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Mosasaur

Mosasaur


Mosasaurinae
Plioplatecarpinae
Tylosaurinae
A mosasaur was not a dinosaur, but rather an ocean-dwelling serpentine marine reptile more closely related to snakes than to monitor lizards (Lee 1997). These predators evolved from terrestrial ancestors in the early Cretaceous and dominated the oceanic food chain during the late Cretaceous Period. Genera include Mosasaurus, Tylosaurus, and Platecarpus.

Description

Mosasaurs breathed air, but were powerful swimmers, so well adapted to living in shallow seas that they gave birth to live young, rather than return to the shoreline to lay eggs, as sea turtles do. Mosasaurs likely descended from varanid lizards. The smallest known mosasaur is Carinodens belgicus, which was about 3 to 3.5 m long and probably lived on the sea floor cracking mollusks and sea urchins with its bulbous teeth. Larger mosasaurs were more typical: mosasaurs ranged in size up to 17 m: Hainosaurus holds the record for longest mosasaur, at 17.5 m. A mosasaur had a body form similar to that of a crocodile, although streamlined for fast swimming in marine waters. Their front leg bones were reduced in length, their paddles strengthened by long finger-bones. Their rear legs were atrophied. Their powerful tails, lashed side to side crocodile-fashion, provided locomotion. Mosasaurs had a loosely-hinged jaw which enabled them to gulp down their prey almost whole, a snakelike habit that has helped identify the stomach contents fossilized within a Mosasaur skeleton, which included the diving seabird Hesperornis, a marine bony fish, a shark, and part of a smaller mosasaur. Mosasaur bones have been found with embedded shark teeth. Based on features such as the loosely-hinged jaw, modified/reduced limbs and probable locomation, many researchers believe that snakes may be descended from mosasaurs, a suggestion advanced in 1869, by Edward Drinker Cope, who coined the term "Pythonomorpha" to include them. The idea lay dormant for more than a century, to be revived in the 1990s [http://www.palaeos.com/Vertebrates/Units/Unit260/260.100.html].

Environment

Sea-levels were high during the Cretaceous, causing marine ingressions in many parts of the world, and a great inland seaway in North America. Mosasaur fossils have been found in the Netherlands and Sweden, in Africa, in Australia, New Zealand, and Vega Island off the coast of Antarctica. In Canada and the United States, complete or partial specimens have been found in Alabama and Georgia and in almost all the states covered by the seaway: Texas, southwest Arkansas, New Mexico, Kansas, Colorado, the Dakotas and Montana. The "dinosaurs" of New Zealand, a volcanic island arc that has never been part of a continent, are a unique series of mosasaurs and plesiosaurs, another group of predatory marine reptiles of the Mesozoic era. Mesozoic

Discovery

The first publicized discovery of a fossil mosasaur preceded any dinosaur fossil discoveries, and drew the Enlightenment's attention to the existence of fossilized animals; the specimen was discovered in 1780 by quarry-workers in a subterranean gallery who quickly alerted Doctor C. K. Hoffman, a surgeon of Maastricht and fossil-hunter though rights of ownership lay with a canon of Maastricht, as owner of the overlying land. Dr. Hoffman's correspondence among men of science made the find famous. When the Revolutionary forces occupied Maastricht, the carefully-hidden fossil was uncovered, betrayed, it is said, by a case of wine, and transported to Paris, where Georges Cuvier was able to describe it for science, though le grand animal fossile de Maastricht was not described as a Mosasaur ("Meuse reptile") until 1822, and not given its official name, Mosasaurus hoffmani, until 1829. A Mosasaur skull that had actually been discovered at Maastricht earlier, has recently been reidentified in the Teylers Museum, Haarlem. The Maastricht limestone beds were rendered so famous they have given their name to the ultimate 6-million-year epoch of the Cretaceous: the Maastrichtian. On November 16 2005, research in Netherlands Journal of Geosciences confirmed that the recently uncovered Dallasaurus turneri, the first Mosasaur discovered in North America, is an early link between land-based, komodo dragon-like varanid lizards and the aquatic mosasaurs [http://www.smu.edu/smunews/dallasaurus/]

Purported modern sightings

Although it is generally accepted that Mosasaurs went extinct around the same time as the dinosaurs, some Cryptozoologists feel that sporatic reports of crocodile-like sea serpents may be surviving Mosasaurs. The Taniwha of Māori lore has also been connected to Mosasaurs by journalists.

