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Jurassic

Jurassic

:For the hip hop group see Jurassic 5. The Jurassic period is a major unit of the geologic timescale that extends from about 200 Ma (million years ago) at the end of the Triassic to 146 Ma at the beginning of the Cretaceous. As with other geologic periods, the rock beds that define the start and end of the period are well identified, but the exact dates are uncertain by 5 - 10 million years. The Jurassic constitutes the middle period of the Mesozoic era, also known as the Age of Dinosaurs. The start of the period is marked by the major Triassic-Jurassic extinction event. The Jurassic was named by Alexandre Brogniart for the extensive marine limestone exposures of the Jura Mountains in the region where Germany, France and Switzerland meet.

Divisions

The Jurassic is usually broken into Lower, Middle, and Upper (or Early, Middle and Late) subdivisions, also known as Lias, Dogger and Malm. The faunal stages from youngest to oldest are:

Paleogeography

During the early Jurassic, the supercontinent Pangea broke up into North America, Eurasia and Gondwana. Still, the early Atlantic and Tethyan Oceans were relatively narrow. In the late Jurassic, the southern continent, Gondwana, started to break up. Climates were warm with no evidence of glaciation. As in the Triassic, apparently there was no land near either pole, and no extensive ice caps existed. The geological record of the Jurassic is well exposed in western Europe, where marine sequences are found along the coasts. A shallow sea (epicontinental sea) called the Sundance Sea was present in parts of the northern plains of the United States and Canada. Most Jurassic exposures in North America are continental. Important Jurassic exposures are also found in Russia, India, South America, Japan, Australasia, and the United Kingdom.

Aquatic and Marine Animals

During the Jurassic, the "highest" life forms living in the seas were fish and marine reptiles. The latter include ichthyosaurs, plesiosaurs, and marine crocodiles of the families Teleosauridae and Metriorhynchidae. In the invertebrate world, several new groups appeared, such as:
- planktonic foraminifera and calpionelids, which are of great stratigraphic relevance;
- rudists, a reef-forming variety of bivalves;
- belemnites; and
- brachiopods of the terebratulid and rinchonelid groups. Ammonites (shelled cephalopods) were particularly common and diverse, forming 62 biozones.

Terrestrial Animals

On land, large archosaurian reptiles remained dominant. Great plant-eating dinosaurs (sauropods) roamed the land, feeding on prairies of ferns and palm-like cycads and bennettitales. They were preyed upon by large theropods (Ceratosaurs, Megalosaurs, and Allosaurs). All these belong to the "lizard hipped" or saurischian branch of the dinosaurs. During the late Jurassic the first birds evolved from small coelurosaur dinosaurs. Ornithischian dinosaurs were less predominant than saurischian dinosaurs, although some like stegosaurs and small ornithopods played important roles as small and medium-to-large (but not sauropod large) herbivores. In the air, pterosaurs were common, filling many ecological roles now taken by birds.

Plants

Because the climate was warmer in the Jurassic, lush jungles covered much of the landscape. Flowering plants had not evolved yet, but conifers were common, as were palms. Tree ferns also made up the forest.

Popular culture

Though the movie Jurassic Park brought the word "Jurassic" to household usage, many of the creatures featured in that film would more likely be found in the Cretaceous period. ko:쥐라기 ja:ジュラ紀

Hip Hop

Hip hop is a cultural movement that began among urban Africans, Jamaicans and Latinos in the Bronx borough of New York City during the early 1970s, and has since spread around the world. The four main aspects, or "elements", of hip hop culture are MCing (rapping), DJing, graffiti, and breakdancing. Some consider beatboxing the fifth element of hip hop; others might add political activism, hip hop fashion, hip hop slang, double dutching (an urban form of rope skipping) or other elements as important facets of hip hop. The term has since come to be a synonym for hip hop music (or rap) to mainstream audiences. hip hop music In recent years the focus has been centrally place on rapping and producing. The origin of the term "hip-hop" itself is unclear; but, over time, the term has taken on a life of its own. The movement that later became known as "hip-hop" is widely accreditted to have begun with the work of DJ Kool Herc in the early 70s, while competing DJ Afrika Bambaataa is often credited with having invented the term "hip-hop" to describe the culture. A variety of mythical etymologies and complex meanings have been attached to the term and continue to propagate within the hip hop community. Beginning in the early 1990s hip hop was almost as popular as rock and roll, and by 2002 was the clear winner in terms of popularity.

