Shark: Paleozoic era, specifically the Devonian period. Lizard: Mesozoic era, specifically the Triassic period. Mammal: Cenozoic era, specifically the Cretaceous period.

1. Based on the information presented in lecture and your text, in which eon and era of earth's
history would the following have first appeared? shark lizard mammal Animals are multicelluar
eukaryotes. Al eukaryotes posses mitochondria which they use for aerobic respiration but
animals are further distinguished as having some form of internal digestive cavity as well as
embryos. Cnidarians, which include such organisms as medusas and anemones, represent some
of the most ancient. animals. The have simple body plans characterized by radial symmetry and
only two distinct types of tissue ectoderm and endoderm (- diploblastic body plan). More
complex animals demonstrate bilateral symmetry and three distinct types of tissues - eco, endo,
and mesoderm (= triploblastic body plan). Flatworms such as the planarian Dugesia represent
some of the simplest of these triploblastic bilaterally symmetrical'organisms. More complex
bilaterally symmetrical triploblastic organisms, such as squid. have internal fluid filled cavities
lined with mesoderm ( c coloems) which are lacking in flatworms. Vertebrates are bilaterally
symmetrical, triploblastic and coclomate animals which have a backbone. The simplest examples
of vertebrates are fish such as the great white shark. Amphibians (such as salamanders) are
vertebrates that have walking legs (= tetrapod) and breath air with lungs. While they can live out
of water, they must lay there eggs in water. More recent vertebrates such as reptiles and
mammals, have an amniotic egg which has a fluid filled sac protected by a shell and this had
freed them of the need to lay their eggs in water. Reptiles (which include both lizards and birds)
possess keratinous scales and birds in addition have feathers which they use for both insulation
and flight. Mammals such as the shrew, have fur instead of keratinous scales and in addition they
have mammary glands which they use to nurse their young after birth. The figures below
summarize these characteristics that are found in examples of all these group5.