Why in herbivores in the process of evolution. The process of animal evolution, or the history of the development of fauna on earth
Differences between omnivores and frugivores: a brief comparison
MUSCULOSKELETAL SYSTEM.
LIMBS The structure of the legs of herbivores differs from the structure of the legs of predators and omnivores in that herbivores, like humans, have straight legs, adapted for long periods of standing while searching and eating plant food. In predators initial position the legs are not straight, but with a bend in the area of the knee and ankle joints. This allows predators to move silently and make powerful leaps from a standing position for a surprise attack on a potential prey.
DIGESTIVE SYSTEM
The SALIVA of predators does not contain enzymes, since predators do not chew their food, but cut it with powerful jaws and swallow it in large portions. In herbivores and humans, saliva contains enzymes and the digestion process begins in the mouth.
The ESOPHAGUS in herbivores and humans is narrow, since food that has already been chewed and softened by saliva enters it.
The STOMACH of predators is extensive, accounting for 60-70% of the total volume digestive system. In humans, the stomach makes up 21-27% of the digestive system, in herbivores it is less than 30%. This explains that carnivores are able to eat up to once a week (since they manage to kill an animal quite rarely), while herbivores and humans must eat several times a day to maintain viability. The acidity of the stomach of predators is much higher than that of humans and herbivores. In predators RN<1 или =1, в то время как у человека и травоядных РН = от 4 до 5.
The LENGTH OF THE SMALL INTESTINE in predators and omnivores is much shorter (from 3 to 6 body sizes of a predator) than in humans and herbivores (10-12 body sizes).
The COLON of carnivores and omnivores is short and smooth. In herbivores and humans, it is long with an uneven surface.
The LIVER of predators and omnivores has the ability to neutralize vitamin A; the liver of herbivores and humans is not able to neutralize vitamin A and its excess can cause poisoning.
The KIDNEYS of carnivores and omnivores produce concentrated urine. In herbivores and humans, they produce less concentrated urine.
STRUCTURE OF THE MOUTH.
Both herbivores and humans have more muscular lips and tongues than carnivores and omnivores. These qualities are intended for the process of chewing food, which is inherent in herbivores, but not in carnivores and omnivores (the latter can only lightly grind food). The developed muscles of the lips and tongue of herbivores and humans help move food around the mouth for repeated grinding by flat teeth. The mouth opening of herbivores and humans is small, which is a consequence of food entering it in small portions. In predators, the structure of the jaw of the mouth allows them to open their mouths very wide for successful hunting and quickly swallowing food.
FACIAL MUSCLES in humans and herbivores are quite developed. Since these animals and humans chew food diligently. In predators, the facial muscles are not developed. In this category of mammals, preference is given to only one direction of jaw movement: vertical for cutting the flesh of the victim.
STRUCTURE OF TEETH
The incisors of carnivores and omnivores are short and pointed towards the open end. Herbivores and humans have longer, wider and flatter ones.
The FANGS of raptors and omnivores are long, sharp and curved. In herbivores they are short and blunt (some are longer for a protective function) and in humans they are short and blunt.
The molars of predators are sharpened in the form of jagged blades. In herbivores and humans they are flat with nodular slides.
VISION. Predators usually do not distinguish colors and do not recognize stationary objects. Their vision mainly captures what is in motion. Herbivores and humans easily distinguish many colors of the rainbow, as well as non-moving objects. This indicates that their main life interest in the process of evolution was concentrated on the plant world, where color and shape help determine the edibility of objects. In addition, most predators and omnivores have excellent night vision, while many herbivores and humans are unable to clearly see surrounding objects in the absence of light.
PERIODS OF ACTIVITY AND REST DURING THE DAY. Predators and omnivores sleep up to 20 hours a day. The main activity occurs at night. Most mammalian herbivores and humans are active most of the day, mainly during the light part of the day. Carnivores and omnivores are able to provide nutrition to the body for several days with one large feeding. Herbivores and humans must eat food several times during the day.
REPRODUCTION OF OFFERS. The period of gestation of offspring by predators and omnivores is 2-3 times shorter than the period of gestation of young by herbivorous mammals and humans. Predators and omnivores typically produce numerous offspring from a single pregnancy. While herbivores and humans usually give birth to one baby (in rare cases, 2). The offspring of predators are born blind, while those of herbivores are born with open eyes.
All these similarities illustrate that man, in the process of evolution, was formed as a frugivorous creature.
COMPARATIVE ANATOMY OF DIGESTION: an extensive article
Article written by Milton Mills, MD
The Comparative Anatomy of Eating
by Milton R. Mills, M.D.
Humans are usually classified as omnivores or omnivores. This classification is based on a simple method of “observation”: people typically eat a wide range of different foods. At the same time, the diet of a particular population group may be influenced by factors such as national culture, traditions and upbringing. Therefore, "observation" may not be the best way to determine the most "natural" diet for a person. While most people "behave as omnivores or omnivores," the question remains whether humans are anatomically designed for a diet that includes animal foods as well as plant foods.
A much more objective method for classification would be to refer to the anatomy and physiology of the human body. Mammals are anatomically and physiologically adapted to find/prey and metabolize certain types of diets. (When working with animal fossils, the anatomical structure is usually studied to determine what the animal ate.) Thus, we know that among mammals there are carnivores (or carnivores, predators), herbivores (or herbivores) and omnivores (or omnivores) and we can trace what anatomical characteristics are inherent in each group of the three above mentioned.