Hip-hop

Main article: Hip hop music The various factors that influenced early hip hop are complex and numerous, and vary from the griots of Africa to the rock of America. Although the majority of influences can be traced to African culture, the multicultural society of New York City resulted in diverse musical influences from all over the world finding their way into hip hop music. Elements of the style and techniques of rapping originate with the griots of West Africa; traveling singers and poets had musical styles that contained elements of what would later evolve into hip-hop music. Some griot traditions came to the United States, the United Kingdom and the Caribbean with the passage of African slaves to the New World. Other notable influences are the spoken word sections of records by soul and funk musicians such as James Brown and Isaac Hayes. One of the many influences on the creation of contemporary hip hop music is the Jamaican style called dub, which arose as a sub-genre of Reggae in the 1960s. Dub music saw producers such as King Tubby creating instrumental versions of popular reggae records for the purpose of clubs and Sound systems; they had discovered that dancers often responded better to the extended, isolated beats of the records, often featuring intense percussion and heavy basslines. Soon, the MCs that hosted the dances began speaking over the instrumental records, and the skills of MCs such as U-Roy, Dr. Alimontado and Dillinger saw them become popular performers in their own right. This tradition continues in contemporary Dancehall music. In 1967, Jamaican immigrants such as DJ Kool Herc applied the methods of Dub to Funk loops that were popular in New York City. According to David Top, Reggae was not popular among most American Hip-Hop fans in the early years of Hip-Hop, despite its influence. In parks and community centres, up and coming DJs were playing to packed crowds of youngsters eager to hear the old funk tunes. Pretty soon (by 1976/77) the DJs and dancers we’re paying special attention to the percussion breaks in records like Jimmy Castor's 'It's Just Begun', Dennis Coffrey's 'Scorpio' and Herman KeIly's 'Dance To The Drummer's Beat': in fact to any record with a good drum break, including tracks by the Rolling Stones and other white rock bands. One of the first Hip-Hop songs to be released was "Rappers Delight" by the Sugarhill Gang, which sampled Chic, a popular disco group. The kids who danced to the breaks started calling themselves B-Boys and their energetic, acrobatic style of dancing which accompanied the playing of the breaks became known as breaking. The most popular Bronx DJs like Kool Herc, Afrika Bambaataa and Grandmaster Flash started mixing two copies of the same record to make the breaks last longer; with fast cutting between the decks a 20-second drum break could be turned into a five-minute mix. Besides experimenting with the technical side of DJ-ing like cutting and scratching, the Bronx Jocks experimented with the the electronic music coming out of Europe. Kraftwerk's 1977 hit 'Trans-Europe Express' was a B-Boy favourite for its cool driving metallic Kraftwerk mixture of computerised drumbreaks and synthesisers. While all this was happening on the hot and sweaty dancefloors of the Bronx, out on the streets another vital element of the hip hop scene was falling into place.

