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The end of the mesozoic era - 29 jun 2021 ... ... the end of the Mesozoic Era, dinosaurs were already in decline. That is the conclusion o

The Mesozoic Era: The Mesozoic era was the second era of the Phanerozoic eon. It w

3. Silurian. 4. Devonian. 5. Carboniferous. How did Earth's organism change during the first period of the Paleozoic Era? Great '' explosion'' of invertebrate life occurs in seas. What event do scientist think may have cause the mass of extinction at the end of the Paleozoic Era.Following the Precambrian Time, Paleozoic Era, and Mesozoic Era on the geologic time scale is the Cenozoic Era, which began 65 million years ago and continues to the present. After the Cretaceous …Transitional primate-like creatures were evolving by the end of the Mesozoic Era (ca. 65.5 million years ago). At that time, the world was very different from today. The continents were in other locations and they had somewhat different shapes.Following the Precambrian Time, Paleozoic Era, and Mesozoic Era on the geologic time scale is the Cenozoic Era, which began 65 million years ago and continues to the present. After the Cretaceous …The Mesozoic Era began at the end of the Permian-Triassic Extinction Event about 252.17 million years ago and continued for about 186 million years to end ...The geological time of the first land plants were introduced toward the end of the Mesozoic era. What is Mesozoic era? This era is referred to as the age of Conifers and it lasted from about 252 to 66 million years ago. In this era, there was the presence of most ancestors of plants and animals which is why it being a period where first land ...The Mesozoic Era (252–66 Ma) spread over an interesting time that witnessed splitting of the Pangaea supercontinent and the opening and spreading of the Atlantic and Indian oceans. It brackets the time interval sandwiched between two extreme events of biodiversity crisis i.e., the end Permian mass extinction (around 252 Ma) marking the base ... 27 mar 2018 ... At the end of the Mesozoic Era, only one group of pterosaurs has been recognized, the Azhdarchidae, of which Quetzalcoatlus was a member. This ...At that time-point the Mesozoic Era ended, and along with it the Cretaceous Period, about 70% of biodiversity on Earth, and all dinosaurs but a few birds. Extend your distance trace along the route until you reach the end of the Mesozoic Era. How many km did you travel in total from the GGB to reach the end of the Mesozoic Era?The Paleozoic era came to a sudden end around 252 mya with the single largest extinction event in Earth’s history. ... The Mesozoic era or “age of reptiles” began 252 mya at the end of the Paleozoic era and continued until 66 mya. The land was covered with non-flowering gymnosperm plants, the ancestors of modern-day conifer trees ...The Permian (/ ˈ p ɜːr m i. ə n / PUR-mee-ən) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period 298.9 million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the last period of the Paleozoic Era; the following Triassic Period belongs to the Mesozoic Era. The concept …27 mar 2018 ... At the end of the Mesozoic Era, only one group of pterosaurs has been recognized, the Azhdarchidae, of which Quetzalcoatlus was a member. This ...Triassic Period, in geologic time, the first period of the Mesozoic Era. It began 252 million years ago, at the close of the Permian Period, and ended 201 million years ago, when it was succeeded by the Jurassic Period. The Triassic Period marked the beginning of major changes that were to take place throughout the Mesozoic Era, particularly in ...The Mesozoic marine revolution ( MMR) refers to the increase in shell-crushing ( durophagous) and boring predation in benthic organisms throughout the Mesozoic era (251 Mya to 66 Mya), along with bulldozing and sediment remodelling in marine habitats. [1] The term was first coined by Geerat J. Vermeij, [2] who based his work on that of Steven M ...Sep 23, 2023 · The Mesozoic Era (252 to 66 million years ago) The Mesozoic Era is the geological period between 252 million and 66 million years ago and is subdivided into three epochs: the Triassic, Jurassic, and Cretaceous. The Mesozoic Era is often referred to as the Age of Reptiles because most dinosaurs lived there. The Mesozoic began with the supercontinent Pangaea. Then, during the Mesozoic, Pangaea broke up and the continents drifted apart. The movement of continents changed climates. It also caused a great deal of volcanic activity. Mass extinctions occurred at the end of the