1. Origin & Evolution of Vertebrates Ch. 34
Lecture Objectives
1. Intro to Phylum Chordata

2. Jaws, mineralized skeleton
Echinodermata
Cephalochordata
ANCESTRAL
DEUTEROSTOME
Urochordata
Notochord
Myxini
Common ancestor of chordates
Petromyzontida
Chondrichthyes
Vertebrae
Figure 34.2a Phylogeny of living chordates (part 1)
Jaws, mineralized skeleton

3. Phylum Chordata 1. Bilateral 2. Segmented Body 3. Triploblastic
4. Coelomate
5. Deuterostomes

4. Chordate Hallmarks * May only appear during embryonic development.
Dorsal,
hollow
nerve cord
Muscle
segments
Notochord
Figure 34.3 Chordate characteristics
Mouth
Anus
Pharyngeal
slits or clefts
Muscular,
post-anal tail
Fig. 34.3

5. Chordate hallmarks con’t:
Notochord
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. Chordate hallmarks con’t:
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. Chordate hallmarks con’t:
Pharyngeal Slits
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

8. Chordate hallmarks con’t.
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. Phylum Chordata Broken into 3 subphyla: Cepahlochordata (lancelets)
Urochordata (tunicates)
Vertebrata (animals w/backbones)
Class Agnatha
Class Amphibia
Class Reptilia
Class Aves
Class Mammalia

10. Subphylum: Cephalochordata (lancelets)
Fig. 34-4
Subphylum: Cephalochordata (lancelets)
Cirri
Mouth
Pharyngeal slits
Atrium
Notochord
Digestive tract
Atriopore
Dorsal, hollow
nerve cord
Figure 34.4 The lancelet Branchiostoma, a cephalochordate
Segmental
muscles
Anus
Tail
Fig. 34.4

11. Subphylum: Urochordata (tunicates)
Fig. 34.5

12. Subphylum Vertebrata: the craniates
1. Chordates w/ a head
2. Higher metabolism
3. Increased muscle
4. 2 chambered heart
5. RBCs w/ hemoglobin
6. Pharyngeal slits  gills
Segmented muscles
Fossil chordate
Pharyngeal slits
Fig. 34.9

13. Extant craniates: SP: Vertebrata, Class Myxini
1.Cyclostomes - Jawless, Ex. Hagfish 2. Cartilaginous skull & skeleton 3. Long & slender, eel-like 4. Bottom scavengers that secrete slime 5. Ingest food by sucking

14. Fig. 34-9
Slime glands
Figure 34.9 A hagfish
Fig. 34.7

15. Extant craniates: SP: Vertebrata, Class Pteromyzontida
1. Cyclostomes, Ex. Lamprey
2. Marine & freshwater
3. Mostly ectoparasites
4. Skeleton made of cartilage

16. Fig. 34.8

17. Gnathostomes (jaw mouth) Ex
Gnathostomes (jaw mouth) Ex. Sharks, Fish, Amphigians, Reptiles, Birds, Mammals
1. Jaws that may have evolved from skeletal supports of the pharyngeal slits
2. An enlarged forebrain associated with enhanced smell and vision
3. lateral line system
Fig

18. Tetrapods – gnathostomes with limbs
Four limbs, and feet with digits (from fins 365 mya)
Ears for detecting airborne sounds
Fig

19. SP: Vertebrata, Class Amphibia
1. Gnathostomes & Tetrapods w/ moist skin  complements the lungs in gas exchange 2. Fertilization is external in most species 3. Eggs require a moist environment
Figs

20. Amniotes: reptiles, birds, mammals
1. Tetrapods w/ terrestrially adapted egg
2. Relatively impermeable skin
3. Ability to use the rib cage to ventilate the lungs
Fig

21. SP: Vertebrata, Class Reptilia
1. Scales that create a waterproof barrier
2. Lay shelled eggs on land (or live birth)
3. Ectothermic or endothermic
4. Ex. lizards, snakes, turtles, crocodilians, and the extinct dinosaurs

22. Figure 34.27 Extant reptiles (other than birds)

23. SP: Vertebrata, Class Aves
1. Wings with keratin feathers 2. Lack of urinary bladder 3. Reduction in reproductive organs 4. Loss of teeth
Flight enhances hunting and scavenging, escape from terrestrial predators, and migration
Flight requires a great expenditure of energy, acute vision, and fine muscle control

24. Finger 1 (b) Bone structure Palm (a) Wing Finger 2 Finger 3 Forearm
Wrist
Figure Form fits function: the avian wing and feather
Shaft
Shaft
Barb
Vane
Barbule
Hook
(c) Feather structure
Fig

25. SP: Vertebrata,Class Mammalia
1. Mammary Glands 2. Hair 3. Larger Brains 4. Differentiated Teeth

26. Variations in Class Mammalia
1. Embryo develops within a placenta in the mother’s uterus
2. Embryonic development completed while nursing in a maternal pouch
Marsupials
3. Egg laying mammals
Monotremes
Opossum and bandicoot

27. Marsupials & Monotremes
Figs

28. Character 
Monotremes
Marsupials and Placental Mammals 
Cloaca
 A single opening in which urine, feces and eggs are deposited before being expulsion from body.  Similar to the mammalian uterus.
Have at least two distinct openings for expulsion of feces and urine and for the birth of young.  Have a true uterus.
 Leathery bill
 Present. It is used to detect prey.
 Not present.
 Nipple
 No true nipple; milk is secreted through the skin of the abdomen.
 Milk is collected into a single duct and exits body through the nipple.
 Spur on hind limb
 Present in males.  Platypus can secrete venom through spur.
 Ear
Primitive development of the inner ear bone, it is less coiled. 
 More highly coiled inner ear.
 Teeth
 Lack of teeth in adults, instead horny pads develop.
 Present in Adults.
 Gait
Reptile-like; limbs are aligned laterally with respect to body.
Limbs are aligned below body.