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The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 419.2 Mya (million years ago), to the beginning of the Carboniferous Period, about 358.9. It is named after Devon, England, where rocks from this period were first studied. The Devonian period experienced the first significant adaptive radiation of terrestrial life. Free-sporing vascular plants began to spread across dry land, forming extensive forests which covered the continents. By the middle of the Devonian, several groups of plants had evolved leaves and true roots, and by the end of the period the first seed-bearing plants appeared. Various terrestrial arthropods also became well-established. Fish reached substantial diversity during this time, leading the Devonian to often be dubbed the “Age of Fish”. The first ray-finned and lobe-finned bony fish appeared, while the placoderms began dominating almost every known aquatic environment.

The Silurian (443.7 to 416.0 million years ago)* was a time when the Earth underwent considerable changes that had important repercussions for the environment and life within it. One result of these changes was the melting of large glacial formations. This contributed to a substantial rise in the levels of the major seas. The Silurian witnessed a relative stabilization of the Earth’s general climate, ending the previous pattern of erratic climatic fluctuations.

Distribution of landmasses, mountainous regions, shallow seas, and deep ocean basins during the Silurian Period by Encyclopedia Britannica

Coral reefs made their first appearance during this time, and the Silurian was also a remarkable time in the evolution of fishes. Not only does this time period mark the wide and rapid spread of jawless fish, but also the highly significant appearances of both the first known freshwater fish as well as the first fish with jaws. It is also at this time that our first good evidence of life on land is preserved, such as relatives of spiders and centipedes, and also the earliest fossils of vascular plants.

Life

The Silurian is a time when many biologically significant events occurred. In the oceans, there was a widespread radiation of crinoids, a continued proliferation and expansion of the brachiopods, and the oldest known fossils of coral reefs. As mentioned earlier, this time period also marks the wide and rapid spread of jawless fish, along with the important appearances of both the first known freshwater fish and the appearance of jawed fish. Other marine fossils commonly found throughout the Silurian record include trilobites, graptolites, conodonts, corals, stromatoporoids, and mollusks.

On the left, Dalmanites limuluris, a trilobite from the Silurian of New York. To the right, Grammysia cingulata, a bivalve from the Upper Ludlow of England.

It is also in the Silurian that we find the first clear evidence of life on land. While it is possible that plants and animals first moved onto the land in the Ordovician, fossils of terrestrial life from that period are fragmentary and difficult to interpret. Silurian strata have provided likely ascomycete fossils (a group of fungi), as well as remains of the first arachnids and centipedes.

Perhaps most striking of all biological events in the Silurian was the evolution of vascular plants, which have been the basis of terrestrial ecology since their appearance. Most Silurian plant fossils have been assigned to the genus Cooksonia, a collection of branching-stemmed plants which produced sporangia at their tips. None of these plants had leaves, and some appear to have lacked vascular tissue. Also from the Silurian of Australia comes a controversial fossil of Baragwanathia, a lycophyte. If such a complex plant with leaves and a fully-developed vascular system was present by this time, then surely plants must have been around already by the Ordovician. In any event, the Silurian was a time for important events in the history of evolution, including many “firsts,” that would prove highly consequential for the future of life on Earth.

Cooksonia, on the left, has usually been considered the oldest known land plant. Fossils assigned to several species are known from North America, Europe, Asia, and Africa, and from both the Late Silurian and Early Devonian. The lycophyte Baragwanathia, on the right, is structurally more complex than Cooksonia, but Silurian fossils of this plant have been found in Australia, significantly earlier than in the Northern Hemisphere.

Stratigraphy

The Silurian’s stratigraphy is subdivided into four epochs (from oldest to youngest): the Llandovery, Wenlock, Ludlow, and Pridoli. Each epoch is distinguished from the others by the appearance of new species of graptolites. Graptolites are a group of extinct colonial, aquatic animals that put in their first appearance in the Cambrian Period and persisted into the early Carboniferous. The beginning of the Silurian (and the Llandovery) is marked by the appearance of Parakidograptus acuminatus, a species of graptolite.

