Many aspects of pterosaur life appearance remain unknown or controversial, although a number of ex- ceptional fossils have provided some surprising details. Pterosaur body hair was reported as early as and described for various Jurassic pterosaurs between the s and s and today it is clear that pterosaurs had bristle-like hairs covering their necks and bodies Figure 4.
The active flapping flight and body hair of pterosaurs suggest that vestibular papillae go away on its own had an elevated metabolism. Other exceptional fossils show that some ptero- saurs possessed a throat pouch, webbing between the toes, and scales on the soles vestibular papillae go away on its own the feet. This specimen preserves parts of the flight mem branes, a throat pouch, and hairs on the neck and back.
Soft tissue crests are now known for a wide diversity of pterodactyloids. Geological Cancer hepatico peritoneal Special Publication London: The Geological Society of London. An unexpected discovery is a soft tissue crest in Pterodactylus, a genus that lacks a bony crest Figure 1.
The presence of a distinctive bone texture on the pterosaur snout, jaw, and palate indicates that pterosaurs were beaked. Pterosaur wing membranes are known from well- preserved specimens from the Solnhofen Limestone and the Early Cretaceous Brazilian Crato and San- tana formations. A membrane called the propatagium extended from the shoulder to the pteroid and per- haps distally to encompass the first three fingers. The main flight membrane, the brachiopatagium also called the cheiropatagiumextended from the tip of the wing finger to the vestibular papillae go away on its own limb, extending as far distally as the knee, shin, or ankle.
Another membrane, the uropatagium, was present between the hind limbs Figure 3. The wing membrane appears to have been complex, with a thin epidermis, a layer of vascular tissues, a layer of stiffening fibres called aktinofibrils, a thin sheet of muscle, and a Figure 6 Skull of the tapejarid pterosaur Topejara navigaus from the Early Cretaceous Crato Formation of Brazil with bony and soft tissue skull crest.
Rhamphorhynchus and probably other vestibular papillae go away on its own pterosaurs possessed a vertical diamond-shaped membrane at the tail tip.
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With skin membranes connecting the wings, body, and legs, pterosaurs may have been superficially bat- like but, because bats are mostly dark-coloured noctur- nal animals, it is doubtful that the similarities were strong. Pterosaurs mostly seem to have been ecological analogues of sea- and water-birds, and it might be that they were patterned in whites, blacks, and greys, although bright colours presumably decorated their crests.
Rather more heterodox recent ideas include the suggestion that pterosaurs are the closest relatives of birds and that pterosaurs are part of the Dinosauria. Several different models have been proposed for the origin of pterosaurs, but the presence in basal ptero- saurs of climbing features and of various details in the hind limb and pelvis indicative of a leaping ability sug- gest that pterosaurs first evolved as tree-climbing leapers.
The Affinities and Origin vestibular papillae go away on its own Pterosaurs Historically, pterosaurs have been allied with Meso- zoic marine reptiles, bats, marsupials, and birds see Fossil Vertebrates: Dinosaurs; Birds.
However, major improvements in the understanding of verte- brate evolution allowed the palaeontologists of the nineteenth and twentieth centuries to realize that pterosaurs were related at least vaguely to dinosaurs see and their allies.
Although it is clear that pterosaurs are part of the major reptile assemblage known as the Diapsida, their affinities within this group are controversial. The presence of an antorbital fenestra has conven- tionally meant that pterosaurs have been regarded as enterobius vermicularis leczenie, the so-called ruling reptile group that incorporates crocodilians, dinosaurs, and kin.
Among archosaurs, pterosaurs share a simple hinge- like ankle joint with vestibular papillae go away on its own and consequently have been regarded as close relatives of dinosaurs in most studies. This view was developed at a time when some workers thought that pterosaurs originated from terrestrial bipedal ancestors and that pterosaurs themselves were bipedal and digitigrade. A small bi- pedal, long-legged archosaur from Late Triassic Scotland, Scleromochlus, was argued to be a ptero- saur ancestor, but recent studies refute this idea.
However, several recent studies have questioned the evidence for this proposed affinity. An alternative hypothesis argues that pterosaurs belong instead to a group of archosaur-like diapsids, the Prolacertiformes. Most prolacertiforms were superficially vestibular papillae go away on its own, but Sharovipteryx from Late Triassic Kyrgyzstan appears to be intermediate be- tween conventional prolacertiforms and pterosaurs.
