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Sauroposeidon

Sauroposeidon

S. proteles
The tallest dinosaur known, Sauroposeidon (meaning "earthquake lizard-god") is an Early Cretaceous sauropod related to the Brachiosaurus. The only specimen to date is represented by four neck vertebrae.

Discovery

The vertebrae were discovered, not far from the Texas border, in a claystone outcrop that dates the fossils to about 110 million years ago (mya). This falls within the Early Cretaceous, specificially between the Aptian and Albian epochs. The four neck vertebrae were discovered in 1994 at the Antlers Formation in Atoka County, Oklahoma by Dr. Richard Cifelli and a team from the Oklahoma Museum of Natural History. While discovered in 1994, the vertebrae were stored until three years later, when Dr. Cifelli gave them to a graduate student, Matt Wedel, to analyze as part of a project. After realizing the significance of the find, a press release was made in October of 1999, followed by official publication in the Journal of Vertebrate Paleontology in March of 2000. The new species was dubbed S. proteles, and the holotype is OMNH 53062.

Etymology

The genera name comes from sauros (Greek for "lizard"), and Poseidon, a sea-god in Greek mythology, who is also associated with earthquakes. The species name proteles also comes from the Greek, and means "perfect before the end" — which refers to the Sauroposeidon's status as the last, and most specialized giant sauropod known in North America during the Early Cretaceous.

Who's the biggest?

:"It's truly astonishing. It's arguably the largest creature ever to walk the earth." ::— Richard Cifelli, discoverer of Sauroposeidon The press release in 1999 immediately garnered international media attention, which led to many (inaccurate) news reports of "the largest dinosaur ever!". While it is true that the Sauroposeidon is probably the tallest known dinosaur, it is neither the longest nor the most massive. The Supersaurus, the Seismosaurus, and the Argentinosaurus are better candidates for the title "World's Largest Dinosaur", though weak fossil evidence makes an exact ranking impossible. The Sauroposeidon find was composed of four articulated, mid-cervical vertebrae (numbers 5 to 8), with the cervical ribs in place. The vertebrae are extremely elongated, with the largest one about 1.2 meters (4 feet) long, which makes it the longest on record. Examination of the bones revealed that they are honeycombed with tiny air cells, and are very thin, like the bones of a chicken or an ostrich, making the neck lighter and easier to lift. Estimates of size are based on a comparison between the four Sauroposeidon vertebrae and the vertebrae of the HM SII specimen of Brachiosaurus brancai, located in the Humboldt Museum in Berlin. The HM SII is the most complete brachiosaur known, though since it is composed of pieces from different individuals its proportions may not be totally accurate. Comparisons to the other brachiosaurid cousins of the Sauroposeidon would be difficult due to limited remains. The neck length of the Sauroposeidon is estimated at 37 to 39.5 feet (11.25 to 12 meters), compared to a neck length of 30 feet (9 meters) for the HM SII Brachiosaurus. This is based on the assumption that the rest of the neck has the same proportions at the Brachiosaurus, which is a reasonably good conjecture. The Sauroposeidon was probably able to raise its head 60 feet (18 meters) above the ground, which is as high as a six-story building. The long neck and the high brachiosaurid shoulders are what makes it the tallest known dinosaur. In some ways, its build is similar to the modern giraffe, with a short body and an extremely long neck. In comparison, the brachiosaur could probably raise its head 45 feet (13.5 meters) into the air, and the previous record holder, the Diplodocus, might have been able to raise its head 50 feet (15 meters). The Sauroposeidon's shoulders were probably 22 to 24 feet (7 meters) off the ground. Its estimated length is just under 100 feet (30 meters). The mass of the Sauroposeidon is estimated at 50 to 60 metric tonnes (55 to 65 tons). While the vertebrate of the Sauroposeidon are 25–33% longer than the brachiosaur's, they are only 10–15% larger in diameter. This means that while the Sauroposeidon probably has a larger body than the Brachiosaurus its body is smaller in comparison to the size of its neck, so it did not weigh as much as a scaled-up brachiosaur. By comparison, the brachiosaur might have weighed 36 to 40 tonnes (40 to 44 tons). This estimate of the brachiosaur is an average of several different methodologies. However, Sauroposeidon has a relatively gracile neck compared to the Brachiosaurus. If the rest of the body turns out to be similarly slender, the mass estimate may be too high. This could be similar to the way the relatively chunky Apatosaurus weighs far more than the longer but much slimmer Diplodocus. In addition, it is possible that sauropods may have an air sac system, like those in birds, which could reduce all sauropod mass estimates by 20% or more.

Environment

:"Sauroposeidon was an unexpected discovery, because it was a huge, gas-guzzling barge of an animal in an age of subcompact sauropods." ::—Matt Wedel, Sauroposeidon team leader The Sauroposeidon may be the last of the giant North American sauropods. Sauropods, which include the largest terrestrial animals of all time, were a very wide ranging and successful group. They first appeared in the Early Jurassic, and it wasn't long before they spread across the world. By the time of the late Jurassic, North America and Africa were dominated by the diplodocids and brachiosaurids, and by the end of the Late Cretaceous, titanosaurids were widespread. But in the middle, in the Early Cretaceous, the fossil record is sparse. Most of the other sauropods at the time were dying out, and as a result few specimens have been found in North American from that time, and those specimens that do exist are often fragmentary or represent juvenile members of their species. Most of the surviving sauropods at the time were also shrinking in size (to a mere 50 feet, or 15 meters, in length, and maybe 10 to 15 tons or tonnes), which makes the discovery of an extremely specialized super-giant like the Sauroposeidon very unusual. The Sauroposeidon lived on the shores of the Gulf of Mexico, which ran through Oklahoma at that time, in a vast river delta, similar to the Mississippi delta today. There were probably no predators who could take down a full-grown Sauroposeidon, but juveniles were likely prey to the Acrocanthosaurus (an Allosaurus a little smaller than a T. rex), and packs of Deinonychus.

References


- "Sauroposeidon proteles, a new sauropod from the Early Cretaceous of Oklahoma", by Mathew J. Wedel, Richard L. Cifelli, and R. Kent Sanders (Journal of Vertebrate Paleontology 29(1), pages 109–114, March 2000).
- "Osteology, paleobiology, and relationships of the sauropod dinosaur Sauroposeidon", by Mathew J. Wedel, Richard L. Cifelli, and R. Kent Sanders (Acta Palaeontologica Polonica 45, pages 343–388, 2000).

External links


- Sauroposeidon's listing in the [http://www.guinnessworldrecords.com/gwr5/content_pages/record.asp?recordid=51066 Guiness Book of World Records].
- A non-technical [http://www.geocities.com/CapeCanaveral/Galaxy/8152/largest.html article] on Dino Land, with links to various news reports.
- An [http://www.geocities.com/CapeCanaveral/Galaxy/8152/mattwedel.html interview] on Dino Land with Matt Wedel, lead researcher on the Sauroposeidon team at the University of Oklahoma.
- The [http://dinosauricon.com/genera/sauroposeidon.html classification] of the Sauroposeidon, at the Dinosauricon.
- [http://www.snomnh.ou.edu/publications/Articles/index.shtml Publications] of the Sam Noble Oklahoma Museum of Natural History, including the two technical papers listed under References. Category:Sauropods

Dinosaur

Dinosaurs are vertebrates that dominated the terrestrial ecosystem for over 160 million years. Non-avian dinosaurs became extinct at the end of the Cretaceous period, 65 million years ago. Knowledge about dinosaurs comes from both fossil and non-fossil records, including fossilized bones, feces, trackways, gastroliths, feathers, impressions of skin, internal organs and soft tissues. Since the first dinosaur was recognized in the 19th century, their mounted, fossilized skeletons have become major attractions at museums around the world. Dinosaurs have become a part of world culture and remain consistently popular, especially among children. They have been featured in best-selling books and blockbuster films such as Jurassic Park, and new discoveries are regularly covered by the media. The term is also used informally to describe any prehistoric reptile, such as the pelycosaur Dimetrodon, the winged pterosaurs, and the aquatic ichthyosaurs, plesiosaurs, and mosasaurs, though none of these are dinosaurs. The on-going dinosaur renaissance began in the 1970s and was triggered, in part, by John Ostrom's discovery of Deinonychus, an active, vicious predator that may have been warm-blooded (homoeothermic), in marked contrast to the prevailing image of dinosaurs as sluggish and cold-blooded. Vertebrate paleontology has also become a global science, with major new discoveries in previously unexploited regions, including South America, Madagascar, Antarctica, and most significantly the amazingly well-preserved feathered dinosaurs in China, which have further solidified the link between dinosaurs and their living descendants, modern birds. The widespread application of cladistics, which rigorously analyzes the relationships between biological organisms, has also proved tremendously useful in classifying dinosaurs, which are still known from an incomplete fossil record.

