Mammalian Animals: Types, Characteristics and Examples

Mammals are that group of vertebrate animals that are distinguished because their females have mammary glands to feed their young. Mammalian animals make up the most abundant and widely distributed animal class on the entire planet, and it is the most studied thanks to the fact that humans are part of that group.

mammal animals

Mammals (Mammalia) are classified within the class of warm-blooded vertebrates, whose distinguishing characteristic is the possession of mammary glands with which they produce milk to feed their young. Most of them are viviparous (except for the monotremes: platypus and echidnas).

They are classified as the scientific classification or group of species descended from a common ancestor (monophyletic taxon or clade), that is, they all descend from the same ancestor possibly dating from the end of the Triassic period, more than 200 million years ago.

They are part of the synapsid clade, which also incorporates many "reptiles" related to mammals, such as pelycosaurs and cynodonts. At present some 5.486 species have been recognized, being 5 of them monotremata, 272 marsupials and the others, 5.209 placentals. As theriology, mammalogy or mammalology, the scientific discipline dedicated to the study of mammals is known.

Characteristics of Mammalian Animals

The group of living beings that make up the mammals is very diverse, despite the moderate number of varieties that constitute them when compared to other taxa of the animal or plant kingdom. The scientific study of mammals is by far the most in-depth in the field of zoology, undoubtedly due to the fact that the human species belongs to it. The heterogeneity of the mammal class is such that it would be difficult for a non-expert to clearly determine which species is a mammal and which is not.

To clarify this phenotypic, anatomical-physiological and ethological variety with an example, it is enough to associate some of its varieties, such as the human being (Homo sapiens), a rufous kangaroo (Macropus rufus), a chinchilla (Chinchilla lanigera), a whale white (Delphinapterus leucas), a giraffe (Giraffa camelopardalis), a ring-tailed lemur (Lemur catta), a jaguar (Panthera onca) or bats ("Chiroptera").

The class of mammals is a monophyletic grouping, since all its members share a succession of unique evolutionary variations (synapomorphies) that are not found in any other animal variety that is not part of said class:

It has sweat glands, altered like mammary glands, with the ability to secrete milk, a substance with which all mammalian offspring are provided. This is its primordial peculiarity, from which its name of mammals comes.
The jaw is made up only of the dental bone, a unique and exclusive quality of this entire class, forming the main attribute that serves to recognize the group.
It has seven vertebrae in the cervical segment of its spine; biological trait that is present in species as disparate as the mouse, the giraffe, the platypus or the blue whale.
The joint of the mandible with the skull takes place between the dentary and the squamosal, an equally unique and exclusive peculiarity of this class.
They have three bones in the middle ear: hammer, anvil and stirrup, except for monotremes, whose ear is reptilian.
Mammals have ear pinnacles, with the exception of whales, dolphins and others that live in the water and that, in their evolution, may have lost them due to hydrodynamic causes.
This class is the only extant animal species with fur present throughout all phases of its existence, and all species, to a greater or lesser degree, possess it (albeit in an embryonic state).
Just like their primitive ancestors, current mammals have only one pair of temporal pits in the skull, in contrast to diapsids (dinosaurs, current reptiles and birds), which have two pairs, and anapsids (turtles), which do not. they have none.
In addition to this skeletal distinction, and others of less significance (such as the relevance of the dental bone in the lower jaw and the ability of the teeth to perform different functions or heterodont condition), the primary features of mammals are the presence of fur and skin glands.

But despite these and other similarities that do not define a class, its variety is such that the existing disparities are more numerous, particularly in relation to external appearance.

Origin and evolution

Today's mammals come from the original synapsids, a group of amniotic tetrapods that began to appear at the beginning of the Permian, about 280 million years ago, and maintained their predominance over terrestrial "reptiles" until about 245 million years (beginning of the Triassic) back, when the first dinosaurs began to stand out. Motivated by their competitive supremacy, the latter caused the disappearance of most of the synapsids.

However, some survived, and their successors, the mammaliaforms, later became the true early mammals towards the end of the Triassic, about 220 million years ago. The oldest known mammals are, on the one hand, the multituberculates and, on the other, the australosphenids, groups that date back to the Middle Jurassic.

However, it must be borne in mind that the Mammalian organization, after an initial success in the Permian and Triassic, was almost totally replaced, in the Jurassic and Cretaceous (by about 100 million years), by diapsid reptiles (dinosaurs, pterosaurs, crocodilians, plesiosaurs, ichthyosaurs, mosasaurs, and pliosaurs), and it was not until the meteorite crash that caused the Cretaceous-Tertiary mass disappearance that mammals became diverse and achieved their predominant role.

The use of resources without having to compete with larger animals implied adapting to inhospitable areas with a regularly cold climate, to night routines, also with low temperatures and to which little lighting was added.

Throughout the evolutionary history of mammals, a succession of events occur that will define the obtaining of the traits that characterize the class. The homeothermic characteristic, that is, of regularizing their body temperature, is undoubtedly the quality that allows mammals a world without competition and abundant in high nutritional resources. It was thanks to her that they were able to occupy cold regions and, particularly, undertake nocturnal activities.

The capillary growth that served to protect the body from heat loss and the development of a vision suitable for low light were the other two events that helped in the occupation of these ecological niches until then without the presence of higher animals. The adaptations of the skeleton were the initial step to achieve greater energy effectiveness based on the increased use of resources and the reduction of spending.

