Chapter 11 Part 2

Animal Diversification

BIOL 108 Intro to Bio Sci

Rob Swatski Assoc Prof Biology

HACC-York

11.13–11.15 The phylum

Chordata includes

vertebrates, animals with a

backbone.

11.13 All vertebrates are members of the phylum Chordata.

Four distinct features of chordates

The Notochord

A rod of tissue extending from the head to the tail

Stiffens the body when muscles contract during locomotion

In advanced chordates • Present only in early embryos

• Replaced by the vertebral column (backbone)

A Dorsal Hollow Nerve Cord

Extends from head to tail

In vertebrates, forms the central nervous system (spinal cord and brain)

In other animals, lies in lower portion of ventral part of body (and is solid instead of hollow)

Pharyngeal Slits

Pharyngeal region

• The area between the back of the mouth and the top of the throat

Pharyngeal slits are present in the embryos of all chordates.

Originally used for breathing and feeding

A Post-Anal Tail

Extends back beyond the end of the trunk

The phylum Chordata contains three sub-phyla:

The Vertebrates: The Most Diverse Subphylum of Chordates

Vertebrates differ from the other chordates in two important ways:

1. They have a backbone.

2. They have a head.

Take-home message 11.13

All chordates have four characteristic structures:

1. A notochord

2. A dorsal hollow nerve cord

3. Pharyngeal gills slits

4. A post-anal tail

Take-home message 11.13

The three subphyla of chordates are superficially very different, but are united by possessing these four structures at some stage of their life cycle.

11.14 The evolution of jaws and fins gave rise to the vast

diversity of vertebrate species.

The evolution of fins paralleled the evolution of jaws because the two structures work together.

Fins get you to the organism you are going to eat.

Jaws capture and kill it.

Take-home message 11.14

The development of two structures—fins and jaws—set the stage for the enormous diversity of modern vertebrates.

11.15 The movement onto land required lungs, a rigid backbone,

four legs, and eggs that resist drying.

Take-home message 11.15

In the transition of vertebrates from life in water to life on land:

• Fins were modified into limbs.

• Vertebrae were modified to transmit the body weight through the limbs to the ground.

• The site of gas exchange was transferred from gills and swim bladders to lungs.

Take-home message 11.15

The only entirely new feature to appear in the early development of terrestrial vertebrates was an egg that resisted drying out.

11.16–11.20 All terrestrial vertebrates

are tetrapods.

Amniotes and non-amniotes

11.16 Amphibians live a double life.

Take-home message 11.16

Amphibians are terrestrial vertebrates, but the adults of most species still lay eggs in water.

The eggs hatch into aquatic juveniles.

11.17 Birds are reptiles in which feathers evolved.

Feathers

Take-home message 11.17

Birds are a branch of the reptile lineage but, unlike other reptiles, possess feathers and can generate body heat.

The complex anatomical and physiological systems that we see in extant animals, such as feathers and endothermy in birds, are the products of hundreds of millions of years of step-by-step changes that began with simple structures.

Take-home message 11.17

Feathers were originally colorful structures used for behavioral displays; additional functions such as insulation and flight evolved later.

11.18 Mammals are animals that have hair and produce milk.

Are all mammals viviparous?

Viviparity—giving birth to babies rather than laying eggs

Monotremes lay eggs, but also produce milk.

Take-home message 11.18

Hair and mammary glands are defining characteristics of mammals.

Monotremes are egg-laying mammals.

Marsupial mammals give birth after a short period of development in the uterus, and the newborn completes its development in the mother’s pouch.

Take-home message 11.18

Placental mammals have a placenta that provides oxygen and nutrients to the fetus as it undergoes a longer development in the uterus.

Take-home message 11.19

Humans’ forward-looking eyes, hands and feet with ten fingers and ten toes, and shoulder and elbow joints that allow the arms to rotate are characteristics we retain from our arboreal ancestors.

Take-home message 11.19

The early ancestors of humans, however, left the trees and took up life on the ground where they walked on two legs.

Our success can be traced to an increase in brain size combined with a generalized body form and a diet that included both animals and plants.