Jurassic period. Key Features

And Switzerland. The beginning of the Jurassic period is determined by radiometric method at 185±5 million years, the end - at 132±5 million years; the total duration of the period is about 53 million years (according to 1975 data).

The Jurassic system in its modern extent was identified in 1822 by the German scientist A. Humboldt under the name “Jurassic formation” in the Jura mountains (Switzerland), Swabian and Franconian Albs (). In the territory, Jurassic deposits were first established by the German geologist L. Buch (1840). The first scheme of their stratigraphy and division was developed by the Russian geologist K. F. Roulier (1845-49) in the Moscow region.

Divisions. All the main divisions of the Jurassic system, which were subsequently included in the general stratigraphic scale, are identified in the territory of Central Europe and Great Britain. The division of the Jurassic system into departments was proposed by L. Buch (1836). The foundations of the staged division of the Jurassic were laid by the French geologist A. d'Orbigny (1850-52). The German geologist A. Oppel was the first to produce (1856-58) a detailed (zonal) division of Jurassic deposits. See table.

Most foreign geologists classify the Callovian Stage as the middle section, citing the priority of the three-member division of the Jurassic (black, brown, white) by L. Bukh (1839). The Tithonian Stage is recognized in the sediments of the Mediterranean biogeographical province (Oppel, 1865); for the northern (boreal) province, its equivalent is the Volgian stage, first identified in the Volga region (Nikitin, 1881).

general characteristics. Jurassic deposits are widespread on all continents and are present in the periphery, parts of ocean basins, forming the base of their sedimentary layer. By the beginning of the Jurassic period, two large continental masses were separated in the structure of the earth's crust: Laurasia, which included platforms and Paleozoic folded regions of North America and Eurasia, and Gondwana, which united the platforms of the Southern Hemisphere. They were separated by the Mediterranean geosynclinal belt, which was the Tethys oceanic basin. The opposite hemisphere of the Earth was occupied by the Pacific Ocean depression, along the margins of which geosynclinal regions of the Pacific geosynclinal belt developed.

In the Tethys oceanic basin, throughout the Jurassic period, deep-sea siliceous, clayey and carbonate sediments accumulated, accompanied in places by manifestations of submarine tholeiitic-basaltic volcanism. The wide southern passive margin of Tethys was an area of ​​accumulation of shallow-water carbonate sediments. On the northern margin, which in different places and at different times had both an active and passive character, the composition of sediments is more variegated: sandy-clayey, carbonate, in places flysch, sometimes with the manifestation of calc-alkaline volcanism. Geosynclinal areas of the Pacific belt developed in the regime of active margins. They are dominated by sandy-clayey sediments, a lot of siliceous ones, and volcanic activity was very active. The main part of Laurasia in the Early and Middle Jurassic was land. Marine transgressions from geosynclinal belts captured in the Early Jurassic only the territories of Western Europe, the northern part of Western Siberia, the eastern margin of the Siberian Platform, and in the Middle Jurassic the southern part of the East European Platform. At the beginning of the Late Jurassic, the transgression reached its maximum, spreading to the western part of the North American platform, the Eastern European platform, all of Western Siberia, the Ciscaucasia and the Transcaspian region. Gondwana remained dry land throughout the Jurassic period. Marine transgressions from the southern edge of Tethys captured only the northeastern part of the African and northwestern part of the Hindustan platform. The seas within Laurasia and Gondwana were vast but shallow epicontinental basins where thin sandy-clayey sediments accumulated, and in the Late Jurassic in areas adjacent to the Tethys - carbonate and lagoonal (gypsum and salt-bearing) sediments. In the rest of the territory, Jurassic deposits are either absent or represented by continental sandy-clayey, often coal-bearing strata, filling individual depressions. The Pacific Ocean in the Jurassic was a typical oceanic basin, where thin carbonate-siliceous sediments and covers of tholeiitic basalts accumulated, preserved in the western part of the basin. At the end of the Middle - beginning of the Late Jurassic, the formation of “young” oceans began; The opening of the Central Atlantic, the Somali and North Australian basins of the Indian Ocean, and the Amerasian basin of the Arctic Ocean occurs, thereby beginning the process of dismemberment of Laurasia and Gondwana and the separation of modern continents and platforms.

