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Qantassaurus is a genus of two-legged, plant-eating ornithischian dinosaur that lived in Australia about 115 million years ago, when the continent was still partly south of the Antarctic Circle. It was described by Patricia Vickers-Rich and her husband Tom Rich in 1999 after a find near Inverloch, and named after Qantas, the Australian airline.

Psittacosaurus (“parrot lizard”) is a genus of extinct ceratopsian dinosaur from the Early Cretaceous of what is now Asia, existing between 126 and 101 million years ago. It is notable for being the most species-rich dinosaur genus. Up to 11 species are known, from across Mongolia, Siberia, China, and possibly Thailand. The species of Psittacosaurus were obligate bipeds at adulthood, with a high skull and a robust beak. One individual was found preserved with long filaments on the tail, similar to those of Tianyulong, and scales across the rest of the animal. Psittacosaurus probably had complex behaviours, based on the proportions and relative size of the brain. It may have been active for short periods of time during the day and night, and had well-developed senses of smell and vision.

Psittacosaurus was discovered in Outer Mongolia in 1922, in the early stages of the famous expeditions undertaken by the American Museum of Natural History between 1922 and 1925. Henry Osborn named it for the beak-like appearance of its face. It is known from a number of well-preserved skeletons, which represent about eight different species from Mongolia, southern Siberia, and northern China, as well as from some lower jaw fragments that were discovered in northern Thailand.

Plateosaurus (probably meaning “broad lizard”, often mistranslated as “flat lizard”) is a genus of plateosaurid dinosaur that lived during the Late Triassic period, around 214 to 204 million years ago, in what is now Central and Northern Europe. Plateosaurus is a basal (early) sauropodomorph dinosaur, a so-called “prosauropod”. As of 2011, two species are recognized: the type species P. engelhardti from the late Norian and Rhaetian, and the slightly earlier P. gracilis from the lower Norian. However, others have been assigned in the past, and there is no broad consensus on the species taxonomy of plateosaurid dinosaurs. Similarly, there are a plethora of synonyms (invalid duplicate names) at the genus level.

The Facts and Theories Behind Dinosaur Gigantism

One of the things that makes dinosaurs so appealing is their sheer size: plant eaters like Diplodocus and Brachiosaurus weighed in the neighborhood of 25 to 50 tons, and a well-toned Tyrannosaurus rex tipped the scales as much as 10 tons. From the fossil evidence, it’s clear that–species by species, individual by individual–dinosaurs were more massive than any other group of animals that ever lived (with the logical exception of certain genera of prehistoric sharks, prehistoric whales and marine reptiles like ichthyosaurs and pliosaurs, the extreme bulk of which were supported by the natural buoyancy of water).

However, what’s fun for dinosaur enthusiasts is often what causes paleontologists and evolutionary biologists to tear their hair out. The giant size of dinosaurs demands an explanation, and one that’s compatible with other dinosaur theories–for example, it’s impossible to discuss dinosaur gigantism without paying close attention to the whole cold-blooded/warm-blooded metabolism debate.

So what’s the current state of thinking about plus-sized dinosaurs? Here are a few more-or-less interrelated theories.

THEORY #1: DINOSAUR SIZE WAS FUELED BY VEGETATION

During the Mesozoic Era–which stretched from the beginning of the Triassic period, 250 million years ago, to the extinction of the dinosaurs at the end of the Cretaceous period, 65 million years ago–atmospheric levels of carbon dioxide were much higher than they are today. If you’ve been following the global warming debate, you’ll know that increased carbon dioxide is directly correlated with increased temperature–meaning the global climate was much warmer millions of years ago than it is today.

This combination of high levels of carbon dioxide (which plants recycle as food via the process of photosynthesis) and high temperatures (an average of 90 or 100 degrees Fahrenheit, even near the poles) meant that the prehistoric world was matted with all kinds of vegetation–plants, trees, mosses, etc.

Like kids at an all-day dessert buffet, sauropods may have evolved to giant sizes simply because there was a surplus of nourishment at hand. This would also explain why certain tyrannosaurs and large theropods were so big; a 50-pound carnivore wouldn’t have stood much of a chance against a 50-ton plant eater.

