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Neogene Period

Saturday, November 19, 2016

The Neogene is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period 23.03 million years ago (Mya) to the beginning of the present Quaternary Period 2.58 Mya. The Neogene is sub-divided into two epochs, the earlier Miocene and the later Pliocene. Some geologists assert that the Neogene cannot be clearly delineated from the modern geological period, the Quaternary.

During this period, mammals and birds continued to evolve into roughly modern forms, while other groups of life remained relatively unchanged. Early hominids, the ancestors of humans, appeared in Africa near the end of the period. Some continental movement took place, the most significant event being the connection of North and South America at the Isthmus of Panama, late in the Pliocene. This cut off the warm ocean currents from the Pacific to the Atlantic ocean, leaving only the Gulf Stream to transfer heat to the Arctic Ocean. The global climate cooled considerably over the course of the Neogene, culminating in a series of continental glaciations in the Quaternary Period that follows.

The Neogene Period and its subdivisions by Encyclopedia Britannica

Geography

The continents in the Neogene were very close to their current positions. The Isthmus of Panama formed, connecting North and South America. The Indian subcontinent continued to collide with Asia, forming the Himalayas. Sea levels fell, creating land bridges between Africa and Eurasia and between Eurasia and North America.

Climate

The global climate became seasonal and continued an overall drying and cooling trend which began at the start of the Paleogene. The ice caps on both poles began to grow and thicken, and by the end of the period the first of a series of glaciations of the current Ice Age began.

Flora and fauna

Scene featuring Miocene (Early Neogene) fauna

Marine and continental flora and fauna have a modern appearance. The reptile group Choristodera became extinct in the early part of the period, while the amphibians known as Allocaudata disappeared at the end. Mammals and birds continued to be the dominant terrestrial vertebrates, and took many forms as they adapted to various habitats. The first hominids, the ancestors of humans, appeared in Africa and spread into Eurasia.

The Neogene Period: A map of the world 20 million years ago

In response to the cooler, seasonal climate, tropical plant species gave way to deciduous ones and grasslands replaced many forests. Grasses therefore greatly diversified, and herbivorous mammals evolved alongside it, creating the many grazing animals of today such as horses, antelope, and bison.

The Pliocene Epoch (5.3-2.6 Million Years Ago)

Saturday, November 19, 2016

 High Arctic camels, like those shown in this illustration, lived on Ellesmere Island during the Pliocene warm period about 3.5 million years ago. Julius Csotonyi

Prehistoric Life During the Pliocene Epoch

By the standards of “deep time,” the Pliocene epoch was relatively recent, commencing only five million years or so before the start of the modern historical record. During the Pliocene, prehistoric life around the globe continued to adapt to the prevailing climatic cooling trend, with some notable local extinctions and disappearances. The Pliocene was the second epoch of the Neogene period (23-2.6 million years ago), the first being the Miocene (23-5 million years ago); all of these periods and epochs were themselves part of the Cenozoic Era (65 million years ago to the present).

Climate and geography. During the Pliocene epoch, the earth continued its cooling trend, with tropical conditions holding at the equator (as they do today) and more pronounced seasonal changes at higher and lower latitudes; still, average global temperatures were 7 or 8 degrees (Fahrenheit) higher than they are today. The major geographic developments were the reappearance of the Alaskan land bridge between Eurasia and North America, after millions of years of submersion, and the formation of the Central American Isthmus joining North and South America.

Not only did this latter development allow an interchange of fauna between the two continents, but it had a profound effect on ocean currents, as the relatively cool Atlantic ocean was cut off from the much warmer Pacific.

Terrestrial Life During the Pliocene Epoch

Mammals. During large chunks of the Pliocene epoch, Eurasia, North America and South America were all connected by narrow land bridges–and it wasn’t all that difficult for animals to migrate between Africa and Eurasia, either. This wreaked havoc on mammalian ecosystems, which were invaded by migrating species, resulting in increased competition, displacement and even outright extinction. For example, ancestral camels (like the huge Titanotylopus) migrated from North America to Asia, while the fossils of giant prehistoric bears like Agriotherium have been discovered in Eurasia, North America and Africa. Apes and hominids were mostly restricted to Africa, though there were scattered communities in Eurasia and North America.

Examples of migrant species in the Americas after the formation of the Isthmus of Panama. Olive green silhouettes denote North American species with South American ancestors; blue silhouettes denote South American species of North American origin.

The most dramatic evolutionary event of the Pliocene epoch was the appearance of a land bridge between North and South America. Previously, South America had been much like modern Australia, a giant, isolated continent populated by a variety of strange mammals, including giant marsupials. (Confusingly, some animals had already succeeded in traversing these two continents, before the Pliocene epoch, by the arduously slow process of “island hopping”; that’s how Megalonyx, the Giant Ground Sloth, wound up in North America.) The winners in this “Great American Interchange” were the mammals of North America, which either wiped out or greatly diminished their southern relatives.

The late Pliocene epoch was also when some familiar megafauna mammals appeared on the scene, including the Woolly Mammoth in Eurasia and North America, Smilodon (the Saber-Toothed Tiger) in North and South America, and Megatherium (the Giant Sloth) and Glyptodon (a gigantic, armored armadillo) in South America. These plus-sized beasts persisted into the ensuing Pleistocene epoch, when they went extinct due to climate change and competition with (combined with hunting by) modern humans.

Birds. The Pliocene epoch marked the swan song of the phorusrhacids, or “terror birds,” as well as the other large, flightless, predatory birds of South America, which resembled meat-eating dinosaurs that had gone extinct tens of millions of years earlier. One of the last surviving terror birds, the 300-pound Titanis, actually managed to traverse the Central American isthmus and populate southeastern North America; however, this didn’t save it from going extinct by the start of the Pleistocene epoch.

