Bone Anchored Hearing Aid- Is it Right for You?
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A popular inquiry these days is bone conduction hearing aid. The current interest in bone conduction hearing aid has led to much internet interest.
TaKe the time to fully investigate bone conduction hearing aid. Find out all the facts about bone conduction hearing aid. To learn more you can search further on bone conduction hearing aid.A bone anchored hearing aid was developed back in 1977, but wasn’t approved for use in the U.S. until 1996. This aid works by being implanted in the bone, so that sound is conducted here rather than through the ear. It proves effective for many cases of conductive and mixed hearing loss, but does not offer much assistance for other types of hearing loss problems.
This aid has an implant, a sound processor, and an external abutment. Together, these parts create sound transmission through the bone, allowing people to hear things without needing the use of their actual middle ear or external canal.
Once the bone anchored hearing aid is put into place, it becomes a part of the bone over time. Vibrations are sent through the bone, which stimulates the nerves in the ear. Once the nerves have been stimulated, the person can hear.
Chronic ear infections, congenital middle ear defects, and those with a dislike for traditional hearing aids can all benefit from the bone implant. This will allow for the middle ear to be bypassed, which is great for suffers of ear infections, because it is known that no more damage will be done to the hearing because of the implant.
The bone anchored hearing aid is also useful in patients who only have one deaf ear. By implanting this device in the deaf ear, the sound is transferred from the deaf ear to the good ear, which offers a sensation of hearing in that ear. So many people can benefit from this great device, but it can prove to be an expensive investment.
Like many other hearing aids, this procedure is medical in nature but has very little support of the insurance companies. Therefore, you must make sure that this is the right treatment for you, but also that you can afford it.
The bone anchored hearing aid is probably the best device that is available for middle ear problems, unilateral deafness, and other people who couldn’t find solutions that suited them before. The implant is unnoticeable and doesn’t get in the way like a hearing aid might, and you don’t have to worry about it slipping out.
Once the device has been implanted, the process is complete and no readjustments are needed. If you suffer from any of these types of hearing loss, this device might benefit you.
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Want to learn more about Hearing Aids? Be sure to visit the authors website where you will find different types of hearing aids at discount prices.
August 11th, 2010 at 10:22 am
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August 12th, 2010 at 8:15 pm
Either the witness saw the some drug materials in a group of inmate and scenario of crime while using the contain of drugs that day and time. and also the court will testify that the witness telling the truth nor have an exact evidence. so that the two group will lessen first the role regulation of the court and to know and discover the truth suspect of the possession case.
August 13th, 2010 at 2:50 pm
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August 17th, 2010 at 3:57 am
If you are still able to work full time in your usual field of work or something similar they are not going to give you disability. I have copd and got it the first time I applied because I can't work.
August 30th, 2010 at 1:38 am
bone nuit
September 1st, 2010 at 10:44 pm
Operation Petticoat
September 15th, 2010 at 9:17 am
Woooootssss I did great this time (tho I was sufferin from so much pain -_- ) n he told me that the improvement of my bone is impressive ♥
October 16th, 2010 at 4:24 am
a computer monitor
sticky notes
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washer/dryer
oven/microwave
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October 30th, 2010 at 7:59 am
In the company or organizations, it is common that, at some point of time, the manger may have to fire a employee for different reasons, such as poor work performance, misconduct, negligence, misconduct, indiscipline and so on. But, can you just terminate the service of the employee as per your wish? If you think you can dismiss the service of the employee easily then, you are greatly mistaken, because there is union and Employment Law, which protects the right of the employee. Thus, as a manager, you must know not only what an employee termination letter is but also what it should include. If not done properly, the letter can cause legal problems later. It is necessary to follow the right procedure for the dismissal in order to avoid law … Termination Letter, Employee Termination Letter, sample term
November 7th, 2010 at 6:52 pm
gee it a rest with the fireworks man :/ im fed up hearing them going off!
December 3rd, 2010 at 9:09 am
Nexus Revamps $80M Target-Anchored Center
December 13th, 2010 at 8:21 am
Tony Lama Kids Crepe Sole Boot. If you’re kids want to dress up like a real cowboy, you’ve found these great Tony Lama! You’ve found them at BootBarn.com Boot Features Brown Leather vamp. Bone Leather shaft. Composition insole. Ivory Crepe outsole. Extra Wide Toe.
December 15th, 2010 at 6:48 pm
In a college class i learned that African americans genetically do not absorb calcium and vitamin D as well especially if lactose intolerant. it could just be growing pains though. Those really ache and hurt if you are rapidly starting to grow.
December 19th, 2010 at 8:43 pm
Article by Bone Digger at 2010-12-19 20:10:15
Categorized in Book Reviews,
January 31st, 2011 at 3:09 am
Iraq has suffered great injustices. They had 32 nations bomb the hell out of the nation in the Desert Storm War. Can you imagine that? 32 nations taking turns dropping bombs? Then 192 nations placing sanctions. The entire world refused all commodities in/ out of the country. 1.5 MILLION Iraqis died as a result. Bombed & Isolated they were left in that condition for 13 years with tons of depleted uranium fired on their land. All this to be followed by 2003 invasion.
