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Topic 3: Evolution & Diversity of

Vertebrates

� What are the protochordates?

� A phylogenetic perspective

� Relationship to craniates

� What are the key characteristics of chordates?

� What are the main Protochordate clades?

� What are the differences between craniates and vertebrates?

What are the protochordates?

� Protochordates are ______________

� Hemichordata

� Pterobranchia

� Enteropneusta –acorn worms

� Urochordata

� Tunicates

� Cephalochordata

� Lancelets

Modified: Liem et al. 2001, Fig. 2-1

Protostomes

Echinoderms

Pterobranchia

Enteropneusta

Urochordata

Cephalochordata

Craniata

Chordata

Hemichordata

Deuterostomes

What are the protochordates?

� What sort of phylogenetic group are protochordates?

� What does this mean?

� ________________ ________________

� ________________ ________________

Modified: Liem et al. 2001, Fig. 2-1

Protostomes

Echinoderms

Pterobranchia

Enteropneusta

Urochordata

Cephalochordata

Craniata

Chordata

Hemichordata

Deuterostomes

What are the protochordates?

� What insights might the study of protochordates give us?

Modified: Liem et al. 2001, Fig. 2-1

Protostomes

Echinoderms

Pterobranchia

Enteropneusta

Urochordata

Cephalochordata

Craniata

Chordata

Hemichordata

Deuterostomes

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What are the key chordate characteristics?

� To understand the

evolution of chordates, we need an

understanding of what

makes up a chordate

� Hemichordates have some of these

� Chordates have all of

these

� 5 key chordate

characteristics:

1. ___________________

2. ___________________

3. ___________________

4. ___________________

5. ___________________

Photo © C Arenz

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3

4

5

1. _______________________

� Develops by invagination

� Results in a neural tube

� Develops from ectoderm, like the epidermis

� Becomes the spinal cord

� Ventral and solid in many non-

chordates

Liem et al. 2001, Fig 2-9; Nature 2002; C Arenz

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What are the key chordate characteristics?

2. _____________________

� Also dorsal in position, ventral to the nerve cord

� Develops from mesoderm, like muscles and skeleton

� Is a ___________________

� Cells in fluid in a tough connective tissue sheath

� Allows flexion

� Resists compression

� Maintains body shape

Liem et al. 2001, Fig 2-9; Kardong 1998 Fig 2-5

2

What are the key chordate characteristics?

2. Notochord

� Skeletal/support function

� Reduced and replaced by

vertebrae in vertebrates

� Intervertebral discs

A Harris; A Morton; Univ Maryland

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What are the key chordate characteristics?

3. ____________________

� Anterior end of gut

� Develops from endoderm,

like the rest of the gut

� Allows ____________ of

water for food particles

Liem et al. 2001, Fig 2-8D; C Arenz

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What are the key chordate characteristics?

3. Perforated pharynx - function

� Protochordates

� Primarily _______ (filtration)

� Fishes

� ___________ (gills, gill slits)

� Also in suction ___________

� Tetrapods

� Slits disappear

� Pharyngeal structures contribute to jaws, ear bones,

endocrine glands…

Photos © U Gille; C Arenz

What are the key chordate characteristics?

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4. _________________

� Seems intuitive

� We define a “tail” this way

� Some animals have a tail-like structure with a gut inside

� Often has a ______________

Liem et al. 2001, Fig 2-8B; C Arenz

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What are the key chordate characteristics?

5. ____________

� Develops from endoderm

� A ciliated groove at the

ventral end of the pharynx

� _________________

� Traps food particles

� Cilia move mucous

posteriorly

� Transport mucous and food to the gut

for digestion

Photos © M Himemiya; C Arenz

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What are the key chordate characteristics?

5. ________________

� Homologous to the thyroid gland in vertebrates� Controversial

� Evidence for homology

� Position

� Endostyle of larval lamprey metamorphoses into adult thyroid

� Both structures associated with iodine

� Tunicate (Urochordate) endostyle has similar genes expressed as a thyroid gland

Ogasawara & Satou 2003; C Arenz

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What are the key chordate characteristics? What are the protochordate clades?

Modified: Liem et al. 2001, Fig. 2-1

Pterobranchia

Enteropneusta

Urochordata

Cephalochordata

Craniata

Chordata

Hemichordata

Protochordates

� ________________� Pterobranchia

� Enteropneusta (acorn worms)

� ~100 species

� All are ___________

� All are ___________

� Pterobranchs are colonial, deepsea, and secrete a tube

� Acorn worms are shallower and fossorial

Photos © Discovery Channel, A Artour, E Balser

What are the

protochordate clades?

� Pterobranchia

� Filter feeders

� Highly specialized

morphology

Liem et al. 2001, Fig 2-2; Sinauer Associates, 2001

What are the protochordate clades?

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Liem et al. 2001, Fig 2-3

What are the protochordate clades?

