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https://paleontology.us/precambrian-era/ Paleontology_US Sat, 30 May 2020 13:26:31 +0000 Facts https://paleontology.us/?p=1347 The Precambrian Era, also known as the Precambrian Supereon, is a period of time in Earth’s history that covered approximately 4 billion years, which is about 90% of the entire history of the Earth. It starts about 4.56 billion years ago when the Earth was formed and ends about 541 million years ago when simple […]

The Precambrian Era, also known as the Precambrian Supereon, is a period of time in Earth’s history that covered approximately 4 billion years, which is about 90% of the entire history of the Earth. It starts about 4.56 billion years ago when the Earth was formed and ends about 541 million years ago when simple organisms began evolving into more complex multi-celled organisms.

This period of time is not only the longest in Earth’s history, however, it is also one of the most obscure. That’s because scientists have a hard time getting information from the Precambrian rocks because over the years they’ve become heavily metamorphosized. This makes it hard to determine how events unfolded during this time. Scientists have broken down this era into 3 distinct eons: the Hadean, the Archean, and the Proterozoic.

The Hadean Eon begins when the Earth formed from swirling dust and gas coalescing into a sphere about 4.56 billion years ago and continues all throughout the geological development of the planet. During this time, Earth had impact craters all over it from asteroids and other celestial bodies crashing into it; had oceans that weren’t filled with water but were instead filled with boiling, liquid rock and had air that was filled with sulfur, carbon dioxide, and dust. This is the time when a large celestial body crashed into the Earth and caused a part of it to be kicked into Earth’s orbit and therefore becoming the moon.

The Archean Eon began approximately 560 million years after the formation of the Earth. During this time, the planet isn’t a living hell like it was during the Hadean Eon. For the most part, the Earth has cooled down and the water vapor that was locked in the atmosphere had begun to cool and condense into massive oceans. A large portion of the carbon dioxide that was a main component of the atmosphere during the last eon, was chemically alter and became limestone for the ocean floor. It was also the time when simple bacteria began to make their first appearance of the Precambrian Era. Scientists believe these original life forms were blue-green algae that swam in the prehistoric oceans.

The Proterozoic Eon began about 2 billion years ago, which is approximately 2 billion years after the formation of the Earth. During this time, Earth was moving toward becoming a planet with a more oxygenated atmosphere. It was also the time when several glaciations occurred—which many scientists believe led to Snowball Earth, although at this point it’s still a hypothesis. Single celled organisms named eukaryotes also began to gain prominence during this period and this was also the time when multi-celled life really began to evolve; both probably as a result of the free oxygen that was now available in the atmosphere.

The Precambrian Era is also known for the formation, and the occasional break-up, of several land masses. This included the supercontinent known as Vaalbara. This supercontinent was formed approximately 3.6 billion years ago. However, it ended up breaking up about 800 million years after its formation. Other super-continents that were created and which eventually broke up during this period of time was Kenorland, the supercontinent Nuna and the one called Rodinia.

It was a period of extraordinary geological change as well as extraordinary biological change. Changes which radically altered the planet and would eventually set the stage for the Paleozoic Era – a period of time that is known for the unprecedented evolution of life and eventually, the rise of human beings.

The Precambrian Era covers 7/8th of Earth’s history although paleontologists have found very few fossils of Precambrian organisms. The Precambrian Era was marked by the formation of Earth 4.6 billion years ago, and ended with the explosion of hard-shelled organisms 600 million years ago. It is divided into the earlier Archaean period, when no life existed, and the later Proterozoic Period, in which life did exist. The state of the Earth was much different back then; and was probably ripe enough for life to spring out of non-living particles. First, the Earth formed. The outer covering of the earth cooled and hardened into a crust. The hot molten insides of the Earth leaked out at weak places in the crust. These volcanoes created more rock surface on the young Earth. The clouds formed by the volcanoes caused huge amounts of rain to fall and the oceans were created. Most life forms during this era were in the form of prokaryotic single-celled organisms, but fossil finds started to increase at the end of the period as complex, soft-bodied invertebrates began to develop. Life never spread out to land during this time, because oxygen and ozone levels in the atmosphere were not abundant yet, but life did thrive in the seas at the very least. Stromatolites are among the most famous “organisms†during the Precambrian era, and are formed from the growth of cyanobacteria, which are bacteria with chlorophyll and were instrumental in developing the Earth’s first supply of oxygen. We do not know of any major extinctions during the Precambrian Era due to a lack of fossils, but we do know that the era ended with the explosion of invertebrate life in the seas.

https://paleontology.us/did-dinosaurs-really-have-feathers/ Paleontology_US Tue, 26 May 2020 11:47:18 +0000 Facts https://paleontology.us/?p=1342 Did Dinosaurs Really Have Feathers? Science is learning more and more about the versatility of form in dinosaurs with each great find in China, the Americas, Antarctica, and elsewhere. During their heyday in the Triassic, Jurassic, and Cretaceous periods, dinosaurs evolved to fill niches in most ecosystems. Some were large, some were small, some walked […]

Did Dinosaurs Really Have Feathers?

Science is learning more and more about the versatility of form in dinosaurs with each great find in China, the Americas, Antarctica, and elsewhere. During their heyday in the Triassic, Jurassic, and Cretaceous periods, dinosaurs evolved to fill niches in most ecosystems. Some were large, some were small, some walked on land, some were amphibious, and some dinosaurs even possessed the ability to fly. But did they have real honest-to-goodness feathers? Recent research shows that they did, but this isn’t the end of the story.

For many years science has known that the only remaining descendants of the dinosaur lineage are the birds. (So, if anyone asks you whether dinosaurs really died out at the end of the Cretaceous, you can point out the window at our feathered friends.) One of the most surprising developments in paleontology in recent years has been the discovery that, like birds, dinosaurs—many dinosaurs, in fact—possessed feathers. It stands to reason that if birds have them, they must have evolved in something older, right?

Let’s take a quick look at feather design. The typical feather in modern birds consists of a central shaft (rachis), with serial paired branches (barbs) forming a flattened, usually curved surface—the vane. The barbs branch into barbules, and the barbules of adjacent barbs are attached to one another by hooks, stiffening the vane. In many birds some or all of the feathers lack the barbules or hooks, and the plumage has a loose hair-like appearance. The precursors of bird feathers were simple, straight, dense, filamentous structures made mostly of keratin. These eventually evolved into branched, then downy, structures in several stalked forms that soon disappeared. Over time, this branched condition resolved itself into a central stalk with vanes on either side, and these vanes later evolved into barbs.

The first dinosaur fossils with structures that could be considered feathers were found in the 1990s. Other discoveries followed. By 2011 some studies were even suggesting that all dinosaurs had some type of feathery covering on at least some parts of their bodies—in much the same way that all mammals have hair but not all mammals are hairy. Even though the first dinosaurs are thought to have emerged some 245 million years ago, dinosaurs with feathers have been dated to only 180 million years ago. Yet, the story does not end there.