ORAL CAVITY
Carnivores (or carnivores, predators) have the ability to open their mouth (mouth) wide. This helps them generate sufficient jaw force to capture, kill and dismember prey.
The muscle mass of the facial part is not developed as it can be an obstacle to wide opening of the mouth, and will not significantly contribute to the act of swallowing food.
In all carnivoran mammals, the lower jaw is controlled by a simple joint located in the same plane as the teeth. This type of joint is the most stable and is something like an axis of a lever mechanism formed by the upper and lower jaws connected by the joint.
The main muscle that moves the carnivore's jaw is the temporalis (in Russian terminology, the temporal muscle that controls the jaw, translator's note). In carnivores, this muscle is large and accounts for most of the flesh on the sides of the head. When we pet a dog, we are petting its temporalis muscles.
The lower jaw of carnivores, as a rule, has almost no muscle mass. Its muscles (which belong to the chewing muscles: masseter and pterygoids) do not have any significance for carnivores, and as a result, the jaw itself is flat, not massive. In addition, the lower jaw of carnivores cannot move forward, and also has a very limited ability to move from side to side.
When the carnivore closes its jaw, the saber-shaped lateral teeth pass tightly next to each other above and below, thereby producing the incisive movement necessary to separate the meat from the bone.
The teeth of carnivores are noticeably thinned out so that parts of food do not get stuck in them.
The front teeth are short and pointed. Used for catching fleas and other auxiliary functions.
The fangs are very long, saber-shaped, so that they can stab the victim, kill him and begin to tear him apart.
The molars are triangular in shape, slightly serrated at the end, and serve like serrated blades.
Thanks to the lever action joint, when the carnivore closes its jaw, its lateral teeth form a movement reminiscent of the blades of scissors.
Carnivore saliva does not contain digestive enzymes. While eating, they quickly throw food inside without chewing. Since the food of carnivores is protein, enzymes that break down the protein mass cannot be present in the mouth due to the danger of breaking down the mouth tissues themselves, carnivores do not need to mix food with saliva. It is enough for them to simply swallow large pieces of flesh.
According to evolutionary theory, the anatomical structure associated with a herbivorous diet represents a later stage of mammalian development than carnivores.
Herbivores have well-developed facial muscles, full lips, a mouth opening with a noticeably limited ability to open, and a thick, developed tongue.
The lips, along with the cheek muscles and tongue, help place food in the mouth and move it around in the mouth for chewing.
In herbivores, the jaw joint is located above the plane of the teeth, and although this position of the joint is less stable than with the lever type of joint in carnivores, it gives much more freedom for the jaw to move along more complex trajectories, which is necessary for thoroughly chewing plant food. In addition to the above, this arrangement of the jaw joint allows the lateral teeth of the upper and lower rows to adjoin each other with their surfaces to form grinding platforms. (This type of jaw joint is of exceptional importance for plant-eating mammals. According to scientists, it has undergone successive improvements and passed through 15 different stages during the evolutionary process).
The lower jaw (mandible) in herbivores is noticeably enlarged in order to provide more space for the attachment of well-developed chewing muscles (masseter and pterygoid - the main chewing muscles of herbivores). These muscles of mastication (masseter and pterygoid) hold the lower jaw in a see-saw position, allowing it to sway from side to side. The temporalis muscle, which closes the jaw, is much less important. In herbivores, the lower jaw produces a pronounced movement from side to side while eating. What is necessary for chewing and grinding food.
The shape of teeth in herbivores can vary depending on the type of plant food consumed by a particular species. However, despite the fact that these animals may have different numbers of teeth of certain types, the teeth of herbivores are similar in structure. The front teeth (incisors) are usually flat, wide and have a blunt, spade-shaped end. The canines can be small, like those of horses, or large, like those of hippopotamuses, pigs, and some primates (used by many for defense), or even absent altogether.
The molars are usually square-shaped at the base, with a rather flat tubercular surface that slightly varies from species to species, to ensure the grinding function. The molars cannot slide along each other above and below to create the cutting motion of a carnivore, but the upper and lower teeth can slide along each other in a horizontal plane. The surface of molars in herbivores also depends on the type of vegetation the species eats.
The teeth are located close to each other: the incisors work as a biting tool, after the incisors the food comes in for grinding by the molars. The cavity formed inside the teeth is large enough to move plant food there.
Herbivores chew their food thoroughly, moving it along the grinding teeth using the tongue and cheek muscles. The thoroughness of this process is explained by the need to break down plant material and mix it with saliva, which in many species of herbivores has enzymes. The process of breaking down food begins in the mouth (with the help of enzymes that break down carbohydrates).
STOMACH AND SMALL INTESTINE
These organs are fundamentally different in carnivores and herbivores.
Carnivores have a simple, single-chamber stomach of rather large volume. The stomach of carnivores accounts for 60 to 70% of the digestive system. Because meat is digested quite quickly, the small intestine, through which the body absorbs food cells, is quite short. Its length is usually 5 - 6 times the length of the animal's body. Since carnivores kill an average of one animal per week, their large stomachs allow them to ingest as much flesh as possible in one go, and then break down and digest it during their subsequent rest. The stomach of carnivores has a special ability to secrete hydrochloride and maintain acidity at pH1 - pH2. This makes it possible to break down proteins and neutralize numerous bacteria-like organisms that are present in abundance in dead flesh.
Due to the high presence of fiber in plant foods, it takes longer to break it down, and in herbivores the gastrointestinal tract is much longer and often has more advanced functions than in carnivores.
