What Is The Evidence Supporting Animal Evolution From A Protist Ancestor?

Pre-Cambrian Animal Life

Early animal life (Ediacaran biota) evolved from protists during the pre-Cambrian period, which is also known equally the Ediacaran period.

Learning Objectives

Describe the types of animals constitute in the Ediacaran period

Key Takeaways

Key Points

• The pre-Cambrian period ( Ediacaran flow ) took place betwixt 635-543 million years agone.
• Early animal life, called Ediacaran biota, evolved from protists; it was previously believed early animal life included only tiny, sessile, soft-bodied sea creatures, simply scientific show suggests more than complex animals lived during this time.
• Sponge-similar fossils believed to represent the oldest animals with hard body parts, named Coronacollina acula, date back as far as 560 1000000 years.
• The fossils of the earliest beast species e'er institute were pocket-size, one-centimeter long, sponge-like creatures, dating before 650 one thousand thousand years, which predates the Ediacaran menstruum.
• The discovery of the fossils of the primeval animal species provided evidence that animals may have evolved before the Ediacaran period during the Cryogenian menses.

Fundamental Terms

• Ediacaran period: period from about 635-543 one thousand thousand years ago; the last period of the belatedly Proterozoic Neoproterozoic Era
• choanoflagellate: whatsoever of a group of flagellate protozoa thought to be the closest unicellular ancestors of animals
• Coronacollina acula: sponge-similar fossils believed to correspond the oldest animals with difficult trunk parts that engagement dorsum every bit far as 560 million years

Pre-Cambrian Creature Life

The fourth dimension before the Cambrian flow is known as the Ediacaran period (between 635-543 million years ago), the final menses of the late Proterozoic Neoproterozoic Era. Information technology is believed that early beast life, termed Ediacaran biota, evolved from protists at this fourth dimension. Some protist species called choanoflagellates closely resemble the choanocyte cells in the simplest animals, sponges. In addition to their morphological similarity, molecular analyses have revealed similar sequence homologies in their DNA.

Earth'due south history: (a) Earth'south history is divided into eons, eras, and periods. The Ediacaran period was the concluding menstruum of the Proterozoic Era which concluded in the Cambrian period of the Phanerozoic Era. (b) Stages on the geological fourth dimension calibration are represented as a spiral.

The primeval life comprising Ediacaran biota was long believed to include merely tiny, sessile, soft-bodied sea creatures. Even so, recently there has been increasing scientific prove suggesting that more varied and circuitous animal species lived during this time, and possibly even before the Ediacaran period.

Fossils believed to stand for the oldest animals with hard body parts were recently discovered in Southward Australia. These sponge-similar fossils, named Coronacollina acula, date back as far as 560 meg years. They are believed to testify the existence of hard body parts and spicules that extended xx–40 cm from the main body (estimated about 5 cm long). Other organisms, such as Cyclomedusa and Dickinsonia, also evolved during the Ediacaran period.

Fossils from Ediacaran period: Fossils of (a) Cyclomedusa and (b) Dickinsonia that evolved during the Ediacaran flow.

Another recent fossil discovery may represent the earliest beast species e'er found. While the validity of this claim is still under investigation, these archaic fossils announced to be pocket-sized, one-centimeter long, sponge-like creatures. These fossils from Southward Australia date dorsum 650 one thousand thousand years, actually placing the putative animal earlier the great ice age extinction consequence that marked the transition betwixt the Cryogenian menstruum and the Ediacaran period. Until this discovery, almost scientists believed that there was no animal life prior to the Ediacaran flow. Many scientists now believe that animals may, in fact, accept evolved during the Cryogenian menstruum.

The Cambrian Explosion of Brute Life

During the Cambrian period, the most rapid evolution of new beast species occurred, but the cause of this explosion is all the same unknown.

