- CHARITH AKLANSS DODANGODAGE -
Humans and other amphibia, reptiles, aves, mammalians and fish are all part of the large clade of animals called the vertebra. The clade is a group of organisms that includes common ancestors of the group and all of its descendants. Vertebrates are part of the larger clade called the chordates which is the group of the animals with a stiff cord on their back. Vertebrates evolution is like a continuously growing tree. 1st vertebrates lived in aquatic environment. Ex: super class Agnatha and fish. Later they gradually adapted to more terrestrial life. Amphibians have both wet skin, mouth and lungs for breathing. Wet skin and mouth help to breath in water and lungs help to breath in terrestrial environment. Their membrane bound fingers help to swim. But they still need water to reproduce. Reptilians are adapted terrestrial environment more than Amphibians. Holds scaly skin to protect it from drying out. Their eggs have shell to protect it from dying out. They have well developed nails to land travel easier. The lungs have to breath. They have four chambered heart for easier blood circulation. Birds carry a lightweight frame as an adaptation to fly. Their anterior limbs are modified into wings. The body takes on an irregular shape to make it easier to fly.
Vertebrate is an animal with a spinal chord surrounded by cartilage or bone. The term come from vertebrae, the bone that make up the spine. Invertebrates are named organisms that are not vertebrates.
Vertebrates are divided to two groups.
1. Agnatha
Gnathostomata is divided again two super classes.
1. Super class Pisces
2. Super class Tetrapoda
Super class Pisces is divided to two classes.
1. Class Chondrichthyes
2. Class Osteichthyes
Super class Tetrapoda also is divided again four classes.
1. Class Amphibia
2. Class Reptilia
3. Class Aves
4. Class Mammalia
Agnatha
Agnatha is the super include jawless fishes. Oldest fossils of agnaths are found from Cambrian evolution stage. Their two species are in still today. They are named lampreys and hagfish. They haven’t paired fins. Notochords presence in larvae and adults. Lampreys have life sensitive pinnal eye. They have no any identified stomach or any other appendages. Fertilization is done in external environment. They have only 30 eggs in life time. They are cold blooded animal. They have cartilaginous skeleton and two chambered heart. They are eating dead animals mostly. Copious slime glands are on their skin. They haven’t dermal or epidermal scales. They do not regulate their own body temperature. Agnathan seeds are unable to up and down.
Specially, Lampreys are in sri Lanka. They still alive in Thambalagamuwa lagoon.
Lampreys
Gnathostomata
1. Class Chondrichthyes
Chondrichthyes; from Greek -chondr- 'cartilage', ichthys 'fish') is a class that contains the cartilaginous fishes: they are jawed vertebrates with paired fins, paired nares, scales, a heart with its chambers in series, and skeletons made of cartilage rather than bone. The class is divided into two subclasses: Elasmobranchii (sharks, rays, skates, and sawfish) and Holocephali (chimaeras, sometimes called ghost sharks, which are sometimes separated into their own class.
Within the infraphylum Gnathostomata, cartilaginous fishes are distinct from all other jawed vertebrates.
Skeleton
The skeleton is cartilaginous. The notochord is gradually replaced by a vertebral column during development, except in Holocephali, where the notochord stays intact. In some deepwater sharks, the column is reduced.
As they do not have bone marrow, red blood cells are produced in the spleen and the epigonal organ (special tissue around the gonads, which is also thought to play a role in the immune system). They are also produced in the Leydig's organ, which is only found in certain cartilaginous fishes. The subclass Holocephali, which is a very specialized group, lacks both the Leydig's and epigonal organs.
Appendages
Apart from electric rays, which have a thick and flabby body, with soft, loose skin, chondrichthyans have tough skin covered with dermal teeth (again, Holocephali is an exception, as the teeth are lost in adults, only kept on the clasping organ seen on the caudal ventral surface of the male), also called placoid scales (or dermal denticles), making it feel like sandpaper. In most species, all dermal denticles are oriented in one direction, making the skin feel very smooth if rubbed in one direction and very rough if rubbed in the other.
