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What If a Giant Asteroid Had Not Wiped Out the Dinosaurs?

Wednesday, December 7, 2016

This impact was actually the least of the dinosaurs’ worries. Illustration by Franco Tempesta, National Geographic

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.

The asteroid hit what is now Mexico (Credit: Joe Tucciarone/Science Photo Library)

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

What If the Supercontinent Pangea Had Never Broken Up?

Wednesday, December 7, 2016

What If the Supercontinent Pangaea Had Never Broken Up?

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.

The breakup of the Pangaea supercontinent. Credit: U.S. Geological Survey

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.

What is Gondwana?

Wednesday, December 7, 2016

The Gondwana supercontinent after amalgamation of West and East Gondwana

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 breakup of the Pangaea supercontinent. Credit: U.S. Geological Survey

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

Tetrapods: Natural Antacid Helped Early Land Creatures Breathe

Wednesday, December 7, 2016

In Late Devonian vertebrate speciation, descendants of pelagic lobe-finned fish — like Eusthenopteron — exhibited a sequence of adaptations: *Panderichthys, suited to muddy shallows *Tiktaalik with limb-like fins that could take it onto land *Early tetrapods in weed-filled swamps, such as: **Acanthostega, which had feet with eight digits **Ichthyostega with limbs Descendants also included pelagic lobe-finned fish such as coelacanth species.

The earliest creatures to crawl out of the water onto land may have concocted antacids out of their own bones, a clever innovation that would’ve let the animals breathe, researchers now find.

The earliest tetrapods, or four-limbed creatures, made their first evolutionary forays onto land about 370 million years ago. Breathing air came with challenges, though. A major one was getting rid of the air’s carbon dioxide, which, when it builds up, reacts with water in the body and forms an acid.

Now, growing evidence in modern reptiles suggests that bones that grew within the skin of early tetrapods may have acted as a natural antacid by releasing their neutralizing chemicals into the bloodstream. The result would have bought the creatures time to spend on land before they had to head back to the water to rid themselves of excess carbon dioxide.

“Now we know that dermal bone can do this and it’s something we didn’t know before, that gives us a basis that maybe this is why tetrapods had this feature, which previously we didn’t have a good explanation for,” study researcher Christine Janis, a paleontologist at Brown University, told LiveScience. “It’s the discovery of this new feature of the physiology of these living animals that lets us go back [in time].”

First on land

So let’s rewind the clock: The first tetrapods evolved from fish in the Devonian period, which spanned from about 416 million years ago to 359 million years ago. These early tetrapods had broad faces, not unlike frogs, and rather immobile ribcages. That means they wouldn’t have been able to get rid of extra carbon dioxide by breathing quickly, as humans and other mammals do with their longer snouts and flexible ribcages. Nor were the tetrapods small enough to exchange carbon dioxide and oxygen via their skin, as modern amphibians do.

An illustration of what the sea creature Tiktaalik may have looked like. Known as a "fishapod," Tiktaalik bridged the gap between sea living and land living creatures, and played an important evolutionary role on our journey to becoming human. Zina Deretsky/National Science Foundation

What tetrapods did have was complex “dermal bone,” or bone that forms from connective tissue in the skin instead of from cartilage like the long bones of the arm or leg. The concept of skin bone may seem strange, but it’s very common: The human skull, for example, is a dermal bone.

Early tetrapod bone showed many pits and furrows, indicating lots of blood supply, Janis said. Her colleagues, including paper co-author and biologist Daniel Warren of Saint Louis University, had found another piece of the puzzle: In modern turtles and alligators, this dermal bone helps the reptiles tolerate carbon dioxide buildup when they’re under water, unable to breathe.

Bone breathing

Tetrapods would have the opposite problem, Janis realized: They’d be able to release carbon dioxide through their skin while in the water, since their skin was more permeable than an alligator’s tough hide. But out on land, they’d need another means of release. It seemed very possible that tetrapods could have used their complex dermal bones as a storage unit for calcium and other acid-neutralizing minerals, releasing them as needed when body acid levels got too high, Janis said.