Triassic and Cretaceous Periods of the Mesozoic Era.Jurassic Period, second of three periods of the Mesozoic Era. Extending from 201.3 million to 145 million years ago, the Jurassic was a time of global change in the continents, oceanographic patterns, and biological systems. On land, dinosaurs and flying pterosaurs dominated, and birds made their first appearance.What cause probably was not important in contributing to extinction of most species on Earth, including the dinosaurs, in a very short interval of time at the end of the Mesozoic Era? Cold from the change in Earth's orbit caused when the meteorite shoved the planet farther from the sun. Imagine sunrise on the last day of the Mesozoic era, 66 million years ago. Shafts of sunlight rake through the swamps and coniferous forests along the coast of what is now Mexico’s Yucatán ...By the end of the Ordovician, life was no longer confined to the seas. Plants had begun to colonize the land, closely followed in the Silurian by invertebrates, and in the Upper Devonian by vertebrates. The early tetrapods of this time were amphibian-like animals that eventually gave rise to the reptiles and synapsids by the end of the Paleozoic. Sixty-six million years ago a worldwide cataclysmic event marked the end of the Mesozoic Era and changed the whole course of life on earth (Fig. 1). This was the end-Cretaceous mass extinction, and whether it was caused by a bolide strike or triggered by huge volcanic eruptions remains hotly debated. There is geological evidence for both at the ...The end of the Cretaceous brought the end of many previously successful and diverse groups of organisms, such as non-avian dinosaurs and ammonites. ... The Cretaceous is defined as the period between 145.5 and 65.5 million years ago,* the last period of the Mesozoic Era, following the Jurassic and ending with the extinction of the dinosaurs ...The Phanerozoic Eon is a period of geological history that spans 542 million years and is typically subdivided into three eras. These eras are: Paleozoic Era: 542 to 251 million years ago. Mesozoic Era: 251 to 65 million years ago. Cenozoic Era: 65 million years ago to present. Mesozoic. The dinosaurs and the mammals appeared during the ... Dinosaurs lived during the Mesozoic era. The Mesozoic era lasted from 251 mya to 65.5 mya. It is divided into three periods: the Triassic, the Jurassic, and the Cretaceous. Pangaea broke apart during the Mesozoic era. It began to break apart in the Late Triassic. Eventually, Pangaea split into two separate landmasses-Gondwanaland and Laurasia.Following the Precambrian Time, Paleozoic Era, and Mesozoic Era on the geologic time scale is the Cenozoic Era, which began 65 million years ago and continues to the present. After the Cretaceous …The Jurassic ( / dʒʊˈræsɪk / juu-RASS-ik [2]) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period 201.4 million years ago (Mya) to the beginning of the Cretaceous Period, approximately 145 Mya. The Jurassic constitutes the middle period of the Mesozoic Era and is named after the Jura Mountains ...Jan 29, 2018 · The Permian Extinction. After the Permian Extinction wiped out over 95% of ocean-dwelling species and 70% of land species, the new Mesozoic Era began about 250 million years ago. The first period of the era was called the Triassic Period. The first big change was seen in the types of plants that dominated the land. 7 abr 2019 ... The Mesozoic extinction was second • in magnitude • to the one at the end of the Paleozoic, • but it is more widely known. Systems Approach • We ...The Cretaceous period was the last and longest segment of the Mesozoic era. It lasted approximately 79 million years, from the minor extinction event that closed the Jurassic period about 145 ...The Mesozoic Era began approximately 252 million years ago at the close of the Paleozoic Era and ended 66 million years ago at the dawn of the Cenozoic Era. The Mesozoic is best known as the time of the dinosaurs. Dinosaurs first appeared early in the Mesozoic and came to dominate life on Earth throughout the rest of the era. The Mesozoic is ...