Herbivores, whose diet consists largely of plant matter high in cellulose, are forced to “ferment” their food (break it down using enzyme bacteria) to more fully extract the nutritional component from it. Here, herbivores are divided into 2 categories: ruminants, those that feed on more coarse
plant foods and ferment it in the stomach and foregut (foregut fermentation) and those that eat relatively soft plant foods and ferment it in the colon - hindgut fermentation. Ruminant herbivores (fermenting in the stomach and small intestine) have multi-chambered stomachs.
Herbivores of the 2nd category (feeding on relatively soft plant matter) do not need a multi-chambered stomach. They usually have a simple single-chamber stomach and a fairly long small intestine. These animals ferment those foods that contain a lot of fiber in the colon. Many animal species in this category have evolved to improve the process and efficiency of their gastrointestinal tract by adding carbohydrate-digesting enzymes to their saliva. For such animals (belonging to the 2nd category, feeding on soft plant foods), a multi-chamber stomach would not be needed. Nutrients and caloric energy would be broken down and lost before reaching the small intestine for absorption.
The small intestine of herbivores is 10 or more times the length of their body.
COLON
The large intestine of carnivores is quite simple and short, its only function is the absorption of salt, electrolytes and water. In carnivores, the large intestine is approximately the same diameter as the small intestine, and therefore has a limited ability to store food. This intestine is not very long and has a smooth, uncorrugated shape. The muscles are evenly distributed along the walls, thereby giving the intestine a smooth cylindrical shape. Carnivores have a number of microorganisms in their colon that perform the function of decomposition.
For herbivores, the large intestine is generally an important organ, responsible for the absorption of water and electrolytes, as well as the production and absorption of vitamins and the fermentation of cellulose-containing parts of food. The large intestine of herbivores is usually larger in diameter than the small intestine and quite long. In some species of herbivores, the large intestine has a corrugated shape due to the way muscle fibers are arranged on the walls of the intestine, forming, as it were, constrictions. In some species of herbivores, the initial part of the large intestine, the cecum, is quite large and serves as either the main or auxiliary fermentation organ.
WHAT ABOUT OMNIVORES?
It can be assumed that omnivores (omnivores) would have anatomical characteristics that allow them to consume both types of diets: meat and plant. According to the theory of evolution, the intestinal structure of carnivores is more primitive than that of herbivores. So maybe the omnivore would be a carnivore with an improved intestinal tract for digesting plant foods?
This is true, and this is true for such animal species as bears, raccoons and certain members of the canine family. (Bears will be taken as an example as the most prominent representatives of anatomical omnivores or omnivores). Bears are classified as carnivores, but they are actually anatomically classified as omnivores. Although they do eat some animal food, 70%-80% of a bear's diet comes from plant foods. (The exception is polar bears, which live in conditions of virtually no vegetation and eat almost entirely animal food). Bears cannot digest vegetation high in cellulose fiber, and they are quite picky eaters. Their diet mainly includes succulent shoots and herbs, rhizomes and berries. Many biologists believe that the reason why bears hibernate is the lack of their main food - succulent vegetation in the winter. (Interestingly, polar bears hibernate in the summer when they cannot get their main food - seals)
In general, bears have the anatomical characteristics of carnivores. Their jaw joint is in the same plane as their teeth. The jaw muscle temporalis is highly developed, and the lower jaw mandible is not voluminous (forms a small angle). The masticatory muscles masseter and pterigoid play a small role.
The small intestine is short (less than 5 bear body lengths) like in the original carnivores. The large intestine is also short, like that of predators, simple and smooth without corrugation.
The most expressive anatomical sign of adaptation to a plant diet is the teeth of bears (and other “anatomical” omnivores). Bears have small speck-shaped front teeth, large fangs, the front root teeth on top and bottom run along each other to perform the cutting function - all of the above is the same as in carnivores, but the rear molars have acquired a square shape with flat tops and small tubercles on them for grinding food.
Bears' nails are the same as those of carnivores - long, strong, sharp claws, and not flat, blunt like those of most herbivores.
An animal that catches, kills and eats animal food must have appropriate weapons to perform the function of a predator. And since bears eat animal flesh, they must have anatomical adaptations to capture and kill prey. In bears, their jaws, muscles and teeth allow them to develop and exert the force necessary to kill and butcher prey, despite the fact that the majority of their diet consists of plant foods. While the structure of the herbivore jaw (where the jaw joint is higher than the plane of the teeth) would allow bears to more efficiently consume plant foods and expand their range, it is a much weaker type of jaw than the crank mechanism of the carnivore jaw. The jaw of herbivores can be dislocated quite easily and this would not allow them to withstand the stress of a fight with a potential victim. In nature, an animal with a dislocated jaw would either die of starvation or would itself become someone's victim. Therefore, the herbivore jaw type is not suitable for a species that partly eats meat. Omnivores cannot switch to a different type of jaw until they completely switch to a plant-based diet, otherwise the species would be in danger of extinction.
WHAT ABOUT ME?
The human gastrointestinal tract is similar to the anatomical structure of the herbivorous tract. The lips are developed, the mouth opening is small. Many of those facial muscles described as facial expression muscles are muscles that promote chewing. The thick, muscular tongue, necessary for chewing food, also served for the development of speech. The jaw joint is located noticeably above the plane of the teeth. The jaw muscle temporalis is small in mass. The expression "square jaw" for some male individuals reflects the more voluminous lower jaw of the mandible, which houses a group of developed masseter/pterygoid muscles of mastication. The human chin can move forward to move the incisors, and can move from side to side to grind food.
