Two of the best known characteristics of animals belonging to the class of mammals, according to a fairly common definition among non-specialists, is that they do not lay eggs and that they have mammary glands. All of these are placentas and neonates, animals whose fetus grows protected and nourished in the mother’s womb, to which it is connected through the placenta. Then there are also mammals and marsupials that follow different embryonic development. But, in principle, no mammals do not lay eggs. approx.
Few famous animals are poorly adapted to animal systematics and attempts at strict classification as the platypus, also called the platypus, is a problematic by definition: an ovulating mammal. The compelling story of their classification—problematic from the start—is about solving a nearly century-old puzzle, which arrived in 1884 and is now considered a key step in changing the way naturalists understand the classification of animals. dealt with it, in Article – Commodity Recently, the magazine date of today.
The platypus – an animal endemic to northern Australia and Tasmania – has caused confusion among scientists in Europe since a dead specimen first arrived in England, in 1798, sent by Governor of the Australian state of New South Wales John Hunter. Astonished by that duck’s beak, thick fur and intertwined feet, some English naturalists suspected that this flesh – however, in a less than perfect state – could be a “real” animal. They suspected that it could have been made by some Japanese embalmer, some of whom were already known for certain at the time. production A fictional animal obtained from the union of fish tails and monkey heads.
The following year, the English botanist and zoologist George Kersley Shaw – who gave it his name platypus anatius – He was able to prove that it was a real animal, but further research among English naturalists was still hampered by the fact that there was not much to work on. The specimen that arrived from Australia was devoid of internal organs, a condition that precluded a study of the anatomy necessary for taxonomic classification, at the time based on the method presented 40 years earlier by the influential Swedish naturalist and academic Carl Linnaeus and based on similarities between organisms.
According to the five levels proposed by Linnaeus for classification (kingdom, class, order, genus, species), there were six classes within the animal kingdom, including mammals, birds, reptiles and amphibians. According to Linnaeus’ definitions, mammals suckle babies through the mammary glands, have teeth, breathe through two lungs, and usually have four limbs. They were often covered with hair and in some cases had tails. On the other hand, the birds laid their eggs covered with a shell of calcium carbonate and had wings. They had no external ears, no external testicles, no uterus, no thoracic membrane, and no bladder. Amphibians lay eggs that are membranous, usually, they do not have a membrane, and sometimes they have a “terrible poison”.
He says Linnaeus’ classification was very logical date of today, but had serious limitations starting from the moral assumption that all animals have always existed in their present forms. By denying any causal affinity between the different types, this assumption made the classifications arbitrary and it was impossible to determine whether and what characteristics were essential to the class. To try to solve the platypus riddle, following this approach, naturalists had no other way than to “catch” and group items together here and there, of different definitions, or guess exactly where the platypus was in creation.
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Theoretically, for Shaw and other English naturalists, it must have been mammals such as sloths, anteaters, and other toothless mammals, given the presence of fur. But there were many things that were not collected, and this animal in some respects continued to have the characteristics of a fish, a bird and a four-legged. And on top of all that, it was very unlike any other animal in particular. In 1800, the German naturalist Johann Friedrich Blumenbach conducted a more rigorous study, renaming this animal perplexed due to the lack of mammary glands. Ornithorhynchus paradoxus, which literally means “the contrast with the bird’s nose”.
Two years later, the Englishman Everard Home noted that the male platypus has two internal testicles, like a reptile, and a cloaca, that is, one opening in which the urinary, digestive and reproductive systems converge. This distinguishes the platypus from mammals in an “unusual way,” Home wrote, because it was believed at the time that the platypus was only found in reptiles, amphibians, and birds, and noted the egg-laying characteristic.
To completely change the classification approach was, in 1809, he published the book zoology philosophy by the French naturalist Jean-Baptiste Lamarck, who described living things as beings in a state of constant change rather than constant. Not only were they able to “acquire” new traits in response to certain environmental factors, but they could pass them on to offspring. Certain limitations of this theoretical model, which were later shown by Charles Darwin’s research, did not prevent naturalists from grasping the scope and implications of Lamarck’s studies: the possibility that, over time, a variety of animals would transform into another species.
Rather than classifying animals by drawing from different definitions, it was possible after Lamarck not only to trace the transformations of animals over time but also to identify the distinguishing characteristics of a class or system and which were not. French naturalist Étienne Jeffroy Saint Helier argued at that point that the platypus – due to the absence of mammary glands – should be included in an entirely new class of vertebrates, which he called monotremes (single), which means “single slot”. A short time later, in an effort to standardize Jeffroy St Helier’s claims, German anatomist Johann Meckel conducted further studies on the platypus and instead ended up complicating matters further.
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Meckel found that the male platypus has a venom gland, usually characteristic of reptiles and amphibians, but he also found, after all, that females have mammary glands. And this, in the eyes of naturalists, has suddenly brought the platypus back to resemble a mammal more than it had recently. In 1832, Scotsman Lauderdale Molly confirmed Meckel’s findings regarding the characteristics of reptiles in the platypus and drew attention to the characteristics of other mammals: both female and male platypus had membranes and were warm-blooded.
This set of features seemed to most scholars an insoluble contradiction. It was almost impossible to imagine that any creature could have functioning mammary glands and could lay eggs: it must be either one thing or another, and this will determine the membership of the platypus in mammals or something else. Many naturalists have formulated incompatible hypotheses. Meckel was convinced that the platypus gave birth to live children, while Geoffroy St Helier tended to lay eggs. Another naturalist, the Englishman Richard Owen, argued that the eggs remained inside the body.
Proof was needed, and that it did not come from Aboriginal people and Australian settlers, who also claimed to have seen platypus incubating their eggs. Over time, due to past negative experiences, naturalists learned not to believe this type of report. To solve the mystery, it was necessary to locate an egg or even capture and kill a pregnant female. Owen then asked the Australian curator, George Bennett, to shoot and analyze the animals to try to find an answer, but soon the number of Bennett’s failed attempts led to fear that the activity might lead to extinction rather than extinction. animal classification.
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It was Scottish zoologist William Hay Caldwell, aged twenty-five, on August 29, 1884, after four months of research on the northeastern coasts of Queensland, Australia, who closed the game and sent what date of today Identifies “the most important telegram written to the platypus”. After he managed to shoot a female platypus, he discovered that she had not only laid an egg, but another when he was able to catch it. He opened it and found the answer to the question that has preoccupied naturalists since 1798.
He then sent a letter to the annual meeting of the British Association for the Advancement of Science (British Association for the Advancement of Science), in Montreal. “Monotermis ovule, ovule of Miraplastic,” she said. In other words: platypus lay eggs, with large yolks, like birds and reptiles. But most of all, the embryos inside were already highly developed, with differentiated vertebrae and brains, indicating that the eggs remained in the parents’ body for some time before being laid and cared for. After the eggs hatch, the hairless pups cling to their mother and are breastfed.
Caldwell’s test proved that the platypus was undoubtedly a mammal, but it belonged to a system of its own, more primitive than the others. This system must have branched off long ago from the last common ancestor of mammals and reptiles, and thus developed new distinctive characteristics, without completely losing those of its past.