THEORY #2: HUGENESS IN DINOSAURS WAS A FORM OF SELF-DEFENSE

If Theory #1 strikes you as a bit simplistic, your instincts are correct: the mere availability of huge amounts of vegetation doesn’t necessarily entail the evolution of giant animals that can swallow it down to the last shoot. (After all, the earth was shoulder-deep in microorganisms for hundreds of millions of years before the appearance of multicellular life, and we don’t have any evidence of one-ton bacteria.) Evolution tends to work along multiple paths, and the fact is that the drawbacks of dinosaur gigantism (such as the slow speed of individuals and the need for limited population size) could easily have outweighed its benefits in terms of food-gathering.

That said, some paleontologists do believe that gigantism conferred an evolutionary advantage on the dinosaurs that possessed it: for example, a jumbo-sized hadrosaur like Shantungosaurus would have been virtually immune to predation when fully grown, even if the tyrannosaurs of its ecosystem hunted in packs.

(This theory also lends some indirect credence to the idea that Tyrannosaurus rex scavenged its food–say, by happening across the carcass of an Ankylosaurus that died of disease or old age–rather than actively hunting it down.) But once again, we have to be careful: of course giant dinosaurs benefited from their size, because otherwise they wouldn’t have been gigantic in the first place, a classic example of an evolutionary tautology.

THEORY #3: DINOSAUR GIGANTISM WAS A BYPRODUCT OF COLD-BLOODEDNESS

This is where things get a bit sticky. Many paleontologists who study giant plant-eating dinosaurs like hadrosaurs and sauropods believe that these behemoths were cold-blooded, for two compelling reasons: first, based on our current physiological models, a warm-blooded Mamenchisaurus would have cooked itself from the inside out, like a potato, and promptly expired; and second, no land-dwelling, warm-blooded mammals living today even approach the size of the largest herbivorous dinosaurs (elephants weigh a few tons, max, and the largest terrestrial mammal in the history of life on earth, Indricotherium, only topped out at about 20 tons).

Here’s where the advantages of gigantism come in. If a sauropod evolved to large-enough sizes, scientists believe, it would have achieved “homeothermy”–that is, the ability to maintain its interior temperature despite the prevailing environmental conditions. This is because a house-sized, homeothermic Argentinosaurus would warm up slowly (in the sun, during the day) and cool down equally slowly (at night), giving it a fairly constant average body temperature–whereas a smaller reptile would be at the mercy of ambient temperatures on an hour-by-hour basis.

The problem is, these speculations about cold-blooded herbivorous dinosaurs run counter to the current vogue for warm-blooded carnivorous dinosaurs. Although it’s not impossible that a warm-blooded Tyrannosaurus rex could have coexisted alongside a cold-blooded Titanosaurus, evolutionary biologists would be much happier if all dinosaurs, which after all evolved from the same common ancestors, possessed uniform metabolisms–even if these were “intermediate” metabolisms that don’t correspond to anything seen in modern animals.

DINOSAUR SIZE: WHAT’S THE VERDICT?

If the above theories leave you as confused as you were before reading this article, you’re not alone. The fact is that evolution toyed with the existence of giant-sized terrestrial animals, over a time span of 100 million years, exactly once, during the Mesozoic Era. Before and after the dinosaurs, most terrestrial creatures were reasonably sized, with the odd exceptions (like the above-mentioned Indricotherium) that proved the rule. Most likely, some combination of theories #1, #2 and #3, along with a possible fourth theory that we have yet to formulate, explains the huge size of dinosaurs; in exactly what proportion, and in what order, will have to await future research.

Source: www.thoughtco.com, www.huffingtonpost.com

QUICK ANSWER

Because dinosaurs are classified as reptiles, one might assume that they are cold blooded, but some scientists suggest that dinosaurs may have been somewhere between cold and warm blooded. Though most animals fall into either category, there have been some intermediary species known to science, with dinosaurs potentially being one of this number.

