Alpha Omega

From the first living organism (or organisms) one may follow the evolution of life from the thermophilic archaeabacteria and other unicellular organisms and multicellular animals and plants up to the wide variety of species living today. It is common for one to refer to all life as either animal or plant. Indeed, at one time all living organisms were considered as either animal or plant.

However, there are three other living kingdoms that have characteristics that are neither animal nor plant and some life forms that can be placed in either the animal kingdom or the plant kingdom. These are the Monera, which are all unicellular; the Protista, which can be either unicellular or multicellular; and the Fungi, which have spore formation during both asexual and sexual reproduction. The latter two are the more recently evolved and are classified as eukaryotic, whereas the monerans are all classified as prokaryotic.

It is generally assumed that some form of prokaryotic bacteria evolved to become the precursor of a non-photosynthetic autotroph, which in turn proliferated and is the ancestral stock of the protists. It was in the kingdom of the protists that many evolutionary advances were made. It was these organisms that gave rise to the first true animals and plants, particular the protozoan protists for the animal kingdom and the unicellular algae protists for the kingdom of the plants.

One may wonder how this evolution is possible since, according to the experiments performed by Pasteur, a species can only reproduce itself, not something different. However, there are variations among the organisms of each species. If there were no variations, then every living animal and plant, indeed, every living organism, would be an exact copy of its parents. It is these genetic variations within the gene pool of each species that supplies the raw material of evolution.

Of those organisms that inherit variations within the gene pool that give them even a slight advantage over other organisms of their species, they will have a better tendency to be selected by nature to perpetuate their species. Conversely, those that do not inherit an advantage will probably not be selected to perpetuate the species. This is because the variations within the species will allow different combinations of genes to be “tested” by the environment in which the organism lives, allowing only the best adapted to pass on their genes.

But one must note that if there is no environmental or evolutionary pressure on the species to change, then the species will not evolve into something different.

This process of change was called natural selection by the English naturalist Charles Darwin (1809 - 1882). Darwin explained how natural selection works in the book On the Origin of the Species and it was proved to be true by the Austrian botanist Gregor Mendel (1822 - 1884).

Experimenting with various types of peas, Mendel showed that when round, smooth coated peas (labeled RR) were continuously bred with round, smooth coated peas, only round, smooth coated peas were produced. Similarly, when wrinkled peas (labeled rr) were bred only with wrinkled peas, only wrinkled peas were produced. But when Mendel interbred the smooth peas with the wrinkled peas, the first generation of these seeds (labeled F1) produced only round, smooth coated peas.

The botanist labeled these new peas Rr and they were called hybrids because the wrinkled characteristic was missing. But when the hybrids were interbred in order to obtain a second generation of pea seeds (labeled F2), Mendel acquired three kinds of peas in a precise ratio. One/fourth were all round, smooth coated peas and subsequent interbreeding of these produced only round smooth coated peas. One/fourth were wrinkled peas and produced only wrinkled peas. But half of the peas were hybrids behaving like the peas of generation F1.

This is a ratio of the smooth over the wrinkled of three to one. Mendel considered the characteristics of the round, smooth pea as being dominant over the hidden characteristics of the wrinkled pea, which was designated as being recessive. The botanist then concluded that the wrinkled pea was a mutation and formulated the law of heredity: any changes in heredity factors (chromosomes) bring about mutations which are then passed on to the next generation. One can therefore conclude that mutual changes in chromosomes of living organisms makes possible the progress of evolution.

One should note that all this breeding was done under the ever watchful eyes of a dedicated monk and botanist, working with controlled environmental conditions. Thus, Mendel was able to achieve the desired goal. But in nature if mutations (genetic variations) occur along a line that helps the organism to survive its environmental living conditions, then the organism will succeed and a new species will evolve — if there is environmental or physiological pressure for the organism to change. However, if a mutation occurs along a line that is harmful to the organism — it frequently is — then the mutation leads to the death of the organism and no new species will evolve.

Of course, one should also note that these genetic variations are rarely apparent to the casual observer. Almost all mutations are recessive, unobserved variations. If such recessive, unobserved variations are beneficial to the organism and environmental or physiological pressures are causing the species to change, then after many generations a change will become great enough for the classification of a new species.