Reptiles. Crocodiles, snakes, lizards and turtles all occupied an evolutionary backseat during the Pliocene epoch (as they did during much of the Cenozoic Era). The most important developments were the disappearance of alligators and crocodiles from Europe (which had now become much too cool to support their cold-blooded lifestyles), and the appearance of some truly gigantic turtles, such as the aptly named Stupendemys of South America.

Marine Life During the Pliocene Epoch

As during the preceding Miocene, the seas of the Pliocene epoch were dominated by the biggest shark that ever lived, Megalodon. Whales continued with their evolutionary progress, approximating the forms familiar in modern times, and pinnipeds (seals, walruses and sea otters) flourished in various parts of the globe. (An interesting side note: the pliosaurs of the Mesozoic Era were once thought to date from the Pliocene epoch, hence their misleading name, Greek for “Pliocene lizards.”)

Plant Life During the Pliocene Epoch

There weren’t any wild bursts of innovation in Pliocene plant life; rather, this epoch continued the trends seen during the preceding Oligocene and Miocene epochs, the gradual confinement of jungles and rain forests to equatorial regions, while vast deciduous forests and grasslands dominated higher northern latitudes, especially in North America and Eurasia.

The Oligocene Epoch (34-23 Million Years ago)

Saturday, November 19, 2016

Oligocene Wildlife by Jay Matternes

Prehistoric Life During the Oligocene Epoch

The Oligocene epoch wasn’t especially innovative with regard to its prehistoric animals, which continued along the evolutionary paths that had been pretty much locked in during the preceding Eocene (and continued on in turn during the ensuing Miocene). The Oligocene was the last major geologic subdivision of the Paleogene period (65-23 million years ago), following the Paleocene (85-56 million years ago) and Eocene (56-34 million years ago) epochs; all of these periods and epochs were themselves part of the Cenozoic Era (65 million years ago to the present).

Climate and geography. While the Oligocene epoch was still fairly temperate by modern standards, this 10-million-year stretch of geologic time saw a decrease in both average global temperatures and sea levels. All of the world’s continents were well on their way toward moving into their present positions; the most striking change occurred in Antarctica, which drifted slowly south, became more isolated from South America and Australia, and developed a polar ice cap.

Giant mountain ranges continued to form, most prominently in western North America and southern Europe.

Mollewide [Oval-Globe] Plate Tectonic Map of the Earth from the Oligocene [35 Ma]

Terrestrial Life During the Oligocene Epoch

Mammals. There were two major trends in mammalian evolution during the Oligocene epoch. First, the spread of newly evolved grasses across the plains of the northern and southern hemispheres opened a new ecological niche for grazing mammals. Early horses (such as Miohippus), distant rhinoceros ancestors (such as Hyracodon), and proto-camels (such as Poebrotherium) were all common sights on grasslands, often in locations you might not expect (camels, for instance, were especially thick on the ground in Oligocene North America, where they first evolved).

The other trend was mostly confined to South America, which was isolated from North America during the Oligocene epoch (the Central American land bridge would not form for another 20 million years) and hosted a bizarre array of megafauna mammals, including the elephant-like Pyrotherium and the meat-eating marsupial Borhyaena (the marsupials of Oligocene South America were every match for the contemporary Australian variety). Asia, meanwhile, was home to the largest terrestrial mammal that ever lived, the 20-ton Indricotherium, which bore an uncanny resemblance to a sauropod dinosaur!

Birds. As with the preceding Eocene epoch, the most common fossil birds of the Oligocene epoch were predatory South American “terror birds” (such as the unusually pint-sized Psilopterus) and giant penguins that lived in temperate, rather than polar, climates–Kairuku of New Zealand being a good example. Other types of birds also undoubtedly lived during the Oligocene epoch; we just haven’t identified many of their fossils yet!

Reptiles. To judge by the limited fossil remains, the Oligocene epoch wasn’t an especially notable time for lizards, snakes, turtles or crocodiles. However, the plenitude of these reptiles both before and after the Oligocene provides at least circumstantial evidence that they must have prospered during this epoch as well; a lack of fossils doesn’t always correspond to a lack of wildlife.

Marine Life During the Oligocene Epoch

The Oligocene epoch was a golden age for whales, rich in transitional species like Aetiocetus,Janjucetus and Mammalodon (which possessed both teeth and plankton-filtering baleen plates).Prehistoric sharks continued to be the apex predators of the high seas; it was toward the end of the Oligocene, 25 million years ago, that the gigantic Megalodon first appeared on the scene. The latter part of the Oligocene epoch also witnessed the evolution of the first pinnipeds (the family of mammals that includes seals and walruses), the basal Puijila being a good example.

Plant Life During the Oligocene Epoch

As remarked above, the major innovation in plant life during the Oligocene epoch was the worldwide spread of newly evolved grasses, which carpeted the plains of North and South America, Eurasia and Africa–and spurred the evolution of horses, deer, and various ruminants, as well as the meat-eating mammals that preyed on them. The process that had begun during the preceding Eocene epoch, the gradual appearance of deciduous forests in place of jungles over the earth’s spreading non-tropical regions, also continued unabated.

The Cenozoic Era (65 Million Years Ago to the Present)

Saturday, November 19, 2016

The Cenozoic Era (65 Million Years Ago to the Present)

Facts About the Cenozoic Era

The Cenozoic Era is easy to define: it’s the stretch of geologic time that kicked off with the Cretaceous/Tertiary Extinction, 65 million years ago, and continues down to the present day. Informally, the Cenozoic Era is often referred to as the “age of mammals,” since it was only after the dinosaurs went extinct that mammals had the chance to evolve into various open ecological niches and dominate terrestrial life on the planet. This characterization is somewhat unfair, however, since (non-dinosaur) reptiles, birds and fish also thrived during the Cenozoic!

