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marsupials and placentals similarities between religions

PDF | There exists a negative allometry between vertebrate brain size and body size. It has been well studied among placental mammals but. Marsupial and placental mammals diverged from a common ancestor more than evolved similarities in overall shape, locomotion, and feeding habits. This phenomenon is called convergent evolution. A good example of this is the similarity between marsupial mammals of South America and Australia and placental. DO I HAVE BITCOIN

Looking at a photo of a live Tasmanian "wolf" shows that they are substantially different from any wolf or dog. Right-click to download pdf. Credits: The sources for these photos are unknown, they seem to be stock photos. I think as mug shots they're okay. The Tasmanian wolf, the last one died in a zoo in the 's. I don't think we know of any living population since then. The dogs and the North American wolf of course are still around. The Tasmanian wolf is a very strange animal.

You can see its stripes, its funny ears, its snout and so forth, but superficial similarities as we have seen are not the basis on which we establish science. Let's take a look at next set of slides. What we've done here is to take actual skulls from our museum. Here's a dog and a wolf. And this is how scientists, real scientists would make these comparisons? Slide 87 : Unlike creationist argumentation, comparative biology is a rigorous science.

Rather than just "eyeballing" similarity as creationists do, biologists systematically identify specific characters. Padian shows five of the standard skull features that dogs and wolves share. For example, tooth formulas are a standard feature used for classifying mammals. Dogs and wolves both have two molars in the upper jaw. Credits: Photos by Andrew Lee, U. Skulls from the U. Museum of Paleontology and the Museum of Vertebrate Zoology. Reproduced with permission. Slide 88 : A direct comparison of a North American wolf and a Tasmanian "wolf," on the other hand, shows that these two species differ in each of these characters.

For example, the tasmanian wolf has four molars instead of two. Oh, yeah, and in each case we have taken features of the jaws and teeth just to show you the comparability among them. I don't need to run through all the features. I just want you to take a look and see that on this slide the no's and the yes's and the numbers line up pretty well between the dog and the wolf.

Do you want me to go through the similarities? Okay, it's close enough for government work. Then the next one here is the North American wolf and the so-called Tasmanian wolf, and in these features again every one of them is opposite, where you get no's, you get yes's, the numbers are wrong, and the carnassial tooth we see in the wolf above is missing in the Tasmanian wolf. So in these features they're completely different.

Let's go to the next slide, just looking at it the front way, which was not shown in Pandas, but the dog and the wolf, just to show that they both have nasal bones that are narrow or pinched in shape, with three incisors. The next slide contrasts the wolf with the Tasmanian wolf. The Tasmanian wolf has wide nasals and it has four incisors, which you wouldn't see from the side shot that the Pandas authors showed.

Slide 89 : Dogs and wolves both have pinched nasals and three incisors on one side of the jaw. Slide 90 : On the other hand, the Tasmanian "wolf" has wide nasals and four Right-click to download pdf. The next slide shows you a few of these skulls from underneath. The Tasmanian wolf has holes in the roof of its mouth, or palatal holes, which are lacked by the dog and the North American wolf. And the next slide shows the jawbones of these animals which have an opposite number of molars and premolar teeth between the Tasmanian wolf, and the dog and wolf.

Slide 91 : Viewing the skull from below shows the same pattern. Dogs and wolves do not have holes in the center of the palate the roof of the mouth. The Tasmanian "wolf" does have palatal holes. Slide 92 : Comparing the lower jaws shows another difference in tooth formula. Dogs and wolves have three molars and four premolars, whereas the Tasmanian "wolf" has the opposite, four molars and three premolars.

Also you'll see that Tasmanian wolf has a couple of structures at the back of the jaw which we call the reflected lamina. The term is not important, but it's just a significant feature that's not present in the dog and the wolf. Well, let's do our next comparison and look at the Tasmanian wolf as it relates to the kangaroo, which we know is a marsupial. In all the features that we've been looking at so far the kangaroo and the Tasmanian wolf correspond exactly with one exception, which is that the kangaroo doesn't have three premolars, and it doesn't have three premolars because the front of its face is modified in a way that many plant eating animals are modified.