The skull is becoming more effective, since its mass is reduced while conserving resistance and making its structures simpler while allowing the development and effectiveness of the muscles added to an increase in the brain (brain) and greater intellectual capacity.

The alterations of the skull also imply the formation of a secondary palate, the constitution of the bony chain of the middle ear and the specialization of the dental pieces. The jaw is formed from a single bone (the dentary) and this is the main feature to conclude if the fossil of an animal is part of the class of mammals, because of the typical loss of soft tissues through the fossilization.

The limbs progressively stop articulating on the sides of the trunk to do so below. In this way, while increasing the mobility of the animal, it reduces energy expenditure by lowering the requirements for locomotion and holding the body upright.

On their side, the internal pregnancy of the offspring and the power to provide them with sustenance for their initial age without having to look for it (milk), made it possible for the mothers to move more freely and with it a progress in their survival capacity, both particular as of the species.

Through all these evolutionary modifications, each and every one of the organic configurations, as well as the physiological processes, were involved. The biological apparatus, when specializing, requested greater effectiveness in breathing and digestion, promoting the improvement of the circulatory and respiratory systems with respect to physiological effectiveness, and that of the digestive system to achieve a greater nutritional benefit of food. These were other successes achieved by these animals throughout their evolution.

The central nervous apparatus gradually obtained a size and histological organization unknown in other animals, and the absence of lighting faced by nocturnal species was compensated by the development of the other senses, particularly hearing and smell. All of these evolutionary events were achieved in several hundred million years, after which we mammals have managed to control life on Earth.

Evolutionary Theory of Mammals

The thesis that mammals evolved from reptiles is apparently unanimously accepted, pointing out that their development was to take advantage of ecological niches to which it was previously impossible to adapt. Their evolution from synapsids ("mammalian reptiles") happened progressively over about 100 million years between the Middle Permian and the Middle Jurassic, with a huge explosion of species taking place in the Middle Triassic.

Its homeothermic quality was the starting point of this gradual process. When the original ancestors of mammals managed to regulate their body temperature, they were able to occupy geographical areas in which low temperatures made it impossible for ectothermic (cold-blooded) varieties to survive, thus managing to adopt nocturnal habits and benefit from the food resources that before they were beyond the reach of their predecessors.

For this purpose they had to alter their structures and functionalities, on the one hand for the preservation and exchange of heat with the environment, and on the other to adapt to the night environment. The development of a complex tissue that would protect them, of a locomotor system capable of saving energy during movement and reducing body area, and of sensory organs to improve essential capacities was the initial step to begin to control the new ecosystems.

By increasing mobility, it became necessary to save energy, for which they developed a more complex and efficient digestive system, which, while reducing digestion time, increased the level at which food was used. For this reason, the circulatory system became more powerful and specialized, bringing with it the improvement of the respiratory system, which increased its volume and adequacy of oxygen exchange.

In this chain of transformations, all the apparatus and organic systems evolved and specialized over a long period of more than one hundred and sixty million years. As a result of the momentous extinction of the dinosaurs (with the exception of their descendants, the birds) at the end of the Cretaceous, some 65 million years ago, and after a provisional period in which giant birds (Gastornis) predominated, mammals ended up prevail in the Cenozoic.

Social behavior

Furthermore, the high energy requirements of these animals determine their behavior, which, while varying substantially from one species to another, is usually aimed at saving energy to maintain body temperature.

While mammals that populate cold regions of the world have to prevent loss of body heat, those that live in hot, dry climates direct their efforts to avoid becoming overheated and dehydrated. The behavior of all of them, therefore, is channeled to sustain the physiological balance, despite the environmental conditions.

Mammals are usually present in all kinds of life forms: there are varieties of arboreal and other terrestrial habits, there are only aquatic mammals and other amphibians, and even those that spend their existence underground digging galleries in the sand. The styles to move are also varied, so: some swim, and others fly, run, jump, climb, crawl or plan.

Likewise, social behavior varies greatly among species: some live alone, others live in pairs, in small family groups, in medium-sized colonies, and even in huge herds of thousands. Furthermore, they are active at different times of the day: diurnal, nocturnal, twilight, evening, and even those, like the yapok (Chironectes minimus), that apparently do not display a circadian rhythm.

Anatomy and Physiology of Mammalian Animals

The synapomorphic aspects of the class of mammals have already been emphasized. All its species present them and they are additionally exclusive to the class:

The dentary as the exclusive bone of the jaw, which is coupled with the squamosal in the skull.
Bone chain of the middle ear: malleus (malleus), incus (incus) and stapes (stapes).
Fur on his body area.
Mammary glands that produce milk.
Seven vertebrae present in the cervical portion of the spine.

Teeth are composed of substances that are not part of the bone system, but rather the covering of an organism or organ, such as skin, nails and hair. The material from which the mass of the tooth is made is ivory or dentin, which is generally covered on the outside by another very hard component, the enamel, while at the base of the tooth the outer covering is made up of a third substance. called cement.

In mammals, the teeth are always embedded in the bones of the skull that comprise the mouth, which are, above, a pair of maxillae and a pair of premaxillae, and below, a mandible or jaw, which is directly attached to the jaw. the braincase.

The latter, for its part, joins the dorsal spine through a pair of prominences, or existing condyles on either side of the orifice through which the spinal cord enters to join the brain.