Feathers, it seems, did not originate with the dinosaurs. According to a recent study, they may have evolved in another group. The pterosaurs, a closely related but separate group of “ruling reptiles†(or archosaurs, a group that, incidentally, also includes birds and crocodiles), also had feathers. A study of pterosaur fossils published in 2019 described the presence of branching featherlike structures called pycnofibres in pterosaur fossils dating to about 160 million years ago. These feathers appeared in tufts; they were not simple and straight, which suggests that the origin of feathers predated both the pterosaurs and the dinosaurs and occurred in a common ancestor some 250 million years old or older.

So, did dinosaurs have feathers? They did—and older forms of life had them too.

https://paleontology.us/quaternary-period/ Paleontology_US Mon, 30 Mar 2020 16:58:30 +0000 Facts http://www.paleontology.us/?p=1062 Quaternary Period Quaternary Period is the current and most recent of the three periods of the  Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.588 ± 0.005 million years ago to the present. The Quaternary Period is divided into two epochs: the Pleistocene (2.588 million years ago to 11.7 thousand years ago) and the Holocene (11.7 thousand […]

Quaternary Period

Quaternary Period is the current and most recent of the three periods of the  Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.588 ± 0.005 million years ago to the present. The Quaternary Period is divided into two epochs: the Pleistocene (2.588 million years ago to 11.7 thousand years ago) and the Holocene (11.7 thousand years ago to today). The informal term “Late Quaternary†refers to the past 0.5–1.0 million years.

The Quaternary Period is typically defined by the cyclic growth and decay of continental ice sheets associated with Milankovitch cycles and the associated climate and environmental changes that occurred.

The Quaternary Period follows the Neogene Period and extends to the present. The Quaternary covers the time span of glaciations classified as the Pleistocene, and includes the present interglacial time-period, the Holocene.

This places the start of the Quaternary at the onset of Northern Hemisphere glaciation approximately 2.6 million years ago. Prior to 2009, the Pleistocene was defined to be from 1.805 million years ago to the present, so the current definition of the Pleistocene includes a portion of what was, prior to 2009, defined as the Pliocene.

Quaternary stratigraphers usually worked with regional subdivisions. From the 1970s, the International Commission on Stratigraphy (ICS) tried to make a single geologic time scale based on GSSP’s, which could be used internationally. The Quaternary subdivisions were defined based on biostratigraphy instead of paleoclimate.

This led to the problem that the proposed base of the Pleistocene was at 1.805 Mya, long after the start of the major glaciations of the northern hemisphere. The ICS then proposed to abolish use of the name Quaternary altogether, which appeared unacceptable to the International Union for Quaternary Research (INQUA).

In 2009, it was decided to make the Quaternary the youngest period of the Cenozoic Era with its base at 2.588 Mya and including the Gelasian stage, which was formerly considered part of the Neogene Period and Pliocene Epoch.

The Anthropocene has been proposed as a third epoch as a mark of the anthropogenic impact on the global environment starting with the  Industrial Revolution, or about 200 years ago. The Anthropocene is not officially designated by the ICS, but a working group has been working on a proposal for the creation of an epoch or sub-period.

The 2.6 million years of the Quaternary represents the time during which recognizable humans existed. Over this geologically short time period, there has been relatively little change in the distribution of the continents due to plate tectonics.

The Quaternary geological record is preserved in greater detail than that for earlier periods.

The major geographical changes during this time period included the emergence of the Strait of Bosphorus and Skagerrak during glacial epochs, which respectively turned the Black Sea and Baltic Sea into fresh water, followed by their flooding (and return to salt water) by rising sea level; the periodic filling of the English Channel, forming a land bridge between Britain and the European mainland; the periodic closing of the Bering Strait, forming the land bridge between Asia and North America; and the periodic flash flooding of Scablands of the American Northwest by glacial water.

The current extent of Hudson Bay, the Great Lakes and other major lakes of North America are a consequence of the Canadian Shield’s readjustment since the last ice age; different shorelines have existed over the course of Quaternary time.

Source : wikipedia.org and natgeo.com

Also read: Paleontologists Are Trying to Understand Why the Buffalo Fossil Record Is Mostly Males

https://paleontology.us/what-is-the-worlds-largest-dinosaur/ Paleontology_US Thu, 26 Mar 2020 00:10:40 +0000 Facts http://www.paleontology.us/?p=1023 The titanosaur dinosaur Dreadnoughtus schrani (pictured above) is the only supermassive dinosaur for which scientists have both the femur and humerus bones from the same individual. That makes it the largest dinosaur for which scientists can confidently calculate a mass. However, Argentinosaurus is likely the largest dinosaur, by mass, on record. The battle for the […]

The titanosaur dinosaur Dreadnoughtus schrani (pictured above) is the only supermassive dinosaur for which scientists have both the femur and humerus bones from the same individual. That makes it the largest dinosaur for which scientists can confidently calculate a mass. However, Argentinosaurus is likely the largest dinosaur, by mass, on record.

The battle for the title of world’s largest dinosaur is complicated.

Here’s why: Paleontologists rarely discover an entire skeleton. They’re more likely to uncover bone fragments and then try to estimate a profile of height and weight. Moreover, there are three categories for largest dinosaur on record: the weightiest, longest and tallest.

Starting with the weightiest, the gold-medal winner is likely Argentinosaurus . This supermassive titanosaur (a titanosaur is a giant sauropod, a long-necked and long-tailed herbivorous dinosaur) that lived about 100 million to 93 million years ago, during the Cretaceous period , in what is now (you guessed it) Argentina.

But estimates of Argentinosaurus’ weight vary widely; the beast weighed 77 tons (70 metric tons), according to London’s Natural History Museum ; up to 90 tons (82 metric tons), according to New York City’s American Museum of Natural History ; and 110 tons (100 metric tons), according to BBC Earth .

It’s no wonder these calculations are all over the place. Argentinosaurus is known from just 13 bones: six midback vertebrae, five fragmentary hip vertebrae, one tibia (a shinbone) and one rib fragment. “There’s a femur that you’ll see with it [in some sketches], but that femur was found 15 kilometers [9 miles] away. So, who knows who that belongs to?†said Kenneth Lacovara, a professor of paleontology and geology and the dean of the School of Earth & Environment at Rowan University in Glassboro, New Jersey.

Another contender is Patagotitan , a titanosaur that weighed a whopping 69 tons (62 metric tons) when it lived about 100 million years ago in what is now Argentina. However, this weight was calculated based on a composite of individuals (there were six found in all), rather than just one dinosaur, Lacovara noted.

Which raises the question: How do scientists calculate the weight of an extinct animal? According to Lacovara, there are three ways.

