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Evolutionary grade

In alpha taxonomy, a grade refers to a taxon united by a level of morphological and/or physiological complexity. The term was coined by British biologist Julian Huxley, to contrast with clade, a strictly phylogenetic unit. Definition An evolutionary grade is a group of species united by morphological and/or physiological traits, that has given rise to another group that differs markedly from the ancestral condition, and is thus not considered part of the ancestral group. The ancestral group will not be phylogenetically complete (i.e. will not form a clade), so will represent a paraphyletic taxon. The most commonly cited example is that of reptiles. In the early 19th century, the French naturalist Latreille was the first to divide tetrapods into the four familiar classes of amphibians, reptiles, birds and mammals. In this system, reptiles are characterized by traits such as laying membranous or shelled eggs, having skin covered in scales and/or scutes, and having a 'cold-blooded' metabolism. However, the ancestors of mammals and birds also had these traits and so can be said to be reptiles, making the remaining reptiles a grade rather than a clade. In microbiology, taxa that are thus seem as excluded fom their evolutionary grade parent group are called taxa in disguise. Paraphyletic taxa will often, but not always, represent evolutionary grades. In some cases paraphyletic taxa are united simply by not being part of any other groups, and give rise to so-called wastebasket taxa which may even be polyphyletic. Grades in systematics The traditional Linnaean way of defining taxa is through the use of anatomical traits. When the actual phylogenetic relationship is unknown, well defined groups sometimes turn out to be defined by traits that are primitive rather than derived. In Linnaean systematics, evolutionary grades are accepted in higher taxonomic ranks, though generally avoided at family level and below. In phylogenetic nomenclature evolutionary grades (or any other form of paraphyly) are not accepted. Where information about phylogenetic relationships is available, organisms are preferentially grouped into clades. Where data is lacking, or groups of uncertain relationship are to be compared, the cladistic method is limited and grade provides a useful tool for comparing organisms. This is particularly common in palaeontology, where fossils are often fragmentary and difficult to interpret. Thus, palaeontological works are often using evolutionary grades as formal or informal taxa, including examples such as Labyrinthodonts, Anapsids, Synapsids, Dinosaurs, Ammonites, Eurypterid, Lobopodes and many of the more well known taxa of human evolution. Evolutionary grades, being united by gross morphological traits are often eminently recognizable in the field. While paraphyletic taxa are sought eliminated in taxonomy, such grades are sometimes kept as formal or informal groups on basis of their usefulness for laymen and field researchers. When referring to a group of organisms, the term "grade" is usually enclosed in quotation marks to denote its status as a paraphyletic term. Examples Bryophytes were long considered a natural group, defined as those land plants which lacked vascular systems. Molecular evidence shows that the bryophytes are not monophyletic since mosses, liverworts and hornworts are in fact separate lineages, with mosses closest to vascular plants. However, the three clades have a similar degree of complexity, and the "bryophyte grade" is a useful benchmark when analysing early plants - it contains information about the status of fossils which cannot always be classified into extant groups. Fish represent a grade, inasmuch as they have given rise to the land vertebrates. In fact, the three traditional classes of fish (Agnatha, Chondrichthyes and Osteichthyes) all represent evolutionary grades. Amphibians in the biological sense (including the extinct Labyrinthodonts) represent a grade, in that they are also the ancestors of the amniotes. Reptiles are composed of the cold-blooded amniotes, this excludes birds and mammals Dinosaurs were proposed to be the ancestors of birds as early as the 1860s. Yet the term sees both popular and scientific use, the dinosaurs representing an easily recognizable group. Lizards as a unit represent an evolutionary grade, defined by their retention of limbs relative to snakes and Amphisbaenans.

From Yahoo Answers

Question:Examples can be from nature, like reptiles surpassing amphibians, or vascular plants surpassing non-vascular plants, or from human history like an invention or discovery. It must start with the letter "B". Thank you. :)

Answers:birth control bread slicing machines (excellent article on Wikipedia) boats (an old invention, but a good one)

Question:Provide an example of convergent and divergent evolution, adaptive radiation, and co-evolution. Then, respond to the following: Choose one of the examples you provided and discuss the implications this example may have for future humans. Please please help me with this one.......

Answers:Convergent evolution: Two different species adapt similarly when they share similar niches. Australia has several examples. Tasmanian tigers are very similar to wolves or dogs. The marsupial lion had many features similar to cats They even had a saber toothed version of a marsupial similar to saber toothed cats. divergent evolution: When species separate into dissimilar niches, they evolve quite differently. The formation of limbs in early amphibians compared to their fish ancestors is an example. Adaptive radiation: When a species spreads in to different niches it forms multiple species. A classic example is the Darwin's finch. The common ancestor split into several species as it occupied the various niches. Coevolution is where two species evolved together. Many species of plants produce flowers that only bats can fertilize. The bats evolved to take advantage of the flowers and the flowers rewarded the bats with nectar and flowering at night. Coevolution of humans and cows: The cows allowed us to exploit land that wasn't suitable to crops. They greatly increase our food supply. Perhaps in the future we will use them in many different ways. The way they convert cellulose to sugar in the guts with microbes could lead to the easy conversion of grass into alcohol to power our cars.

