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Turtle

For other uses, see Turtle (disambiguation).
Families
Testudines, Chelonia

Turtles are reptiles of the order Testudines (all living turtles belong to the crown group Chelonia), most of whose body is shielded by a special bony or cartilagenous shell developed from their ribs. The term turtle is usually used for the aquatic species, though aquatic fresh water turtles are also called terrapins. The term is sometimes used (esp. in North America) to refer to all members of the order, including tortoises, which are predominantly land-based. The order of Testudines includes both extant (living) and extinct species. About 300 species are alive today. Some species of turtles are highly endangered.

Description

All turtles have a protective shell around their bodies. The top part of the shell is called the carapace, the bottom is called the plastron, and the two are connected by a bridge. Some are known to be able to breathe through their rectums as well. Reference the Rheodytes leukops species.

Sea turtles grow to large sizes and live in the oceans in the temperate and tropical regions of Earth. Pond turtles (terrapins) are usually much smaller, while some land terrapins (tortoises) are as large as sea turtles. The sizes of turtles vary from a few centimetres (forest and jungle species) to two metres (the leatherback turtle and the Galapagos tortoise).

Turtles generally live a long time; some individuals are known to have lived longer than 150 years. The oldest tortoise on record is Tui Malila, known to have lived at least 188 years.

Sea turtles lay their eggs on dry sandy beaches. The eggs of the largest species are spherical, while the eggs of the rest are elongated. Their albumen is white and will not coagulate when cooked because of the protein it contains which is different to that of bird eggs. Turtle eggs prepared to eat consist mainly of yolk. In some species, temperature of the egg during development determines whether an egg develops into a male or a female: a higher temperature causes a female, a lower temperature causes a male.

Although they spend large proportions of their lives underwater, turtles are air-breathing reptiles, and must surface at regular intervals to refill their lungs with fresh air. However, aquatic respiration in Australian freshwater turtles is currently being studied. Some species have large cloacal cavities lined with many finger-like projections. These projections, called "papillae", have a rich blood supply, and increase the surface area of the cloaca. The turtles can take up dissolved oxygen from the water through these papillae, in much the same way that fish use gills.

Turtles have a gelatinous substance in their upper and lower shell, called calipash and calipee respectively, the calipash being of a dull greenish and the calipee of a light yellow color.

Evolution

The first turtles are believed to have existed in the era of the dinosaurs, 200 million years ago. Their exact ancestry is disputed. It was believed that they are the only surviving branch of the ancient clade Anapsida, which includes groups such as procolophonoids, millerettids, protorothyrids and pareiasaurs. All Anapsid skulls lack a temporal opening, while all other extant amniotes have temporal openings (although in mammals the hole has become the zygoid arch). Most anapsids became extinct in the late Permian period, except procolophonoids and possibly the precursors of the testudines (turtles).

However, it was recently suggested that the Anapsid-like turtle skull may be due to convergent evolution rather than to anapsid descent. More recent phylogenetic studies with this in mind placed turtles firmly within diapsids, slightly closer to Squamata than to Archosauria. All molecular studies have strongly upheld this new phylogeny, though some place turtles closer to Archosauria. Re-analysis of prior phylogenies suggests that they classified turtles as anapsids both because they assumed this classification (most of them studying what sort of anapsid turtles are) and because they did not sample fossil and extant taxa were broadly enough for constructing the cladogram. While the issue is far from resolved, most scientists now lean towards a Diapsid origin for turtles.

Order Testudines - Turtles

Gulf Coast Box Turtle, Terrapene carolina major (Emydidae) A slider of genus Trachemys A Leatherback Sea Turtle. Photo credit: NOAA

Suborder Paracryptodira (extinct)

Suborder Cryptodira

Suborder Pleurodira


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Suborder Pleurodira.
. Suborder Cryptodira. However, Tivos and DVRs are the main competitors with the VHS in home recording. Suborder Paracryptodira (extinct)
. It can also be more convenient to use VHS tapes because they can be rewritten easily, and VCRs can be easier than DVD recorders to use. While the issue is far from resolved, most scientists now lean towards a Diapsid origin for turtles. Despite DVD's better quality, however, VHS is still widely used in home recording of television programs, due to the large installed base and the lower cost of VHS recorders.