Although the number of vertebrae in the backbone fluctuates greatly according to species, there are seven cervical or neck vertebrae in all mammals, excluding sloths that can have up to 10 and manatees that only have six. . However, added to this, there are other characteristics related to these species by which we can recognize them as part of the taxon:

Mammals are recognized as the only class of animals that have a single bone in each jaw, the dentary, directly attached to the skull. The jaw bones of reptiles became two of the three bones that make up the bony chain of the ear, the hammer (joint) and the anvil (square). The stapes comes from the only bone that reptiles show in the ear, the columella.
The teeth have become highly specialized by virtue of eating habits, and are generally replaced once in a lifetime (diphyodontia).
There is a secondary palate which has the ability to divide the passage of air to the trachea from the passage of water and food to the digestive organs.
The diaphragm is a muscle structure that divides the thoracic chamber from the abdominal chamber and helps in digestive and respiratory performance. It is only found in mammals and all species have it.
The heart is divided into four chambers and in adults only the left aortic arch is developed.
Red blood cells are anuclear cells in most varieties of mammals.
The cerebral lobes are quite differentiated and the cerebral cortex highly evolved, with pronounced protuberances more evident in species with greater intellectual aptitude.
From the very moment of the constitution of the zygote by the sexual chromosomes, the sex is determined: two different in males (XY), two identical in females (XX).
Fertilization is internal in all species.
All varieties are endothermic, which means that they can generate heat with their body, and, additionally, most are homeothermic, which means that they can maintain their temperature within a specific range. Only monotremes show some limitations of this ability.

Animal Skin Mammals

The skin, usually dense, is made up of an outer layer or epidermis, an inner layer or dermis, and a subcutaneous layer filled with fat whose utility is to protect against heat loss, since mammals are homeothermic species. Two of the synapomorphies of the mammalian class are found in the skin: the fur and the mammary glands.

The skin is directly involved in animal protection, thermoregulation, waste elimination, animal communication, and milk production (mammary glands). Other horny cutaneous bodies present in mammals include nails, claws, hooves, horns, and the beak of platypuses.

Locomotor apparatus

The locomotor system is the intricate network of tissues of a different nature that allow the maintenance of the animal's body and its movement.

Axial Skeleton:

Head: skull and jaw.
Vertebral Column: cervical, thoracic, lumbar, sacral and caudal or coccygeal vertebrae.
Thoracic Chamber: sternum and ribs.

Appendicular skeleton:

Shoulder Girdle: clavicle and shoulder blades or scapulae.
Former Members: humerus, ulna, radius, carpus, metacarpus and phalanges.
Pelvic girdle: ilium, ischium and pubis.
Hindquarters: femur, patella, tibia, fibula, tarsus, metatarsus and phalanges.

In addition to this, there are other bony bodies such as the bones of the hyoid apparatus (support of the tongue), the middle ear, the penile bone of certain carnivores and even the cardiac bones of certain bovids in which the new bone material for cartilage is created. cardiac. In addition to the bone system, the musculoskeletal system is made up of the muscular system and the joint system.

Digestive apparatus

The digestive system is made up of an entrance duct, or esophagus, an intestinal tube through whose end the waste is discarded to the outside and a stomach, plus a set of attached glands, where the most important are the liver and the pancreas.

With a few exceptions, before food enters the digestive system, it is first prepared by chewing, which is performed by the teeth, which are hard organs that protect the mouth and whose number and shape vary significantly depending on the diet of each species.

In most cases there are, first of all, some cutting teeth, called incisors, followed by fangs, or canines, which are suitable for tearing, and, finally, others that are useful for crushing and grinding, which They are called teeth or molars.

In general, mammals have a succession of teeth in their youth and later they are replaced by others. The digestive system of mammals is a tubular visceral system in which food is subjected to a deep treatment to get the most benefit from its nutrients.

Through the digestive transit from the time it is ingested until it is expelled, the food is subjected to a strong process of mechanical and chemical decomposition in which a series of strategically concatenated organs and tissues participate.

Diagram of the Digestive Transit:

Mouth: chewing and insalivation with assimilation of few components.
Esophagus: transit with little assimilation.
Stomach: mechanical and chemical digestive process with partial assimilation of nutrients.
Small intestine: mechanical and chemical digestion (enzymatic and bacterial) with considerable digestion of nutrients.
Large intestine: mechanical and chemical (bacterial) digestion with assimilation of water and mineral salts, primarily.
Year: Expulsion.

The physiology and anatomy of this organ system is largely determined by the animal's diet.

Respiratory and Circulatory Apparatus

These two systems are responsible for the exchange of gases and their distribution throughout the body. Mammals inhale oxygen from the air, which is sucked in through the respiratory tract (mouth, nose, larynx, and trachea) and is distributed through the bronchi and bronchioles to the entire saccular system, which is made up of the pulmonary alveoli.

The blood from the tissues carries carbon dioxide and upon reaching the alveolar capillaries, discards it while taking in oxygen. This will be conducted back to the heart and from there to all tissues to provide them with the gas required for cellular respiration, returning to transfer the remaining carbon dioxide to the lungs.

The design and operation of all these organs and tissues is completely synchronized to make the process profitable, particularly in aquatic or subterranean varieties where the oxygen supply is restricted.

Nervous System and Sense Organs

The nervous apparatus is an intricate conglomerate of highly specialized cells, tissues and organs whose mission is to perceive stimuli of various kinds, convert them into electro-chemicals to drive them to the brain, decipher them here and send a response that will be communicated again as electrochemical signals. -chemical to the organ or tissue compromised in its execution.

