Ecology and Behaviour of Mesozoic Reptiles


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The second order of Synapida, the Therapsida Sect. The rocks of the Karoo basin of southern Africa are littered with the fossilised bones of these synapsid reptiles. Some of the former were quite large. One genus, Moschops Fig. Although the limbs and head were comparatively small, the skull was considerably thickened, as in other dinocephalians, and may have been adapted in this manner for head-butting contests at the time of mating.

These thick-skinned reptiles formed the prey of carnivorous forms such as the small Titanosuchus Dinocephalia; Fig. Although the former was a slender hunter that probably fed mainly on smaller herbivores and juveniles, many of the other titanosuchids were large, heavily-built predators and could not have been very agile or fast.

The most common of the herbivorous therapsids were the Dicy- Synapsid Reptiles 17 n Fig. Moschops Therapsida; Middle Permian; length ca. These had large, sausage-shaped bodies, short legs and tails. They either possessed no teeth at all, or had just a pair of tusks; and they sliced the vegetation with sharp, horny beaks. A complex chewing cycle allowed them to exploit a wide variety of plants. When feeding,the lower jaw was first thrust forward, slid back forcibly cutting the food, and then opened from a backwards position.

They were preyed on by gorgonopsians along with the carnivorous and other plant-eating dinocephalians. Neither dinocephalians nor n Fig. Titanosuchus Therapsida; Middle Permian; length ca. Sauroctonus Therapsida; Upper Permian; length ca. The mass extinction at the end of the Permian period ca. It has been estimated that considerably more than half the families of animals that had existed during the Late Permian abruptly disappeared. These included numerous groups of marine invertebrates such as the trilobites, many kinds of coral, and most of the brachiopods.

Molluscs and fishes also suffered severely. The effects were equally devastating on land. Most of the primitive amphibians and of the mammal-like reptiles vanished Jablonski ; Hallam and Wignall ; Benton Although surviving groups of the latter were eventually to give rise to the mammals which almost certainly evolved from dicynodonts the predominant reptiles of the Mesozoic Era were Diapsida. The former included the marine ichthyosaurs and plesiosaurs: we shall deal with them before considering aerial and terrestrial reptiles. Benton has given a very clear account of continental drift and of conditions during the Carboniferous and Permian periods.

The flora at that time was surprisingly varied: it included dense growths of increasingly tall club mosses, horsetails, and ferns. The Carboniferous mya and Permian mya periods were both warm in the northern hemisphere. In the south, however, a large ice cap developed which covered considerable portions of Gondwanaland Benton , Until the Carboniferous period, land plants had been restricted to moist areas around rivers, ponds and lakes: they were by no means large. During the Carboniferous, however, when reptiles first appeared, giant horsetails, ferns, and seed ferns or pteridosperms evolved.

Seed ferns resembled true ferns pteridophytes in many ways, but had already evolved seeds. They bridged the gulf between ferns and cycads. The latter are palm-like plants and the pteridosperms were more closely related to them than to pteridophytes. Ferns, tree ferns — which reached to a height of 9—15 m — horsetails and giant club mosses were characteristic of the Carboniferous period. One genus of the club mosses, Sigillaria, grew to ca. Its cones grew directly from the trunk, just below the apex.

Spore-bearing ferns predominated in the Early Permian, but by the end of the period they had been largely replaced by gymnosperms coniferous trees. This change in the vegetation during the Permian was very pronounced, and marked a transition from the early to the middle phase of plant development. Giant club mosses gradually disappeared, along with many pteridosperms and some of the horsetails, while new types of ferns and ginkgo trees appeared as the climate became drier.

In Gondwanaland, ferns of the genus Glossopteris, with long, tongue-shaped leaves and central veins, as well as of Gangamopteris, with leaves from which the central veins were absent, were characteristic of this time. About mya, during the Late Triassic and Early Jurassic, the continental plates of Laurasia and Gondwanaland were united. Some portions of what are now central Asia and China may have remained as separate islands, but most of the landmass of the world was concentrated into the single supercontinent, Pangaea, as we have seen.

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Consequently, both plants and animals were remarkably similar everywhere. The main vegetation types consisted of seed ferns and conifers which were adapted to the dry climate, while massive horsetails dominated the damper regions. The terrestrial fauna comprised mainly earthworms, again in moister places, snails, arachnids, insects, and reptiles, which either captured earthworms and arthropods in the undergrowth, or else chewed the tough vegetation. Crustaceans, molluscs and fishes populated the lakes and rivers where they were preyed upon by amphibians and phytosaurs — distant relatives of the crocodilians Sect.

Piscivorous ichthyosaurs and nothosaurs dominated the oceans, while early pterosaurs skimmed squids and fishes from the surface water. Numerous marine taxa became extinct at the end of the Triassic, including the primitive archosaurs — the phytosaurs, aetosaurs, and rauisuchians. These extraordinary animals will be discussed in the following chapters. The dinosaurs evolved from thecodont reptiles, and the mammals from theropsids about mya.

The first flowering of giant dinosaurs began towards the end of the Early Jurassic, and a wealth of dinosaurian fossils has been found in Late Jurassic strata. Indeed, the Late Jurassic was the time during which the largest of the dinosaurs existed. In many ways, the climates of the Cretaceous —65 mya resembled those of the Jurassic, but towards the end of the period the world became drier and, as already mentioned, the climate seasonal. During the Early Cretaceous, the sea level was some 25 m higher than it is today. About mya, however, it rose dramatically to about m above the present level.

All the above-mentioned factors may have contributed to the extinctions that occurred at the end of the Mesozoic Era Chap.

