The Fossil Record: Evidence for Evolution

Evidences of evolution - Fossil Record! → The fossil may be an entire organism, buried in sediments or snow, which changed into a mould or cast of the entire organism or its part, or its replica, boot prints or even its imprint. → According to Sir Charles Lyell, "fossil" is defined as "Any body or trace of body of animal or plant buried & preserved by natural means". Types of fossil:- → There are different types of fossil. (1) Body fossil:- → These occur in all shapes & sizes & ranges from microscopic sea dwellers to large terrestrial dinosaurs. This fossil contains remains of hard parts of an organism such as shell, bone etc. (1) Macrofossils: The fossils which are more than one cm in size are called macro fossils. → It includes more advanced plants & animals, such as skeletons or corals etc. (2) Microfossils: These are fossils of organisms which are less than 0.5 mm in size. → Sometimes, their skeletal remains are found upto 10 cm in length. (3) Subfossils: These fossils are less than 10,000 years old & were formed after the last ice age, during Holocene Epoch. → These include fossils of bison in frozen ice & mammoth. (4) Trace fossils: These are imprints & mould of organisms which are formed due to day to day activities of organisms, such as walking, boring, burrowing, feeding or breeding etc. → Ex. Foot prints of dinosaurs, burrows of clams, trails of worms etc. (5) Bioclasts: These fossils are fragments of fossils, which found in sediment or usually seen under microscopes. (7) Coprolites: These are fossils of fecal matters of various sizes of animals. → It provides valuable information regarding food habits of fossil bears. (8) Burrow & Borings:- These are fossils of animal which live in burrows, holes, wood or rocks for shelter & food. → The borings in wood are also considered as fossils. (9) Gastroliths: These are fossils of the contents of the organisms which are found in stomach. (10) Pseudofossils: Fossils of inorganic origin, resembling organisms, sedimentary rocks are referred to as pseudofossils. (11) Unusual fossils: The fossils of most of the organisms formed by the combination of various conditions. Examples: The famous deposits of Solenhofen limestone of Southern Germany & Burgess Shale of Canada contains unusual fossils of: (i) Mammoths found from Siberian waste. (ii) Archaeopteryx, the 1st bird. Transitional fossils → A transitional fossil is any to silized version of a life form that exhibits traits common to both, an ancestral group & its derive descendant group. → These transitions are supported by both fossil & DNA evidences. Example: 1) The fish-tetrapod transition → The earliest fossil fish dates back to Cambrian period, 600 million years ago (MYA). → About 360 million years ago in Devonian period, the first tetrapods evolve. All the group of tetrapods share a common ancestry with bony fish. → Modern bony fish is divided into 2 groups- lobe fin fish & ray fin fish. → Lobe fin fishes have paired fins which contain strong bones (having tetrapod's) suggesting that tetrapods are closely related to the fish during. → Eusthenopteron is a fossil dating back to around 385 million years ago. It looks very much like a fish with tetrapods including nostrils, bones with details like ulna & radius & hind fins with a series of bones. These are all rare bone structures, as in our own limbs. → Tiktaalik had a primitive wrist joint & strong ribs to help support its body weight. → Ichthyostega is a transitional fossil about 5 feet long with a big & strong vertebrae. It could breathe out of water. (2) Dinosaur-bird transition: → The 1st clue for dinosaur-bird transition came from the study of birds bones. → The birds bones were most similar to those of reptiles, so biologists suspected birds were closely related to them. → The well-known fossil Archaeopteryx shows several features of birds such as feathers & reverse perching toe on the hind foot. → But, it also shows characteristics of dinosaur such as a sharp teeth & similar bones of dinosaur. It also had a bony tail. → Sinosauropteryx: A small bat-running dinosaur had a downy feather-like covering on its back, which possibly evolved into the wings. → There are still others like protoarcheopteryx which had feathers & a bony tail. → The ability to take-off from the ground to make flight above suggests that birds evolved from dinosaurs. Early species may have been boys runners & wind their feathered boslimbs to help them glide over horizontal