Origen and Evolution of Verebrates

Chordate

member of bilateria deuterostomata, notochord, dorsol hollow nerve cord, and post anal tail

Notochord

helps with locomotion, allows for lateral bending, movement support

notochord structure

semirigid elongated structure of fluid filled cells enclosed by fibrous sheath

Dorsal hollow nerve cord

single, dorsal, parallel to digestive track and notochord. coordinates movement

Pharyngeal puches/ slits

later forms gills

Protochordates

Filter feeding apparatus

Aquatic vertebrates

Give rise to gills

Tetrapodes

Give rise to different structures like tonsils and glands.

Postanal tail

In humans, coccyx. Evolved for propulsion in water

Human vestigial traits

Post anal tail and pharyngeal slits

Subphylums of Phylum chordata

Urochordata, cephalochordata, vertebrata

Examples of Urochordata

Tunicates/sea squirts

Examples of cephalochordata

Lancelots

When do subphylum urochordatas exibit chordate characteristics?

In the larval stage

Vertebrates characteristics

Skeleton with backbone, neural crest cells, complex nervous system, Hox genes.

Neural crest cells

Cells that give rise to teeth, bones, & skull.

How did jaws originate

Evolved from anterior gill arches.

Why are fossil records incomplete

Only some environments allow for fossilization and mostly hard parts fossilize.