To test the idea, the researchers analyzed the skeletons of tetrapods. As you might expect, the tetrapods known by the skeletons to spend more time out of the water had the most complex dermal bones. The evolutionary history of the animal supports the hypothesis, as well.

“When [the dermal bone] gets lost, it gets lost in the lineage leading to modern reptiles when they start getting more mobile ribs,” Janis said.

She and her colleagues reported their work Tuesday (April 24) in the journal Proceedings of the Royal Society B.

End of the early tetrapods

While the evidence is consistent with Janis’ theory, there’s no proof yet that tetrapods really used their bones in this way. The next step, Janis said, will be to look for chemical or other clues in modern reptiles who use their bones as antacid. If any telltale signs are established, researchers can then hunt for the same signals in ancient tetrapods.

The terrestrial tetrapods studied by Janis and her colleagues went extinct during the Permian period 299 million to 251 million years ago. It was a changing world, Janis said, and atmospheric carbon dioxide was increasing. It’s possible that tetrapods’ bone-dependent breathing wasn’t as effective in this new atmosphere.

“Who knows?” Janis asked. “I think the point to make is that this was probably a perfectly good way to live for awhile — millions of years — but in the end, there were things that had figured out better ways of how to get rid of carbon dioxide.”

Source: www.livescience.com/19876-bone-antacid-early-land-animals.html

Trilobites

Wednesday, December 7, 2016

Trilobites - Ehmania sp. by Onikaizer

Trilobites are distant relatives of lobsters, spiders and insects that died off more than 250 million years ago, before the dinosaurs even came into existence. They prowled the seas for roughly 270 million years, longer than the Age of Dinosaurs, and new species of trilobites are unearthed every year, making them the single most diverse class of extinct life known.

Tiny Orgy: Billions of Beasts Fossilized in Act of ‘Naked’ Sex

Orgies of sometimes billions of trilobites have been discovered, ones captured in a torrent of mud right after these extinct creatures ditched their hard shells to get up close and personal.

These findings, which will be presented March 20 at the Geological Society of America regional meeting in Pittsburgh, help show how social these ancient beasts were.

A group of trilobites fossilized after being trapped in mud in what is now western New York. Credit: Carlton Brett

A key problem when it comes to investigating any extinct creature is deducing how it might have once behaved. Now scientists are unearthing mass graves of trilobites, revealing details regarding how they acted in groups.

Mating madness

Trilobites, like other arthropods, shed their hard exoskeletons from time to time in order to grow larger. They appeared to have gathered in large groups for safety in numbers when they molted their armor, just like modern crabs and lobsters.

Moreover, trilobites seem to have used these gatherings as opportunities to mate, just like many of their distant living relatives do. Preserved together are large groups of similar-sized and therefore similarly aged trilobites, separated by species; they may have reproduced essentially “naked” after molting.

“It’s an orgy,” said researcher Carlton Brett, an invertebrate paleontologist and sedimentary geologist at the University of Cincinnati.

The first hints that Brett and his then-graduate student Stephen Speyer had that such orgies took place were actually discovered about two decades ago in 385-million-year-old rocks in New York. Since then, a lot of new material has come into light that strengthened those claims — in 390-million-year-old rocks in Germany, 400-million-year-old sites in Morocco, 450-million-year-old groups near Cincinnati, and up to 470-million-year-old areas holding remains of trilobite orgies in Oklahoma.

“The fact that you can find this in many different places and ages among many different species of trilobites suggests that this behavior might have been pretty general to the entire group, and that it likely began fairly early on in the evolution of trilobites,” Brett told LiveScience.

“There were different groups segregated by species at these sites, yet they all seemed to be molting in synchrony — this is something we see today in modern marine animals as well,” Brett said. “They may have spawned in response to some external trigger from the environment, such as a new moon tide in a particular season of the year.”

Head to tail

Graduate student Adrian Kin of Jagiellonian University in Krakow, Poland, also recently discovered long chains of more than a dozen trilobites arranged head to tail in 360-million-year-old rocks in the Holy Cross Mountains of Poland. This seems to be evidence of another behavior seen in their living relatives — migration.

“The recent discovery of rows of more than a dozen specimens provides the oldest evidence of migratory queues similar to those seen in modern crustaceans,” Brett said.