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Unlike the Triassic and Jurassic periods, which are both divided into three epochs, the Cretaceous is separated into two. The predominant elements of the Mesozoic flora were gymnosperms Fig. Among them were various Cycadoidea — low forms with short, globular or barrel-shaped trunks sometimes bearing large and brightly coloured flowers. There were also tree-like species with slender stems that branched only occasionally. The Jurassic and Cretaceous Periods 21 n Fig. The Mesozoic landscape Both types bore rich crowns of long, palm-like leaves.

When the conifers appeared they spread rapidly and soon became abundant.

The Age of Reptiles in Three Acts

Alongside these were various types of ginkgo, pine-like taxodiums, and huge sequoias. Cryptograms lost their former leading position among the vegetation. Ferns and horsetails still grew in damp places along the banks of rivers or lakes, but they were much smaller than they had been previously. In the absence of grass, the ground was either bare or covered by algae, bryophytes, and pteridophytes. Finally, during the Cretaceous period, as the seasons set in, deciduous plants appeared. The vegetation during the Mesozoic Era was not only different from that of earlier times, but was also more diverse.

Consequently the fauna diversified also to fill the numerous ecological niches that appeared. This diversity is reflected among the wonderful reptiles discussed in the following chapters. Colbert followed the same procedure, as did Palmer amongst others. Land-dwelling vertebrates did not turn to life in the sea until the Triassic period, but this trend has been repeated several times since then. Many amphibians were aquatic in the Palaeozoic Era and in the Triassic period, but few of them were marine.

The reason for this probably lies mainly in their osmotic relations. Reptiles were better equipped to evolve the adaptations necessary for a marine existence. Not only did they have efficient lungs which had replaced their long-lost ancestral gills, but their limbs were easily transformed into paddles. These, like their tails, in some cases, acquired functions very similar to those of the fins and tails of fishes.

Furthermore, reptiles had cleidoic eggs Sect.

The factors that most influence the ways in which animals have evolved and specialised are, first, the environment in which they live and move and, second, what they feed on. Tetrapod reptiles evolved and first diversified on land. Some of them then returned to water and became adapted for swimming; others developed wings and took to the air like birds. The theropod origin of the latter forms the subject matter of Sect. The majority of reptiles, however, remained on land. These will be discussed in Chapters 7— The above is, of course, a very great over-simplification: between such broad groupings are many intermediate forms.

Some of the land-living reptiles were shore-dwelling but semi-aquatic or amphibious forms that spent some parts of the day on land and some in water as modern crocodilians do. They moved reasonably well on land Sect. Not only were many Mesozoic reptiles amphibious, but several became truly aquatic. A total of seven subclasses or orders — either entirely or in a large portion — became aquatic and returned to the waters in which their distant rhipidistian ancestors originally evolved.

One of these was the family Mesosauridae, an example of which, Mesosaurus Fig. Another mesosaur, Stereosternum, has only been found in southern Brazil. Were any needed, this distribution provides unequivocal evidence for continental drift. Although the mesosaurs have sometimes been regarded as suspension feeders, this reconstruction depends upon interpretation of the mandibular teeth as being small, marginal upper teeth. Benton , among others, has favoured the latter, Collin and Janis the former. Turtles almost fly through the water with their front flippers but, even so, they are not as fast as most fishes and dolphins of comparative size.

Some reptiles, however, especially the pliosaurs and ichthyosaurs, were streamlined and extremely fast Chap. They swam with the aid of flattened bodies and fish-like tails. When an eel swims, the inner sides of the curves on its sinuous body press against the water. The resistance is increased by the expansion of the dorsal, caudal and ventral fins which are combined into one. Lissman Gray and consists of three parts — the vertebral column, the axial musculature and the lateral surfaces of the body, including the caudal fins.

The vertebral column can be regarded as a series of rigid units, hinged so that the body can bend only in a transverse lateral plane. The whole tail is essentially a shortened continuation of such units. Eel-like or anguilliform movement is similar to the serpentine locomotion of a snake. Its dependence upon the thrust made by the inner side of each curve of the body can be illustrated by the inability of an eel or snake to crawl across a polished surface.

Both, however, can pass through a series of smooth pegs projecting from the surface of a polished board Fig. The same is true of the swimming eel. In most fishes, and other animals whose bodies are relatively much shorter than those of eels and snakes, the lateral surfaces and caudal fins represent Locomotion 25 n Fig.

Snake gliding past a series of smooth pegs projecting from the surface of a polished board. Cloudsley-Thompson Further explanation in the text only sections of the sinuous curve. Furthermore, the separated dorsal, ventral and caudal fins then often have more than one function Gray ; McGowan When snakes swim, much of the energy is wasted because their rounded bodies present little resistance to the water. Even in sea snakes, the tails are only slightly flattened see Cloudsley-Thompson The mechanics of swimming have been analysed very thoroughly by McGowan Each of these was characterised by a different mode of swimming.

After Massare 26 Amphibious and Early Marine Mesozoic Reptiles These had deep, streamlined bodies, deepest in the pectoral region and tapering posteriorly to the caudal fin. They propelled themselves by oscillating the tail, while the fin-like limbs were used mainly for steering. The general shape of the body was within the optimal range to minimise drag and for efficient swimming. Probably the fastest marine reptiles capable of sustained swimming, they were predators that hunted fishes and other prey over large areas. Bauplan II contained the mosasaurs, thalattosaurs, marine crocodilians, pachypleurosaurs, and the remaining Triassic ichthyosaurs.