The end of the Jurassic period is the time of manifestation of the Late Cimmerian phase of Mesozoic folding in geosynclinal belts. In the Mediterranean belt, folding movements manifested themselves in places at the beginning of the Bajocian, in Pre-Callovian time (Crimea, Caucasus), and at the end of the Jurassic (Alps, etc.). But they reached a particular scale in the Pacific belt: in the Cordillera of North America (Nevadian folding), and the Verkhoyansk-Chukotka region (Verkhoyansk folding), where they were accompanied by the introduction of large granitoid intrusions, and completed the geosynclinal development of the regions.

The organic world of the Earth in the Jurassic period had a typically Mesozoic appearance. Among marine invertebrates, cephalopods (ammonites, belemnites) flourish; bivalves and gastropods, six-rayed corals, and “irregular” sea urchins are widespread. Among vertebrates in the Jurassic period, reptiles (lizards) predominated sharply, reaching gigantic sizes (up to 25-30 m) and great diversity. There are known terrestrial herbivores and predatory lizards (dinosaurs), sea-swimming ones (ichthyosaurs, plesiosaurs), and flying lizards (pterosaurs). Fish are widespread in water basins; the first (toothed) birds appear in the air in the Late Jurassic. Mammals, represented by small, still primitive forms, are not very common. The land cover of the Jurassic period is characterized by the maximum development of gymnosperms (cycads, bennetites, ginkgos, conifers), as well as ferns.

Eras. Lasted for 56 million years. Began 201 million years ago and ended 145 million years ago. The geochronological scale of the history of the Earth of all eons, eras and periods is located.

The name “Jura” was given by the name of the mountain range of the same name in Switzerland and France, where deposits of this period were first discovered. Later, geological strata of the Jurassic period were discovered in many other places on the planet.

During the Jurassic period, the Earth almost completely recovered from the largest in history. Various life forms - marine organisms, land plants, insects and many animal species - begin to flourish and increase their species diversity. In the Jurassic period, dinosaurs reigned - large, and sometimes simply gigantic lizards. Dinosaurs existed almost anywhere and everywhere - in the seas, rivers and lakes, in swamps, forests, and open spaces. Dinosaurs have become so diverse and widespread that over millions of years of evolution, some of them began to differ radically from each other. Dinosaurs included both herbivores and carnivores. Some of them were the size of a dog, while others reached a height of more than ten meters.

One of the species of lizards in the Jurassic period became the ancestor of birds. Archeopteryx, which existed just at this time, is considered an intermediate link between reptiles and birds. In addition to lizards and giant dinosaurs, warm-blooded mammals already lived on earth. Mammals of the Jurassic period were mostly small in size and occupied rather insignificant niches in the living space of the earth of those times. Against the background of the prevailing number and diversity of dinosaurs, they were practically invisible. This will continue throughout the Jurassic and subsequent periods. Mammals will become the rightful masters of the Earth only after the Cretaceous-Paleogene extinction, when all dinosaurs disappear from the face of the planet, opening the way for warm-blooded animals.

Animals of the Jurassic period

Allosaurus

Apatosaurus

Archeopteryx

Barosaurus

Brachiosaurus

Diplodocus

Dryosaurs

Giraffatitan

Camarasaurus

Camptosaurus

Kentrosaurus

Liopleurodon

Megalosaurus

Pterodactyls

Rhamphorhynchus

Stegosaurus

Scelidosaurus

Ceratosaurus

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And was replaced by chalk, and had a duration of about 56 million years.

Geography and climate

During the Jurassic period, the supercontinent Pangea began to split into two separate continents:

• the northern part known as Laurasia (which eventually split into North America and Eurasia, opening basins to the Atlantic Ocean and the Gulf of Mexico)
• the southern part - Gondwanaland - drifted east (and eventually divided into Antarctica, Madagascar, India and Australia, and its western part formed Africa and South America).