Originally, the pectoral and pelvic girdles, which do not contain any dermal elements, did not connect. In later forms, each pair of fins became ventrally connected in the middle when scapulocoracoid and puboischiadic bars evolved. In rays, the pectoral fins are connected to the head and are very flexible.
One of the primary characteristics present in most sharks is the heterocercal tail, which aids in locomotion.
Body covering
Chondrichthyans have toothlike scales called dermal denticles or placoid scales. Denticles usually provide protection, and in most cases, streamlining. Mucous glands exist in some species, as well.
It is assumed that their oral teeth evolved from dermal denticles that migrated into the mouth, but it could be the other way around, as the teleost bony fish Denticeps clupeoides has most of its head covered by dermal teeth (as does, probably, Atherion elymus, another bony fish). This is most likely a secondary evolved characteristic, which means there is not necessarily a connection between the teeth and the original dermal scales.
The old placoderms did not have teeth at all but had sharp bony plates in their mouth. Thus, it is unknown whether the dermal or oral teeth evolved first. It has even been suggested that the original bony plates of all vertebrates are now gone and that the present scales are just modified teeth, even if both the teeth and body armor had a common origin a long time ago. However, there is currently no evidence of this.
Respiratory system
All chondrichthyans breathe through five to seven pairs of gills, depending on the species. In general, pelagic species must keep swimming to keep oxygenated water moving through their gills, whilst demersal species can actively pump water in through their spiracles and out through their gills. However, this is only a general rule and many species differ.
A spiracle is a small hole found behind each eye. These can be tiny and circular, such as found on the nurse shark (Ginglymostoma cirratum), to extended and slit-like, such as found on the wobbegongs (Orectolobidae). Many larger, pelagic species, such as the mackerel sharks (Lamnidae) and the thresher sharks (Alopiidae), no longer possess them.
Nervous system
The above is are the regions of a Chondrichthyes brain colored and labeled on dissected skate. The rostral end of the skate is to the right.
In chondrichthyans, the nervous system is composed of a small brain, 8-10 pairs of cranial nerves, and a spinal chord with spinal nerves. They have several sensory organs which provide information to be processed. Ampullae of Lorenzini are a network of small jelly filled pores called electroreceptors which help the fish sense electric fields in water. This aids in finding prey, navigation, and sensing temperature. The Lateral line system has modified epithelial cells located externally which sense motion, vibration, and pressure in the water around them. Most species have large well-developed eyes. Also, they have very powerful nostrils and olfactory organs. Their inner ears consist of 3 large semicircular canals which aid in balance and orientation. Their sound detecting apparatus has limited range and is typically more powerful at lower frequencies. Some species have electric organs which can be used for defense and predation. They have relatively simple brains with the forebrain not greatly enlarged. The structure and formation of myelin in their nervous systems are nearly identical to that of tetrapods, which has led evolutionary biologists to believe that Chondrichthyes were a cornerstone group in the evolutionary timeline of myelin development.
Immune system
Like all other jawed vertebrates, members of Chondrichthyes have an adaptive immune system.
Reproduction
Fertilization is internal. Development is usually live birth (ovoviviparous species) but can be through eggs (oviparous). Some rare species are viviparous. There is no parental care after birth; however, some chondrichthyans do guard their eggs.
Capture-induced premature birth and abortion (collectively called capture-induced parturition) occurs frequently in sharks/rays when fished. Capture-induced parturition is often mistaken for natural birth by recreational fishers and is rarely considered in commercial fisheries management despite being shown to occur in at least 12% of live bearing sharks and rays (88 species to date).