Also, many species are able to evolve from one parent species. That is, a parent species is often the primogenitor of several different species should successive descendants be reacting differently to differently changing environmental or physiological pressures.

One must distinguish between changing environment and changing environmental or evolutionary pressures. As one knows, the environment is constantly changing, but this does not necessarily mean that organisms are constantly changing. Some classical examples of animals that have not changed are the common house roach, some species of shark and the alligator. These animals have not evolved for millions of years because the ecological niche they occupy has not changed. They have not been under any environmental or physiological pressures to change.

The animals that Darwin observed on the Galapagos Islands give a classic example of this branching of the parent species.

For example, the original population of Finches was probably only one species. But the birds spread out to the different islands where varying selective pressures caused divergent evolution to occur. That is, the ecological niche occupied by the original population of Finches was tested differently on each island and each island population reacted differently. Each island population evolved a different species of Finch. Today the various populations of Finches are unable to reproduce with one another.

The same is true with other species living on the Galapagos Islands and throughout the world. They all evolved from one stem to what they are today. In the words of the English naturalist: “Thus from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, . . . directly follows. There is grandeur in this view of life, with its several powers, having been originally breathed by the Creator into a few forms or into one; and that, . . . from so simple a beginning endless forms most beautiful and most wonderful have been, and are being evolved.”

It is impractical, nor is it within the capacity of this book, to explore the evolution of all known animal and plant phyla of this world. Especially since all this information may easily be found by searching through most any good book on evolution or through most any other zoology or botany book. However, it does seem important to recall a noteworthy event that took place while the earliest of the simple, photosynthetic life forms were evolving.

Photodissociation had already altered the atmosphere from one of ammonia, methane and water vapor to one of nitrogen, carbon dioxide and water vapor. Then unicellular algae, evolving from a non-photosynthetic autotrophic genealogy, helped produce still another change in the earth’s atmosphere. Giving rise to the plant kingdom, these organisms, which take in carbon dioxide and give off oxygen during photosynthesis, helped convert the atmosphere to one of free nitrogen, oxygen and water vapor with only a small amount of carbon dioxide.

It is as though a new day has dawned! The evolution of an atmosphere with an abundance of oxygen at last paved the way for the evolution of animal life onto dry land.

One should note that this conversion from carbon dioxide to free oxygen was an ever gradual clearing that took many millennia to accomplish. It started soon after the evolution of the simple, photosynthetic autotrophs and it was not completed until long after the waters of the earth were teeming with all kinds of life forms. But comparing the carbon dioxide atmosphere of an earlier age to the nitrogen and oxygen atmosphere that eventually developed, one cannot be extravagantly criticized by calling it a new clear day of fresh sunshine.

The evolution of the plants from an algae genealogy up to the wide variety of species living today may be learned through most any botany or paleontology book. Although this is a very important subject, the evolution of plants is not important to this treatise and therefore will not be discussed at this time. Nor is the origin of the invertebrates important to this treatise. Therefore, they will not be discussed either.

For now it is enough to say that all metaphytes (changed plants) and all metazoans (changed animals) evolved from a single celled eukaryotic pedigree and that the earliest metaphytes first appear in the Archeozoic Era (Early Precambrian Period), while the first of the invertebrates are not found in the fossil record until the following Proterozoic Era (Late Precambrian Period).

One should note that it is changes in the fossil record that geologists use to distinguish one geologic time zone from another. Dramatic changes mark the divisions in eras, while somewhat smaller changes mark the changes in periods and epochs.

For example, at the end of the Paleozoic Era mollusks began to increase in numbers and there were many extinctions, including an entire class of marine invertebrates, the trilobites. So great was the change in marine invertebrate life that there is an almost complete reversal in types of organisms from the Paleozoic Era to the Mesozoic Era. Those that were abundant became sparse, while those that were less numerous began to dominate the seas.

To date, no fossils have been found of the invertebrate ancestors to the Phylum Chordata. Paleontologists can only speculate on their probable evolution. However, this speculation is based on strong but indirect evidence. This is found ia a few fossils of Pikaia. This animal had a fish-like body and is regarded as the earliest known primitive chordate. Instead of separate vertebrae segments these animals have a solid, flexible rod similar to that found in vertebrate embryos.