Minimum shaft circumference method : Scientists measure the minimum circumference of the humerus (the upper arm bone) and femur (the thigh bone) from the same individual. Then, they plug these numbers in to a formula. The result is highly correlative with the animal’s mass. “It makes sense,†Lacovara said, “since all quadrupeds have to put all of the weight of the body on just those four bones. [So], the structural properties of those four bones are going to correlate closely with the mass.â€

There are caveats, however. If the humerus and femur bone are from different individuals, as they were with Patagotitan , “the result is an estimate of a composite individual that never actually existed,†Lacovara said. Moreover, if only a single bone (a humerus or a femur) is used, the proportions of the missing bone are a guess. “Obviously, this introduces even more uncertainty,†he said. “Examples of this are Notocolossus and Paralititan .â€

The largest known dinosaur that has a humerus and femur bone from the same individual is the 77-million-year-old Dreadnoughtus , a 65-ton (59 metric tons) titanosaur that Lacovara and his team excavated in Argentina.

Volumetric method : In this approach, researchers determine the body volume of the dinosaur and use that number to calculate the animal’s weight. This is challenging, because most titanosaur skeletons are incomplete. ( Dreadnoughtus is the most complete, at 70 percent. Argentinosaurus is just 3.5 percent complete.) In addition, researchers have to guess how much space the lungs and other air-filled structures took up. Experts also have to speculate how “blubbery or shrink-wrapped†the skin on these dinosaurs was.

“In my view, this method is unworkable and lacks replicability, which is one of the hallmarks of science,†Lacovara said.

Wild guesses : This is how scientists estimate the weight of dinosaurs that don’t have any preserved humerus or femur bones. “ Argentinosaurus, Futalognkosaurus and Puertasaurus are examples of this,†Lacovara said. “They are clearly huge, but there is no systematic, replicable way to estimate their mass.â€

Moving on, what’s the longest dinosaur? That honor likely goes to Diplodocus or Mamenchisaurus , which can be described as slender and elongated sauropod dinosaurs, Lacovara said. “Both are known from reasonably complete skeletons, and both would be about 115 feet [35 m] long.â€

In contrast, the titanosaurs were shorter. For example, Dreadnoughtus was “only†about 85 feet (26 m) long.

But this category is still rife with uncertainty. “Some dinosaurs claimed to be the longest are extremely fragmentary,†Lacovara said. “For example, Sauroposeidon is known from just four neck vertebrae. So, really, who knows?†Meanwhile, Amphicoelias , a sauropod known from only a sketch of a single vertebra in a notebook from the 19th century paleontologist Edward Cope, is sometimes cited as the longest, tallest and heaviest dinosaur.

“The vertebra was apparently lost or destroyed in transport — or maybe never existed,†Lacovara said. “You can’t have a dinosaur represented by nothing, so as far as I’m concerned, Amphicoelias is not a thing.â€

As for the tallest dinosaur, the winner is likely Giraffatitan , a 40-foot-tall (12 m) sauropod dinosaur that lived in the late Jurassic about 150 million years ago in what is now Tanzania.

As for that dinosaur’s actual height, the devil is in the details.

“This, of course, depends on whether these animals could lift their necks up to maximum height,†Lacovara said. “Their forelimb and shoulder structure looks like they were angling their necks upward, but we may never know the degree to which they could do this.â€

Source: Live Science .

Also read: The Smallest Dinosaur Discovered on the Planet

https://paleontology.us/mesozoic-era/ Paleontology_US Tue, 17 Mar 2020 21:53:58 +0000 Facts http://www.paleontology.us/?p=929 Following both the Precambrian Time and the Paleozoic Era on the Geologic Time Scale came the Mesozoic Era. The Mesozoic Era is sometimes called the “age of the dinosaursâ€Â because dinosaurs were the dominant animals for much of the era. The Permian Extinction After the Permian Extinction wiped out over 95% of ocean-dwelling species and 70% of land species, the new […]

Following both the Precambrian Time and the Paleozoic Era on the Geologic Time Scale came the Mesozoic Era. The Mesozoic Era is sometimes called the “age of the dinosaurs†because dinosaurs were the dominant animals for much of the era.

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. Most of the species of plants that survived the Permian Extinction were plants that had enclosed seeds, like gymnosperms.

The Paleozoic Era

Since most of the life in the oceans became extinct at the end of the Paleozoic Era, many new species emerged as dominant. New types of corals appeared, along with water-dwelling reptiles. Very few types of fish remained after the mass extinction, but those that did survive flourished. On land, the amphibians and small reptiles like turtles were dominant during the early Triassic Period. By the end of the period, small dinosaurs began to emerge.

The Jurassic Period

After the end of the Triassic Period, the Jurassic Period began. Most of the marine life in the Jurassic Period stayed the same as it was in the Triassic Period. There were a few more species of fish that appeared, and toward the end of the period, crocodiles came into being. The most diversity occurred in plankton species.

Land Animals

Land animals during the Jurassic Period had more diversity. Dinosaurs got much bigger and the herbivorous dinosaurs ruled the Earth. At the end of the Jurassic Period, birds evolved from dinosaurs.

The climate changed to more tropical weather with a lot of rain and humidity during the Jurassic Period. This allowed land plants to undergo a large evolution. In fact, jungles covered much of the land with many conifers in higher elevations.

The Mesozoic Era

The last of the periods within the Mesozoic Era was called the Cretaceous Period. The Cretaceous Period saw the rise of flowering plants on land. They were helped along by the newly formed bee species and the warm and tropical climate. Conifers were still really abundant throughout the Cretaceous Period as well.

The Cretaceous Period

As for marine animals during the Cretaceous Period, sharks and rays became commonplace. The echinoderms that survived the Permian Extinction, like starfish, also became abundant during the Cretaceous Period.

On land, the first small mammals started to appear during the Cretaceous Period. Marsupials evolved first, and then other mammals. More birds evolved, and reptiles got bigger. Dinosaurs were still dominant, and carnivorous dinosaurs were more prevalent.

Another Mass Extinction

At the end of the Cretaceous Period, and the end of the Mesozoic Era came another mass extinction. This extinction is generally called the K-T Extinction. The “K†comes from the German abbreviation for Cretaceous, and the “T†is from the next period on the Geologic Time Scale – the Tertiary Period of the Cenozoic Era. This extinction took out all dinosaurs, except birds, and many other forms of life on Earth.

There are different ideas as to why this mass extinction occurred. Most scientists agree it was some sort of catastrophic event that caused this extinction. Various hypotheses include massive volcanic eruptions that shot dust into the air and caused less sunlight to reach the surface of the Earth causing photosynthetic organisms like plants and those who depended on them, to die off slowly. Some others believe a meteor hit causing the dust to block the sunlight. Since plants and animals that ate plants died off, this caused top predators like carnivorous dinosaurs to also perish.

Also read: Cretaceous Period

https://paleontology.us/cretaceous-period/ Paleontology_US Mon, 09 Mar 2020 12:38:34 +0000 Facts http://www.paleontology.us/?p=770 Cretaceous Period, in geologic time, the last of the three periods of the Mesozoic Era. The Cretaceous began 145.0 million years ago and ended 66 million years ago; it followed the Jurassic Period and was succeeded by the Paleogene Period (the first of the two periods into which the Tertiary Period was divided). The Cretaceous is the longest period of the  Phanerozoic Eon. […]

Cretaceous Period , in geologic time, the last of the three periods of the Mesozoic Era . The Cretaceous began 145.0 million years ago and ended 66 million years ago; it followed the Jurassic Period and was succeeded by the Paleogene Period (the first of the two periods into which the Tertiary Period was divided). The Cretaceous is the longest period of the  Phanerozoic Eon. Spanning 79 million years, it represents more time than has elapsed since the extinction of the dinosaurs , which occurred at the end of the period.