FULL ANSWER

The lack of certainty and the assertion that dinosaurs may have been neither warm nor cold blooded stems from the fact that birds, which may be the dinosaurs’ closest living relatives, are warm blooded, unlike modern reptiles, which are cold blooded. There is also evidence to suggest that dinosaurs had faster metabolisms than cold-blooded animals typically have.

Dinosaurs were neither warm nor cold blooded

Source: www.SciNews.com

During the Mesozoic, or “Middle Life” Era, life diversified rapidly and giant reptiles, dinosaurs and other monstrous beasts roamed the Earth. The period, which spans from about 252 million years ago to about 66 million years ago, was also known as the age of reptiles or the age of dinosaurs.

Boundaries

English geologist John Phillips, the first person to create the global geologic timescale, first coined the term Mesozoic in the 1800s. Phillips found ways to correlate sediments found around the world to specific time periods, said Paul Olsen, a geoscientist at the Lamont-Doherty Earth Observatory at Columbia University in New York.

The Permian-Triassic boundary, at the start of the Mesozoic, is defined relative to a particular section of sediment in Meishan, China, where a type of extinct, eel-like creature known as a conodont first appeared, according to the International Commission on Stratigraphy.

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 and traces of iridium and other elements from the asteroid impact that wiped out the dinosaurs. The Mesozoic Era is divided up into the Triassic, Jurassic, and Cretaceous periods.

Life and climate

The Mesozoic Era began roughly around the time of the end-Permian extinction, which wiped out 96 percent of marine life and 70 percent of all terrestrial species on the planet. Life slowly rebounded, eventually giving way to a flourishing diversity of animals, from massive lizards to monstrous dinosaurs.

The Triassic Period, from 252 million to 200 million years ago, saw the rise of reptiles and the first dinosaurs, the Jurassic Period, from about 200 million to 145 million years ago, ushered in birds and mammals, and the Cretaceous Period, from 145 million to 66 million years ago is known for some of its iconic dinosaurs, such as Triceratops and Pteranodon.

Coniferous plants, or those that have cone-bearing seeds, already existed at the beginning of the era, but they became much more abundant during the Mesozoic. Flowering plants emerged during the late Cretaceous Period. The lush plant life during the Mesozoic Era provided plenty of food, allowing the biggest of the dinosaurs, such as the Argentinosaurus, to grow up to 80 tons, according to a 2005 study in the journal Revista del Museo Argentino de Ciencias Naturales.

Earth during the Mesozoic Era was much warmer than today, and the planet had no polar ice caps. During the Triassic Period, Pangaea still formed one massive supercontinent. Without much coastline to moderate the continent’s interior temperature, Pangaea experienced major temperature swings and was covered in large swaths of desert. Yet the region still had a belt of tropical rainforest in regions around the equator, said Brendan Murphy, an earth scientist at St. Francis Xavier University in Antigonish, Canada.

Extinctions

The Mesozoic Era was bookended by two great extinctions, with another smaller extinction occurring at the end of the Triassic Period, Olsen said.

Around 252 million years ago, the end-Permian extinction wiped out most life on Earth over about 60,000 years, according to a February 2014 study in the journal Proceedings of the National Academy of Sciences (PNAS). At the end of the Triassic Period, roughly 201 million years ago, most amphibious creatures and crocodile-like creatures that lived in the tropics were wiped out. About 65 million years ago, a giant asteroid blasted into Earth and formed a giant crater at Chicxulub in the Yucatan Peninsula.

Because the fossil record is incomplete, it’s difficult to say exactly what caused the extinctions, or even how rapidly they occurred. After all, certain species or traces of catastrophic events could be missing in the fossil record simply because the sediments may have disappeared over tens of millions of years, Olsen said.

“Nature is very efficient at getting rid of its corpses,” Olsen told Live Science.

However, there are a few prime suspects in each of the extinctions.

At the end of the Permian, the Siberian Traps underwent massive volcanic eruptions, which most geologists believe caused the world’s biggest extinction. Exactly how, however, is up for debate.

