Lecture 7: Chordates

Question 1

What are the 4 key characteristics of Chordates

Answer 1

1. notochord
2. dorsal, hollow nerve cord
3. pharyngeal slits or clefts
4. muscular, post-anal tail

Question 2

notochord

Answer 2

• longitudinal rod between digestive tube and nerve cord
• provides a form of skeletal support

Question 3

nerve cord

Answer 3

• develops from a plate of ectoderm cells that rolls into neural tube
• nerve cord is dorsal to notochord in embryonic development
• develops into central nervous system (brain and spinal cord)

Question 4

pharyngeal clefts

Answer 4

• grooves on side of pharynx in chordate embryos
• develop into slits w/function of gas exchange/suspension feeding (gills)
• in tetrapods (4 limbs) develop into parts of ear and jaw

Question 5

muscular, post-anal tail

Answer 5

• posterior to anus
• if present beyond early development contains skeletal elements and muscles; aquatic propelling force
• greatly reduced and only present during embryonic development in vertebrates

Question 6

What are the differences between cephlochordata and urochodata ?

Question 7

Which of these two phyla (cephlochordata and urochodata) were the likely ancestors of vertebrates?

Answer 7

Tunicates

Question 8

Lancelets (cephlochordata)

Answer 8

• named for shape
• feeble swimmers
• live mostly buried in sand, feed on plankton

Question 9

Which subphylum is the sister group to vertebrates

Answer 9

urochordata

Question 10

Tunicates (urochordata)

Answer 10

• more closely related to other chordates than lancets
• aka sea squirts
• larval form is most defining morphological trait showing close relationship

Question 11

In the clade vertebrata, what is the significance of the neural crest in development?

Answer 11

• neural crest consists of bilateral bands of cells near margins of embryonic folds, forming neural tube
• neural crest cells migrate to distant sites in the embryo
• migrating neural crest cells gave rise to a variety of structures, including some of the bones and cartilage of the skull

Question 12

what is a chordate?

Answer 12

members of bilateria, and within bilateria deuterostomata

Question 13

what 3 derived characteristics do vertebrates have

Answer 13

1. vertebrates have two clusters of Hox genes;
2. neural crest, collection of cells near dorsal margins of closing neural tube in an embryo
3. neural crest gave rise to a variety of structures, including some of the bones and cartilage of the skull

Question 14

Lampreys

Answer 14

• oldest living lineage of vertebrates
• jawless vertebrates
• cartilaginous segments surrounding notochord and arching partly over the nerve cord

Question 15

what development in vertebrates led to diversification

Answer 15

evolution of jaws (gnathostomes)

Question 16

Clade Gnathostomes

Answer 16

• vertebrates that have jaws
• have jaws that might have evolved from skeletal supports of the pharyngeal slits
• two clades within: chondrichthyes & osteichthyes

Question 17

placoderms

Answer 17

earliest known jawed vertebrates (440 mya)

Question 18

conodonts

Answer 18

jawless vertebrates with tooth-like elements

Question 19

haikouella

Answer 19

an early lancelet-like chordate

Question 20

steps of jaw originating

Answer 20

1. jawless state, as in lampreys
2. ancestral gnathostome state, as in extinct placoderms
3. derived gnathostome state, as in sharks

Question 21

what is the adaptive value of jaws?

Answer 21

1. more efficient respiration
2. structure that can hold teeth
3. anti-predator defense
4. allowed major diversification in diet and feeding modes (herbivory and carnivory)

Question 22

extant fishes (Chondrichthyes)

Answer 22

• sharks, skates, rays, and ratfishes
• mostly marine
• entirely cartilaginous skeleton

Question 23

Phylum Actinopterygii

Answer 23

• ray-finned fishes
• 95% of all fishes
• 50% of vertebrate diversity
• marine and freshwater

Question 24

the evolution of _____ was a huge leap that allowed breathing air

Answer 24

lungs

Question 25

phyla Actinistia + Dipnoi

Answer 25

• lobe-finned fishes
• rod-shaped bones surrounded by layer of muscle in pelvic and pectoral fins
• 2 species of coelacanths (Actinistia): marine
• 6 species of lungfishes (Dipnoi) : evolved in ocean but now all freshwater; breath using gills and at surface by gulping air into lungs

Question 26

Which two groups can be the sister group to Tetrapoda?

Answer 26

lungfishes or coelacanths

Question 27

lungfishes

Answer 27

• underwater walking on pectoral and pelvic fins
• air-breathing

Question 28

coelacanths

Answer 28

• skeletal structure of fins
• pattern of swimming: pectoral and pelvic fins alternate synchronously