The name Cretaceous is derived from creta, Latin for “chalk,†and was first proposed by J.B.J. Omalius d’Halloy in 1822. D’Halloy had been commissioned to make a geologic map of France, and part of his task was to decide upon the geologic units to be represented by it. One of his units, the Terrain Crétacé, included chalks and underlying sands. Chalk is a soft, fine-grained type of limestone composed predominantly of the armourlike plates of coccolithophores, tiny floating algae that flourished during the Late Cretaceous. Most Cretaceous rocks are not chalks, but most chalks were deposited during the Cretaceous. Many of these rocks provide clear and easily accessed details of the period because they have not been deformed or eroded and are relatively close to the surface—as can be seen in the white cliffs bordering the Strait of Dover between France and England.

The Cretaceous Period began with Earth’s land assembled essentially into two continents, Laurasia in the north and Gondwana in the south. These were almost completely separated by the equatorial Tethys seaway, and the various segments of Laurasia and Gondwana had already started to rift apart. North America had just begun pulling away from Eurasia during the Jurassic, and South America had started to split off from Africa, from which India, Australia, and Antarctica were also separating. When the Cretaceous Period ended, most of the present-day continents were separated from each other by expanses of water such as the North and South Atlantic Ocean. At the end of the period, India was adrift in the Indian Ocean, and Australia was still connected to Antarctica.

The lengthy Cretaceous Period constitutes a major portion of the interval between ancient life-forms and those that dominate Earth today. Dinosaurs were the dominant group of land animals, especially “duck-billed†dinosaurs (hadrosaurs), such as Shantungosaurus , and horned forms, such as Triceratops . Giant marine reptiles such as ichthyosaurs, mosasaurs , and plesiosaurs were common in the seas, and flying reptiles (pterosaurs) dominated the sky. Flowering plants arose close to the beginning of the Cretaceous and became more abundant as the period progressed. The Late Cretaceous was a time of great productivity in the world’s oceans, as borne out by the deposition of thick beds of chalk in western Europe , eastern Russia, southern Scandinavia, the Gulf Coast of North America , and western Australia . The Cretaceous ended with one of the greatest mass extinctions in the history of Earth , exterminating the dinosaurs, marine and flying reptiles, and many marine invertebrates.

The Cretaceous Environment

Paleogeography

The position of Earth ’s landmasses changed significantly during the Cretaceous Period—not unexpected, given its long duration. At the onset of the period there existed two supercontinents, Gondwana in the south and Laurasia in the north. South America, Africa (including the adjoining pieces of what are now the Arabian Peninsula and the Middle East), Antarctica,  India, Madagascar , Australia,  and several smaller landmasses were joined in Gondwana in the south, while North America, Greenland, and Eurasia (including Southeast Asia) formed Laurasia. Africa had split from South America, the last land connection being between Brazil and Nigeria. As a result, the South Atlantic Ocean joined with the widening North Atlantic. In the region of the Indian Ocean, Africa and Madagascar separated from India, Australia, and Antarctica in Late Jurassic to Early Cretaceous times. Once separated from Australia and Antarctica, India began its journey northward, which culminated in a later collision with Asia during the Cenozoic Era . Madagascar broke away from Africa during the Late Cretaceous, and Greenland separated from North America. Australia was still joined to Antarctica. These were barely attached at the junction of what are now North and South America.

Sea level was higher during most of the Cretaceous than at any other time in Earth history, and it was a major factor influencing the paleogeography of the period. In general, world oceans were about 100 to 200 metres (330 to 660 feet) higher in the Early Cretaceous and roughly 200 to 250 metres (660 to 820 feet) higher in the Late Cretaceous than at present. The high Cretaceous sea level is thought to have been primarily the result of water in the ocean basins being displaced by the enlargement of midoceanic ridges.

As a result of higher sea levels during the Late Cretaceous, marine waters inundated the continents, creating relatively shallow epicontinental seas in North America, South America, Europe, Russia , Africa, and Australia. In addition, all continents shrank somewhat as their margins flooded. At its maximum, land covered only about 18 percent of Earth’s surface, compared with approximately 28 percent today. At times, Arctic waters were connected to the Tethys seaway through the middle of North America and the central portion of Russia. On several occasions during the Cretaceous, marine animals living in the South Atlantic had a seaway for migration to Tethys via what is presently Nigeria, Niger , Chad, and Libya . Most of western Europe, eastern Australia, parts of Africa, South America, India, Madagascar, Borneo, and other areas that are now land were entirely covered by marine waters for some interval of Cretaceous time.

Detailed study indicates 5 to 15 different episodes of rises and falls in sea level. The patterns of changes for the stable areas throughout history are quite similar, although several differences are notable. During most of the Early Cretaceous, parts of Arctic Canada , Russia, and western Australia were underwater, but most of the other areas were not. During the middle Cretaceous, east-central Australia experienced major inundations called transgressions. In the Late Cretaceous, most continental landmasses were transgressed but not always at the same time. One explanation for the lack of a synchronous record is the concept of geoidal eustacy, in which, it is suggested, as Earth’s continents move about, the oceans bulge at some places to compensate. Eustacy would result in sea level being different from ocean basin to ocean basin.

Water circulation and mixing were not as great as they are today, because most of the oceans (e.g., the developing North Atlantic) were constricted, and the temperature differences between the poles and the Equator were minimal. Thus, the oceans experienced frequent periods of anoxic (oxygenless) conditions in the bottom waters that reveal themselves today as black shales. Sometimes, particularly during the mid-Cretaceous, conditions extended to epicontinental seas, as attested by deposits of black shales in the western interior of North America.

The Cretaceous world had three distinct geographic subdivisions: the northern boreal, the southern boreal, and the Tethyan region. The Tethyan region separated the two boreal regions and is recognized by the presence of fossilized reef-forming rudist bivalves , corals , larger foraminiferans (single-celled organisms known for their glasslike shells, or tests), and certain ammonites (a group of extinct cephalopods known for their spiral shells) that inhabited only the warmer Tethyan waters. Early in the Cretaceous, North and South America separated sufficiently for the marine connection between the Tethys Sea and the Pacific to deepen substantially. The Tethys-to-Pacific marine connection allowed for a strong westward-flowing current, which is inferred from faunal patterns. For example, as the Cretaceous progressed, the similarity between rudist bivalves of the Caribbean and western Europe decreased, while some Caribbean forms have been found on Pacific seamounts, in Southeast Asia , and possibly in the Balkans .

The remnants of the northern boreal realm in North America, Europe, Russia, and Japan have been extensively studied. It is known, for instance, that sediments in the southwestern Netherlands indicate several changes of temperature during the Late Cretaceous. These temperature swings imply that the boundary between the northern boreal areas and the Tethys region was not constant with time. Russian workers recognize six paleobiogeographic zones: boreal, which in this context is equivalent to Arctic ; European; Mediterranean, including the central Asian province; Pacific; and two paleofloristic zonations of land. Southern boreal areas and the rocks representing the southern Tethys margin lack this level of detail.