1. Class Osteichthyes
Osteichthyes are knows as the bony fish. They have bony endoskeletons primarily composed of bone tissue. Bones are covering the head and pectoral girdles. The vast majority of fish are members of Osteichthyes, which is an extremely diverse and abundant group consists of 45 orders , and over 435 families and 28,000 species. These group is divided into two types the ray-finned fish (Actinopterygii) and lobe-finned fish (Sarcopterygii) in the subphylum vertebrata. Their fossils are 420million years old. Early sarcopterygians and actinopterygians are originated during the Silurian period. And sarcopterygians are believed to have given rise to the amphibians in the Devonian period (360 - 400 million years ago)
Ray – finned fish
Majority of fish are this this type. Around 27,000 of species include for this type. Fins are supported by bony structures called ray. Thin fins consist of webs of skin over flexible spines. They serve as a major source of protein for humans, who have harvested them for thousands of year. Teleost is the most advanced ray finned fish. Another examples : Boarfish, Tuna, mudskipper ,Squirrel fish…
Lobe – finned fish
Fines are stump – like appendages. Fines consist of long, fleshy muscular lobe, supported by a central core of bones. Lobe fins is the presence of rod-shaped bones surrounded by a thick layer of muscle in their pectoral and pelvic fins. This thought to be the ancestor of amphibians. During the Devonian period many lobe fin fishes lived in coastal wetlands. They used their lobed fins to swim and walk underwater. Some Devonian lobe fines were gigantic. It is not uncommon to find spike shaped fossils of Devonian lobe fin teeth as big as our thumb. By the end of Devonian period the lob fin diversity was dwindling. In the present we have only few species. Examples : Lungfish and Coelacanth.
· Following are the parts of Bony fish
They have a streamlined body which accommodates their body while moving forward to filter the water friction. They can be found in marine water and freshwater environment including caves, deep sea habitats, thermal springs and vents. They have terminal mouth and have bony teeth. Also, they have four pair of gill slit and each side is covered by an operculum. They are cold – blooded animals. That means ectotherms. They carry inner ear only. They have not middle ear or outer ear. And also, these types of fish have well-develop eyes, but they have not eyelids. Their skin covered by cycloid or ctenoid scales. And also, they have developed swim bladder and a two chambered heart. If a fish swims into deeper of the water or towards the surface, where water pressure differs, the fish shuttles gas between its blood and swim bladder, keeping the volume of gas in the bladder constant. Their excretory organ is the kidney. They carry twelve cranial nerves. They have platelike scales, a skull with sutures. Lateral line of fish is runs across the side of their body. This line is a series of sensory organs called neuromasts. It helps to sense vibrations and water pressure and help fish navigate and locate prey. These fish have ability to see in colour, unlike most other fish.
Bony fish have separate sex. Fertilization is external and lay eggs. They have direct development mode of life; they have not larval stage is formed. Their body sizes different from tiny species such as the pygmy goby (12mm) to the enormous Marlins and Swordfishes (4.5cm) and Ocean Sunfish (weight – 900kg)
Examples for Osteichthyes
3. Class Amphibia
There are about 6150 species in this class. There are three living orders of amphibians. They are Salamanders, frogs and toads and caecilians. They vary greatly in size and structure. They have first appeared about 340 million years ago. Many amphibians are obligate breeders in standing water. Most amphibians are found in damp habitats such as swamp and rain forests. They adapted to drier habitats spend much of their time in burrows or under moist leaves.
Amphibians display more evolutionary experiments in reproductive mode than any other vertebrate group. Some have aquatic eggs and larvae, whereas others embed their eggs in the stomach, mouth, or skin on the back of the female.
In other groups, the young develop within the oviduct, with the embryos feeding on the wall of the oviduct. The fertilization is external. The eggs lack shells and dehydrate quickly in air. They deposit large numbers of eggs in water; clutches of the tiger salamander may exceed 5,000 eggs. Large bullfrogs produce clutches of 45,000 eggs. Egg size and water temperature are important factors that influence an embryo’s development time.
(The eggs that are lack shells)
Adult amphibians consume a wide variety of foods. Some frogs eat earthworms. Caecilians eat earthworms as their diet. Salamanders feed primarily on insects and other arthropods. Large salamanders eat small vertebrates. Most salamanders locate prey by sight, although some use their sense of smell.
The circulatory and respiratory systems of amphibians work with the integument to provide cutaneous respiration. They typically have a moist skin and rely heavily on skin-surface respiration. Aerial respiration requires a cycle of airflow in and out of the lung. This flow refreshes the air and provides a steep diffusion gradient for the exchange of oxygen and carbon dioxide across the tissue interface separating air and blood.