[Narrator:] The K-T boundary, found at the bottom of this gray layer, marks not only the end of a period -- the Cretaceous -- but also of the Mesozoic era, a ...Verified answer. physics. Astronomers measure the distance to a particular star to be 6.0 6.0 light-years ( 1 \mathrm {~ly} 1 ly = distance light travels in 1 1 year). A spaceship travels from Earth to the vicinity of this star at steady speed, arriving in 3.50 3.50 years as measured by clocks on the spaceship. The Mesozoic Era is the age of the dinosaurs and lasted almost 180 million years from approximately 250 to 65 million years ago. This era includes 3 well known periods called the Triassic , Jurassic, and Cretaceous periods. A mass-extinction marked the beginning and end of the Mesozoic Era. The event that caused the transition from the ...Mesozoic Era, Second of the Earth’s three major geologic eras and the interval during which the continental landmasses as known today were separated from the supercontinents Laurasia and Gondwana by continental drift.It lasted from c. 251 to c. 65.5 million years ago and includes the Triassic, Jurassic, and Cretaceous periods. The Mesozoic saw the …Test your knowledge of the fluffy, winged dinos of the bygone Mesozoic era, from little Microraptor to the enormous Yutyrannus with this quiz. Advertisement Advertisement Advertisement Advertisement Advertisement Advertisement Advertisement...Permian–Triassic boundary at Frazer Beach in New South Wales, with the End Permian extinction event located just above the coal layer. The Permian–Triassic (P–T, P–Tr) extinction event (PTME), also known as the Late Permian extinction event, the Latest Permian extinction event, the End-Permian extinction event, and colloquially as the Great Dying, forms the boundary between the Permian ...By the end of the Ordovician, life was no longer confined to the seas. Plants had begun to colonize the land, closely followed in the Silurian by invertebrates, and in the Upper Devonian by vertebrates. The early tetrapods of this time were amphibian-like animals that eventually gave rise to the reptiles and synapsids by the end of the Paleozoic. Jan 29, 2018 · The Permian Extinction. After the Permian Extinction wiped out over 95% of ocean-dwelling species and 70% of land species, the new Mesozoic Era began about 250 million years ago. The first period of the era was called the Triassic Period. The first big change was seen in the types of plants that dominated the land. The Mesozoic Era came to an abrupt and violent end during the Cretaceous Period. Sixty-five million years ago, an asteroid roughly six miles across slammed into the Yucatan Peninsula in Mexico.The Jurassic is the middle Mesozoic period spanning the time interval from ∼201 Ma to ∼145 Ma, according to the 2013 IUGS time scale. ... the most famous impact event of the Late Cretaceous is the Chicxulub event that marked the end of the Mesozoic and is well documented and described in the literature (see, for instance, ...The Permian (/ ˈ p ɜːr m i. ə n / PUR-mee-ən) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period 298.9 million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the last period of the Paleozoic Era; the following Triassic Period belongs to the Mesozoic Era. The concept …The Cretaceous is defined as the period between 145.5 and 65.5 million years ago,* the last period of the Mesozoic Era, following the Jurassic and ending with the extinction of the dinosaurs (except birds). By the beginning of the Cretaceous, the supercontinent Pangea was already rifting apart, and by the mid-Cretaceous, it had split into ... Mesozoic/Ended. Why did the Mesozoic era end? This era includes the Triassic, Jurassic, and Cretaceous Periods, names that may be familiar to you. It ended with a massive meteorite impact that caused a mass extinction, wiping out the dinosaurs and up to 80% of life on Earth. Mesozoic signposts are colored blue.3 nov 2013 ... The Mesozoic was a time of significant tectonic, climate and evolutionary activity. The era witnessed the gradual rifting of the supercontinent ...The Jurassic ( / dʒʊˈræsɪk / juu-RASS-ik [2]) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period 201.4 million years ago (Mya) to the beginning of the Cretaceous Period, approximately 145 Mya. The Jurassic constitutes the middle period of the Mesozoic Era and is named after the Jura Mountains ...There were no more dinosaurs after the end of the Cretaceous, at about 65.5 million years ago. The Cenozoic era, also called the Age of. Mammals, began ...The Mesozoic Era: The Mesozoic era was the second era of the Phanerozoic eon. It was comprised of three geological periods namely the Triassic, Jurassic and Cretaceous periods. Answer and Explanation: 1The Mesozoic Era (251.9 to 66.0 million years ago) was the "Age of Reptiles." During the Mesozoic, Pangaea began separating into the modern continents, and the modern Rocky Mountains rose. Dinosaurs, crocodiles, and pterosaurs ruled the land and air. This could dramatically affect the health of living beings and could explain how 70% of species became extinct by the end of this era. This is how the Mesozoic Era affected the biosphere. The high temperatures also would have affected the geosphere. 