Magnetically, the Cretaceous was quiet relative to the subsequent Paleogene Period . In fact, magnetic reversals are not noted for a period of some 42 million years, from the early Aptian to the late Santonian ages. The lengths of Earth’s months ( see synodic period) have changed regularly for at least the past 600 million years because of tidal friction and other forces that slow Earth’s rotation. The rate of change in the synodic month was minimal for most of the Cretaceous but has accelerated since. The reasons for these two anomalies are not well understood.

Paleoclimate

In general, the climate of the Cretaceous Period was much warmer than at present, perhaps the warmest on a worldwide basis than at any other time during the Phanerozoic Eon . The climate was also more equable in that the temperature difference between the poles and the Equator was about one-half that of the present. Floral evidence suggests that tropical to subtropical conditions existed as far as 45° N, and temperate conditions extended to the poles. Evaporites are plentiful in Early Cretaceous rocks—a fact that seems to indicate an arid climate, though it may have resulted more from constricted ocean basins than from climatic effects. The occurrence of evaporites mainly between latitudes 10° and 30° N suggests arid subtropics, but the presence of coals poleward of 30° indicates humid midlatitudes. Occurrences of Early Cretaceous bauxite and laterite, which are products of deep weathering in warm climates with seasonal rainfall, support the notion of humid midlatitudes.

Temperatures were lower at the beginning of the period, rising to a maximum in the mid-Cretaceous and then declining slightly with time until a more accentuated cooling during the last two ages of the period. Ice sheets and glaciers were almost entirely absent except in the high mountains , so, although the end of the Cretaceous was coolest, it was still much warmer than it is today.

Models of Earth’s climate for the mid-Cretaceous based on the positions of the continents, location of water bodies, and topography suggest that winds were weaker than at present. Westerly winds were dominant in the lower to midlatitudes of the Pacific for the entire year. In the North Atlantic, however, winds blew from the west during winter but from the east during summer. Surface water temperatures were about 30 °C (86 °F) at the Equator year-round, but at the poles they were 14 °C (57 °F) in winter and 17 °C (63 °F) in summer. A temperature of 17 °C is suggested for the ocean bottom during the Albian Age , but it may have declined to 10 °C (50 °F) by the Maastrichtian . These temperature values have been calculated from oxygen isotope measurements of the calcitic remains of marine organisms. The data support models that suggest diminished ocean circulation both vertically and latitudinally. As stated in the section Paleogeography, above, low circulation could account for the periods of black shale deposition during the Cretaceous.

Other paleontological indicators suggest details of ocean circulation. The occurrence of early and mid-Cretaceous rudists and larger Tethyan foraminiferans in Japan may very well mean that there was a warm and northward-flowing current in the region. A similar occurrence of these organisms in Aptian-Albian sediments as far south as southern Tanzania seems to indicate a southward-flowing current along the east coast of Africa. The fact that certain warm-water life-forms found in the area of present-day Argentina are absent from the west coast of Africa suggests a counterclockwise gyre in the South Atlantic. In addition, the presence of larger foraminiferans in Newfoundland and Ireland indicates the development of a “proto- Gulf Stream †by the mid-Cretaceous.

Cretaceous Life

The Cretaceous Period is biologically significant because it is a major part of the transition from the early life-forms of the Paleozoic Era to the advanced diversity of the current Cenozoic Era . For example, most if not all of the flowering plants made their first appearance during the Cretaceous. Although dinosaurs were the dominant animals of the period, many modern animals, including the placental mammals , made their debut during the Cretaceous. Other groups—such as clams and snails, snakes and lizards, and most fishes—developed distinctively modern characteristics before the mass extinction marking the end of the period.

Marine life

The marine realm can be divided into two paleobiogeographic regions, the Tethyan and the boreal. This division is based on the occurrence of rudist -dominated organic reeflike structures. Rudists were large, rather unusual bivalves that had one valve shaped like a cylindrical vase and another that resembled a flattened cap. The rudists were generally dominant over the corals as framework builders. They rarely existed outside the Tethyan region, and the few varieties found elsewhere did not create reeflike structures. Rudist reeflike structures of Cretaceous age serve as reservoir rocks for petroleum in Mexico, Venezuela, and the Middle East .

Other organisms almost entirely restricted to the Tethys region were actaeonellid and nerineid snails, colonial corals, calcareous algae , larger bottom-dwelling (benthic) foraminiferans , and certain kinds of ammonites and echinoids. In contrast, belemnites were apparently confined to the colder boreal waters. Important bivalves of the boreal realm were the reclining forms (e.g., Exogyra and Gryphaea ) and the inoceramids, which were particularly widespread and are now useful for distinguishing among biostratigraphic zones.

Marine plankton took on a distinctly modern appearance by the end of the Cretaceous. The coccolithophores became so abundant in the Late Cretaceous that vast quantities accumulated to form the substance for which the Cretaceous Period was named—chalk. The planktonic foraminiferans also contributed greatly to fine-grained calcareous sediments. Less-abundant but important single-celled animals and plants of the Cretaceous include the diatoms, radiolarians, and dinoflagellates. Other significant marine forms of minute size were the ostracods and calpionellids.

Ammonites were numerous and were represented by a variety of forms ranging from the more-usual coiled types to straight forms. Some of the more-unusual ammonites, called heteromorphs, were shaped like fat corkscrews and hairpins. Such aberrant forms most certainly had difficulty moving about. Ammonites preyed on other free-swimming or benthic invertebrates and were themselves prey to many larger animals, including the marine reptiles called mosasaurs .

Other marine reptiles were the long-necked plesiosaurs and the more fishlike ichthyosaurs . Sharks and rays (chondrichthians) also were marine predators, as were the teleost (ray-finned) fishes. One Cretaceous fish, Xiphactinus , grew to more than 4.5 metres (15 feet) and is the largest known teleost.

Mass extinction

At or very close to the end of the Cretaceous Period, many animals that were important elements of the Mesozoic world became extinct. On land the dinosaurs perished, but plant life was less affected. Of the planktonic marine flora and fauna, only about 13 percent of the coccolithophore and planktonic foraminiferan genera survived the extinction. Ammonites and belemnites became extinct, as did such marine reptiles as ichthyosaurs, mosasaurs, and plesiosaurs. Among the marine benthos, the larger foraminiferans (orbitoids) died out, and the hermatypic corals were reduced to about one-fifth of their genera. Rudist bivalves disappeared, as did bivalves with a reclining life habit, such as Exogyra and Gryphaea . The stratigraphically important inoceramids also died out. Overall, approximately 80 percent of animal species disappeared, making this one of the largest mass extinctions in Earth’s history.