Somewhat confusingly, the Cenozoic Era is divided into various “periods” and “epochs,” and scientists don’t always use the same terminology when describing their discoveries. (This situation stands in stark contrast to the preceding Mesozoic Era, which is neatly divided into the Triassic, Jurassic and Cretaceous periods.) Here’s an overview of the subdivisions of the Cenozoic Era; just click on the appropriate links to see more in-depth articles about the geography, climate and prehistoric life of that period or epoch.

The Periods and Epochs of the Cenozoic Era

The Paleogene period (65-23 million years ago) was the age when the mammals began their rise to dominance. The Paleogene comprises three separate epochs:

* The Paleocene epoch (65-56 million years ago) was fairly quiet in evolutionary terms. This is when the tiny mammals that survived the K/T Extinction first tasted their newfound freedom and began to tentatively explore new ecological niches.

* The Eocene epoch (56-34 million years ago) was the longest epoch of the Cenozoic Era. The Eocene witnessed a vast profusion of mammalian forms; this was when the first even- and odd-toed ungulates appeared on the planet, as well as the first recognizable primates.

* The Oligocene epoch (34-23 million years ago) is notable for its change in climate from the preceding Eocene, which opened up even more ecological niches for mammals. This was the epoch when certain mammals (and even some birds) began to evolve to respectable sizes.

The Neogene period (23-2.6 million years ago) witnessed the continuing evolution of mammals and other forms of life, many of them to enormous sizes. The Neogene comprises two epochs:

* The Miocene epoch (23-5 million years ago) takes up the lion’s share of the Neogene. Most of the mammals, birds and other animals that lived during this time would have been vaguely recognizable to human eyes, though often considerably bigger or stranger.

* The Pliocene epoch (5-2.6 million years ago), often confused with the ensuing Pleistocene, was the time when many mammals migrated into the territories that they continue to inhabit during the present day. Horses, primates, elephants, and other animal types continued to make evolutionary progress.

The Quaternary period (2.6 million years ago to the present) is, so far, the shortest of all the earth’s geologic periods. The Quaternary comprises two even shorter epochs:

* The Pleistocene epoch (2.6 million-12,000 years ago) is famous for its large megafauna mammals, such as the Woolly Mammoth and the Saber-Toothed Tiger, that died off at the end of the last Ice Age (thanks partly to predation by the earliest humans).

* The Holocene epoch (10,000 years ago-present) comprises pretty much all of modern human history. Unfortunately, this is also the epoch when many mammals, and other forms of life, have gone extinct due to the ecological changes wrought by human civilization.

The Eocene Epoch (56-34 Million Years Ago)

Saturday, November 19, 2016

Eocene by Kim Thompson

Prehistoric Life During the Eocene Epoch

The Eocene epoch began 10 million years after the extinction of the dinosaurs, 65 million years ago, and continued for another 22 million years, up to 34 million years ago. As with the preceding Paleocene epoch, the Eocene was characterized by the continuing adaptation and spread of prehistoric mammals, which filled the ecological niches left open by the dinosaurs’ demise. The Eocene constitutes the middle part of the Paleogene period (65-23 million years ago), preceded by the Paleocene and succeeded by the Oligocene epoch (34-23 million years ago); all of these periods and epochs were part of the Cenozoic Era (65 million years ago to the present).

Climate and geography. The Eocene epoch picked up where the Paleocene left off, with a continuing rise in global temperatures to near-Mesozoic levels. The later part of the Eocene saw a pronounced cooling trend, probably related to decreasing levels of carbon dioxide in the atmosphere, which culminated in the re-formation of ice caps at both the north and south poles.

The earth’s continents continued to drift toward their present positions, having broken apart from the northern supercontinent Laurasia and the southern supercontinent Gondwana, though Australia and Antarctica were still connected. The Eocene epoch also witnessed the rise of North America’s western mountain ranges.

Map of the Earth 50 mya

Terrestrial Life During the Eocene Epoch

Mammals. Perissodactyls (odd-toed ungulates, such as horses and tapirs) and artiodactyls (even-toed ungulates, such as deer and pigs) can all trace their ancestry back to the primitive mammalian genera of the Eocene epoch. Phenacodus, a small, generic-looking ancestor of hoofed mammals, lived during the early Eocene, while the late Eocene witnessed much bigger “thunder beasts” like Brontotherium and Embolotherium. Carnivorous predators evolved in synch with these plant-munching mammals: the early Eocene Mesonyx only weighed as much as a large dog, while the late Eocene Andrewsarchus was the largest terrestrial meat-eating mammal that ever lived. The first recognizable bats (such as Palaeochiropteryx), elephants (such as Phiomia), and primates (such as Eosimias) also evolved during the course of the Eocene epoch.

Birds. As is the case with mammals, many modern orders of birds can trace their roots to the Eocene epoch (even though birds as a whole evolved, perhaps more than once, during the Mesozoic Era). The most notable birds of the Eocene were giant penguins, as typified by the 100-pound Inkayacu of South America and the 200-pound Anthropornis of Australia. Another important Eocene bird was Presbyornis, a toddler-sized prehistoric duck.

Reptiles. Crocodiles (such as the weirdly hooved Pristichampsus), turtles (such as the big-eyed Puppigerus) and snakes (such as the 33-foot long Gigantophis) all continued to flourish during the Eocene epoch, many of them attaining substantial sizes as they filled the niches left open by their dinosaur relatives. Much tinier lizards, like the three-inch-long Cryptolacerta, were also a common sight (and food source for larger animals).

