1. Chordates

2. Chordates are Deuterostomes

3. Protostome vs. Deuterostome

4. Echinoderms are sister group with chordates
Bilateral symmetry
Deuterostome lineage

5. Four Distinct Chordate Characteristics
Notochord
Single tubular, dorsal nerve chord
Pharyngeal pouches
Post-anal tail

6. Notochord Flexible rod-like structure Attachment point for muscles
Often forms bony or cartilaginous vertebrae

7. Dorsal Nerve Cord Dorsal to alimentary canal and notochord
Forms as a tube derived from ectoderm
Anterior end thickens to form brain

8. Pharyngeal Pouches Openings in pharynx to outside
Early chordates – filter feeding
Evolved into gills, ear canal, parathyroid gland Eustachian tube etc…

9. Segmentation and Postanal Tail
Segmented muscles act on notochord
Tail structure extends past anus
Swimming

10. Subphylum Urochordata Tunicates

11. Tunicate Body Plan Adult
Sessile filter feeder
Pharyngeal slits used for capturing food in mucus
Most Chordate features not exhibited in adult form

12. Tunicate Development

13. Competing hypotheses
Cephalochordate hypothesis: vertebrates evolved from essentially lancelet-like ancestors
Calcichordate hypothesis: vertebrates evolved from armored bilateral echinoderms which were early chordates, distantly related to modern echinoderms.

14. Cephalochordate hypothesis
Lancelet-like organism is the common ancestor of all vertebrates
Cephalochordate Pikaia
Rare fossils that extend back 530 million years

15. Calcichordate hypothesis
The calcichordate hypothesis
Not widely accepted
Calcichordates
Echinoderm-like skeletons
Ambiguous chordate-like features
Chordate features may be homologous with echinoderm structures
May be too young to be direct vertebrate ancestors

16. Calcichordate Has both echinoderm and chordate features?
Probably a filter feeder

17. Tunicates and Chordate Evolution
Garstang’s Hypothesis
Paedomorphosis – larval form does not develop into adult

18. Subphylum Cephalochordata Amphioxus
Free swimming filter feeder
Has all basic chordate features

19. Conodonts Early Chordate with some vertebrate features
Conodont teeth are very common fossils, known since early 1800s, but animal body only described in 1983

20. Conodonts May or may not be true vertebrates Vertebrate characters
sense organs with capsules
CaPO4 mineralization
Non-vertebrate characters
V-shaped myomeres
notochord but no trace of vertebrae

21. Subphylum Vertebrata Features
Cranium – brain encased in cartilage or bone
Most have cartilage or bone endoskeleton
Complex nervous system

22. Development of Head Structures
Derived from neural crest cells
Cells that migrate during early development and form various structures

23. Neural Crest Migrations
Facial and skull bones
Lower Jaw
Hyoid
Heart

24. Development of Vertebrae
Cartilage or bone surrounds notochord and nerve cord
Segmented to allow flexibility

25. Development of Gills Capillaries line pharyngeal slits
Increases surface area of gas exchange

26. Development of Complex Nervous systems
Anterior brain
Anterior sense organs
Vision
Auditory
Olfactory

27. Early Vertebrates Agnathans Gnathostomes Ostracoderms Jawless
Placoderms
Jawed

28. Early Vertebrates

29. Evolution of the Jaw