The volcanic eruptions caused a spike in carbon dioxide in the atmosphere, though the 2014 PNAS study suggests that the spike was brief. The eruptions may have increased sea surface temperatures and led to ocean acidification that choked out sea life. And another study published in March 2014 in PNAS proposed that the eruptions released huge troves of the element nickel, which fueled a feeding frenzy by nickel-munching microbes known as Methanosarcina. Those microbes may have belched out huge amounts of methane, superheating the planet.

Most scientists agree that an asteroid impact wiped out the dinosaurs at the end of the Cretaceous Period. The impact would have kicked up so much dust that it blocked the sun, halted photosynthesis, and led to such a huge disruption in the food chain that everything that wasn’t a scavenger or very small died.

But the Deccan Traps, in what is now India, were spewing massive amounts of lava both before and after the asteroid impact, and a few scientists believe these flows either directly caused or accelerated the dinosaurs’ demise.

Volcanism may also be to blame for the end-Triassic extinction. Though volcanism in general leads to global warming, after an initial volcanic eruption, huge amounts of sulfur spew into the air and cause a brief period of global cooling. Such cooling-heating cycles may have occurred hundreds of times over 500,000 years. Similar cold snaps have been tied to huge crop failures in historical times, such as in Iceland in the 1700s, Olsen said.

As a result, animals used to constant, balmy temperatures in the tropics were wiped out, while animals that were insulated with proto-feathers, such as pterosaurs, or that lived at higher latitudes and were already adapted to big temperature variations, did just fine, Olsen said.

“When you have these volcanic winters, where temperatures may have dropped even below freezing in the tropics, it was devastating,” Olsen said.

Source: www.livescience.com/38596-mesozoic-era.html

During the new DC Comics Universe series “Flashpoint,” in which a time-traveling supervillain alters the past to warp the present, Life’s Little Mysteries presents a 10-part series that examines what would happen if a major event in the history of the universe had gone just slightly different.

Part 2: What if … a giant asteroid had not killed off the dinosaurs?

Other factors were involved in dinosaurs’ extinction, but the resounding death knell was the impact of a 6-mile-wide asteroid in present-day Mexico’s Yucatan Peninsula 65 million years ago, creating what is known as the 110-mile-wide, 6-mile-deep Chicxulub crater. The event unleashed mega-tsunamis, planetwide wildfires and kicked up enough dust and debris to block the sun and cause a period of global cooling, which killed off many plants.

Life would be: Still dinosauric in all likelihood, assuming no other catastrophic, extinction-level events transpired. After all, dinos had a good long run of dominance on land for 160 million years prior, and if that continued, primates like us would not be around, said Damian Nance, a professor of geosciences at Ohio University. Mammals did co-evolve alongside dinosaurs, but they occupied fringe ecological niches and grew no larger than rodents in most cases.

Only with dinosaur plant-devourers gone would there be enough food for mammals to seize the day and eventually give rise to us (knocking out the predators that would eat mammals helped, too). Researchers have speculated that intelligent “dinosauroids” might have evolved in humanity’s place, based on the relatively large brain size of late-emerging trodontid species, which were bird-like predators.

Of course, some of those dinosaurs that have survived into modern day — becoming birds — are quite smart, but not smart enough to have ended up on the other side of the insult “bird-brained.”

Source: BBC Nature

During the new DC Comics Universe series “Flashpoint,” in which a time-traveling supervillain alters the past to warp the present, Life’s Little Mysteries presents a 10-part series that examines what would happen if a major event in the history of the universe had gone just slightly different.

Part 3: What if … the supercontinent Pangaea never broke up?

From about 300 million to 200 million years ago, all seven modern continents were mashed together as one landmass, dubbed Pangaea. The continents have since “drifted” apart because of the movements of the Earth’s crust, known as plate tectonics. Some continents have maintained their puzzle piece-like shapes: Look at how eastern South America tucks into western Africa.

Life would be: Far less diverse. A prime driver of speciation the development of new species from existing ones is geographical isolation, which leads to the evolution of new traits by subjecting creatures to different selective pressures. Consider, for example, the large island of Madagascar, which broke off from Gondwana, Pangaea’s southern half, 160 million years ago. About nine out of 10 of the plant and mammal species that have evolved on the island are not found anywhere else on the planet, according to Conservation International.