Marine Life During the Eocene Epoch

The Eocene epoch was when the first prehistoric whales left dry land and opted for a life in the sea, a trend that culminated in the middle Eocene Basilosaurus, which attained lengths of up to 60 feet and weighed in the neighborhood of 50 to 75 tons. Sharks continued to evolve as well, but few fossils are known from this epoch. In fact, the most common marine fossils of the Eocene epoch are of tiny fish, like Knightia and Enchodus, that plied the lakes and rivers of North America in vast schools.

Plant Life During the Eocene Epoch

The heat and humidity of the early Eocene epoch made it a heavenly time for dense jungles and rainforests, which stretched almost all the way to the North and South Poles (the coast of Antarctica was lined with tropical rainforests about 50 million years ago!) Later in the Eocene, global cooling produced a dramatic change: the jungles of the northern hemisphere gradually disappeared, to be replaced by deciduous forests that could better cope with seasonal temperature swings. One important development had only just begun: the earliest grasses evolved during the late Eocene epoch, but didn’t spread worldwide (providing sustenance for plains-roaming horses and ruminants) until millions of years later.

Allosaurus

Saturday, November 19, 2016

Allosauruses by deskridge on DeviantArt

Allosaurus is a genus of large theropod dinosaur that lived 155 to 150 million years ago during the late Jurassic period (Kimmeridgian to early Tithonian). The name “Allosaurus” means “different lizard”. It is derived from the Greek ἄλλος/allos(“different, other”) and σαῦρος/sauros (“lizard / generic reptile”). The first fossil remains that could definitively be ascribed to this genus were described in 1877 by paleontologist Othniel Charles Marsh. These remains became known as Antrodemus. As one of the first well-known theropod dinosaurs, it has long attracted attention outside of paleontological circles. Indeed, it has been a top feature in several films and documentaries about prehistoric life.

Allosaurus was a large bipedal predator. Its skull was large and equipped with dozens of sharp, serrated teeth. It averaged 8.5 m (28 ft) in length, though fragmentary remains suggest it could have reached over 12 m (39 ft). Relative to the large and powerful hindlimbs, its three-fingered forelimbs were small, and the body was balanced by a long and heavily muscled tail. It is classified as an allosaurid, a type of carnosaurian theropod dinosaur. The genus has a complicated taxonomy, and includes an uncertain number of valid species, the best known of which is A. fragilis. The bulk of Allosaurus remains have come from North America’s Morrison Formation, with material also known from Portugal and possibly Tanzania. It was known for over half of the 20th century as Antrodemus, but study of the copious remains from the Cleveland-Lloyd Dinosaur Quarry brought the name “Allosaurus” back to prominence, and established it as one of the best-known dinosaurs.

Allosaurus vs Trex size comparison

As the most abundant large predator in the Morrison Formation, Allosaurus was at the top of the food chain, probably preying on contemporaneous large herbivorous dinosaurs, and perhaps even other predators. Potential prey included ornithopods, stegosaurids, and sauropods. Some paleontologists interpret Allosaurus as having had cooperative social behavior, and hunting in packs, while others believe individuals may have been aggressive toward each other, and that congregations of this genus are the result of lone individuals feeding on the same carcasses. It may have attacked large prey by ambush, using its upper jaw like a hatchet.

Description

Allosaurus was a typical large theropod, having a massive skull on a short neck, a long tail and reduced forelimbs. Allosaurus fragilis, the best-known species, had an average length of 8.5 m (28 ft), with the largest definitive Allosaurus specimen (AMNH 680) estimated at 9.7 meters (32 feet) long, and an estimated weight of 2.3 metric tons (2.5 short tons). In his 1976 monograph on Allosaurus, James Madsen mentioned a range of bone sizes which he interpreted to show a maximum length of 12 to 13 m (39 to 43 ft). As with dinosaurs in general, weight estimates are debatable, and since 1980 have ranged between 1,500 kilograms (3,300 pounds), 1,000 to 4,000 kg (2,200 to 8,800 lb), and 1,010 kilograms (2,230 pounds) for modal adult weight (not maximum). John Foster, a specialist on the Morrison Formation, suggests that 1,000 kg (2,200 lb) is reasonable for large adults of A. fragilis, but that 700 kg (1,500 lb) is a closer estimate for individuals represented by the average-sized thigh bones he has measured. Using the subadult specimen nicknamed “Big Al”, researchers using computer modelling arrived at a best estimate of 1,500 kilograms (3,300 lb) for the individual, but by varying parameters they found a range from approximately 1,400 kilograms (3,100 lb) to approximately 2,000 kilograms (4,400 lb).

Mounted skeleton of “Big Al II” (specimen SMA 0005). Author: “The_Wookies”

Several gigantic specimens have been attributed to Allosaurus, but may in fact belong to other genera. The closely related genus Saurophaganax (OMNH 1708) reached perhaps 10.9 m (36 ft) in length, and its single species has sometimes been included in the genus Allosaurus as Allosaurus maximus, though recent studies support it as a separate genus. Another potential specimen of Allosaurus, once assigned to the genus Epanterias (AMNH 5767), may have measured 12.1 meters (40 feet) in length. A more recent discovery is a partial skeleton from the Peterson Quarry in Morrison rocks of New Mexico; this large allosaurid may be another individual of Saurophaganax.