External links


- [http://www.palaeos.com/Vertebrates/Units/Unit260/260.100.html Palaeos: Vertebrates: Mosasaurs]
- [http://www.bbc.co.uk/science/seamonsters/factfiles/giantmosasaur.shtml BBC Science and Nature: Mosasaurs]
- [http://www.oceansofkansas.com/nz-aus.html Mike Everhart and David Lewis, "Mesozoic marine monsters of the Mangahouanga"]: New Zealand fossil fauna
- [http://www.oceansofkansas.com/mosa-sty.html Mike Everhart, "A day in the life of a Mosasaur"]: life in the Sea of Kansas, illus. by Carl Buell
- [http://www.oceansofkansas.com/mosahoff.html Mike Everhart, "Mosasaurus hoffmani"] until 1829.
- [http://www.tmm.utexas.edu/exhibits/mosasaur/ Mosasaurus maximus mounted skeleton at University of Texas Memorial Museum]

Reference


- Lee, 1997, "The phylogeny of varanoid lizards and the affinities of snakes," in Phil. Trans. R. Soc. Lond. B 352: 53-91. Category:Prehistoric reptiles

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

Reptile


 Testudines - Turtles
 Rhynchocephalia - Tuataras
 Squamata
  Suborder Sauria- Lizards
  Suborder Serpentes - Snakes
  Suborder Amphisbaenia - Worm lizards
 Crocodilia - Crocodilians
 Pterosauria - Flying reptiles
Superorder Dinosauria
 Saurischia
 Ornithischia Reptiles are tetrapods, and also are amniotes, animals whose embryos are surrounded by an amniotic membrane. Today they are represented by four surviving orders:
- Crocodilia (crocodiles and alligators): 23 species
- Rhynchocephalia (tuataras from New Zealand): 2 species
- Squamata (lizards, snakes and amphisbaenids ("worm-lizards") ): approximately 7,600 species
- Testudines (turtles): approximately 300 species Reptiles are found on every continent except for Antarctica, although their main distribution comprises the tropics and subtropics. Though all cellular metabolism produces some heat, modern species of reptiles do not generate enough to maintain a constant body temperature. (See the Leatherback Sea Turtle for an exception to this.) Instead they rely on gathering and losing heat from the environment to regulate their internal temperature, e.g, by moving between sun and shade, or by preferential circulation — moving warmed blood into the body core, while pushing cool blood to the periphery. In their natural habitats, most species are adept at this, and can maintain core body temperatures within a fairly narrow range, comparable to that of mammals and birds, the two surviving groups of "warm-blooded" animals. While this lack of adequate internal heating imposes costs relative to temperature regulation through behavior, it also provides a large benefit by allowing reptiles to survive on much less food than comparably-sized mammals and birds, who burn much of their food for warmth. While warm-blooded animals move faster in general, an attacking lizard, snake or crocodile moves very quickly. Most reptile species are oviparous (egg-laying). Many species of squamates, however, are capable of giving live birth. This is achieved, either through ovoviviparity (egg retention), or ovoviviparity (babies born without use of calcified eggs). Many of the viviparous species feed their fetuses through various forms of placenta, just like mammals (Pianka & Vitt, 2003 pgs: 116-118). They often provide considerable initial care for their hatchlings. However, note the taxonomy issues described below; mammals and birds can also be viewed as descendants of reptiles.