Many theories have been proposed to explain the Late Cretaceous mass extinction. Since the early 1980s, much attention has been focused on the asteroid theory formulated by American scientists Walter and Luis Alvarez . This theory states that the impact of an asteroid on Earth may have triggered the extinction event by ejecting a huge quantity of rock debris into the atmosphere, enshrouding Earth in darkness for several months or longer. With no sunlight able to penetrate this global dust cloud, photosynthesis ceased, resulting in the death of green plants and the disruption of the food chain. There is much evidence in the rock record that supports this hypothesis . A huge crater 180 km (112 miles) in diameter dating to the latest Cretaceous has been discovered buried beneath sediments of the Yucatán Peninsula near Chicxulub, Mexico. In addition, tektites (fractured sand grains characteristic of meteorite impacts) and the rare-earth element iridium, which is common only deep within Earth’s mantle and in extraterrestrial rocks, have been found in deposits associated with the extinction. There is also evidence for some spectacular side effects of this impact, including an enormous tsunami that washed up on the shores of the Gulf of Mexico and widespread wildfires triggered by a fireball from the impact. (For more detailed information on this hypothesis, see dinosaur: Extinction .)

The asteroid theory has met with skepticism among paleontologists, partly because the amount of iridium dispersed by the collision is more typical of that of a smaller object, such as a comet. Furthermore, terrestrial factors may have also played a role in the extinction. A huge outpouring of lava, known as the Deccan Traps, occurred in India during the latest Cretaceous. Some paleontologists believe that the carbon dioxide that accompanied these flows created a global greenhouse effect that greatly warmed the planet. Others note that tectonic plate movements caused a major rearrangement of the world’s landmasses, particularly during the latter part of the Cretaceous. The climatic changes resulting from such continental drift could have caused a gradual deterioration of habitats favourable to the dinosaurs and other animal groups that suffered extinction. It is, of course, possible that sudden catastrophic phenomena such as an asteroid or comet impact contributed to an environmental deterioration already brought about by terrestrial causes.

Terrestrial life

Although the fossil record is irregular in quality and quantity for the Early Cretaceous, it is obvious that dinosaurs continued their lengthy dominance of the land. The Late Cretaceous record is much more complete, particularly in the case of North America and Asia. It is known, for instance, that during the Late Cretaceous many dinosaur types lived in relationships not unlike the present-day terrestrial mammal communities. Although the larger dinosaurs, such as the carnivorous Tyrannosaurus and the herbivorous Iguanodon , are the best-known, many smaller forms also lived in Cretaceous times. Triceratops , a large three-horned dinosaur, inhabited western North America during the Maastrichtian Age. The titanosaurs, a group of sauropods that included Argentinosaurus and Dreadnoughtus , emerged during the second half of the period and were the largest land animals that ever lived.

Cretaceous Geology

Economic significance of Cretaceous deposits

In the course of approximately 30 million years during the middle of the Cretaceous Period, more than 50 percent of the world’s known petroleum reserves were formed. Almost three-fourths of this mid-Cretaceous petroleum accumulated in a relatively small region around what is now the Persian Gulf. Much of the remainder accumulated in another limited region, of the Americas between the Gulf of Mexico and Venezuela. Evidently the low-latitude Tethys seaway collected along its margins large amounts of organic matter, which today are found as petroleum in the Gulf Coast of the United States and Mexico, the Maracaibo Basin in Venezuela, the Sirte (or Surt) Basin in Libya, and the Persian Gulf region. Other mineral deposits of commercial value occur in the circum-Pacific mountain systems and chain of island arcs. Such metals as gold, silver, copper,  molybdenum, tungsten, tin, iron, lead, zinc, and manganese were concentrated into ore deposits of various dimensions during episodes of igneous activity in the late Mesozoic.

Source: https://www.britannica.com/

Also read: Devonian Period: Facts & Information

https://paleontology.us/10-ceratosaurus-facts/ Paleontology_US Mon, 02 Mar 2020 10:16:45 +0000 Facts http://www.paleontology.us/?p=707 Ceratosaurus Facts Ceratosaurus popped up in Jurassic Park III at one point – but what do we know about the dinosaur? Below you will find 10 Ceratosaurus Facts Facts. Like a ’56 T-Bird parked in a car park full of hybrids, Ceratosaurus shared its range with several less-archaic carnivores. This primitive predator really stands out in films and in […]

Ceratosaurus Facts

Ceratosaurus popped up in Jurassic Park III at one point – but what do we know about the dinosaur? Below you will find 10 Ceratosaurus Facts Facts.

Like a ’56 T-Bird parked in a car park full of hybrids, Ceratosaurus shared its range with several less-archaic carnivores. This primitive predator really stands out in films and in museums, which helps explain the odd dino’s enduring popularity.

1. Ceratosaurus Had an Armored Backside.

A row of bony plates called osteoderms ran down the animal’s spine. They probably didn’t offer much defense, but they sure helped Ceratosaurus score some major style points!

2. It Might Have had Semi-Aquatic Habits.

Like modern gators, Ceratosaurus came with a strong, broad, and flexible tail—and the animal’s teeth are sometimes found scattered near lungfish skeletons. So was it amphibious? According to paleontologist Robert Bakker, the idea has merit. He’s even envisioned Ceratosaurus as a wannabe crocodile of sorts, stealthily lurking beneath Jurassic rivers. But while this dinosaur was likely a halfway-decent swimmer, many feel that Bakker’s very speculative hypothesis can’t keep its head above the water.

3. It’s Been a Movie Star for Over 100 Years.

Audiences watched the bonafide celebrity stalk cavemen in Brute Force (1914), take on Triceratops in One Million Years B.C. (1966), and gag at the sight of Spinosaurus poop in Jurassic Park III (2001).

4. Some Argue that This Creature Directly Competed with the Better-Known Allosaurus.

Both carnivores stalked Utah and Colorado 150 million years ago, and both had nasty jaws designed for slicing (as opposed to crushing bone and all that fun stuff). Because similar bites often mean similar diets, maybe these two titans hunted the same game. Or they might have found separate niches and steered clear of each other— Allosaurus did have proportionately-smaller teeth, after all. Regardless, the late Jurassic was clearly a tough time to be an herbivore.

5. Scientists Still Aren’t Sure About What Ceratosaurus Did With its Dynamic Nasal Horn.

In 1920, an American geologist named Charles Whitney Gilmore wrote that Ceratosaurus ’ horn “formed a useful weapon for offense and defense.†Nowadays, however, this thing’s function no longer seems quite so clear-cut.  Thin and probably on the fragile side, most 21 ^st -century specialists hold that Ceratosaurus’ best-known feature was better-suited for display than combat.

6. It Featured Unusually Long Teeth.

One specimen manages to look just as scary with its mouth shut. This dino’s upper teeth are so long that—when the creature’s maw assumes a “closed†position—they extend below the lower jaw!

7. Ceratosaurus was Relatively Rare

Allosaurus seems to have been far more common than Ceratosaurus. The latter, bumpy-snouted predator is only known from a relative handful of skeletons. Meanwhile, very few dinos are as well-represented by the fossil record as Allosaurus : A single quarry contains assorted bones belonging to at least 44 individuals. How many Ceratosaurus specimens has this same site yielded? One.