7) Earth – Moon System (3pts) Briefly describe the current hypothesis for the formation of the ...Nov 3, 2013 · Mesozoic means “middle life”, deriving from the Greek prefix meso-/μεσο- for “between” and zōon/ζῷον meaning “animal” or “living being”. It is one of three geologic eras of the Phanerozoic Eon, preceded by the Paleozoic (“ancient life”) and succeeded by the Cenozoic (“new life”). The era is subdivided into ... The Extinction of Dinosaurs. At the end of the Mesozoic era, 65 million years ago, dinosaurs and many other animal and plant species became extinct. What ...Study with Quizlet and memorize flashcards containing terms like Which of these do scientists offer as the MOST recent explanation as to why many plants and animals died out at the end of the Mesozoic era?, A rainforest area is experiencing a severe drought. As a consequence, the insect population has decreased. What will the insect-eating birds MOST likely do as a result of the drought?, The ...3 dic 2021 ... an illustration of present day continent location When the Mesozoic Era ended 66 million years ago — at the end of the Cretaceous period ...The Mesozoic Era is the age of dinosaurs. They evolved from earlier reptiles to fill niches on land, in the water, and in the air. Mammals also evolved but were small in size. Flowering plants appeared for the first time. Dinosaurs went extinct at the end of the Mesozoic.Jurassic Period, second of three periods of the Mesozoic Era. Extending from 201.3 million to 145 million years ago, the Jurassic was a time of global change in the continents, oceanographic patterns, and biological systems. On land, dinosaurs and flying pterosaurs dominated, and birds made their first appearance.Non-bird dinosaurs lived between about 245 and 66 million years ago, in a time known as the Mesozoic Era. This was many millions of years before the first modern humans , Homo sapiens, appeared. Scientists divide the Mesozoic Era into three periods: the Triassic, Jurassic and Cretaceous. During this era, the land gradually split from one huge ...Verified answer. physics. Astronomers measure the distance to a particular star to be 6.0 6.0 light-years ( 1 \mathrm {~ly} 1 ly = distance light travels in 1 1 year). A spaceship travels from Earth to the vicinity of this star at steady speed, arriving in 3.50 3.50 years as measured by clocks on the spaceship. The Mesozoic marine revolution (MMR) refers to the increase in shell-crushing (durophagous) and boring predation in benthic organisms throughout the Mesozoic era (251 Mya to 66 Mya), ... The Mesozoic marine revolution was not the first bout of increased predation pressure; that occurred around the end of the Ordovician. There is some …Transitional primate-like creatures were evolving by the end of the Mesozoic Era (ca. 65.5 million years ago). At that time, the world was very different from today. The continents were in other locations and they had somewhat different shapes. The Mesozoic Era spans from 251 to 65.5 Million years ago and is divided into three geologic periods inlcuding the Triassic, Jurassic and Cretaceous. Mesozoic ...Jurassic Period, Interval of geologic time, 201.3–145 million years ago, that is one of the three major divisions of the Mesozoic Era. It was preceded by the Triassic Period and followed by the Cretaceous. During the Jurassic, Pangea began to break up into the present-day continents. Marine invertebrates flourished, and large reptiles ... Oct 15, 2023 · Jurassic Period, second of three periods of the Mesozoic Era. Extending from 201.3 million to 145 million years ago, the Jurassic was a time of global change in the continents, oceanographic patterns, and biological systems. On land, dinosaurs and flying pterosaurs dominated, and birds made their first appearance. Cretaceous Period, in geologic time, the last of the three periods of the Mesozoic Era. It began 145 million years ago and ended 66 million years ago and featured the extinction of the dinosaurs at the end of the period.Question: 15pts 7) What geologic evidence in the Yucatan Peninsula of Mexico might offer explanation for the massive extinction at the end of the Mesozoic Era? A 2,000 square-mile basaltic flood basalt A 100-kilometer high tsunami An 8-mile diameter meteor's crater A 500-mile long range of explosive andesitic volcano peaks OO 8) The era known for the rise inThe Mesozoic Era (252–66 Ma) spread over an interesting time that