A classic example of a notochord bearing animal is the Lancelot of the Subphylum Cephalochordata. These invertebrate chordates have a number of characteristics that give them a fish-like appearance and many marine biologists consider them specialized descendants of the ancestors of the Phylum Echinodermata. It is this latter group of invertebrates that probably have as yet an unknown common Early Paleozoic Era ancestor with the Phylum Chordata.

One may continue from here and learn how the first of the chordates evolved during the Mid-Cambrian Period from their Early Cambrian invertebrate ancestors. Although they were not the first organisms to be completely nektonic (swimming organisms), these early chordates soon became masters of the seas, feeding off planktonic (floating) organisms or benthonic (bottom dwelling) organisms or upon each other. Then, toward the middle of the Ordovician Period, the first of the Subphylum Vertebrata began to appear.

There is some evidence suggesting that the agnaths or jawless fish were among the earliest true species of vertebrates. Many scientists believe that they are the ancestors of three other classes of fish: The extinct placoderms, which died out by the end of the Devonian Period; the Chondrichthyes or cartilaginous fish, which are more commonly known as sharks and rays; and the Osteichthyes or bony fish, which are believed to have pushed the placoderms into extinction.

But other scientists believe that these latter fish evolved from the extinct Acanthodii or spiny sharks. The placoderms evolved during the Silurian Period, while the latter two classes evolved in the following Devonian. The bony fish also diverged into two different directions during the Devonian Period. In one direction were the lobe-finned fish or Sarcopterygii and in another direction were the ray-finned fish or Actinopterygii.

The dominance of the fish at this time was so complete that the Devonian Period is often referred to as the “Age of the Fishes.” It was these animals, particularly the fresh water lobed-finned fish, that gave rise to the earliest of the amphibians.

One should note that the amphibians were not the first animals to make the transition to land. Arachnids (spiders and scorpions) and insects evolved terrestrial species in the Late Silurian Period or possibly the Early Devonian Period. But their evolution is not important to this trilogy and therefore will not be iscussed at this time.

Frequently considered as the ancestral tetrapod, Ichthyostega evolved in the Devonian Period and had a short heyday during the following Carboniferous Period. The scientists are not sure what caused the first amphibians to make the transition to land — warmth for their bodies, escape from predators, climatic changes, search for food or search of new streams and ponds during dry seasons — but whatever it was the amphibians were still bound to their fresh water ponds for reproduction. While they are completely terrestrial as adults, they must lay their eggs in water and their larvae are also aquatic.

It was not until the earliest and most primitive reptiles known, the Anapsida, evolved with the leathery, amniote egg that the vertebrates became completely independent of the water. Emerging from an amphibian ancestry and with very little competition on land except from one another, the cotylosaurs or stem reptiles went through a rapid expansion.

The Permian Period marks a time of competition with the more numerous amphibians but it also manifests the reptiles ever growing dominance over them. So prolific was the explosive radiation of the reptiles, which began their long dominance of the land, that the following three periods, comprising the 160 million year Mesozoic Era, are often called the “Age of the Reptiles.” During this time they flourished in size from only a few centimeters to great brutes more than 25 meters (82 ft.) in length and weighing several tons each.

The Order Cotylosauria gave rise to several orders of reptiles before becoming extinct at the end of the Triassic Period. Among the first to evolve from these stem reptiles was the mammal-like Subclass Synapsida, an animal that dominated during the Permian Period and has two orders, the Pelycosauria and the Therapsida. The former evolved during the Late Carboniferous Period or the Early Permian Period and was the first animal to depart from the standard reptilian style. They also have fewer mammalian characteristics than the therapsids. It is for these reasons that many paleontologists believe that the pelycosaurs gave rise to the therapsids.

Two other orders that emerged from a stem reptile genealogy were the Ichthyosauria and the Plesiosauria. These great “sea monsters” fed off fish and other marine life before becoming extinct at the end of the Cretaceous Period. The Orders Chelonia (turtles), Squamata (lizards and snakes) and Rhynchocephalia (which has only one species, Sphenodon and lives on the islands off the coast of New Zealand) are the only surviving descendants of the cotylosaurs.