These animals had narrow, elongated bodies and long, broad tails. Propulsion was achieved by undulation of part or all of the body along with the tail. Consequently, the tail could be used to produce a sudden thrust, and the prey must have been caught by rapid bursts of speed. Bauplan III is exemplified by nothosaurs, pliosaurs and plesiosaurs; these had stiff, ellipsoidal bodies with two pairs of elongated limbs, wing-shaped in the plesiosaurs.

The nothosaurs and plesiosaurs had long necks and small heads, while the pliosaurs had shorter necks, larger heads and more compact bodies. Although not so speedy as the ichthyosaurs, but like them, the pliosaurs were probably predators that pursued their prey over long distances. In contrast, the other taxa would have been much slower. Movement of their necks and heads must have tended to cause them to veer off course if they moved too fast; so they ambushed their prey by stealth and seized it with a sudden movement of the neck.

Finally, Bauplan IV, found in placodonts and sea turtles, was a body compressed dorsoventrally and covered by bony armour.

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Locomotion was therefore not an important factor to them in the acquisition of food. Romer , once remarked that tortoises, terrapins and turtles are commonplace objects to us only because they are still living. Were they extinct, their shells would have been a cause of wonder, as they represent the most complete defensive armour found among tetrapod vertebrates. The Testudines or Chelonia is an ancient order of reptiles long considered to belong to the subclass Anapsida and therefore descended from the Captorhinidae or cotylosaurs discussed in Chapter 2 Sect.

Turtles and their relations are the only living descendants of this varied taxon, and there are no other anapsid reptiles alive today. Chelonians are probably descended from the Permian Eunotosauria, and true turtles ap- Testudines 27 n Fig. Left Proganochelys Testudines; Upper Triassic; length ca.


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Right Triassochelys Testudines; Upper Triassic; length ca. Modern turtles have no teeth, but the Triassic chelonians Proganochelys and Triassochelys Fig. So, too, had the Australochelidae from the Late Triassic of South America and the Early Jurassic of Africa, which still retained some palate teeth as in Australochelys.

Teeth had disappeared almost completely by the time the Jurassic forms evolved. Furthermore, the lungs are emptied when those species that are able to do so withdraw their heads and limbs into the shell. A turtle or tortoise that has been attacked or disturbed may have to remain in this state for a long period.

It is able to do so, however, thanks to the evolution of a number of physiological mechanisms which must already have been present in its Mesozoic forebears. These include the ability to tolerate high levels of carbon dioxide in the blood. In other vertebrates these increase the acidity or decrease the pH , but in chelonians this effect is counteracted by means of a buffering system of bicarbonate ions, serum proteins, and haemoglobin in the blood. In addition, turtles are capable of filling and emptying their lungs more completely than most other vertebrates can.

In consequence, when the head and limbs are withdrawn, the lungs initially contain very little carbon dioxide. The muscles of turtles are often surprisingly red, due to their high myoglobin content. These animals are therefore able to store significant amounts of 28 Amphibious and Early Marine Mesozoic Reptiles oxygen, not only in the haemoglobin of the blood but also in the myoglobin of the muscles.

In setting up an oxygen debt, energy is supplied to the muscles by the anaerobic conversion of ionised pyruvic acid, with the production of lactic acid, which is stored in the muscles and later conveyed to the liver to be oxidised. Although it is somewhat toxic, turtles can tolerate much higher levels of lactic acid than most other animals. A modern land tortoise can voluntarily holds its breath for periods of 15 or 20 min and may, in this way, economise in water Cloudsley-Thompson The ability to spend long periods without respiring is useful, not only to terrestrial chelonians that retract their extremities when disturbed, but also to aquatic species, enabling them to remain submerged for long periods.

These periods are extended by bradycardia slowing of the heart rate , which occurs automatically when aquatic turtles dive. Furthermore, these reptiles are able to extract dissolved oxygen from the surrounding water through their buccal linings or thin papillose skin Pritchard Movement of air in and out of the lungs is achieved in a number of ways. The pressure in the lungs is continuously being changed by the heartbeat and the movements of the limb girdles, limbs and neck.

A membrane behind the lungs can also compress these organs causing exhalation. In marine turtles whose limbs are not retractable, some expansion of the lungs is possible because there is skeletal flexibility of the bridge between the carapace and plastron. No doubt their life styles also have not altered much during the Era; but Proganochelys and Triassochelys Proganochelyidae; Fig.

Both these genera were found in the Upper Triassic Keuper sediments of Europe. They were probably semi-aquatic, like modern terrapins: marine turtles did not appear until the Jurassic period. Could that ecological niche have been already occupied by the placodonts Sect. Undoubtedly, tortoises and turtles on the shore would, in Late Triassic times, have seen nothosaurs, placodonts, plesiosaurs and ichthyosaurs in the waters beyond the beaches Colbert From the Jurassic to the present day, Testudines have comprised two major groups, the Pleurodira and Cryptodira.

The former withdraw their heads by bending their necks sideways, while the cryptodires bend them vertically. Although living pleurodires, such as the matamata Chelus fimbriatus and other snake necks Chelyidae , are all freshwater animals of southern continents, fossil species have been found in all parts of the world and may include marine as well as freshwater forms. Placodonts and Nothosaurs 29 n Fig. Archelon Testudines; Upper Cretaceous; length ca. The giant turtle Archelon ischyrios Cryptodira; Fig. These ribs were probably covered by a thick coat of rubbery skin, as is the extant leatherback turtle Dermochelys coriacea , rather than by the usual horny plates.

There were fewer predators in the sea than on land in those days, so the greater manoeuverability afforded by reduction in weight would have offset the defensive advantages of heavy armour on the back. Furthermore, the limbs were powerful with extremely long, webbed digits that formed broad flippers to propel the animal through the water. No marine turtle, either extinct or extant, has been able to retract its head or limbs into the shell as terrestrial chelonians do. These slow, massive reptiles had stout bodies, short necks and tails, and paddle-like limbs.