Skull

The skull and teeth of Allosaurus were modestly proportioned for a theropod of its size. Paleontologist Gregory S. Paul gives a length of 845 mm (33.3 in) for a skull belonging to an individual he estimates at 7.9 m (26 ft) long. Each premaxilla (the bones that formed the tip of the snout), held five teeth with D-shaped cross-sections, and each maxilla (the main tooth-bearing bones in the upper jaw) had between 14 and 17 teeth; the number of teeth does not exactly correspond to the size of the bone. Each dentary (the tooth-bearing bone of the lower jaw) had between 14 and 17 teeth, with an average count of 16. The teeth became shorter, narrower, and more curved toward the back of the skull. All of the teeth had saw-like edges. They were shed easily, and were replaced continually, making them common fossils.

Allosaurus skull

The skull had a pair of horns above and in front of the eyes. These horns were composed of extensions of the lacrimal bones, and varied in shape and size. There were also lower paired ridges running along the top edges of the nasal bones that led into the horns. The horns were probably covered in a keratin sheath and may have had a variety of functions, including acting as sunshades for the eye, being used for display, and being used in combat against other members of the same species (although they were fragile). There was a ridge along the back of the skull roof for muscle attachment, as is also seen in tyrannosaurids.

Inside the lacrimal bones were depressions that may have held glands, such as salt glands. Within the maxillae were sinuses that were better developed than those of more basal theropods such as Ceratosaurus and Marshosaurus; they may have been related to the sense of smell, perhaps holding something like Jacobson’s organ. The roof of the braincase was thin, perhaps to improve thermoregulation for the brain. The skull and lower jaws had joints that permitted motion within these units. In the lower jaws, the bones of the front and back halves loosely articulated, permitting the jaws to bow outward and increasing the animal’s gape. The braincase and frontals may also have had a joint.

Classification

Allosaurus was an allosaurid, a member of a family of large theropods within the larger group Carnosauria. The family name Allosauridae was created for this genus in 1878 by Othniel Charles Marsh, but the term was largely unused until the 1970s in favor of Megalosauridae, another family of large theropods that eventually became a wastebasket taxon. This, along with the use of Antrodemus for Allosaurus during the same period, is a point that needs to be remembered when searching for information on Allosaurus in publications that predate James Madsen’s 1976 monograph. Major publications using the name “Megalosauridae” instead of “Allosauridae” include Gilmore, 1920, von Huene, 1926, Romer, 1956 and 1966, Steel, 1970, and Walker, 1964.

Following the publication of Madsen’s influential monograph, Allosauridae became the preferred family assignment, but it too was not strongly defined. Semi-technical works used Allosauridae for a variety of large theropods, usually those that were larger and better-known than megalosaurids. Typical theropods that were thought to be related to Allosaurus included Indosaurus, Piatnitzkysaurus, Piveteausaurus, Yangchuanosaurus, Acrocanthosaurus, Chilantaisaurus, Compsosuchus, Stokesosaurus, and Szechuanosaurus. Given modern knowledge of theropod diversity and the advent of cladistic study of evolutionary relationships, none of these theropods is now recognized as an allosaurid, although several, like Acrocanthosaurus and Yangchuanosaurus, are members of closely related families.

The cladogram of the classification of Allosauroidea by Drew R. Eddy, Julia A. Clarke

Allosauridae is one of four families in Carnosauria; the other three are Neovenatoridae, Carcharodontosauridae and Sinraptoridae. Allosauridae has at times been proposed as ancestral to the Tyrannosauridae (which would make it paraphyletic), one recent example being Gregory S. Paul’s Predatory Dinosaurs of the World, but this has been rejected, with tyrannosaurids identified as members of a separate branch of theropods, the Coelurosauria. Allosauridae is the smallest of the carnosaur families, with only Saurophaganax and a currently unnamed French allosauroid accepted as possible valid genera besides Allosaurus in the most recent review. Another genus, Epanterias, is a potential valid member, but it and Saurophaganax may turn out to be large examples of Allosaurus. Recent reviews have kept the genus Saurophaganax and included Epanterias with Allosaurus.

Species and taxonomy

There are currently four valid and one undescribed species of Allosaurus (A. amplusA. europaeus, the type species A. fragilis, the as-yet not formally described “A. jimmadseni”, and A. lucasi).

A. fragilis, “A. jimmadseni”, A. amplus, and A. lucasi are all known from remains discovered in the Kimmeridgian–Tithonian Upper Jurassic-age Morrison Formation of the United States, spread across the states of Colorado, Montana, New Mexico, Oklahoma, South Dakota, Utah, and Wyoming. A. fragilis is regarded as the most common, known from the remains of at least sixty individuals. For a while in the late 1980s and early 1990s it was common to recognize A. fragilis as the short-snouted species, with the long-snouted taxon being A. atrox; however, subsequent analysis of specimens from the Cleveland-Lloyd Quarry, Como Bluff, and Dry Mesa Quarry showed that the differences seen in the Morrison Formation material could be attributed to individual variation. A study of skull elements from the Cleveland-Lloyd site found wide variation between individuals, calling into question previous species-level distinctions based on such features as the shape of the lacrimal horns, and the proposed differentiation of “A. jimmadseni” based on the shape of the jugal. A. europaeus was found in the Kimmeridgian-age Porto Novo Member of the Lourinhã Formation, but may be the same as A. fragilis.

Allosaurus tendagurensis was found in Kimmeridgian-age rocks of Tendaguru, in Mtwara, Tanzania. Subsequent studies classified it as a non-coelurosaurian tetanuran, either a megalosaurid or carcharodontosaur. Although obscure, it was a large theropod, possibly around 10 meters (33 feet) long and 2.5 metric tons (2.8 short tons) in weight.