What is a dinosaur?

Definition

fossil record at the Smithsonian National Museum of Natural History.]] The superorder or clade "Dinosauria" was formally named by the English scientist Richard Owen in 1842. The term is a combination of the Greek words deinos ("terrible" or "fearfully great" or "formidable") and sauros ("lizard" or "reptile"). Contrary to popular perception, the name was chosen to express Owen's awe at the size and majesty of the extinct animals, not out of fear or trepidation at their size and formidable arsenal. Dinosaurs are extremely varied. Some were herbivorous, others carnivorous. Some dinosaurs were bipedal, others quadrupedal, while others could walk easily on both two and four legs, such as the dinosaur Ammosaurus. Under phylogenetic taxonomy, Dinosaurs are defined as all descendants of the most recent common ancestor of Triceratops and modern birds. Ornithischia is defined as all taxa sharing a more recent common ancestor with Triceratops than with Saurischia. Saurischia is defined as all taxa sharing a more recent common ancestor with birds than with Ornithischia. It has also been suggested that Dinosauria be defined as as all the descendants of the most recent common ancestor of Megalosaurus and Iguanodon There is an almost universal consensus among paleontologists that birds are the descendants of theropod dinosaurs. Using the strict cladistical definition that all descendants of a single common ancestor are related, modern birds are dinosaurs and dinosaurs are, therefore, not extinct. Modern birds are classified by most paleontologists as belonging to the subgroup Maniraptora, which are coelurosaurs, which are theropods, which are saurischians, which are dinosaurs. However, birds are morphologically distinct from their reptilian ancestors, and referring to birds as "avian dinosaurs" and to all other dinosaurs as "non-avian dinosaurs" is clumsy. Birds are still birds, at least in popular usage and among ornithologists. It is also technically correct under the older Linnaean classification system, which accepts taxa that exclude some descendants of a single common ancestor (paraphyletic taxa). Paleontologists mostly use cladistics in their classifications, which classifies birds as dinosaurs, but many other scientists do not. As a result, this article will use "dinosaur" as a synonym for "non-avian dinosaur", and "bird" as a synonym for "avian dinosaur".

Size

Only a tiny percentage of animals ever fossilize, and most of these remain buried in the earth. As a result, the smallest and largest dinosaurs will probably never be discovered. Even among those specimens that are recovered, few are known from complete skeletons, and impressions of skin and soft tissue are rare. Reconstructing a skeleton by comparing the size and morphology of bones to those of similar, better-known species is inexact, and restoring the muscles and other organs is, at best, educated guesswork. smallest and largest dinosaurs.]] smallest and largest dinosaurs While the largest and smallest dinosaurs will probably remain unknown, and a comparison between existing specimens is imprecise, it is clear that, as a group, dinosaurs were large. By dinosaur standards the sauropods were gigantic. The smallest sauropods were larger than anything else in their habitat, and the largest were an order of magnitude more massive than anything else that has ever walked the Earth. The tallest and heaviest dinosaur known from a complete skeleton is the Brachiosaurus, which was discovered in Tanzania between 1907–12. It is now mounted in the Humboldt Museum of Berlin and is 12 m (38 ft) tall and probably weighed between 30,000–60,000 kg (30–70 short tons). The longest dinosaur is the 27 m (89 ft) long Diplodocus, which was discovered in Wyoming and mounted in Pittsburgh's Carnegie Natural History Museum in 1907. There were larger dinosaurs, but they are only known from a scant number of fossil samples. The largest specimens on record all date from the 1970s or later, and include the massive Argentinosaurus, which may have weighed 80,000–100,000 kg (90–110 tons); the longest, the 40 m (130 ft) long Supersaurus; and the tallest, the 18 m (60 ft) Sauroposeidon, which could have reached a sixth-floor window. Dinosaurs were the largest of all terrestrial animals. The largest elephant on record weighed 12,000 kg (13.5 tons), and the tallest giraffe was 6 m (20 ft) tall. Even the giant prehistoric mammals such as the Indricotherium and the Columbian mammoth were dwarfed by the giant sauropods. Only a small handful of aquatic animals approach it in size, of which the blue whale is largest, reaching up to 190,000 kg (210 tons) and 33.5 m (110 ft) in length. Not including modern birds like the bee hummingbird, the smallest dinosaurs known were about the size of a crow or a chicken. The Microraptor, Parvicursor, and Saltopus were all under 60 cm (2 ft) in length. In fact, most dinosaurs were much smaller than we would expect, with the average size of a dinosaur being around the size of a large sheep.

Behavior

Interpretations of behavior based on the pose of a body fossil and its habitat, computer simulations of their biomechanics, and comparison with modern animals in similar ecological niches rely on speculation and promise to generate controversy for the foreseeable future. However, it is likely that at least the behaviors common in both of their closest living relatives, crocodiles and birds, are also common among dinosaurs. It should be of note that nearly all interpretations of evidence are subject to change, as theories surrounding dinosaurs evolve continuously. The first evidence of herding behavior was the 1878 discovery of 31 Iguanodon that perished together in Bernissart, Belgium, after they fell down a deep ravine, drowning as the latter was filled with rainwater. Similar mass deaths and trackways suggest that herd or pack behavior was common among many dinosaur groups. Trackways of hundreds or even thousands of herbivores indicate that duck-bills (hadrosaurids) may have moved in great herds, like the American Bison or the African Springbok. Sauropod tracks document that they traveled in groups composed of several different species, at least in Oxford, England, and others kept their young in the middle of the herd for defense according to trackways at Davenport Ranch, Texas. Dinosaurs may have congregated in herds for defense, migration, or to care for their young. migration Jack Horner's 1978 discovery of a Maiasaura ("good mother dinosaur") nesting ground in Montana demonstrated parental care long after birth among the ornithopods, and similar nesting behavior and even huge nesting colonies like those of penguins have been discovered of other Cretaceous dinosaurs like the Patagonian sauropod Saltasaurus (in 1997). The Mongolian maniraptoran Oviraptor was even discovered in a chicken-like brooding position in 1993, which may mean it was covered with an insulating layer of feathers that kept the eggs warm. Trackways have also confirmed parental behavior among sauropods and ornithopods from the Isle of Skye in the United Kingdom. Nests and eggs are known from most major groups of dinosaurs, and it appears likely that dinosaurs communicated with their young, like modern birds and crocodiles. The crests and frills of some dinosaurs, like the marginocephalians, theropods and lambeosaurines, may have been too fragile for active defense, so they were probably used for sexual or aggressive displays, though little is known about dinosaur mating and territorialism. Communication is also an enigma, but the hollow crests of the lambeosaurines may have been resonance chambers used for a wide range of vocalizations. One of the most valuable fossils, a Velociraptor attacking a Protoceratops, was discovered in the Gobi Desert in 1971, proving that dinosaurs did indeed attack and eat each other. While cannibalistic behavior among theropods is no surprise, it was confirmed by tooth marks from Madagascar in 2003. Compared to the later mammalian radiation in the Cenozoic, there seem to be no burrowing and few climbing dinosaurs. Biomechanics has given insight into how fast dinosaurs could run, whether diplodocids could create sonic booms by snapping their tails like a whip, whether giant theropods had to slow down when rushing for food to avoid fatal injuries, and if sauropods could float.

Study of dinosaurs

Fields of study

Information on dinosaurs is obtained from a variety of fields of study including Physics, Chemistry, Biology, and the Earth Sciences (which includes Paleontology). Activities include the discovery, reconstruction and conservation of dinosaur fossils and the interpretation of those fossils to better understand the evolution, classification and behavior of dinosaurs.

Classification

Main article: Dinosaur classification Dinosaurs (including birds) are archosaurs, like modern crocodilians. These are set apart by having diapsid skulls, having two holes where jaw muscles attach, called temporal fenestrae. Most reptiles (including birds) are diapsids; mammals, with only one temporal fenestra, are called synapsids; and turtles, with no temporal fenestra, are anapsids. Dinosaurs also have teeth that grow from sockets (an archosaur characteristic) rather than as direct extensions of the jaw bones, as well as various other characteristics. Within this group, the dinosaurs are set apart most noticeably by their gait. Instead of legs that sprawl out to the side, as found in lizards and crocodylians, they have legs held directly under their body. All dinosaurs were land animals. Many other types of reptiles lived at the same time as the dinosaurs. Some of these are commonly, but incorrectly, thought of as dinosaurs: these include plesiosaurs (which are not closely related to the dinosaurs) and pterosaurs, which developed separately from reptilian ancestors in the late Triassic. Dinosaurs are divided into two major orders, the Saurischia and the Ornithischia, on the basis of hip structure. Saurischians (from the Greek meaning "lizard hip") are dinosaurs that retained the hip structure of their ancestors. They include all the theropods (bipedal carnivores) and sauropods (long-necked herbivores). Ornithischians (from the Greek meaning "bird-hip") is the other dinosaurian order, most of which were quadrupedal herbivores.

