Flashcards in Chordates Deck (74)
What are the 4 major characteristics of the chordates?
Dorsal hollow nerve cord
Pharyngeal gill slits
What is a chordate?
An animal with a notochord present at any stage of its life cycle
Give 6 defining characteristics of chordates which they share with other taxa.
Segmented and regionally differentiated body plan
Ventral heart with closed circulation
Ventral blood flow from heart to anterior
What is cephalisation?
Development of a brain
What are the 2 basic rules when deducing the course of chrodate evolution?
Principle of Maximum Parsimony
Distinguishing homologous from analogous characteristics
What is the Principle of Maximum Parsimony?
The simplest explanation that is consistent with the facts
What do analogous characteristics indicate?
What 7 things can we learn from when deducing the course of vertebrate evolution?
Comparative (statistical) analysis
Give an example of a living fossil
Where does the coelacanth live?
When were the coelacanths thought to have died out?
Over 65 mya
When was the coelacanth first seen alive?
What are the 3 candidate ancestors for chordates?
Who suggested annelids as an ancestor for chordates?
Semper and Dohrn, 1875
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
Why were annelids rejected as a chordate ancestor?
Solid ventral nerve cord
No gill slits
What 5 characteristics for annelids share with chordates?
Longitudinal nerve cord
What hypothesis supports echinoderms being chordate ancestors?
What is the GBR hypothesis?
Chordates arose from the motile larval stage of marine echinoderms through paedomorphosis
What is paedomorphosis?
When the larval stage becomes sexually mature and independent of changes in adult morphology
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
How is it suggested chordates evolved from hemichordates?
Progressive alteration of an active adult over millions of years
What is the most likely ancestor of the chordates?
What are the 3 chordate sub-phyla?
What are urochordata known as?
Tunicates (sea squirts)
What stage of a tunicate's life cycle bears chordate characteristics?
How many species of tunicates are there?
What kind of habitat do tunicates live in?
Are tunicates sessile or motile?
Most are sessile