Human teeth are similar in structure to the teeth of herbivores, and unlike some species of monkeys (whose fangs are usually used for protection), our fangs are not developed.
Our teeth are wide, flat and usually spaced closely together. The incisors are flat in the shape of a blunt-pointed shovel, suitable for the function of cleaning fruits. The front and back molars are square-shaped and flat with small rounded cusps for grinding food.
Human saliva contains an enzyme that breaks down carbohydrates: salivary amylase. This enzyme plays a decisive function for the breakdown and subsequent digestion of starchy substances. The pharynx (esophagus) in humans is narrow, adapted for swallowing small portions of well-chewed food. If a person tries to eat in a hurry, or swallow large portions of food, especially fibrous, poorly chewed food (especially large pieces of meat), he can easily choke.
The human stomach is single-chambered, with slight acidity. If a clinical analysis determines that the patient has an acidity (pH) of the stomach with the presence of food in it below 4-5 (the lower the pH, the higher the acidity), then this is a cause for concern.
The volume of the human stomach is 21-27% of the total volume of the gastrointestinal tract. Our stomach acts as a container for mixing food and diluting it with liquid, while regulating the flow of this mixture into the small intestine. The human small intestine is long. It is 10-11 times longer than the length of the human body (our small intestine is about 7.5 - 10 meters. The length of the human body is measured from the top of the head to the lowest point of the spine and is 0.75 - 1 meter in an adult).
The human large intestine has a corrugated shape due to muscle constrictions, the same as in herbivores; like the latter, it is larger in diameter than the small intestine and relatively long. The colon absorbs water and electrolytes and produces and absorbs vitamins. In addition, it undergoes an intensive process of fermentation of fibrous plant foods with the release and absorption of energy (in the form of volatile fatty acids with a short molecular chain - volitile SCFA). A detailed study of the process of fermentation and absorption of metabolic products in the human colon has only recently begun to receive serious attention.
CONCLUSION
We have observed that the human gastrointestinal tract belongs to the type of “convinced” herbivores. Humanity as an animal species does not have the transitional anatomical features that can be found in omnivores such as bears or raccoons. By comparing the human gastrointestinal tract with the gastrointestinal tract of herbivores, omnivores and carnivores, we are convinced that the human gastrointestinal tract is adapted for a purely plant-based diet.
Facial muscles
Jaw type
Location of the jaw joint
Jaw movement
Main muscle that moves the jaw
Size of open mouth in relation to head size
Teeth (front)
Teeth (fangs)
Teeth (molars)
Chewing
Saliva
Stomach type
Stomach acidity
Stomach volume
Small intestine length
Colon
Liver
Kidneys
Nails
Following the intake and absorption of food, the stage of breakdown of complex polymer structures into monomers follows. This occurs under the influence of hydrolytic enzymes.
The resulting monomers are absorbed into the internal environment of the body. The initial stage of food assimilation, i.e., the transformation of initial food structures into components that lack species specificity and are suitable for absorption and participation in intermediate metabolism, is referred to as the process of digestion.
The ability of different animal species to digest food of a certain quality was formed during evolution. Due to the different nature of nutrition and different living conditions of animals in the process of phylogenesis, the digestive apparatus also develops differently. Plant foods are less nutritious than animal foods, and therefore herbivores are forced to absorb significantly more food than carnivores. So, a cow weighing 600-700 kg eats about 100 kg of feed per day. In this regard, herbivores have a much longer digestive tract than carnivores. Here are some data showing differences in the ratio of body length to intestinal length in different animal species.
Bat - 1:2
Rabbit - 1:10
Ermine - 1:4
Horse - 1:12
Dog - 1:5
Cow - 1:20
As can be seen, feeding on indigestible substances, especially those rich in fiber, in all groups of animals leads to an elongation of the digestive canal and is accompanied by the development of its additional sections. Particularly indicative in this regard is the digestive tract of ruminants, in the digestion of which symbionts (bacteria and protozoa) play a huge role. A similar complication of the digestive system is observed in small ruminants - the hind intestines of small herbivorous mammals are well developed and designed for protozoal and bacterial hydrolysis of cellulose.
Based on the study of the digestive system, we can conclude that the main direction of evolution of herbivorous species, starting from the early Miocene (4th period of the Cenozoic era), was the transition from protein-lipid to fiber nutrition. This process was greatly accelerated due to the process of the great steppeification of the land that occurred during the Pliocene period. Changing a protein type of diet to a fiber diet means a transition from eating high-calorie, but hard-to-obtain foods to consuming low-calorie, but easily obtained foods. This transition led to a reduction in the individual area and, consequently, to a decrease in the mobility of animals, to an increase in the total volume of food consumed and to a corresponding adaptive morphophysiological change in the gastrointestinal tract.
With the simplification of finding food, the locomotor organs are simplified and the sense organs are reduced: smell, vision, taste. The digestive system also changes. Thus, with an increase in the volume of food consumed, the chewing muscles strengthen. At the same time, the nature of the movement of the jaws changes (grinding), and in connection with this, the dental apparatus is also transformed (tubercy is replaced by folding). The sensory papillae of the tongue are reduced, the size of the digestive tube increases, and the length of the small and large intestines increases. The liver changes, and since bile must be released continuously when eating low-calorie food, this in some cases leads to a reduction in the gallbladder (in horses, elk, deer, camels). Adaptation of the digestive apparatus occurred in full accordance with classical ideas coming from Cuvier (1812), who believed that when living conditions change, the organs of one system are transformed more or less synchronously in the same direction. This situation is well illustrated by the example of adaptive restructuring of parts of the digestive tract.