Evolution

Dinosaurs split off from their archosaur ancestors during the Triassic period. The first known dinosaurs appeared approximately 230 Mya, about 20 million years after the Permian-Triassic extinction event wiped out about 70 percent of all biological diversity on the planet. A few lines of primitive dinosaurs diversified rapidly after the Triassic, and quickly expanded until they filled most of the vacant ecological niches. During the reign of the dinosaurs, which encompassed the ensuing Jurassic and Cretaceous periods, nearly every terrestrial animal larger than 1 m in length (that we know of) was a dinosaur. The Cretaceous-Tertiary extinction event, 65 Mya at the end of the Cretaceous, caused the extinction of all dinosaurs except for the line that had already led to the first birds.

Areas of debate

Warm-blooded?

Cretaceous-Tertiary extinction event Scientists have waged a constant and vigorous debate over the temperature regulation of dinosaur blood; at first over its possibility, then over its method, a debate first popularized by Robert T. Bakker, also known as Bob Bakker. From the first discovery of dinosaurs, paleontologists posited that they were ectothermic creatures: "terrible lizards" as their name suggested. This axiomatic expectation implied that dinosaurs were mostly slow, sluggish organisms, comparable to modern reptiles, which need the sun to heat their bodies. However, new evidence of dinosaurs in chilly temperate climates, of polar dinosaurs in Australia and Antarctica where they experienced a six-month chilly and dark winter, of feathered dinosaurs whose feathers provided regulatory insulation, and analysis of blood-vessel structures that are typical of endotherms within dinosaur bone, confirmed the possibility that some dinosaurs regulated their body temperature by internal biological methods, some aided partly by their very bulk. Skeletal structures suggest active lifestyles for theropods and other creatures, behavior more suitable for an endothermic cardiovascular system. Sauropods exhibit fewer endothermic characters. Perhaps some dinosaurs were endothermic and others not. Scientific debate over the details continues, although many paleontologists would now agree that endothermic systems are more likely (Parsons et al., 2001). Complicating this debate, warm-bloodedness can emerge from more than one mechanism. Most discussions of dinosaur endothermia compare them to average birds or mammals, which expend energy to elevate body temperature above that of the environment. Small birds and mammals also possess insulation of some sort, such as fat, fur, or feathers, to slow down heat loss. However, large mammals, such as elephants, face a different problem due to their relatively small surface area to volume ratio (Haldane's principle). This ratio compares the volume of an animal with the area of its skin: as an animal gets bigger, its surface area increases more slowly than its volume. At a certain point, the amount of heat radiated away through the skin drops below the amount of heat produced inside the body, forcing animals to use additional methods to avoid overheating. In the case of elephants, they lack fur, and have large ears which increase their surface area, and have behavioral adaptations as well, such as using the trunk to spray water on themselves and mud wallowing. These behaviors increase cooling through evaporation. Large dinosaurs would presumably have faced the same situation: their size would dictate that they lost heat relatively slowly to the surrounding air, and so could have been what are called bulk endotherms, animals that are warmer than their environments through sheer size rather than any special adaptations like those of birds and mammals. However, so far this theory fails to explain the vast multitudes of dog- and goat-sized dinosaurs, which made up the bulk of the ecosystem in the mesozoic.

Feathered dinosaurs and the bird connection

A number of similiarities occur between birds and non-avian dinosaurs, in fact over a hundred distinct anatomical features are shared by avian dinosaurs and theropod dinosaurs. Feathers bulk endotherms.]] The first good specimen of a "feathered dinosaur" was the 1861 discovery of the Archaeopteryx in Germany, in the Solnhofen limestone, which is a lagerstätte; one of the rare and remarkable geological formations known for their superbly detailed fossils. Coming just two years after Darwin's seminal The Origin of Species, the evidence of a transitional fossil between reptiles and birds spurred the debates between evolutionary biology and creationism. This early bird is so dinosaur-like that, without a clear impression of feathers in the surrounding rock, the specimens are commonly mistaken for Compsognathus. Since the 1990s, a number of feathered dinosaurs have been found, providing clear evidence of the close relationship between dinosaurs and birds. Most of these specimens were local to Liaoning province in northeastern China, which was part of an island continent in the Cretaceous. However, the feathers were only preserved by the lagerstätte of the Yixian Formation; it is therefore possible that dinosaurs elsewhere in the world may have been feathered too, even though the feathers have not been preserved. The feathered dinosaurs discovered so far include Beipiaosaurus, Caudipteryx, Dilong, Microraptor, Protarchaeopteryx, Shuvuuia, Sinornithosaurus, and Sinosauropteryx, and potentially Adasaurus; and dinosaur-like birds like Confuciusornis; all of which come from the same area and formation in northern China. The dromaeosauridae family in particular seems to have been heavily feathered, and at least one dromaeosaurid, Cryptovolans, may have been capable of flight. Skeleton Because feathers are often associated with birds, feathered dinosaurs are often touted as the missing link between birds and dinosaurs. However, the association of multiple skeletal features also shared by the two groups is the more important link for paleontologists. Furthermore, it is increasingly clear that the relationship between birds, dinosaurs and the evolution of flight is more complex than has been previously realized. For example, while it was once believed that birds evolved from dinosaurs in one linear progression, some scientists, most notably Gregory S. Paul, conclude that some dinosaurs, such as the dromaeosaurs, may have evolved from birds, losing the power of flight while keeping their feathers in a manner similar to the ostrich and other ratites. Comparisons of bird and dinosaur skeletons, as well as cladistic analysis, strengthens the case for the link, particularly for a branch of theropods called maniraptors. Skeletal similarities include: the neck, pubis, wrists (semi-lunate carpal), arm and pectoral girdle, shoulder blade, clavicle and breast bone. Reproduction biology breast bone.]] A discovery in a Tyrannosaurus rex skeleton provided more evidence that dinosaurs and birds evolved from a common ancestor and for the first time allowed paleontologists to sex a dinosaur. When laying eggs, female birds have a special type of bone, called a medullary bone, that grows in their limbs, forming a layer inside the hard outer bone. It is rich in calcium and used for making eggshells. The presence of endosteally derived bone tissues lining the interior marrow cavities of portions of the Tyrannosaurus rex specimen's hind limb elements suggested similar reproductive strategies, and revealed the specimen to be female (Schweitzer et al., 2005). A dinosaur embryo was found without teeth, which suggests some parental care was required to feed the young dinosaur, possibly the adult dinosaur regurgitated nutrition into the young dinosaur's mouth. This behavior is seen in numerous modern-day bird species; the parent birds regurgitated food into the hatchling's mouth. Lungs Big meat-eating dinosaurs had a complex system of air sacs similar to the setup in today's birds, according to an investigation led by Patrick O'Connor of Ohio University. The lungs of theropod dinosaurs, carnivores that walked on two legs and had birdlike feet, likely pumped air into hollow sacs in their skeletons, as is the case in birds. "What was once formally considered unique to birds was present in some form in the ancestors of birds", O'Connor said. The study was funded in part by the National Science Foundation. Heart and sleeping posture Modern computerized tomography (CT) scans of dinosaur chest cavities, conducted in 2000, found the apparent remnants of complex four-chambered hearts, much like those of today's mammals and birds. A recently discovered troodont fossil demonstrates that the dinosaurs slept like certain birds today, with their heads tucked under their arms. This would allow the head to be kept warm as is shown by modern birds. Gizzard Another piece of evidence that birds and dinosaurs are closely connected is that both birds and dinosaurs have used gizzard stones. The stones are swallowed by the animal to aid digestion and break down hard fibres and food once it enters the stomach. When found in association with fossils, they are called gastroliths. Paleontologists use the stones found in the dinosaur's stomach to determine migration routes, for example, the stone could have been swallowed at a certain point before being carried to another point during migration.

Evidence for Cenozoic dinosaurs

It has been claimed that fossils from El Ojo, South America, represent remains of dinosaurs surviving the extinction and still thriving in the Paleocene epoch. There are also other sporadic claims of post-Cretaceous dinosaur fossils (even a very doubtful finding of dinosaur eggs as late as Eocene). While it is certainly not improbable that some scattered population of some (presumably small) dinosaur species could have survived at least some hundreds of years after the mass extinction, evidence now points to El Ojo (and most other) findings as Cretaceous fossils contaminating Paleocene strata. Nevertheless, it is still theorized that some dinosaur population could have survived the main extinction event isolated in Antarctica, and then being killed by the climatic change.