They lose those front cheek teeth and they developed the very most front teeth in the skull into a cropping organism that they use to, a cropping organ that they use to crop grass and other plants. Except for that, the features of the two skulls correspond. The next one, if you like that here's the Tasmanian wolf against the possum, and although -- Slide 93 : Now the Tasmanian "wolf" is compared to a kangaroo -- according to modern biology a much closer evolutionary relative.

Pandas claims that "the determination of homologies [is] a matter of subjective judgment" p. If this is true, the comparative biologist should have difficulty finding the homologies that unite the Tasmanian "wolf" with the kangaroo. Padian shows that these two marsupials share the exact characters that were different between the placental wolf and marsupial "wolf. Corresponding author.

The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. The key to this interpretation is the meaning that Darwin assigned to the graphic elements points, lines, and spaces he used to construct the preliminary sketches and the diagram.

David Archibald, and Heather Brink-Roby.

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This ability to survive on a varied food source that no other mammal can eat, makes them stand apart from other mammals. Gum trees can survive drought better than most other trees. Due to this, koalas always have food and water available.

There are three kinds of mammals; placental mammals, marsupials and monotremes. Monotremes are very small in number while the rest of the mammals are in large numbers. The placental mammals are especially dominant and they are existing on earth for over million years. They have over species. The marsupials, on the other hand, have only about species, and are found in Australia and America. The Virginia Opossum is the only species of marsupial that inhabits North America.

After Gondwana was split up, Australia was separated and has remained so till today. Marsupials moved to Australia prior to the division and have been living separately from placental mammals. Both placental mammals and marsupials are covered in fur or hair. They are warm-blooded tetrapods.

The examples of marsupials are the koala, kangaroo, opossums, the Tasmanian Devil, wallabies, pademelons, quokkas, marsupial mice, bandicoot, wombats, the marsupial mole, numbat, bilby and musky rat-kangaroo. The examples of placental mammals are humans, whales, elephants, otters, horses, rodents, cows, deer, horses, cats, lions, tigers, dogs and many others.

Way of Giving Birth Placental mammals give birth to well-developed and nourished babies, after keeping them in the womb for a certain period, where they are nurtured and sustained through the mother's placenta. The placenta is an organ, which attaches the embryo of a placental mammal to the mother's blood, which provides the embryo with nutrients for growth.

Marsupials give birth earlier that placental mammals, but to an undeveloped offspring. They do not possess a placenta. The yolk and uterine secretions in the uterus provide nutrition for the embryo during its early development. When they are born, their eyes, ears and rear limbs are very poorly developed. They climb up to their mother's pouches so their front legs are more well-developed than the rest of their bodies at the time of birth. In the pouch, the offspring of marsupials attach themselves to the nipples and feed on their mother's milk and continue developing.

After they mature, they move out of the pouch. According to the Animal Diversity Web, some marsupial species are born with pouches, and others develop a pouch at the start of the reproduction process. The body temperature of an animal decides the metabolic rate within the animal.

The total energy expenditures during reproduction in marsupials is also lower than placental mammals. Teeth Tooth form varies substantially among species of marsupials. A simple characteristic to determine the members of the group is that the number of incisors in the upper jaw varies from the number in the lower. This number is same in almost all placentals. The numbers are for pairs of incisors, canines, premolars and molars in the upper and lower jaws respectively. Placental mammals usually have two sets of teeth.

One set grows in young animals and another set of adult teeth replace full sets of baby teeth. In these species it remains after the first birth and is called the median vagina. The 2 lateral vaginas receive sperm and the baby passes through the median vagina at birth.