Amphibians also employ various combinations of branchial and pulmonary strategies to breathe. In addition to its roles in respiration and maintaining water balance, the integument of amphibians contains poison glands that release toxins. The amphibian auditory system is also specially adapted. One modification is the papilla amphibiorum, a patch of sensory tissues that is sensitive to low-frequency sound.
Frogs are better suited to the land than salamanders. The larval stage of s frog called a tadpole. They are usually an aquatic vertebrate and they have long, finned tail. The tadpoles initially lack legs and it swims by undulating its tail.
During the metamorphosis, the tadpoles develop legs, lungs, a pair of external eardrums and a digestive system adapted to a carnivorous diet. Frogs and toads show the greatest diversity in humid tropical environments. They have leathery skin. They are long sticky tong, and they are able to nab insects and other prey by that. Many poisonous species have colour patters that camouflage them or have bright coloration. The long, sticky tounge helps to them to nab insects and other prey.
Some salamanders are aquatic and some live on the land as adults or the whole life. Paedomorphosis is a common aquatic salamander. They have tails and two pairs of limbs of roughly the same size. They are somewhat less specialized in body form than the other two orders Salamanders have small heads and long slender bodies. They made up of four limbs and a tail.
(Salamander)
Caecilians are limbless, wormlike, and highly adapted for a burrowing existence. Caecilian moving over soil. All caecilians, except for a few aquatic species, lead subterranean existences and thus have similar specialized morphologies. They have a wormlike appearance. The caecilian cannot extend its tongue from the buccal cavity. The nasal organs of them are well developed. The sense of hearing is probably less sensitive than others.
Amniotes are tetrapods that have a terrestrially adapted egg. They have adaptations to the life on the land. For example, they use their rib cage to ventilate their lungs. As well as their eggs have shells.
4.Class Reptelia
The origin of reptiles dates back to about 310–320 million years ago, in the vapor marshes of the late Carboniferous. The first reptiles evolved from advanced reptiles. Cassinaria is the oldest known amniotic fluid. A series of footprints on the fossil layer of Nova Scotia up to 315 Ma show traces of the fingers and scales of ordinary reptiles. These tracks are attributed to the oldest reptile, the Hylonomus. It was a small lizard-like animal about 20 to 30 centimeters long, with a sharp set of teeth showing an insectivorous diet. Other examples include Westlotiana (considered a reptile rather than a true amniotic fluid) and Paleothyris, with similar build-up and presumably similar habits.
Rise of reptiles
The oldest amniotics, including stem-reptiles ,were largely inhabited by large trunk-tetrapods such as cochlear and remained a small, invisible part of the species until the collapse of the carboniferous rainforest. This sudden crash affected several large groups. Primitive tetrapods were particularly devastated and trunk reptiles became better adapted to later dry conditions. Like modern amphibians, primitive tetrapods must return to the water to lay eggs; In contrast, modern reptiles, such as the amniotic fluid - which have a shell that allows them to lay their eggs - adapted better to new conditions. Amniotes acquired new habitats at a faster rate than before the crash and even faster than the primary tetrapods. They acquired new nutritional strategies, including herbivores and carnivores. From here, reptiles dominated communities and set the stage for the Mesozoic (known as the Age of the Reptiles), which is much more diverse than the primitive tetrapods. The Mesozoic is one of the earliest primitive reptiles. It is a variant of the early Permian. He came back into the water and ate the fish.