It has pterosaur-like hind limbs and vertebrae and membranes between its hind limbs and tail. Some other models for pterosaur ancestry have been proposed. InS. Christopher Bennett argued that Pterosaur Diversity and Phylogeny It was recognized in that pterosaurs could be divided into two groups: the toothed, mostly long- tailed Rhamphorhynchoidea, and the short-tailed Pterodactyloidea including both toothed and tooth- less kinds. Today, it is clear that rhamphorhynchoids include the ancestors of pterodactyloids and, conse- quently, Rhamphorhynchoidea is a grade and not a clade.
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Pterosaurs previously referred to as rhamphor- hynchoids are nowadays termed basal pterosaurs or non-pterodactyloids. Although basal pterosaurs were diverse, it is notable that they were small compared with the majority of Cretaceous pterodactyloids.
The evolutionary relationships of pterosaurs are relatively understudied and only recently has pterosaur phylogeny been analysed. Although some areas of con- sensus have emerged, authors disagree on the details. Perhaps the most basal pterosaur is Preondactylus from the Late Triassic of Italy.
Это было низкое, гулкое уханье, не складывавшееся в членораздельную речь, хотя было очевидно, что существо пытается с ними разговаривать.
Олвину стоило только пожелать, и стены превращались в окна, выходящие, по его выбору, на любую часть города.
Конечно, - добавил он, - его разум может быть столь отдаленного порядка, что мы не сможем его понять - но почему-то подобное объяснение мне не кажется правильным.
Знакомый, но по-прежнему внушавший трепет голос зазвучал так тихо и так близко, что Элвину показалось, будто эскорт ничего не слышит.
Но именно такие комнаты и были домом для большей части человечества на протяжении значительного отрезка его истории.
Когда-то, видимо, Диаспар стоял совсем рядом с морем, хотя даже в самых древних хрониках об этом не было ни малейшего упоминання.
This form has a shorter coracoid and humerus and longer legs than other pterosaurs. Dimorphodontids, which include Dimor- phodon from Early and perhaps Middle Jurassic Figure 7 Cladogram depicting the relationships of all the major pterosaur groups. Reproduced from David Unwin. A surprising recent discovery is the persistence of anurognathids into the Early Cretaceous. Two basal pterosaurs, Eudimorphodon from Late Triassic Italy and Greenland and Campy- lognathoides from Early Jurassic Germany and India, are united in the Campylognathoididae based on a distinctive lower jaw in which two pairs of large conical teeth are followed by multiple smaller ones.
Rhamphorhynchids were successful Jurassic ptero- saurs known from Eurasia, North America, and Africa. Rhamphorhynchus from Late Jurassic Europe exhibits a laterally compressed, ventrally directed vestibular papillae go away on its own jaw tip and an array of forward-pointing teeth. It probably used these to grab fish and other small prey from the water. Another rhamphorhynchid lineage, the scaphognathines, had deeper skulls with teeth perpendicular to the jaw margins.
The Pterodactyloids Pterodactyloids, the advanced short-tailed pterosaurs, originated from a rhamphorhynchid-like ancestor during the Middle Jurassic. The pterodactyloid radi- ation consisted of four major groups: the robust-jawed ornithocheiroids, the slim-jawed ctenochasmatoids, the low-crested dsungaripteroids, and the long-necked, crested azhdarchoids.
A fifth group, the lonchodectids from Early Cretaceous England, are of uncertain affin- ity. Lonchodectids were small wingspan, 1—2 m with long, dorsoventrally flattened jaws with small teeth, each of which was supported by a low bony collar at its base. Ornithocheiroids were large predatory pterosaurs wingspan, 2—9 m with robust beaks, often housing recurved, fang-like teeth at their tips Figure 8.
Their jaws frequently possessed keel-like dorsal and ventral crests, and some forms also possessed crests on the back of the skull.
The toothless pteranodontids and nyctosaurids appear to be members of this group. The earliest known ornithocheiroids appear at the start of the Cretaceous, while nyctosaurids survived to the very end of the Cretaceous. Ctenochasmatoids had needle-like meshes of teeth set in long, thin jaws.