Classification of reptiles

From the classical standpoint, reptiles included all the amniotes except birds and mammals. Thus reptiles were defined as the set of animals that includes crocodiles, alligators, tuatara, lizards, snakes, amphisbaenians and turtles, grouped together as the class Reptilia (Latin repere, "to creep"). This is still the usual definition of the term. However, in recent years, many taxonomists have begun to insist that taxa should be monophyletic, that is, groups should include all descendants of a particular form. The reptiles as defined above would be paraphyletic, since they exclude both birds and mammals, although these also developed from the original reptile. Colin Tudge writes: :Mammals are a clade, and therefore the cladists are happy to acknowledge the traditional taxon Mammalia; and birds, too, are a clade, universally ascribed to the formal taxon Aves. Mammalia and Aves are, in fact, subclades within the grand clade of the Amniota. But the traditional class reptilia is not a clade. It is just a section of the clade Amniota: the section that is left after the Mammalia and Aves have been hived off. It cannot be defined by synamorphies, as is the proper way. It is instead defined by a combination of the features it has and the features it lacks: reptiles are the amniotes that lack fur or feathers. At best, the cladists suggest, we could say that the traditional Reptila are 'non-avian, non-mammalian amniotes'. (Tudge, p.85) Some cladists thus redefine Reptilia as a monophyletic group, including both the classic reptiles as well as the birds and perhaps the mammals (depending on ideas about their relationships). Others abandon it as a formal taxon altogether, dividing it into several different classes. However, other biologists believe that the common characters of the standard four orders are more important than the exact relationships, or feel that redefining the Reptilia to include birds and mammals would be a confusing break with tradition. A number of biologists have adopted a compromise system, marking paraphyletic groups with an asterisk, e.g. class Reptilia
- . Colin Tudge notes other uses of this compromise system: :By the same token, the traditional class Amphibia becomes Amphibia
- , because some ancient amphibian or other gave rise to all the amniotes; and the phylum Crustacea becomes Crustacea
- , because it may have given rise to the insects and myriapods (centipedes and millipedes). If we believe, as some (but not all) zoologists do, that myriapods gave rise to insects, then they should be called Myriapoda
- ....by this convention Reptilia without an asterisk is synonymous with Amniota, and includes birds and mammals, whereas Reptilia
- means non-avian, non-mammalian amniotes. (Tudge, p.85)

Evolution of the reptiles

Aves Several thousand fossil species showing a clear smooth transition from the ancestors of reptiles to present-day reptiles exist. Hylonomus is the oldest-known reptile, and was about 8 to 12 inches (20 to 30 cm) long. Westlothiana has been suggested as the oldest reptile, but is for the moment considered to be more related to amphibians than amniotes. Petrolacosaurus, Araeoscelis, Paleothyris, Hylonomus, Ophiacodontidae, Archaeothyris, mesosaurs and Ophiacodon are other examples. The first true "reptile" or Amniotes are categorized as Anapsids, having a solid skull with holes only for nose, eyes, spinal cord, etc. Turtles are believed by some to be surviving Anapsids, as they also share this skull structure; but this point has become contentious lately, with some arguing that turtles reverted to this primitive state in order to improve their armor. Both sides have strong evidence, and the conflict has yet to be resolved. Shortly after the first reptiles, two branches split off, either from the Anapsids or simply from each other, leaving no proper Anapsids. One group, the Synapsida, had a pair of holes in their skulls behind the eyes, which were used to both lighten the skull and increase the space for jaw muscles. The other group, Diapsida, possessed the same holes, along with a second pair located higher on the skull. The Synapsida eventually evolved into mammals, while Diapsida split yet again into two lineages, the lepidosaurs (which contain modern snakes, lizards and tuataras, as well as (in debate) the extinct sea reptiles of the Mesozoic) and the archosaurs (modernly represented by only crocodiles and birds, but containing pterosaurs and dinosaurs).

