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Flashcards in Chordates Deck (74)
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1

What are the 4 major characteristics of the chordates?

Notochord
Post-anal tail
Dorsal hollow nerve cord
Pharyngeal gill slits

2

What is a chordate?

An animal with a notochord present at any stage of its life cycle

3

Give 6 defining characteristics of chordates which they share with other taxa.

Cephalisation
Segmented and regionally differentiated body plan
Bilateral symmetry
Ventral heart with closed circulation
Ventral blood flow from heart to anterior
Active

4

What is cephalisation?

Development of a brain

5

What are the 2 basic rules when deducing the course of chrodate evolution?

Principle of Maximum Parsimony
Distinguishing homologous from analogous characteristics

6

What is the Principle of Maximum Parsimony?

The simplest explanation that is consistent with the facts

7

What do analogous characteristics indicate?

Convergent evolution

8

What 7 things can we learn from when deducing the course of vertebrate evolution?

Geology
Palaeontology
Fossils
'Living fossils'
Extant organisms
Anatomy
Comparative (statistical) analysis

9

Give an example of a living fossil

Coelacanth

10

Where does the coelacanth live?

Indian ocean

11

When were the coelacanths thought to have died out?

Over 65 mya

12

When was the coelacanth first seen alive?

1938

13

What are the 3 candidate ancestors for chordates?

Annelids
Echinoderms
Hemichordates

14

Who suggested annelids as an ancestor for chordates?

Semper and Dohrn, 1875

15

How would the proposed annelid flip-over make annelids a more likely ancestor of chordates?

Blood would flow forward ventrally
Relocation of mouth and anus

16

Why were annelids rejected as a chordate ancestor?

Flip-over unlikely
Solid ventral nerve cord
Complete segmentation
No notochord
No gill slits

17

What 5 characteristics for annelids share with chordates?

Bilateral symmetry
Segmented
Active
Cephalisation
Longitudinal nerve cord

18

What hypothesis supports echinoderms being chordate ancestors?

GBR hypothesis

19

What is the GBR hypothesis?

Chordates arose from the motile larval stage of marine echinoderms through paedomorphosis

20

What is paedomorphosis?

When the larval stage becomes sexually mature and independent of changes in adult morphology

21

What are the 3 problems with the GBR hypothesis?

Paedomorphosis is doubted
Gutmann's (1981) 'Chordates into Echinoderms' theory
Recent molecular evidence shows only a subset of genes persist from tunicate larvae to adult

22

How is it suggested chordates evolved from hemichordates?

Progressive alteration of an active adult over millions of years

23

What is the most likely ancestor of the chordates?

Hemichordates

24

What are the 3 chordate sub-phyla?

Urochordata
Cephalochordata
Vertebrata

25

What are urochordata known as?

Tunicates (sea squirts)

26

What stage of a tunicate's life cycle bears chordate characteristics?

Larval stage

27

How many species of tunicates are there?

2000

28

What kind of habitat do tunicates live in?

Marine

29

Are tunicates sessile or motile?

Most are sessile

30

Are tunicates solitary or colonial?

Most are colonial