It has traditionally been assumed that the first reptiles retained an Anapsid skull inherited from their ancestors. This type of skull has a cranial roof and only holes for the nostrils, eyes and pineal gland. The discovery of cyanopsid-like openings in the roof of the skull of several members of the parentheplia, lanthanosucoids, milletoids, bolosorides, some nitroletaroids, some protoclophonoids, and at least some mesosores have made it even more obscure and obscure. skulls like anapsid-like or synapsid. These animals are traditionally referred to as "anapsids" while other groups form an evolved paraphilic base. Shortly after the first amniotic sac appeared, a lineage called the synapsida was broken; This group was characterized by a temporary opening in the skull behind each eye to allow the jaw muscles to move. These are the "mammalian amniotic" or stem-mammals that later produced real mammals. Before long, another group developed a similar trait, this time having a double opening behind each eye, naming them diapsida ("two arches"). The function of the pores in these groups was to relax the skull and allow the jaw muscles to move. Turtles are traditionally believed to be parasitic reptiles, based on their anaphylactic skull structure and assumed to be a primitive trait. The argument for this classification is controversial, with some arguing that turtles evolved from anapsid skulls to improve armor. Subsequent morphological phylogenetic studies have shown that turtles are firmly entrenched in diapsid. All molecular studies have strongly confirmed the lo With the closure of Carboniferous, the amniotic tetrapod became a species. Primitive, terrestrial reptiles still exist, and the first truly terrestrial megaphones evolved in the form of pelicos, such as the Synopsis amniotic, Edaphosorus, and the carnivorous Dimetrodon. By the middle of the Permian period, the climate had dried up and as a result the species had changed: polycosores were replaced by therapists. Parapetiles with no posterior pit holes in large skull roofs continued and prospered throughout the Permian. The Pariasoriyan parapeptiles reached gigantic proportions in the late Permian and eventually disappeared by the end of that period (turtles were able to survive).
During the early part of this period, modern reptiles, or crown reptiles, evolved into two main genera: Acosoromopha (ancestors of turtles, crocodiles and dinosaurs) and Lepidosoromopha (predecessors of modern lizards and turtles). Both groups were lizard-like and relatively small and did not appear during the Permian period. calization of turtles in diode.
Vernus pruritus is a giant carnivorous lizard, sometimes up to 7 meters long and weighing 1,940 kilograms.
With the end of the Cretaceous, the Mesozoic reptilian megaphone died out. Of the large marine reptiles, only sea turtles remain; Of the large non-marine reptiles, only semi-aquatic crocodiles and broadly similar choreographers survived extinction. The second is extinct in the Miocene. Of the large dinosaurs that dominated the Mesozoic, only small beaked birdssurvived. This dramatic extinction pattern eventually led to the cenozoic. Mammals and birds filled the empty nests left by reptile megaphones, slowing down reptile diversification and making a national turn on bird and mammal diversification. However, reptiles were still important features of the megaphone, especially in the form of large and giant tortoises.
By the end of the Cretaceous, after the extinction of many archeological and marine reptile lines, reptile diversification continued throughout the Cenozoic. It was ten million years after the Skomets suffered a massive blow at the Katie event that it recovered, But after they were cured, they were subjected to a massive radiation event and today skomites are the majority of living reptiles. About 10,000 existing traditional reptile species are known, adding about 10,000 more birds, about twice the size of mammals, and representing about 5,700 species.
Circulation
All squirrels and turtles have a three-chambered heart with two atria. The amount of oxygen and deoxygenated blood mixing in a three-chambered heart varies according to specific and physical conditions. Under various conditions, deoxidized blood can be transferred back to the body, or oxygenated blood can be transferred back to the lungs. This variation in blood flow has been hypothesized for more thermoregulated heat circulation and longer diving times for aquatic species but has not been shown to be a suitability advantage.
The inferior iguana heart divides into left and right arteries and travels through the spine
For example, the iguana heart, like most hearts, consists of three chambers, two aortae and one ventricle, the voluntary muscle of the heart. The major structures of the heart are sinus venous, pacemaker, left atrium, right atrium, atrioventricular valve, caudal venous, caudal pulmonary, muscular ridge, vertebral artery, pulmonary artery and pulmonary artery.
Some species of skomets have three-chambered hearts that, when contracted, become active four-chambered hearts. This can be done by a muscle ridge that divides the vertebrae within the vertebral diastole and completely divides between the vertebral systols. Because of this mountain range, some of these scomets are able to produce vertebral pressure differentials similar to those of mammals and birds.
Crocodiles have four heart-like structures similar to those of birds and have two systemic aortas, thus avoiding their pulmonary circulation.