Bringing dinosaurs back to life

Antarctica.]] There has been much speculation about the availability of technology to bring dinosaurs back to life. The idea proposed in Michael Crichton's book Jurassic Park, using blood from fossilized mosquitos that have been suspended in tree sap since the Mesozoic and then filling in the gaps with frog genes to create the DNA of a dinosaur, is probably impossible. A problem with this theory is that DNA decays over time by exposure to air, water and radiation, thus depleting the chances of salvaging any useful DNA. Decay can be measured by a racemization test. There have been two claims about the successful extraction of ancient DNA from dinosaur fossils, but upon further inspection, neither of these reports could be confirmed (Wang et al., 1997). However, a working visual peptide of a (theoretical) dinosaur has been inferred using analytical phylogenetic reconstruction methods on gene sequences of still-living related species (reptiles and birds) (Chang et al., 2002).

Discovery of probable soft tissue from dinosaur fossils

In the March 2005 issue of Science, (Schweitzer et al.) announced material, after rehydrating, that resembled soft tissue was discovered inside a Tyrannosaurus rex leg bone from the Hell Creek Formation in Montana, from about 68 million years ago. When the fossilized bone was treated over several weeks to remove mineral content (demineralize) from the fossilized bone marrow cavity, Schweitzer found evidence of intact structures such as blood vessels, bone matrix, and connective tissue (bone fibers). Scrutiny under microscope further revealed the putative dinosaur soft tissue had retained fine structures (microstructures) even at the cellular level. It has not been made clear of what this flexible material is actually composed, although many news reports immediately linked it with the movie "Jurassic Park", and the interpretation of the artifact as well as the relative importance of Dr. Schweitzer's discovery is still undecided.

Extinction theories

The extinction of the non-avian dinosaurs is one of the most intriguing problems in paleontology. Only since the 1970s has the nature of this extinction become researched in detail, showing some possible causes of the dinosaur extinction.

Asteroid collision

paleontology, the impact of which may have caused the Dinosaur extinction.]] The theory first proposed by Walter Alvarez in the late 1970s, linked the extinction event at the end of the Cretaceous period to a bolide impact about 65.5 million years ago, based on a sudden change in Iridium levels in fossilized layers. The bulk of the evidence now indicates that a 10 km wide bolide hit the Yucatán Peninsula 65 million years ago, creating the 170 km wide Chicxulub Crater and causing the extinction. Scientists are still disputing whether dinosaurs were in steady decline or still thriving before the meteor struck. Some scientists state that the meteor would have caused an unnatural winter, while others claim that it would have created an unusual heat wave. Although the speed of extinction cannot be deduced from the fossil record alone, the latest models suggest the extinction was extremely rapid. It appears to have been caused by heat from the meteorite impact and the matter ejected from the crater reentering the Earth's atmosphere around the world.

The Oort cloud

Similar to Alvarez's theory, which involved a single comet, the Oort cloud suggests that a vast shower of comets that were dislodged in an astral phenomenon hit the Earth at the same time, causing world wide extinction. The end result would again be an unnatural winter, ultimately freezing the dinosaurs.

Environment changes

The environment during the late Cretaceous was changing dramatically. Volcanic activity was decreasing. This led to a cooling trend as the levels of carbon dioxide diminished. At the eras peak, sea levels are estimated to have been between 100 metres (330 feet) to 250 metres (820 feet) higher than now with no polar ice caps. The planet's temperature was much more uniform, with only a 25 degrees C difference from the polar regions to the equator and much warmer with the poles 50 degrees C warmer than today. The atmosphere's composition had carbon dioxide levels 12 times higher than today's levels, and oxygen formed 32 to 35 percent of the atmosphere, as compared with 21 percent today. But toward the end of the Cretaceous, these levels started to fluctuate wildly. Some hypothesize that climate change combined with the fall of oxygen levels might have led to many species demise, especially if the dinosaurs had a respiratory system commonly found in today's birds - something that would be difficult for an animal as large as a dinosaur with lower oxygen levels to breathe in. Other groups besides dinosaurs became extinct at the same time, including ammonites (nautilus-like mollusks), mosasaurs, plesiosaurs, pterosaurs, herbivorous turtles and crocodiles, most kinds of birds, and many groups of mammals.

History of discovery

Dinosaur fossils have been known about for millennia, though their true nature was not recognized; the Chinese considered them to be dragon bones, while Europeans believed them to be the remains of giants and other creatures killed by the Great Flood. The first dinosaur species to be identified and named was Iguanodon, discovered in 1822 by the English geologist Gideon Mantell, who recognized similarities between his fossils and the bones of modern iguanas. Two years later, the Rev William Buckland, professor of geology at Oxford University, became the first person to describe a dinosaur in a scientific journal, in this case Megalosaurus bucklandii, found near Oxford. The study of these "great fossil lizards" became of great interest to European and American scientists, and in 1842 the English paleontologist Richard Owen coined the term "dinosaur". He recognized that the remains that had been found so far, Iguanodon, Megalosaurus and Hylaeosaurus, had a number of features in common, so decided to present them as a distinct taxonomic group. With the backing of Prince Albert of Saxe-Coburg-Gotha, husband of Queen Victoria, Owen established the Natural History Museum in South Kensington, London, to display the national collection of dinosaur fossils and other biological and geological exhibits. London London In 1858, the first known American dinosaur was discovered in marl pits of the small town of Haddonfield, New Jersey (although fossils had been found before, their nature had not been identified). The creature was named Hadrosaurus foulkii, after the town and the discoverer, William Parker Foulke. It was an extremely important find: Hadrosaurus was the first nearly complete dinosaur skeleton ever found and it was clearly a bipedal creature. This was a revolutionary discovery, as most scientists had thought that dinosaurs walked on four feet like lizards. Foulke's discoveries sparked a dinosaur mania in the United States, which was exemplified by the fierce rivalry of Edward Drinker Cope and Othniel Charles Marsh, who each competed to outdo the other in finding new dinosaurs in what came to be known as the Bone Wars. The feud was probably started when Marsh criticized Cope for putting the bones of a Elastomosaurus on back to front. This started the jealousy and madness of a fight which ensued for the next 30 years, only ending in 1897 when Cope died after spending his entire fortune in the dinosaur hunt. Marsh won the contest by virtue of being better funded through the US Geological Survey. Unfortunately, many of the valuable dinosaur specimens were destroyed or damaged due to the pair's rough approach; often the diggers used dynamite to unearth bones. All together, they discovered 142 new species of dinosaur, with Marsh unearthing 86 new species, while Cope only discovered 56 species. Cope's collection is now at the American Museum of Natural History in New York, while Marsh's is displayed at the Peabody Museum of Natural History at Yale University. Since then, the search for dinosaurs has been carried to every continent on Earth. This includes Antarctica, where the first dinosaur, a nodosaurid Ankylosaurus, was discovered on Ross Island in 1986, though it was 1994 before an Antarctic dinosaur, the Cryolophosaurus ellioti, was formally named and described in a scientific journal. Current "hotspots" include southern South America (especially Argentina) and China, which has produced many exceptional feathered dinosaur specimens due to the arid climate having preserved the skeleton.