In Pterodaustro from late Early Cretaceous Argentina, the upturned lower jaw contains approximately bristle-like teeth. These were surely used for filtering small organisms from the water.
Unlike ornithocheiroids, ctenochasmatoids had elongate cervical vertebrae and were generally small wingspan, 50 cm to 2 malthough Cearadac- tylus from Early Cretaceous Brazil was a giant with a wingspan of 5.
Figure 8 Jaw tips of the Cretaceous ornithocheiroid pterosaur Coloborhynchus. Note the massive fang like anterior teeth and the low keel like crests on both jaws.
This specimen is from the Santana Formation of Brazil and would have belonged to an animal with a skull of approximately 1 m in length. Like some ctenochasma- toids, dsungaripteroids had a midline crest on the top of the skull.
Their beaks often had toothless tips and they may have been predators of molluscs and crustaceans. Finally, the strangest pterodactyloids must be the azhdarchoids. These include the long-necked azh- darchids and the crested tapejarids. Azhdarchids may have exceeded wingspans of 11 m and were widely distributed in the Late Cretaceous. They may have been ecological generalists akin to storks, and were probably not specialist carrion feeders or mud probers as has been proposed. Determining the life style of the tapejarids is more difficult.
The vaguely parrot-like skull of Tapejara Figure 6 from Lower Cretaceous Brazil led some workers to propose that it was a fruit eater, but it might better be imagined as an auk analogue. Recently, it has been suggested that Thalassodromeus, also vestibular papillae go away on its own Lower Cretaceous Brazil, was a fish eater that trawled its blade-like lower jaw through the water.
Pterosaur Palaeobiology Because pterosaurs are unique and extinct, recon- structing their palaeobiology is difficult and nothing is known about several aspects of their lives.
Limited evidence does allow us, however, to reconstruct their sensory abilities, feeding behaviours, and styles of locomotion. The large orbits of pterosaurs show that they had large eyes, and the abundance of visual display phylum Mollusca, is one of the most familiar of all invertebrate taxa.
Modern representatives, such as mussels, cockles, oysters, and scallops, are well known from excursions to the coast, and in many parts of the world they are important commercial species. Their generally excellent fossil record has allowed their evolutionary history to be traced back to the Early Palaeozoic and, for much of this time, they have been important components of many faunas.
From rather modest beginnings, they have conquered a range of habitats from the deep sea to freshwater, exploited a wide range of life habits from deep burrowing to swimmingand undergone a near-exponential taxonomic proliferation, a spec- tacular example of an adaptive radiation.
Bivalves come in all manner of shapes and sizes, from tiny, thin-shelled commensals that live in as- sociation with sea anemones, to giant clams and the extinct rudists and inoceramids which reach ed sizes well over 1 m.
Shell morphology is extremely plastic, but all are modifications of the same basic theme. The intimacy of the shell morphology to life habit has been a great benefit in reconstructing the life habits of extinct bivalves, but has also frustrated many attempts to establish vestibular papillae go away on its own relationships between different groups within the class.
Bivalves have been proven to be good palaeoenvironmental indicators, but they have only limited use in biostratigraphy.
As the name implies, endometrial cancer and metastasis comprise two calcar- eous valves. These are arranged laterally left and rightare joined dorsally by a partially calcified elas- tic ligament, and enclose the soft tissue.
Each valve has clearly differentiated posterior vestibular papillae go away on its own anterior fea- tures, i. The primitive arrangement, retained by most bivalves, was to have a plane of symmetry parallel to the commissure the join be- tween the two valvesresulting in valves which are mirror images of one another i.
Al- though this symmetry is found in virtually all bivalves which live with the commissural valve perpendicular to the substrate surface orthotheticit has been lost in those which have adopted a pleurothetic habit where they lie on one valve e. In these cases, there is a tendency for the two valves to become dissimilar i.
Shell Morphology All bivalves possess a pair of shells which may be shut to provide protection from both environmental stresses e. Most shells are reasonably robust, which has provided the class with a generally excellent fossil record. Although shell morphology in bivalves is very variable and intimately linked to their life habits see belowall shells are simple modifica- tions of the basic shell secretion model used by all shelled molluscs. The shell is secreted by the mantle lobes vestibular papillae go away on its own grows by marginal accretion, as evidenced by the vestibular papillae go away on its own lines on the surface of the valve Figures 1A and 2A.