A chain of trilobites preserved in Poland’s Holy Cross Mountains. Credit: Adrian Kin

“These trilobites were blind, eyeless,” Brett added. “They lived in relatively deep and probably no-light zones. They were probably relying on their tactile senses to literally keep in touch with each other as they migrated.”

These cases of mass burials may have occurred when runoff from hurricanes propelled tons of mud over the trilobites. These catastrophic deposits smothered the creatures so rapidly that they were delicately preserved in the last positions they held when they were alive, essentially recording snapshots of their behavior much the way ancient Roman life was recorded at Pompeii by volcanic ash.

“We find trilobite beds that we can trace across distances of 80 miles (130 kilometers), all the effect of a single event,” Brett said. “The numbers of individuals caught in those must easily be in the billions. These were probably extraordinarily rare events in terms of human scales, but on the grand scale of geological time, you can have a number of these extraordinarily bad days that record these amazing glimpses into what the lives of ancient organisms were like.”

Source: www.LiveScience.com

Cambrian Period: Facts & Information

Wednesday, December 7, 2016

Cambrian Period

The Cambrian Period is the first geological time period of the Paleozoic Era (the “time of ancient life”). This period lasted about 53 million years and marked a dramatic burst of evolutionary changes in life on Earth, known as the “Cambrian Explosion.” Among the animals that evolved during this period were the chordates — animals with a dorsal nerve cord; hard-bodied brachiopods, which resembled clams; and arthropods — ancestors of spiders, insects and crustaceans.

Though there is some scientific debate about what fossil strata should mark the beginning of the period, the International Geological Congress places the lower boundary of the period at 543 million years ago with the first appearance in the fossil record of worms that made horizontal burrows. The end of the Cambrian Period is marked by evidence in the fossil record of a mass extinction event about 490 million years ago. The Cambrian Period was followed by the Ordovician Period.

The period gets its name from Cambria, the Roman name for Wales, where Adam Sedgwick, one of the pioneers of geology, studied rock strata. Charles Darwin was one of his students. (Sedgwick, however, never accepted Darwin’s theory of evolution and natural selection.)

Trilobites were the dominant species during the Cambrian Period, 540 to 490 million years ago. Credit: Bill Frische | Shutterstock

Climate of the Cambrian Period

In the early Cambrian, Earth was generally cold but was gradually warming as the glaciers of the late Proterozoic Eon receded. Tectonic evidence suggests that the single supercontinent Rodinia broke apart and by the early to mid-Cambrian there were two continents. Gondwana, near the South Pole, was a supercontinent that later formed much of the land area of modern Africa, Australia, South America, Antarctica and parts of Asia. Laurentia, nearer the equator, was composed of landmasses that currently make up much of North America and part of Europe. Increased coastal area and flooding due to glacial retreat created more shallow sea environments.

Cambrian map

At this point, no life yet existed on land; all life was aquatic. Very early in the Cambrian the sea floor was covered by a “mat” of microbial life above a thick layer of oxygen-free mud. The first multicellular life forms had evolved in the late Proterozoic to “graze” on the microbes. These multicellular organisms were the first to show evidence of a bilateral body plan. These near-microscopic “worms” began to burrow, mixing and oxygenating the mud of the ocean floor. During this time, dissolved oxygen was increasing in the water because of the presence of cyanobacteria. The first animals to develop calcium carbonate exoskeletons built coral reefs.

The middle of the Cambrian Period began with an extinction event. Many of the reef-building organisms died out, as well as the most primitive trilobites. One hypothesis suggests that this was due to a temporary depletion of oxygen caused by an upwelling of cooler water from deep ocean areas. This upwelling eventually resulted in a variety of marine environments ranging from the deep ocean to the shallow coastal zones. Scientists hypothesize that this increase in available ecological niches set the stage for the abrupt radiation in life forms commonly called the “Cambrian Explosion.”

Fossils of the Cambrian Period

Scientists find some of the best specimens for the “evolutionary experiments” of the Cambrian Period in the fossil beds of the Sirius Passet formation in Greenland; Chenjiang, China; and the Burgess Shale of British Columbia. These formations are remarkable because the conditions of fossilization led to impressions of both hard and soft body parts and the most complete records of the varieties of organisms alive in the Cambrian Period.