Emceeing

The old, black tradition of using rhyming slang to brag or put down your enemies (or friends) had developed, through the street jive of the early Seventies, to become for many urban youngsters a new way of talking. In a larger sense, this was a continuation of a verbal tradition that goes back as far as the African griots. Half speaking, half singing the rhythmic street talk of Rapping was soon in the clubs, with aspiring rappers doing their thing over the local sound systems, the DJs providing backing tracks of instrumental loops of the latest dance hits. Another significant influence is Blues music. In many ways, hip hop is a continuation of an oral historical tradition dating back to the griots and traced through the Blues that came out of slavery. One of the main influences Blues had on rapping was the Call/Response aspect of the music. This survived into the tradition of "toasting" over Dub music, a tradition which was transferred to hip hop by Jamaicain immigrants like Kool Herc. This became most pronounced in the MC "Battles" of the early 1980's. Freestyle rapping of improvised lyrics is also part of a tradition that began with musicians improvising on their instruments in Jazz and the Blues. Rappers such as Guru give credit to the Jazz element that influences Hip-Hop. Rapping]Herc was one of the most popular DJs in early 70s New York, playing at neighborhood parties (also known as block parties). After his first gig on Sedgwick Ave. in the Bronx in 1973, Herc quickly switched from using reggae records to funk, rock and disco, as he found that the New York audience did not particularly like reggae. Herc and other DJs found that dancers often preferred the funky, percussive breaks of the records, and began extending them using an audio mixer and two records. Within a highly-competitive atmosphere, Herc's friends and competitors quickly developed other mixing techniques in order to keep audiences excited. As in Jamaica, these events were often hosted by a performer who spoke while the music played; these were originally called MCs (Masters of Ceremonies) and, later, rappers. Early rappers focused on introducing themselves, the DJ and others in the audience, although they quickly progressed to including improvisation and a simple four-count beat, along with a simple chorus. Later MCs added more complex and often humorous lyrics, and incorporated a focus on sexual themes and all around boasting. Although it was yet to be recorded, hip hop music steadily grew in popularity, and by the end of the 1970s was beginning to become a major artistic force which had spread throughout the United States. During the 1980s and 1990s, hip hop gradually became mainstream (a transition usually considered to have been completed in 1992) in the US and, to a lesser degree, worldwide. By the 2000s hip-hop became the most popular music genre in the United States, at times occupying every top ten spot on the music charts. Famous rappers of the past and present include Melle Mel, Whodini, LL Cool J, Slick Rick, MC Lyte, Run DMC, Beastie Boys, Tupac Shakur, Rakim, Notorious BIG, Snoop Dogg, OutKast, Eminem, Jay-Z, Nas, Wu-Tang Clan, 50 Cent and NWA

DJing

Main article: DJing Hip-Hop DJing, referred to by some as turntablism, is the practice of using a turntable as a musical instrument. Skills associated with turntablism include record scratching, beat juggling, and mixing. A DJ should not necessarily be considered a producer of a music track (though there is considerable overlap between the two roles). Today, the terms are often used exchangably, similar to 'rapper' and 'MC'. Famous DJs include Grandmaster Flash, Grandwizard Theodore (credited with "inventing" scratching), Mr. Magic, DJ Jazzy Jeff, DJ Scratch from EPMD, DJ Pete Jones, Prince Paul (widely lauded for collaborations with De La Soul and assorted solo ventures), DJ Premier from Gang Starr, Pete Rock, DJ Scott La Rock from Boogie Down Productions, DJ Miz, DJ Muggs from Cypress Hill, Jam Master Jay from Run-DMC, Eric B., DJ Shadow, RJD2, DJ Q-Bert, Diamond D, Mr. Khaliyl (an associate of Mos Def and Jurassic 5), Young Einstein, DJ Nu-Mark, James Lavelle, Cut Chemist, DJ Format, DJ Serious, Mister Cee, DJ Paul Nice, DJ Aladdin, Mix Master Mike, DJ D-Styles, DJ Signify, DJ Rhettmatic, DJ Babu, DJ Kay Slay, DJ Quik, DJ Spooky, Mr. DJ, and DJ Spinderella (of Salt-N-Pepa). Before they became the center of attention, an MC's role was to get the crowd into the DJ's mix. In general, Hip hop has focused on getting one's audience to dance, although relatively large niche audiences have formed in present day that focus on lyrics rather than dance such as Tech N9ne. Disillusioned by the centrality of emcees, with this new culture, some DJs further explored the art of spinning records, creating the turntablist scene. A DJ generally needs turntables, a good sound system, and scratch material, which typically comes in the form of vinyl records. Some early recorded rap music does not contain any sampling or DJing, however; for example, none of the members of the Sugarhill Gang were involved in the Bronx DJing scene and thus couldn't have done any, which explains the session player remake of "Good Times".