The nervous system is basically schematized as follows:

Central Nervous System:

Encephalon: Cerebrum, cerebellum, and brainstem.
Spinal cord.

Peripheral nervous system:

Nerves.
neural ganglia.

Each sense organ, on its side, is a body with abundant nerve endings that has the ability to decipher external stimuli into information to link the individual with their environment. In general, smell, hearing, sight and touch are the most important in mammals, although in certain groups, other sensitivities such as echolocation, magnetosensitivity or taste are more relevant.

Reproduction

In the majority of mammals, the separation of the sexes is present and reproduction is of a viviparous nature, excluding the group of monotremes, which is oviparous. The evolution of the embryo is accompanied by the formation of a succession of embryonic appendages, such as the chorion, amnion, allantois and yolk sac.

The hair of the chorion, together with the allantois, stick to the wall of the uterus giving rise to the placenta, which is attached to the embryo through the umbilical cord, and it is through it that substances from the body circulate maternal to fetus.

The gestation period and the number of offspring per litter change a lot according to the groups. Regularly, the larger the size of the animal, the longer the gestation period and the lower the number of offspring. Most mammals provide their children with parental attention.

Finally, its way of reproducing is equally typical of mammals. Although certain species are oviparous, that is, the fertilized ovum emerges to the outside forming an egg, in the vast majority, the embryo evolves inside the mother's body and is born in a relatively advanced condition. From there comes an initial classification of the group in mammals that aovan (lay eggs) and viviparous mammals.

The second group is called therians, a word that derives from classical Greek meaning "animals", and those that are oviparous, prototherians, which means "first animals", since the available fossils make it possible to suppose that the primitive mammals that emerged in the world were part of this category.

Even within the therians, it is necessary to differentiate between those mammals whose children are born in a precarious developmental condition, for which they have to spend some time in the bag that the female has in the skin of the belly, and the others in which they do not. such uniqueness occurs.

Those that are indicated first are the metatherians (also called marsupials), which means, "the animals that arrive behind", those that continue the prototherians, and those that appear last are the eutherians or placental mammals. In the class to which we dedicate ourselves, these make up the vast majority.

Animal Diversity Mammals

Simply equating the most important animal species that ever lived, with its 160-ton blue whale (Balaenoptera musculus) and Kitti's hog-nosed bat (Craseonycteris thonglongyai), regarded as the tiniest mammal whose adults only weigh 2 grams, we can see that the difference between the body masses of the largest and smallest volume species is 80 million times.

The great adaptability of the individuals that make up this class has led them to populate all the ecosystems of the globe, which has given rise to a multiplicity of anatomical, physiological and behavioral distinctions, transforming them as a whole into one of the predominant groups on Earth.

They have been able to conquer the green mantle of the jungle and the subsoil of the deserts, the icy polar ice and the temperate tropical waters, the unbreathable environments of the high peaks and the fruitful and vast savannahs and prairies.

Some can crawl, others jump while others can run, swim or fly. Many of them are able to benefit from the most diverse repertoire of food resources, while others specialize in specific foods. These infinity of circumstances have forced these animals to evolve, acquiring a multiplicity of forms, configurations, capacities and performances.

It is curious to confirm how, in numerous cases, species that are very distant from each other, both geographically and phylogenetically, have followed similar morphological configurations, physiological tasks and behavioral aptitudes. This peculiarity is known as convergent evolution. The resemblance between the head of a gray wolf (Canis lupus, a placental) and a thylacine (Thylacinus cynocephalus, a marsupial) is striking, with both species being so far apart phylogenetically.

Adaptation to Very Diverse Environments

The great variety of mammals results from an exceptional ability to adapt that has enabled them to spread over much of the planet's areas. The practices developed by each variety to achieve adaptation to the environment progressed autonomously.

In such a way that, while some species such as the polar bear (Ursus maritimus) sheltered from the cold with a thick coat of fur that appears white when reflected by light, others such as pinnipeds or cetaceans managed to do so by producing a thick layer of fatty tissue under your skin.

On other occasions, varieties that are very distant phylogenetically resort to similar mechanisms for their adaptation to similar circumstances. The evolution of the ear pinnae of the fennec fox (Vulpes zerda) and the African elephant (Loxodonta africana) to increase the heat exchange area and benefit homeostasis is an obvious example.

The return to water by animals that were only terrestrial is another manifestation of the adaptive capacity of mammals. Different groupings of the class have developed completely autonomously to return to the aqueous environment and take advantage of the sea and river niches.

To mention some examples that expose the versatility of the mechanisms that have developed to adapt to life in the water, two orders whose varieties are precisely aquatic, Cetacea and Sirenia, the families of carnivores Odobenidae (walrus), Phocidae (seals) and Otariidae (bears and sea lions), mustelids such as the sea otter (Enhydra lutris) and other river varieties, rodents such as the beaver (Castor sp.) or the capybara (Hydrochoerus hydrochaeris), the Pyrenean desman (Galemys pyrenaicus), the hippopotamus (Hippopotamus amphibius), yapok (Chironectes minimus), platypus (Ornithorhynchus anatinus)…

Just like birds and the extinct pterosaurs, a group of mammals, bats have had the ability to move through active flight. Not only have they been able to develop essential anatomical configurations such as wings, but they have also developed physiological adaptations that enable energy savings, thus counteracting the enormous expense involved in flying.