This process of Pangea's separation, along with warmer global temperatures, allowed reptiles such as dinosaurs to diversify and dominate the Earth for long periods of time.

Plant life

During the Mesozoic era, plants developed the ability to lead a terrestrial lifestyle and not be limited only to the oceans. By the beginning of the Jurassic, life came from bryophytes, low-growing bryophytes and liverworts, which had no vascular tissue and were limited to wet, marshy areas.

Ginkgo trees

Ferns and gingaceae, which had roots and vascular tissue for transporting water and nutrients, and reproduced by spores, were the dominant plants of the Early Jurassic. During the Jurassic period, a new way of plant reproduction appeared. Gymnosperms, such as conifers, have evolved pollen that is dispersed over long distances by the wind to pollinate female cones. This method of reproduction made it possible to significantly increase the number of gymnosperms by the end of the Jurassic period. Flowering plants did not evolve until the Cretaceous period.

Age of Dinosaurs

As depicted in the movie Jurassic Park, reptiles were the dominant animal life form during the Jurassic period. They overcame evolutionary obstacles that limited . Reptiles had strong, ossified skeletons with advanced muscular systems to support and move the body. Some of the largest animals that ever lived were the dinosaurs of the Jurassic period. Reptiles could also develop amniotic eggs that were incubated on land.

sauropods

Sauropods (lizard-footed dinosaurs) are herbivorous quadrupeds with long necks and heavy tails. Many sauropods, such as brachiosaurs, were huge. Representatives of some genera had a body length of about 25 m, and weight ranged from 50-100 tons, which makes them the largest land animals that have ever existed on Earth. Their skulls were relatively small, with nostrils raised high towards the eyes. Such small skulls meant very small brains. Despite their small brains, this group of animals flourished during the Jurassic period and had a wide geographic distribution. Sauropod fossils have been found on every continent except Antarctica. Other famous Jurassic dinosaurs include stegosaurs and flying pterosaurs.

Carnosaurs were one of the main predators of the Mesozoic era. The genus Allosaurus was one of the most widespread carnosaurs in North America. They are similar to later tyrannosaurs, although studies have shown that they have little in common. Allosaurs had strong hind limbs, heavy front legs and long jaws.

Early mammals

Adelobazilevs

Dinosaurs may have been the dominant land animals, but they were not the only fauna. Early mammals were mostly very small herbivores or insectivores, and did not compete with larger reptiles. Adelobasileus is a predatory ancestor of mammals. He had a special structure of the inner ear and jaws. This animal appeared at the end of the Triassic period.

In August 2011, scientists from China announced the discovery of Yuramaya. This tiny mid-Jurassic animal caused excitement among scientists because it was a clear ancestor of placental mammals, indicating that mammals evolved much earlier than previously thought.

Sea life

Plesiosaur

The Jurassic period was also very diverse. The largest marine predators were plesiosaurs. These carnivorous marine reptiles typically had wide bodies and long necks with four flipper-shaped limbs.

Ichthyosaur is a marine reptile that was most common in the Early Jurassic period. Because some fossils have been found with smaller individuals of their species inside their bodies, it is suggested that these animals may have been among the first to experience internal pregnancy and give birth to live young.

Cephalopods were also widespread during the Jurassic period and included the ancestors of modern squids. Among the most beautiful fossils of marine life are the spiral-shaped shells of ammonites.

For the first time, deposits of this period were found in the Jura (mountains in Switzerland and France), hence the name of the period. The Jurassic period is divided into three divisions: Leyas, Doger and Malm.

The deposits of the Jurassic period are quite diverse: limestones, clastic rocks, shales, igneous rocks, clays, sands, conglomerates, formed in a wide variety of conditions.

Sedimentary rocks containing many representatives of fauna and flora are widespread.

Intense tectonic movements at the end of the Triassic and the beginning of the Jurassic periods contributed to the deepening of large bays, which gradually separated Africa and Australia from Gondwanaland. The gulf between Africa and America has deepened. Depressions formed in Eurasia: German, Anglo-Paris, West Siberian. The Arctic Sea flooded the northern coast of Laurasia.