Anchisaurus

Saturday, November 19, 2016

Anchisaurus

Anchisaurus is a genus of basal sauropodomorph. An early herbivorous dinosaur, it lived during the Early Jurassic period; more specifically, the Pliensbachian to Toarcian ages, 190 to 174 million years ago. Until recently it was classed as a member of Prosauropoda. The name comes from the Greek αγχι/agkhi anchi-; “near, close” + Greek σαυρος/sauros; “lizard”. Anchisaurus was coined as a replacement name for Amphisaurus, which was itself a replacement name for Hitchcock’s Megadactylus, both of which had already been used for other animals.

Anchisaurus was a rather small dinosaur, with a length of just over 2 metres (6.6 ft), which helps explain why it was once mistaken for human bones. It probably weighed around 27 kilograms (60 lb). However, Marsh’s species A. major (also known as Ammosaurus) was larger, from 2.5 to 4 metres (8 ft 2 in to 13 ft 1 in) and some estimates give it a weight of up to 70 pounds (32 kg). Gregory S. Paul estimated its length at 2.2 meters and its weight at 20 kg in 2010.

Anchisaurus size

Sauropodomorph remains were first discovered in North America in 1818, when some large bones were uncovered by Mr. Solomon Ellsworth Jr while with gunpowder excavating a well in East Windsor, Connecticut. At the time of their discovery it was thought that the bones might be those of a human, but the presence of tail vertebrae in 1821 falsified that idea. They are now recognized as those of an indeterminate sauropodomorph, possibly more closely related to the plateosaurian prosauropods.

Due to its primitive appearance, Anchisaurus was previously classified as a prosauropod, a member of a group of animals related to or ancestral to the sauropods. Recent investigations show that a group of traditional prosauropods form a monophyletic sister-group to Sauropoda, and that Anchisaurus is instead closer to sauropods.

The family Anchisauridae was first proposed by Othniel Charles Marsh in 1885 and later defined as a clade consisting of Anchisaurus and its nearest relatives. However, it is not clear which other genera are included in the family; many of the dinosaurs once included have since been moved elsewhere, and the group is not used in most current taxonomies.

Atlascopcosaurus

Saturday, November 19, 2016

Atlascopcosaurus

Atlascopcosaurus (meaning “Atlas Copco lizard”) is a genus of herbivorous basal euornithopod dinosaur from the Early Cretaceous of the present Australia.

The type specimen, NMV P166409, was found in 1984 at the Dinosaur Cove East site at the coast of Victoria, in layers of the Eumeralla Formation dating from the early Cretaceous, Aptian-Albian. This holotype consists of a piece of the upper jaw, a partial maxilla with teeth. Nothing else is known about it; as the rest of the skeleton remains undiscovered it can only be inferred from closely related species that the genus represents a small bipedal herbivore. By extrapolation it has been estimated that it was about two to three metres (6.5–10 ft) long and weighed appoximately 125 kg. Because the teeth are not species-specific and the maxilla fragment is little informative, the taxon is today commonly seen as a nomen dubium.

Atlascopcosaurus

The type species, Atlascopcosaurus loadsi, was named and described by Tom Rich and Patricia Vickers-Rich in 1988/1989. The generic name refers to the Atlas Copco Company who had provided equipment for the dig that discovered this dinosaur in 1984. The project revealed 85 fossil bone fragments of various species. This opened the door for more excavation and, along with other companies, Atlas Copco helped over ten years excavate about sixty metres of tunnel in a cliff wall at the sea shore. The specific name, loadsi, honours William Loads, the state manager for Atlas Copco at the time, who assisted during the dig.

Atlascopcosaurus was in 1988 assigned to the Hypsilophodontidae. These are today seen as an unnatural (paraphyletic) group and Atlascopcosaurus is now simply considered a basal member of the Ornithopoda.

Ankylosaurus

Saturday, November 19, 2016

Ankylosaurus by WillDynamo55 on DeviantArt

Ankylosaurus is a genus of armored dinosaur. Fossils of Ankylosaurus have been found in geological formations dating to the very end of the Cretaceous Period, between about 68–66 million years ago, in western North America, making it among the last of the non-avian dinosaurs. It was named by Barnum Brown in 1908, and the only species classified in the genus is A. magniventris. The genus name means “fused lizard” and the specific name means “great belly”. A handful of specimens have been excavated to date, but a complete skeleton has not been discovered. Though other members of Ankylosauria are represented by more extensive fossil material, Ankylosaurus is often considered the archetypal member of its group.

Size of the largest known specimen (green), compared to a human

The largest known ankylosaurid, Ankylosaurus measured up to 6.25 m (20.5 feet) in length, 1.7 m (5.6 feet) in height, and weighed 6 tonnes (13,000 lb). It was a quadrupedal animal, with a broad, robust body. It had a wide, low skull, with two horns pointing backwards from the back of the head, and two horns below these that pointed backwards and down. The front part of the jaws were covered in a beak, with rows of small, leaf-shaped teeth further behind it. It was covered in armor plates, or osteoderms, with bony half-rings covering the neck, and had a large club on the end of its tail. Bones in the skull and other parts of the body were fused, increasing their strength, and this feature is the source of the genus name.

Ankylosaurus is a member of the family Ankylosauridae, and its closest relatives appear to be Anodontosaurus and EuoplocephalusAnkylosaurus is thought to have been a slow moving animal, able to make quick movements when necessary. Its broad muzzle indicates it was a non-selective browser. Sinuses and nasal chambers in the snout may have been for heat and water balance or played a role in vocalization. The tail club is thought to have been used in defense against predators or in intraspecific combat. Ankylosaurus has been found in the Hell Creek, Lance, and Scollard formations, but appears to have been rare in its environment. Although it lived alongside a nodosaurid ankylosaur, their ranges and ecological niches do not appear to have overlapped, and Ankylosaurus may have inhabited upland areas. Ankylosaurus also lived alongside dinosaurs such as TyrannosaurusTriceratops, and Edmontosaurus.