Metabolism
Modern avian reptiles exhibit some form of cold-blood hemorrhage that has limited physical means of maintaining a constant body temperature and is often dependent on external heat sources. Because birds and mammals have a less stable moderate temperature, reptile biochemistry requires enzymes that can maintain greater temperature range efficiency than warm-blooded animals.
The optimum body temperature range varies with species but is generally lower than that of warm-blooded animals; For most lizards, it falls in the 24 ° –35 range C range, and for heat-adapted species such as the American desert Iguana Dipsosorus dorsalis the optimum physiological temperature in mammals is between 35 40 and 40 C. The optimum temperature is often found when the animal is active, while the body temperature drops rapidly when the low basal metabolic animal is inactive.
Like all animals, reptile muscle activity produces heat. In larger reptiles, such as leatherback turtles, the lower surface-to-volume ratio allows these metabolically generated heat to keep animals warm in their environment, even if they do not have a warm-blooded metabolism. This form of homeotherm is called gigantotherm; It has been suggested that it is common among large dinosaurs and large extinct reptiles.
Respiratory system
All reptiles breathe using their lungs. Aquatic turtles have more permeable skin and some species have changed their coat to increase the area for gas exchange. Even with these adaptations, breathing without the lungs is never complete. Lung ventilation is performed differently in each major reptile group. The lungs in the skomet are ventilated by the axillary muscles. This is the only muscle used in train engines. Because of this obstruction, many comets are forced to hold their breath during intense running. However, some have found a way around it. Warrenid and several other lizard species use buccal pumping to supplement their normal "axial breathing." This allows the animal to fill the lungs completely in a tight area, making it aerobically active for a long time. Tegucigal lizards are known to have proto-diaphragms that separate the pulmonary cavity from the visual cavity.
Skin
The skin of reptiles is covered with a horned epidermis, which is not water resistant and allows reptiles to live in a dry land unlike amphibians. Compared to mammalian skin, reptiles are thinner and do not have the same skin layer that mammalian skins produce. The exposed parts of the reptile are protected by scales or scars, sometimes with a bony base, forming an armor. The entire skin of lipidosaurs, such as lizards and snakes, is covered by epidermal scales. Such scales were once thought to be similar to the Reptilia class as a whole, but are now found only in the Lipidosaurus. The scales found in turtles and crocodiles are epidermal, rather than dermatological, and are properly referred to as scars.
The skin of reptiles without Erna dermis is not as strong as that of mammals. It is used for shoes, belts and handbags, especially for leather goods for decorative purposes for crocodile skin.
Reproduction
Reptiles usually reproduce sexually. All reproductive activity takes place through the single exit / entry at the base of the tail, the waste disposal sheath. Most reptiles have copulatory organs that are usually retracted or inversely stored in the body. In turtles and crocodiles, the male has a single central penis, and the skomts, including snakes and lizards, have a pair of hemispheres that are usually used in one session. However, Tuatara does not have cohesive organs and males and females press the male cloak together when ejaculating. Some reptiles exhibit temperature-dependent sex determination (TDSD). TDSD is common in turtles and crocodiles and is also found in lizards and toads. To date, it has not been confirmed whether TDSD occurs in snakes.
Nerves
The nervous system of reptiles contains a basic part similar to the amphibian brain, but the reptile brain and brain are slightly larger. Most common sensory organs are well developed with some exceptions, especially in the absence of external ears to the snake. There are twelve pairs of spinal nerves. Because of their short cochlea, reptiles use electronic tuning to expand their auditory frequency range.
Digestion
Most reptiles are insectivorous or carnivorous and have simple and relatively short digestive tracts because the meat is quite simple to break down and digest. Digestion is slower than in mammals, reflecting their low resting metabolism and inability to digest and masticate their food. Their piciloterm metabolism has very low energy requirements, allowing large reptiles such as crocodiles and large conductors to live for months on a single large meal. Modern reptiles are primarily carnivorous, and several groups in the early history of reptiles produced herbivorous megaphones: Paleozoic, Pariasor; And a few rows of dinosaurs in the Mesozoic. Today, turtles are primarily herbivorous reptiles, but several Agama and Iguana lines have evolved to live entirely or partially on plants.