Graffiti art

Main article: Graffiti, Types of graffiti Types of graffitiGraffiti as an urban art form had been known since at least the 1950s, but began developing in earnest in the late 1960s and flourished during the 1970s. Hip-hop graffiti began during these periods on the subways of New York, and later expanded to the city walls themselves. This movement from trains to walls was encouraged by efforts by the city's Metropolitan Transportation Authority to eradicate graffiti on their property (the M.T.A. officially declared the transit graffiti-free in 1989). The first forms of subway graffiti were quick spray-painted or marker signatures ("tags"), which quickly evolved into large elaborate calligraphy, complete with color effects, shading, and more. Finding original techniques was very important for graffiti artists; for example, in 1972, one well-respected graffiti artist called Super Kool replaced the dispersion cap on his spray paint with a wider one, found on a can of oven cleaner. This is still a common practice. By 1976, graffiti artists like Lee Quinones began painting entire murals using advanced techniques. Some of the most memorable of Quinones' work were political in nature, calling for an end to the arms race, for example. The book Subway Art (New York: Henry Holt & Co, 1984) and the TV program Style Wars (first shown on the PBS channel in 1984) were among the first ways the mainstream public were introduced to graffiti. Quickly the rest of the globe imitated and adapted hip hop graffiti. Today, there are also strong scenes in Europe, South America, Australia and Japan. (Graffitti is a European-origin tradition. The word comes from the Italian term "graffito.") Graffiti has long been villainized by those in authority because of its (perceived) ties to gangs, violence, drug culture and street crime. Although it is a crime, falling under the category of vandalism, many artists are not violent criminals and do not engage in such activity as the brands that their art form has been labeled. This may be true in some cases, but most "writers", as they are often called, are in fact true artists that spend painstaking hours practicing and refining their skill to create something that is beautiful, at least in their own eyes. Demonizing their art by saying it is nothing more than a nuisance that might not be aesthetically pleasing has resulted in knee-jerk legislation, such as the 3-strike laws in Los Angeles, California. These can send a young artist to prison for life just for writing on a wall, even if it is the only crime they have ever committed, because it is has been classified as "gang related activity".

Breakdancing

Main article: Breakdancing Breakdancing, also known as B-boying or B-girling by its practitioners and followers, is a dynamic style of dance. The term "breakdancer" originates from the dancers at DJ Kool herc's parties who would save their best dance moves for the break section of the song. Breaking is one of the major elements of hip hop culture, commonly associated with, but distinct from, "popping", "locking", "hitting", "ticking", "boogaloo", and other funk styles that evolved independently in New York during the late 20th century. It was common during the 1980s to see groups of people in a playground, basketball court, or sidewalk with a radio performing breakdancing shows for a large audience. While breaking in its current form began in the South Bronx alongside the other elements of hip-hop, it is similar in style to and may possibly derive from the Capoeira form of dancing/martial arts, which was developed by slaves in Brazil. "Hip-Hop" as a form of dance is becoming more popular. Derived from, but not wholly consisting of, breakdancing moves, it is a dance without any limitations to positions and is an expression of how a dancer feels on the inside. The style of hip-hop dance incorporates a lot of fast paced combinations and rhythm. Hip-hop is very casual and fun. The modern moves and energy make it a great form of fun and exercise for teens and pre-teens of today. Certain shoes can be worn at some studios, preferably the dance sneaker or jazz shoe.

Beatboxing

Main article: Beatboxing Beatboxing, considered by many to be the "fifth element" of hip hop, is the vocal percussion of hip hop culture. It is primarily concerned with the art of creating beats, rhythms, and melodies using the human mouth. Early pioneers of the art include Mahjeed Marrow, Doug E. Fresh, Biz Markie, and Buffy of the Fat Boys. The term 'beatboxing' is derived from the mimicry of the first generation of drum machines, then known as beatboxes. The art form enjoyed a strong presence in the '80s. Beatboxing declined in popularity along with breakdancing in the late 80s, and almost slipped even deeper than the underground. Beatboxing has been enjoying a resurgence since the late '90s, marked by the release of "Make the Music 2000." by Rahzel of The Roots (known for even singing while beatboxing) The Internet has greatly aided the rebirth of modern beatboxing—on a global level never seen before—with thousands of beatboxers from over a dozen countries interacting on the UK's Humanbeatbox.com. The art form has radically evolved, extending its reach to include physical theater routines, and has integrated itself into hip hop (and other forms of theater). Vocal percussion is a standby of a capella groups, as well. Beatboxing has also recently branched beyond its traditional scope (mimicry of "beat boxes" to create hip-hop beats) to several new stand alone forms. It is now widely practiced as a form of human Drum & Bass, a style of heavy electronic music. The range of sounds that can be reproduced by the human vocal chords are staggering to many unfamiliar with this musical practice. A recent development in the area of hip hop performance is hip hop theatre.