8. Its Remains Have Been Found on Three Different Continents.

Though frequently cited as a North American creature, Ceratosaurus material has also turned up in Portugal and Tanzania.

9. Size-Wise, Not all Ceratosaurus Were Created Equal.

Ceratosaurus dentisculatus could have really done some damage. While the 18-foot Ceratosaurus nasicornis is, by far, this genus’ most famous species, C. dentisculatus was noticeably longer, with an estimated length of over 23 feet (7 metres)—and it may been twice as massive.

10. Ceratosaurus was Named by One of America’s Greatest Paleontologists.

Othniel Charles Marsh (1832-1899) also introduced the world to such prehistoric icons as Stegosaurus , Triceratops , Allosaurus , Diplodocus , and Apatosaurus . Plus, he lobbied for Native American rights, regularly corresponded with Charles Darwin, and was among the first to suggest that present-day birds evolved from dinosaurs.

Source: www.mentalfloss.com

Also read: 10 Cool Facts About Giganotosaurus

https://paleontology.us/paleontologists-find-one-billion-year-old-green-seaweed-fossils/ Paleontology_US Sat, 29 Feb 2020 21:52:00 +0000 Facts http://www.paleontology.us/?p=684 Paleontologists have discovered the microscopic fossilized remains of green seaweed near Dalian in the Liaoning province of northern China. The microfossils are approximately one billion years old. They represent a previously unknown species of green seaweed, named Proterocladus antiquus, and are barely visible to the naked eyed at 2 mm in length, or roughly the size […]

Paleontologists have discovered the microscopic fossilized remains of green seaweed near Dalian in the Liaoning province of northern China. The microfossils are approximately one billion years old. They represent a previously unknown species of green seaweed, named Proterocladus antiquus , and are barely visible to the naked eyed at 2 mm in length, or roughly the size of a typical flea.

“These new fossils suggest that green seaweeds were important players in the ocean long before their land-plant descendants moved and took control of dry land,†said senior author Professor Shuhai Xiao, a researcher in the Department of Geosciences and Global Change Center at Virginia Tech.

“The entire biosphere is largely dependent on plants and algae for food and oxygen, yet land plants did not evolve until about 450 million years ago.â€

“Our study shows that green seaweeds evolved no later than one billion years ago, pushing back the record of green seaweeds by about 200 million years. What kind of seaweeds supplied food to the marine ecosystem.â€

The current hypothesis is that land plants — the trees, grasses, food crops, bushes, even kudzu — evolved from green seaweeds, which were aquatic plants. Through geological time they moved out of the water and became adapted to and prospered on dry land, their new natural environment.

“These fossils are related to the ancestors of all the modern land plants we see today,†Professor Xiao said.

“However, the caveat that not all geobiologists are on the same page — that debate on the origins of green plants remains.â€

“Not everyone agrees with us; some scientists think that green plants started in rivers and lakes, and then conquered the ocean and land later.â€

There are three main types of seaweed: brown (Phaeophyceae), green (Chlorophyta), and red (Rhodophyta), and thousands of species of each kind.

Fossils of red seaweed, which are now common on ocean floors, have been dated as far back as 1.047 billion years old.

“There are some modern green seaweeds that look very similar to the fossils that we found,†Professor Xiao said.

“A group of modern green seaweeds, known as siphonocladaleans, are particularly similar in shape and size to the fossils we found.â€

Photosynthetic plants are, of course, vital to the ecological balance of the planet because they produce organic carbon and oxygen through photosynthesis, and they provide food and the basis of shelter for untold numbers of mammals, fish, and more.

“Yet, going back 2 billion years, Earth had no green plants at all in oceans,†Professor Xiao said.

“ Proterocladus antiquus seaweeds display multiple branches, upright growths, and specialized cells known as akinetes that are very common in this type of fossil,†said lead author Dr. Qing Tang, a postdoctoral researcher in the Department of Geosciences and Global Change Center at Virginia Tech.

“Taken together, these features strongly suggest that the fossil is a green seaweed with complex multicellularity that is circa one billion years old. These likely represent the earliest fossil of green seaweeds. In short, our study tells us that the ubiquitous green plants we see today can be traced back to at least one billion years.â€

The discovery is described in a paper in the journal Nature Ecology & Evolution .

Q. Tang et al . A one-billion-year-old multicellular chlorophyte. Nat Ecol Evol , published online February 24, 2020; doi: 10.1038/s41559-020-1122-9

Source: www.sci-news.com/

Also read: Devonian Period: Facts & Information

https://paleontology.us/paleozoic-era-facts-information/ Paleontology_US Thu, 27 Feb 2020 12:56:55 +0000 Facts http://www.paleontology.us/?p=658 The Paleozoic Era, which ran from about 542 million years ago to 251 million years ago, was a time of great change on Earth. The era began with the breakup of one supercontinent and the formation of another. Plants became widespread. And the first vertebrate animals colonized land. Life in the Paleozoic Era The Paleozoic […]

The Paleozoic Era, which ran from about 542 million years ago to 251 million years ago, was a time of great change on Earth. The era began with the breakup of one supercontinent and the formation of another. Plants became widespread. And the first vertebrate animals colonized land.

Life in the Paleozoic Era

The Paleozoic began with the Cambrian Period, 53 million years best known for ushering in an explosion of life on Earth. This “Cambrian explosion†included the evolution of arthropods (ancestors of today’s insects and crustaceans) and chordates (animals with rudimentary spinal cords).

In the Paleozoic Era, life flourished in the seas. After the Cambrian Period came the 45-million-year Ordovician Period, which is marked in the fossil record by an abundance of marine invertebrates. Perhaps the most famous of these invertebrates was the trilobite, an armored arthropod that scuttled around the seafloor for about 270 million years before going extinct.

After the Ordovician Period came the Silurian Period (443 million years ago to 416 million years ago), which saw the spread of jawless fish throughout the seas. Mollusks and corals also thrived in the oceans, but the big news was what was happening on land: the first undisputed evidence of terrestrial life.

This was the time when plants evolved, though they most likely did not yet have leaves or the vascular tissue that allows modern plants to siphon up water and nutrients. Those developments would appear in the Devonian Period, the next geological period of the Paleozoic. Ferns appeared, as did the first trees. At the same time, the first vertebrates were colonizing the land. These vertebrates were called tetrapods, and they were widely diverse: Their appearance ranged from lizardlike to snakelike, and their size ranged from 4 inches (10 cm) long to 16 feet (5 meters) long, according to a study released in 2009 in the Journal of Anatomy.

As the tetrapods took over, they had company: The Devonian Period saw the rise of the first land-living arthropods, including the earliest ancestors of spiders.

Evolution on Paleozoic Era

Life continued its march in the late Paleozoic. The Carboniferous Period, which lasted from about 359 million years ago to 299 million years ago, answered the question, “Which came first — the chicken or the egg?†definitively. Long before birds evolved, tetrapods began laying eggs on land for the first time during this period, allowing them to break away from an amphibious lifestyle.