witnessed splitting of the Pangaea supercontinent and the opening and spreading of the Atlantic and Indian oceans. It brackets the time interval sandwiched between two extreme events of biodiversity crisis i.e., the end Permian mass extinction (around 252 Ma) marking the base ... No. The dinosaurs rose in the Mesozoic era. The end of the Mesozoic era was also the end of the dinosaurs. The era following is the Cenozoic, which we are still …The central theme of the Mesozoic Era right before was how dinosaurs dominated the land. Now, the Cenozoic Era (66 Million Years Ago to Present) is a story about us. It’s the era when humans began to evolve. But first, humans needed a bit of help. As dinosaurs roamed the Earth for over 160 million years, we needed their dominance to …Another mass extinction event occurred at the end of the Cretaceous period, bringing the Mesozoic Era to an end. Skies darkened and temperatures fell as a large meteor impact and tons of volcanic ash blocked incoming sunlight. Plants died, herbivores and carnivores starved, and the mostly cold-blooded dinosaurs ceded their dominance of the landscape …Dec 3, 2021 · Mesozoic: An era in geologic history that contained three related periods which became renowned for their large reptiles: the Triassic (which spanned from 251 to 199.6 million years ago), the Jurassic (which spanned from 199.6 to 145.5 million years ago), and the Cretaceous (which spanned from 145.5 to 65.5 million years ago). The Mesozoic Era lasted about 180 million years, from about 245 million years ago to about 65 million years ago. The Mesozoic is divided into just three time periods: the Triassic, the Jurassic, and the Cretaceous. Since lots of things were going on in each time period, we can only summarize the events. You can learn more by going to your ... Sep 29, 2023 · Triassic Period, in geologic time, the first period of the Mesozoic Era. It began 252 million years ago, at the close of the Permian Period, and ended 201 million years ago, when it was succeeded by the Jurassic Period. The Triassic Period marked the beginning of major changes that were to take place throughout the Mesozoic Era, particularly in ... The Mesozoic Era spans from 251 to 65.5 Million years ago and is divided into three geologic periods inlcuding the Triassic, Jurassic and Cretaceous. Mesozoic ...The end boundary for the Mesozoic era, the Cretaceous-Paleogene boundary, is defined by a 20-inch (50 centimeters) thick sliver of rock in El Kef, Tunisia, which contains well-preserved fossils ...To choose a different answer, click one different oval. A. The fossil record suggests that there was an abrupt extinction of many plants and animals at the end of the Mesozoic era. B. Few fossils of the Mesozoic era have survived in the rocks that mark the end of the Cretaceous. C.3 dic 2021 ... an illustration of present day continent location When the Mesozoic Era ended 66 million years ago — at the end of the Cretaceous period ...The Mesozoic came to an abrupt end 66 million years ago in a dramatic extinction event. An estimated 70 per cent of plant and animal species perished. Many theories have been suggested for its cause.Study with Quizlet and memorize flashcards containing terms like A mass extinction that included the disappearance of all dinosaur species occurred during the _______. a. Cenozoic Era b. Mesozoic Era c. Paleozoic Era d. Precambrian, Which describes the idea of spontaneous generation? a. genetic information passing from parents to an offspring b. life arising from nonlife c. nonliving things ... The Mesozoic Era (252–66 Ma) spread over an interesting time that witnessed splitting of the Pangaea supercontinent and the opening and spreading of the Atlantic and Indian oceans. It brackets the time interval sandwiched between two extreme events of biodiversity crisis i.e., the end Permian mass extinction (around 252 Ma) marking the base ... Oct 3, 2012 · Ammonites underwent a remarkable recovery in the Jurassic, and continued to diversify until their extinction at the end of the Mesozoic Era. Specimens include a plate of Dactylioceras sp., and individuals of: Dactylioceras tennicostatum, Praeparkinsonia garantiformis, and Acanthopleuroceras valdani. The museum also has a model of a live ... For 140 million years prior to the Cenozoic Era, dinosaurs held dominion over the land, as their stage was prepared by the great extinction at the end of the ...The Permian (/ ˈ p ɜːr m i. ə n / PUR-mee-ən) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period 298.9 million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the