References


- (1999) Light, Alan, ed. The VIBE History of Hip-Hop. New York: Three Rivers Press.

External links


- [http://www.hhdirecto.net Spanish Hip Hop]
- [http://www.hiphop-blogs.com Hip hop discussion and community]
- [http://www.rap.about.com Rap.about.com] Vast Hip-hop culture resource
- [http://www.westlord.com/rapdictionary/ Rap Dictionary] the oldest and ultimate resource for looking up hip-hop slang.
- [http://www.hiphop-battles.com/ HipHop-Battles.com] - Audio Battle Platform for MCs and Beatboxer
- [http://www.jumpoff.tv JumpOff.tv] Big Hip Hop Battle Events Category:Pop culture Category:Electronic music Category:Electronica als:Hip Hop ko:힙합 ja:ヒップホップ

Jurassic 5

Jurassic 5 is a six-piece hip hop crew that was formed in 1993 (see 1993 in music) at the Los Angeles, California venue Good Life. Rappers Chali 2na, Akil, Zaakir aka Soup, Mark 7even, and turntable maestros DJ Nu-Mark and DJ Cut Chemist came together from two separate crews, the Rebels of Rhythm and Unity Committee. They debuted for TVT Records in 1995 with the "Unified Rebelution" single. Their acclaimed position in the 1990s alternative hip hop movement, alongside artists including Company Flow, Black Star and Kool Keith, was confirmed when the Jurassic 5 EP was released in December 1997. The tracks harked back to the old school attitude of New York's Native Tongues Posse, the seminal late 1980s coalition of artists including De La Soul, the Jungle Brothers and A Tribe Called Quest who reaffirmed rap's social agenda. This was evident on "Concrete Schoolyard" ("Let's take it back to the concrete streets/Original beats from real live MCs"), which even provided the troupe with a surprise UK Top 40 single when it reached number 35 in November 1998 (see 1998 in music). The other stand-out track, "Jayou", was built around a hypnotic flute loop from Bob Marley's "Get Up, Stand Up". Cut Chemist and Chali 2na also record with the Latin funk/hip-hop crew Ozomatli, while Chemist collaborated with Shortkut from Invisibl Skratch Piklz on 1998's Live at Future Primitive Sound Session. Jurassic 5 then signed to Interscope Records, making their major label debut in June 2000 (see 2000 in music) with Quality Control. Their sophomore album, Power In Numbers was released in 2002. In summer of 2003, Jurassic 5 toured with the newly-revived Lollapalooza festival. Jurassic 5 is known for:
- A musical approach that evokes old school hip hop
- Tag-team delivery, with the four MCs trading off lyrics (and in some cases, individual words)
- Positive and inventive lyrics, rather than relying on sex/drug/violence/gang clichés
- Touring outside of hip-hop circles, including the 2003 Lollapalooza, the 2000 Warped Tour and festivals such as Bonnaroo

Discography


- Jurassic 5 (1998, Pan Records)
- Quality Control (20 June 2000, Interscope Records)
- Power In Numbers (8 October 2002, Interscope Records) In Australia, a two-disc version of Quality Control was released, the second disc comprising of instrumental versions of the album. A second version of Power In Numbers was released, which included a DVD. There is also a vinyl edition of Power In Numbers comprising of instrumental versions of the tracks from the original album. Jurassic 5 are currently on tour (without Cut Chemist), and a new album is due to be released later this year.

Sound clip

Jurassic 5's "Jurass Finish First" from 2000's Quality Control - note: lyrical inventiveness is the hallmark of Jurassic 5, shown in this song by the frequent use of alliteration, rhyme, word-plays and assonance; these literary techniques are so widespread that the song is difficult to decipher in spite of relatively clear diction and medium tempo

External links


- [http://www.jurassic5.com/ Official Jurassic 5 site]
- [http://www.interscope.com/ Official Interscope Records site] Jurassic 5 Category:Alternative hip hop musicians

Annum

Annum is a Latin term meaning year.
- Per annum means "occurring every year".
- Mega-annum, usually abbreviated as Ma, is a unit of time equal to one million (106) years. It is commonly used in scientific disciplines such as geology and paleontology to signify very long time periods in the past. For example, the dinosaur species Tyrannosaurus rex emerged approximately 65 Ma (65 million years) ago.
- Giga-annum, usually abbreviated as Ga, is a unit of time equal to one billion (109) years. It is commonly used in scientific disciplines such as cosmology to signify extremely long time periods in the past. For example, the formation of the Earth occurred approximately 4.55 Ga (4.55 billion years) ago. As is clear from the notation, billion as used here is on the short scale.