These animals, additionally, having to perform in the most rigorous darkness of the night and inside the caves, have developed by optimizing the echolocation system that enables them to accurately perceive the world around them. Moles and other burrowing species, primarily rodents, lagomorphs, and certain marsupials dwell underground, some remaining entombed for most of their lives.

They have managed to occupy the underground space, but the perception of the external world, the underground movement, the links between individuals and the nutritional and respiratory needs have been some of the issues that they have had to solve throughout their evolution, experimenting through of it important transformations and indispensable specializations.

And this specialization in turn transforms these animals into those with greater power and greater vulnerability. Throughout its evolutionary progress, there have been many species, families and even entire orders that have become extinct when the natural environment in which they lived has changed.

Consequently, today, perhaps another mammal, Homo sapiens, has been the direct or indirect cause of the disappearance of a large number of other species. In such a way that the decline of virgin hunting grounds is causing the disappearance of the Iberian lynx (Lynx pardina), the most threatened feline on the planet, indiscriminate deforestation is about to cause the extinction of the giant panda (Ailuropoda melanoleuca) or the incorporation of foreign varieties such as cats, dogs or foxes, with the marsupial cats of Australia.

Ecological Paper

It is as difficult to try to summarize the ecological role played by the almost 5.000 varieties of mammals as it is to try to do so in relation to all living things and their environment. The variety of occupied ecosystems, biological and social behaviors as well as anatomy and morphological adaptations of all of them, causes a versatility ignored in any other animal or plant group on the planet, despite being the least numerous group in terms of diversity.

On the other hand, the high energy requirements demanded by the need to keep their body temperature constant notoriously restrict the scope of the interactions of these species with the environment. In general, it is considered that predators have an enormous impact on the number of their prey, which in a high number are other mammalian varieties, to the extent that precisely these can in some cases be the food base of many others.

There are species that, with just a few individuals, create large-scale ecological interactions, such as beavers and the waterways they block. Other species, however, exert immense pressure on the number of individuals that congregate, as is the case with the vast herds of herbivores found in prairies or savannas. A separate consideration is the interaction humans have with the entire ecosystem, whether populated by humans or not.

Geographical distribution

Mammals are considered to be the only animals capable of spreading over almost the entire earth's surface, excluding the frigid lands of Antarctica, despite the fact that certain species of seal populate its coasts. On the opposite side, the area where the hispid seal (Pusa hispida) is distributed reaches the outskirts of the North Pole.

Another exception is that made up of remote islands, far from continental coasts, where there are only cases of species carried by man, with the customary ecological disaster that this entails. In land areas they are achieved from sea level to a height of 6.500 meters, occupying all available biomes.

And they do it not only on the surface but also below it, and even above it, both through the branches of the trees and having undergone anatomical alterations that allow them to fly actively, as occurs with bats, or passively, as in the case of colugos. gliders and flying squirrels.

The waters have also been occupied by these animals. There is evidence that, everywhere on the planet, mammals settle in rivers, lakes, wetlands, coastal areas, seas, and oceans, reaching depths greater than 1000 meters. Indeed, cetaceans and marine carnivores are two of the most widely distributed mammal groups on the planet.

As taxonomic groups, rodents and bats, added to being the most numerous in varieties, are the ones that have inhabited the largest areas, because with the exception of Antarctica, they can be located throughout the world, including on islands not so close to the coast, whose colonization is impossible for other land species.

On the other hand, the orders with few species are those that are least distributed globally, with particular mention to two of the three orders of American marsupials that are restricted to a more or less limited area of the southern subcontinent, particularly the monito del monte (Dromiciops australis), solitary member of the order Microbiotheria.

Sirenians, although with restricted areas for each of the few species with living specimens, can be found in Asia, Africa, Central and South America, and Oceania. Certain orders are typical of specific continents, their evolution being isolated from the rest of the mammals, as is the case of the cingulates in South America, the tubulidentates in Africa or the dasyuroformes in Oceania, to name a few examples.

If we exclude humans (Homo sapiens), and the animals related to them, both domesticated and wild, among the other species, perhaps the gray wolf (Canis lupus) and the red fox (Vulpes vulpes) are the most widely distributed, since their specimens are found in most of the northern hemisphere. Similarly, the leopard (Panthera pardus), found from Africa to India, and the puma (Puma concolor), from Canada to southern Patagonia, are two varieties with very vast distribution areas.

The lion (Panthera leo), the tiger (Panthera tigris) or the brown bear (Ursus arctos) are other carnivores that have spread over numerous regions of the earth until more or less recent times, despite the fact that their distribution areas have been gradually reduced until it fragmented and ended up disappearing from a large part of them today.

In contrast, a much larger number of them populate limited surfaces and not all because they have been diminished for some reason, but because throughout their evolutionary process they have not been able or have not been required to expand beyond the currently occupied.

Even so, not only certain varieties have been the ones that have become extinct from relatively vast areas of the planet, but certain entire groups of mammals that once inhabited specific continents have not been able to survive until today.

Equidae, for example, which used to live in the wild in almost the entire world, today only exist in freedom in Asia and Africa, having been reintroduced by man in a domestic state in other regions of the planet. On the other hand, the accidental or intentional introduction of some species in areas where they did not exist has put native varieties at risk and has even caused the extinction of them.