In popular culture

feathered dinosaur Dinosaurs were highly successful life forms for some 150 million years; however, even more than their success, it is their extinction that has become part of human culture. Hence dinosaur is sometimes used as a metaphor for people and things that are perceived as being out of date or no longer in touch with the spirit of the times, and therefore ought to be extinct. An example was the manner in which the punk movement described the "progressive" bands that preceded them as "dinosaur groups". One of the most ground breaking movies of its time, Jurassic Park, brought dinosaurs into the media spotlight, proving that dinosaurs were a good selling point for producers. Jurassic Park led to two sequels, The Lost World: Jurassic Park and Jurassic Park 3, both blockbusters in their own right. Due to the popularity of the movies, and their portrayal of T rex as king of the dinosaurs, dinosaurs have become a permanent fixture in today's world, with the Tyrannosaurus rex being the most popular due to the movies portraying him as king of the dinosaur. The Jurassic Park movies also inspired a couple of console games, such as Jurassic Park the video game. Dinosaurs, because of their sizes and perceived aggressiveness, have both long fascinated and terrified the public mind in fictional as well as non-fictional works. This makes them a favorite of both young and old. fictional.]] Notable examples of fictional works include Arthur Conan Doyle's book The Lost World, the 1933 film King Kong and Godzilla. Thus, the possibility of humans and dinosaurs living together has been a recurring theme in fiction: The Valley of Gwangi (1969) and One Million Years BC (1966) (famously starring Raquel Welch in a fur bikini). Ray Harryhausen brought the dinosaurs to life in both films using model animation. Other classic films where dinosaurs have been in the spotlight are Pterodactyl and Spot from The Munsters. The Munsters The development of Computer-generated imagery further enhanced that fantasy and also allowed the production of documentaries; 1999 BBC series Walking with Dinosaurs is a notable example. Dinosaurs, however are not only depicted as cold-blooded reptiles but also as warm-loving and even with friendly personalities, either to appeal to young children such as the 1970s show Land of the Lost, the 1990s' Dinosaurs and the more recent Barney & Friends. For cartoons The Flintstones showcased a stone age family living with dinosaurs, while comic strips such as Calvin and Hobbes and The Far Side feature dinosaur orientated strips frequently. Due to their consumer appeal, many computer and console games have featured dinosaurs as characters. Crash Bandicoot: Warped, Ape Escape, the Turok series, and even Zoo Tycoon have involved dinosaurs in their story lines.

Notes

#Dal Sasso, C. and Singnore, M. (1998). Exceptional soft-tissue preservation in a theropod dinosaur from Italy. Nature 292:383-387. [http://www.dinosauria.com/jdp/misc/scipionyx.html See commentary on the article] # Schweitzer, M.H., Wittmeyer, J.L. and Horner, J.R. (2005). Soft-Tissue Vessels and Cellular Preservation in Tyrannosaurus rex. Science 307:1952 - 1955. [http://news.bbc.co.uk/2/hi/science/nature/4379577.stm See commentary on the article] #[http://news.nationalgeographic.com/news/2002/05/0529_020529_sauropods.html Sauropod tracks] Sauropod tracks are giving paleontologists new information. # Lessem, D. and Glut, D.F. (1993). The Dinosaur Society's Dinosaur Encyclopedia. Random House Inc. ISBN 0679417702. [http://www.isgs.uiuc.edu/faq/dino-faqs/pdq76.html See commentary on the article] # [http://www.browningmontana.com/dinosaurs.html Juvenile Tyrannosaur] A juvenile Tyrannosaur skeleton was found. # [http://search.eb.com/dinosaurs/dinosaurs/BRa.html Oviraptor nesting] Oviraptor nests or Protoceratops? # [http://news.bbc.co.uk/1/hi/scotland/3255494.stm Dinosaur family tracks] Footprints show maternal instinct after leaving the nest. # [http://www.amnh.org/exhibitions/fightingdinos/ex-fd.html Joined forever in death] The discovery of two fossil dinosaurs entangled together proved many theories. # [http://news.nationalgeographic.com/news/2002/12/1219_021219_dinocannibal.html Cannibalistic Dinosaur] The mystery of a dinosaur cannibal. # [http://www.nsf.gov/od/lpa/news/03/pr0336.htm Madagascar cannibal] A cannibal dinosaur is uncovered in Madagascar. # [http://palaeo.gly.bris.ac.uk/Palaeofiles/Tracks/Report7/Speed.html Gait and Dinosaur speed] Gait and his formula on estimating a dinosaur's speed. # [http://www.shef.ac.uk/~es/DINOC01/dinocal1.html Calculate your own Dinosaur speed] More on Gait and his speed calculations. # [http://news.bbc.co.uk/1/hi/sci/tech/78905.stm Injuries from rushing] Dinosaurs were so eager to eat food, they broke their ribs! # [http://www.nserc.ca/news/features/dinosaurs_e.htm Sauropods that floated] Sauropods were the largest animals to float. # [http://news.nationalgeographic.com/news/2005/12/1201_051201_archaeopteryx_2.html Archaeopteryx related to the Deinonychosaurs?] Archaeopteryx is proven to be closely related to Deinonychosaurs. # O'Connor, P.M. and Claessens, L.P.A.M. (2005). Basic avian pulmonary design and flow-through ventilation in non-avian theropod dinosaurs. Nature 436:253. # [http://www.guardian.co.uk/life/news/story/0,12976,1326559,00.html Bird-like sleeping position for Dinosaur] Even more evidence proving birds are dinosaurs. # [http://www.sciencemag.org/cgi/content/full/sci;307/5717/1952 Cellular preservation inside T rex blood vessels] Can these cells be used to bring the Tyrannosaurus rex back to life? # Koeberl, C. and MacLeod, K.G. (2002). Catastrophic Events and Mass Extinctions. Geological Society of America. ISBN 0813723566.

See also


- Fossils
- List of dinosaurs
- List of dinosaur classifications
- Prehistoric life
- Prehistoric reptiles
- Various forms of Creationism dispute the age and significance of dinosaur fossils

References


- Kevin Padian, and Philip J. Currie. (1997). Encyclopedia of Dinosaurs. Academic Press. ISBN 0122268105. (Articles are written by experts in the field).
- Paul, Gregory S. (2000). The Scientific American Book of Dinosaurs. St. Martin's Press. ISBN 0312262264.
- Paul, Gregory S. (2002). Dinosaurs of the Air: The Evolution and Loss of flight in Dinosaurs and Birds. Baltimore: The Johns Hopkins University Press. ISBN 0801867630.
- M Schweitzer, JL Wittmeyer and JR Horne (2005). Gender-Specific Reproductive Tissue in Ratites and Tyrannosaurus rex. Science 308; 5727:1456-60.
- Weishampel, David B. (2004). The Dinosauria. University of California Press; 2nd edition. ISBN 0520242092.
- Keith M Parsons. (2001). Drawing Out Leviathan. Indiana University Press. ISBN 0253339375. ;Technical papers
- Belinda S. W. Chang, Karolina Jönsson, Manija A. Kazmi, Michael J. Donoghue and Thomas P. Sakmar. (2002). [http://mbe.oupjournals.org/cgi/content/full/19/9/1483 Recreating a functional ancestral archosaur visual pigment]. Molecular Biology and Evolution 19 (9), 1483–1489.
- Hai-Lin Wang, Zi-Yang Yan and Dong-Yan Jin. (1997). [http://mbe.oupjournals.org/cgi/reprint/14/5/589 Reanalysis of published DNA sequence amplified from Cretaceous dinosaur egg fossil]. Molecular Biology and Evolution 14 (5), 589–591.

External links and sources

;For children
- [http://www.mantyweb.com/dinosaur/ Dinosaur Time Machine from MantyWeb Educational Software] From MantyWeb Educational Software. Kid's site, facts, games.
- [http://yahooligans.yahoo.com/content/science/dinosaurs Dinopedia] From Yahooligans! Science. Glossaries, dino cards and indexes.
- [http://www.enchantedlearning.com/subjects/dinosaurs/ Zoom Dinosaurs] From Enchanted Learning. Kid's site, info pages, theories, history. ;Popular
- [http://www.nhm.ac.uk/nature-online/life/dinosaurs-other-extinct-creatures/index.html Dinosaurs & other extinct creatures] From the Natural History Museum. London popular site, well illustrated dino directory.
- [http://www.arches.uga.edu/~rfreeman/GEOL3350_'4HistoryDinoSt.htm History of Dinosaur discovery] Timeline of the discovery of Dinosaurs.
- [http://pubs.usgs.gov/gip/dinosaurs/ Dinosaurs: Facts and Fiction] From the United States Geological Survey. Popular overview.
- [http://www.bbc.co.uk/dinosaurs/ Dinosaurs] From the BBC. Popular site, very well illustrated.
- [http://www.dinodata.net/Discussions/dinosaurs.html Discussions] From DinoData. Summaries of modern debates about dinosaurs.
- [http://www.ucmp.berkeley.edu/diapsids/dinosaur.html Dinosauria] From UC Berkeley Museum of Paleontology Detailed information - scroll down for menu.
- [http://www.dinosaurnews.org/ The Dinosaur News] The Dino-headlines from around the world. Recent news on dinsaurs, including finds and discoveries, lots of links.
- [http://www.bowdoin.edu/~dbensen/ OPUS: Dinosaur by Daniel Bensen] A gallery of dino-paintings. ;Technical
- [http://www.prehistoricplanet.com/ Prehistoric Planet] From PaleoClones. Current dino news.
- [http://www.wired.com/news/technology/0,1282,63613,00.html A Fiery Death for Dinosaurs? by Amit Asaravala] From Wired. Article on the rapid extinction of dinosaurs.
- [http://www.newscientist.com/hottopics/dinosaurs/ The Rex Files] From the New Scientist. Articles, latest news but out of date.
- [http://palaeo-electronica.org/ Palaeontologia Electronica] From Coquina Press. Online technical journal.
- [http://www.thunderbolts.info/tpod/2005/arch05/050623impossible-dinosaur.htm Impossible Dinosaurs] Article on a gravity-based approach for the extinction by David Talbott and Wallace Thornhill.
- [http://uk.arxiv.org/abs/hep-ph/0002255 TeV scale gravity, mirror universe, and ... dinosaurs] Article from [http://th-www.if.uj.edu.pl/acta/ Acta Physica Polonica B] by Z.K. Silagadze. ;Very technical
- [http://www.dinodata.net DinoData] Technical site, essays, classification, anatomy.
- [http://www.dinosauria.com/dml/dml.htm Dinosauria On-Line] Technical site, essays, pronunciation, dictionary.
- [http://dino.lm.com/ The Dinosauricon] By T. Michael Keesey. Technical site, cladogram, illustrations and animations.
- [http://www.palaeos.com/Vertebrates/Units/Unit310/000.html Dinosauromorpha Cladogram] From [http://www.Palaeos.com Palaeos]. A detailed and wonderful amateur site about all things paleo.
- [http://palaeo.gly.bris.ac.uk/dinobase/dinopage.html Dinobase] AA dinosaur database with dinosaur lists, classification, pictures, and more. ;Bird-dinosaur discussion
- [http://www.ucmp.berkeley.edu/diapsids/avians.html DinoBuzz] Are birds Dinosaurs?
- [http://www.dinosauria.com/ Dinosauria] Site focussing on the Dino-Bird aspect.
- Category:Paleontology Category:Paleozoology Category:Prehistoric reptiles