See also


- Before Present
- bya
- Geologic time scale
- Gya
- mya Category:Units of time

Triassic

The Triassic is a geologic period that extends from about 245 to 202 Ma (million years ago). As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both start and end of the Triassic are marked by major extinction events. The extinction event that closed the Triassic period has recently been more accurately dated, but as with most older geologic periods, the rock beds that define the start and end are well identified, but the exact dates of the start and end of the period are uncertain by a few million years. The characteristic sediments of the Triassic are red sandstones and evaporites, which suggest a warm dry climate. There is no evidence of glaciation; as far as can be determined, there was no land or ice caps near either pole. The supercontinent Pangaea was rifting during the Triassic but had not yet separated; the first marine sediments in the earliest rift, which separated New Jersey from Morocco, are Late Triassic in origin. Because of the limited shoreline of one super-continental mass, Triassic marine deposits are globally relatively rare, despite their prominence in Western Europe, where the Triassic was first studied. In North America, for example, marine deposits are limited to a few exposures in the West. Thus Triassic stratigraphy is mostly based on organisms living in lagoons and hypersaline environments, such as Estheria crustaceans. During the Triassic both marine and continental life show an adaptative radiation, following the Permian-Triassic extinction. Corals of the hexacorallia group make their first appearance. The first flowering plants (Angiosperms) may have evolved during the Triassic, as did the first flying vertebrates, the pterosaurs.

Triassic naming

The Triassic was named in 1834 by Friedrich Von Alberti from the three distinct layers (Latin trias meaning triad) —red beds, capped by chalk, followed by black shales— that are found throughout Germany and Northwest Europe, called the 'Trias'.

Triassic dating and subdivisions

The Triassic is usually separated into Early, Middle, and Late Triassic Epochs. The faunal stages from the youngest to oldest are:

Triassic paleogeography

During the Triassic, almost all the Earth's land mass was concentrated into a single supercontinent centered more or less on the equator, called Pangea ("all the land"). This took the form of a giant "Pac-Man" with an East-facing "mouth" constituting the Tethys sea, a vast gulf that opened farther westwards in the mid-Triassic. The remainder was the world-ocean known as Panthalassa ("all the sea"). Almost all the deep-ocean sediments laid down during the Triassic have disappeared through subduction of oceanic plates, thus very little is known of the Triassic open ocean.

Triassic climate

The Triassic climate was generally hot and dry, forming typical redbed sandstones. It was a seasonal, continental climate, with strong monsoons. Polar regions were moist and temperate.

