The movement of all animals may have started with நிடேரியா. Almost all cnidarians possess நரம்பு and தசைs and, because they are the simplest விலங்குs to possess it, their direct மூதாதைs 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 Ma
தட்டைப்புழு மூளையுடன் தோன்றிய முதல் ஊயிரினம் தட்டைப்புழுவாகும். The simplest animals alive to have bilateral symmetry. They are also the simplest animals with organs that form from three germ layers.
The Lancelet, still living today, retains some characteristics of the primitive முதுகுநாணிs. It resembles Pikaia
Other earliest known chordate-like fossils is from a conodonts a "eel-shaped animal of 4-20 cm (1½-8 in) long" with a pair of huge eyes at the head end were and a complex basket of teeth.
The Placodermi were prehistoric fishes. Placoderms were the first of the jawed fishes, their jaws evolving from the first of their gill arches [5]. Their head and thorax were covered by articulated armoured plates and the rest of the body was scaled or naked.
400 Ma
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 வாழும் தொல்லுயிர் எச்சம்.
375 Ma
Tiktaalik is a genus of sarcopterygian (lobe-finned) fishes from the late Devonian with many tetrapod-like features.
Primitive tetrapods developed from a lobe-finned fish (an "osteolepid Sarcopterygian"), with a two-lobed மனித மூளை 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 எலும்புs. 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.[6]
Acanthostega is an extinct நீர்நில வாழ்வன, among the first animals to have recognizable limbs. It is a candidate for being one of the first முள்ளந்தண்டுளிs to be capable of coming onto land. It lacked wrists, and was generally poorly adapted for life on land. The limbs could not support the animal's weight. Acanthostega had both நுரையீரல் and செவுள், also indicating it was a link between lobe-finned fish and terrestrial vertebrates.
From amphibians came the first reptiles: Hylonomus is the earliest known ஊர்வன. It was 20 cm (8 in) long (including the tail) and probably would have looked rather similar to modern பல்லியோந்திகள்s. It had small sharp teeth and probably ate millipedes and early பூச்சிs. It is a precursor of later amniotes and mammal-like reptiles.
Evolution of the amniotic egg gives rise to the Amniota, ஊர்வனs that can reproduce on land and lay eggs on dry land. They did not need to return to water for reproduction. This adaptation gave them the capability to colonize the uplands for the first time.
Reptiles have advanced nervous system, compared to நீர்நில வாழ்வன. They have twelve pairs of cranial nerves.
Shortly after the appearance of the first ஊர்வனs, two branches split off. One branch is the Diapsida from which come the modern ஊர்வனs. The other branch is Synapsida which had தலையோடு, a pair of holes in their skulls behind the eyes, which were used to increase the space for jaw muscles.
The earliest mammal-like reptiles are the pelycosaurs. The pelycosaurs were the first animals to have temporal fenestra. Pelycosaurs are not Therapsida but soon they gave rise to them. The Therapsida are the direct ancestor of பாலூட்டி.
The therapsids have temporal fenestrae larger and more mammal-like than pelycosaurs, their teeth show more serial differentiation; and later forms had evolved a secondary palate. A secondary palate enables the animal to eat and breathe at the same time and is a sign of a more active, perhaps warm-blooded, way of life.[8]
220 Ma
One sub-group of therapsids, the cynodonts evolved more mammal-like characteristics.
The jaws of cynodonts resemble modern mammal jaws. It is very likely this group of animals contains a species which is the direct ancestor of all modern mammals.[9]
From eucynodonts (cynodonts) came the first பாலூட்டிs. Most early mammals were small and shrew-like animals that fed on insects. Although there is no evidence in the fossil record, it is likely that these animals had a constant body temperature, milk glands for their young. The neocortex region of the மனித மூளை first evolved in mammals and thus is unique to them.
Eomaia scansoria, a eutherian mammal, leads to the formation of modern placental mammals. It looks like modern dormouse, climbing small shrubs in Liaoning, சீன மக்கள் குடியரசு.
A group of small, nocturnal and arboreal, insect-eating mammals called the Euarchonta begins a speciation that will lead to the முதனி, treeshrew and flying lemurorders. The Primatomorpha is a subdivision of Euarchonta that includes the primates and the proto-primate Plesiadapiformes. One of the early proto-primates is Plesiadapis. Plesiadapis still had claws and the eyes located on each side of the head, because of that they were faster on the ground than on the top of the trees, but they begin to spend long times on lower branches of trees, feeding on பழம்s and leaves. The Plesiadapiformes very likely contain the species which is the ancestor of all primates.[10]
முதனிs diverge into suborders Strepsirrhini (wet-nosed primates) and Haplorrhini (dry nosed primates). Strepsirrhini contains most of the prosimians; modern examples include the லெமூர்s and lorises. The haplorrhines include the three living groups the prosimian tarsiers, the simian குரங்குs, and மனிதக் குரங்குs. One of the earliest haplorrhines is Teilhardina asiatica, a mouse-sized, diurnal creature with small eyes.
Haplorrhini splits into infraorders Platyrrhini and Catarrhini. Platyrrhines, New World monkeys, have prehensile tails and males are color blind. They may have migrated to South America on a raft of vegetation across the Atlantic ocean (circa 4,500 km, 2,800 mi). Catarrhines mostly stayed in ஆப்பிரிக்கா as the two continents drifted apart. One ancestor of catarrhines might be Aegyptopithecus.
Proconsul was an early பேரினம் (உயிரியல்) of catarrhine primates. They had a mixture of Old World monkey and மனிதக் குரங்கு characteristics. Proconsul's குரங்கு-like features include thin பல் enamel, a light build with a narrow chest and short forelimbs, and an arboreal quadrupedal lifestyle. Its ape-like features are its lack of a tail, ape-like elbows, and a slightly larger brain relative to body size.