Finally, the thecodonts are the most famous of the cotylosaurian descendants. These latter animals gave rise to all the archosaurs or ruling reptiles. These are the Order Crocodilia, which includes the alligators and crocodiles, the Order Pterosauria or flying reptiles and the Orders Saurischia (Theropods and Sauropods) and Ornithischia.

The Theropods were bipedal carnivores and the Sauropods were quadruped herbivores, while the Ornithischia were all herbivores and included the ornithopods, the stegosaurs, the ankylosaurs and the ceratopsians. The Saurischia and Ornithiscia are more commonly known under the collective title of dinosaur, which some paleontologists would like to put into a class by themselves.

The reason that many would like to put these Triassic, Jurassic, and Cretaceous Period reptiles into a separate class, called Dinosauria, is because of the mammal-like characteristics many of them possessed. Many of them lived in herds, shared their food and maintained a structured social life. Many dinosaurs showed signs of parental care and nurtured their young to maturity. The carnivores among them manifested an active predatory life style; some of them hunted in packs.

Neither the herbivores nor the carnivores had the awkward locomotion of the amphibians or reptiles. All the dinosaurs were either biped, like the birds or had an erect posture and walked with their limbs directly beneath their body, as in most present day mammals.

Finally, many dinosaurs, particularly the theropods, appear to have been endothermic or warm-blooded. However, many Sauropods and some other large dinosaurs appear to have been ectothermic or cold-blooded. But those who want a separate class for the dinosaurs point out that this is only incidental and should not prevent the formation of a new class for the dinosaurs.

There is evidence suggesting that the Dromaeosaurids, which are more commonly known as raptors, had a common ancestor with the Archaeopteryx, a Jurassic bird with a number of reptilian traits. Bird fossils are extremely rare which makes it difficult to trace their proliferation. What is thus far known is that the birds of the Jurassic Period had many reptilian features. Even the birds of the following Cretaceous Period still retained some reptilian traits, as is evident from fossils of the Ichthyornis.

It was not until the Cenozoic Era that birds became the modernized species of flight that they are today. They have evolved into 32 different orders, comprising more than one hundred billion species the world over. However, this treatise is concerned primarily with the rise of the mammals and it seems wise to return to this subject.

But before doing so, one should note that some paleontologists would also like to place the birds in the class Dinosauria, because of their common ancestry with the dinosaurs. But others point out that dinosaurs did not have perching feet and only some of them had feathers. Further, no one knows which dinosaurs were endothermic or ectothermic. Since all birds are endothermic, many believe they should remain in the Class Aves.

This book does not propose to solve this issue; its purpose is to present the facts of the creation. One can only wait for further research by the scientists to answer the question on the taxonomy of the dinosaurs and birds.

As mentioned previously, the mammal-like reptiles proliferated and dominated during the Permian Period. The pelycosaurs, early mammal-like reptiles, developed into three suborders — all of which became extinct before the end of the Triassic Period. The Order Therapsida also branched into three suborders and competed with the dinosaurs for dominance before losing out to them at the end of the Triassic Period. But before doing so, these advanced mammal-like animals became the primogenitor of the mammals in the Triassic Period.

Regardless of their name, the mammal-like reptiles did not look very much like their descendants, the mammals. First of all, their legs were not directly beneath their body, as with dinosaurs and mammals. Their legs extended outward from their sides. This made their locomotion rather awkward and is probably what caused their demise by the dinosaurs. Nor did they have a large brain relative to their body size, as do mammals, which is probably what helped their descendants, the mammals, survive the dinosaurian dominance.

However, their jaw was almost completely mammalian. They had muscles for complex chewing and were able to move their lower jaw up and down, forward and backward and side to side, just as mammals do today. Never-the-less, their denture was definitely reptilian. The teeth of their young were for eating, not nursing.

Finally, evidence suggests that the mammal-like reptiles had an improved sense of smell, improved hearing and had a higher metabolic rate than ordinary reptiles. These are all characteristics of species that are in the process of evolving active mammal-like ways.

The most primitive mammals known to date were of the Subclass Prototheria. This is an archaic mammal with a number of reptilian characteristics. There is some evidence manifesting that these were the ancestors of the Order Monotremata; who are today placed in that subclass. The Prototheria probably gave rise to the other group of mammals, those of the Subclass Theria, which may be further subdivided into the extinct Pantotheria, the first of the therians and two infra classes: Metatheria (marsupials) and Eutheria (placental mammals).