Thus, in the process of historical development, some mammals switched to feeding on plant foods, which differ sharply from foods of animal origin.
1. Plant foods are easily available for consumption, but are not so beneficial for digestion and absorption.
2. Plant feeds are significantly inferior to feeds of animal origin in nutritional value.
3. Plant feeds contain, unlike animal feeds, a large percentage of carbohydrates, including indigestible ones (cellulose, hemicellulose, etc.).
4. The main structural component of the plant body, cellulose (fiber), is not broken down in most animals due to the absence of the enzyme cellulase in the digestive juices. This enzyme is synthesized only by bacteria, protozoa and some invertebrates. As for mammals, they are not able to synthesize cellulase. Therefore, the use of plants as food by mammals can only be realized with the help of symbiotic microorganisms capable of synthesizing and secreting cellulase.
5. Plant foods are characterized by a low protein and lipid content and, what is especially significant, a poor amino acid composition. Eating roughage plant foods resulted in many anatomical and physiological transformations of the digestive organs: changes in the dental system, an increase in the volume of the digestive tract, and the formation of special chambers (forestomachs and cecum).
The skull of Ichthyostega was similar to the skull of a lobe-finned fish Eusthenopteron, but a pronounced neck separated the body from the head. While Ichthyostega had four strong limbs, the shape of its hind legs suggests that this animal did not spend all its time on land.
The first reptiles and the amniotic egg
Hatching of a turtle from an egg
One of the greatest evolutionary innovations of the Carboniferous period (360 - 268 million years ago) was the amniotic egg, which allowed early reptiles to move away from coastal habitats and colonize dry areas. The amniotic egg allowed the ancestors of birds, mammals and reptiles to reproduce on land and prevent the embryo inside from drying out, so they could survive without water. This also meant that, unlike amphibians, reptiles could produce fewer eggs at any given time as the risks of hatchlings dying were reduced.
The earliest date for the development of an amniotic egg is about 320 million years ago. However, reptiles did not experience any significant adaptive radiation for another 20 million years or so. Modern thinking is that these early amniotes still spent time in the water and came ashore primarily to lay their eggs rather than feed. Only after the evolution of herbivores did new groups of reptiles emerge capable of exploiting the abundant floristic diversity of the Carboniferous period.
Gilonomous
Early reptiles belonged to an order called captorhinids. Hylonomus were representatives of this order. They were small animals about the size of a lizard, with amphibian skulls, shoulders, pelvises and limbs, as well as intermediate teeth and vertebrae. The rest of the skeleton was reptilian. Many of these new "reptilian" features are also seen in small, modern amphibians.
First mammals
Dimetrodon
A major transition in the evolution of life occurred when mammals evolved from a single line of reptiles. This transition began during the Permian period (286 - 248 million years ago), when a group of reptiles that included Dimetrodon gave rise to the "terrible" therapsids. (The other major lineage, the sauropsids, gave rise to birds and modern reptiles). These mammalian reptiles in turn gave rise to cynodonts such as Thrinaxodon ( Thrinaxodon) during the Triassic period.
Trinaxodon
This evolutionary line provides an excellent series of transitional fossils. The development of a key feature of mammals, the presence of a single bone in the lower jaw (compared to several in reptiles), can be traced through the fossil history of this group. It includes excellent transitional fossils, Diarthrognathus And Morganucodon, whose lower jaws have both reptilian and mammalian articulations with the upper jaws. Other new features found in this lineage include the development of different types of teeth (a feature known as heterodontity), the formation of a secondary palate, and an increase in dentary bone in the lower jaw. The legs were located directly below the body, an evolutionary advance that occurred in the ancestors of dinosaurs.
The end of the Permian period was marked by perhaps the greatest. According to some estimates, up to 90% of species have become extinct. (Recent studies have suggested that this event was caused by an asteroid impact, which triggered climate change.) During the subsequent Triassic period (248 - 213 million years ago), survivors of the mass extinction began to occupy vacant ecological niches.
However, at the end of the Permian period it was dinosaurs, not reptilian mammals, that took advantage of the newly available ecological niches to diversify into dominant land vertebrates. In the sea, ray-finned fish began a process of adaptive radiation, which made their class the most species-rich of all vertebrate classes.
Classification of dinosaurs
One of the major changes in the group of reptiles that gave rise to dinosaurs was the posture of the animals. The location of the limbs has changed: previously they protruded on the sides, and then began to grow directly under the body. This had significant implications for locomotion as it allowed for more energy-efficient movements.
Triceratops
Dinosaurs, or “terror lizards,” are divided into two orders based on the structure of the hip joint: lizard-hipped and ornithischian. Ornithischians include Triceratops, Iguanodon, Hadrosaurs and Stegosaurs). Lizards are further divided into theropods (such as Coelophysis and Tyrannosaurus rex) and sauropods (such as Apatosaurus). Most scientists agree that they are from theropod dinosaurs.
Although dinosaurs and their immediate ancestors dominated the terrestrial world during the Triassic, mammals continued to evolve during this time.
Further development of early mammals
Mammals are advanced synapsids. Synapsids are one of the two great branches of the amniote family tree. Amniotes are a group of animals that are characterized by the presence of embryonic membranes, including reptiles, birds and mammals. The other major amniotic group, the Diapsids, includes birds and all living and extinct reptiles except turtles. Turtles belong to the third group of amniotes - Anapsids. Members of these groups are classified according to the number of openings in the temporal region of the skull.