These growth lines are particu- larly marked in bivalves from intertidal and shallow temperate habitats, where the animals experience pronounced seasonality and largely stop growing during the winter months. Bivalves which experience more equable conditions do not show such obvious or regular patterns. Inspection of the growth lines in sectioned valves shows that, although most shell ma- terial is added ventrally, the shell is also thickened during growth Figure 2Bdemonstrating that the entire mantle surface is responsible for adding mater- ial.
The outermost part of the shell is an organic layer called the periostracum secreted at the mantle edge Figure 2C. The thickness of the periostracum varies between taxa, from less than 1 mm in oysters and Figure 1 A Mercenaria mercenariaa shallow burrowing bi valve from the Pliocene of Florida.
Note the prominent annual growth bands. B Pecten maximaa free living epifaunal scallop from the Holocene Vestibular papillae go away on its own.
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In many cases, the periostracum is lost by abrasion and decay during the life of the animal, particularly on the older parts of the shell, and there is no real prospect vestibular papillae go away on its own it being preserved in any but the most exceptional circumstances. The primary func- tion of the periostracum is to act as the template on vestibular papillae go away on its own the calcareous part of the shell is deposited, but it may also provide protection from both corrosive waters and predators that dissolve the shell.
It is particularly noticeable that freshwater bivalves have very thick periostraca. The main part of the shell, however, is calcareous. The protein- aceous matrix controls both the polymorph of cal- cium carbonate used and the arrangement of the crystals. All bivalves contain aragonite in their shells and the vast majority are wholly so. Some taxa, how- ever, chiefly those exploiting epifaunal life habits, also secrete calcite in their outer layers.
A Marked comarginal growth lines on the shell surface. B Section through the shell along the line indicated in A show ing the arrangement of growth lines within the shell.
C The relationship between the shell and the underlying mantle edge close up details of the circled area in B. Molluscan shell is immensely strong, vestibular papillae go away on its own fact often much stronger than vertebrate bone. There are a number of different microstructures Figure 3each with different mechanical properties, and most shells are made up of two or three arranged in different layers. Different taxa show different arrangements and these are considered to be of phylogenetic signifi- cance.
It is apparent that the earliest bivalves were wholly aragonitic and chiefly composed of nacre Figure 3Aand that subsequent evolution has pro- duced the wide array of microstructural arrangements seen today.
The effect of differing crystal sizes, amount of organic material, and polymorph used has affected the preservation potential of different taxa; many of the Palaeozoic and Mesozoic taxa that were originally aragonitic are either preserved as internal moulds or are replaced by calcite. Details of the internal features of the shell are shown in Figure 4. The hinge plate is situated dorsally and houses the ligament and teeth. The ligament is an elastic, partially calcified layer that provides a very energy-efficient opening mechanism.
During valve closure, energy is stored in the ligament as it is flexed by the contracted adductor muscle s Figure 4C. When the muscle is relaxed, the ligament springs the valves apart causing them to gape. This passive valve opening mechanism is the reason why many fossil bivalves are found in a disarticulated state.
Although the ligament itself is seldom preserved, its position may be inferred from the presence of the ligament pits in which it is anchored Figures 4 and 5. Most bivalves have teeth on the hinge plate which fit into corresponding sockets on the opposite valve and func- tion to keep the valves in perfect alignment. Both ligamenture and dentition vary markedly amongst higher taxa of bivalves, and both are often used as informative characters in establishing phylogenies. Some of the range of vestibular papillae go away on its own plate architectures is shown in Figure 5.
A number of attachment scars mark the locations where muscles are anchored to the shell. The most significant of these are the adductor scars Figures 4A and 4B.
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Покажи дорогу, ведущую из города, любому человеку в Диаспаре - дорогу, которая может выглядеть точно так же, как находящаяся сейчас перед нами - и он не сможет пройти по .
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Часто ли ты думал над Несколько секунд учитель и ученик задумчиво разглядывали друг друга, и каждый, вероятно, смог лучше, чем прежде, представить себе точку зрения другого.
If the adductor scars are paired i. If an animal is monomyarian, the single muscle the pos- terior occupies a more central position.