However, there are some who believe that the protothers are the ancestors of only one group of mammals during this time, the marsupials and that it is these latter who were the primogenitors of the placental mammals in the Cretaceous Period.

One should note that it is not important to this trilogy as to which subclass gave rise to which subclass or infra class. The important thing to remember here is that the mammal-like reptile Therapsida gave rise to the Mesozoic Mammals in the Triassic Period and that it was these animals who were the ancestors of all modern mammals; the latter evolving in the Cretaceous Period.

These Mesozoic Mammals were mostly small, unobtrusive animals that fed on seeds, leaves and other small plants; they fed on insects and other small animals; or they were scavengers, feeding off the remains of dead carcasses. It is also important to note that because of the dominance by the archosaurs, nature favored those Mesozoic Mammals that remained small and unobtrusive. This, along with a more efficient locomotion, helped them escape extinction with the mammal-like reptiles during the dominance of the dinosaurs.

However, with the evolution of mammary glands (the ultimate protection for offspring and paternal care) the mammals were assured a future. Feeding off insects, other small animals and plants and the dead carcasses left by the archosaurs, they soon began to proliferate and the “Age of the Mammals” began to dawn.

This is not to insinuate that the mammals pushed the dinosaurs into extinction. In fact, the dinosaurs had such a strong hold on the environmental niches that they occupied, it is doubtful that any other animal could have evolved to a point where it could compete with the archosaurs for these various ecological niches. The fossil evidence indicates that the archosaurs held their dominant status for over 140 million years and that they would have maintained their privileged position had they not suddenly died out at the end of the Mesozoic Era.

Most paleontologists believe that a gigantic asteroid, about eight to sixteen kilometers (5 to 10 miles) across, struck the earth and spewed trillions (perhaps tens of trillions) of tons of rock, debris and dust into the atmosphere. This catastrophe also initiated widespread tsunamis, volcanoes, forest fires and earthquakes. Smoke, soot and other air borne debris from this great disaster blocked out much of the sunlight.

A cloud of dust would have eventually circled the earth. The cloud cover would have plunged the earth into a constant twilight (some scientists believe it would have been a total blackout) for several weeks or even a couple of months.

In the absence of sunlight many photosynthetic autotrophs would have died. Those organisms that depend on these plants for their food source would then have begun to die. This would have set off a chain reaction that would eventually have led to the extinction of nearly every organism on earth, including the dinosaurs. The only animals to survive would have been those best able to cope with a prolonged period of cold and dark, those that were adapted to scavenging and those that could eat carrion.

There exists a group of asteroids, the Apollo Asteroids, which are known to cross earth’s orbit. In 1931, one of them, Eros, came within 23 million km (14.29 million mi) of earth and in 1968, another one, Icarus, came within four million km (2.5 million mi) of earth. Eros has an oblong shape, being 30 km (18.64 mi) in its largest dimension and Icarus is spherical, measuring about one kilometer (.62 mi) in diameter. Finally, asteroid 1997 XF11, about 1.6 km wide (one mi) is expected to pass within 965,000 km (600,000 mi) of the earth in the year 2028.

Any one of these asteroids are large enough to cause widespread destruction if they should strike the earth. The same is true of any large asteroid or comet that would strike the earth. This is just what most scientists believe happened 65 million years ago. A gigantic asteroid struck the earth. The debris thrown into the air by this extremely rare, catastrophic event blocked out much of the sunlight for few weeks or a couple of months at most and thus temporally cooled the overall temperature of the earth. The event also caused widespread fires, tsunamis, acid rain and many other environmental problems.

These environmental disasters and the period of constant twilight killed off most of the microorganisms that rely on the sunlight for photosynthesis. Many of those organisms that relied on these microorganisms for their life soon died. A chain reaction was thus started which altered the food chain for a few years. This was just long enough to force the dinosaurs and every other animal over 25 kilograms (55 pounds), into extinction. It is this catastrophic event, more than anything else, that gave birth to the Age of the Mammals and the Cenozoic Era.

Alpha Omega

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