Today mammals are considered one of the most advanced classes.This group is characterized by a number of important features.According to the known research in the world today there are more than five thousand members of the class.Although it is worth noting that this figure is very approximate, as scientists to this day are engaged in search of new species.
mammals and their distribution
mammals considered quite unique representatives of fauna.They are spread throughout the world.
members of this class can be found in almost all the major habitats of the Earth.These animals are beautiful creatures in hot, dry desert climate in the highland regions.They can be seen in the polar regions and the tropical rainforests.They occur even in an aqueous medium.
perhaps the only areas that are not populated by mammals are domestic territory of Antarctica and the deep part of the ocean.
Interestingly, the scope of monotremes animals (eg, the platypus) are clearly limited to the territories of New Guinea and Australia.Marsupials representatives extended to the islands of Oceania, as well as in Australia and in the territory of the Americas.Another interesting fact is that on the Australian continent inhabited only some placental mammals until the arrival of the first settlers.
mammals: the main features of a class
As already mentioned, this group of animals has a number of unique characteristics, showing the high level of organization:
- Almost viviparous mammals.
- females suckle their young with milk produced by glands in the specific (by the way, due to this fact of mammals got their name).
- representative of the class have a specific hair growth will sebaceous and sweat glands.
- for mammals is characterized by so-called homeothermy or warm-blooded - their body temperature does not depend on conditions and ambient temperature.
- particularly important feature of this group of animals is a well-developed brain, in particular, the final part of it.Here is the center through which the representatives tend to be very complex behaviors.
- In mammals formed the pinna, external ear canal, as well as all three auditory ossicles, which, incidentally, is a modified bone of the lower jaw.
- to members of the class are characterized by advanced four-chambered heart and left aortic arch, which provide separation of blood on the venous and arterial (for example, in reptiles, venous and arterial blood is mixed in the heart).
- distinctive feature can be considered and the alveolar structure of the lungs.
- Furthermore, there are differences in the structure of blood cells - red blood cells of these animals do not contain nuclei, but respiratory pigment.
- mammals have seven vertebrae in the neck.
- For members of this class are characterized by a kind of teeth (the incisors, canines, molars).Thus the teeth via roots immersed in the jawbone.
origin of mammals
Scientists believe that the ancestors of modern mammals were reptiles that appeared in the Paleozoic.These animals still retained some similarity with amphibians, in particular, the presence of skin glands and possibly a double occipital condyle.
especially close relatives of modern mammal-like species are considered.Representatives of this group were characterized by the presence of different teeth (molars, incisors and canines).Upper and lower jaw bone were joined by special, which turned into a mammalian auditory ossicles.But representatives of the extinct mammal-like in the Upper Triassic.
Already in the Jurassic period there was separation of live-bearing species from those members that have laid eggs.
actually form a clear theory of the origin of mammals can not be, because to this day, paleontologists and other scientists are actively research in this field.