Proconsul africanus is a possible ancestor of both great and lesser apes, and humans.
15 Ma
Hominidae (great apes) speciate from the ancestors of the கிப்பன் (lesser apes).
Pierolapithecus had special adaptations for tree climbing, just as humans and other great apes do: a wide, flat ribcage, a stiff lower spine, flexible wrists, and shoulder blades that lie along its back.
Hominina speciate from the ancestors of the chimpanzees. The latest common ancestor is Sahelanthropus tchadensis (ca. 7 Ma). The earliest known human ancestor post-dating the separation of the human and the chimpanzee lines is Orrorin tugenensis (Millennium Man, Kenya; ca. 6 Ma).
Both chimpanzees and humans have a குரல்வளை that repositions during the first two years of life to a spot between the pharynx and the lungs, indicating that the common ancestors have this feature, a precursor of speech.
Homo erectus evolves in ஆப்பிரிக்கா.
Homo erectus would bear a striking resemblance to modern humans, but had a brain about 74 percent of the size of modern man. Its forehead is less sloping and the teeth are smaller. It is believed to be an ancestor of modern humans (with Homo heidelbergensis usually treated as an intermediary step).
Three 1.5 m (5 ft) tall Homo heidelbergensis left footprints in powdery volcanic ash solidified in Italy. Homo heidelbergensis is the common ancestor of both நியண்டர்தால் மனிதன் and Homo sapiens. It is morphologically very similar to Homo erectus but Homo heidelbergensis had a larger brain-case, about 93% the size of that of Homo sapiens. The species was tall, 1.8 m (6 ft) on average, and more muscular than modern humans. Beginning of the Middle Paleolithic.
இழைமணியப் பழையோள் கிழக்காப்பிரிக்காவில் வாழும் காலம். இழைமணியப் பழையோள் என்பது வாழும் மாந்தரின் தாய்வழி மூதாதையர்கள் அனைவருக்கும் பொதுவாக இருந்ததாகக் கருத இடம் தரும் ஒரு பெண் தொன்முது தாயைக் (மூதாயைக்) குறிக்கும் சொற்றொடர். இப்பெண்ணின் இழைமணி மரபுப்பொருளின் (மைட்டோக்கோன்றிய டி.என்.ஏ யின்) ஒரு படியுருதான் வழிவழியாக ஒவ்வொறு தாயிடமிருந்தும் குழந்தைகளுக்குச் சென்று இன்று வாழும் மனிதர்களின் கண்ணறைகளின் உள்ளுறுப்புகளானன இழைமணிகளுக்குள் இருக்கின்றன.
↑"'Experiments with sex have been very hard to conduct,' Goddard said. 'In an experiment, one needs to hold all else constant, apart from the aspect of interest. This means that no higher organisms can be used, since they have to have sex to reproduce and therefore provide no asexual control.' Goddard and colleagues instead turned to a single-celled organism, yeast, to test the idea that sex allows populations to adapt to new conditions more rapidly than asexual populations." Sex Speeds Up Evolution, Study Finds (URL accessed on ஜனவரி 9, 2005)
↑"Proterospongia is a rare freshwater protist, a colonial member of the Choanoflagellata." "Proterospongia itself is not the ancestor of sponges. However, it serves as a useful model for what the ancestor of sponges and other metazoans may have been like." http://www.ucmp.berkeley.edu/protista/proterospongia.html Berkeley University
↑"Bones of first gill arch became upper and lower jaws." (Image) (URL accessed on நவம்பர் 16, 2006)
↑"Lungfish are believed to be the closest living relatives of the tetrapods, and share a number of important characteristics with them. Among these characters are tooth enamel, separation of pulmonary blood flow from body blood flow, arrangement of the skull bones, and the presence of four similarly sized limbs with the same position and structure as the four tetrapod legs." http://www.ucmp.berkeley.edu/vertebrates/sarco/dipnoi.html Berkeley University
↑"Tlvinaxodon, like any fossil, should be thought of as a cousin of our ancestor, not the ancestor itself. It was a member of a group of mammal-like reptiles called the cynodonts. The cynodonts were so mammal-like, it is tempting to call them mammals. But who cares what we call them? They are almost perfect intermediates." ரிச்சர்ட் டாக்கின்சு 2004 The Ancestor's Tale page 211, பன்னாட்டுத் தரப்புத்தக எண்0-618-00583-8
↑"Fossils that might help us reconstruct what Concestor 8 was like include the large group called plesiadapi-forms. They lived about the right time, and they have many of the qualities you would expect of the grand ancestor of all the primates" ரிச்சர்ட் டாக்கின்சு 2004 The Ancestor's Tale page 136, பன்னாட்டுத் தரப்புத்தக எண்0-618-00583-8
↑Raauma, Ryan, Sternera, K., (2005) "Catarrhine primate divergence dates estimated from complete mitochondrial genomes", Journal of Human Evolution 48: 237-257 [1]
↑"Rubin also said analysis so far suggests human and Neanderthal DNA are some 99.5 percent to nearly 99.9 percent identical." Neanderthal bone gives DNA clues (URL accessed on நவம்பர் 16, 2006)
↑"The conclusion is the old saw that we share 98.5% of our DNA sequence with chimpanzee is probably in error. For this sample, a better estimate would be that 95% of the base pairs are exactly shared between chimpanzee and human DNA." Britten, R.J. (2002). "Divergence between samples of chimpanzee and human DNA sequences is 5%, counting indels". PNAS99: 13633. doi:10.1073/pnas.172510699. பப்மெட்:12368483.