The Sirius Passet formation has fossils estimated to be from the early Cambrian Period. Arthropods are the most abundant, although the groups are not as diverse as those found in the later Burgess Shale formation.

The Sirius Passet has the first fossil indications of complex predator/prey relationships. For example, Halkieria were slug-shaped animals with shell caps at either end. The rest of the body was covered in smaller armor plates over a soft snail-like “foot.” It is unclear whether they are more closely related to the annelids, such as modern-day earthworms and leeches, or are a primitive mollusk. Some specimens have been found in curled up defensive postures like modern pill bugs. Predator/prey relationships provide intensive selection pressures that lead to rapid speciation and evolutionary change.

Evidence in the fossil record shows that all major phylla were established in the transition from Late Precambiran to Early Cambrian time. Author: Mario Barletti

Burgess Shale fossils are from the late Cambrian. Diversity had increased dramatically. There are at least 12 species of trilobite in the Burgess Shale; whereas in the Sirius Passet, there are only two. It is clear that representatives of every animal phylum, excepting only the Bryozoa, existed by this time.

The largest predator was Anomalocaris, a free-swimming animal that undulated through the water by flexing its lobed body. It had true compound eyes and two claw-tipped appendages in front of its mouth. It was the largest most fearsome predator of the Cambrian Period, but did not survive into the Ordovician. The earliest known chordate animal, the Pikaia, was about 1.5 inches (4 centimeters) long. Pikaia had a nerve cord that was visible as a ridge starting behind its head and extending almost to the tip of the body. The fine detail preserved in the Burgess Shale clearly shows that Pikaia had the segmented muscle structure of later chordates and vertebrates. Haikouichythes, thought by some to be the earliest jawless fish, were also found in the Burgess Shale.

A mass extinction event closed the Cambrian Period. Early Ordovician sediments found in South America are of glacial origin. James F. Miller of Southwest Missouri State University suggests that glaciers and a colder climate may have been the cause of the mass extinction of the fauna that evolved in the warm Cambrian oceans. Glacial ice would have also locked up much of the free ocean water, reducing both the oxygen in the water and the area available for shallow water species.

Paleozoic Era

Wednesday, December 7, 2016

Paleozoic underwater

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

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.

The skeleton of Eryops, one of the earliest land-walking tetrapods. Credit: © Christine M. Janis

Paleozoic evolution

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.

Paleozoic geology and climate

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.

Source: www.livescience.com

Synapsids

Wednesday, December 7, 2016

Dimetrodons, the most famous Synapsid

Synapsids (Greek, ‘fused arch’), synonymous with theropsids (Greek, ‘beast-face’), are a group of animals that includes mammals and every animal more closely related to mammals than to other living amniotes. They are easily separated from other amniotes by having a temporal fenestra, an opening low in the skull roof behind each eye, leaving a bony arch beneath each; this accounts for their name. Primitive synapsids are usually called pelycosaurs or pelycosaur-grade synapsids; more advanced mammal-like ones, therapsids. The non-mammalian members are described as mammal-like reptiles in classical systematics; they can also be called stem mammals or proto-mammals. Synapsids evolved from basal amniotes and are one of the two major groups of the later amniotes; the other is the sauropsids, a group that includes modern reptiles and birds. The distinctive temporal fenestra developed in the ancestral synapsid about 312 million years ago, during the Late Carboniferous period.

Fossil skeleton of Dimetrodon grandis, National Museum of Natural History, Washington, DC.

Synapsids were the largest terrestrial vertebrates in the Permian period, 299 to 251 million years ago, although some of the larger pareiasaurs at the end of Permian could match them in size. As with other groups then extant, their numbers and variety were severely reduced by the Permian–Triassic extinction. By the time of the extinction at the end of Permian, all the older forms of synapsids (known as pelycosaurs) were already gone, having been replaced by the more advanced therapsids. Though the dicynodonts and Eutheriodontia, the latter consisting of Eutherocephalia (Therocephalia) and Epicynodontia (Cynodontia), continued into the Triassic period as the only known surviving therapsids, archosaurs became the largest and most numerous land vertebrates in the course of this period. The cynodont group Probainognathia, which includes Mammaliaformes, were the only synapsids who outlasted the Triassic. After the Cretaceous–Paleogene extinction event, the synapsids (in the form of mammals) again became the largest land animals.