Re-analysis of prior phylogenies suggests that they classified turtles as anapsids both because they assumed this classification (most of them studying what sort of anapsid turtles are) and because they did not sample fossil and extant taxa were broadly enough for constructing the cladogram. Commentators predict that 2006 will be the final year of new releases on VHS, as major studios continue to phase out VHS. All molecular studies have strongly upheld this new phylogeny, though some place turtles closer to Archosauria. Moreover, most television programs released as box sets are for sale in DVD format only. More recent phylogenetic studies with this in mind placed turtles firmly within diapsids, slightly closer to Squamata than to Archosauria. Many films released to theaters from 2004 onwards have later been released only on DVD and not on VHS, and many other new feature films are being released solely on DVD. However, it was recently suggested that the Anapsid-like turtle skull may be due to convergent evolution rather than to anapsid descent. retailers Circuit City and Best Buy stopped selling VHS tapes in 2002 and 2003, respectively.

Most anapsids became extinct in the late Permian period, except procolophonoids and possibly the precursors of the testudines (turtles). Major U.S. All Anapsid skulls lack a temporal opening, while all other extant amniotes have temporal openings (although in mammals the hole has become the zygoid arch). The DVD format was introduced in 1997 and has since overtaken VHS in sales and rentals. It was believed that they are the only surviving branch of the ancient clade Anapsida, which includes groups such as procolophonoids, millerettids, protorothyrids and pareiasaurs. In addition, it offers superior audiovisual quality, and the storage of data in digital format on tape makes for improved transfer and editing. Their exact ancestry is disputed. MiniDV has largely replaced 8mm tapes as the de facto camcorder standard in more recent years as it is smaller still (some MiniDV camcorders being no larger than one's hand).

The first turtles are believed to have existed in the era of the dinosaurs, 200 million years ago. 8mm tapes, introduced in the early 1980s, succeeded as a format for camcorders (both in the consumer, and to an extent, professional market), as VHS and Betamax camcorders were unsuitably large and heavy in comparison. Turtles have a gelatinous substance in their upper and lower shell, called calipash and calipee respectively, the calipash being of a dull greenish and the calipee of a light yellow color. As these cassettes are much more compact in design — which also means the hardware to play and record the tapes has to be more compact than VHS, and therefore more expensive — they are much more suited to portable applications such as camcorders. The turtles can take up dissolved oxygen from the water through these papillae, in much the same way that fish use gills. Other formats such as 8mm video cassettes and MiniDV have emerged since, but these formats are by no means in complete competition with VHS. These projections, called "papillae", have a rich blood supply, and increase the surface area of the cloaca. Netscape.

Some species have large cloacal cavities lined with many finger-like projections. Windows and Microsoft vs. However, aquatic respiration in Australian freshwater turtles is currently being studied. IBM, Macintosh vs. Although they spend large proportions of their lives underwater, turtles are air-breathing reptiles, and must surface at regular intervals to refill their lungs with fresh air. The format war and the "marketing over technology" claims have taken on a life of their own, and have been used as analogies in the battles of the computer industry, including Apple vs. In some species, temperature of the egg during development determines whether an egg develops into a male or a female: a higher temperature causes a female, a lower temperature causes a male. Sony ultimately conceded the fight in the late '80s, bringing out a line of VHS VCRs.

Turtle eggs prepared to eat consist mainly of yolk. Ultimately Betamax did manage to make up some of the difference on recording time, but this was too little, too late. Their albumen is white and will not coagulate when cooked because of the protein it contains which is different to that of bird eggs. The longer tape time is sometimes cited as the defining factor in the format war, as the longer VHS tapes allowed consumers to record entire programs unattended, and arguably created the entire video rental industry by providing sufficient playing time for most feature films to be distributed on a single cassette. The eggs of the largest species are spherical, while the eggs of the rest are elongated. Betamax held an early lead in the format war, offering some technical advantages, but by 1980 VHS was gaining due to its longer tape time (3 hours maximum, compared to just 60 minutes for Betamax) and JVC's less strict licensing program. Sea turtles lay their eggs on dry sandy beaches. In fact, however, the root causes of VHS' victory are somewhat more complex.