Lizard

: Many, see text. Lizards are reptiles of the order Squamata, which they share with the snakes (Ophidians). They are usually four-legged, with external ear openings and movable eyelids. Species range in adult length from a few centimeters (some Caribbean geckos) to nearly three meters (Komodo dragons). Some lizard species called "glass snakes" or "glass lizards" have no functional legs, though there are some vestigial skeletal leg structures. They are distinguished from true snakes by the presence of eyelids and ears. Many lizards can change color in response to their environments or in times of stress. The most familiar example is the chameleon, but more subtle color changes occur in other lizard species as well (most notably the anole, also known as the "house chameleon" or "chamele"). Lizards typically feed on insects or rodents. A few species are omnivorous or herbivorous; a familiar example of the latter is the iguana, which is unable to properly digest animal protein. Until very recently, it was thought that only two lizard species were venomous: the Mexican beaded lizard and the closely-related Gila monster, both of which live in northern Mexico and the southwest United States. However recent research at the University of Melbourne, Australia and Pennsylvania State University has revealed that in fact many lizards in the iguanians and monitor (lizard) families have venom-producing glands. None of these poses much danger to humans, as their poison is introduced slowly by chewing, rather than injected as with poisonous snakes. Nine toxins previously thought to only occur in snakes have been discovered, and a number of previously unseen chemicals as well. These revelations are prompting calls for a complete overhaul of the classification system for lizard species to form a venom clade. "These papers threaten to radically change our concepts of lizard and snake evolution, and particularly of venom evolution," says Harry Greene, a herpetologist at Cornell University in New York. Most other lizard species are utterly harmless to humans (most species native to North America, for example, are incapable even of drawing blood with their bites). Only the very largest lizard species pose any threat at all; the Komodo dragon, for example, has been known to attack and kill humans and their livestock. The chief impact of lizards on humans is positive; they are significant predators of pest species; numerous species are prominent in the pet trade; some are eaten as food (for example, iguanas in Central America); and lizard symbology plays important, though rarely predominant roles in some cultures (e.g. Tarrotarro in Australian mythology). Most lizards lay eggs, though a few species are capable of live birth. Many are also capable of regeneration of lost limbs or tails. A brief courtship and mating season occurs between mid-May and early-June. Twenty days after breeding, the female will lay from 2-21 creamy-white leathery eggs in a burrow beneath a large rock. The young hatch 2-3 months later, averaging 3-4 inches in length. Lizards in the Scincomorpha family, which include skinks (such as the blue-tailed skink), often have shiny, iridescent scales that appear moist. However, like all other lizards, they are dry-skinned and generally prefer to avoid water (though all lizards are able to swim if needed). blue-tailed skink

Classification

Suborder Sauria (Lacertilia) - (Lizards)
- Infraorder Iguania
  - Family Agamidae (agamas)
  - Family Chamaeleonidae (chameleons)
  - Family Corytophanidae (casquehead lizards)
  - Family Crotaphytidae (collared and leopard lizards)
  - Family Hoplocercidae (wood lizards, clubtails)
  - Family Iguanidae (iguanas and spinytail iguanas)
  - Family Leiocephalidae (see Tropidurinae)
  - Family Leiosauridae (see Polychrotinae)
  - Family Liolaemidae (see Tropidurinae)
  - Family Opluridae (Madagascar iguanids)
  - Family Phrynosomatidae (earless, spiny, tree, side-blotched and horned lizards)
  - Family Polychrotidae (anoles)
  - Family Tropiduridae (neotropical ground lizards)
- Infraorder Gekkota
  - Family Gekkonidae (geckos)
  - Family Pygopodidae (legless lizards)
  - Family Dibamidae (blind lizards)
- Infraorder Scincomorpha
  - Family Scincidae (skinks)
  - Family Lacertidae (wall lizards or true lizards)
  - Family Teiidae (tegus and whiptails)
  - Family Cordylidae (spinytail lizards)
  - Family Gerrhosauridae (plated lizards)
  - Family Gymnophthalmidae (spectacled lizards)
  - Family Xantusiidae (night lizards)
- Infraorder Diploglossa
  - Family Anguidae (glass lizards)
  - Family Anniellidae (American legless lizards)
  - Family Xenosauridae (knob-scaled lizards)
- Infraorder Platynota (Varanoidea)
  - Family Varanidae (monitor lizards)
  - Family Lanthanotidae (earless monitor lizards)
  - Family Helodermatidae (gila monsters) gila monster.]]

References


- [http://webhost.ua.ac.be/funmorph/anthony/lizards/animals.html Anthony Herrel's lizard page]
- The [http://www.embl-heidelberg.de/~uetz/LivingReptiles.html EMBL reptile database]
- [http://news.bbc.co.uk/hi/english/sci/tech/newsid_1689000/1689313.stm Tiny gecko] - the 'world's smallest' lizard
- Venom found to be widespread in lizards [http://www.newscientist.com/channel/life/mg18825264.600;jsessionid=PEKEKIHAKIMI] Category:Scaled reptiles Category:Pet reptiles

Cretaceous

The Cretaceous period is one of the major divisions of the geologic timescale, reaching from the end of the Jurassic period, about 146 million years ago (Ma), to the beginning of the Paleocene epoch of the Tertiary period (65.5 Ma). The end of the Cretaceous also defines the boundary between the Mesozoic and Cenozoic eras.

Name and dating

As with other older geologic periods, the rock beds that define the Cretaceous are well identified, but the exact dates of the period's start and end are uncertain by a few million years. No great extinction or burst of diversity separated the Cretaceous from the Jurassic. However, the end of the period is most sharply defined, being placed at an iridium-rich layer found worldwide that is believed to be associated with the Chicxulub impact crater in Yucatan and the Gulf of Mexico. This layer has been tightly dated at 65.5 Ma. This bolide collision is probably responsible for the major, extensively-studied Cretaceous-Tertiary extinction event. The Cretaceous (from Latin creta, for chalk) was named for the extensive beds of chalk (calcium carbonate deposited by the shells of marine invertebrates) found in the upper Cretaceous of Britain and adjacent continental Europe.

Divisions

The Cretaceous is usually separated into Lower and Upper Cretaceous Epochs. The faunal stages from youngest to oldest are:

Paleogeography

During the Cretaceous, the late Paleozoic - early Mesozoic supercontinent of Pangea completed its breakup into present day continents, although their positions were substantially different at the time. As the Atlantic Ocean widened and South America drifted westwards, Gondwana itself broke up as Antarctica and Australia rifted away from Africa (though India and Madagascar remained attached). Such active rifting lifted great undersea mountain chains along the welts, raising eustatic sea levels worldwide. To the north of Africa the Tethys Sea continued to narrow. Within the continents, a broad shallow sea advanced across central North America (the Western Interior Seaway) and then started to recede, leaving thick marine deposits sandwiched between coal beds. Other important Cretaceous exposures occur in Europe and China. In the area that is now India, massive lava beds called the Deccan Traps were laid down in the very late Cretaceous and early Paleocene. Climates were warm, and even polar regions had no permanent ice.

