Figure 01a Ediacara Fauna [view large image]

• FA of exoskeletal material - It really is a crust secreted by the skin (a laminated crust that in most living arthropods is made up of three layers).
• FA of many invertebrate phyla - Life took off in the Cambrian period (the Cambrian Explosion). By its end, all the main lines of animal types, whose descendants fill the world today, had been established. All of this diversity flourished in the sea; there was still no life on land.
• FA of vertebrates¹ (jawless fish, ostracoderm) - Fish without jaws were the first vertebrates. Just like the molluscs and arthropods, the early fish had a hard outer covering. This armor plating around their front ends was made of bone. They had probably ate by sucking in mud through their mouths. They filtered out particles of food as the water left through their gills. Some jawless fish still survive today. They are the lampreys and hagfish.

Figure 01b Cambrian Period [view large image]

Figure 01c Chengjiang Fossils [view large image]

Figure 01d Evolution of Complexity
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• Shallow seas covered large area of the world, lichen-like plants had begun to adapt themselves to life on land.
• Post-Cambrian trilobites had diversified into many forms including the Cryptolithus shown in bottom of Figure 02.
• Echinoderms were characteristic inhabitants in this period. To the left is a primitive species that carried its bulging body on a short stalk. Another species (right) was also rounded or pear-shaped, but anchored itself by the tapering end of its body. The sea lilies (the red ones on extreme left) belong to the same group.
• Brachiopods (white shells, right) furnish the most abundant invertebrate remains in Ordovician sediments.
• Cephalopods (nautilus) were the early version of the present-day cuttlefish. They are active hunters with arms

Figure 02 Ordovician Period [view large image]

• Cephalopods diversified to a variety of shapes and sizes (see Figure 03). Eventually, a lineage progressed to ammonites in the late Silurian period.
• Also in the picture is a group of sea lilies (right); in front of them lie rounded clumps of flat corals and a few skeletons of horn-shaped (wrinkled) rugosa corals.
• FA of jawed fish - Placoderms (=plate skin) are armored by their extensive dermal skeleton. These dermal bones (or plates) form head and thoracic shields that are either articulated by distinctive joints or fused into a single unit. Pectoral fins are typically well developed. Bony shearing or crushing structures on the jaws substitute for true teeth, which are absent. The jaw joint is simple.

Figure 03 Silurian Period [view large image]

• FA of insects - The primitive (wingless) types still survive in springtails. Insects are the largest and most successful class of arthropods; in fact, they are the most successful group in the entire animal kingdom. The insect body is sharply divided into head, thorax, and abdomen. Six legs are attached to the thorax. Young, or larvae, may be aquatic and breathe with gills, but adults take air into tubes. Most adult insects also have hard, chitinous exoskeletons.
• FA of bony fishes - There are two groups, those with ray-like fins, ancestors of most fishes today (more than 90% of species) from carp to salmon, and sea-horse to tuna, and the lobefins. The ray-fins of the Devonian include

Figure 04 Devonian Period [view large image]

Figure 04a Fossil [view large image]

Figure 04b First Land Animal [view large image]

• The land surface was at this point widely covered by genuine forests, whose fallen logs and other plant material eventually formed many of the coal and oil deposits.
• A small group of creatures, cotylosaurs, gradually found new ways to sever their ties to rivers and ponds. From the cotylosaurs, an evolutionary intermediate between amphibians and reptiles, emerged the first true reptiles. These creatures were distinguished by their small size, agile limbs and the amniote egg. With its large shell and protective membranes, the amniote egg gave reptile the

Figure 05 Carboniferous Period [view large image]

• As the environment became drier and hotter, reptiles thrived at the expense of amphibians. Figure 06 shows many types of the reptiles living way up in the mountain. They are representatives of the groups of pelycosauria, "mammalian" reptiles from which the evolutionary line to the first mammals can be traced. They shared with mammals a particular type of skull. A single large opening in the wall of the skull behind the eye socket allowed highly efficient jaw-closing muscles to develop, greatly increasing the power of the jaws. The huge dorsal fan may have acted as temperature regulator. The amphibians with the tapering head were evidently the prey of the reptiles.
• Mass extinction of marine life near the end of the Permian period - Groups made extinct include trilobites, sea lilies, and rugose corals. Other marine invertebrates severely affected. Fish are generally unaffected. According to recent investigation, the disaster that killed off almost 90% of all life on Earth about 251 MYA, was likely caused by a huge asteroid or comet crashing into the planet.