Synapsid opening

Synapsids as a reptilian subclass

Synapsids were originally defined at the turn of the 20th century as one of the four main subclasses of reptiles, on the basis of their distinctive temporal openings. These openings in the cheek bones allowed the attachment of larger jaw muscles, hence a more efficient bite. Synapsids were considered to be the reptilian lineage that led to mammals; they gradually evolved increasingly mammalian features, hence the name “mammal-like reptiles”, which became a broad, traditional description for all Paleozoic synapsids.

The “mammal-like reptiles”

The traditional classification of synapsids as reptiles is continued by some palaeontologists (Colbert & Morales 2001). In the 1990s, this approach was complemented by a cladistic one, according to which the only valid groups are those that include common ancestors and all of their descendants: these are known as monophyletic groups, or clades.

Phylogenetically, synapsids are the entire synapsid/mammal branch of the tree of life, though in practice the term is most often used when referring to the reptile-grade synapsids. The term “mammal-like reptiles” represents a paraphyletic grade, but is commonly used both colloquially and in the technical literature to refer to all non-mammalian synapsids. The actual monophyly of Synapsida is not in doubt, however, and the expressions “Synapsida contains the mammals” and “synapsids gave rise to the mammals” both express the same phylogenetic hypothesis.

Primitive and advanced synapsids

The synapsids are traditionally divided into a primitive group and an advanced group, known respectively as pelycosaurs and therapsids. ‘Pelycosaurs’ make up the six most primitive families of synapsids. They were all rather lizard-like, with sprawling gait and possibly horny scutes. The therapsids contain the more advanced synapsids, having a more erect pose and possibly hair, at least in some forms. In traditional taxonomy, the Synapsida encompasses two distinct grades successively closer to mammals: the low-slung pelycosaurs have given rise to the more erect therapsids, who in their turn have given rise to the mammals. In traditional vertebrate classification, the Pelycosauria and Therapsida were both considered orders of the subclass Synapsida.

In phylogenetic nomenclature, the terms are used somewhat differently, as the daughter clades are included. Most papers published during the 21st century have treated “Pelycosauria” as an informal grouping of primitive members. Therapsida has remained in use as a clade containing both the traditional therapsid families and mammals. However, in practical usage, the terms are used almost exclusively when referring to the more basal members that lie outside of Mammaliaformes.

Permian

Tuesday, December 6, 2016

Permian landscape

The Permian Period was the final period of the Paleozoic Era. Lasting from 299 million to 251 million years ago, it followed the Carboniferous Period and preceded the Triassic Period. By the early Permian, the two great continents of the PaleozoicGondwana and Euramerica, had collided to form the supercontinent Pangaea. Pangaea was shaped like a thickened letter “C.” The top curve of the “C” consisted of landmasses that would later become modern Europe and Asia. North and South America formed the curved back of the “C” with Africa inside the curve. India, Australia and Antarctica made up the low curve. Inside the “C” was the Tethys Ocean, and most of the rest of Earth was the Panthalassic Ocean. Because Pangaea was so immense, the interior portions of the continent had a much cooler, drier climate than had existed in the Carboniferous.

International Commission on Stratigraphy Subcommission on Permian Stratigraphy

Marine life

Little is known about the huge Panthalassic Ocean, as there is little exposed fossil evidence available. Fossils of the shallower coastal waters around the Pangaea continental shelf indicate that reefs were large and diverse ecosystems with numerous sponge and coral species. Ammonites, similar to the modern nautilus, were common, as were brachiopods. The lobe-finned and spiny fishes that gave rise to the amphibians of the Carboniferous were being replaced by true bony fish. Sharks and rays continued in abundance.