It has long been believed that the arrangement of the birth canal and the small size of the 2 uteri are the reasons marsupial young are so small at birth. This is yet to be proven. In monotremes the yolk content of the egg is greatly reduced compared to that of reptiles, to the point where it is not sufficient to maintain development. Nutrients secreted by the endometrial gland are absorbed, probably being absorbed by the yolk sac, as occurs in the pre-attachment marsupial.

In the monotremes there are structural similarities to the progestational condition as seen in viviparous mammals in the luteal phase of the oestrus cycle. The allantois enlarges in the egg of Tachyglossus after the egg is laid, makes contact with the chorion then becomes highly vascular See Griffiths, It has been shown to cover half the inner surface of the shell, the vascularised yolk sac covering the remainder of the shell Semon, After the egg leaves the uterus of Tachyglossus there is no need for a nutritional route but the entire surface becomes vascularised as it essential for respiratory exchange, probably the reason for the vascularisation.

Monotremes were excluded from the character 'placenta' in the development of characters for a cladistic analysis Marshall, , which increases the apparent separation between the 2 groups. It has been suggested Gregory, there is a possibility that there is not a lot of difference between organogenesis continuing for 10 days in the uterus or in an externally held egg, as the products are so similar. The definition of oviparity is not consistent with the egg accumulating so much nutrient material after the shell has been laid down.

It has been suggested that the evolution of the eutherian villous allantoic placenta allowed a greatly increased exchange to take place thereby allowing the retention of the fetus during its major phase of growth Luckett, It has been suggested that as the marsupials didn't evolve a trophoblast that was able to mask histocompatibility antigens on its surface there could be only a brief attachment period in the gestation of marsupials, intolerance of the mother's immune system for the fetal tissues would cause any attachment that was longer to fail Moors, It was suggested that this is the reason for the very short-lived chorioallentoic placenta attachment, that is very intimate in Peramelidae Tyndale-Biscoe, The development of the thesis that a trophoblast layer differentiated that was able to mask the histocompatibility antigens on its surface was a major adaptation enabling gestation to be greatly lengthened in eutherian mammals, and that this was the main dichotomy with marsupials Lillegraven, ; Cox, There have been 2 attempts to test the hypothesis that the trophoblast of marsupials does not have the ability to mask histocompatibility antigens failed to support the hypothesis.

It has been acknowledged Lillegraven, but he suggests that as a result of the species used, Macropus eugenii being derived from an island population the animals may have been closely related so would not provide a good test of the hypothesis. Birth size The largest living marsupials are Macropus giganteus, the eastern grey kangaroo, and Macropus rufus, the red kangaroo. Females of these large kangaroos weigh about 28 kg, but at birth their single young weigh about mg, 0.

Among the marsupials, the birth weight is about mg, some of the smaller dasyurids weigh as little as 10 mg, though the smallest newborn marsupial, the honey possum, is about 4 mg. As with the placental mammals, where the young are much more advanced at birth, the young marsupials control the onset of their own birth. It has been suggested that the small size is the result of the short gestation of marsupials. Some marsupials do have a short gestation period, in some cases less than 2 weeks, but others have gestation periods that are longer than in placentals of similar size.

The main difference between the reproductive strategies of marsupials and placentals is the advanced stage of development at birth in placentals, most of the development having taken place in utero, which can occur because of the well-developed placenta. As a result, the young of many placentals are 'ready to roll' a very short time after birth, especially in the case of prey species, where they need to be ready to escape predators as soon as possible, or keep up with the herd.

In marsupials, most development takes place after birth. The females of both marsupials and placentals make investments in their young, the placental before birth, the marsupial after birth. In marsupials, the gestation is often short, but the lactation is long and complex, requiring large changes in the quantity and composition of the milk before the young can reach the stage of development attained by placental newborns. This difference has been exploited by kangaroos, that inhabit some of the driest parts of the driest vegetated continent, with the most erratic climate, the land of 'drought and flooding rain'.