February 8th, 2011 at 5:54 pm
Because we give up the most either way
April 16th, 2011 at 10:25 pm
We'll see about tonight. Roz is anchored to the couch. Down for a flick tomorrow though.
April 26th, 2011 at 2:16 am
The best answer I can give you kiddo is to go to an orthodonist and either get braces or veneers.
May 3rd, 2011 at 7:19 pm
yeeeeep.
May 16th, 2011 at 10:01 am
i would neevr wanna be arranged on risers like that all seperated from your parts..
May 17th, 2011 at 4:02 pm
I look real nature like right now..lol
May 22nd, 2011 at 10:48 am
ANCHORED IN FOG
June 7th, 2011 at 1:45 pm
Couric to debut ABC talk show in 2012
CBC.ca
Having dominated morning television and anchored the evening news, broadcaster Katie Couric is now set to tackle daytime. ABC confirmed on Monday it had struck a multi-year deal with Couric for a syndicated daytime talk show to be based in New York and …
and more »
June 8th, 2011 at 5:47 am
she was a bitch
June 14th, 2011 at 6:55 am
see if you could do like the paperwork end of that job.
June 17th, 2011 at 8:51 am
Oh, Sonja…
June 22nd, 2011 at 4:46 pm
Doug Terry, a researcher at Microsoft Research Silicon Valley, who chairs the ACM Cloud Computing Tech Pack, told attendees at the “24 Hours in the Clouds” virtual conference that cloud computing promises to radically change the way that computer applications and services are constructed, delivered, and managed. In a keynote address on June 1, Terry said the potential benefits are clear, but realizing these benefits requires new techniques for sharing resources among applications, providing unlimited scalability, protecting privacy, and integrating diverse devices. The virtual keynote, Technology in the Cloud – Plus Some Challenges and Opportunities, presented at a conference produced by GITCA, is anchored in the content of the ACM Tech Pack on Cloud Computing.
June 25th, 2011 at 9:07 pm
Maria Kittou had rushed to Syntagma Square on hearing that the next wave of austerity measures would include biting tax increases that would hit the poor hard. “They are pushing us to the edge,” snarled the pensioner. Pointing at the Greek parliament building and shouting herself hoarse, she added: “These people aren’t worthy of the Greek flag. They have brought us nothing but shame. They have to go.” At 75, Kittou has endured the ravages of Greece’s brutal German occupation, bloody civil war, authoritarian rightwing rule and military dictatorship. Thirty-seven years after the return of democracy, there is a growing sense that the country is at war again, only this time fighting a battle of epic economic proportions. “It is the lack of any light at the end of the tunnel that makes it so hard,” said Kittou, one of many who have turned Athens’s main plaza into Europe’s pre-eminent fiscal battleground. This week, as the country confronts what EU president José Manuel Barroso, pictured…
June 26th, 2011 at 4:07 pm
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July 17th, 2011 at 8:42 am
lmfaooo I know right x)
August 10th, 2011 at 5:36 am
i keep hearing about this dude..and never listen to him..is he really cold?
September 2nd, 2011 at 11:28 am
RT #IMAGINEM O deve está balançando a perna ajeitando o cabelo e o boné de um em um segundo de tão ansioso que deve tá! kkk
September 4th, 2011 at 3:55 pm
How is BP being protected by the Republican Party? BP has been extremely charitable in the wake of the oil spill. In my opinion BP was exploited by the Obama administration and the US’s reputation has been damaged, by the aggressive litigation that is being directed at BP. All of the political posturing by folks like the fmr. congressman, the President, and others is nauseating. Business looks down at politics for good reason.
September 15th, 2011 at 11:10 pm
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October 14th, 2011 at 7:55 pm
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October 19th, 2011 at 8:03 am
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November 7th, 2011 at 12:17 pm
Pterosaurs ( /ˈtɛrəsɔr/, from the Greek πτερόσαυρος, pterosauros, meaning “winged lizard”) were flying reptiles of the clade or order Pterosauria. They existed from the late Triassic to the end of the Cretaceous Period (220 to 65.5 million years ago). Pterosaurs are the earliest vertebrates known to have evolved powered flight. Their wings were formed by a membrane of skin, muscle, and other tissues stretching from the legs to a dramatically lengthened fourth finger. Early species had long, fully toothed jaws and long tails, while later forms had a highly reduced tail, and some lacked teeth. Many sported furry coats made up of hair-like filaments known as pycnofibres, which covered their bodies and parts of their wings. Pterosaurs spanned a wide range of adult sizes, from the very small Nemicolopterus to the largest known flying creatures of all time, including Quetzalcoatlus and Hatzegopteryx.[1][2][3]
Pterosaurs are often referred to in the popular media and by the general public as flying dinosaurs, but this is incorrect. The term “dinosaur” is properly restricted to a certain group of reptiles with a unique upright stance (superorder Dinosauria, which includes birds), and therefore excludes the pterosaurs, as well as the various groups of extinct marine reptiles, such as ichthyosaurs, plesiosaurs, and mosasaurs.