Number of Species by Countries

Neither the total number of species, nor all the countries are detailed in the following section about the number of mammal species globally:

Africa: Democratic Republic of the Congo (430), Kenya (376), Cameroon (335), Tanzania (359).
North America: Mexico (523), USA (440), Canada (193).
Central America: Guatemala (250), Panama (218), Costa Rica (232), Nicaragua (218), Belize (125), El Salvador (135), Honduras (173).
South America: Brazil (648), Peru (508), Colombia (442), Venezuela (390), Argentina (374), Ecuador (372), Bolivia (363).
Asia: Indonesia (670), China (551), India (412), Malaysia (336), Thailand (311), Burma (294), Vietnam (287).
Europe: Russia (300), Turkey (116), Ukraine (108).
Oceania: Australia (349), Papua New Guinea (222).

Relationship between humans and other mammals

By constituting the human in that mammal whose superior evolution led him to become a thinking being, he managed to have dominion not over his environment but over all the other species present. From this dependency a series of facts emerge that can be of positive or negative significance and which we refer to below.

Negative aspects

At times, humans have considered many species negative under practical analysis but at other times it has been under unfounded fears. Certain varieties of mammals eat grains, fruits, and other plant sources, taking advantage of human crops for food.

On their side, carnivores can be considered a threat to the existence of livestock and even of man himself. Other mammals live in urban and suburban areas causing certain problems for the population: car accidents, destruction and rendering useless of material goods, contagious and parasitic pests, etc. It should be noted that this group includes both wild or quasi-wild animals and domestic animals.

Among the animals that can serve as examples of situations of real or potential danger to humans are kangaroos in Australia, raccoons in North America or foxes and wild boars in Mediterranean Europe. In addition, other varieties of mammals, regularly in close relationship with humans, are closely linked to diseases such as rabies, bubonic plague, tuberculosis, toxoplasmosis or leishmaniasis.

To this we must add that domestic varieties, particularly species incorporated into new ecosystems, have caused and are causing authentic ecological calamities in the local flora and fauna, which indirectly influences negatively not only humans, but also the rest of the world. of the living species of the planet, be they animals or plants.

In many oceanic islands, the incorporation of domestic animals such as dogs or cats, goats or sheep has implied the total or partial extinction of numerous species.

Positive aspects

Mammals are considered as a relevant economic resource for human beings. Numerous species have been domesticated to obtain from them resources to feed themselves: the milk of cows, buffaloes, goats and sheep, the meat of these varieties and others such as pork, rabbit, horse, capybara and other rodents and even the dog in some areas of Southeast Asia.

On the other hand, we have used mammals for transportation or for tasks that require strength or other capabilities that man does not have: equidae such as the donkey, the horse and its hybrid the mule, camelids such as the llama or the Dromedary, bovids such as the ox or the yak, the Asian elephant or the dogs that pull sleds are examples that we can cite.

However, before achieving this supremacy, it is very likely that the original mammals had to transform into nocturnal animals to avoid competition with the dinosaurs. And it is possible that, to overcome the cold at night, they began to develop endothermy, that is, the internal control of their body temperature (commonly called "warm blood"), thanks to the appearance of fur and of the sebum that isolates it (the secretion of the sebaceous glands), and to the perspiration of the sweat glands.

As endothermy developed, true early mammals honed their competitive fitness against other terrestrial tetrapods, as their constant metabolism enabled them to withstand harsh weather, grow faster, and produce more offspring. In addition to the skeletal and other aspects already mentioned, the presence of fur and skin glands, which gave them predominance on land since the Paleocene, mammals show other less distinguishing features.

Fibers and leathers can be obtained from other mammals for the manufacture of clothing, footwear and other implements: the wool of sheep, alpacas, llamas and goats, the leather of slaughtered cattle for consumption, or that of fur animals raised in captivity for For this purpose, they can serve as examples.

Other mammals have been domesticated to be pets, the dog being undoubtedly the closest to man on almost the entire planet and the most versatile (herding, rescue, security, hunting, show...). There are others such as the cat, the hamster, the guinea pig, the rabbit, the ferret, the short tail, and certain primates that are among the pets with the greatest global expansion.

Hunting is another activity from which humans benefit from mammals. From the dawn of humanity to the present day, hunting has been, and continues to be, a vital food resource in certain human societies. Likewise, certain mammals are domesticated for sporting or gaming activities: practices such as horseback riding involve the use of one of the most well-known and appreciated varieties of mammals in almost all cultures and civilizations: the horse (Equus caballus).

Both circus attractions and zoos are also two initiatives in which man takes advantage of mammals and other species. Also certain wild mammals mean a direct benefit to man without him participating in anything. In other words, bats are of great help against insect pests in plantations or populated areas, thus also regulating the carriers of some contagious and parasitic diseases that would place the health of the inhabitants at serious risk.

Conservation

In the last five hundred years, more than 80 different species have disappeared. The exaggerated exploitation of the land, the devastation of the habitat, the disintegration of the territories through which they are distributed, the incorporation of exotic species and other influences exerted by man are a threat to mammals throughout the planet.