Figure 06 Permian Period [view large image]

• The continents reached their maximum phase of fusion (the Pangaea) with much of the land lay in the equatorial belt. The climates were hot and monsoonal. Following the massive extinction at the end of the Permian, the survivors underwent adaptive radiations as they diversified and began to reoccupy many of the now-vacated environmental roles.
• FA of dinosaurs - Out of the thecodonts in the Triassic came a most fantastic array of reptiles, the dinosaurs (terrible lizard). They were the stock from which the crocodiles and birds, as well as the dinosaurs and winged reptiles, developed. They evolved into two main groups in this period. Those shown on the right of Figure 07 are the meat-eating

Figure 07 Triassic Period

• Dinosaurs became dominant, reaching their largest size. The brontosaurus (thunder lizard) was a huge sauropod with length up to 80 feet and a total weight of 30 to 35 tons (see the gigantic beast in Figure 08). The large size probably helped them to escape predation by carnivorous dinosaurs. In the same picture, the stegosaur protected itself by the elaborate armour. Its small brain was compensated by large ganglia (a mass of never cells) between the shoulders and another one above the hips; those are sometimes referred to as the second brain.
• The dinosaurs also diversified into water and air - Kuehneosaurus were the gliding reptile, pterosaurs

Figure 08 Jurassic Period

• FA flowering plants (angiosperms) - The modern types of flowering plant became common some time in the middle of the Cretaceous. Hardwood trees slowly replaced the conifers as the dominant trees of the forests (see Figure 09). These new plants provided fruits, flowers and nectar as new sources of food, causing great changes in all life on land.
• Dinosaurs continued to dominate the land. But the fauna was very different from that of the late Jurassic. Large sauropods were rare, and the medium-sized coelurosaurs had been replaced by the ostrich-like ornithomimids, which included the duck-billed hadrosaurs and the armoured ankylosaurs and ceratopsians. The 30 feet long sea monsters called mosasaurs were the descendants of nothosaurs.
• Carnivorous mammals such as Repenomamus were beginning to come out of the shadows. A complete fossil of this animal was found at the base of the Yixian Formation in northeastern China. On its left side, under the ribs where a mammal's stomach might well have been, lies a fragmentary and disarticulated skeleton of a young dinosaur about 14 cm long. The devourer of this little dinosaur was more than a meter long, and is estimated to have weighed 4 - 6 kg.

Figure 09 Cretaceous Period [view large image]

• After the K-T impact, the previously obscure mammals proliferated to fill the environmental niche left by the dinosaurs. The landscape and its plants would be familiar to a visitor from the present day, although some of the creatures might look somewhat strange. A typical scenery is shown in Figure 10. The big animals are the brontotherium that stood eight feet tall at the shoulder, belonged to a group of odd-toed ungulate (hoofed). The threatening carnivores are sabre-toothed tigers. While a leopard attacked an early horse.

Figure 10 Tertiary Period
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• When mammals first appeared, in the late Triassic, the continents of the world were united into one large landmass, Pangaea. The climate was generally warmer and drier than at present. The small, primitive mammals of that time were able to move much more freely from one region to another. This is the Mor- ganucodon, which is thought of as ancestral to the

Figure 11 Mammal Evolution
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Figure 12 Diversification
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• The oldest hominid (upright-walking primate) remains was discovered recently (July 2002) in northern Chad, Africa with a complete cranium and dated back to nearly seven million years ago (see Figure 13). It may thus represent the earliest human forebear on record and is dubbed Sahelanthropus tchadensis. It is generally believed that human has its root in Africa. Figure 14 depicts groups of different species foraging in the same area around Lake Turkana, Northern Kenya 1.8 million years ago.

Figure 13 Oldest Hominid
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Figure 14 Hominids in Africa [view large image]

Figure 15 Family Tree
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Figure 16 Human Evolution
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• During this period four Ice Ages, separated by warmer interglacial periods, covered the northern land areas. As the ice slowly advanced and retreated, so the climate zones and their mammal faunas moved across the continents via the Bering region and Panama Isthmus. An unexplained feature of this period was the appearance of giant representatives of nearly every order of mammals, from platypus, kangaroo and lemur, to deer, beaver, edentate and unusually large elephant (the mammoth as shown in Figure 17).

Figure 17 Quaternary Period [view large image]