Triassic lifeforms

In the Triassic, three categories of organisms can be distinguished: holdovers from the Permian-Triassic extinction, some new groups which flourished briefly, and new groups which went on to dominate the Mesozoic world. In marine environments new, modern types of corals appeared in the early Triassic, forming small patches of reefs, nothing compared to the great reef systems of Devonian times or modern reefs. The shelled cephalopods called Ammonites recovered, diversifying from a single line that survived the Permian extinction. The fish fauna was remarkably uniform, reflecting the fact that very few families survived the Permian extinction. There were also many types of marine reptiles. These including the Sauropterygia, which featured pachypleurosaurs and nothosaurs (both common during the Middle Triassic, especially in the Tethys region), placodonts, and the first plesiosaurs; the rather lizardlike Thalattosauria (Askeptosaurs); and the highly successful ichthyosaurs, which appeared in Early Triassic seas and soon diversified, some eventually developing to huge size during the late Triassic. On land, the holdover plants included the lycophytes, the dominant cycads, ginkgopyta (represented in modern times by Ginkgo biloba) and glossopterids. Seed plants dominated the land. In the northern hemisphere, conifers flourished. Glossopteris (a seed fern) was the dominant southern hemisphere tree during the Early Triassic period. Temnospondyl amphibians were among those groups that survived the P-T extinction, some (e.g. Trematosaurs) lineages flourishing briefly in the early Triasic, while others (e.g. Capitosaurs) remained successful throughout the whole period, or only came to prominance in the Late Triassic (e.g. Plagiosaurs, Metoposaurs). As for other amphibians, the first Lissamphibia are known from the early Triassic, but the group as a whole does not become common until the Jurassic, when the temnospondyls had become very rare. Archosauromorph reptiles – especially archosaurs – progressively replaced the synapsids that had dominated the Permian. Although Cynognathus was a chracteristic top preditor in earlier Triassic (Olenekian and Anisian) Gondwana, and both Kannemeyeriid dicynodonts and gomphodont cynodonts remained important herbivores during much of the period, by the end of the Triassic, synapsids played only bit parts. During the Carnian (early part of the late Triassic), some advanced cynodont gave rise to the first mammals. At the same time the Ornithodira, which until then had been small and insignificant, evolved into pterosaurs and a variety of dinosaurs. The Crurotarsi were the other important archosaur clade, and during the Late Triassic these also reached the height of their diversity, with various groups including the Phytosaurs, Aetosaurs, several distinct lineages of Rauisuchia, and the first crocodylians (the Sphenosuchia). Meanwhile the stocky herbivorous rhynchosaurs and the small to medium-sized insectivorous or piscivorous Prolaceriformes were important basal archosauromorph groups throughout most of the Triassic Among other reptiles, the earliest turtles, like Proganochelys and Proterochersis, appeared during the Norian (middle of the late Triassic). The Lepidosauromorpha - specifically the Sphenodonta, are first known in the fossil record a little earlier (during the Carnian). The Procolophonidae were an important group of small lizard-like herbivores.

Triassic Lagerstätten

The Monte San Giorgio lagerstätte, now in the Lake Lugano region of northern Italy and Switzerland, was in Triassic times a lagoon behind reefs with an anoxic bottom layer, so there were no scavengers and little turbulence to disturb fossilization, a situation that can be compared to the better-known Jurassic Solnhofen limestone lagerstätte. The remains of fish, and various marine reptiles (including the common pachypleurosaur Neusticosaurus, and the bizarre long-necked archosauromorph Tanystropheus), along with some terrestrial forms like Ticinosuchus and Macrocnemus, have been recovered from this locality. All these fossils date from the Anisian/Ladinian transition (about 237 million years ago)