Intense volcanism and mountain-building processes determined the formation of the Verkhoyansk fold system. The formation of the Andes and Cordilleras continued. Warm sea currents reached Arctic latitudes. The climate became warm and humid. This is evidenced by the significant distribution of coral limestones and the remains of thermophilic fauna and flora. Very few deposits of dry climates are found: lagoonal gypsum, anhydrites, salts and red sandstones. The cold season already existed, but it was characterized only by a decrease in temperature. There was no snow or ice.

The climate of the Jurassic period depended not only on sunlight. Many volcanoes and outpourings of magma onto the bottom of the oceans heated the water and atmosphere, saturating the air with water vapor, which then rained onto the land, flowing in stormy streams into lakes and oceans. This is evidenced by numerous freshwater deposits: white sandstones alternating with dark loams.

The warm and humid climate favored the flourishing of the plant world. Ferns, cycads, and conifers formed vast swampy forests. Araucarias, thujas, and cycads grew on the coast. Ferns and horsetails formed the undergrowth. In the Lower Jurassic, throughout the northern hemisphere, vegetation was quite monotonous. But starting from the Middle Jurassic, two plant zones can be identified: the northern, in which ginkgo and herbaceous ferns predominated, and the southern with bennetites, cycads, araucarias, and tree ferns.

The characteristic ferns of the Highland period were matonia, which are still preserved in the Malayan

archipelago. Horsetails and mosses were almost no different from modern ones. The place of extinct seed ferns and cordaites is taken by cycads, which still grow in tropical forests.

Ginkgo plants were also widespread. Their leaves turned edge-on to the sun and resembled huge fans. From North America and New Zealand to Asia and Europe, dense forests of coniferous plants - araucarias and bennetites - grew. The first cypress and possibly spruce trees appear.

Representatives of the Jurassic conifers also include sequoia - the modern giant California pine. Currently, redwoods remain only on the Pacific coast of North America. Some forms have been preserved. even more ancient plants, such as glassopteris. But there are few such plants, since they were replaced by more advanced ones.

The lush vegetation of the Jurassic period contributed to the widespread distribution of reptiles. Dinosaurs have evolved significantly. Among them, lizard-hatched and ornithischian are distinguished. Lizards moved on four legs, had five toes on their feet, and ate plants. Most of them had a long neck, small head and long tail. They had two brains: one small one in the head; the second is much larger in size - at the base of the tail.

The largest of the Jurassic dinosaurs was the Brachiosaurus, reaching a length of 26 m and weighing about 50 tons. It had columnar legs, a small head, and a thick long neck. Brachiosaurs lived on the shores of Jurassic lakes and fed on aquatic vegetation. Every day, the brachiosaurus needed at least half a ton of green mass.

Diplodocus is the oldest reptile, its length was 28 m. It had a long thin neck and a long thick tail. Like a brachiosaurus, Diplodocus walked on four legs, the hind legs being longer than the front ones. Diplodocus spent most of its life in swamps and lakes, where it grazed and escaped from predators.

Brontosaurus was relatively tall, had a large hump on its back and a thick tail. Its length was 18 m. The vertebrae of the brontosaurus were hollow. Chisel-shaped small teeth were densely located on the jaws of the small head. The brontosaurus lived in swamps and on the shores of lakes.

160 million years ago, the rich plant world provided food for the giant sauropods that had emerged by this time, and also provided shelter for a huge number of small mammals and dinosaurs. At this time, conifers, ferns, horsetails, tree ferns and cycads were widespread.

A distinctive feature of the Jurassic period was the appearance and flourishing of giant lizard-hipped herbivorous dinosaurs, sauropods, the largest land animals that ever existed. Despite their size, these dinosaurs were quite numerous.

Their fossilized remains are found on all continents (except Antarctica) in rocks from the Early Jurassic to the Late Cretaceous, although they were most common in the second half of the Jurassic. At the same time, sauropods reach their largest sizes. They survived until the Late Cretaceous, when the huge hadrosaurs ("duck-billed dinosaurs") began to dominate the terrestrial herbivores.