Systems

Circulatory

Most reptiles have closed circulation via a three-chamber heart consisting of two atria and one, variably-partitioned ventricle. There is usually one pair of aortic arches. In spite of this, due to the fluid dynamics of blood flow through the heart, there is little mixing of oxygenated and deoxygenated blood in the three-chamber heart. Furthermore, the blood flow can be altered to shunt either deoxygenated blood to the body or oxygenated blood to the lungs, which gives the animal greater control over its blood flow, allowing more effective thermoregulation and longer diving times for aquatic species. There are some interesting exceptions among reptiles. For instance, crocodilians have an incredibly complicated four-chamber heart that is capable of becoming a functionally three-chamber heart during dives (Mazzotti, 1989 pg 47). Also, it has been discovered that some snake and lizard species (e.g., monitor lizards and pythons) have three-chamber hearts that become functional four-chamber hearts during contraction. This is made possible by a muscular ridge that subdivides the ventricle during ventricular diastole and completely divides it during ventricular systole. Because of this ridge, some of these squamates are capable of producing ventricular pressure differentials that are equivalent to those seen in mammalian and avian hearts (Wang et al, 2003). squamates

Respiratory

All reptiles breathe using lungs. Reptiles don't normally breathe through their skin. The only exceptions to this are in aquatic turtles. These animals have developed more permeable skin, and even gills in their anal region, for some species (Orenstein, 2001). Even with these adaptations, breathing is never fully accomplished without lungs. Lung ventilation is accomplished differently in each main reptile group. In squamates the lungs are ventilated almost exclusively by the axial musculature. This is also the same musculature that is used during locomotion. Because of this constraint, most squamates are forced to hold their breath during intense runs. Some, however, have found a way around it. Varanids, and a few other lizard species, employ buccal pumping as a complement to their normal "axial breathing." This allows the animals to completely fill their lungs during intense locomotion, and thus remain aerobically active for a long time. Tegu lizards are known to possess a proto-diaphragm, which separates the pulmonary cavity from the visceral cavity. While not actually capable of movement, it does allow for greater lung inflation, by taking the weight of the viscera off the lungs (Klein et al, 2003). Crocodilians actually have a muscular diaphragm that is analogous to the mammalian diaphragm. The difference is that the muscles for the crocodilian diaphragm pull the pubis (part of the pelvis, which is movable in crocodilians) back, which brings the liver down, thus freeing space for the lungs to expand. This type of diaphragmatic setup has been referred to as the "hepatic piston." Also, there are the Turtles & Tortoises. How these animals breathe has been the subject of much study. To date, only a few species have been studied thoroughly enough to get an idea of how turtles do it. The results indicate that turtles & tortoises have found a variety of solutions to this problem. The problem is that most turtle shells are rigid and do not allow for the type of expansion and contraction that other amniotes use to ventilate their lungs. Some turtles such as the Indian flapshell (Lissemys punctata) have a sheet of muscle that envelopes the lungs. When it contracts, the turtle can exhale. When at rest, the turtle can retract the limbs into the body cavity and force air out of the lungs. When the turtle protracts its limbs, the pressure inside the lungs is reduced, and the turtle can suck air in. Turtle lungs are attached to the inside of the top of the shell (carapace), with the bottom of the lungs attached (via connective tissue) to the rest of the viscera. By using a series of special muscles (roughly equivalent to a diaphragm), turtles are capable of pushing their viscera up and down, resulting in effective respiration, since many of these muscles have attachment points in conjunction with their forelimbs (indeed, many of the muscles expand into the limb pockets during contraction). Breathing during locomotion has been studied in three species, and they show different patterns. Adult female green sea turtles do not breathe as they crutch along their nesting beaches. They hold their breath during terrestrial locomotion and breathe in bouts as they rest. North American box turtles breathe continuously during locomotion, and the ventilation cycle is not coordinated with the limb movements (Landberg et al., 2003). They are probably using their abdominal muscles to breathe during locomotion. The last species to have been studied is red-eared sliders, which also breathe during locomotion, but they had smaller breaths during locomotion than during small pauses between locomotor bouts, indicating that there may be mechanical interference between the limb movements and the breathing apparatus. Box turtles have also been observed to breathe while completely sealed up inside their shells (ibid). Most reptiles lack a secondary palate, meaning that they must hold their breath while swallowing. Crocodylians have evolved a bony secondary palate that allows them to continue breathing while remaining submerged (and protect their brains from getting kicked in by struggling prey). Skinks (family Scincidae) also have evolved a bony secondary palate, to varying degrees. Snakes took a different approach and extended their trachea instead. Their tracheal extension sticks out like a fleshy straw, and allows these animals to swallow large prey without suffering from asphyxiation.