Pterosaurs are also incorrectly referred to as “pterodactyls”, particularly by journalists.[4] This usage is discouraged. “Pterodactyl” refers specifically to members of the genus Pterodactylus,[5] and more broadly to members of the suborder Pterodactyloidea.[6][7]
Contents [hide]
1 Description
1.1 Wings
1.1.1 Parts of the pterosaur wing
1.2 Skull, teeth and crests
1.3 Pycnofibres
2 History of discovery
3 Paleobiology
3.1 Flight
3.2 Air sacs and respiration
3.3 Nervous system
3.4 Ground movement
3.5 Natural predators
3.6 Reproduction and life history
3.7 Daily activity patterns
4 Evolution and extinction
4.1 Origins
4.2 Classification
4.3 Extinction
4.4 Well-known genera
5 In popular culture
6 See also
7 References
8 External links
[edit]Description
The anatomy of pterosaurs was highly modified from their reptilian ancestors for the demands of flight. Pterosaur bones were hollow and air-filled, like the bones of birds. They had a keeled breastbone that was developed for the attachment of flight muscles and an enlarged brain that shows specialised features associated with flight.[8] In some later pterosaurs, the backbone over the shoulders fused into a structure known as a notarium, which served to stiffen the torso during flight, and provide a stable support for the scapula (shoulder blade).
[edit]Wings
Reconstructed wing planform of Quetzalcoatlus northropi compared to the Wandering Albatross Diomedea exulans and the Andean Condor Vultur gryphus (not to scale)
Pterosaur wings were formed by membranes of skin and other tissues. The primary membranes attached to the extremely long fourth finger of each arm and extended along the sides of the body to the legs.
While historically thought of as simple, leathery structures composed of skin, research has since shown that the wing membranes of pterosaurs were actually highly complex and dynamic structures suited to an active style of flight. First, the outer wings (from the tip to the elbow) were strengthened by closely spaced fibers called actinofibrils.[9] The actinofibrils themselves consisted of three distinct layers in the wing, forming a crisscross pattern when superimposed on one another. The actual function of the actinofibrils is unknown, as is the exact material from which they were made. Depending on their exact composition (keratin, muscle, elastic structures, etc.), they may have been stiffening or strengthening agents in the outer part of the wing.[10] The wing membranes also contained a thin layer of muscle, fibrous tissue, and a unique, complex circulatory system of looping blood vessels.[11]
As evidenced by hollow cavities in the wing bones of larger species and soft tissue preserved in at least one specimen, some pterosaurs extended their system of respiratory air sacs (see Paleobiology section below) into the wing membrane itself.[12]
[edit]Parts of the pterosaur wing
Sordes, as depicted here, evidences the possibility that pterosaurs had a cruropatagium (a membrane connecting the legs, but leaving the tail out unlike the chiropteran uropatagium)
The pterosaur wing membrane is divided into three basic units. The first, called the propatagium (“first membrane”), was the forward-most part of the wing and attached between the wrist and shoulder, creating the “leading edge” during flight. This membrane may have incorporated the first three fingers of the hand, as evidenced in some specimens.[11] The brachiopatagium (“arm membrane”) was the primary component of the wing, stretching from the highly elongated fourth finger of the hand to the hind limbs (though where exactly on the hind limbs it anchored is controversial and may have varied between species, see below). Finally, at least some pterosaur groups had a membrane that stretched between the legs, possibly connecting to or incorporating the tail, called the uropatagium; the extent of this membrane isn’t certain, as studies on Sordes seem to suggest that it simply connected the legs but did not involve the tail (rendering it a cruropatagium). It is generally agreed though that non-pterodactyloid pterosaurs had a broader uro/cruropatagium, with pterodactyloids only having membranes running along the legs; Pteranodon in particular might have developed/redeveloped an uropatagium, given the structure of the tail.[citation needed]
Wing anatomy
A bone unique to pterosaurs, known as the pteroid, connected to the wrist and helped to support a forward membrane (the propatagium) between the wrist and shoulder. Evidence of webbing between the three free fingers of the pterosaur forelimb suggests that this forward membrane may have been more extensive than the simple pteroid-to-shoulder connection traditionally depicted in life restorations.[11] The position of the pteroid bone itself has been controversial. Some scientists, notably David Unwin, have argued that the pteroid pointed forward, extending the forward membrane.[13] However, this view was strongly refuted in a 2007 paper by Chris Bennett, who showed that the pteroid did not articulate as previously thought and could not have pointed forward, but rather inward toward the body as traditionally thought.[14]