Dimetrodon
Synapsids are characterized by having a pair of additional holes in the skull behind the eyes. This discovery gave synapsids (and similarly diapsids, which have two pairs of openings) stronger jaw muscles and better biting abilities than early animals. Pelycosaurs (such as Dimetrodon and Edaphosaurus) were early synapsids; they were reptilian mammals. Later synapsids included therapsids and cynodonts, which lived during the Triassic period.
Cynodont
Cynodonts had many characteristic mammalian features, including a reduced number or complete absence of lumbar ribs, suggesting the presence of a diaphragm; well developed canines and secondary palate; increased size of the dentition; openings for nerves and blood vessels in the lower jaw, indicating the presence of vibrissae.
By about 125 million years ago, mammals had already become a diverse group of organisms. Some of these would have been similar to today's monotremes (such as the platypus and echidna), but early marsupials (a group that includes modern kangaroos and possums) were also present. Until recently, placental mammals (the group to which most living mammals belong) were thought to have a later evolutionary origin. However, recently discovered fossils and DNA evidence suggest that placental mammals are much older, possibly evolving more than 105 million years ago.
Note that marsupials and placental mammals provide excellent examples of convergent evolution, where organisms that are not particularly closely related evolved similar body shapes in response to similar environmental influences.
Plesiosaurs
However, despite having what many consider to be "advanced" mammals were still minor players on the world stage. When the world entered the Jurassic period (213 - 145 million years ago), the dominant animals on land, sea and air were reptiles. Dinosaurs, more numerous and unusual than during the Triassic, were the main land animals; crocodiles, ichthyosaurs and plesiosaurs ruled the sea, and the air was inhabited by pterosaurs.
Archeopteryx and the evolution of birds
Archeopteryx
In 1861, an intriguing fossil was discovered in the Jurassic Solnhofen Limestone in southern Germany, a source of rare but exceptionally well-preserved fossils. The fossil appeared to combine features of both birds and reptiles: a reptilian skeleton accompanied by a clear impression of feathers.
While Archeopteryx was originally described as a feathered reptile, it has long been considered a transitional form between birds and reptiles, making the animal one of the most important fossils ever discovered. Until recently, it was the earliest known bird. Scientists recently realized that Archeopteryx bears more similarities to maniraptorians, a group of dinosaurs that includes the infamous Velociraptor from Jurassic Park, than to modern birds. Thus, Archeopteryx provides a strong phylogenetic link between these two groups. Fossil birds have been discovered in China that are even older than Archeopteryx, and other discoveries of feathered dinosaurs support the theory that theropods evolved feathers for insulation and temperature regulation before birds used them for flight.
A closer look at the early history of birds is a good example of the concept that evolution is neither linear nor progressive. The lineage of birds is disordered, and many "experimental" forms appear. Not all achieved the ability to fly, and some looked completely different from modern birds. For example, Microraptor gui, which appears to have been a flying animal and had asymmetrical flight feathers on all four limbs, was a dromaeosaurid. Archeopteryx itself did not belong to the lineage from which true birds evolved ( Neornithes), but was a member of the now extinct enantiornhis birds ( Enantiornithes).
The end of the dinosaur era
Dinosaurs spread throughout the world during the Jurassic period, but during the subsequent Cretaceous period (145 - 65 million years ago) their species diversity declined. In fact, many of the typically Mesozoic organisms, such as ammonites, belemnites, ichthyosaurs, plesiosaurs and pterosaurs, were in decline during this time, even though they were still giving rise to new species.
The emergence of flowering plants during the Early Cretaceous period caused a major adaptive radiation among insects, with new groups emerging such as butterflies, moths, ants, and bees. These insects drank nectar from flowers and acted as pollinators.
The mass extinction at the end of the Cretaceous period, 65 million years ago, wiped out the dinosaurs along with any other land animal weighing more than 25 kg. This paved the way for the expansion of mammals on land. In the sea at this time, fish again became the dominant vertebrate taxon.
Modern mammals
At the beginning of the Paleocene (65 - 55.5 million years ago), the world was left without large land animals. This unique situation was the starting point for a great evolutionary diversification of mammals, which were previously nocturnal animals the size of small rodents. By the end of the era, these representatives of the fauna occupied many of the free ecological niches.
The oldest confirmed primate fossils date back about 60 million years. Early primates evolved from ancient nocturnal insectivores, something like shrews, and resembled lemurs or tarsiers. They were probably arboreal animals and lived in or subtropical forests. Many of their characteristic features were well suited to this habitat: hands designed for grasping, rotating shoulder joints, and stereoscopic vision. They also had a relatively large brain size and clawed toes.
The earliest known fossils of most modern mammal orders appear over a short period during the early Eocene (55.5–37.7 million years ago). Both groups of modern ungulates, the Artiodactyls (the order that includes cows and pigs) and the Odd-toed ungulates (including horses, rhinoceroses, and tapirs), became widespread throughout North America and Europe.
Ambulocetus
At the same time as mammals diversified on land, they also returned to the sea. The evolutionary transitions that led to whales have been extensively studied in recent years, with extensive fossil finds from India, Pakistan and the Middle East. These fossils indicate a change from the land-based Mesonychia, which are the likely ancestors of whales, to animals such as Ambulocetus and primitive whales called Archaeocetes.