The oldest tortoise on record is Tui Malila, known to have lived at least 188 years. Since Betamax was widely perceived at the time as the better format, it is often stated that VHS' eventual victory was a victory of marketing over technical excellence. Turtles generally live a long time; some individuals are known to have lived longer than 150 years. As mentioned, VHS was the winner of a protracted and somewhat bitter format war during the early 1980s against Sony's Betamax format. The sizes of turtles vary from a few centimetres (forest and jungle species) to two metres (the leatherback turtle and the Galapagos tortoise). Conversely, an E-300 tape runs for 300 minutes in PAL-SP, but 200 minutes in NTSC-SP. Pond turtles (terrapins) are usually much smaller, while some land terrapins (tortoises) are as large as sea turtles. For example, a T-120 tape runs for 120 minutes in NTSC-SP, but 180 minutes in PAL-SP.

Sea turtles grow to large sizes and live in the oceans in the temperate and tropical regions of Earth. It can easily be derived by multiplying with 3/2 or 2/3, respectively. Reference the Rheodytes leukops species. It is perfectly possible to record and play back a blank T-XXX tape in a PAL machine or a blank E-XXX tape in an NTSC machine, but the resulting playing time will be different than indicated. Some are known to be able to breathe through their rectums as well. In order to avoid confusion, manufacturers indicate the playing time in minutes that can be expected for the market the tape is sold in:. The top part of the shell is called the carapace, the bottom is called the plastron, and the two are connected by a bridge. Both NTSC and PAL/SECAM VHS cassettes are physically identical (although the signals recorded on the tape are incompatible.) However, as tape speeds differ between NTSC and PAL/SECAM, the playing time for any given cassette will vary accordingly between the systems.

All turtles have a protective shell around their bodies. Likewise, S-VHS machines for the Brazilian market record in NTSC and convert to/from PAL-M. . S-VHS machines sold in SECAM markets record internally in PAL, and convert to/from SECAM during record/playback, respectively. Some species of turtles are highly endangered. S-VHS only exists in PAL/625/25 and NTSC/525/30. About 300 species are alive today. Dedicated multistandard machines can usually handle all standards listed, some high end model can even convert a tape from one standard to another by using a built-in standards converter.

The order of Testudines includes both extant (living) and extinct species. regular VHS machines sold in Europe nowadays can typically handle PAL, MESECAM for record and playback, plus NTSC for playback only. in North America) to refer to all members of the order, including tortoises, which are predominantly land-based. E.g. The term is sometimes used (esp. These can handle VHS tapes of more than one standards. The term turtle is usually used for the aquatic species, though aquatic fresh water turtles are also called terrapins. Since the 1990s dual- and multistandard VHS machines have become more and more common.

Turtles are reptiles of the order Testudines (all living turtles belong to the crown group Chelonia), most of whose body is shielded by a special bony or cartilagenous shell developed from their ribs. The following signal varieties exist in conventional VHS:. Superfamily Pelomedusoidea. Typically, a VHS machine can only handle signals of the country it was sold in. Superfamily Chelonioidea. However, a machine must be designed to record a given standard. Superfamily Kinosternoidea. VHS can record and play back all varieties of analogue television signals in existence at the time VHS was devised.

Superfamily Trionychoidea. This format is most notably used by Fox for some of its cable networks. Superfamily Testudinoidea. This format is the least expensive format to support a pre-read edit. There is also a JVC-designed component digital professional production format known as Digital-S or (officially) D9 that uses a VHS form factor tape and essentially the same mechanical tape handling techniques as an S-VHS recorder. This development hampered the sales of the Betamax system somewhat, because the Betamax cassette geometry prevented a similar development.