Learning Objectives

Compare the theories that attempt to explain the Cambrian Explosion

Key Takeaways

Key Points

• Echinoderms, mollusks, worms, chordates, and arthropods (including arthropods called trilobites which were the one of the kickoff species to exhibit a sense of vision) developed during the Cambrian period.
• Environmental changes such every bit ascent levels of atmospheric oxygen and an increase in oceanic calcium concentrations may accept caused The Cambrian Explosion.
• A continental shelf with numerous shallow pools that provided the necessary living space for larger numbers of different types of animals to co-exist may have caused the Cambrian Explosion.
• The Cambrian Explosion may have been a result of ecological relationships between species, such equally changes in the food web, contest for food and space, and predator-prey relationships.
• The evolution of Hox control genes resulting in animal complication and flexibility may take provided the necessary opportunities for increases in possible animal morphologies.

Key Terms

• Ordovician menstruum: covers the time between 485-443 million years ago; followed the Cambrian menstruum
• Cambrian explosion: the relatively rapid advent (over a period of many millions of years), effectually 530 meg years ago, of nigh major creature phyla as demonstrated in the fossil record

The Cambrian Explosion of Animal Life

The Cambrian period, occurring betwixt approximately 542–488 meg years ago, marks the most rapid evolution of new brute phyla and animal diversity in earth'south history. It is believed that nearly of the animal phyla in existence today had their origins during this time, oftentimes referred to as the Cambrian explosion. Echinoderms, mollusks, worms, arthropods, and chordates arose during this period. I of the most dominant species during the Cambrian flow was the trilobite, an arthropod that was amid the first animals to exhibit a sense of vision.

Trilobites: These fossils (a–d) belong to trilobites, extinct arthropods that appeared in the early Cambrian menses 525 meg years ago and disappeared from the fossil record during a mass extinction at the end of the Permian catamenia about 250 million years ago.

Cambrian period: An creative person's rendition depicts some organisms from the Cambrian catamenia.

The causes of the Cambrian explosion are withal debated. In that location are many theories that attempt to answer this question. Ecology changes may accept created a more than suitable surroundings for animal life. Examples of these changes include ascent atmospheric oxygen levels and large increases in oceanic calcium concentrations that preceded the Cambrian catamenia. Some scientists believe that an expansive, continental shelf with numerous shallow lagoons or pools provided the necessary living space for larger numbers of different types of animals to co-exist. There is also support for theories that contend that ecological relationships betwixt species, such as changes in the food spider web, contest for food and space, and predator-prey relationships, were primed to promote a sudden, massive coevolution of species. All the same other theories claim genetic and developmental reasons for the Cambrian explosion. The morphological flexibility and complexity of animal development afforded by the development of Hox control genes may accept provided the necessary opportunities for increases in possible fauna morphologies at the time of the Cambrian menses. Theories that attempt to explicate why the Cambrian explosion happened must exist able to provide valid reasons for the massive animal diversification, as well as explicate why information technology happened when information technology did. In that location is evidence that both supports and refutes each of the theories described above. The reply may very well be a combination of these and other theories.

Earth'southward oxygen concentration: The oxygen concentration in earth's atmosphere rose sharply around 300 million years ago.

Unresolved questions almost the animal diversification that took place during the Cambrian period remain. For instance, we do not understand how the evolution of so many species occurred in such a short catamenia of time. Was in that location actually an "explosion" of life at this particular time? Some scientists question the validity of this idea considering there is increasing evidence to suggest that more animate being life existed prior to the Cambrian menstruation and that other similar species' so-called explosions (or radiations) occurred later in history as well. Furthermore, the vast diversification of animal species that appears to have begun during the Cambrian menstruation continued well into the following Ordovician period. Despite some of these arguments, well-nigh scientists agree that the Cambrian period marked a time of impressively-rapid beast development and diversification that is unmatched elsewhere during history.

Post-Cambrian Development and Mass Extinctions

The mail service-Cambrian era was characterized past animate being evolution and variety where mass extinctions were followed past adaptive radiations.

