Chordate Evolution Lecture 13

Question 1

Biggest question in Chordate phylogeny?

Answer 1

Origin of the fish-like tadpole of the tunicates and the non-chordate ancestor that it arose from

Question 2

Possibilities of chordate ancestor (3)

Answer 2

1. fish-like, similar to amphioxus
2. resembled larval stages of tunicates
3. Resembled adult appendicularian (tadpole-like)
   (outside of the chordates, only Hemichordates possess gill slits and rudimentary chordate characters)

Question 3

Dorsoventral axis inversion hypothesis

Answer 3

Non-chordate characters of Enteropneust worms will align with characters of chordates, when the ventral side of Enteropneusts is compared to the dorsal side of chordates

Question 4

Ancestor 1.

Answer 4

Larvae form of tunicates, has all possible chordate characters (but losses most as adult)

Question 5

Paedomorphosis

Answer 5

Process where juvenile characters of ancestors are retained in descendant adult forms

Question 6

forms of Paedomorphosis (2)

Answer 6

Neoteny- development of body is slowed, while sexual maturity is on time
Progenesis- gonads develop early

Question 7

Possible early chordate

Answer 7

Haikouella

Question 8

Oldest known ancestor of modern chordates

Answer 8

Pikaia (resembles living chordate amphioxus)

-primitive proto-notochord

Question 9

Larval transfer hypothesis

Answer 9

Larvae originated as adults in separate taxa and their genomes hybridized
Hybrid, started as larval form similar to one parent, and metamorphosed into adult of other parent
Claim (Ascidians and salps are the hybrids of appendicularia and Tunicata)

Question 10

Basal within the Hemichordates

Answer 10

through molecular analysis:

Burrowing Enteropneusts basal to sessile Pterobranchs

Question 11

Basal within Urochordata

Answer 11

Appendicularians, capacity for swimming are basal to the sessile ascidians

Question 12

Peramorphosis or paedomorphosis?

Answer 12

Peramorphosis more liekly for tunicates

(appendicularian adult)-> Ascidian larvae

Question 13

Adult early chordates

Answer 13

free-living cilliary mucous suspension feeders

axial swimming and a dorsal fin

Question 14

Chordates: ascidian like ancestor or amphioxus-like animal?

Answer 14

Chordate ancestors were most likely filter feeding torpedoes that resembled Amphioxus
(our primitive niche): motile grazers on suspended particles