Three lines of evidence, morphological, developmental and histological, indicate that the pteroid is a true bone, rather than ossified cartilage. The origin of the pteroid is unclear: it may be a modified carpal, the first metacarpal, or a neomorph (new bone).[15]
The pterosaur wrist consists of two inner (proximal) and four outer (distal) carpals (wrist bones), excluding the pteroid bone, which may itself be a modified distal carpal. The proximal carpals are fused together into a “syncarpal” in mature specimens, while three of the distal carpals fuse to form a distal syncarpal. The remaining distal carpal, referred to here as the medial carpal, but which has also been termed the distal lateral, or pre-axial carpal, articulates on a vertically elongate biconvex facet on the anterior surface of the distal syncarpal. The medial carpal bears a deep concave fovea that opens anteriorly, ventrally and somewhat medially, within which the pteroid articulates.[16]
There has been considerable argument among paleontologists about whether the main wing membranes (brachiopatagia) attached to the hind limbs, and if so, where. Fossils of the rhamphorhynchoid Sordes,[17] the anurognathid Jeholopterus,[18] and a pterodactyloid from the Santana Formation seem to demonstrate that the wing membrane did attach to the hindlimbs, at least in some species.[19] However, modern bats and flying squirrels show considerable variation in the extent of their wing membranes and it is possible that, like these groups, different species of pterosaur had different wing designs. Indeed, analysis of pterosaur limb proportions shows that there was considerable variation, possibly reflecting a variety of wing-plans.[20]
Many if not all pterosaurs also had webbed feet.[21]
[edit]Skull, teeth and crests
Tooth, possibly from Coloborhynchus
Most pterosaur skulls had elongated, beak-like jaws. Some advanced forms were toothless (such as the pteranodonts and azhdarchids), though most sported a full complement of needle-like teeth.[22] In some cases, actual keratinous beak tissue has been preserved, though in toothed forms, the beak is small and restricted to the jaw tips and does not involve the teeth.[23]
Unlike most archosaurs, which have several openings in the skull in front of the eyes, in pterodactyloid pterosaurs the antorbital opening and the nasal opening was merged into a single large opening, called the nasoantorbial fenestra. This likely evolved as a weight-saving feature to lighten the skull for flight.[22]
Reconstruction of crests: three crested tapejarids. From top to bottom: Tapejara wellnhoferi, “Tapejara” navigans, Tupandactylus imperator (drawn to scale).
Pterosaurs are well known for their often elaborate crests. The first and perhaps best known of these is the distinctive backward-pointing crest of some Pteranodon species, though a few pterosaurs, such as the tapejarids and Nyctosaurus sported incredibly large crests that often incorporated keratinous or other soft tissue extensions of the bony crest base.
Since the 1990s, new discoveries and more thorough study of old specimens have shown that crests are far more widespread among pterosaurs than previously thought, due mainly to the fact that they were frequently extended by or composed completely of keratin, which does not fossilize as often as bone.[11] In the cases of pterosaurs like Pterorhynchus and Pterodactylus, the true extent of these crests has only been uncovered using ultraviolet photography.[23][24] The discovery of Pterorynchus and Austriadactylus, both crested “rhamphorhynchoids”, showed that even primitive pterosaurs had crests (previously, crests were thought to be restricted to the more advanced pterodactyloids).[11]
[edit]Pycnofibres
At least some pterosaurs were covered with hair-like filaments known as pycnofibres, similar to but not homologous (sharing a common structure) with mammalian hair. Pycnofibres were not true hair as seen in mammals, but a unique structure that developed a similar appearance through convergent evolution. Although in some cases actinofibrils (internal structural fibres) in the wing membrane have been mistaken for pycnofibres or true hair, some fossils such as those of Sordes pilosus (which translates as “hairy demon”) and Jeholopterus ninchengensis do show the unmistakable imprints of pycnofibres on the head and body, not unlike modern-day bats, another example of convergent evolution.[17] The presence of pycnofibres (and the demands of flight) imply that pterosaurs were endothermic (warm-blooded).