Plants

On land, the giant swamp forests of the Carboniferous began to dry out. The mossy plants that depended on spores for reproduction were being replaced by the first seed-bearing plants, the gymnosperms. Gymnosperms are vascular plants, able to transport water internally. Gymnosperms have exposed seeds that develop on the scales of cones and are fertilized when pollen sifts down and lands directly on the seed. Today’s conifers are gymnosperms, as are the short palm like cycads and the gingko.

Permian peat forest

Insects

Arthropods continued to diversify during the Permian Period to fill the niches opened up by the more variable climate. True bugs, with mouthparts modified for piercing and sucking plant materials, evolved during the Permian. Other new groups included the cicadas and beetles.

Land animals

Two important groups of animals dominated the Permian landscape: Synapsids and Sauropsids. Synapsids had skulls with a single temporal opening and are thought to be the lineage that eventually led to mammals. Sauropsids had two skull openings and were the ancestors of the reptiles, including dinosaurs and birds.

The earliest known fossil for the synapsid is 312 million years old, while the earliest known fossil for the sauropsid is about 306 million years old. This might indicate that mammal-like traits and reptilian-like traits emerged at around the same time. Therefore one did not necessarily evolve from the other but rather shared common ancestors more similar to the reptile-like amphibians. Very few of the non-mammalian synapsids (mammal-like reptiles) outlasted the Triassic period, although survivors persisted into the Cretaceous and are considered, as a phylogenetic unit, to include mammals as descendants.The Mesozoic era has three major periods: the Triassic, Jurassic, and Cretaceous, and is also known as The Age Of The Reptiles. Author: Miroslav Tuketic

In the early Permian, it appeared that the Synapsids were to be the dominant group of land animals. The group was highly diversified. The earliest, most primitive Synapsids were the Pelycosaurs, which included an apex predator, a genus known as Dimetrodon. This animal had a lizard-like body and a large bony “sail” fin on its back that was probably used for thermoregulation. Despite its lizard-like appearance, recent discoveries have concluded that Dimetrodon skulls, jaws and teeth are closer to mammal skulls than to reptiles. Another genus of Synapsids, Lystrosaurus, was a small herbivore — about 3 feet long (almost 1 meter) — that looked something like a cross between a lizard and a hippopotamus. It had a flat face with two tusks and the typical reptilian stance with legs angled away from the body.

In the late Permian, Pelycosaurs were succeeded by a new lineage known as Therapsids. These animals were much closer to mammals. Their legs were under their bodies, giving them the more upright stance typical of quadruped mammals. They had more powerful jaws and more tooth differentiation. Fossil skulls show evidence of whiskers, which indicates that some species had fur and were endothermic. The Cynodont (“dog-toothed”) group included species that hunted in organized packs. Cynodonts are considered to be the ancestors of all modern mammals.

At the end of the Permian, the largest Synapsids became extinct, leaving many ecological niches open. The second group of land animals, the Sauropsid group, weathered the Permian Extinction more successfully and rapidly diversified to fill them. The Sauropsid lineage gave rise to the dinosaurs that would dominate the Mesozoic Era.

A 1968 stamp from Fujeira featured a Dimetrodon. Credit: Brendan Howard / Shutterstock.com

The Great Dying

The Permian Period ended with the greatest mass extinction event in Earth’s history. In a blink of Geologic Time — in as little as 100,000 years — the majority of living species on the planet were wiped out of existence.  Scientists estimate that more than 95 percent of marine species became extinct and more than 70 percent of land animals. Fossil beds in the Italian Alps show that plants were hit just as hard as animal species. Fossils from the late Permian show that huge conifer forests blanketed the region. These strata are followed by early Triassic fossils that show few signs of plants being present but instead are filled with fossil remnants of fungi that probably proliferated on a glut of decaying trees.

Scientists are unclear about what caused the mass extinction. Some point to evidence of catastrophic volcanic activity in Siberia and China (areas in the northern part of the “C” shaped Pangaea). This series of massive eruptions would have initially caused a rapid cooling of global temperatures leading to increased glaciations. This “nuclear winter” would have led to the demise of photosynthetic organisms, the basis of most food chains. Lowered sea levels and volcanic fallout would account for the evidence of much higher levels of carbon dioxide in the oceans, which may have led to the collapse of marine ecosystems. Other scientists point to indications of a massive asteroid impacting the southernmost tip of the “C” in what is now Australia. Whatever the cause, the Great Dying closed the Paleozoic Era.