Learning Objectives

Differentiate amongst the causes of mass extinctions and their effects on animate being life

Key Takeaways

Key Points

• During the Ordovician period, plant life offset appeared on land, which allowed aquatic animals to move on to land.
• Periods of mass extinction caused by cataclysmic events similar volcanic eruptions and meteor strikes have erased many genetic lines and created room for new species.
• The largest mass extinction upshot in earth's history, which occurred at the end of the Permian period, resulted in a loss of roughly 95 percent of the existing species at that time.
• The disappearance of some dominant species of Permian reptiles and the warm and stable climate that followed fabricated information technology possible for the dinosaurs to emerge and diversify.
• Another mass extinction outcome caused by a meteor strike and volcanic ash eruption occurred at the cease of the Cretaceous menses, bringing the Mesozoic Era to an end and pushing dinosaurs into extinction.
• The disappearance of dinosaurs led to the dominance of plants, which created new niches for birds, insects, and mammals; animal diversity was also brought on by the creation of continents, islands, and mountains.

Key Terms

• Cenozoic: a geologic era about betwixt 65 1000000 years agone to the present when the continents moved to their electric current position and modernistic plants and animals evolved
• mass extinction: a precipitous decrease in the full number of species in a relatively short period of time
• Cretaceous: the concluding geologic period within the Mesozoic era from well-nigh 146 to 65 million years ago; concluded with a big mass extinction

Mail-Cambrian Evolution and Mass Extinctions

The periods that followed the Cambrian during the Paleozoic Era were marked by further animal evolution and the emergence of many new orders, families, and species. Equally creature phyla connected to diversify, new species adapted to new ecological niches. During the Ordovician period, which followed the Cambrian period, found life get-go appeared on land. This change allowed formerly-aquatic animal species to invade land, feeding directly on plants or decaying vegetation. Continual changes in temperature and moisture throughout the remainder of the Paleozoic Era due to continental plate movements encouraged the development of new adaptations to terrestrial existence in animals, such as limbs in amphibians and epidermal scales in reptiles.

Changes in the surround often create new niches (living spaces) that contribute to rapid speciation and increased diversity. On the other mitt, cataclysmic events, such as volcanic eruptions and meteor strikes that obliterate life, can outcome in devastating losses of diversity. Such periods of mass extinction have occurred repeatedly in the evolutionary record of life, erasing some genetic lines while creating room for others to evolve into the empty niches left behind. The end of the Permian menses (and the Paleozoic Era) was marked by the largest mass extinction effect in Earth's history, a loss of roughly 95 percent of the extant species at that time. Some of the dominant phyla in the world'due south oceans, such as the trilobites, disappeared completely. On land, the disappearance of some dominant species of Permian reptiles made it possible for a new line of reptiles to sally: the dinosaurs. The warm and stable climatic conditions of the ensuing Mesozoic Era promoted an explosive diversification of dinosaurs into every believable niche in state, air, and water. Plants, too, radiated into new landscapes and empty niches, creating complex communities of producers and consumers, some of which became extremely large on the abundant food bachelor.

Mass extinctions: Mass extinctions have occurred repeatedly over geological time.

Another mass extinction upshot occurred at the stop of the Cretaceous menstruation, bringing the Mesozoic Era to an terminate. Skies darkened and temperatures fell as a large meteor impact expelled tons of volcanic ash, blocking incoming sunlight. Plants died, herbivores and carnivores starved, and the mostly cold-blooded dinosaurs ceded their dominance of the landscape to more warm-blooded mammals. In the following Cenozoic Era, mammals radiated into terrestrial and aquatic niches once occupied by dinosaurs. Birds, the warm-blooded offshoots of one line of the ruling reptiles, became aerial specialists. The advent and dominance of flowering plants in the Cenozoic Era created new niches for insects, as well as for birds and mammals. Changes in animate being species diversity during the late Cretaceous and early Cenozoic were too promoted by a dramatic shift in globe'due south geography, as continental plates slid over the crust into their current positions, leaving some animal groups isolated on islands and continents or separated by mountain ranges or inland seas from other competitors. Early on in the Cenozoic, new ecosystems appeared, with the development of grasses and coral reefs. Tardily in the Cenozoic, further extinctions followed past speciation occurred during water ice ages that covered high latitudes with ice and then retreated, leaving new open spaces for colonization.

Source: https://courses.lumenlearning.com/boundless-biology/chapter/the-evolutionary-history-of-the-animal-kingdom/

Posted by: eldercovis1990.blogspot.com

Share this post