Trilobites were fading as fish became more diverse. The ancestors of conifers appeared, and dragonflies ruled the skies. Tetrapods were becoming more specialized, and two new groups of animals evolved. The first were marine reptiles, including lizards and snakes. The second were the archosaurs, which would give rise to crocodiles, dinosaurs and birds. Most creepily, this era is sometimes referred to as the “Age of the Cockroaches,†because roaches’ ancient ancestor ( Archimylacris eggintoni ) was found all across the globe during the Carboniferous.

The last period of the Paleozoic was the Permian Period, which began 299 million years ago and wrapped up 251 million years ago. This period would end with the largest mass extinction ever: the Permian extinction.

Before the Permian mass extinction, though, the warm seas teemed with life. Coral reefs flourished, providing shelter for fish and shelled creatures, such as nautiloids and ammonoids. Modern conifers and ginkgo trees evolved on land. Terrestrial vertebrates evolved to become herbivores, taking advantage of the new plant life that had colonized the land.

Geology and Climate on Paleozoic Era

All this evolution took place against the backdrop of shifting continents and a changing climate. During the Cambrian Period of the Paleozoic, the continents underwent a change. They had been joined as one supercontinent, Rodinia, but during the Cambrian Period, Rodinia fragmented into Gondwana (consisting of what would eventually become the modern continents of the Southern Hemisphere) and smaller continents made up of bits and pieces of the land that would eventually make up today’s northern continents.

The Cambrian was warm worldwide, but would be followed by an ice age in the Ordovician, which caused glaciers to form, sending sea levels downward. Gondwana moved further south during the Ordovician, while the smaller continents started to move closer together. In the Silurian Period, the land masses that would become North America, central and northern Europe, and western Europe moved even closer together. Sea levels rose again, creating shallow inland seas.

In the Devonian, the northern land masses continued merging, and they finally joined together into the supercontinent Euramerica. Gondwana still existed, but the rest of the planet was ocean. By the last period of the Paleozoic, the Permian, Euramerica and Gondwana became one, forming perhaps the most famous supercontinent of them all: Pangaea . The giant ocean surrounding Pangaea was called Panthalassa. Pangaea’s interior was likely very dry, because its massive size prevented water-bearing rain clouds from penetrating far beyond the coasts.

https://paleontology.us/worlds-biggest-t-rex-discovered/ Paleontology_US Mon, 24 Feb 2020 21:35:20 +0000 Facts http://www.paleontology.us/?p=623 A fossil site in Canada has yielded the heaviest Tyrannosaurus rex specimen ever found—an animal that weighed an estimated 19,500 pounds in life, far heftier than most elephants alive today. The dinosaur, unveiled last week in The Anatomical Record, consists of a skeleton that’s about 65 percent complete, including the skull and hips along with some of its ribs, […]

A fossil site in Canada has yielded the heaviest Tyrannosaurus rex specimen ever found—an animal that weighed an estimated 19,500 pounds in life, far heftier than most elephants alive today.

The dinosaur, unveiled last week in The Anatomical Record , consists of a skeleton that’s about 65 percent complete, including the skull and hips along with some of its ribs, leg bones, and tail bones. Nicknamed “Scotty,†the tyrannosaur was a senior by this species’ standards, making it to at least the age of 28.

Some 68 million years ago, the Canadian landscape Scotty knew was a subtropical coastal paradise—but life was no vacation. The dinosaur’s remains include a broken and healed rib, a massive growth of bone in between two teeth—a sign of infection—and broken tailbones possibly maimed by another tyrannosaur’s bite.

“It was not an easy life, even for the king of predatory dinosaurs, judging by all these injuries,†says Nizar Ibrahim , a paleontologist at the University of Detroit Mercy who wasn’t involved with the study.

The find suggests that large predatory dinosaurs probably got older and bigger than paleontologists would have surmised based on currently available fossils. Among the known species, T. rex is one of the best represented extinct dinosaurs, with more than 20 fossil individuals identified.

“As more specimens of those other theropods are found, we’re going to find their Scottys: their particularly large, particularly old individuals,†says study leader Scott Persons , a postdoctoral researcher at the University of Alberta. “It would not surprise me that those animals turn out to increase the range of body size—potentially to overlap or even surpass what we know from T. rex .â€

It has taken more than two decades, however, for scientists to come to full grips with Scotty’s remains. The animal’s massive bones were firmly stuck in very hard rock, making them extremely difficult to extract for study. But once Scotty’s bones were freed, Persons’s team could finally reconstruct the dinosaur’s age and size.

Cross-sections of its bones show that their structure is remarkably robust, resembling that of a different T. rex known to have died around the age of 28. And its main leg bone, or femur, in particular provided a vital clue to Scotty’s size.

By studying many living animals, scientists have found that the wider an animal’s femur, the more weight that the bone tends to hold up. Scotty’s femur was a whopping eight inches across—which means that Scotty’s two legs could hold up more than 19,500 pounds, give or take a couple tons. When the same methods are applied to Sue, the famously complete T. rex at the Field Museum, that fossil comes out about 900 pounds lighter.

Lean and mean

However, this bone-measuring method isn’t foolproof. For one, animals don’t use their skeletons to passively hold up their weight; bones also endure the forces of motion. There’s some evidence that tyrannosaurs may have been faster and more agile than other groups of large predatory dinosaurs, such as the earlier allosaurs. Perhaps tyrannosaur leg bones were slightly over-engineered to take the stress of running, which would lead researchers to overshoot Scotty’s actual weight.

In addition, body mass is just one way of parsing bigness, and not all predatory dinosaurs had the same dimensions. Tyrannosaurs such as T. rex appear to have had stockier builds, while other species had longer, more slender bodies. This variety, some researchers argue, may even hold within the T. rex species, which includes some more “slender†specimens.

No species demonstrates this conundrum better than Spinosaurus , a semiaquatic dinosaur that lived in what’s now northern Africa about a hundred million years ago. The animal was about 50 feet long from its snout to the tip of its tail, which would make it longer than T. rex . But when estimating Spinosaurus ‘s weight based only on femur size, it comes out at just 3,600 pounds.

Realistically, Spinosaurus almost certainly weighed more. The dinosaur is thought to have spent much of its time in the water, letting it get away with tinier hind limbs. Also, its bones were far denser than those in other predatory species, a trait that helps maintain buoyancy in living semiaquatic dinosaurs, such as penguins.

“Spinosaurus is sort of breaking the mold,†says Ibrahim, the National Geographic grantee who rediscovered the remains of Spinosaurus. “It’s a highly specialized theropod with a unique ecology and environmental context—it’s more like a river monster.

For now, Persons’s gaze will remain on land. He’s continuing to study Scotty’s remains in detail, starting with the tyrannosaur’s dramatic eye crests and flaring “horns†on the sides of its skull.

“The big thing that everyone is talking about is just how large this particular individual is,†he says, “but my favorite part of the specimen is actually the smaller details—the little bits of weirdness.â€

Also read: Rare fossil of crocodile cousin are found in Brazil

Source: www.nationalgeographic.com/