Mr. ChapmanBiology 20

VERTEBRATE ORIGINS

VERTEBRATES ARE DIVERSE…

PHYLUM CHORDATA

The phylum Chordata is made up of three groups. One group includes all of the vertebrates. The other two groups are invertebrates.

Vertebrates are large, active animals that have a well-developed brain encased in a hard skull.

CHORDATES

Despite their enormous differences in body plans and ways of life, all chordates share four common features at some stage in their development.

1. Notochord – flexible skeletal support rod in the animal’s back.

2. Hollow nerve cord – runs along the animal’s back

3. Pharyngeal slits – water can enter and leave through them without passing through the rest of the body

4. Tail – contains segments of muscle tissue for movement, extends beyond anal opening.

You can see that at one point, the sea squirt larva shows all four characteristics of chordates. By the time it is an adult, however, it has one.

In case you didn’t realize, this means that at some point in your life, you had a tail just like a monkey!

VERTEBRATES SHARE COMMON FEATURES

Vertebrates are able to grow large due to the presence of the endoskeleton.

An endoskeleton is an internal skeleton built of bone or cartilage. This is the skeleton that humans possess.

Bone and cartilage consist of collagen fibers embedded in a matrix of harder materials for strength.

4 FEATURES OF A VERTEBRATE’S

ENDOSKELETON1. Braincase – a braincase or a cranium

protects the brain.

2. Vertebrae – a series of short, stiff vertebrae are separated by joints. Replaces the notochord and can resist forces produced by large muscles.

3. Bones – support and protect the body’s soft tissues and provide points for muscle attachment.

4. Gill arches – found in the pharynx of fish and some amphibians, and support the gills.

EARLY VERTEBRATES

The first recognizable vertebrates were fish. The earliest fossil fish around found in 530-million-year-old rocks from China.

In fact, the majority of all vertebrates species are fish.

EVOLUTIONARY RELATIONSHIPS

Open up the

textbook to

page 760 & 761