Flora

Flowering plants first appeared, although they did not become predominant until near the end of the period (Campanian age). Their evolution aided by the appearance of bees, in fact angiosperms and insects are a good example of mutual evolution. The first representatives of many modern trees, including figs, planes and magnolias for example, appear in the Cretaceous. At the same time, some earlier Mesozoic gymnosperms, like Conifers continued to thrive, although other taxa like Bennettitales died out before the end of the period.

Fauna

Land animals

On land, mammals were a small and still relatively minor component of the fauna. The fauna was dominated by archosaurian reptiles, especially dinosaurs, which were at their most diverse. Pterosaurs were common in the early and middle Cretaceous, but as the Cretaceous proceeded faced growing competition from the adaptive radiation of birds, and by the end of the period only two highly specialised families remained. A fascinating glimpse of life in the Early Cretaceous is provided by the Liaoning lagerstätte (Chaomidianzi formation) in China, where the beautifully preserved remains of a number of types of small dinosaurs, birds, and mammals have been found. The coelurosaur dinosaurs found there represent a number of types of the group maniraptora, which is transitional between dinosaurs and birds, and are remarkable for the presence of hair-like feathers. During the Cretaceous the insects began to diversify, and the oldest known ants, termites and butterflies appeared. Aphids, grasshoppers, and gall wasps appeared. Another important insect to evolve was the eusocial bee, which was integral to the ecology and evolution of flowering plants.

Marine animals

In the seas, rays, modern sharks and teleosts became common. Marine reptiles included ichthyosaurs in the early and middle of the Cretaceous, plesiosaurs throughout the entire period, and mosasaurs in the late Cretaceous. Baculites, a straight-shelled form of ammonite, flourished in the seas. The Hesperornithiformes were flightless, marine diving birds that swam like grebes. Globotruncanid Foraminifera thrived. The Cretaceous also saw the first radiation of the diatoms in the oceans (freshwater diatoms did not appear until the Miocene).

Extinction

Main article: Cretaceous-Tertiary extinction event In the extinction event that defines the end of the Cretaceous, a significant number of species (~50%) and known families (~25%) disappeared. Plants were nearly unscathed, while marine organisms were hit the hardest. These include a large number (~95%) of types of planktic foraminifers (excepting the Globigerinida), an even larger number of Coccolithophores, all the ammonite and belemnite cephalopods, and all reef-forming rudist molluscs), as well as all marine reptiles except turtles and crocodiles. Dinosaurs are the most famous victims of the Cretaceous extinction. Dinosaurs that were unique to the very end of the period (such as Tyrannosaurus rex, Triceratops, and Ankylosaurus) were wiped out. The last of the pterosaurs went extinct and the vast majority of birds did as well, including the Enantiornithes and Hesperornithiformes.

See also


- Chalk Formation
- Gault Clay
- Western Interior Seaway

References and further reading

Neal L Larson, Steven D Jorgensen, Robert A Farrar and Peter L Larson. Ammonites and the other Cephalopods of the Pierre Seaway. Geoscience Press, 1997. ja:白亜紀

Brachiosaurus


B. altithorax (type)
B. atalaiensis
B. nougaredi
For many decades, Brachiosaurus (brack-ee-oh-SORE-us) was the largest dinosaur known. It has since been exceeded in sheer mass by a number of giant titanosaurids like the Argentinosaurus and it was finally surpassed in height by another brachiosaurid, the Sauroposeidon. It was, however, still the largest dinosaur known from a relatively complete skeleton. However, even that may no longer be true, since the largest known specimens are now considered to be part of the new Giraffatitan genus. This new genus includes the famous mounted Brachiosaurus in the Humboldt Museum of Berlin, which is the tallest mounted skeleton in the world. Brachiosaurus is estimated to weigh from 30 to 80 tonnes (35 to 90 tons), to reach 13 meters (42 feet) in height, and 25 meters (82 feet) in length. Higher estimates are usually based on the Ultrasauros, which was originally considered to be an extremely large Brachiosaurus. However, Ultrasauros is now believed to be a chimera, composed of neck bones from a Supersaurus, and a shoulder bone (scapulacoracoid) from a Brachiosaurus smaller than the largest Giraffatitan specimens.

Description and environment

Brachiosaurus was a sauropod, one of a group of four-legged, plant-eating dinosaurs with long necks and tails, and tiny brains. Unlike other families of sauropods, it had a giraffe-like build, with long forelimbs and a very long neck, which, as a recent study has proven, it did not raise above its head. It had teeth like chisels (spatulate), and nostrils on the top of its head, which may indicate it had a good sense of smell. It had a number of holes in its skull to reduce weight. The first toe on its front foot, and the first three on its hind feet had claws. They may have traveled in herds. It used to be theorized that it used the nostrils on the top of its head like a snorkel, and spent most of its time submerged in water to help support its great mass. However, it is now believed that it was a fully terrestrial animal. Studies have shown that the water pressure would be too great for it to breathe while submerged, and its feet are too narrow, and would sink into the mud. Like all of the other "long-necked" dinosaurs, the Brachiosaurus’ neck was heavy and when it held it in a upright position for too long time, it would not get any blood to the brain. It might have stood at the edge of the forests and waved the head up and down, while it systematically removed all the eatable food on the trees. If the Brachiosaurus was warm-blooded, it is estimated that it would take ten years to reach full size. If it were cold-blooded, then it would take over 100 years to do so. If it were warm-blooded, it would have to eat more than 400 lbs. (200 kg) a day, but a lot less if it were not.

Berlin's brancai and Chicago's high flyer

The mounted skeleton of a B. brancai (or Giraffatitan) in the Humboldt Museum in Berlin is 4 stories tall, reaching 12 meters (39 feet) into the air, and is 23 meters (74 feet) long. It is the tallest mounted skeleton in the world, though the bones come from several different specimens. A Brachiosaurus is also mounted in the B Concourse of United Airlines' Terminal One in O'Hare International Airport in Chicago, courtesy of the Field Museum of Chicago. It is a model, not a collection of fossils.

Classification

Field Museum Brachiosaurus has three known species:
- B. alataiensis de Lapparent & Zbyszewski, 1957: Is known from back bones (vertebrae), and parts of the hip and limbs, which were recovered in Estremadura, Portugal. It lived about 150 million years ago, during the Kimmeridgian age of the late Jurassic period.
- B. altithorax Riggs, 1903: The type species is known from two partial skeletons recovered in Colorado and Utah in the United States. It lived from 145 to 150 million years ago, during the Kimmeridgian to Tithonian ages.
- ?B. nougaredi de Lapparent, 1960: While it may not be a distinct species (nomen dubium?) it is known from set of fused bones over the hip (sacrum), and parts of a forelimb, which were recovered in Wargla, Algeria in Africa. It lived 100 to 110 million years ago, during the Albian to Cenomanian ages of the middle Cretaceous period. The best specimens of Brachiosaurus were from the species B. brancai, which was found in the Tendaguru Beds of Tanzania, in Africa. In 1991, George Olshevsky placed them in a new genus, Giraffatitan because they do not sharederived characteristics with Brachiosaurus. Giraffatitan has withers over its shoulder, and a rounded crest over its nostrils.
- Giraffatitan brancai Janensch, 1914 (formerly B. brancai): The new type species, it is known from five partial skeletons, including at least three skulls, and some limb bones, which were recovered in Mtwara, Tanzania, in Africa. It lived from 145 to 150 million years ago, during the Kimmeridgian to Tithonian ages of the late Jurassic period.

Discovery

The first Brachiosaurus was discovered in 1900 by Elmer S. Riggs, in the Grand River Canyon of western Colorado, in the United States. He named the new species and genera in 1903 after its long front limbs — Brachiosaurus means "arm lizard", from the Greek brachion ("arm") and sauros ("lizard"). Starting in 1909, Werner Janensch found many new specimens in Tanzania, Africa, including some nearly complete skeletons, which were widely used in Brachiosaurus reconstructions. These are now considered to be Giraffatitan fossils.