Description

Ankylosaurus is the largest known ankylosaurid dinosaur, estimated to have been up to 6.25 m (20.5 feet) long, 1.5 m (4.9 feet) wide, and 1.7 m (5.6 feet) tall at the hip. This length has been proposed by American palaeontologist Kenneth Carpenter, and is based on the largest known skull (specimen NMC 8880), which is 64.5 cm (25.4 inches) long and 74.5 cm (29.3 inches) wide. The smallest known skull (specimen AMNH 5214) is 55.5 cm (21.9 inches) long and 64.5 cm (25.4 inches) wide, and this specimen is estimated to have been 5.4 m (17.7 feet) long and around 1.4 m (4.6 feet) tall. Other authors have proposed a body length of 7 m (23 feet), 8–9 m (26.2–29.5 ft), or more than 9 m (29.5 feet). The weight of the animal has been estimated at 6 tonnes (13,000 lb).

The structure of much of the skeleton of Ankylosaurus, including most of the pelvis, tail and feet, is still unknown. It was quadrupedal, and its hind limbs were longer than the forelimbs. The scapula (shoulder blade) and coracoid (a rectangular bone connected to the lower end of the scapula) of specimen AMNH 5895 were fused, and had entheses (connective tissue) for various muscle attachments. The scapula was 61.5 cm (24.2 inches) long. The humerus (upper arm bone) was short and very broad, and about 54 cm (21 inches) long in specimen AMNH 5214. The femur (thigh bone) was very robust, and 67 cm (26 inches) long in AMNH 5214. While the feet of Ankylosaurus are incompletely known, the hindfeet probably had three toes, as is the case in related animals.

Skull

The three known Ankylosaurus skulls differ in various details, but this is thought to be the result of taphonomy (changes happening during fossilisation of the remains) and individual variation. The skull was low and triangular in shape, wider than it was long. It had a broad beak on the premaxillae. The orbits (eye sockets) were almost round to slightly oval and did not face directly sideways, because the skull tapered towards the front. Crests above the orbits merged into the upper squamosal horns (their shape has been described as “pyramidal”), which pointed backwards to the sides from the back of the skull. The crest and horn were probably separate elements originally, as seen in the related Pinacosaurus and Euoplocephalus. Below the upper horns, jugal horns were present, which pointed backwards and down. The horns may have originally been osteoderms (armor plates) that fused to the skull. However, the scale pattern on the skull surface was instead the result of remodelling of the skull. This obliterated the sutures between skull elements, which is common for adult ankylosaurs. The scale pattern of the skull was variable between specimens, though some details are shared; it had a diamond-shaped scale (internarial scale) at the font of the snout, two squamosal osteoderms above the orbit, and a ridge of scales at the back of the skull.

Cast of Ankylosaurus skull (AMNH 5214) in front view, Museum of the Rockies

Armor

 A prominent feature of Ankylosaurus was its armor, consisting of knobs and plates of bone known as osteoderms or scutes embedded in the skin. These have not been found in articulation, so their exact placement on the body is unknown, though inferences can be made based on related animals. The osteoderms ranged from 1 cm (0.4 inches) in diameter to 35.5 cm (14.0 inches) in length, and also varied in shape. The osteoderms of Ankylosaurus were generally thin walled and hollowed on the underside. Compared to Euoplocephalus, the osteoderms of Ankylosaurus were smoother in texture. The osteoderms covering the body were very flat, though with a low keel at one margin. In contrast, the nodosaurid Edmontonia had high keels, stretching from one margin to the other on the midline of its osteoderms. Ankylosaurus had some smaller osteoderms with a keel across the midline. Some osteoderms without keels may have been placed above the hip region, as in Euoplocephalus. Flattened, pointed plates resemble those on the sides of the tail of Saichania. Osteoderms with oval keels could have been placed on the upper side of the tail or the side of the limbs. Small osteoderms and ossicles likely occupied the space between the larger ones.

Only known tail club (AMNH 5214), American Museum of Natural History

Classification

Brown considered Ankylosaurus so distinct that he made it the type genus of a new family, Ankylosauridae (members of which are called ankylosaurids), typified by massive, triangular skulls, short necks, stiff backs, broad bodies, and osteoderms. He also classified Palaeoscincus (only known from teeth), and Euoplocephalus (then only known from a partial skull and osteoderms) as part of the family. Due to the fragmentary remains, Brown was unable to fully distinguish between Euoplocephalus and Ankylosaurus. Only having few, incomplete members of the family to compare with, he believed the group was part of the suborder Stegosauria. In 1923, Osborn coined the name Ankylosauria (members of which are called ankylosaurs or ankylosaurians), thereby placing the ankylosaurids in their own suborder.

Ankylosauria and Stegosauria are now grouped together within the clade Thyreophora. This group first appeared in the Sinemurian age, and survived for 135 million years, until disappearing in the Maastrichtian. They were widespread and inhabited a broad range of environments. As more complete specimens and new genera have been discovered, theories about ankylosaurian interrelatedness have become more complex, and hypotheses have often changed between studies. In addition to Ankylosauridae, Ankylosauria has been divided into the families Nodosauridae, and sometimes Polacanthidae (these families lacked tail clubs). Ankylosaurus is considered part of the subfamily Ankylosaurinae (members of which are called ankylosaurines) within Ankylosauridae. Ankylosaurus appears to be most closely related to Anodontosaurus and Euoplocephalus. The following cladogram is based on a 2015 phylogenetic analysis of the Ankylosaurinae conducted by Arbour and Currie:

Phylogenetic analysis of the Ankylosaurinae

Since Ankylosaurus and other Late Cretaceous North American ankylosaurids grouped with Asian genera (in a tribe the authors named Ankylosaurini), Arbour and Currie suggested that earlier North American ankylosaurids had gone extinct by the late Albian or Cenomanian ages of the Middle Cretaceous. Ankylosaurids thereafter recolonised North America from Asia during the Campanian or Turonian ages of the Late Cretaceous, and diversified there again, leading to genera such as AnkylosaurusAnodontosaurus, and Euoplocephalus. This explains a 30 million year gap in the fossil record of North American ankylosaurids between these ages.