The Llandovery (443.7-428.2 million years ago*) preserves its fossils in shale, sandstone, and gray mudstone sediment. Its base (beginning) is marked by the appearance of the graptolites Parakidograptus acuminatus and Akidograptus ascensus. The Llandoverian epoch is subdivided into the Rhuddanian, Aeronian, and Telychian stages.

At the close of the Telychian stage, the appearance of Cyrtograptus centrifugus marks the start of the Wenlockian epoch (428.2 to 422.9 million years ago).* The fossils are found in siltstone and mudstone under limestone. Missing from the fossil record of the Wenlock was the conodont Pterospathodus amorphognathoides, present in earlier strata. This is an epoch with excellent preservations of brachiopod, coral, trilobite, clam, bryozoan, and crinoid fossils. The Wenlock is subdivided into the Sheinwoodian and Homerian stages.

The Ludlow (422.9 to 418.7 million years ago)* consists of siltstone and limestone strata, marked by the appearance of Neodiversograptus nilssoni. There is an abundance of shelly animal fossils. The Gorstian and Ludfordian stages make up the Ludlow epoch.

Platy limestone strata rich in cephalopods and bivalves characterize the Pridolian (418.7 to 416.0 million years ago),* the final epoch of the Silurian. It is marked by the appearance of the index fossil Monograptus parultimus, and also by two new species of chitinozoans (marine plankton), Urnochitina urna and Fungochitina kosovensis, which appear at the base or just above the base of the Pridoli.

Tectonics and paleoclimate

Although there were no major periods of volcanism during the Silurian, the period is marked by major orogenic events in eastern North America and in northwestern Europe (the Caledonian Orogeny), resulting in the formation of the mountain chains there. The ocean basins between the regions known as Laurentia (North America and Greenland), Baltica (central and northern Europe and Scandinavia) and Avalonia (western Europe) closed substantially, continuing a geologic trend that had begun much earlier. The modern Philippine Islands were near the Arctic Circle, while Australia and Scandinavia resided in the tropics; South America and Africa were over the South Pole. While not characterized by dramatic tectonic activity, the Silurian world experienced gradual continental changes that would be the basis for greater global consequences in the future, such as those that created terrestrial ecosystems. A deglaciation and rise in sea levels created many new marine habitats, providing the framework for significant biological events in the evolution of life. Coral reefs, for example, made their first appearance in the fossil record during this time.

The Silurian Period’s condition of low continental elevations with a high global stand in sea level can be strongly distinguished from the present-day environment. This is a result of the flood of 65% of the shallow seas in North America during the Llandovery and Wenlock times. The shallow seas ranged from tropical to subtropical in climate. Coral mound reefs with associated carbonate sediments were common in the shallow seas. Due to reduced circulation during the Ludlow and Pridoli times, the process of deposition of evaporites (salts) was set in motion. Some of these deposits are found in northern Europe, Siberia, South China and Australia.

Source: www.ucmp.berkeley.edu

The Ordovician Period lasted almost 45 million years, beginning 488.3 million years ago and ending 443.7 million years ago.* During this period, the area north of the tropics was almost entirely ocean, and most of the world’s land was collected into the southern supercontinent Gondwana. Throughout the Ordovician, Gondwana shifted towards the South Pole and much of it was submerged underwater.

The Ordovician is best known for its diverse marine invertebrates, including graptolites, trilobites, brachiopods, and the conodonts (early vertebrates). A typical marine community consisted of these animals, plus red and green algae, primitive fish, cephalopods, corals, crinoids, and gastropods. More recently, tetrahedral spores that are similar to those of primitive land plants have been found, suggesting that plants invaded the land at this time.

From the Lower to Middle Ordovician, the Earth experienced a milder climate — the weather was warm and the atmosphere contained a lot of moisture. However, when Gondwana finally settled on the South Pole during the Upper Ordovician, massive glaciers formed, causing shallow seas to drain and sea levels to drop. This likely caused the mass extinctions that characterize the end of the Ordovician in which 60% of all marine invertebrate genera and 25% of all families went extinct.

