- 600 It is thought that the earliest multicellular life on Earth was a sponge-like creature.
Sponges are among the simplest of animals, with partially differentiated tissues but without muscles, nerves, or internal organs.
Sponges ( Porifera) are the phylogenetically oldest animal phylum extant today.
In some ways they are closer to being cell colonies than multicellular organisms.
- 580 The movement of all animals may have started with cnidarians. Almost all cnidarians possess nerves and muscles and, because they are the simplest animals to possess it, their direct ancestors were very likely the first animals to use nerves and muscles together. Cnidarians are also the first animals with an actual body of definite form and shape. They have radial symmetry.
- 550 Flatworm
Flatworms are the earliest animals to have a brain, and the simplest animals alive to have bilateral symmetry. They are also the simplest animals with organs that form from three germ layers.
| - 543 - 248 Paleozoic Era (Ancient Life)
|- 543 - Present Phanerozoic Era |- 540 Acorn worms are considered more highly specialised and advanced than other similarly shaped worm-like creatures. They have a circulatory system with a heart that also functions as a kidney. Acorn worms have the gill-like structure it uses for breathing, a structure similar to that of primitive fish. Acorn worms are thus sometimes said to be a link between vertebrates and invertebrates.
- 530 Pikaia the earliest known ancestor of the chordates. It is the first known animal with a notochord.Pikaia is believed to be the ancestor of all chordates and vertebrates.
The Lancelet, still living today, retains some characteristics of the primitive chordates. It resembles Pikaia
Other earliest known chordate-like fossils is from a conodonts a "eel-shaped animal of 4-20 cm long" with a pair of huge eyes at the head end were and a complex basket of teeth.
- 505 Agnatha, the first vertebrates appear: the ostracoderms, jawless fish related to present-day lampreys and hagfishes. Haikouichthys and Myllokunmingia are examples of these jawless fish, or Agnatha. (See also prehistoric fish). They were jawless and their internal skeletons were cartilaginous. They lacked the paired (pectoral and pelvic) fins of more advanced fish. They were the Precursors to the bony fish.
Geologic - Two major land masses form: Laurasia (North America, Greenland, Eurasia, and Scandinavia) to the north of the equator, and Gondwana (South America, Africa, peninsular India, Australia, and Antarctica) to the south. Collisions between Laurasia and Gondwana form major mountain ranges. Coal-forming sediments are laid down in vast swamps.
Global climatic changes occur, changing from warm and wet to cooler and drier. The result is a long interval of glaciation in the southern hemisphere.
Biologic - The first reptiles appeared. Great swamp forests covered the land.
Geologic - Europe and North America collide, forming the northern part of the ancestral Appalachian mountain range. Europe and North America straddle the equator. Africa and South America are positioned over the South Pole.
The climate is generally warm and moist.
Biologic - The first amphibians, insects and spiders appeared.
The diversification of fish from the Devonian Period continues in both marine and freshwater environments, though armored fish become extinct. Benthic (bottom-dwelling) marine communities include a variety of invertebrates: crinoids, blastoids, and brachiopods. The ammonites are common in open marine waters.
Insects, such as cockroaches, flourish. The first reptiles evolve.
Land environments are dominated by plants, from small, shrubby growths to tall trees. Early club mosses, horsetails, forest trees (Cordaites), and ferns are common.
This period is dominated by various forms of fish—armored fish, lungfish, and sharks.
Ammonites evolve from nautiloids and become one of the dominant invertebrate forms.
As the ozone layer forms, the first air-breathing arthropods—spiders and mites—evolve on land. Amphibians evolve and venture onto land.
Plant life, including lowland forests of giant psilophyta plants, develop and spread over the planet.
Biologic - First land plants and
- Eurypterids, first
giant sea scorpions appeared.
- Life in seas still dominated by invertebrates:
corals, arthropods, and crinoids.
- Rapid evolution occurs among suspension feeders, and pelagic (open ocean) predators, such as nautiloids, become abundant. Fish evolve jaws. Late in the Silurian Period, the first sharks appear.
The earliest land plants are represented by leafless, vascular plants called psilophytes.
Geologic - The North American, European, and Asian land masses are situated on or near the equator. Laurentia and Baltica collide. Gondwana sits in the south polar region. Shallow flooding of continental areas deposits sediments; later withdrawal of ocean water leaves oxidized "red beds" and extensive salt deposits.