Externally, all sauropods looked similar to each other: with an extremely long neck, an even longer tail, a massive but relatively short body, four column-like legs and a relatively small head. In different species, only the position of the body and the proportions of individual parts could change. For example, such sauropods of the Late Jurassic period as brachiosaurs (Brachiosaurus - “shouldered lizard”) were higher in the shoulder girdle than in the pelvic girdle, while contemporary diplodocus (Diplodocus - “double appendage”) were significantly lower, and at the same time their hips rose above their shoulders. Some sauropod species, such as Camarasaurus ("chamber lizard"), had a relatively short neck, only slightly longer than the body, while others, such as diplodocus, had a neck more than twice as long as the body.

Teeth and diet

The external similarity of sauropods masks the unexpectedly wide diversity in the structure of their teeth and, consequently, in their feeding methods.

The Diplodocus skull helped paleontologists understand the feeding method of this dinosaur. The abrasion of the teeth indicates that he plucked leaves either from below or from above him.

Many books on dinosaurs used to mention the "small, thin teeth" of sauropods, but it is now known that the teeth of some of them, such as Camarasaurs, were massive and strong enough to grind even very hard plant food, while the long and thin ones Diplodocus's pencil-shaped teeth do appear unable to withstand the significant stress of chewing hard plants.

diplodocus (Diplodocus). Its long neck allowed it to “comb” food from the tallest coniferous plants. It is believed that Diplodocus lived in small herds and ate tree shoots.

In a study of diplodocus teeth carried out in recent years in England, unusual wear on their lateral surfaces was discovered. This pattern of tooth wear provided the key to understanding how these huge animals could feed. The side surface of the teeth could only wear down if something moved between them. Apparently, Diplodocus used its teeth to tear apart tufts of leaves and shoots, acting as a comb, while its lower jaw could move slightly back and forth. Most likely, when the animal stripped plants captured below by moving its head up and back, the lower jaw was moved back (the upper teeth were located in front of the lower ones), and when it pulled the branches of tall trees located above down and back, it pushed the lower jaw forward (the lower teeth were in front of the upper teeth).

Brachiosaurus probably used its shorter, slightly pointed teeth to pluck only high-lying leaves and shoots, since the vertical orientation of its body, due to the longer front legs, made it difficult to feed on plants growing low above the soil.

Narrow specialization

Camarasaurus, somewhat smaller in size than the giants mentioned above, had a relatively short and thicker neck and most likely fed on leaves located at an intermediate height between the feeding levels of brachiosaurs and diplodocus. It had a tall, rounded and more massive skull compared to other sauropods, as well as a more massive and stronger lower jaw, indicating a better ability to grind hard plant food.

The details of the anatomical structure of sauropods described above show that within the same ecological system (in the forests that covered most of the land at that time), sauropods ate different plant foods, obtaining them differently at different levels. This division by feeding strategy and type of food, which can be seen in herbivore communities today, is called “tropical partitioning.”

Brachiosaurus reached more than 25 m in length and 13 m in height. Their fossilized remains and fossilized eggs are found in East Africa and North America. They probably lived in herds like modern elephants.

The main difference between today's herbivore ecosystems and those of the Late Jurassic, which were dominated by sauropods, concerns only the mass and height of the animals. None of the modern herbivores, including elephants and giraffes, reach a height comparable to that of most large sauropods, and no modern land animal requires such enormous amounts of food as these giants.

The other end of the scale

Some sauropods that lived in the Jurassic period reached fantastic sizes, for example, the brachiosaurus-like Supersaurus, whose remains were found in the USA (Colorado), probably weighed about 130 tons, that is, it was many times larger than a large male African elephant. But these supergiants shared land with tiny creatures hiding underground that did not belong to dinosaurs or even reptiles. The Jurassic period was a time of existence of numerous ancient mammals. These small, furred, viviparous, milk-feeding warm-blooded animals were called multitubercular because of the unusual structure of their molars: numerous cylindrical “tubercles” fused together to form uneven surfaces, perfectly adapted to grinding plant food.

