The Big Bang (the begining of every thing)

 

Animal appearance

• The Trezona Formation of South Australia's 665 million-year-old rocks contain the earliest fossils that may be related to mammals. These fossils are thought to have once been early sponges.

• The Ediacaran biota, which dates back to the end of the Precambrian period, some 610 million years ago, contains the oldest species. Although it had previously been questioned whether these included animals, the finding of the animal fat cholesterol in Dickinsonian fossils has proven that they did.
• In layers like the Burgess shale, several animal phyla made their first appearance in the fossil record during the Cambrian boom, which began approximately 542 million years ago.
• Molluscs, brachiopods, onychophorans, tardigrades, arthropods, echinoderms, and hemichordates are among the extant phyla found in these rocks, in addition to numerous now-extinct species like the carnivorous Anomalocaris. The fossil record's artefacts rather than the appearance of all these species at once may be to blame for the event's apparent suddenness. 

Animal classification

Vertebrates	Warm blood	Mammals	A group of vertebrate animals in which females give birth, and suckle their babies milk from a special mammary gland (breast).
		Birds	Any warm-blooded vertebrate of the class Aves that has a feathered body, forelimbs transformed into wings, scaly legs, a beak, and no teeth is referred to as a bird. Birds also give birth to their young in hard-shelled eggs.
	Cold blood	Fish	The term "fish" refers to a variety of cold-blooded, aquatic vertebrates with gills, fins, and often an elongated body coated in scales.
		Reptiles	a reptile is a group of scaly animals that typically reproduces by egg-laying. Reptiles include lizards, snakes, turtles, and alligators. Animals with cold blood include reptiles.
		Amphibians	Vertebrate creatures called amphibians, like frogs, spend some of their lives in the water and some on land.
Invertebrates	Insects		Any animal of the Insecta class, which includes small, air-breathing arthropods with a body separated into three segments (head, thorax, and abdomen), three pairs of legs, and typically two pairs of wings, is considered an insect.
	Arachnids		Arachnids are any wingless, carnivorous arthropods of the class Arachnida, such as spiders, scorpions, mites, ticks, and daddy-long-legs, that have eight appendages instead of antennae and a body separated into two halves, the cephalothorax and the abdomen.
	Mollusca		Any soft-bodied invertebrate belonging to the phylum Mollusca is classified as a Mollusca. These creatures are typically entirely or partially encased in a calcium carbonate shell that is secreted by a soft mantle that covers their bodies.
	Annelids		Any segmented worm belonging to the phylum Annelida is referred to as an annelid, and this includes earthworms, leeches, and several marine species.
	Crustaceans		Any mostly aquatic arthropod of the class Crustacea is considered a crustacean, as are lobsters, shrimp, crabs, barnacles, and wood lice. Crustaceans often have a hard shell or crust covering their bodies.
	Echinoderms		Echinoderms include starfish, sea urchins, sea cucumbers, and other marine animals of the invertebrate phylum Echinodermata that have a radial arrangement of components and a body wall strengthened by calcareous fragments that may protrude as spines.

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