Life

Ordovician strata are characterized by numerous and diverse trilobites and conodonts (phosphatic fossils with a tooth-like appearance) found in sequences of shale, limestone, dolostone, and sandstone. In addition, blastoids, bryozoans, corals, crinoids, as well as many kinds of brachiopods, snails, clams, and cephalopods appeared for the first time in the geologic record in tropical Ordovician environments. Remains of ostracoderms (jawless, armored fish) from Ordovician rocks comprise some of the oldest vertebrate fossils.

Despite the appearance of coral fossils during this time, reef ecosystems continued to be dominated by algae and sponges, and in some cases by bryozoans. However, there apparently were also periods of complete reef collapse due to global disturbances.

Source: www.ucmp.berkeley.edu

The Tyrannosaurus family, of which the most famous species is T. rex, were among the last dinosaurs to appear on the planet, around 80 million years ago. These large carnivorous theropods were only on the planet for a relatively short time, but they had a huge impact on our understanding of dinosaurs – partly because more specimens exist from these final stages than any earlier time in history.

Trix is a Tyrannosaurus rex specimen excavated in 2013 in Montana, USA by a team of paleontologists from the Naturalis Biodiversity Center in Leiden in the Netherlands. It is the oldest known Tyrannosaurus specimen, with an age of more than thirty years, and has been considered the third most complete tyrannosaurus found, with between 75% to 80% of its bone volume recovered. The specimen was named Trix after the Dutch former Queen Beatrix and is the only Tyrannosaurus specimen on permanent exhibit in mainland Europe.

According to Peter Larson, director of the Black Hills Institute, Trix is the third most complete Tyrannosaurus found, after Sue and Stan. About half of the bones have been found. These represent between 75% and 80% of its bone volume. The main missing parts include the tip of the snout, the front lower jaws, at least seven vertebrae of the middle tail, the point of the tail, the right shoulder blade, the arms, the left hindlimb and the right foot. Parts never before discovered in a Tyrannosaurus fossil include a turbinal bone in the nasal cavity. A rare element present is the furcula and the stapes of the ear. There is some root damage from plant growth and some bones had been gnawed by scavengers. A smaller shed tooth was found, attributed to Nanotyrannus. Trix in 2016 was the most complete Tyrannosaurus specimen permanently exhibited outside of the USA. Tyrannosaurus skeletons part of the collection of the Natural History Museum, London, are more fragmentary.

Name

For formal use, the BHI referred to the skeleton as the “Murray T. rex”. Because of her age, gender and face injuries, the tyrannosaurus was nicknamed “grandma pusface”. Naturalis preferred Grand Old Lady. Wim Pijbes, the director of the Amsterdam Rijksmuseum, called the skeleton “the Nightwatch of Natural History”. She has also been called the “Mona Lisa of Naturalis”, because of her enigmatic smile. Both Larson and the museum concluded it was “the most beautiful tyrannosaurus of the world”. Naturalis decided that the skeleton needed an official name, as all main exemplars of Tyrannosaurus possess. In the press, it was speculated it would be called “Michelle” after its discoverer, as had happened with many specimens. Naturalis asked the Dutch public to suggest a name. On 23 June 2016 it was announced that the name overwhelmingly chosen was “Trix”, as both an allusion to “T-rex” and former Queen Beatrix of the Netherlands. Trix thus became known as the “Queen of the Cretaceous”.

T. rex in Town is a temporary exhibit from September 10, 2016 to June 5, 2017 in the Naturalis Biodiversity Center in Leiden, The Netherlands.

 Source. www.Wikipedia.org

What would happen if dinosaurs roamed the earth today? Originally appeared on Quora – the knowledge sharing network where compelling questions are answered by people with unique insights.

Answer by Ben Waggoner, Ph.D in Integrative Biology, paleontologist, and evolutionary biologist, on Quora:

Massive devastation of trendy Manhattan wine bars.

Huh?

Okay, first of all, one subgroup of dinosaurs is still roaming the Earth today: the birds. So dinosaurs poop on your car, visit your feeders, and feed you well on Thanksgiving. But I assume you meant what would happen if the extinct, non-bird dinosaurs could somehow roam the Earth today.