The term “pycnofibre”, meaning “dense filament”, was first coined in a paper on the soft tissue impressions of Jeholopterus by palaeontologist Alexander W.A. Kellner and colleagues in 2009.[10]
[edit]History of discovery
Engraving of the original P. antiquus specimen by Egid Verhelst II, 1784
The first pterosaur fossil was described by the Italian naturalist Cosimo Collini in 1784. Collini misinterpreted his specimen as a seagoing creature that used its long front limbs as paddles.[25] A few scientists continued to support the aquatic interpretation even until 1830, when the German zoologist Johann Georg Wagler suggested that Pterodactylus used its wings as flippers.[26] Georges Cuvier first suggested that pterosaurs were flying creatures in 1801,[27] and coined the name “Ptero-dactyle” 1809 for the specimen recovered in Germany.[5] However, due to the standardization of scientific names, the official name for this genus became Pterodactylus, though the name “pterodactyl” continued to be popularly and incorrectly applied to all members of Pterosauria.[4] Paleontologists now avoid using “pterodactyl” and prefer the term “pterosaur”. They relegate the term “pterodactyl” specifically for members of the genus Pterodactylus or more broadly for members of the suborder Pterodactyloidea.[6]
Since the first pterosaur fossil was discovered in the Late Jurassic Solnhofen limestone in 1784, twenty-nine kinds of pterosaurs have been found in those deposits alone. A famous early UK find was an example of Dimorphodon by Mary Anning, at Lyme Regis in 1828. The name Pterosauria was coined by Johann Jakob Kaup in 1834, though the name Ornithosauria (or “bird lizards”, Bonaparte, 1838) was sometimes used in the early literature.[2]
The three-dimensionally preserved skull of Anhanguera santanae, from the Santana Formation, Brazil
Most pterosaur fossils are poorly preserved. Their bones were hollow and, when sediments piled on top of them, the bones were flattened. The best preserved fossils have come from the Araripe Plateau, Brazil. For some reason, when the bones were deposited, the sediments encapsulated the bones, rather than crushing them. This created three-dimensional fossils for paleontologists to study. The first find in the Araripe Plateau was made in 1974.
Most paleontologists now believe that pterosaurs were adapted for active flight, not just gliding as was earlier believed. Pterosaur fossils have been found on every continent. At least 60 genera of pterosaurs have been found to date, ranging from the size of a small bird to wingspans in excess of 10 metres (33 ft).
[edit]Paleobiology
[edit]Flight
Skeletal reconstruction of a quadrupedally launching Pteranodon longiceps
The mechanics of pterosaur flight are not completely understood or modeled at this time.[28][29]
Diagrams showing breathing motion (top two) and internal air sac system (bottom two)
Katsufumi Sato, a Japanese scientist, did calculations using modern birds and decided that it is impossible for a pterosaur to stay aloft.[30] In the book Posture, Locomotion, and Paleoecology of Pterosaurs it is theorized that they were able to fly due to the oxygen-rich, dense atmosphere of the Late Cretaceous period.[31] However, one must note both Katsufumi and the authors of Posture, Locomotion, and Paleoecology of Pterosaurs based their research on the now outdated theories of pterosaurs being seabird-like, and the size limit doesn’t apply to terrestrial pterosaurs like azhdarchids and tapejarids [3] Furthermore, Darren Naish concluded that atmospheric differences between the present and the Mesozoic weren’t needed for the giant size of pterosaurs.[32]
However, Mark Witton and Mike Habib, of the University of Portsmouth and Johns Hopkins University, respectively, argue that pterosaurs used a vaulting mechanism to obtain flight.[33] Once in air, pterosaurs could reach speeds up to 120 kilometres per hour (75 mph) and travel thousands of kilometres.[33]
It may be of relevance that in 1985 the Smithsonian Institution commissioned aeronautical engineer Paul MacCready to build a half-scale working model of Quetzalcoatlus northropi. The replica was launched with a ground-based winch. It flew several times in 1986 and was filmed as part of the Smithsonian’s IMAX film On the Wing. However, the model was not anatomically correct and embodied vertical and horizontal tail stabilizers that were lacking in pterosaurs. The weight distribution of the model was also different due to the longer tail of the model.
[edit]Air sacs and respiration
A 2009 study showed that pterosaurs had a lung-air sac system and a precisely controlled skeletal breathing pump, which supports a flow-through pulmonary ventilation model in pterosaurs, analogous to that of birds. The presence of a subcutaneous air sac system in at least some pterodactyloids would have further reduced the density of the living animal.[12]
[edit]Nervous system
A study of pterosaur brain cavities using X-rays revealed that the animals (Rhamphorhynchus muensteri and Anhanguera santanae) had massive flocculi. The flocculus is a brain region that integrates signals from joints, muscles, skin and balance organs.[8]
The pterosaurs’ flocculi occupied 7.5% of the animals’ total brain mass, more than in any other vertebrate. Birds have unusually large flocculi compared with other animals, but these only occupy between 1 and 2% of total brain mass.[8]
The flocculus sends out neural signals that produce small, automatic movements in the eye muscles. These keep the image on an animal’s retina steady. Pterosaurs may have had such a large flocculus because of their large wing size, which would mean that there was a great deal more sensory information to process.[8]
[edit]Ground movement
The probable azhdarchid trace fossil Haenamichnus uhangriensis.
Pterosaur’s hip sockets are oriented facing slightly upwards, and the head of the femur (thigh bone) is only moderately inward facing, suggesting that pterosaurs had a semi-erect stance. It would have been possible to lift the thigh into a horizontal position during flight as gliding lizards do.