Question:need 3 examples of isotonic, hypertonic and hypotonic solutions for biology need 3 examples EACH

Answers:Do you know what does isotonicity or hypertonicity and hypotonicity mean??? By the way, 0.9g% normal saline is isotonic to mammals (e.g. Locke's Solution, Tyrode's Solution, and Dale's Solution); 0.65g% normal saline is isotonic to amphibians (e.g. Ringer's Solution). Any saline preparations having salt concentration higher than the isotonic value are hypertonic and less than that are hypotonic but no trade names are available.

Question:ok so my sister had to go to the hospital tonight so i didn't et to finish this test. PLEASE! can someone help me??? it would mean sooooo much!!!! each answer has to be in paragraph form. 1. suppose you are studying two species of chordates that share a particular adaption. What would you need to know to determine wether this sharing was the result of convergent evolution? 2. Discuss the advantages and disadvantages of being an endotherm and an ectotherm in an enviornment where the air temperture drops to an average of 5 degrees celcius during the winter. 3. How is the body design of a fish well suited for living in water? explain. 4. Describe the basic characteristics os amphibians, and cite three examples of amphibians that do not share all of these characteristics. 5. Describe the changes in structure and behavior that occur as a frog develops from a larva into an adult. 6. What improvements in jaw design have contributed to the success of snaes as predators? 7. flying requires a great amount of energy. What adaptions in the respiratory system allow birds to meet their high energy needs? 8. List the major characteristics of mammals. 9. Suppose a group of scientists discover an unidentified female mammal in new guinea. How might they determine wether the mammal is a monotreme, a marsupial, or a placental mammal? 10. What is the evolutionary relationship between the angiosperms and gymnosperms living today? did the angiosperms evolve from the gymnosperms? 11. compare and contrast the sporophyte stages of mosses and ferns. include at least 2 similarities and two differences. then do the same for their gametophyte stages. 12. explain how a forest fire can affect the germination of certain pine seeds and the recovery of a forest from a fire. 13. describe grafting and budding, and explain why these methods of proppagation are used. 14. explain why sealing fruit in a bag might cause the fruit to ripen quickly. 15. Identify 3 factors that affect the rate of photosynthesis and explain the affect of each. THANK YOU SO MUCH IF YOU HELP ME OUT!!

Answers:OKAY! im gonna try my best to help you out! these might not be in order....im just gonna answer what i can! 8. List the major characteristics of mammals. -have mammary glands (meaning they make milk for their offspring) -they have hair on some part of their body -they have middle ear bones 12. explain how a forest fire can affect the germination of certain pine seeds and the recovery of a forest from a fire. well pine seeds are gymnosperm, so they disperse their seeds by cones and a forest fire would not only destroy the original trees where the cones originated from, but since the seeds themeselves are dependent on being dispersed from the cone "exploding" they lay on the ground, where they are vulnerable to being burned, as opposed to some plants that use animals or the wind for dispersal of seeds, thus giving the seeds a greater chance of getting away from the fire. of cource, the lack of seeds would effect the rate of regrowth one the fire has burned out. 10. What is the evolutionary relationship between the angiosperms and gymnosperms living today? did the angiosperms evolve from the gymnosperms? angeosperm are so far the last and most complex plant type yet to evolve, so yes, they did evolve from gymnosperm. both are vascular seeded plants. 6. What improvements in jaw design have contributed to the success of snaes as predators? i would assume that the snakes ability to swallow its prey whole and extend its jaw so wide has effected its sucess rate as a predator 4. Describe the basic characteristics os amphibians, and cite three examples of amphibians that do not share all of these characteristics. this is a difficult question as far as the examples go, because as earth itself evolved, amphibians had a harder time surviving as the air temperatures cooled and water evaporated. to this day, there are only three main types of amphibians left living, the frog, toad, and salamander. most amphibians hit their evolutionary "dead end" when they tried to adapt to living on land, and failed to be able to adapt to maintian mosture and adapt to gravity never the less, some distinctive characteristics of amphibains are that they lay their eggs underwater. this really distinguishes them from reptiles, who evolved from amphibians, and adapted to laying their eggs on the land. amphibians also maintin the ability to breath throught their skin through a gas exchange. I HOPE THIS CAN HELP YOU A BIT!!!

From Youtube

Walking With Monsters 5 of 9 :British documentary film series about life in the Paleozoic, bringing to life extinct arthropods, fish, amphibians, synapsids, and reptiles.it is narrated by Kenneth Branagh, and by Avery Brooks in the American version. Using state-of-the-art visual effects, this prequel to Walking with Dinosaurs shows for example how a two-ton predatory fish came on land to hunt. The series draws on the knowledge of over 600 scientists and shows nearly 300 million years of Paleozoic history, from the Cambrian Period (530 million years ago) to the Early Triassic Period (248 million years ago). It was written and directed by Tim Haines. As with some of the other BBC specials, it was renamed in North America, where its title was Before the Dinosaurs - Walking with Monsters.