That raises the point that different dinosaur species lived at different times and places. Tyrannosaurus never feasted on Stegosaurus, for example, because Steggy lived something like 100 million years before Rexy ever existed. Tyrannosaurus never got to taste Giraffatitan because they not only lived 80 million years apart, they lived on separate continents. (This is one of my beefs with Jurassic Park; Dilophosaurus, the critter that spit poison in Wayne Knight’s face, lived about 120 million years and 6000 miles away from Velociraptor, the critters that ate Bob Peck.) So if all the extinct dinosaurs suddenly started roaming the Earth together at the same time … well, you’d have utter ecological chaos, as the Velociraptors discovered that their tactics for hunting Protoceratops were ineffective against unfamiliar Ankylosaurus, and Triceratops found out that it had no idea how to dodge Allosaurus. You might as well turn some polar bears, bison, tree sloths, and kangaroos loose on the Serengeti plain.

But let’s keep it simple. Suppose we could magically transport a decent sample of the dinosaurs from one place and time into the present day. Let’s pick up a herd of duckbills—say, Edmontosaurus or Maiasaura —and a herd of Triceratops, a few smallish predators like Dakotaraptor, and a couple of Tyrannosaurus. All of these lived in the same general area (western North America) in the same general time frame (late Cretaceous). So we plop all of these down in North America today, and …

There were flowering plants in the Late Cretaceous, but they didn’t yet dominate the landscape. The typical landscape in Cretaceous North America seems to have been “fern savannas”—somewhat like prairies, but dominated by small ferns, not grasses—broken up by tracts of forests dominated by conifers, ginkgos, ferns, and cycads. There were flowering plants, including decent-sized trees, but again, nothing like the diversity we have now.

And here’s the problem: Modern flowering plants have had ~100 million years to evolve anti-herbivore defenses, and just to evolve complex chemistry in general. We don’t know enough about dinosaur biochemistry to know exactly what they would find poisonous. Suffice it to say that as soon as the herbivores started eating the local plants, they would be exposed to a whole range of chemicals that they had no adaptations to handle. They might not even have the sensory receptors to taste them.

The actual effects are anyone’s guess. The simplest case would be that the herbivores would get sick and die, like modern sheep or cows in the West that eat death camas or lupine. Some might end up tripping out, like humans eating ergot-infected rye or jimsonweed, or livestock eating Oxytropis or Astragalus “locoweeds”. Survivors might fail to lay viable eggs, or lay eggs that would hatch into deformed offspring—like sheep and goats eating false hellebore and giving birth to lambs and kids with cyclopia.

The carnivorous dinosaurs might have easy pickings for a while, as they feasted on dead or incapacitated herbivorous dinosaurs. This wouldn’t last long, though. Sooner or later, Tyrannosaurus rex has to find living prey, or possibly fresh carrion, depending on whether it was a predator or scavenger (that’s another story). There were mammals alive at the same time and place as T. rex, but none very big—and for all we know, modern mammal flesh might be unpalatable. But recall that birds belong within the dinosaurian clade. T. rex may run out of Triceratops to eat, but if it can find large, relatively slow birds to munch, it might survive for a while, assuming that it can run fast enough to catch them (a controversial question). A T. rex that was lucky enough to find a turkey farm would probably eat the birds like so much popcorn. The few ostrich ranches in the America West could find their business nipped in the bud, if by “nipped” you mean “messily dismembered.”

The herbivores would be equally hard to manage. Imagine: a herd of Triceratops eats a patch of Datura stramonium and promptly levels downtown Bismarck, North Dakota, hallucinating like a Grateful Dead show gone horribly wrong. Twitching, retching, slobbering duckbills collapse across I-94, blocking traffic into Fargo for hours, after getting into a patch of Apocynum cannabinum (hemp dogbane). A photo of a poor baby Edmontosaurus whose mamma tried hellebore, with a single eye and adorably deformed face, threatens to displace the “I Can Has Cheezburger?” cat as the most viral meme on the Internet …

And a herd of Maiasaura, starving and desperate, wanders into Manhattan and discovers a wine bar decorated with lush ferns and rare tropical cycads. Minutes later, the wine bar is flattened, its greenery devoured. Newly invigorated by their first decent meal in weeks, the Maiasaura rampage from one fern bar to the next. Hundreds of Wall Street middle-management flunkies who were hoping to score that night are severely inconvenienced.