Palaeoecology

Ankylosaurus existed between 68 and 66 million years ago, in the final, or Maastrichtian, stage of the Late Cretaceous Period. It was among the last dinosaur genera that appeared before the Cretaceous–Paleogene extinction event. The type specimen is from the Hell Creek Formation of Montana, while other specimens have been found in the Lance Formation of Wyoming and the Scollard Formation in Alberta, Canada, all of which date to the end of the Cretaceous. Fossils of Ankylosaurus are rare in these sediments, and the distribution of its remains suggest that it was restricted to the uplands of the formations, rather than the coastal lowlands. Another ankylosaur, an indeterminate nodosaur (formerly referred to as Edmontonia sp.), is also found in the same formations, but the range of the two genera does not seem to have overlapped. Their remains have so far not been found in the same localities, and the nodosaur appears to have inhabited the lowlands. The narrow muzzle of the nodosaur suggests it had a more selective diet than Ankylosaurus, further indicating ecological separation.

Map showing where Ankylosaurus fossils have been discovered

The Hell Creek, Lance and Scollard Formations represent different sections of the western shore of the Western Interior Seaway that divided western and eastern North America during the Cretaceous. They represent a broad coastal plain, extending westward from the seaway to the newly formed Rocky Mountains. These formations are composed largely of sandstone and mudstone, which have been attributed to floodplain environments. The regions where Ankylosaurus and other Late Cretaceous ankylosaurs have been found had a warm subtropical/temperate climate, which was monsoonal, had occasional rainfall, tropical storms, and forest fires. In the Hell Creek Formation, many types of plants were supported, primarily angiosperms, with less common conifers, ferns and cycads. An abundance of fossil leaves found at dozens of different sites indicates that the area was largely forested by small trees. Ankylosaurus shared its environment with dinosaurs including the ceratopsids Triceratops and Torosaurus, the hypsilophodont Thescelosaurus, the hadrosaurid Edmontosaurus, an indeterminate nodosaur, the pachycephalosaurian Pachycephalosaurus, and the theropods StruthiomimusOrnithomimusTroodon, and Tyrannosaurus.

Apatosaurus

Saturday, November 19, 2016

Apatosaurus by Manuelsaurus on DeviantArt

Apatosaurus is a genus of sauropod dinosaurs that lived in North America during the Late Jurassic period. Othniel Charles Marsh described and named the first-known species, A. ajax in 1877, and a second species, A. louisae, was discovered and named by William H. Holland in 1916. They lived about 152 to 151 million years ago (mya), during the early Tithonian age, and are now known from fossils in the Morrison Formation of modern-day Colorado, Oklahoma, and Utah, in the United States. Apatosaurus had an average length of 21–22.8 m (69–75 ft), and an average mass of 16.4–22.4 t (16.1–22.0 long tons; 18.1–24.7 short tons). A few specimens indicate a maximum length of 11–30% greater than average and a mass of 32.7–72.6 t (32.2–71.5 long tons; 36.0–80.0 short tons).

The cervical vertebrae of Apatosaurus are less elongated and more heavily constructed than those of Diplodocus, a diplodocid like Apatosaurus, and the bones of the leg are much stockier despite being longer, implying that Apatosaurus was a more robust animal. The tail was held above the ground during normal locomotion. Apatosaurus had a single claw on each forelimb and three on each hindlimb. The skull of Apatosaurus, long thought to be similar to Camarasaurus, is much more similar to that of DiplodocusApatosaurus was a generalized browser that likely held its head elevated. To lighten its vertebrae, Apatosaurus had air sacs that made the bones internally full of holes. Like that of other diplodocids, its tail may have been used as a whip to create loud noises.

Mounted A. louisae holotype (specimen CM 3018), Carnegie Museum of Natural History

The skull of Apatosaurus was confused with that of Camarasaurus and Brachiosaurus until 1909, when the holotype of A. louisae was found, and a complete skull just a few meters away from the front of the neck. Henry Fairfield Osborn disagreed with this association, and went on to mount a skeleton of Apatosaurus with a Camarasaurus skull cast. Until 1970, Apatosaurusskeletons were mounted with speculative skull casts, when McIntosh showed that more robust skulls assigned to Diplodocuswere more likely from Apatosaurus.

Apatosaurus is a genus in the family Diplodocidae. It is one of the more basal genera, with only Amphicoelias, and possibly a new, unnamed genus more primitive. While the subfamily Apatosaurinae was named in 1929, the group was not used validly until an extensive 2015 study. Only Brontosaurus is also in the subfamily, with the other genera being considered as synonyms or reclassified as diplodocines. Brontosaurus has long been considered a junior synonym of Apatosaurus; its only species was reclassified as A. excelsus in 1903. However, the 2015 study concluded that Brontosaurus was a valid genus of sauropod distinct from Apatosaurus. Nevertheless, not all paleontologists agree with this division. As it existed in North America during the late Jurassic, Apatosaurus would have lived aside dinosaurs such as AllosaurusCamarasaurusDiplodocus, and Stegosaurus.

Infographic explaining the history of Brontosaurus and Apatosaurus according to Tschopp et al. 2015

 

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