An Introduction to Animal Diversity

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Sponges

Other animals

Animals

Individual

choanoflagellate

Collar cell

(choanocyte)

Slide 9

Early members of the animal fossil record include the Ediacaran biota, which dates from 565 to 550 million years ago

(a) Mawsonites spriggi

(b) Spriggina floundersi

1.5 cm

0.4 cm

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Paleozoic Era (542–251 Million Years Ago)

The Cambrian explosion (535 to 525 million years ago) marks the earliest fossil appearance of many major groups of living animals.

There are several hypotheses regarding the cause of the Cambrian explosion

New predator-prey relationships

A rise in atmospheric oxygen

The evolution of the Hox gene complex.

Slide 11

A Cambrian seascape

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Mesozoic Era (251–65.5 Million Years Ago)

Animal diversity continued to increase through the Paleozoic, but was punctuated by mass extinctions.

Animals began to make an impact on land by 460 million years ago.

Vertebrates made the transition to land around 360 million years ago.

Coral reefs emerged, becoming important marine ecological niches for other organisms.

During the Mesozoic era, dinosaurs were the dominant terrestrial vertebrates.

The first mammals emerged.

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Cenozoic Era (65.5 Million Years Ago to the Present)

The beginning of the Cenozoic era followed mass extinctions of both terrestrial and marine animals.

These extinctions included the large, nonflying dinosaurs and the marine reptiles.

Modern mammal orders and insects diversified during the Cenozoic.

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Animals can be characterized by “body plans”

Zoologists sometimes categorize animals according to a body plan, a set of morphological and developmental traits.

A grade is a group whose members share key biological features.

A grade is not necessarily a clade, or monophyletic group.

Slide 15

Body Plan -- Symmetry

Animals can be categorized according to the symmetry of their bodies, or lack of it.

Some animals have radial symmetry.

Two-sided symmetry is called bilateral symmetry.

Animals with bilateral symmetry have:

A dorsal (top) side and a ventral (bottom) side

A right and left side

Anterior (head) and posterior (tail) ends

Cephalization, the development of a head. (Brain…)

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