Today, the International Union for Conservation of Nature and Natural Resources (IUCN) estimates that nearly 1,000 more species are at serious risk of extinction. Several factors contribute to the potential disappearance of species, including:

There are species that are unusual by nature, and their low number of specimens is a relevant element of risk.
Likewise, those that require vast territories are under threat, this time due to the loss of spaces free from human presence and territorial fragmentation, as in the case of the Iberian lynx.
Any species that is a danger to humans or to their goods or properties is severely threatened by the harassment and persecution to which they are subjected, as is the case of the thylacine.
The wild varieties that are used as food or economic means by man, are regularly at critical levels, an example of this are the whales and rhinoceroses.
Obviously, climate change that alters the habitat is a danger, not only for mammals but for all living things on the planet.

Examples of Animals Mammals

Mammals are living species that have been characterized because females feed their young through mammary glands that produce milk. Here is a list of some of the most representative mammals of the class.

Whale: It is a cetacean, this is a mammal adapted to life in the water. In contrast to fish, cetaceans have lung breathing despite having a body similar to that of those, since both have hydrodynamic physiognomies.

Horse: This is a perosidactyl mammal, that is, it has odd fingers that end in hooves. The configuration of its legs and hooves are not found in any other organism. Its diet is herbivorous.

Chimpanzee: Primate of great genetic proximity to man, which indicates that the two species have a related ancestor.

Dolphin: There are varieties of oceanic dolphins and river dolphins. They are cetaceans, just like whales.

Elephant: It is the largest land mammal, weighing over 7 tons, despite averaging a height of three meters. Some elephants live up to 90 years. They can communicate by making vibrations in the ground.

Cat: Although the dog seems to be the quintessential home animal, the cat has lived with humans for about 9 thousand years ago. They have enormous dexterity, thanks to the flexibility of their limbs, the use of their tail and their "righting reflex" that allows them to turn their body in the air when they descend and thus always perch on their legs. Due to their stupendous plasticity, they withstand falls from considerable heights.

Gorilla: It is the largest of the primates and inhabits the African forests. Its diet is herbivorous and its genes are 97% similar to those of humans. They can reach a height of 1,75 meters and their weight can rise to 200 kilograms.

common hippopotamus: Semi-aquatic mammal, that is, it spends the day in the water or in the mud and only at dusk does it come ashore in search of herbs to feed on. There is a related ancestor between hippos and cetaceans (whales, porpoises, and others). Their weight can reach three tons, and yet, thanks to their powerful limbs, they can run fast, despite their great bulk, and at a speed similar to that of an average human being.

GiraffeIt is an artiodactyl mammal, meaning its limbs have an even number of toes. Its main presence is on the African continent and it is the tallest terrestrial mammal, reaching almost 6 meters. It inhabits a variety of ecosystems, such as plains, grasslands, and open forests. Its stature is believed to be an evolutionary adaptation that enables it to reach tree leaves that are out of reach of other animals.

Sea lion: It is a sea mammal, from the same family as seals and walruses. Like other marine mammals, it has fur on certain areas of the body, such as around the mouth, and a layer of fat to contain heat loss.

Lion: Feline mammal that lives in sub-Saharan Africa and northwestern India. It is a species at risk of extinction, so numerous specimens are kept in reserves. It is a carnivorous beast, a predator primarily of other large mammals such as wildebeests, impalas, zebras, buffalo, nilgós, wild boars and deer. In order to obtain their food, these animals usually hunt in groups.

Bat: They are known as the only mammals that have the ability to fly.

otters: Carnivorous mammals that dwell primarily in the water, but did not lose their fur like other aquatic mammals. Their diet is based on fish, birds, frogs and crabs.

Platypus: Monotreme, this is one of the few mammals (like echidnas) that lay eggs. It is toxic and attractive due to its appearance, since, despite the fact that its body is covered with hair like most mammals, it has a snout very similar to the beak of a duck. Its presence is only known in eastern Australia and on the island of Tasmania.

Polar Bear: It is considered one of the largest existing land mammals. It lives in the cold regions of the northern hemisphere. Its body has adapted to low temperatures thanks to several layers of hair and fat.

Rhino: They are mammals that live in Africa and Asia. They are easily recognized by the horns on their snouts.

Human being: Humans are part of the class of mammals and a large proportion of the general traits of all of them are equally shared by humans. Human body hair is the evolutionary trace of the fur of other apes.

Tigre: Feline mammal that lives in the Asian continent. It is an important predator, not only of modest mammals and birds, but also of other predators such as wolves, hyenas and crocodiles.

Fox: Mammals usually solitary life. Their mammary glands are overdeveloped. As part of his attack and defense system, he has superior hearing as well as highly evolved vision to see in the dark.

Dog: It is a species of the wolf order, of the canidae family. More than 800 breeds of dog are known, which openly exceeds any other species. Each variety has notable differences in all its traits, from hair and size to behavior and lifespan.

Other examples of mammals are: Almiquí, Koala, Alpaca, Leopard, Squirrel, Llama, Armadillo, Raccoon, Kangaroo, Porpoise, Pig, Orca, Deer, Grizzly Bear, Coati, Anteater, Weasel, Sheep, Rabbit, Panda, Devil of Tasmanian, Panther, Seal, Rat, Cheetah, Mouse, Hyena, Mole, Jaguar, Cow, etc.

The Evolutionary Success of Mammalian Animals

Fossil discoveries in recent times have revealed that, before a meteorite ended life and the dominance of the dinosaurs, mammals were already laying the foundations for their future dominance in the world. Researchers have often wondered when and how mammals became the preponderant vertebrates. However, until then not enough fossils had been found in this regard.