- 480 Placodermi were prehistoric fish. Placoderms were the first of the jawed fishes, their jaws evolving from the first of their gill arches .Their head and thorax were covered by articulated armoured plates and the rest of the body was scaled or naked.
Geologic - The barren continents of Laurentia, Baltica, Siberia, and Gondwana are separated by large oceans. Shallow seas cover much of North America at the beginning of the period. As the seas recede, they leave a thick layer of limestone. Later in the period, the seas recover North America, depositing quartz, sandstones, and more limestone.
Biologic - The first nautiloids appeared. Corals and trilobites were common. Metazoan invertebrates are still the dominant form of life on Earth. Corals, crinoids, and clams evolve, as well as the first early vertebrates—primitive fish with bony armor plates.
Late in the Ordovician Period, mass extinctions of marine life occur, opening niches for benthic (bottom-dwelling) and planktonic (floating, swimming) organisms.
- 400 First Coelacanth appears; this order of animals had been thought to have no extant members until living specimens were discovered in 1938. It is often referred to as a living fossil.
- 375 Tiktaalik is a genus of sarcopterygian (lobe-finned) fishes from the late Devonian with many tetrapod-like features.
- 365 Some fresh water lobe-finned fish ( Sarcopterygii) develop legs and give rise to the Tetrapoda. The first tetrapods evolved in shallow and swampy freshwater habitats.
Primitive tetrapods developed from a lobe-finned fish (an "osteolepid Sarcopterygian"), with a two-lobed brain in a flattened skull, a wide mouth and a short snout, whose upward-facing eyes show that it was a bottom-dweller, and which had already developed adaptations of fins with fleshy bases and bones. The "living fossil" coelacanth is a related lobe-finned fish without these shallow-water adaptations. These fishes used their fins as paddles in shallow-water habitats choked with plants and detritus. The universal tetrapod characteristics of front limbs that bend backward at the elbow and hind limbs that bend forward at the knee can plausibly be traced to early tetrapods living in shallow water.
- Panderichthys is a 90-130 cm long fish from the Late Devonian period. It have a large tetrapod-like head. Panderichthys exhibits features transitional between lobe-finned fishes and early tetrapods. Lungfishes retain some characteristics of the early Tetrapodas. One example is the Australian Lungfish.
- 315 Acanthostega Ichthyostega is an extinct amphibian, among the first animals to have recognizable limbs. It is a candidate for being one of the first vertebrates to be capable of coming onto land. It lacked wrists, and was generally poorly adapted to come onto land. The limbs could not support the animal's weight. Acanthostega had both lungs and gills, also indicating it was a link between lobe-finned fish and terrestrial vertebrates.
Geologic - The supercontinent of Pangea begins to breakup as North America separates from Eurasia and Africa. The Atlantic Ocean begins to form. Tectonic plate subduction along western North America causes the Earth's crust to fold and mountains form in the western part of the continent.
Biologic - The first birds appeared (e.g. Archaeopteryx).
Dinosaurs included diplodocus, stegasaurus, brachiosaurus.
Reptiles adapt to life in the sea, in the air, and on land. Dinosaurs are the dominant reptile on land.
Archaeopteryx, the first bird, evolves.
Early amphibians, extinct by the late Triassic, are succeeded by the first frogs, toads, and salamanders.
Mammals are small, shrew-like animals.
Plant forms are dominated by the
cycads and cycadeoides. Conifers and gingkoes are widespread.
Ichthyostega is an early tetrapod. Being one of the first animals with legs, arms, and finger bones, Ichthyostega is seen as a hybrid between a fish and an amphibian. Ichthyostega' had legs but its limbs probably weren't used for walking, they may have spent very brief periods out of water and would have used their legs to paw their way through the mud.
Amphibia were the first four-legged animals to develop lungs.
Amphibians living today still retain many characteristics of the early tetrapods.
Carboniferous Period 354 - 290
Geologic - Sedimentary rocks (sandstone, shale, limestone, conglomerate) form in shallow seas over the continents. Rodinia begins to break up into northern and southern portions. Gondwana in the south incorporates South America, Africa, Antarctica, and Western Australia as well as peninsular India and parts of Arabia.
The global climate is generally mild.
Biologic - The first fish, corals, trilobites and shellfish appeared.
Marine metazoans with mineralized skeletons, such as sponges, bryozoans, corals, brachiopods, molluscs, arthropods, and echinoderms, flourish. One group of arthropods, the trilobites, are particularly dominant in the shallow-water marine habitats.
Plant life is limited to marine algae.