Henodus Placodontia; Lower Triassic; length ca. Their large, flattened plate-like teeth were obviously adapted for crushing shellfish, and placodonts probably dived to the bottom of the shallow waters to dig up brachiopods, clams, and other molluscs. In some genera, including Henodus, the teeth have disappeared altogether, as we have seen and, as in modern chelonians, the jaws were probably covered with horny plates.

Ellis suggested that grooves in the jaws might have held n Fig. Placodus Placodontia; Lower Triassic; length ca. Left Head of Placodus; right head of Placochelys. Like the Mesosauria and all other aquatic reptiles, the Placodontia were secondarily aquatic. The latter were an odd collection of possibly unrelated Permian and Triassic reptiles, some lizard-like in appearance, others with small limbs, elongated bodies, and extremely long necks. The fossil of Henodus Fig.

It was one of the last of the placodonts. The skull of the placodonts was short and the nostrils had retreated to a position immediately anterior to the eyes. The front teeth of Placodus Figs. These were then crushed by the blunt grinding teeth, brought together by strong jaw muscles. As can be seen in Fig. It had a tapering, toothless snout that may have been used like forceps, and fewer grinding teeth than Placodus Fig. Smaller, elongated marine reptiles, they existed contemporaneously with the placodonts and early ichthyosaurs, reaching the peak of their development in Late Triassic times.

Their paddle-shaped limbs and feet were strong, their necks long and flexible, and their nostrils had moved slightly backwards from their snouts. Nothosaurus Nothosauria; Upper Triassic length ca. Nothosaurus Fig. The nothosaurs probably spent part of their time fishing at sea, part resting on land. Their feet had five long toes that were webbed to varying degrees — as in Lariosaurus, Ceresiosaurus, and Pistosaurus Fig. Lariosaurus was one of the smaller nothosaurs, but by no means the smallest, for some measured only 20 cm in length. Its short neck and toes were primitive features.

The small webs between its toes would not have been of much use in n Fig. Above Lariosaurus Nothosauria; Middle Triassic; length ca. Centre Ceresio- saurus Nothosauria; Middle Triassic; length ca. Below Pistosaurus Nothosauria; Middle Triassic; length ca. After Palmer Placodonts and Nothosaurs 33 swimming.

Indeed, Lariosaurus probably spent much of its time paddling around in coastal shallows, feeding on small fishes, crustaceans, and molluscs. In contrast, the toes of Ceresiosaurus were relatively much longer than those of most other nothosaurs. In addition, the animal exhibited hyperphalangy — the phenomenon in which the number of phalanges in each toe is increased. The flippers would therefore have been efficient swimming organs, anticipating the great oar-like limbs of the plesiosaurs of the Jurassic period Palmer Indeed,the nothosaurs may well have been ancestral to the Plesiosauria Sect.

The claudiosaurians were diapsids and, like the nothosaurs, have been regarded as being ancestral to the plesiosaurs. They have also been proposed as a sister taxon to them. In the absence of information on groups specifically ancestral to the thalattosaurs, plesiosaurs, and ichthyosaurs, their origin remains a mystery Carroll Claudiosaurus was a long-necked, lizard-like marine reptile whose lifestyle may well have been similar to that of the marine iguana Amblyrhynchus cristatus of the Galapagos Islands.

It probably fed under water between episodes of basking in the sun, poking its long, flexible neck and small head into fronds of seaweed to find edible plants and animals. Its feet were not webbed, and its legs would have been folded against the body when it swam. Propulsion must have been achieved by undulations of the body and long, narrow tail. Buoyancy would have been enhanced by the large amount of cartilage present in the skeleton. The sternum was not well developed, nor was it ossified as in true terrestrial animals: this indicates that Claudiosaurus was not well adapted for locomotion on land Palmer Claudiosaurus order uncertain; Permian-Triassic; length ca.

The first known sphenodontians Sect. Their limbs were reduced while the tail was even longer than the elongated body and probably used for propulsion — there were up to 57 vertebrae in some genera. The nostrils opened back on the snout near the eyes, another adaptation to life in water.

True lizards Squamata were represented by mosasaurs such as the well-known North American Tylosaurus Fig. Thalattosaurus from the Upper Triassic of California was somewhat smaller than Tylosaurus, but both had paddle-like limbs and elongated skulls. As with many aquatic animals, the neck and body were long and slim in Thalattosaurus, the tail elongated so that the animal would have swum in an eel-like fashion, using its feet mainly for steering and braking. They were also used on land when the animals came ashore to lay their eggs.

Askeptosaurus Fig. Its eyes were large and probably adapted for vision in the twilight zone of the ocean. They were strengthened by a ring of bony plates that would have resisted the pressure of the water when the animal dived deeply after its prey. Other varanid-like sea lizards of the Mesozoic were n Fig.

Pleurosaurus Rhynchocephalia; Upper Jurassic; length ca. Tylosaurus Mosasauria; Upper Cretaceous; length ca. Cloudsley-Thompson the Aigialosauria and Dolichosauria. These appeared in Early Cretaceous times and were small animals, only partly adapted for marine life. Indeed, the aigialosaurs appear to have been ancestral to the Upper Cretaceous mosasaurs, which were among the most highly specialised marine reptiles.