� Enteropneusta

� More generalized

� Worm-like

� ______________

� Mucous is used to

trap food on ________

� Cilia then transport

the food and mucous into the mouth

� Enteropneusta

� Locomotion

� Anchoring with collar

� Probing with proboscis

� Pulling body along

� No notochord

� Have some chordate characteristics

� Pharyngeal slits

� Dorsal, hollow nerve cord formed by

invagination

Liem et al. 2001, Fig 2-3

What are the protochordate clades?

� ____________________

� Chordates

� What does this tell you?

� All are marine

� __________________

� Pelagic, mobile

� Non-feeding

� Finds a place to settle

� __________________

� Sessile, attached to substrate

� Filter feeding

� Covered in tough tunic

Photos © C Arenz, I Frank, I Sayers, USGS

What are the

protochordate clades?

� ___________ (tunicates)

� Have all chordate characteristics at some

point in life cycle

� Larva

� Dorsal hollow nerve cord

� Notochord

� Pharynx with slits is rudimentary, not used

� Post-anal tail

� Future anus near

excurrent siphon

� Endostyle is rudimentary

Liem et al. 2001, Fig 2-7, C Arenz

What are the

protochordate clades?

� Urochordata (tunicates)

� Have all chordate characteristics at some point in life cycle

� Adult

� _____________________

� _____________________

� Other characteristics are lost due to

sessile nature

Liem et al. 2001, Fig 2-6, N Hobgood

What are the

protochordate clades?

� _________________

� Also chordates

� Ciliated neurula larva

� Filter feeding, burrowing adult

� Both stages are motile

� Lancelets/Amphioxus

� ~45 species

Liem et al. 2001, Fig 2-10; C Arenz

What are the protochordate clades?

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� __________________

� All chordate characteristics

� Feeding:

� Wheel organ and velar tentacles create current

� Endostyle secretes mucous

� Pharynx filters out food

� Water exits through atriopore

Liem et al. 2001, Fig 2-8B; C Arenz

Dorsal Hollow Nerve Cord

Notochord

Perforated Pharynx

Post-anal Tail

Endostyle

What are the protochordate clades?What are the differences between

craniates and vertebrates?

Modified: Liem et al. 2001, Fig. 2-1

Pterobranchia

Enteropneusta

Urochordata

Cephalochordata

Craniata

Chordata

Hemichordata

Protochordates

� Craniata and

Vertebrata

� Which is more inclusive?

� What are hagfishes?

� What are lampreys?

� Both are highly

specialized parasites of fishes

Modified: Liem et al. 2001, Fig. 3-1

Myxiniformes (Hagfishes)

Petromyzontiformes (Lampreys)

Chondrichthyes (Sharks and Rays)

Actinopterygii (Ray-Finned Fishes)

Dipnoi (Lungfishes)

Amphbians

Amniotes

Tetra

poda

Verte

brata

Gnathostomata

Craniata

What are the differences between

craniates and vertebrates?

� _______________

� Hagfishes

� Tear parts off dead and

dying fishes

� Use clamping mouth parts

� Use a knot behavior to

gain leverage

� Little is known about them

� Non-vertebrate craniates

� Cartilaginous brain case

� No vertebrae

� Segmental muscles, like amphioxus and vertebrates

Photo © C Ortlepp

What are the differences between

craniates and vertebrates?

� ____________________

� Lampreys

� ___________________

� Freshwater larvae

� Marine adults

� Feed on fish body fluids

� Rasping mouth parts

� Basal vertebrates

� Cartilaginous brain case

� Cartilaginous arcualia

Photos © U Thomas, EPA, Tree of Life

Notochord

Arcualia

What are the differences between

craniates and vertebrates?

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An Evolutionary Perspective

� Protochordates allow us to study the evolution of vertebrates

� Allows us to consider the evolution of many structures

1. Pharyngeal slits

2. Dorsal hollow nerve cord

3. Notochord

4. Post-anal tail

5. Endostyle

6. Segmentation

7. Brain case

8. Vertebrae (arcualia) Other Vertebrates

Lampreys

Hagfishes

Cephalochordates

Urochordates

Enteropneusts

Pterobranchs

Vertebrata

Craniata

Chordata

Hemichorata

Protochordates

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Craniates and

Vertebrates

� Vertebrates are very diverse and the focus of this course

� Some major nested groups:

� ____________

� _____________

� Sarcopterygii

� ___________

� _________

� Diapsida

� Archosauria

� Mammalia

Liem et al. 2001, Fig 3-1

Myxiniformes

Petromyzontif.

Eutheria

Testudines

Lissamphibia

Dipnoi

Actinistia

Actinopterygii

Chondrichthyes

Metatheria

Monotremata

Aves

Crocodylia

Lepidosauria

Craniates and Vertebrates

� Morphological diversity will be

one course focus

� Also appreciate the species

richness:

� ~48,000 Vertebrates

� ~25,000 are Fishes

� ~4,000 Amphibians

� ~15,000 Reptiles

� ~6,000 Crocs,

Turtles, Lepidosauria

� ~9,000 Birds

� ~4,000 Mammals

� 5 Hominids

Vertebrate Life, Fig. 1-1