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Pliosaurus (meaning ‘more lizard’) is a genus of thalassophonean pliosaurid known from the Kimmeridgian and Tithonian stages (Late Jurassic) of Europe and South America. Their diet would have included fish, cephalopods, and marine reptiles. This genus has contained many species in the past but recent reviews found only six to be valid, while the validity of two additional species awaits a petition to the ICZN. Pliosaurus currently consists of the type species P. brachydeirus, and also P. brachyspondylus, P. carpenteri, P. funkei, P. kevani, P. macromerus, P. rossicus and P. westburyensis, as well as the invalid P. portentificus. Most species of Pliosaurus are notable for their large body size, while the others, P. brachydeirus, P. brachyspondylus and P. portentificus, are known exclusively from immature individuals. Species of this genus are differentiated from other pliosaurids based on seven autapomorphies, including teeth that are triangular in cross section.

A specimen found in the Svalbard islands of northern Europe has been estimated to have been 15 metres (49 ft) long, 45,000 kilograms (99,000 lb) in weight and had teeth 30 centimetres (12 in) long. It is estimated to have lived approximately 147 million years ago and was named Pliosaurus funkei in Knutsen et al 2012, with estimated skull lengths of 160-200 cm and a forelimb legnth of 300 cm for the holotype (PMO 214.135), and an estimated skull length of 200-250 cm for the referred specimen (PMO 214.136), suggesting that the animal had proportionally bigger flippers than other pliosaurs compared to the skull size and dimensions of the vertebrae. Analysis of bones from the four flippers suggest that the animal cruised using just two fore-flippers, using the back pair for extra speed when pursuing and capturing prey. P. funkei’s brain was of a similar type and size, proportionally, to that of today’s great white shark, the team says.

Paleontologists believe that there were several reasons why this animal went extinct. First of all, Mosasaurs came on the scene at about this time and competed heavily with Pliosaurus for its main food source – fish. That’s because Mosasaurs were faster and agiler than Pliosaurus. They were also more vicious animals. This was just enough of an edge for them to out-compete Pliosaurus for fish. Second, water temperatures began to change during this time and this creature may not have been able to adapt quickly enough. Which is probably why this animal went extinct some 145 million years ago.

Source: www.WildNature.org, www.Wikipedia.org

Tarascosaurus (“Tarasque lizard”) is a genus of, perhaps abelisaurid, theropod dinosaur from Late Cretaceous of France.

The holotype PSL 330201 was found in the Fuvelian Beds, dating from the lower Campanian. It consists of the upper part of a thigh bone, 22 centimetres (8.7 in) long. PSL 330202, consisting of two dorsal vertebrae, was made a paratype; these bones may belong to the same individual. Referred was PSL 330203, a damaged tail vertebra. The femur, with an undamaged length estimated at 35 centimetres (14 in), indicates a body length of two and a half to three metres. Some fossils from Spain were also referred to the genus.

In 2003 Oliver Rauhut concluded that Tarascosaurus itself was also a nomen dubium because the material was not diagnostic.

Tarascosaurus was placed in the Abelisauridae in 1991. It was then seen as the only known abelisaurid from the Northern Hemisphere apart from Betasuchus of the Maastrichtian of the Netherlands. However, in 2003 Ronan Allain et al. concluded that the type lacked any uniquely abelisaurid traits.

Source: www.Wikipedia.org, www.NatGeo.com

Kronosaurus (meaning “lizard of Kronos”) is a genus of short-necked pliosaur. With an estimated length of 9–10.5 metres (30–34 ft), it was among the largest pliosaurs, and is named after the leader of the Greek Titans, Cronus. It lived in the Early Cretaceous Period (Aptian-Albian). Fossil material has been recovered from Queensland in Australia, and from the Paja Formation in Boyacá, Colombia, and assigned to two species.

