • Give rise to a variety of structures, including some of the bones and cartilage of the skull

16. 5 mm (a)Haikouella. Discovered in 1999 in southern China, Haikouella had eyes and a brain but lacked a skull, a derived trait of craniates. (b) Haikouichthys.Haikouichthys had a skull and thus is considered a true craniate. The Origin of Craniates • Craniates evolved at least 530 million years ago during the Cambrian explosion • The most primitive of the fossils are those of the 3-cm-long Haikouella In other Cambrian rocks paleontologists have found fossils of even more advanced chordates, such as Haikouichthys

17. Slime glands Hagfishes • The least derived craniate lineage that still survives is class Myxini, the hagfishes • Hagfishes are jawless marine craniates • That have a cartilaginous skull and axial rod of cartilage derived from the notochord • They lack vertebrae

18. Origin of Vertebrates • Vertebrates are craniates that have a backbone • During the Cambrian period a lineage of craniates evolved into vertebrates • Derived Characters of Vertebrates • Vertebrae enclosing a spinal cord • An elaborate skull • Fin rays, in aquatic forms

19. Lampreys (Class Cephalaspidomorphi) • Represent the oldest living lineage of vertebrates • Have cartilaginous segments surrounding the notochord and arching partly over the nerve cord • Are jawless vertebrates • Inhabit various marine and freshwater habitats

20. Dorsal viewof head Dentalelements Fossils of Early Vertebrates • Conodonts were the first vertebrates with mineralized skeletal elements in their mouth and pharynx

21. Origins of Bone and Teeth • Mineralization appears to have originated with vertebrate mouthparts • The vertebrate endoskeleton became fully mineralized much later

22. Gill slits Cranium Mouth Skeletal rods Gnathostomes • Are vertebrates that have jaws • Today, jawless vertebrates are far outnumbered by those with jaws • Gnathostome characteristics • Jaws that evolved from skeletal supports of the pharyngeal slits. • Enhanced sensory systems, including the lateral line system • An extensively mineralized endoskeleton • Paired appendages

23. Chondrichthyans (Sharks, Rays, and Their Relatives) • Members of class Chondrichthyes • Have a skeleton that is composed primarily of cartilage • The cartilaginous skeleton • Evolved secondarily from an ancestral mineralized skeleton

24. Blacktip reef shark (Carcharhinus melanopterus).Fast swimmers with acute senses, sharks have paired pectoral and pelvic fins. Pelvic fins Pectoral fins Southern stingray (Dasyatis americana).Most rays are flattened bottom-dwellers thatcrush molluscs and crustaceans for food. Some rays cruise in open water and scoop food into their gaping mouth. Sharks and Rays • The largest and most diverse subclass of Chondrichthyes includes the sharks and rays • Most sharks have a streamlined body and are swift swimmers and have acute senses

25. Spotted ratfish(Hydrolagus colliei). Ratfishes, typically live at depths greaterthan 80 m and feed on shrimps, molluscs, and sea urchins. Some species have a poisonous spine at the front of their dorsal fin. Ratfish • Another subclass is composed of a few dozen species of ratfishes

26. Ray-Finned Fishes and Lobe-Fins • The vast majority of vertebrates belong to a clade of gnathostomes called Osteichthyes • Nearly all living osteichthyans have a bony endoskeleton • Aquatic osteichthyans • Are the vertebrates we informally call fishes • Control their buoyancy with an air sac known as a swim bladder

27. Adipose fin(characteristic oftrout) Dorsal fin Caudal fin Swim bladder Spinal cord Brain Nostril Cut edge of operculum Anal fin Gills Anus Gonad Liver Heart Lateral line Stomach Urinary bladder Kidney Intestine Pelvic fin Fish anatomy • Fishes breathe by drawing water over four or five pairs of gills • Located in chambers covered by a protective bony flap called the operculum

28. (a) Yellowfin tuna (Thunnus albacares), a fast-swimming, schooling fish that is an important commercial fish worldwide (b) Clownfish (Amphiprion ocellaris), a mutualistic symbiont of sea anemones (c) Sea horse (Hippocampus ramulosus), unusual in the animal kingdom in that the male carries the young during their embryonic development (d) Fine-spotted moray eel (Gymnothorax dovii), a predator that ambushes prey from crevices in its coral reef habitat Ray-Finned Fishes (Class Actinopterygii) Includes nearly all the familiar aquatic osteichthyans. The fins, supported by long, flexible rays are modified for maneuvering, defense, and other functions.