When times are bad enough for the milk supply to dry up, they lose any young in the pouch, or out of the pouch but still depending on milk, or the pouch young leaves the pouch, the young that are still at an early stage of development in the uterus that has stopped growing, embryo diapause , resumes development. Because of their method of reproduction, the females of kangaroo species can have one young out of the pouch but suckling, another still-developing young attached to the other teat and the a third still in the uterus that stops development, embryonic diapause, until the more advanced of its larger siblings is weaned, when it resumes development.

Each teat produces milk with the composition and volume suitable for the stage of development of the young that feeds from it. When the 'joey' is weaned, the teat it has fed from since its birth 'resets', producing milk with the appropriate composition, and of the appropriate quantity, for the developing young in the uterus to attach to after it is born.

This allows the kangaroo population to quickly rebound after it has been reduced by severe conditions, such as a prolonged drought, during which reproduction ceases, but with an embryo that resumes development when required. Sexual Differentiation - placentals vs marsupials The external genitalia of marsupials and placentals are superficially similar, but there are differences in development.

Sexual differentiation occurs during gestation in the foetus of placentals, at which point the external appearance of both sexes is the same, hence the term 'the indifferent stage'. In male foetuses, the production of testosterone by the developing testes causes the genital tubercle to develop into a penis, and behind it, a scrotum. The same structures develop into a clitoris and the outer lips of the vulva respectively in female foetuses, where testosterone is normally absent.

The nipples and mammary glands are formed in both sexes and retained throughout life. The processes that occur after the indifferent stage is controlled by the 'sex determining region', the SRY gene, on the Y chromosome. When this gene is present, as in normal males, it causes the testes to develop from the gonads, the testosterone produced by the testes taking on the orchestration of the changes that occur to produce the rest of the male reproductive structures.

The foetus develops as a female if the the SRY gene is absent. In both marsupials and placentals, it is normal for an individual to have 2 X chromosomes in females, and 1 Y chromosome and 1 X chromosome in males. If there is an X chromosome but no Y chromosome, XO, the individual is female.

Development of sexual characteristics is different in marsupials, development of the scrotum beginning as 2 bulges in front of the genital tubercle. In female marsupials there is no structure equivalent to the outer lips of the vulva present in female placentals. The pouch and mammary glands don't develop in male marsupials. Male marsupials have a Y chromosome with an SRC gene, which directs the development of the gonads into testes, from which the testosterone secreted leads to the development of internal male genitalia, and the development of the genital tubercle into the male form.

The differentiation of mammary pouch and scrotum is not controlled by the developing testes. In genetic males, scrotal bulges develop many days prior to the stage at which the gonads can be distinguished as an ovary or testis, and in genetic females, the mammary glands and pouch also develop many days before the ovary and testis can be distinguished. The later production of sex hormones does not affect these reproductive organs. It is currently believed that in marsupials the external reproductive organs, such as scrotum, mammary glands or pouch, are probably controlled directly by the sex chromosome constitution of the tissues involved, especially the X chromosome Cooper, In normal male marsupials, the X chromosome is involved in the development of scrotal bulges, as well as being involved in the production of the mammary glands and pouch in normal females Renfrew et al.

Tammars that are genetically abnormal, XO individuals, have internal female organs but no external female organs, mammary glands or pouch, though they posses a well-developed scrotum, that is empty. XXY tammars have internal male reproductive organs and a well-developed penis, as a result of having a Y chromosome, but they have mammary glands and a small pouch in place of the scrotum, as they have 2 X chromosomes Sharman et al.

Physiological Differences - marsupials vs other mammals As with other mammals and birds, marsupials maintain a constant body temperature, the basal body temperature BBT , though at a different level than mammals and birds. The BBTs of the different animal groups ranges from 30o C in monotremes, Reptiles have a BBT of 30o C that they maintain by moving between sunlight and shade. The reason for the different BBTs of the various groups is not known, though it appears to be genetically determined.

The BBT of marsupials has as great an effect on their lives as does their reproductive mode.

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