Excretion

Excretion with two small kidneys. Uric acid is the main nitrogenous waste product.

Nervous

Advanced nervous system compared to amphibians. They have twelve pairs of cranial nerves.

Sexual

Most reptiles reproduce sexually. Asexual reproduction has been identified in squamates in six families of lizards and one snake. In some species of squamates, a population of females are able to produce a unisexual diploid clone of the mother. This asexual reproduction called parthenogenesis occurs in several species of gecko, and is particularly widespread in the teiids (expecially Aspidocelis) and lacertids (Lacerta). Parthenogentic species are also suspected to occur among chameleons, agamids, xantusiids, and typhlopids. Amniotic eggs covered with leathery or calcareous shells: Amnion, chorion, and allantois present during embryonic life. No larval stages.

See also


- List of reptiles
- List of regional reptiles lists

External links


- [http://tolweb.org/tree?group=Amniota&contgroup=Terrestrial_Vertebrates Tree of Life Website]
- [http://www.reptile-database.org The EMBL Reptile Database]
- [http://www.whozoo.org/herps/herpphylogeny.html Reptile Phylogeny]
- [http://reptilis.net The Reptipage]
- [http://www.interaktv.com/MS/MSReptiles.html Mississippi Reptile Checklist]

References


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- Category:Chordates Category:Reptiles ko:파충류 ms:Reptilia ja:爬虫類 simple:Reptile th:สัตว์เลื้อยคลาน

Monitor lizard

Many, see text. Monitor lizards are the family Varanidae, a group of lizards which includes the largest living lizard, the Komodo Dragon. Varanidae contains only a single genus: Varanus. In Australia monitor lizards are known as goannas (See main article).

Evolutionary Overview

Monitor lizards are considered to be the most highly developed lizards, possessing a relatively rapid metabolism for reptiles, several sensory adaptations that benefit the hunting of live prey, and a lower jaw that may be unhinged to facilitate eating large prey animals. Recent work also indicates that the Varanid lizards, including the Komodo dragon, produce venom. These latter two adaptations are shared with snakes, which are thought to have evolved from a sister group to the Varanidae as part of a larger venom clade.

Origin of Name

It has been said that the name of monitor lizards is derived from a superstition that the creatures would give a warning about the presence of crocodiles. However, this explanation may be apocryphal. According to [http://www.wildwatch.com/resources/other/monitors.asp Wildwatch], the name actually resulted from a mishearing of the Arabic word oaran (lizard) as the German warnen (to warn), which was subsequently Latinized into monitor.

Trivia

The movie monster Varan takes its name from this genus.