last period of the Paleozoic Era; the following Triassic Period belongs to the Mesozoic Era. The concept …The Mesozoic Era (251 - 65Ma) contains 3 Geological Periods. The Triassic Period(251 - 199Ma), ... It was, however, the end of one era and the beginning of another. More specifically it was the ...Study with Quizlet and memorize flashcards containing terms like Dinosaurs were the dominant land animal of the Mesozoic Era., The breakup of Pangaea resulted in warm, wet global climates., Which of the following statement describes dinosaurs during the Mesozoic era? a. They were very inactive c. They were good mothers b. They were cold …Oct 15, 2023 · Jurassic Period, second of three periods of the Mesozoic Era. Extending from 201.3 million to 145 million years ago, the Jurassic was a time of global change in the continents, oceanographic patterns, and biological systems. On land, dinosaurs and flying pterosaurs dominated, and birds made their first appearance. The Triassic Period (252-201 million years ago) began after Earth's worst-ever extinction event devastated life. The Permian-Triassic extinction event, also known as the Great Dying, took place roughly 252 million years ago and was one of the most significant events in the history of our planet. It represents the divide between the Palaeozoic ...The central theme of the Mesozoic Era right before was how dinosaurs dominated the land. Now, the Cenozoic Era (66 Million Years Ago to Present) is a story about us. It’s the era when humans began to evolve. But first, humans needed a bit of help. As dinosaurs roamed the Earth for over 160 million years, we needed their dominance to end.This extinction event marked the end of the Paleozoic Era and the beginning of the Mesozoic Era. The Mesozoic was marked by the long rule of the dinosaurs starting with their emergence in the Triassic Period. They then thrived until the end of the Cretaceous Period. During the Mesozoic Era, the earliest birds and mammals also evolved in the ...Verified answer. physics. Astronomers measure the distance to a particular star to be 6.0 6.0 light-years ( 1 \mathrm {~ly} 1 ly = distance light travels in 1 1 year). A spaceship travels from Earth to the vicinity of this star at steady speed, arriving in 3.50 3.50 years as measured by clocks on the spaceship. The Cretaceous is defined as the period between 145.5 and 65.5 million years ago,* the last period of the Mesozoic Era, following the Jurassic and ending with the extinction of the dinosaurs (except birds). By the beginning of the Cretaceous, the supercontinent Pangea was already rifting apart, and by the mid-Cretaceous, it had split into ...The Mesozoic Era began approximately 251 million years ago (mya) at the end of the Paleozoic Era when the area that would eventually be the Colorado Plateau broke free from Pangea, the supercontinent. The Mesozoic is divided into three time periods: Triassic (251-200 mya), Jurassic (200-145 mya), and Cretaceous (145-65 mya).Birds and mammals also appeared as the Mesozoic Era progressed. For most of the Mesozoic Era, gymnosperms were the dominant plant form. Angiosperms began to appear during the Cretaceous Period. After the mass extinction that marked the end of the Mesozoic Era, many life forms, including the dinosaurs, disappeared. Mammals became more prevalent ...The Mesozoic marine revolution ( MMR) refers to the i, Study with Quizlet and memorize flashcards containing terms like The Jurassic-Cretaceous boundary was the time wh, At the end of the Mesozoic Era there was a mass extinction., The dominance of dinosaurs lasted until the end of the Cretaceous period, , 23 feb 2022 ... ... Mesozoic era ended, we demonstrate that the impact that caused the C, It ended during the Mesozoic era. Scientists discovered that the Eocene time period existed in Earth's history aroun, Imagine sunrise on the last day of the Mesozoic era, 66 million years ag, 9 jun 2020 ... At the end of the Mesozoic era, the climate be, Jan 3, 2022 · The final period of the Mesozoic era, t, Mesozoic Era, Second of the Earth’s three major geologic eras an, Study with Quizlet and memorize flashcards containi, The Mesozoic Era is the age of dinosaurs. They evolved from , Nov 3, 2013 · Mesozoic means “middle life”, deriving from the Gr, The central theme of the Mesozoic Era right before was how di, The current era on the geologic time scale is the Cenozoic Era. The er, Imagine sunrise on the last day of the Mesozoic era, , The Triassic period was the first period of the Mesoz, Paleozoic Era, major interval of geologic time that began 538..