There was considerable debate whether pterosaurs ambulated as quadrupeds or as bipeds. In the 1980s, paleontologist Kevin Padian suggested that smaller pterosaurs with longer hindlimbs such as Dimorphodon might have walked or even run bipedally, in addition to flying, like road runners.[34] However, a large number of pterosaur trackways were later found with a distinctive four-toed hind foot and three-toed front foot; these are the unmistakable prints of pterosaurs walking on all fours.[35][36]
Unlike most vertebrates, which walk on their toes with ankles held off the ground (digitigrade), fossil footprints show that pterosaurs stood with the entire foot in contact with the ground (plantigrade), in a manner similar to humans and bears. Footprints from azhdarchids show that at least some pterosaurs walked with an erect, rather than sprawling, posture.[21]
Fossil trackways show that pterosaurs like Quetzalcoatlus northropi were quadrupeds.
Though traditionally depicted as ungainly and awkward when on the ground, the anatomy of at least some pterosaurs (particularly pterodactyloids) suggests that they were competent walkers and runners.[37] The forelimb bones of azhdarchids and ornithocheirids were unusually long compared to other pterosaurs, and in azhdarchids, the bones of the arm and hand (metacarpals) were particularly elongated. Furthermore, azhdarchid front limbs as a whole were proportioned similarly to fast-running ungulate mammals. Their hind limbs, on the other hand, were not built for speed, but they were long compared with most pterosaurs, and allowed for a long stride length. While azhdarchid pterosaurs probably could not run, they would have been relatively fast and energy efficient.[21]
The relative size of the hands and feet in pterosaurs (by comparison with modern animals such as birds) may indicate what type of lifestyle pterosaurs led on the ground. Azhdarchid pterosaurs had relatively small feet compared to their body size and leg length, with foot length only about 25%-30% the length of the lower leg. This suggests that azhdarchids were better adapted to walking on dry, relatively solid ground. Pteranodon had slightly larger feet (47% the length of the tibia), while filter-feeding pterosaurs like the ctenochasmatoids had very large feet (69% of tibial length in Pterodactylus, 84% in Pterodaustro), adapted to walking in soft muddy soil, similar to modern wading birds.[21]
[edit]Natural predators
Pterosaurs are known to have been eaten by theropods. In the 1 July 2004 edition of Nature, paleontologist Eric Buffetaut discusses an early Cretaceous fossil of three cervical vertebrae of a pterosaur with the broken tooth of a spinosaur embedded in it. The vertebrae are known not to have been eaten and exposed to digestion, as the joints still articulated.[38]
[edit]Reproduction and life history
Fossil pterodactyloid flapling from the Solnhofen Limestone
Very little is known about pterosaur reproduction, and pterosaur eggs are very rare. The first known pterosaur egg was found in the quarries of Liaoning, the same place that yielded the famous ‘feathered’ dinosaurs. The egg was squashed flat with no signs of cracking, so evidently the eggs had leathery shells, as in modern lizards.[39] This was supported by the description of an additional pterosaur egg belonging to the genus Darwinopterus, described in 2011, which also had a leathery shell and, also like modern reptiles but unlike birds, was fairly small compared to the size of the mother.[40] A study of pterosaur eggshell structure and chemistry published in 2007 indicated that it is likely pterosaurs buried their eggs, like modern crocodiles and turtles. Egg-burying would have been beneficial to the early evolution of pterosaurs, as it allows for more weight-reducing adaptations, but this method of reproduction also would have put limits on the variety of environments pterosaurs could live in, and may have disadvantaged them when they began to face ecological competition from birds.[41]
Wing membranes preserved in pterosaur embryos are well developed, suggesting pterosaurs were ready to fly soon after birth.[42] Fossils of pterosaurs only a few days to a week old (called flaplings) have been found, representing several pterosaur families, including pterodactylids, rhamphorhinchids, ctenochasmatids and azhdarchids.[22] All preserve bones which show a relatively high degree of hardening (ossification) for their age, and wing proportions similar to adults. In fact, many pterosaur flaplings have been considered adults and placed in separate species in the past. Additionally, flaplings are normally found in the same sediments as adults and juveniles of the same species, such as the Pterodactylus and Rhamphorhynchus flaplings found in the Solnhofen limestone of Germany, and Pterodaustro flaplings from Brazil. All are found in deep aquatic environment far from shore.[43]
It is not known whether pterosaurs practiced any form of parental care, but their ability to fly as soon as they emerged from the egg and the numerous flaplings found in environments far from nests and alongside adults has led most researchers, including Christopher Bennett and David Unwin, to conclude that the young were only dependent on their parents for a very short period of time, while the wings grew long enough to fly, and left the nest to fend for themselves within days of hatching.[22] Alternatively, they may have used stored yolk products for nourishment during their first few days of life, as in modern reptiles, rather than depend on parents for food.[43]
Growth rates of pterosaurs once they hatched varied across different groups. In more primitive, long-tailed pterosaurs (“rhamphorhynchoids”) such as Rhamphorhynchus, the average growth rate during the first year of life was 130% to 173%, slightly faster than the growth rate of alligators. Growth in these species slowed after sexual maturity, and it would have taken more than three years for Rhamphorhynchus to attain maximum size. In contrast, the more advanced, large pterodactyloid pterosaurs such as Pteranodon grew to adult size within the first year of life. Additionally, pterodactyloids had determinate growth, meaning that the animals reached a fixed maximum adult size and stopped growing.[43]