The trend towards a cooler global climate that occurred during the Oligocene epoch (33.7 - 22.8 million years ago) favored the emergence of grasses, which were to spread to extensive grasslands during the subsequent Miocene (23.8 - 5.3 million years ago ). This change in vegetation led to the evolution of animals, such as more modern horses, with teeth that could cope with the high silica content of grasses. The cooling trend has also affected the oceans, reducing the abundance of marine plankton and invertebrates.
Although DNA evidence suggests that hominids evolved during the Oligocene, abundant fossils did not appear until the Miocene. Hominids, on the evolutionary line leading to humans, first appear in the fossil record in the Pliocene (5.3 - 2.6 million years ago).
During the entire Pleistocene (2.6 million - 11.7 thousand years ago), there were about twenty cycles of cold ice ages and warm interglacial periods at intervals of about 100,000 years. During the Ice Age, glaciers dominated the landscape, spreading snow and ice into the lowlands and transporting vast amounts of rock. Because a lot of water was trapped in the ice, the sea level dropped to 135 m than it is now. Wide land bridges allowed plants and animals to move. During warm periods, large areas were again submerged under water. These repeated episodes of environmental fragmentation led to rapid adaptive radiation in many species.
The Holocene is the current epoch of geological time. Another term that is sometimes used is the Anthropocene because its main characteristic is global changes caused by human activities. However, this term can be misleading; modern people were already created long before the era began. The Holocene era began 11.7 thousand years ago and continues to this day.
When warming came on Earth, it gave way. As the climate changed, very large mammals that adapted to extreme cold, such as the woolly rhinoceros, became extinct. Humans, once dependent on these "mega mammals" as their main source of food, switched to smaller animals and began collecting plants to supplement their diet.
Evidence shows that around 10,800 years ago the climate underwent a sharp cold turn that lasted several years. The glaciers did not return, but animals and plants were scarce. As temperatures began to recover, animal populations grew and new fauna species emerged that still exist today.
Currently, the evolution of animals continues, as new factors arise that force representatives of the animal world to adapt to changes in their environment.
Terrestrial Community vertebrates in the Cenozoic developed independently in three separate territories, with virtually no faunal contacts between them. Australia (with its marsupials and monotremes) is isolated to this day, and South America maintained its isolation from the rest of the land until the Pliocene, when the Isthmus of Panama arose; This is where the modern division of the world into three zoogeographic regions comes from: Notogea (Australia), Neogea (South America) and Arctogea (Eurasia, Africa and North America). So, according to Zherikhin (1993), in all these three areas, grass biomes arose independently, on the basis of completely different complexes of large mammals; in fact, there are serious reasons to believe that mammals truly emerged into a large size class only in grass biomes.
The earliest time (in the Middle Eocene) this process began in South America. There, among the originally leaf-eating “South American ungulates,” the first herbivorous forms appear, and giant herbivorous glyptodont armadillos also appear, resembling a small tank (54, a). In the Middle Eocene, pollen spectra with a high content of cereal pollen, steppe-type paleosols, and fossilized dung balls belonging to dung beetles were first discovered in South America. Later, in the Oligocene and especially in the Miocene, a highly unique complex of grazing herbivores arose here. It included incomplete edentates (glyptodonts and ground sloths), “South American ungulates” (various litopterns show strong convergent similarities, partly with horses, partly with camels, Pyrotheriums have much in common with elephants, and among the notoungulates there were forms similar to both rhinoceroses and with hippopotamuses and rabbits (54, b-d), as well as giant caviomorphic rodents (some of these relatives of the guinea pig reached the size of a rhinoceros) and existed until the establishment of land connections with North America in the Pliocene.
As for predators, they were always in short supply in the ancient South American fauna. None of the local placental orders, for reasons that are not entirely clear, gave rise to carnivorous forms - this role was played exclusively by marsupials. Quite a variety of borghyenids were somewhat reminiscent of dogs (but even more so of Thylacine, the Tasmanian marsupial wolf), and Thylacosmilus well deserves the name “marsupial saber-toothed tiger” and is a striking example of convergence with saber-toothed cats of the Northern Hemisphere (54, e-f). . The shortage of mammalian predators (the “imbalance” of the local faunas was noted by A.S. Rautian and N.N. Kalandadze, 1987) led to the fact that this niche was filled by the most unexpected characters.
Thus, from the Paleocene to the Miocene, sebecosuchia existed here - land crocodiles with a high and narrow muzzle (it is assumed that their lifestyle was reminiscent of modern Komodo monitor lizards), and in the Eocene, fororacos, which survived until the Pleistocene, appeared - gigantic (up to 3 m tall) flightless birds of prey, belonging to the crane-like
In Australia (Notogea), the formation of the grass biome began much later, in the Neogene; here the drift of this continent clearly played a role in the direction from the pole to the equator - as a result, a significant part of its territory fell into arid climate conditions.
The basis of the local community of grazing mammals was made up of large herbivorous marsupials - kangaroos and diprotodonts, extinct in human memory (they are sometimes, due to their two large incisors, not very successfully called “rabbits the size of a rhinoceros”). As in the ancient South American fauna, a shortage of predators is clearly visible here: only two large-sized predatory mammals are known - the thylacine (Tasmanian marsupial wolf) and the arboreal thylacoleo, which by analogy can be called the “marsupial leopard”. The lack of mammalian predators was compensated (again as in South America) by reptiles - gigantic megalania monitor lizards up to 7 m long and land crocodiles, similar in lifestyle to sebecosuchians; no flightless birds of prey arose here, but some of the Australian ostriches, apparently, served as scavengers.