The magnetic tape on VHS-C cassettes is wound on one main spool and uses a gear wheel to advance the tape; the wheel and spool can also be moved by hand. Since VHS-C tapes are based on the same magnetic tape as full size tapes, they can be played back in standard VHS players using a mechanical adapter, without the need of any kind of signal conversion. Another variant is VHS-C (C for compact), used in some camcorders. W-VHS caters for high definition video.

Devices have also been invented which directly connect a personal computer to VHS tape recorders for use as a data backup device. Several improved versions of VHS exist, most notably S-VHS, an improved analog standard, and D-VHS, which records digital video onto a VHS form factor tape. There was a time when higher-end VCRs provided functions for manually removing and adding these index marks — so that, for example, they coincide with the actual start of the program — but this feature has become hard to find in recent models. These are normally written at the beginning of each recording session, and can be found using the VCR's index search function: this will fast-wind forward or backward to the nth specified index mark, and resume playback from there.

The control track can additionally hold index marks. Since good tracking depends on the exact distance between the rotating drum and the fixed control/audio head reading the linear tracks, which usually varies by a couple of micrometers between machines due to manufacturing tolerances, most VCRs offer tracking adjustment, either manual or automatic, to correct such mismatches. Another linear control track, at the tape's lower edge, holds pulses that mark the beginning of every frame of video; these are used to fine-tune the tape speed during playback and to get the rotating heads exactly on their helical tracks rather than having them end up somewhere between two adjacent tracks (a feature called tracking). These advanced features are impossible to find on later-model VCRs due to the rise of digital video formats.

Another high-end feature was manual audio level control, which made the VHS HiFi format much more useful for high-quality audio-only recording purposes as discussed above. (Due to the different ways in which linear and HiFi audio are recorded, these kinds of dubbing were not possible with the HiFi tracks). Without the dubbing features, this task would've required the tape to be copied to another tape which would cause generational loss. This was useful, for example, for laying a song over a previously edited-together montage of short video clips that were the same total duration as that song.

These would move the tape past the heads and keep the video unchanged while recording new linear audio or keep the linear audio unchanged while recording new video, respectively. Some higher-end VHS and S-VHS VCRs once offered "audio dubbing" and "video dubbing" functions. Of course, for backward compatibility, hi-fi VCRs still write the linear audio track during recording, and can automatically read it during playback if the hi-fi audio is not present. The excellent sound quality of hi-fi VHS has gained it some popularity as an audio format in certain applications; in particular, ordinary home hi-fi VCRs are sometimes used by home recording enthusiasts as a handy and inexpensive medium for making high-quality stereo mixdowns and master recordings from multitrack audio tape.

When the video signal is written by the following video head, it erases and overwrites the audio signal at the surface of the tape, but leaves the deeper portion of the signal undisturbed. These audio tracks take advantage of depth multiplexing: since they use lower frequencies than the video, their magnetization signals penetrate deeper into the tape. More recent hi-fi VCRs add higher-quality stereo audio tracks which are read and written by heads located on the same spinning drum that carries the video heads, frequency modulated to the unused frequency range in between the chroma and luma signals. In the original VHS format, audio was recorded unmodulated in a single (monaural) linear track at the upper edge of the tape, which was limited in frequency response by the tape speed.

The video bandwidth is achieved with a relatively low tape speed by the use of helical scan recording of a frequency modulated luminance (black and white) signal, to which a frequency-reduced "color under" chroma (hue and saturation) signal is added. The vertical resolution of VHS (and all other analog recording methods) is determined by the TV standard — a maximum of 486 lines are visible in NTSC and a maximum of 576 lines in PAL. The frequency modulation of the luminance signal makes higher resolutions impossible within the VHS standard, no matter how advanced the recorder's technology. VHS tapes have approximately 3 MHz of video bandwidth, and a horizontal resolution of about 240 discernible lines per scanline [1].