Disposal
Disposal is done mainly by two small kidneys. In dihydride, uric acid is the major nitrogen contaminant; Turtles, like mammals, mainly excrete urea. Unlike the kidneys of mammals and birds, reptile kidneys are unable to produce more concentrated liquid urine than their body fluids. This is due to a special structure found in the nephrons of birds and mammals called the Henle Loop. Because of this, many reptiles use the large intestine to reabsorb water. Some may also take in water stored in the bladder. Excess salts are excreted by the nasal and lingual salivary glands in some reptiles.
In all reptiles, both the urethra and the anus are referred to as the skull. In some reptiles, the middle wall of the mantle may open into the bladder, but not all. It is found in all turtles and turtles as well as in many lizards but the monitor lizards have no legless lizards. It is not found in snakes, alligators and crocodiles.
5. Class Aves
All birds are classified as members of kingdom animalia, phylum cordata and class Aves which comes under vertebrates. According to cladistic analyses of birds and reptilian fossils the evolution of birds has begun in the Jurassic period. The earliest bird has derived from a group of dinosaurs called Paraves which is a clade of theropod dinosaurs. Several species of dinosaurs were closely related to the characteristics of birds. Some had feathers with vanes, some had filamentous feathers. About 160 million years ago these feathered theropods have evolved into birds. According to fossil evidence Archaeopteryx was the earliest known bird which had feathered wings but also had retained ancestral characters such as teeth, clawed digits and long tail. After that fossils of later birds showed gradual loss of ancestral dinosaur features with the evolution process.
(Fossils of an Archaeopteryx and an imaginary picture of an Archaeopteryx)
In the world there are about more than 10000 living bird species. Birds can be divided into species by their profile, colour, flying styles and beak shape also. Birds are also called as reptiles with feathers who have adaptations to fly. They are more related to reptiles than mammals. There are some birds that cannot fly which are called as flightless birds.
Examples: Ostrich, Kiwi, Emu
And there are penguins also cannot fly but use the flying technique to “fly” in the water.
Birds have their unique characteristics. They have a special shape which is called as the streamlined shape which helps them to move easily in the air by offering less resistance thus helping them to move freely. Their body has four main parts as head, neck(throat), body and tail. The skin is covered with feathers and their feet are covered with scaled skin. This scaly skin strengthens the feet. Their forelimbs evolved to become wings and the hindlimbs are modified to walk. Their short tail is covered with feathers and the mouth is modified as a beak without teeth. Their ears have the three parts as outer ear, middle ear, and the inner ear. And also, they have light bones with a strict skeletal template. The birds have eyes with lateral eyelids and moisture membranes. And also, they have a four chambered heart and 12 pairs of cranial nerves.
They conduct their respiration through lungs. And they have a pair of kidneys as the urinary organs and the main excretory product is uric acid. Birds lay eggs which are covered with hard Calcium Carbonate (CaCO3) shells.
(Streamlined shape of a bird)
Except for their characteristics they have almost every feature of their anatomy modified as an adaptation to facilitate flight. And also, they have weight saving modifications which make flying more efficient. For examples, the female birds have only one ovary, Birds lack a urinary bladder, reproductive organs of both males and females are usually small except during breeding season. And there are air chambers among their light bones which help to lessen the weight of their body. And also living birds are also toothless as an adaptation that minimize the weight of bird head. Birds dispose stools immediately as an adaptation of losing weight.
The most obvious adaptations for flight of birds are the wings and feathers. These feathers are made from β-keratin protein which can be found in scales of reptiles also. Their feathers have specially shaped and arranged to form the wings into airfoils. They follow some principles of aerodynamics as same as airplane wings. The power of flapping the wings come from the large breast muscles anchored to the breastbone. Flying requires a lot of energy from an active metabolism. In this case birds use their own metabolic heat to maintain a high constant body temperature as Aves is an endothermic class. And also feathers and additional layer of fat provide insulation to maintain the body heat of birds. They have lungs with tiny tubes and air sacs which help to improve the air flow and oxygen uptake. This efficient respiratory system and their four chambered heart give a good oxygen and nutrient supply to the tissues and it supports a high rate of metabolism. The other adaptations for flight of birds are their excellent eyesight and colour vision as they have a large brain with well-developed visual and motor areas.