[edit]Daily activity patterns
Comparisons between the scleral rings of pterosaurs and modern birds and reptiles have been used to infer daily activity patterns of pterosaurs. The pterosaur genera Pterodactylus, Scaphognathus, and Tupuxuara have been inferred to be diurnal, Ctenochasma, Pterodaustro, and Rhamphorhynchus have been inferred to be nocturnal, and Tapejara has been inferred to be cathemeral, being active throughout the day for short intervals. As a result, the possibly fish-eating Ctenochasma and Rhamphorhynchus may have had similar activity patterns to modern nocturnal seabirds, and the filter-feeding Pterodaustro may have had similar activity patterns to modern anseriform birds that feed at night. The differences between activity patterns of the Solnhofen pterosaurs Ctenochasma, Rhamphorhynchus, Scaphognathus, and Pterodactylus may also indicate niche partitioning between these genera.[44]
[edit]Evolution and extinction
[edit]Origins
Restoration of two Scleromochlus on a tree
Because pterosaur anatomy has been so heavily modified for flight, and immediate “missing link” predecessors have not so far been described, the ancestry of pterosaurs is not well understood. Several hypotheses have been advanced, including links to ornithodirans like Scleromochlus, an ancestry among the basal archosauriforms like Euparkeria, or among the prolacertiformes (which include gliding forms like Sharovipteryx).[22]
Two researchers, Chris Bennett (1996) and David Peters (2000), have found pterosaurs to be prolacertiformes or closely related to them. Bennett only recovered pterosaurs as close relatives of the prolacertiformes after removing characteristics of the hind limb from his analysis, in an attempt to test the idea that these characters are the result of convergent evolution between pterosaurs and dinosaurs. However, subsequent analysis by Dave Hone and Michael Benton (2007) could not reproduce this result. Hone and Benton found pterosaurs to be closely related to dinosaurs even without hind limb characters. They also criticized previous studies by David Peters, raising “serious questions” about the methods he used to recover pterosaurs among the prolacertiformes. Hone and Benton concluded that although more primitive pterosauromorphs are needed to clarify their relationships, pterosaurs are best considered archosaurs, and specifically ornithodirans, given current evidence. In Hone and Benton’s analysis, pterosaurs are either the sister group of Scleromochlus or fall between it and Lagosuchus on the ornithodiran family tree.[45] Sterling Nesbitt (2011) found strong support for a clade composed of Scleromochlus and pterosaurs.[46]
[edit]Classification
For more details on this topic, see List of pterosaur classifications.
Classification of pterosaurs has historically been difficult, because there were many gaps in the fossil record. Many new discoveries are now filling in these gaps and giving a better picture of the evolution of pterosaurs. Traditionally, they are organized into two suborders:
Rhamphorhynchoidea (Plieninger, 1901): A group of early, basal (“primitive”) pterosaurs, many of which had long tails and short metacarpal bones in the wing. They were small, and their fingers were still adapted to climbing[citation needed]. They appeared in the Late Triassic period, and lasted until the late Jurassic. Rhamphorhynchoidea is a paraphyletic group (since the pterodactyloids evolved directly from them and not from a common ancestor), so with the increasing use of cladistics it has fallen out of favor in most technical literature.
Pterodactyloidea (Plieninger, 1901): The more derived (“advanced”) pterosaurs, with short tails and long wing metacarpals. They appeared in the middle Jurassic period, and lasted until the Cretaceous-Tertiary extinction event wiped them out at the end of the Cretaceous.
Zhejiangopterus, an azhdarchid from the Cretaceous of China
Rhamphorhynchus, a rhamphorhynchid from the Jurassic of Germany
Listing of families and superfamilies within Pterosauria, after Unwin 2006 unless otherwise noted.[22]
ORDER PTEROSAURIA (extinct)
Suborder Rhamphorhynchoidea *
Family Anurognathidae
Family Campylognathoididae
Family Dimorphodontidae
Family Rhamphorhynchidae
Suborder Pterodactyloidea
Superfamily Ornithocheiroidea
Family Istiodactylidae
Family Nyctosauridae
Family Ornithocheiridae
Family Pteranodontidae
Superfamily Ctenochasmatoidea
Family Ctenochasmatidae
Family Gallodactylidae
Family Pterodactylidae
Superfamily Dsungaripteroidea
Family Dsungaripteridae
Family Germanodactylidae
Superfamily Azhdarchoidea
Family Azhdarchidae
Family Chaoyangopteridae[47]
Family Lonchodectidae
Family Tapejaridae
The precise relationships between pterosaurs is still unsettled. However, several newer studies are beginning to make things clearer. Cladogram simplified after Unwin.[48]
Pterosauria
Preondactylus
Macronychoptera
Dimorphodontidae
Caelidracones
Anurognathidae
Lonchognatha
Campylognathoididae
Breviquartossa
Rhamphorhynchidae
Pterodactyloidea (see below)
Pterodactyloidea
Ornithocheiroidea
Istiodactylidae
Euornithocheira
Ornithocheiridae
Pteranodontidae
Lophocratia
Ctenochasmatoidea
Gallodactylidae
Euctenochasmatia
Pterodactylus
Lonchodectes
Ctenochasmatidae
Dsungaripteroidea
Germanodactylidae
Dsungaripteridae
Azhdarchoidea
Tapejaridae
Azhdarchidae
[edit]Extinction
It was once thought that competition with early bird species may have resulted in the extinction of many of the pterosaurs.[citation needed] By the end of the Cretaceous, only large species of pterosaurs are known. The smaller species seem to have become extinct, their niche filled by birds.[49] However, pterosaur decline (if actually present) seems unrelated to bird diversity.[50] At the end of the Cretaceous period, the Cretaceous–Tertiary extinction event which wiped out all non-avian dinosaurs and most avian dinosaurs as well, and many other animals, seemed to also take the pterosaurs. Alternatively, most pterosaurs may have been specialised for an ocean-going lifestyle.[citation needed] Consequently, when the Cretaceous–Tertiary extinction event severely affected marine life that most pterosaurs fed on, they went extinct. However, forms like azhdarchids and istiodactylids were not marine in habits.