An unofficial LP mode with half the standard speed exists on some NTSC machines, but is not part of the VHS standard. Because of this, commercial prerecorded tapes were almost always recorded in SP mode. Of course, these speed reductions cause corresponding reductions in video quality; also, tapes recorded at the lower speed often exhibit poor playback performance on recorders other than the one they were produced on. More recent machines usually allow the selection of longer recording times by lowering the tape speed: LP mode (for PAL and some NTSC machines) halves the tape speed and doubles the recording time, while EP mode (for NTSC and some newer PAL machines, aka SLP mode) drops the tape speed to one-third, for triple the recording time.

Most cassettes have lower recording times because they use thicker tape, which helps avoid jams; careful users generally avoid the thinnest tapes. A cassette holds a maximum of about 430 m of tape at the lowest acceptable tape thickness, giving a maximum playing time of about 3.5 hours for NTSC and 5 hours for PAL at "standard" (SP) quality. The tape speed is 3.335 cm/s for NTSC, 2.339 cm/s for PAL. A VHS cassette contains a ½ inch (12.7 mm) wide magnetic tape wound between two spools, allowing it to be slowly passed over the various playback and recording heads of the video cassette recorder.

. Most newer VHS machines do not perform this unthreading step, as due to improved engineering, head-tape contact is no longer an impediment to fast winding. Early VHS machines could rewind and fast forward the tape considerably faster than a Betamax VCR since they unthreaded the tape from the playback heads before commencing any high-speed winding. VHS initially offered a longer playing time than the Betamax system, and it also had the advantage of a far less complex tape transport mechanism.

VHS became a standard format for consumer recording and viewing in the 1980s and 1990s after competing in a fierce format war with Sony's Betamax and, to a lesser extent, Philips' Video 2000. Some early reports claim the name originally stood for Victor Helical Scan System. VHS officially stands for Video Home System, but it initially stood for Vertical Helical Scan, after the relative head/tape scan technique. The Video Home System, first released in September 1976, better known by its abbreviation VHS, is a recording and playing standard for video cassette recorders (VCRs), developed by JVC (with some of its critical technology under lucrative licensing agreements with Sony) and launched in 1976.

Viz Video (1993-). Buena Vista Home Entertainment (1989-). Miramax Home Entertainment, a unit of Buena Vista Home Entertainment (1989-). New Line Home Entertainment, a TimeWarner Company (1989-).

Carolco Home Video, a division of Artisan Entertainment, a Lions Gate Company (1988-1995). Orion Home Video, a Sony Pictures Entertainment Company (1988-1997). Anchor Bay Entertainment (1980s-). Hi-Tops Video, a Heron Communications Company (1985-1992).

Simitar Entertainment (1980s-1990s). Touchstone Home Entertainment, a unit of the Walt Disney Company (1984-). Artisan Entertainment, a Lions Gate Company (1984-). Family Home Entertainment, a division of Artisan Entertainment, a Lions Gate Company (1982-).

NBC Home Video, an NBC/Universal Company (1981-). Universal Studios Home Video, an NBC/Universal Company (1980-). Magnetic Video, the first duplicator/distributor of movies on video cassette for home use (1977-1981). Vestron Video, a division of Artisan Entertainment, a Lions Gate Company (1979-).

MGM Home Entertainment, a Sony Pictures Entertainment Company (1979-). Media Home Entertainment, a Heron Communications Company (1978-1992). Warner Home Video, a TimeWarner Company (1978-). HBO Video, a TimeWarner Company (1978-).

Sony Pictures Home Entertainment (1978-). Walt Disney Home Entertainment (1978-). Twentieth (20th) Century-Fox Home Entertainment, a News Corporation Company (1977-). Paramount Home Video, a Viacom Company (1976-).

E-XXX indicates playing time for PAL or SECAM in SP speed. T-XXX indicates playing time for NTSC or PAL-M in SP speed. PAL-M, Brazil). PAL/525/30 (i.e.

NTSC/525/30 (Most parts of North and South America, Japan, South Korea). MESECAM/625/25 (most other SECAM countries, notably Eastern Europe and Middle East). SECAM/625/25 (SECAM, French variety). PAL/625/25 (most of Western Europe, many parts of Asia and Africa).

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