The third case of the formation of a grass biome is Arctogaea.
Here the situation is complicated by the fact that it is formed on a single taxonomic basis (condylarthic), but, apparently, independently in Eurasia and North America. The community of grazing mammals initially consists of equids (tapirs, rhinoceroses in the broad sense, and chalicotheriums) and non-ruminant artiodactyls (pisiformes and camels); a little later, primitive three-toed horses and ruminant artiodactyls (deer) are added to them (55). In addition to the descendants of condylarthra, only dinocerata, specialized descendants of some extremely primitive therian mammals, attempted to occupy the niche of large herbivores (55, b), but already in the Eocene this group became completely extinct. The unity of the complex of “northern” ungulates is quite high; the most interesting thing is that although almost all of these groups are of American origin (they penetrated into Eurasia through Beringia - the area around the Bering Strait, where vast areas of the shelf then dried out), grass biomes with their participation in Asia begin to take shape noticeably earlier than in America. In Central Asia, savannas appeared already at the end of the Eocene (giant hornless rhinoceroses like Indricotherium, a “hybrid of an elephant and a giraffe”, which appeared at that time, the largest land mammal with a height of 6 m at the withers ~ clearly lived in an open landscape, and not in a forest), then as in America this occurs in the Oligocene. In Africa, however, grass biomes do not appear to have existed until the Miocene; artiodactyls and odd-toed ungulates penetrated here from Eurasia relatively late, and proboscideans endemic to this continent (elephants and
As for predatory mammals, in the north they, unlike the southern continents, were only placental: marsupials generally existed here for a very short time and were never able to leave the niche of small insectivores. Before specialized carnivorous forms from creodonts (56, a) and modern carnivores (Carnivora) appeared in these regions, peculiar ungulates - mesonychids (56, b-c) - played this role.
Mesonychids were omnivores (thought to be "more carnivorous than the wild boar, but less carnivorous than the bear"); they often reached the size of a hyena, and Andrewsarchus from the Paleocene of Inner Mongolia was the largest land predatory mammal - its skull reaches a length of 85 cm. Surprisingly, it is from mesonychids that cetaceans originate.
Before the Oligocene, the situation in the grass biomes of Arctogea and South America developed in parallel. In both places, the main herbivores were ungulates, descendants of various condylartrae (in the North, odd-toed and artiodactyls, in the South - “South American ungulates”). In both cases, predators were clearly more primitive than their victims (in the South there were marsupials, in the North - archaic omnivorous ungulates, mesonychids): a situation that strikingly distinguishes the Paleogene from the Mesozoic.
From America come herbivorous (in the sense of not leaf-eating) horses, from Asia - bovids (bulls and antelopes), from Africa - proboscideans (elephants and mastodons); together with some other groups of ungulates, both “new” (giraffes and hippos) and “old” (rhinoceros), they form the so-called hipparion fauna (hipparion is one of the three-toed horses). The same picture is with the carnivores that are part of the Hipparion fauna: cats originated in America, canines - initially too, but the gregarious social organization (which became a key success factor for this group) was acquired already in Asia by hyenas (at that time among them there were not only carrion eaters, but also active predators such as the cheetah) - in Africa.
Interestingly, cats were originally saber-toothed; later, in the Miocene, cats of the modern type arose, but the return to saber-toothing (which, obviously, provides advantages when hunting large prey with a strong skin) occurred in cats repeatedly and independently.
The final results of the Great American Exchange (as J. Simpeon, 1983 called these events) turned out, however, to be very different for the North and South. The North American fauna was simply enriched by three exotic “immigrants” (the opossum, the nine-banded armadillo and the arboreal porcupine), while in the South a real catastrophe occurred, worse than any asteroid impact: here the entire grassland complex of “South American ungulates”, giant cavimorphic rodents, predatory marsupials and fororacos, which could not withstand competition with higher ungulates and carnivorous predators (57). One must assume that the fate of Australian marsupials and monotremes, if this continent had had direct land contact with Asia, would have been just as unenviable... In general, in the history of the Great American Exchange it is easy to see direct (and sad) analogies with human history: let’s remember how it turned out “contact” with European civilization for the ancient original cultures of pre-Columbian America and Black Africa.
In natural communities, animals of the same and different species live together and interact with each other. In the process of evolution, certain relationships are developed between animals that reflect the connections between them. Each animal species performs a specific role in the community in relation to other living organisms.
The most obvious form of relationship between animals is predation. In natural communities, there are herbivores that eat vegetation, and there are carnivores that catch and eat other animals. In relationships, herbivores act victimsami, and carnivores - predatorami. Moreover, each victim has its own predators, and each predator has its own “set” of victims. For example, lions hunt zebras and antelopes, but not elephants or mice. Insectivorous birds only catch certain types of insects.
Predators and prey have evolved to adapt to each other so that some have developed body structures that allow them to catch better, while others have a structure that allows them to better run away or hide. As a result, predators catch and eat only the weakest, sickest and least adapted animals.
Predators don't always eat herbivores. There are second- and third-order predators that eat other predators. This often occurs among aquatic inhabitants. Thus, some species of fish feed on plankton, others on these fish, and a number of aquatic mammals and birds eat the latter.
Competition- a common form of relationships in natural communities. Typically, competition is most intense between animals of the same species living in the same territory. They have the same food, the same habitats. Competition between animals of different species is not so intense, since their lifestyles and needs are somewhat different. So a hare and a mouse are herbivores, but they eat different parts of plants and lead different lifestyles.