In the recent 15 years there have been a succession of discoveries that have offered information about the diversification and triumph of this class and that clarify the role played by the disappearance of the dinosaurs. Such discoveries have revealed that mammals originated much earlier than imagined and that they developed a range of specializations during the dominance of the dinosaurs. The sudden extinction of the dinosaurs paved the way for placental mammals.

On a winter evening in early 1824, the English scholar and theologian William Buckland addressed the Geological Society of London. The room stirred with anticipation. Buckland had gained fame for his impassioned lectures at Oxford University, in which it was said that, dressed in all his academic garb, he would pass on animal parts and fossils among his ardent students.

For years the rumor had circulated that it housed huge fossil bones, found by stonemasons in the scree of the English countryside. After nearly ten years of study, he was ready to release it publicly. He told the audience that these bones were part of a remote animal similar to a lizard but much older than any reptile today, which he called Megalosaurus. The crowd was absorbed. Buckland had introduced the first dinosaur.

That sunset was a pivotal moment in the history of science, sparking a fascination with dinosaurs that continues to this day. But what tends to be forgotten is that on the same date Buckland made another revelation; of much smaller magnitude, but equally revolutionary. Through the study of the other fossils found together with the megalosaurus in the scree, he analyzed the "amazing" finding of two modest mammalian snouts, similar in size to the jaws of a mouse.

Until now, scholars considered mammals to be of more recent date and to have emerged much later on the geological scale, after the decline of lizards and gigantic salamanders. The two tiny jaws bore typical mammalian canines and were the initial clue that the history of this class was much older.

Those snouts posed a succession of puzzles: How old were the mammals? What were they like and how did they manage to live through the long dominance of the dinosaurs? How did its features (skin, mammary glands, larger brain, complex dentition, and developed senses) emerge? And why was one group, the placentals, which were known for giving birth to more developed offspring and today comprising more than 5.000 species, from tiny bats to gigantic whales, able to conquer the world?

Almost two centuries after Buckland's conference, these questions continued to be difficult to answer, given the very low number of fossils of these early mammals. But in the last fifteen years there have been many paleontological discoveries that, after all, are making it possible to delineate its evolution, from the tiny vermin that dwelt in the shadow of the megalosaurus to the amazing range of today.

Humble Beginnings

Like many dynasties, mammals originated from a modest cradle. In scientific parlance, in the organization of the tree of life, the zoological class of mammals includes monotremes (oviparous), marsupials (carrying their tiny young in a pouch), and placentals, as well as all of the descendants, now disappeared, of the common ancestor.

The early animals whose appearance and behavior resembled that of modern mammals were a diverse grouping called the mamaliaforms, a very apt name for the closest relatives of true mammals. They came from the cynodonts, primitive varieties that maintained many reptilian aspects.

Origin of the Mammalian Brain

A more sophisticated sense of smell and touch may predate the evolution of the mammalian brain. The analysis of the fossilized cranial remains of animals prior to the initial mammals indicates that the areas of the brain linked to smell and touch, as well as neuromuscular harmonization, promoted the evolution of the brain in the evolutionary path that gave rise to mammals.

Examinations of fossils from about 190 million years ago were carried out, specifically of Morganucodon and Hadrocodium, ancestors of mammals, obtained from a Jurassic fossil deposit in China. Both had a larger brain than expected for specimens of their time and in proportion to the mass of their body.

Although the external features of the skulls of these extinct varieties had been analyzed for years, their internal features were unknown. Through high-resolution computerized axial tomography (CAT), researchers have now been able to create a virtual prototype of the brains they housed. The casts matched CT scans of fossils from 12 other varieties, including cynodonts, early reptiles that predated mammals, and nearly 200 present-day mammal species.

Based on such comparisons, it has been concluded that, in Morganucodon and Hadrocodium, the brain surfaces that direct the senses of smell and touch, as well as neuromuscular harmonization, had undergone more advanced development than the rest of the brain. The presence of a more accurate sense of smell and touch may have been instrumental in helping mammals survive and thrive at the earliest stage of our evolutionary history.

Animals Mammals that have disappeared from South America

The most recently found fossils in the Chilean Andes are references to unique mammals that once roamed South America. Such discoveries are disrupting existing ideas about geological events on the continent.

At the edge of a vast grassland, two hoofed, horse-like herbivores, a notoungulate reminiscent of an antelope, and a ground sloth, calmly feed, unconcerned by the threat that awaits them. Also engrossed are the chinchilla and a tiny mouse-like marsupial nibbling on seeds in the vicinity.

Suddenly, catastrophe strikes: one of the cracked, snow-covered volcanoes on the horizon erupts. A torrent of muddy ash is thrown down its steep slopes. Some time later, that cloudy mass invades the plains and buries the unsuspecting animals on its way.

For the animals that were buried, this volcanic torrent was catastrophic. For paleontology, by contrast, it would turn out to be lucky. Tens of millions of years after the premature demise of those mammals, the exhuming strength of orogenesis and subsequent erosion uncovered remnants of their fossil bones in the Andes of central Chile.

They were discovered in 1988, while searching for traces of dinosaurs in a steep valley of the Tinguiririca River, near the border with Argentina. The discovery was so fruitful that since that date the area has been returned to annually to continue the study of the remains. To date, more than 1.500 fossils of ancient mammals have been unearthed in dozens of paleontological sites in the central Andes of Chile.

Mammals That Are in Danger of Extinction

Other articles that may interest you are:

Marine animals
Land animals