As time passed, the Mosasauridae, like many other marine vertebrates, gradually became larger and larger: Tylosaurus reached over 9 m in length. Their adaptations included a retreat of the nostrils to a posterior position on the top of the skull as in Pleurosaurus, modification of the limbs, and broadening of the tail. There n Fig. Askeptosaurus Thalattosauria; Middle Triassic; length ca. After Palmer 36 Amphibious and Early Marine Mesozoic Reptiles was no bending of the backbone either up or down, the tail extending in side view in a straight line from the pelvic region to the tip Fig.

Clearly, the mosasaurs were highly efficient swimmers, propelling themselves through the water by lateral undulations of the elongated body and flattened tail, and using their limbs for balancing and steering Colbert The Mosasauridae were among the most rapacious predators of the Upper Cretaceous seas. Their jaws were very long and beset with rows of strong conical teeth.

The centre of the lower jaw was hinged, which made the gape very elastic so that large chunks of food could be swallowed. No fossils of young mosasaurs have been found, which suggests that the females may have left the oceans and ascended rivers to breed. The young could then have spent their early lives in that more sheltered environment before migrating back to the ocean. Like modern varanid lizards and in common with many other reptiles both living and extinct, the mosasaurs probably used their long, whip-like tails to great effect in defence.

Among the former were the Choristodera, a strange assembly of crocodile-like reptiles that diverged from the main diapsid line during the Lower Cretaceous period, some mya. One of the genera included was Champsosaurus Fig. This arose n Fig. Champsosaurus Choristodera; Upper Cretaceous; length ca. After Palmer Champsosaurs, Phytosaurs and Crocodilians 37 in the Late Cretaceous period, persisted into the Eocene epoch, and became extinct only about 50 mya.

Champsosaurus lived in the rivers and swamps of Europe and North America. It had long, narrow jaws with pointed teeth — like those of the modern gharial Gavialis gangeticus. Although the Lepidosauria and Archosauria were and are both diapsids, they are not closely related. The similarity between Gavialis and Champsosaurus is due to convergence. Narrow jaws are an adaptation for eating fishes. These are caught with a sideways sweep of the head through the water: it would not be possible to move a broad snout quite so rapidly.

It probably ate birds and mammals as well as fishes, as does the Indian gharial. These creatures resembled crocodilians very closely in structure and, presumably, in habits — but were not ancestral to them. Nevertheless, phytosaur genera such as Parasuchus, Rutiodon and Phytosaurus Fig. Left Rutiodon Thecodontia; Upper Triassic; length ca. After Palmer Right Phytosaurus Thecodontia; Upper Triassic; length ca. After Colbert 38 Amphibious and Early Marine Mesozoic Reptiles jaws, and rows of sharp conical teeth — showed remarkable parallel evolution with crocodiles.

Like those of crocodiles, their hind limbs were longer than the fore limbs; but their nostrils were elevated on a bony lump near their eyes, far back in their skulls. In crocodiles the nostrils are placed at the tip of the snout. Furthermore, the phytosaurs had no palate. As in crocodiles, the forms illustrated in Fig. Phytosaurus as reconstructed by M. Colbert is shown about to scavenge on the decaying carcass of a dinosaur. All the thecodonts, including the phytosaurs, became extinct at the end of the Triassic period but the ecological niche they had once occupied was eventually exploited by true crocodiles.

The earliest of the latter were Sphenosuchia, of which Gracilisuchus Fig. This tiny creature n Fig. Early crocodilians. After Palmer Champsosaurs, Phytosaurs and Crocodilians 39 was originally classified with the ornithosuchians Sect. Moreover, it was bipedal and probably chased small lizards, killing them with its powerful jaws armed with sharp, recurved teeth. The structure of its skull, cervical vertebrae, and limb joints prove unmistakeably that it was a crocodilian.

Surprisingly, therefore, the ancestors of true crocodiles must have been small, bipedal animals such as Terrestrisuchus Fig. All these probably fed on small reptiles, insects and other arthropods. Despite their general appearance and insectivorous mode of life, the Saltoposuchidae, like the Sphenosuchidae, possessed a number of diagnostic crocodilian features.

These included the elongation of the main wrist bones into rod-shaped elements and a long backwardly pointing spine on the lower part of the pectoral girdle, while the pelvis had an open acetabulum hip socket. In addition, there were a number of crocodilian specialisations in the skull Parrish ; Benton Terrestrisuchus was smaller and more delicately built than Gracilisuchus. Its body was shorter, its limbs long and slim, and its tail almost twice the length of its head and body combined.

It roamed over the semi-arid plains of Europe during the Late Triassic, snapping up insects and small lizards with its elongated jaws. No doubt it moved mainly on four limbs but, like its ecological equivalents of today, the frilled lizard Chlamydosaurus kingii; Agamidae , the basilisk Basiliscus basiliscus; Iguanidae and the collared lizard Crotaphytus collaris; Iguanidae , it would have reached its greatest speed bipedally. It must have sprinted on two legs, not only when in pursuit of prey but — even more importantly — when escaping from predators.

It was a small, lightly built, quadrupedal animal whose hind limbs were longer than the forelimbs and thereby indicated its bipedal ancestry. In Fig. Several other crocodilian characters in the skeleton have been outlined by Benton Only four families of Mesozoic crocodiles were fully aquatic: Teleosaurus Teleosauridae; Fig. Teleosaurus, from the Lower Jurassic of Europe, was similar in appearance to the gharial see Sect. Its powerful jaws were narrow and elongated, the sharp teeth interlocking when the mouth was closed.

Its back was heavily armoured, its forelimbs short. This richly illustrated book clothes the skeletons of dinosaurs and other Mesozoic reptiles with flesh, and shows how these fascinating animals evolved and probably lived. Expert author John L. Cloudsley-Thompson synthesizes current views on ecology, physiology and behaviour, and outlines the various hypotheses that have been proposed to explain their extinction. Numerous beautiful drawings of the animals and their environment illustrate this exciting monograph.

