LESSONS # 25

Animals Follow Plants onto the Land1- It was the phylum Arthropods that first moved to the land, about 440 Mya. (10)

Modern arthropods include insects, arachnids and crustaceans

Arthropods have a tough external skeleton, which prevent water loss and guard against sun’s rays The insect pioneers were wingless, (11). The first flying insects developed several million years after, (12) For millions of years, the insects and their fellows arthropods were the only animals on land

Dragonflies are descendants of the insects that first developed the ability to fly

Vertebrates Move onto Land At the time of Cambrian explosion almost all animals existed on the ancient ocean floor, including animals with back bone, known as vertebrates.

One later-arriving type of gnathostomes is the “lobe-finned fish”, which has four lobed fins. These fins had small bones.

The four lobed fins that these creatures possessed are the precursors to the four limbs that are found in all tetrapod vertebrates, including ourselves.

The lobe-finned fish gave rise to amphibians, and early, salamander-like amphibians gave rise to reptiles.

About 450 Mya we get the rise of the family of fishes. The gnathostomes ( the first creature to have jaws) are the ancestors of nearly all the fishes species still alive today. (13)

Vertebrates Move onto Land The lobe-finned fish had small bones in their that enabled

them to pull out of the water and support their weight on land.

From Amphibians to Reptiles Amphibians eggs require a watery environment. They have no outer shell and dry out if taken out the water, thus killing the embryo inside The eggs of the early reptiles had a hard outer shell, egg white and membranes around the growing embryo. These structures help supply nutrients and get rid of waste for the embryo With this hardy egg, the tie to the water had been broken. Reptile could move inland. (14)

One line of reptile evolved, about 220 Mya, into the dinosaurs (15). Dinosaurs dominated terrestrial ecosystems for over 160 million years, until the Cretaceous extinction (16). Another line of reptile evolved into the mammals.

These animals fed their young on milk derived special female mammary glands. In addition, they probably possessed fur coats over the skin, to feed at night when dinosaurs were less active.

They were insect-eating animals, none bigger that a rat. They lived scurrying about the underbrush when the dinosaurs reigned.

THE MAMMALS

The extinction of the dinosaurs caused by the asteroid 65 Mya, brought the mammals out of hiding. (16)

Mammals become the dominant form of large land animals, a status they retain to this day.

The first mammals appeared about 210 Mya, about 10 million years later than dinosaurs. (15)

A species of mammals gave rise to the order of mammals called primates.

-Large front-facing eyes

-Opposable first digit

-Tree dwelling existence