Examples for class Aves : Eagle, Crow, Parrot, Swan, peacock, hummingbirds etc.
6. Class Mammalia
Mammals are most evolved class in the animal kingdom. They have mammary glands for feeding their younger ones. Shrews and bats are smallest mammals and can weight as little 3 grams. Blue whale is largest mammal which can weight 160 metric tons.
Mammals are evolved to live in all terrestrial habitats and aquatic habitats. They are live in every terrestrial biome, from deserts to tropical rainforests to polar icecaps. And also, mammals have different locomotion styles such as fly, glide, swim, run burrow of jump. They are warm blooded animals who give birth to their babies. Mammals have brain part known as Neocortex. Sebaceous glands and sudoriferous glands are on the mammal skin. Their bodies are covered by heir. It helps to adapt their environmental conditions. They have different types of teeth. Mammal have cervical vertebrae. Their skull is dicondylic. Their trunk is divided in to thorax and abdomen. Their respire is done using lungs. Mammals can hear well more than other vertebrates. Because they have three middle ear bones known as malleus, incus and steps. They have four chambered heart. It helps to good circulatory system. Mammals brain is well developed more than other animals and it divided in to cerebrum, cerebellum and medulla. They possess 12 pairs of cranial nerves. Mammals are evolved to live in all terrestrial habitats and aquatic habitats. They are live in every terrestrial biome, from deserts to tropical rainforests to polar icecaps. And also, mammals have different locomotion styles such as fly, glide, swim, run burrow of jump. They are warm blooded animals who give birth to their babies. Sebaceous glands and sudoriferous glands are on the mammal skin. Their bodies are covered by heir. It helps to adapt their environmental conditions. They have different types of teeth. Mammal have cervical vertebrae. Their skull is dicondylic. Their trunk is divided in to thorax and abdomen. Their respire is done using lungs. Mammals can hear well more than other vertebrates. Because they have three middle ear bones known as malleus, incus and steps. They have four chambered heart. It helps to good circulatory system. Mammals brain is well developed more than other animals and it divided in to cerebrum, cerebellum and medulla. They can lay egg or baby animal. They have lower jaw made by single bone, a muscular diaphragm separating thoracic and abdominal cavities and a secondary plate separating air and four passages in the mouth. This is only one class that has placenta. It helps to combine mother and fetus for feeding. Mammals should maintain their physiological balance like body heat. Nucleus is lack of all mammal’s mature red blood cells.
Mammals have brain part known as Neocortex. They possess 12 pairs of cranial nerves. Mammalians’ nerve system is most complex nerves system on the planet. It works as a sensor system. It takes senses and transmit information to brain. Mammalians, specially humans are fastest reflexed animal in the world because their well-developed nerves system. They can also easily adapt to new ecosystem. Their nerve is based on brain and spinal cord. Signals are transferred using nerve endings. Their nerves system is divided to four main parts. These are the central nerves system, the peripheral nerves system, the somatic nerves system and the autonomic nerves system. Their nerves system is response to mammals interpret what the happening in the external environment, maintain homeostasis, maintain heartbeat, breathing and other body functions. Their brain is divided to two parts, left and right hemispheres. It is divided again certain parts to responsible for certain functions such as balance, hear and speech. Mammals have simply collection of nerve cells called ganglia. If there is any injury to nerve system, it can cause paralysis or even death for the mammals.
Mammals excretion system is adopted to excrete urine through the kidneys, carbon dioxide through the lungs and sodium chloride the skin. They can lay egg or baby animal. They have lower jaw made by single bone, a muscular diaphragm separating thoracic and abdominal cavities and a secondary plate separating air and four passages in the mouth. This is only one class that has placenta. It helps to combine mother and fetus for feeding. Mammals should maintain their physiological balance like body heat. Nucleus is lack of all mammal’s mature red blood cells.
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