29. Lobe-Fins (Class Sarcopterygii) • Have muscular and pectoral fins • Include coelacanths, lungfishes, and tetrapods

30. 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 • Tetrapods have some specific adaptations • Four limbs and feet with digits • Ears for detecting airborne sounds

31. Bonessupportinggills Tetrapodlimbskeleton The Origin of Tetrapods • In one lineage of lobe-fins • The fins became progressively more limb-like while the rest of the body retained adaptations for aquatic life

32. Millions of years ago 420 370 340 310 295 280 265 415 400 385 355 325 Silurian Devonian Carboniferous Permian To present Paleozoic Ray-finned fishes Coelacanths Lungfishes Eusthenopteron Panderichthys Elginerpeton Metaxygnathus Acanthostega lchthyostega Hynerpeton Greerpeton Amphibians Amniotes Origin of Tetrapods

33. The tadpole is an aquatic herbivore With a fishlike tail and internal gills. 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. During metamorphosis, the gills and tail are resorbed, andwalking legs develop. Amphibians • Class Amphibia is represented by about 4,800 species of organisms • Most amphibians have moist skin that complements the lungs in gas exchange • Amphibian means “two lives” (a reference to the metamorphosis of an aquatic larva into a terrestrial adult)

34. Origin of Amphibians

35. Order Urodela. Urodeles (salamanders) retain their tail as adults. Order Urodela • Includes salamanders, which have tails

36. Order Anura. Anurans, such as this poison arrow frog, lack a tail as adults. Order Anura • Includes frogs and toads, which lack tails

37. Order Apoda. Apodans, or caecilians, are legless, mainly burrowing amphibians. Order Apoda • Includes caecilians, which are legless and resemble worms

38. Amniotes • Amniotes are a group of tetrapods • Whose living members are the reptiles, including birds, and the mammals • that have a terrestrially adapted egg • the amniotic egg contains specialized membranes that protect the embryo • Amniotes also have other terrestrial adaptations such as relatively impermeable skin and the ability to use the rib cage to ventilate the lungs • Early amniotes appeared in the Carboniferous period

39. dinosaurs other Saurischian than birds Ornithischiandinosaurs Crocodilians Ichthyosaurs Plesiosaurs Squamates Mammals Pterosaurs Parareptiles Tuatara Turtles Birds Saurischians Dinosaurs Lepidosaurs Archosaurs Synapsids Diapsids Reptiles Ancestralamniote A phylogeny of amniotes

40. Traditionally, lizards, snakes, and crocs are classified together in the Class Reptilia with birds in a separate class (Aves) But crocodiles may actually be more closely related to birds than to lizards and snakes

41. Chorion. The chorion and the membrane of the allantois exchange gases between the embryo and the air. Oxygen and carbon dioxide diffuse freely across the shell. Allantois. The allantois is a disposal sac for certain metabolic wastes pro- duced by the embryo. The membrane of the allantois also functions with the chorion as a respiratory organ. Extraembryonic membranes 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”). Amnion. The amnion protectsthe embryo in a fluid-filled cavity that cushions againstmechanical shock. Embryo Amniotic cavitywith amniotic fluid Yolk (nutrients) Albumen Shell The extraembryonic membranes

42. Reptiles • The reptile clade includes • The tuatara, lizards, snakes, turtles, crocodilians, birds, and the extinct dinosaurs • Reptiles • Have scales that create a waterproof barrier • Lay shelled eggs on land • 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) Hatching Komodo dragon

43. The Origin and Evolutionary Radiation of Reptiles • The oldest reptilian fossils date to about 300 million years ago • The first major group of reptiles to emerge were the parareptiles, which were mostly large, stocky herbivores • As parareptiles were dwindling the diapsids were diversifying • The diapsids are composed of two main lineages • The lepidosaurs and the archosaurs • Snakes and lizards are surviving forms of lepidosaurs • Crocs and gators are an archosaur lineage

44. Deinonychus Dinosaurs Diversified into a vast range of shapes and sizes Included the long-necked giants called the theropods • Traditionally, dinosaurs were considered slow, sluggish creatures • But fossil discoveries and research have led to the conclusion that dinosaurs were agile and fast moving • Paleontologists have also discovered signs of parental care among dinosaurs Nesting Oviraptor and eggs

45. Tuatara (Sphenodon punctatus) Lepidosaurs • One surviving lineage of lepidosaurs is represented by two species of lizard-like reptiles called tuatara Found only in New Zealand…endangered

46. Australian thorny devil lizard (Moloch horridus) Squamates • 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

47. Wagler’s pit viper (Tropidolaemus wagleri) Snakes • Snakes are legless lepidosaurs that evolved from lizards

48. Eastern box turtle (Terrapene carolina carolina) Turtles • 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

49. American alligator (Alligator mississipiensis) Alligators and Crocodiles • Crocodilians • Belong to an archosaur lineage that dates back to the late Triassic

50. Evolution of birds