Original source: www.LiveScience.com

Parasaurolophus

Tuesday, December 6, 2016

Parasaurolophus

Parasaurolophus (meaning “near crested lizard” in reference to Saurolophus) is a genus of ornithopod dinosaur that lived in what is now North America during the Late Cretaceous Period, about 76.5–74.5 million years ago. It was a herbivore that walked both as a biped and a quadruped. Three species are recognized: P. walkeri (the type species), P. tubicen, and the short-crested P. cyrtocristatus. Remains are known from Alberta (Canada), and New Mexico and Utah (United States). The genus was first described in 1922 by William Parks from a skull and partial skeleton found in Alberta.

Size of a P. walkeri (10 metres long) compared to a human (1.8 metres tall). Author: Marmelad

Parasaurolophus was a hadrosaurid, part of a diverse family of Cretaceous dinosaurs known for their range of bizarre head adornments. This genus is known for its large, elaborate cranial crest, which at its largest forms a long curved tube projecting upwards and back from the skull. Charonosaurus from China, which may have been its closest relative, had a similar skull and potentially a similar crest. Visual recognition of both species and sex, acoustic resonance, and thermoregulation have been proposed as functional explanations for the crest. It is one of the rarer hadrosaurids, known from only a handful of good specimens.

P. walkeri with scalation detail. Author: Steveoc 86

With its snout bones drawn up into a giant snorkel-like structure, Parasaurolophus was one of the most bizarre of all the hadrosaurs. It lacked a hole in its apex, and because of this it is clear that this bony structure was not used as a breathing apparatus while the animal was swimming or feeding underwater. It seems more likely that it helped Parasaurolophus produce noises for signaling to mates or, if it was colored, for courtship displays. We know from the specimens that have been discovered that soft tissues adorned the bony crest.

Like most dinosaurs, the skeleton of Parasaurolophus is incompletely known. The length of the type specimen of P. walkeri is estimated at 10 m (33 ft), and its weight is estimated at 3.2 tonnes (3.5 short tons). Its skull is about 1.6 m (5 ft 3 in) long, including the crest, whereas the type skull of P. tubicen is over 2 m (6 ft 7 in) long, indicating a larger animal. Its single known forelimb was relatively short for a hadrosaurid, with a short but wide shoulder blade. The thighbone measures 103 cm (41 in) long in P. walkeri and is robust for its length when compared to other hadrosaurids. The upper arm and pelvic bones were also heavily built.

Parasaurolophus Used its Head Crest for Communication

The most noticeable feature was the cranial crest, which protruded from the rear of the head and was made up of the premaxilla and nasal bones. William Parks, who named the genus, hypothesized that a ligament ran from the crest to the notch to support the head, and cited the presence of possibly pathological notch as evidence. Although this idea seems unlikely, Parasaurolophus is sometimes restored with a skin flap from the crest to the neck. The crest was hollow, with distinct tubes leading from each nostril to the end of the crest before reversing direction and heading back down the crest and into the skull. The tubes were simplest in P. walkeri, and more complex in P. tubicen, where some tubes were blind and others met and separated. While P. walkeri and P. tubicen had long crests with only slight curvature, P. cyrtocristatus had a short crest with a more circular profile.

Teratophoneus attacking a P. cyrtocristatus

As a hadrosaurid, Parasaurolophus was a large bipedal/quadrupedal herbivore, eating plants with a sophisticated skull that permitted a grinding motion analogous to chewing. Its teeth were continually being replaced; they were packed into dental batteries containing hundreds of teeth, only a relative handful of which were in use at any time. It used its beak to crop plant material, which was held in the jaws by a cheek-like organ. Vegetation could have been taken from the ground up to a height of around 4 m (13 ft). As noted by Bob Bakker, lambeosaurines have narrower beaks than hadrosaurines, implying that Parasaurolophus and its relatives could feed more selectively than their broad-beaked, crestless counterparts.

Parasaurolophus skeleton

Source: www.natgeo.com

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