Cloudsley-Thompson provides an interesting synthesis of current views on their ecology, physiology and behaviour, and outlines the various hypotheses Ecology and Behaviour of Mesozoic Reptiles. The benefit of a low resting metabolism is that it requires far less fuel to sustain bodily functions. By using temperature variations in their surroundings, or by remaining cold when they do not need to move, reptiles can save considerable amounts of energy compared to endothermic animals of the same size.

It is generally assumed that reptiles are unable to produce the sustained high energy output necessary for long distance chases or flying. Energetic studies on some reptiles have shown active capacities equal to or greater than similar sized warm-blooded animals. All reptiles breathe using lungs. Aquatic turtles have developed more permeable skin, and some species have modified their cloaca to increase the area for gas exchange. Lung ventilation is accomplished differently in each main reptile group. In squamates , the lungs are ventilated almost exclusively by the axial musculature.

This is also the same musculature that is used during locomotion. Because of this constraint, most squamates are forced to hold their breath during intense runs. Some, however, have found a way around it. Varanids, and a few other lizard species, employ buccal pumping as a complement to their normal "axial breathing". This allows the animals to completely fill their lungs during intense locomotion, and thus remain aerobically active for a long time. Tegu lizards are known to possess a proto- diaphragm , which separates the pulmonary cavity from the visceral cavity. While not actually capable of movement, it does allow for greater lung inflation, by taking the weight of the viscera off the lungs.

Crocodilians actually have a muscular diaphragm that is analogous to the mammalian diaphragm. The difference is that the muscles for the crocodilian diaphragm pull the pubis part of the pelvis, which is movable in crocodilians back, which brings the liver down, thus freeing space for the lungs to expand. This type of diaphragmatic setup has been referred to as the " hepatic piston ". The airways form a number of double tubular chambers within each lung. On inhalation and exhalation air moves through the airways in the same direction, thus creating a unidirectional airflow through the lungs.

A similar system is found in birds, [85] monitor lizards [86] and iguanas. Most reptiles lack a secondary palate , meaning that they must hold their breath while swallowing. Crocodilians have evolved a bony secondary palate that allows them to continue breathing while remaining submerged and protect their brains against damage by struggling prey.

Skinks family Scincidae also have evolved a bony secondary palate, to varying degrees. Snakes took a different approach and extended their trachea instead. Their tracheal extension sticks out like a fleshy straw, and allows these animals to swallow large prey without suffering from asphyxiation.

How turtles and tortoises breathe has been the subject of much study. To date, only a few species have been studied thoroughly enough to get an idea of how those turtles breathe. The varied results indicate that turtles and tortoises have found a variety of solutions to this problem. The difficulty is that most turtle shells are rigid and do not allow for the type of expansion and contraction that other amniotes use to ventilate their lungs. Some turtles, such as the Indian flapshell Lissemys punctata , have a sheet of muscle that envelops the lungs. When it contracts, the turtle can exhale.

When at rest, the turtle can retract the limbs into the body cavity and force air out of the lungs. When the turtle protracts its limbs, the pressure inside the lungs is reduced, and the turtle can suck air in. Turtle lungs are attached to the inside of the top of the shell carapace , with the bottom of the lungs attached via connective tissue to the rest of the viscera. By using a series of special muscles roughly equivalent to a diaphragm , turtles are capable of pushing their viscera up and down, resulting in effective respiration, since many of these muscles have attachment points in conjunction with their forelimbs indeed, many of the muscles expand into the limb pockets during contraction.

Breathing during locomotion has been studied in three species, and they show different patterns. Adult female green sea turtles do not breathe as they crutch along their nesting beaches. They hold their breath during terrestrial locomotion and breathe in bouts as they rest. North American box turtles breathe continuously during locomotion, and the ventilation cycle is not coordinated with the limb movements.

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The last species to have been studied is the red-eared slider, which also breathes during locomotion, but takes smaller breaths during locomotion than during small pauses between locomotor bouts, indicating that there may be mechanical interference between the limb movements and the breathing apparatus. Box turtles have also been observed to breathe while completely sealed up inside their shells. Reptilian skin is covered in a horny epidermis , making it watertight and enabling reptiles to live on dry land, in contrast to amphibians. Compared to mammalian skin, that of reptiles is rather thin and lacks the thick dermal layer that produces leather in mammals.

In lepidosaurians , such as lizards and snakes, the whole skin is covered in overlapping epidermal scales. Such scales were once thought to be typical of the class Reptilia as a whole, but are now known to occur only in lepidosaurians. Lacking a thick dermis, reptilian leather is not as strong as mammalian leather. It is used in leather-wares for decorative purposes for shoes, belts and handbags, particularly crocodile skin. Reptiles shed their skin through a process called ecdysis which occurs continuously throughout their lifetime. In particular, younger reptiles tend to shed once every 5—6 weeks while adults shed 3—4 times a year.

Once full size, the frequency of shedding drastically decreases. The process of ecdysis involves forming a new layer of skin under the old one. Proteolytic enzymes and lymphatic fluid is secreted between the old and new layers of skin. Consequently, this lifts the old skin from the new one allowing shedding to occur. Traumatic injuries on the other hand, form scars that will not allow new scales to form and disrupt the process of ecdysis. Excretion is performed mainly by two small kidneys.