External links


- [http://www.fieldmuseum.org/museum_info/press/press_brachiosaurus.htm Expect awe-struck travelers], from the Field Museum. (O'Hare airport mount)
- [http://www.lhl.lib.mo.us/events_exhib/exhibit/ex_paper_dino.shtml Paper Dinosaurs, 1824-1969 — 18. Sauropods in the American West, 1883], from the Linda Hall Library. Category:Jurassic Park species Category:Sauropods ja:ブラキオサウルス

Vertebrae

s]] ] Vertebrae (singular: vertebra) are the individual bones that make up the vertebral column (aka spine) — a flexuous and flexible column. There are thirty-three (33) vertebrae in humans, including the five that are fused to form the sacrum (the others are separated by intervertebral discs) and the four coccygeal bones which form the tailbone. The upper three regions comprise the remaining 24, and are grouped under the names cervical (7 vertebrae), thoracic (12 vertebrae) and lumbar (5 vertebrae), according to the regions they occupy. This number is sometimes increased by an additional vertebra in one region, or it may be diminished in one region, the deficiency often being supplied by an additional vertebra in another. The number of cervical vertebrae is, however, very rarely increased or diminished. With the exception of the first and second cervical, the true or movable vertebrae (the upper three regions) present certain common characteristics which are best studied by examining one from the middle of the thoracic region.

General structure

A typical vertebra consists of two essential parts: an anterior (front) segment, which is the vertebral body; and a posterior part – the vertebral or neural arch – which encloses the vertebral foramen. The vertebral arch is formed by a pair of pedicles and a pair of laminae, and supports seven processes, four articular, two transverse, and one spinous. When the vertebrae are articulated with each other, the bodies form a strong pillar for the support of the head and trunk, and the vertebral foramina constitute a canal for the protection of the medulla spinalis (spinal cord or spinal column), while between every pair of vertebrae are two apertures, the intervertebral foramina, one on either side, for the transmission of the spinal nerves and vessels. Two transverse processess and one spinous process are posterior to (behind) the vertebral body. The spinous process comes out the back, one transverse process comes out the left, and one on the right. The spinous processes of the cervical and lumbar regions can be felt through the skin. Superior and inferior articular facets on each vertebra act to restrict the range of movement possible.

Cervical vertebrae

Note: For more detailed information, see Cervical vertebrae These are generally small and delicate. Their spinous processes are short (with the exception of C7 which has the first palpable spinous process), and often split. Numbered top-to-bottom from C1-C7, atlas (C1) and axis (C2), are the vertebrae that allow the neck so much rotation. Specifically, the atlas allows the skull to move up and down, while the axis allows the upper neck to twist left and right. The axis also houses the first intervertebral disk of the spinal, which ends in the sacrum.

Lumbar vertebrae

Note: For more detailed information, see Lumbar vertebrae These vertebrae are very robust in construction, as they must support more weight than other vertebrae. They allow significant flexion and extension, moderate lateral flexion (sidebending), and a small degree of rotation. The discs between these vertebrae create a lumbar lordosis (curvature that is concave posteriorly) in the human spine.

References


- [http://www.bartleby.com/107/ Gray's Anatomy]: [http://www.bartleby.com/107/19.html The Vertebral column] - The 1917 Gray's Anatomy is available via the [http://www.bartleby.com Bartleby] project. It is available with full colour diagrams, and provides an excellent starting point in anatomy, as well as a relatively complete source for gross anatomy. This article was copied and pasted from the 1917 Gray's Anatomy, which is in the public domain. Category:Skeletal system ja:脊椎

Texas

Texas is a state located in the United States of America. The 28th U.S. state, Texas joined the United States in 1845. Its postal abbreviation is TX. The state name derives from a word in a Caddoan language of the Hasinai, táysha (or tejas, as the Spaniards spelled it), meaning friends or allies. Spanish explorers mistakenly applied the word to the people and their location. With an area of 696,241 km2 and a population of 22.5 million, Texas is the second largest U.S. state in both area and population, and the largest state in the contiguous 48 states in area. (Alaska is the largest U.S. state in area and California is the most populous.) Texas has historically had a "larger than life" reputation, especially in cowboy films.

History

Texas can claim that "Six Flags" have flown over its soil: the Fleur-de-lis of France, and the national flags of Spain, Mexico, the Republic of Texas, the United States of America and the Confederate States of America. Native American tribes that once lived inside the boundaries of present-day Texas include Apache, Atakapan, Bidai, Caddo, Comanche, Cherokee, Kiowa, Tonkawa, and Wichita. Currently, there are three federally recognized Native American tribes which reside in Texas: the Alabama-Coushatta Tribe of Texas, the Kickapoo Traditional Tribe of Texas, and the Ysleta Del Sur Pueblo of Texas. On November 6, 1528 shipwrecked Spanish conquistador Álvar Núñez Cabeza de Vaca became the first known European to set foot on Texas. A member of the Narváez expedition, he was later enslaved by a Native American tribe of the upper Gulf coast, and explored what are now the U.S. states of Texas, New Mexico and Arizona on foot from coastal Louisiana to Sinaloa, Mexico, over a period of roughly six years. He returned to Europe in 1537, where he wrote about his experiences in a work called La relación ("The Tale"). Álvar Núñez Cabeza de Vaca] Prior to 1821, Texas was part of the Spanish colony of New Spain. After Mexican independence in 1821, Texas became part of Mexico and in 1824 became the northern section of Coahuila y Tejas. On 3 January 1823, Stephen F. Austin began a colony of 300 American families along the Brazos River in present-day Fort Bend County and Brazoria County, centered primarily in the area of what is now Sugar Land. This group became known as the "Old Three Hundred." The "Conventions" of 1832 and 1833 responded to rising unrest at the policies of the ruling Mexican government. Policies that most irritated the Texians included the Mexican ban on slavery, the forcible disarmament of Texian settlers, and the expulsion of illegal immigrants from the United States of America. The example of the Centralista forces' suppression of dissidents in Zacatecas also inspired fear of the Mexican government. Zacatecas On March 2, 1836, the "Convention of 1836" signed the Texas "Declaration of Independence," declaring Texas an independent nation. On April 21, 1836 the Texans won their independence when they defeated the Mexican forces of Santa Anna at the Battle of San Jacinto. Santa Anna himself passed into captivity, and on May 14, Republic of Texas officials and General Santa Anna signed the treaty of Velasco. The Republic of Texas included all the area now included in the state of Texas, although its self-proclaimed western and northwestern borders extended as far west as Santa Fe and as far northwest as present-day Wyoming, respectively. In 1845, Texas was admitted to the United States as a constituent state of the Union. Annexation was mutually beneficial to Texas and the United States. Texas was in a very susceptible position following independence, with a weak government, little industry, and minimal infrastructure. The U.S. could not allow such a tenuous nation to sit right on its border. Texas also lay partially in the way of the U.S. expansion to the Pacific, and its "Manifest Destiny." The major stumbling block of annexation, besides the potential for war with Mexico, was the fact that Texas was a slave state and potentially would tip the balance between free and slave states due to its huge size. Some southerners were pushing for the ability to divide Texas into multiple states, thereby increasing the number of slave states even more. A compromise was reached in that if Texas were divided, any states north of the Missouri Compromise would be free states. During the Civil War, Texas seceded from the Union and joined the Confederate States of America. In 1870, the United States Congress readmitted Texas into the Union. Texas today is a state thoroughly steeped in tradition, yet equally embracing of new social and technological developments. From the state capital of Austin (also headquarters of Dell Computers and known as "Silicon Hills") to the cosmopolitan air of Dallas, to the oil-and-finance rich industry of Houston to the Latinesque cultures of San Antonio and El Paso, the state tourism slogan truly fits: "Texas: It's like a whole other country."

Geography

1870

Location

Texas borders New Mexico on the west, Oklahoma on the north (across the Red River), and Louisiana (across the Sabine River) and Arkansas on the east. To the southwest, across the Rio Grande, Texas borders the Mexican states of Chihuahua, Coahuila, Nuevo León, and Tamaulipas. To the southeast of Texas lies the Gulf of Mexico. Texas lies in the south-central part of the United States of America. Texas is considered to form part of the US South and part of the U.S. Southwest. Some regions of Texas are associated with the Southwest more than the South, while other regions are associated with the South more than the Southwest. Texas shares some cultural elements with both regions, with more similarities with the South, especially Arkansas and Louisiana, in East Texas, and more similarities with the Southwest, especially Mexico and New Mexico, in West Texas and South Texas. Texas is so large in its east-west expanse that El Paso, in the western corner of the state, is closer to San Diego, California than to Beaumont, near the Louisiana state line; Beaumont, in turn is closer to Jacksonville, Florida than it is to El Paso. The north-south extent is similarly impressive; Dalhart, in the nortwestern corner of the state, is closer to the state capitals of Kansas, Colorado, and Wyoming than it is to the Texas state capital (Austin).

Human Geography

Articles on Texas regions:
- Arklatex
- Big Bend
- Central Texas
- Dallas/Fort Worth Metroplex
- Deep East Texas
- East Texas
- Edwards Plateau
- Greater Houston
- North Texas
- Northeast Texas
- Piney Woods
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