barriers. (3) go-ape/ The descent of man:- → Chimpanzee are the closest living relative to humans & apes. With since the time of our common ancestors (5-7 MYA) both humans & chimpanzees have followed their own unique evolutionary paths. → The evolution of human towards an ape ancestor is supported by DNA & fossil evidences. The last common ancestor of chimpanzees & humans was an ape. (4) Outaloppithecus afarensis: → It represent a transition between modern bipedal humans & their quadrupedal ape ancestors. → The pelvis of Australopithecus afarensis was more human-like than an ape being markedly wide with laterally oriented blades. → The femur angles toward the knee than the hip. This straight strongly indicates, habitual bipedal locomotion, besides locomotion they also had a slightly larger brain than modern chimpanzee & head teeth not wax more human like. Evolution of Horse: → Occurred over a geological timescale of 50 million years, transforming the small, dog-sized Eohippus into the modern horse. Eocene Horse: → The 1st fossil remains of horse found in North America was Eohippus (Dawn Horse). → Eohippus was very short (about 1 feet). → It was discovered in early Eocene. → It had a small head, back arched & flexible. → 44 teeth, teeth were low crowned on both front & hind feet. → 4 toes present on front & 3 toes in the hind feet. 2) Orohippus: → In North America & New Mexico. → Little increase in the size of the horse (1.3 feet), 4 toes in the front foot & 3 toes in the hind feet. 3) Epihippus: → The last 2 premolars were molariform. Browsers. → 4 toes in the fore feet & 3 toes in the hind feet. Oligocene Horses: Oligocene horses were directly derived from Epihippus. Mesohippus: → By Badlands of South Dakota. → Size increased. Head was Equus like, neck shorter & less flexible, trunk & legs was long & slender. → Back somewhat more arched behind & broad head. → 3 functional toes. 5) Miohippus: → Retained relatively low-crowned teeth, 3 toes in each foot, browsing in habit. All Miocene horses found were 3-toed. 6) Anchitherium: → N. America, Europe, Asia, 3-toed, very simple type of cheek teeth. 7) Hypohippus: → Large in size (40'), low crowned teeth. 8) Archaeohippus: → Pigny horses of Miocene. → Smaller in size → retaining many 9) Parahippus: → Teeth became adapted for grinding & chewing. 10) Merychippus: → You found with radius, fibula lost in shaft. 11) Pliohippus: → Milk teeth (short, crowned & cemented) permanent teeth (highly crowned & cemented) Pliocene horses: By the end of Miocene, the grazing horses had split into at least 6 fairly distinct forms & most of them have 3 toes. 12) Hipparion: → Asia & Europe origin. → 3-toed grazers, retained complete size-toes or one may apply 13) Neohipparion: → Complete size-toes, teeth like Pliohippus, presence of peculiar eye orbit, 1st one-toed horse, heels longer. 14) Equus: → Discovered from South America. → Equus evolved from Pliohippus (4-4.5 mya) during Pleistocene. → It shows even greater development of brain & teeth, longer cheek teeth. Geological Time scale (GTS) → Geologists used geological time scale to record various stages in earth history. → It represents the chronological order of earth, history of its events. EONS ERAS PERIODS EPOCHS AGES → Eon is the largest section of GTS. → Eras divided into Periods. (Permian divided into Epochs) → Periods divided in to Epochs & ages. 2 EONs - (1) Cryptozoic eon (Precambrian time) → no ozone layer. → nat ozone originate (life started) Cryptozoic Era (Precambrian Era) Proterozoic Fon (Proterozoic Era) Paleozoic Era (Palaeozoic Era) (Age of invertebrates) Cambrian Ordovician Silurian Devonian Carboniferous Permian Mesozoic Era (Age of reptiles) Triassic Jurassic Cretaceous Cenozoic Era (Age of mammals) Eocene Oligocene Miocene Pliocene Pleistocene Holocene Extinction → It is the process of evolution that lead to the disappearance of a population or species. → When a species becomes extinct, all its genetic heritage is lost. → The species evolve into new species in order to adapt to the environmental changes or changes in the genetic heritage. Causes: → These could happen naturally due to change in the climate or because of human activity like over-hunting or the destruction of habitats. → The causes of extinction include: (i) changing climates (ii) ecological imbalance (iii) loss of biodiversity (iv) habitat loss (v) natural calamities (vi) biological pollutants (vii) introduction of exotic species (viii) overexploitation (ix) human activities