In diapsids, uric acid is the main nitrogenous waste product; turtles, like mammals , excrete mainly urea. Unlike the kidneys of mammals and birds, reptile kidneys are unable to produce liquid urine more concentrated than their body fluid. This is because they lack a specialized structure called a loop of Henle , which is present in the nephrons of birds and mammals.

Because of this, many reptiles use the colon to aid in the reabsorption of water. Some are also able to take up water stored in the bladder. Excess salts are also excreted by nasal and lingual salt glands in some reptiles. In all reptiles the urinogenital ducts and the anus both empty into an organ called a cloaca. In some reptiles, a midventral wall in the cloaca may open into a urinary bladder, but not all. It is present in all turtles and tortoises as well as most lizards, but is lacking in the monitor lizard , the legless lizards. It is absent in the snakes, alligators, and crocodiles.

Many turtles, tortoises, and lizards have proportionally very large bladders. Turtles have two or more accessory urinary bladders, located lateral to the neck of the urinary bladder and dorsal to the pubis, occupying a significant portion of their body cavity. The right section is located under the liver, which prevents large stones from remaining in that side while the left section is more likely to have calculi.

Most reptiles are insectivorous or carnivorous and have simple and comparatively short digestive tracts due to meat being fairly simple to break down and digest. Digestion is slower than in mammals , reflecting their lower resting metabolism and their inability to divide and masticate their food. While modern reptiles are predominantly carnivorous, during the early history of reptiles several groups produced some herbivorous megafauna : in the Paleozoic , the pareiasaurs ; and in the Mesozoic several lines of dinosaurs. Herbivorous reptiles face the same problems of mastication as herbivorous mammals but, lacking the complex teeth of mammals, many species swallow rocks and pebbles so called gastroliths to aid in digestion: The rocks are washed around in the stomach, helping to grind up plant matter.

The reptilian nervous system contains the same basic part of the amphibian brain, but the reptile cerebrum and cerebellum are slightly larger. Most typical sense organs are well developed with certain exceptions, most notably the snake 's lack of external ears middle and inner ears are present. There are twelve pairs of cranial nerves. Reptiles are generally considered less intelligent than mammals and birds. Larger lizards, like the monitors , are known to exhibit complex behavior, including cooperation.

The Komodo dragon is even known to engage in play, [] as are turtles, which are also considered to be social creatures, [ citation needed ] and sometimes switch between monogamy and promiscuity in their sexual behavior. Most reptiles are diurnal animals. The vision is typically adapted to daylight conditions, with color vision and more advanced visual depth perception than in amphibians and most mammals. In some species, such as blind snakes , vision is reduced. Some snakes have extra sets of visual organs in the loosest sense of the word in the form of pits sensitive to infrared radiation heat.

Such heat-sensitive pits are particularly well developed in the pit vipers , but are also found in boas and pythons. These pits allow the snakes to sense the body heat of birds and mammals, enabling pit vipers to hunt rodents in the dark. Reptiles generally reproduce sexually , though some are capable of asexual reproduction.

Most reptiles have copulatory organs , which are usually retracted or inverted and stored inside the body. In turtles and crocodilians, the male has a single median penis , while squamates, including snakes and lizards, possess a pair of hemipenes , only one of which is typically used in each session. Tuatara, however, lack copulatory organs, and so the male and female simply press their cloacas together as the male discharges sperm. Most reptiles lay amniotic eggs covered with leathery or calcareous shells.

An amnion , chorion , and allantois are present during embryonic life. The eggshell 1 protects the crocodile embryo 11 and keeps it from drying out, but it is flexible to allow gas exchange. The chorion 6 aids in gas exchange between the inside and outside of the egg.

It allows carbon dioxide to exit the egg and oxygen gas to enter the egg. The albumin 9 further protects the embryo and serves as a reservoir for water and protein.

Ecology and Behaviour of Mesozoic Reptiles - Mesozoic Reptiles

The allantois 8 is a sac that collects the metabolic waste produced by the embryo. The amniotic sac 10 contains amniotic fluid 12 which protects and cushions the embryo. The amnion 5 aids in osmoregulation and serves as a saltwater reservoir. The yolk sac 2 surrounding the yolk 3 contains protein and fat rich nutrients that are absorbed by the embryo via vessels 4 that allow the embryo to grow and metabolize. The air space 7 provides the embryo with oxygen while it is hatching.

This ensures that the embryo will not suffocate while it is hatching. There are no larval stages of development. Viviparity and ovoviviparity have evolved in many extinct clades of reptiles and in squamates. In the latter group, many species, including all boas and most vipers, utilize this mode of reproduction. The degree of viviparity varies; some species simply retain the eggs until just before hatching, others provide maternal nourishment to supplement the yolk, and yet others lack any yolk and provide all nutrients via a structure similar to the mammalian placenta.

The earliest documented case of viviparity in reptiles is the Early Permian mesosaurs , [] although some individuals or taxa in that clade may also have been oviparous because a putative isolated egg has also been found. Several groups of Mesozoic marine reptiles also exhibited viviparity, such as mosasaurs , ichthyosaurs , and Sauropterygia , a group that include pachypleurosaurs and Plesiosauria. Asexual reproduction has been identified in squamates in six families of lizards and one snake. In some species of squamates, a population of females is able to produce a unisexual diploid clone of the mother.

This form of asexual reproduction, called parthenogenesis , occurs in several species of gecko , and is particularly widespread in the teiids especially Aspidocelis and lacertids Lacerta. In captivity, Komodo dragons Varanidae have reproduced by parthenogenesis. Parthenogenetic species are suspected to occur among chameleons , agamids , xantusiids , and typhlopids. Some reptiles exhibit temperature-dependent sex determination TDSD , in which the incubation temperature determines whether a particular egg hatches as male or female.