[edit]Well-known genera
Main article: List of pterosaurs
Examples of pterosaur genera include:
Pteranodon was 1.8 metres (six ft) long, with a wingspan of 7.5 m (25 ft), and lived during the late Cretaceous period.
Pterodactylus had a wingspan of 50–75 centimetres (20 to –30 inches), and lived during the late Jurassic on lake shores.
Pterodaustro was a Cretaceous pterosaur from South America with a wingspan around 1.33 metres and with over 500 tall, narrow teeth, which were presumably used in filter-feeding, much like modern flamingos. Also like flamingos, this pterosaur’s diet may have resulted in the animal having a pink hue. It was South America’s first pterosaur find.
Quetzalcoatlus had a wingspan of 10–11 metres (33–36 ft), and was among the largest flying animals ever. It lived during the late Cretaceous period.
Hatzegopteryx was the largest flying animal known to science. Although no complete fossil has been discovered, what little fossils paleontologists have found give the creature an estimated wingspan of roughly 12 metres (40 ft.)
Rhamphorhynchus was a Jurassic pterosaur with a vane at the end of its tail, which may have acted to stabilise the tail in flight.
[edit]In popular culture
Quetzalcoatlus models in South Bank, created by Mark Witton for the Royal Society’s 350th anniversary
Pterosaurs have been a staple of popular culture for as long as their cousins the dinosaurs, though they are usually not featured as prominently in films, literature or other art. Additionally, while the depiction of dinosaurs in popular media has changed radically in response to advances in paleontology, a mainly outdated picture of pterosaurs has persisted since the mid 20th century.[51]
The number and diversity of pterosaurs in the popular consciousness is also not as high as it has been historically for dinosaurs. While the generic term “pterodactyl” is often used to describe these creatures, the animals depicted frequently represent either Pteranodon or Rhamphorhynchus, or a fictionalized hybrid of the two.[51] Many children’s toys and cartoons feature “pterodactyls” with Pteranodon-like crests and long, Rhamphorhynchus-like tails and teeth, a combination that never existed in nature. However, at least one type of pterosaur did have at least the Pteranodon-like crest and teeth—for example, the Ludodactylus, a name that means “toy finger” for its resemblance to old, inaccurate children’s toys.[52] Also, some depictions of pterosaurs incorrectly identify them as “birds”, when in real life they were flying reptiles, and birds are actually descended from theropod dinosaurs.
Pterosaurs were first used in fiction in Arthur Conan Doyle’s 1912 novel The Lost World, and subsequent 1925 film adaptation. They have been used in a number of films and television programs since, including the 1933 film King Kong, and 1966′s One Million Years B.C.. In the latter, animator Ray Harryhausen had to add inaccurate bat-like wing fingers to his stop motion models in order to keep the membranes from falling apart, though this particular error was common in art even before the film was made. Pterosaurs were mainly absent from notable film appearances until 2001, with Jurassic Park III. However, paleontologist Dave Hone has noted that even after the 40 intervening years, the pterosaurs in this film had not been significantly updated to reflect modern research. Among the errors he noted as persisting from the 1960s to the 2000s were teeth even in toothless species (the Jurassic Park III pterosaurs were intended to be Pteranodon, which translates as “toothless wing”), nesting behavior that was known to be inaccurate by 2001, and leathery wings, rather than the taut membranes of muscle fiber which was actually present and required for pterosaur flight.[51]
A fictionalized mutation of a pterosaur was introduced in the 1956 Japanese film Rodan. The film was released by Toho, the same studio responsible for Godzilla. The character later appeared in a number of Godzilla films between 1964 and 2004.
[edit]
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