Late Triassic extinction event

Main article: Triassic-Jurassic extinction event The Triassic period ended with a mass extinction, which was particularly severe in the oceans; the conodonts disappeared, and all the marine reptiles except ichthyosaurs and plesiosaurs. Invertebrates like brachiopods, gastropods, and molluscs were severely affected. In the oceans, 22 percent of marine families and possibly about half of marine genera went missing, according to University of Chicago paleontologist Jack Sepkoski. Though the end-Triassic extinction event was not equally devastating everywhere in terrestrial ecosystems (see below), several important clades of Crurotarsi (large archosaurian reptiles previously grouped together as the thecodonts) disappeared, as did most of the large labyrinthodont amphibians, a number of groups of small reptiles, and some synapsids (except for the proto-mammals). Some of the early, primitive dinosaurs also went extinct, but other, more adaptive dinosaurs survived to evolve in the Jurassic. Surviving plants that went on to dominate the Mesozoic world included modern conifers and, cycadeoids. It is not certain what caused this late Triassic extinction, which was accompanied by huge volcanic eruptions about 208-213 million years ago, the largest recorded volcanic event since the planet cooled and stabilized, as the supercontinent Pangaea began to break apart. Other possible causes for the extinction events include global cooling or even a bolide impact, for which an impact crater surrounding Manicouagan Reservoir, Quebec, Canada, has been singled out. At the Manicouagan impact crater (see illustration at the entry), however, recent research has shown that the impact melt within the crater has an age of 214±1 Ma. The date of the Triassic-Jurassic boundary has also been more accurately fixed recently, at 202±1 Ma. Both dates are gaining accuracy by using more accurate forms of radiometric dating, in particular the decay of uranium to lead in zircons formed at the impact. So the evidence suggests the Manicougan impact preceded the end of the Triassic by approximately 12±2 Ma. Therefore it could not be the immediate cause of the observed mass extinction (Hodych & Dunning, 1992). The number of late Triassic extinctions is disputed. Some studies suggest that there are at least two periods of extinction towards the end of the Triassic, between 12 and 17 million years apart. But arguing against this is a recent study of North American faunas. In the Petrified Forest of northeast Arizona there is a unique sequence of latest Carnian-early Norian terrestrial sediments. An analysis in 2002 ([http://gsa.confex.com/gsa/2002AM/finalprogram/abstract_42936.htm]) found no significant change in the paleoenvironment. Phytosaurs, the most common fossils there, experienced a change-over only at the genus level, and the number of species remained the same. Some Aetosaurs, the next most common tetrapods, and early dinosaurs, passed through unchanged. However, both Phytosaurs and Aetosaurs were among the groups of archosaur reptiles completely wiped out by the end-Triassic extinction event. It seems likely then that there was some sort of end-Carnian extinction, when several herbivorous archosauromorph groups died out, while the large herbivorous therapsids— the Kannemeyeriid dicynodonts and the Traversodont cynodonts— were much reduced in the northern half of Pangaea (Laurasia). These extinctions within the Triassic and at its end allowed the dinosaurs to expand into many niches that had become unoccupied. Dinosaurs would become increasingly dominant, abundant and diverse, and remained that way for the next 150 million years. The true "Age of Dinosaurs" is the Jurassic and Cretaceous, rather than the Triassic.

See also

Geologic timescale

External links


- [http://www.palaeos.com/Mesozoic/Triassic/Triassic.htm Best overall introduction.]
- [http://rainbow.ldgo.columbia.edu/courses/v1001/9.html 'The Triassic world'.]
- [http://gallery.in-tch.com/~earthhistory/triassic%20page%201.html Douglas Henderson's illustrations of Triassic animals.]
- [http://palaeo.gly.bris.ac.uk/Palaeofiles/Triassic/triextict.htm Paleofiles page on the Triassic extinctions.]

Sources


- Emiliani, Cesare, 1992, Planet Earth : Cosmology, Geology and the Evolution of Life and Environment
- van Andel, Tjeerd, (1985) 1994, New Views on an Old Planet : A History of Global Change, Cambridge University Press ko:트라이아스기 ja:三畳紀

Mesozoic

The Mesozoic is one of three geologic eras of the Phanerozoic eon. The division of time into eras dates back to Giovanni Arduino in the 18th century, although his original name for the era now called the Mesozoic was "Secondary" (see Tertiary.) Mesozoic gets its name from the Greek meso (middle) and zoo (animals) and is often called the "Age of Medieval Life." The Mesozoic includes three geologic periods: from oldest to youngest, they are the Triassic, the Jurassic and the Cretaceous periods. It extended from roughly 251 million years ago (Ma) to roughly 65 Ma. The Mesozoic followed the Paleozoic Era and preceded the Cenozoic Era. The lower (oldest) boundary is set by the Permian extinction. The upper (youngest) boundary is set at the Cretaceous extinction. The Mesozoic spans the period when terrestrial life was dominated by large sophisticated reptiles, the basis for its popular designation as "the Age of the Dinosaurs". The era also witnessed the development of early birds and mammals, and of the first flowering plants (angiosperms). At the end of the Mesozoic, all the major body plans of modern life were in place although in some cases—notably the mammals—the forms that existed at the end of the Cretaceous were relatively primitive. Geologically, the Mesozoic starts with almost all the Earth's land surface collected into a supercontinent called Pangaea. During the Mesozoic Era, however, Pangaea split into a northern continent Laurasia and a southern continent Gondwana. Laurasia subsequently divided into North America and Eurasia, whilst Gondwana broke up progressively into the four present continents of South America, Africa, Australia and Antarctica. The Mesozoic's end saw the dinosaur extinction.

See also


- Geologic time scale

References and further reading


- British Mesozoic Fossils, 1983, The Natural History Museum, London. ko:중생대 ja:中生代

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