Classification

Genus Varanus
- Varanus acanthurus: Spiny-tailed goanna or Ridge-tailed monitor
- Varanus albigularis: White-throated monitor
- Varanus auffenbergi Peacock monitor
- Varanus baritji Northern ridge-tailed goanna
- Varanus beccarii Black tree monitor
- Varanus bengalensis Bengal monitor
- Varanus bogerti Louisiade tree monitor
- Varanus brevicauda Short-tailed monitor
- Varanus caerulivirens Blue pin-spot monitor
- Varanus caudolineatus Stripe-tailed goanna
- Varanus cerambonensis Ceram mangrove monitor
- Varanus doreanus Blue-tailed monitor
- Varanus dumerilii Rough-necked monitor
- Varanus eremius Desert pygmy monitor
- Varanus exanthematicus: Savannah monitor
- Varanus finschi Finsch's monitor
- Varanus flavescens: Yellow mangrove monitor
- Varanus giganteus: the Perentie
- Varanus gilleni Pygmy mulga goanna
- Varanus glauerti Kimberley rock monitor
- Varanus glebopalma Black-palmed rock monitor
- Varanus gouldii Sand goanna (also Gould's goanna, or Ground goanna)
- Varanus griseus Desert monitor
- Varanus indicus Mangrove monitor
- Varanus jobiensis Peach-throat monitor
- Varanus juxtindicus Hakoi
- Varanus keithhornei Canopy goanna
- Varanus kingorum King's goanna
- Varanus komodoensis: Komodo dragon
- Varanus mabitang Panay monitor
- Varanus macraei Blue tree monitor
- Varanus melinus Quince monitor
- Varanus mertensi: Mertens' water monitor
- Varanus mitchelli Mitchell's water monitor
- Varanus nebulosus Clouded monitor
- Varanus niloticus: Nile monitor
- Varanus olivaceus Gray's monitor, Butaan
- Varanus ornatus Ornate monitor
- Varanus panoptes Argus monitor, Yellow-spotted goanna, Floodplain goanna
- Varanus pilbarensis Pilbara rock monitor
- Varanus prasinus: Emerald tree monitor
- Varanus primordius Blunt-spined goanna
- Varanus rosenbergi Rosenberg's goanna
- Varanus rudicollis: Roughneck monitor
- Varanus salvadorii: Crocodile monitor, Artrelia
- Varanus salvator: Water monitor
- Varanus scalaris Spotted tree goanna
- Varanus semiremex Mangrove pygmy goanna
- Varanus spenceri Spencer's goanna
- Varanus spinulosus St. Isabel mangrove monitor
- Varanus storri Storr's goanna
- Varanus telenesetes Lia (Biri), Rossel Island tree monitor
- Varanus timorensis: Timor tree monitor or Timor monitor
- Varanus tristis Black-headed tree goanna
- Varanus varius: Lace goanna
- Varanus yemenensis Yemen monitor
- Varanus yuwonoi Tricolor monitor Category:Lizards Category:Monitor lizards

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

Food chain

Food chains and food webs or food networks describe the feeding relationships between species in a biotic community. In other words, they show the transfer of material and energy from one species to another within an ecosystem. As usually diagrammed, an organism is connected to another organism for which it is a source of food energy and material by an arrow representing the direction of biomass transfer. Organisms are grouped into trophic levels—from the Greek for nourishment, trophikos—based on how many links they are removed from the primary producers. Primary producers, or autotrophs, are species capable of producing complex organic substances (essentially "food") from an energy source and inorganic materials. These organisms are typically photosynthetic plants or algae, but in rares cases, like those organisms forming the base of deep-sea vent food webs, can be chemotrophic.

Food chain

A food chain describes a single pathway that energy and nutrients may follow in an ecosystem. There is one organism per trophic level, and trophic levels are therefore easily defined. They usually start with a primary producer and end with a top predator. Here is an example of a food chain: ::phytoplankton → copepod → fish → squid → seal → Orca This "chain" can be described as follows: Killer whales (Orca) feed upon seals, that feed upon squid, that eat small fish, that feed on copepods, that feed on microscopic algae. In this example, algae—autotrophs by virtue of their ability to photosynthesize—are the base of the food chain. It is always the case that numbers—or at least biomass—decreases from the base of the chain to the top. In other words, the number and mass of phytoplankton cells is much greater than the number and mass of copepods being supported by the phytoplankton. Viewed another way: to support one Orca requires many seals, large numbers of squid, huge numbers of fish, and so on down the chain (see energy pyramid). Food chains are overly simplistic as representatives of what typically happens in nature. The food chain shows only one pathway of energy and material transfer. Most consumers feed on multiple species and are, in turn, fed upon by multiple other species.

Food web

energy pyramid A food web or food network extends the food chain concept from a simple linear pathway to a complex network of interactions. The direct steps as shown in the food chain example above seldom reflect reality. Food sources of most species in an ecosystem are much more diverse, resulting in a complex web of relationships as shown in the figure on the right. In this figure, the grouping of Phytoplankton → Herbivorous zooplankton → Carnivorous zooplankton → Arctic char → Capelin on the far right is a food chain; the whole complex network is a food web.

External Links

[http://www.coolantarctica.com/Antarctica%20fact%20file/wildlife/whales/food%20web.htm Antarctic Food Web and Chains]

See also


- Bioaccumulation Category:Photosynthesis Category:Ecology ja:食物連鎖

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