A locked-in Pangaea further constrains life’s possibilities because much of its interior would be arid and hot, said Damian Nance, a professor of geosciences at Ohio University. “Because of Pangaea’s size, moisture-bearing clouds would lose most of their moisture before getting very far inland,” Nance told Life’s Little Mysteries.

Excess mass on a spinning globe shifts away from the poles, so the supercontinent would also become centered on the equator, the warmest part of the planet. Reptiles could deal with such a climate better than most, which is partly why dinosaurs, which emerged during the time the planet’s surface was one giant chunk, thrived before mammals.

Gondwana was an ancient supercontinent that broke up about 180 million years ago. The continent eventually split into landmasses we recognize today: Africa, South America, Australia, Antarctica, the Indian subcontinent and the Arabian Peninsula.

The familiar continents of today are really only a temporary arrangement in a long history of continental movement. Landmasses on Earth are in a constant state of slow motion, and have, at multiple times, come together as one. These all-in-one supercontinents include Columbia (also known as Nuna), Rodinia, Pannotia and Pangaea (or Pangea).

Gondwana was half of the Pangaea supercontinent, along with a northern supercontinent known as Laurasia.

The creation of Gondwana

Gondwana’s final formation occurred about 500 million years ago, during the late Ediacaran Period. By this time, multicellular organisms had evolved, but they were primitive: The few fossils left from this period reveal segmented worms, frond-like organisms and round creatures shaped like modern jellyfish.

In this world, Gondwana conducted its slow grind to supercontinent status. Bits and pieces of the future supercontinent collided over millennia, bringing together what are now Africa, India, Madagascar, Australia and Antarctica.

This early version of Gondwana joined with the other landmasses on Earth to form the single supercontinent Pangaea by about 300 million years ago. About 280 million to 230 million years ago, Pangaea started to split. Magma from below the Earth’s crust began pushing upward, creating a fissure between what would become Africa, South America and North America.

As part of this process, Pangaea cracked into a northernmost and southernmost supercontinent. The northern landmass, Laurasia, would drift north and gradually split into Europe, Asia and North America.

The southern landmass, still carrying all those bits and pieces of the future southern hemisphere, headed southward after the split. This supercontinent was Gondwana.

Gondwana’s breakup

During Gondwana’s stint as the southerly supercontinent, the planet was much warmer than it was today — there was no Antarctic ice sheet, and dinosaurs still roamed the Earth. By this time, it was the Jurassic Period, and much of Gondwana was covered with lush rainforest.

The great supercontinent was still under strain, however. Between about 170 million and 180 million years ago, Gondwana began its own split, with Africa and South America breaking apart from the other half of Gondwana. About 140 million years ago, South America and Africa split, opening up the South Atlantic Ocean between them. Meanwhile, on the eastern half of the once-supercontinent, Madagascar made a break from India and both moved away from Australia and Antarctica.

Australia and Antarctica clung together longer; in fact, Antarctica and Australia didn’t make their final split until about 45 million years ago. At that point, Antarctica started to freeze over as Earth’s climate cooled, while Australia drifted northward. (Today, the Australian continent still moves north at a rate of about 1.2 inches (3 centimeters) a year.)

Gondwana theory

The exact mechanisms behind Gondwana’s split are still unknown. Some theorists believe that “hot spots,” where magma is very close to the surface, bubbled up and rifted the supercontinent apart. In 2008, however, University of London researchers suggested that Gondwana instead split into two tectonic plates, which then broke apart.

The existence of Gondwana was first hypothesized in the mid-1800s by Eduard Suess, a Viennese geologist who dubbed the theoretical continent “Gondwanaland.” Suess was tipped off by similar fern fossils found in South America, India and Africa (the same fossils would later be found in Antarctica). At the time, plate tectonics weren’t understood, so Suess didn’t realize that all of these continents had once been in different locations. Instead, he developed a theory of sea level rise and regression over time that would have linked together the southern hemisphere continents with land bridges.

Suess got the name Gondwanaland from the Gondwana region of central India, where geological formations match those of similar ages in the southern hemisphere.

Source: www.NatGeo.com