Like other pliosaurs, Kronosaurus was a marine reptile. It had an elongated head, a short neck, a stiff body propelled by four flippers, and a relatively short tail. The posterior flippers were larger than the anterior. Kronosaurus was carnivorous, and had many long, sharp, conical teeth. A feature of the genus Kronosaurus is the first three maxillary teeth are enlarged to fangs. Current estimates put Kronosaurus at around 9–10.5 meters (30–34 feet) in length. In 2009, K. queenslandicus was estimated to weigh up to 11,000 kilograms (11 metric tons).

Body-length estimates, largely based on the 1959 Harvard reconstruction, had previously put the total length of Kronosauru sat 12.8 meters (42 feet). However, more recent studies, comparing fossil specimens of Kronosaurus to other pliosaurs suggests that the Harvard reconstruction may have included too many vertebrae, exaggerating the previous estimate, with the true length probably only 9–10.5 meters (30–34 feet).

Fossil stomach contents from Northern Queensland show that Kronosaurus preyed on turtles and plesiosaurs. Fossil remains of giant squid have been found in the same area as Kronosaurus; it may have fed on them, but no direct evidence for this exists.

Large, round bite-marks have been found on the skull of an Albian-age Australian elasmosaurid (Eromangasaurus) that could be from a Kronosaurus attack.

Kronosaurus is known from Australia and Colombia. Both areas were covered by shallow inland seas when Kronosaurus inhabited them.

Source: www.NatGeo.com, www.Wikipedia.org

Paleontologists have discovered fossils of a 2-m-long lobster-like animal that lived in the seas of what is now Morocco during the early Ordovician period, about 480 million years ago.

The newly-discovered animal, named Aegirocassis benmoulae in honor of the Moroccan fossil hunter Mohamed Ben Moula who discovered the fossils, belongs to the extinct family Anomalocarididae (or anomalocaridids), which first appeared 520 million years ago.

This marine monster attained a size of at least 7 feet (2 m), ranking it among the biggest arthropods that ever lived.

“This would have been one of the largest animals alive at the time,” said Dr Allison Daley of Oxford University, who is a co-author of the paper published in the journal Nature.

“Aegirocassis benmoulae is a truly remarkable looking creature,” added co-author Dr Derek Briggs of the Yale Peabody Museum of Natural History and the Yale University’s Department of Geology and Geophysics.

While most anomalocaridids were apex predators, similar to present-day sharks that hunt other animals for food, Aegirocassis benmoulae is more like present-day whales, which filter seawater to find their food.

“These animals are filling an ecological role that hadn’t previously been filled by any other animal,” Dr Daley said.

“While filter feeding is probably one of the oldest ways for animals to find food, previous filter feeders were smaller, and usually attached to the sea-floor.”

“We have found the oldest example of gigantism in a freely swimming filter feeder.”

Lead author Dr Peter Van Roy of Yale University added: “giant filter-feeding sharks and whales arose at the time of a major plankton radiation, and Aegirocassis benmoulae represents a much, much older example of this trend.”

Dr Van Roy excavated an exceptionally well-preserved 3D fossil of the new species. Most previous anomalocaridid fossils were flat, like a dried leaf pressed within the pages of a book.

“Without these 3D remains, we may never have got the insight into these animals’ anatomy that we did,” Dr Daley said.

Aegirocassis benmoulae had two pairs of swim flaps per body segment, rather than the one pair found in previous anomalocaridid fossils.

The paleontologists show that the two pairs of swim flaps correspond the two branches of the double branched legs found in present-day arthropods, but at a stage before they fused together into one leg.

“We were excited to discover that it shows features that have not been observed in older Cambrian anomalocaridids – not one but two sets of swimming flaps along the trunk, representing a stage in the evolution of the two-branched limb, characteristic of modern arthropods such as shrimps,” Dr Briggs said.

_____

Peter Van Roy et al. Anomalocaridid trunk limb homology revealed by a giant filter-feeder with paired flaps. Nature, published online March 11, 2015; doi: 10.1038/nature14256

Source: www.sci-news.com