Amphibians and Reptiles (Important Facts) {Part-13}

THE EARLIEST KNOWS AMPHIBIANS, such as Acanthostega and Ichthyostega, lived about 363 million years ago at the end of the Devonian period (409-363 million years ago).

Fossil Skull of Acanthostega

Model of Ichthyostega

Their limbs may have evolved from the muscular fins of lungfish-like creatures. These fish can use their fins to push themselves along the bottom of lakes and some can breathe at the water's surface. While amphibiains exist on land, they are dependent on a wet environment because their skin does not retain moisture and most and most species must retain to the water to lay their eggs.

Skeleton of Eryops

 Evolving from amphibians, reptiles first appeared during the Carboniferous period (363-290 million years ago):  Westlothiana  a possible early reptile, lived on land 338 million years ago. The development of the amniotic egg, with an embryo enclosed in its own wet environment (the amnion) and protected by a waterproof shell, freed reptiles from the amphibian's dependence on a wet habitat. A scary skin protected the reptile from desiccation on land and enabled it to exploit ways of life closed to its amphibian ancestors. Reptiles include the dinosaurs, which came to dominate life on land during the Mesozoic era (245-65 million years ago).

Early signs of Life (Important Facts) {Part-12}

FOR ALMOST A THOUSAND MILLION YEARS after its formation, there was no known life on Earth. The first simple, sea-dwelling organic structures appeared about 3,500 million years ago; they may have formed when certain chemical molecules joined together.

Stromatolitic Limestone

Prokaryotes, single-celled micro-organisms such as blue-green algae, were able to photosynthesize , and thus produce oxygen had built up in the earth's atmosphere to allow multicellular organisms to proliferate in the Precambrian seas (before 570 million years ago).

Fossilized Jawless Fish

Soft-bodied jellyfish, corals and seaworms flourished about 700 million years ago. Trilobites, the first animals with hard body frames, developed during the Cambrian period (570-519 million years ago).

Fossilized Trilobite

However, it was not until the beginning of the Devonian period (409-363 million years ago) that early land plants, such as Asteroxylon, formed a water-retaining cuticle, which ended their dependence on an amphibians crawled onto the land, although they probably still returned to the water to lay their soft eggs.
By the time the first reptiles and synapsids appeared late in the Carboniferous, animals with backbones ad become fully independent of water.

Quaternary Period (Important Facts) {Part-11}

THE QUATERNARY PERIOD (1.6 million years ago- present) forms the second part of the Cenozoic era ( 65 million years ago- present), it has been characterized by alternating cold (glacial) and warm (interglacial) periods. During cold periods, ice sheets and glaciers have formed repeatedly on northern and southern continents.

Quaternary Period

The cold environments in North America and Eurasia, and to a lesser extent in southern South America and parts of Australia, have caused the migration of many life forms towards the Equator.

Examples of Tertiary Plant Groups:-

     Birch (Betula lenta)

Sweetgum (Liquidambar styraciflua)

Only the specialized ice age mammals such as Mammuthus & Caelodonia, with their thick wools and fat insulation, were suited to life in very cold climates.

Examples of Tertiary Animal groups:-

Procoptodon

Diprotodon

Deinotherium

Australopithecus

Humans developed throughout and Pleistocene period (1.6 million- 10,000 years ago) in Africa and migrated northward into Europe and Asia, Modern humans, Homo sapiens, lived on the cold European continent 30,000 years ago and hunted other mammals. 

The end of the last ice age and the climatic changes that occurred about 10,000 years ago brought extinction to many Pleistocene mammals, but enabled humans to flourish.