TDSD is most common in turtles and crocodiles, but also occurs in lizards and tuatara. Many small reptiles, such as snakes and lizards that live on the ground or in the water, are vulnerable to being preyed on by all kinds of carnivorous animals. Thus avoidance is the most common form of defense in reptiles. Reptiles tend to avoid confrontation through camouflage. Two major groups of reptile predators are birds and other reptiles, both of which have well developed color vision. Thus the skins of many reptiles have cryptic coloration of plain or mottled gray, green, and brown to allow them to blend into the background of their natural environment.

When camouflage fails to protect them, blue-tongued skinks will try to ward off attackers by displaying their blue tongues, and the frill-necked lizard will display its brightly colored frill. These same displays are used in territorial disputes and during courtship. Rattlesnakes rapidly vibrate the tip of the tail, which is composed of a series of nested, hollow beads to ward of approaching danger. In contrast to the normal drab coloration of most reptiles, the lizards of the genus Heloderma the Gila monster and the beaded lizard and many of the coral snakes have high-contrast warning coloration, warning potential predators they are venomous.

Camouflage does not always fool a predator. When caught out, snake species adopt different defensive tactics and use a complicated set of behaviors when attacked. Some first elevate their head and spread out the skin of their neck in an effort to look large and threatening. Failure of this strategy may lead to other measures practiced particularly by cobras, vipers, and closely related species, which use venom to attack. The venom is modified saliva, delivered through fangs from a venom gland.

When a crocodilian is concerned about its safety, it will gape to expose the teeth and yellow tongue.

Ecology and Behaviour of Mesozoic Reptiles

If this doesn't work, the crocodilian gets a little more agitated and typically begins to make hissing sounds. After this, the crocodilian will start to change its posture dramatically to make itself look more intimidating. The body is inflated to increase apparent size. If absolutely necessary it may decide to attack an enemy. Some species try to bite immediately. Some will use their heads as sledgehammers and literally smash an opponent, some will rush or swim toward the threat from a distance, even chasing the opponent onto land or galloping after it.

Many species also possess canine -like teeth. These are used primarily for seizing prey, but are also used in fighting and display. Geckos , skinks , and other lizards that are captured by the tail will shed part of the tail structure through a process called autotomy and thus be able to flee. The detached tail will continue to wiggle, creating a deceptive sense of continued struggle and distracting the predator's attention from the fleeing prey animal. The detached tails of leopard geckos can wiggle for up to 20 minutes. In the shingleback skink and some species of geckos, the tail is short and broad and resembles the head, so that the predators may attack it rather than the more vulnerable front part.

Reptiles that are capable of shedding their tails can partially regenerate them over a period of weeks. The new section will however contain cartilage rather than bone, and will never grow to the same length as the original tail. It is often also distinctly discolored compared to the rest of the body and may lack some of the external sculpting features seen in the original tail.

Dinosaurs have been widely depicted in culture since the English palaeontologist Richard Owen coined the name dinosaur in As soon as , the Crystal Palace Dinosaurs were on display to the public in south London. The depictions range from the realistic, as in the television documentaries of the s and first decade of the 21st century, or the fantastic, as in the monster movies of the s and s.

The snake or serpent has played a powerful symbolic role in different cultures. In Egyptian history , the Nile cobra adorned the crown of the pharaoh. It was worshipped as one of the gods and was also used for sinister purposes: murder of an adversary and ritual suicide Cleopatra. In Greek mythology snakes are associated with deadly antagonists, as a chthonic symbol, roughly translated as earthbound. The nine-headed Lernaean Hydra that Hercules defeated and the three Gorgon sisters are children of Gaia , the earth. Medusa was one of the three Gorgon sisters who Perseus defeated.

Medusa is described as a hideous mortal, with snakes instead of hair and the power to turn men to stone with her gaze. After killing her, Perseus gave her head to Athena who fixed it to her shield called the Aegis. The Titans are depicted in art with their legs replaced by bodies of snakes for the same reason: They are children of Gaia, so they are bound to the earth. The cobra is seen on the neck of Shiva , while Vishnu is depicted often as sleeping on a seven-headed snake or within the coils of a serpent.

There are temples in India solely for cobras sometimes called Nagraj King of Snakes , and it is believed that snakes are symbols of fertility. In the annual Hindu festival of Nag Panchami , snakes are venerated and prayed to. The turtle has a prominent position as a symbol of steadfastness and tranquility in religion, mythology, and folklore from around the world.

Deaths from snakebites are uncommon in many parts of the world, but are still counted in tens of thousands per year in India. To produce antivenom, a mixture of the venoms of different species of snake is injected into the body of a horse in ever-increasing dosages until the horse is immunized. Blood is then extracted; the serum is separated, purified and freeze-dried.

Geckos have also been used as medicine, especially in China.

Ecology and Behaviour of Mesozoic Reptiles Ecology and Behaviour of Mesozoic Reptiles
Ecology and Behaviour of Mesozoic Reptiles Ecology and Behaviour of Mesozoic Reptiles
Ecology and Behaviour of Mesozoic Reptiles Ecology and Behaviour of Mesozoic Reptiles
Ecology and Behaviour of Mesozoic Reptiles Ecology and Behaviour of Mesozoic Reptiles
Ecology and Behaviour of Mesozoic Reptiles Ecology and Behaviour of Mesozoic Reptiles
Ecology and Behaviour of Mesozoic Reptiles Ecology and Behaviour of Mesozoic Reptiles
Ecology and Behaviour of Mesozoic Reptiles Ecology and Behaviour of Mesozoic Reptiles

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