Polytubercles were the largest and most diverse group of mammals of the Jurassic and Cretaceous periods. They are the only omnivorous mammals of the Mesozoic era (the others were specialized insectivores or carnivores). They are known from Late Jurassic deposits, but recent finds show that they are close to a little-known group of extremely ancient mammals of the Late Triassic, the so-called. Haramides.

The structure of the skull and teeth was very similar to today's rodents; they had two pairs of protruding incisors, giving them the appearance of a typical rodent. Behind the incisors there was a gap that did not contain teeth, followed by molars to the very end of the small jaws. However, the multitubercular teeth closest to the incisors had an unusual structure. In fact, these were the first false-rooted (premolar) teeth with curved sawtooth edges.

This unusual dental structure has reappeared in the process of evolution in some of the modern marsupials, for example, in the rat kangaroos of Australia, whose teeth are of the same shape and located in the same place in the jaw as the false-rooted teeth of polytubercles. When chewing food at the moment of closing the jaws, multituberculates could move the lower jaw back, moving these sharp saw-toothed teeth across the food fibers, and the long incisors could be used to pierce dense plants or the hard exoskeletons of insects.

A saurian megalosaurus (Megalosaurus) and its young that overtook an ornithischian scelidosaurus (Scelidosaurus). Scelidosaurus is an ancient species of dinosaur of the Jurassic period with unevenly developed limbs, reaching 4 m in length. Its dorsal shell helped protect itself from predators.

The combination of sharp front incisors, serrated blades and chewing teeth means that the feeding apparatus of multitubercles was quite versatile. Today's rodents are also a very successful group of animals, thriving in a wide variety of ecological systems and habitats. Most likely, it was the highly developed dental apparatus, which allows them to eat a variety of foods, that became the reason for the evolutionary success of multitubercles. Their fossilized remains, found on most continents, belong to different species: some of them apparently lived in trees, while others, reminiscent of modern gerbils, were probably adapted to exist in arid desert climates.

Changing Ecosystems

The existence of polytubercles spans a period of 215 million years, extending from the Late Triassic through the entire Mesozoic era to the Oligocene epoch of the Cenozoic era. This phenomenal success, unique among mammals and most terrestrial tetrapods, makes polytubercles the most successful group of mammals.

Small animal ecosystems of the Jurassic period also included small lizards of a wide variety of species and even their aquatic forms.

Thrinadoxon (cynodont species). Its limbs protruded slightly to the sides, and were not located under the body, as in modern mammals.

They and the rarely encountered reptiles of the group of synapsids (“beast-like reptiles”), tritylodonts, who survived to this time, lived at the same time and in the same ecosystems as polytubercular mammals. Tritylodonts were numerous and widespread throughout the Triassic period, but, like other cynodonts, suffered greatly during the Late Triassic extinction event. They are the only group of cynodonts to survive into the Jurassic period. In appearance, they, like multitubercular mammals, were very similar to modern rodents. That is, a significant part of the ecosystems of small animals of the Jurassic period consisted of animals resembling rodents: trilodonts and polytubercular mammals.

Polytuberculates were by far the most numerous and diverse group of mammals of the Jurassic period, but other groups of mammals existed at this time, including: morganacodonts (the oldest mammals), amphilestids (peramurids), amphitherids (amphitherids), tynodonts ( tinodontids) and docodonts.

At the end of the Jurassic period, significant changes occurred at the other end of the size scale in the group of large bipedal predatory dinosaurs, theropods, represented at this time by allosaurs (AUosaurus - “strange lizards”). At the end of the Jurassic period, a group of theropods emerged, called spinosaurids (“spiny or spiny lizards”), whose distinctive feature was a crest of long processes of the trunk vertebrae, which, perhaps, like the dorsal sail of some pelycosaurs, helped them regulate body temperature. Spinosaurids such as Siamosaurus (“lizard from Siam”), which reached a length of 12 m, along with other theropods shared the niche of the largest predators in the ecosystems of that time.

Spinosaurids had non-serrated teeth and elongated, less massive skulls compared to other theropods of this time. These structural features indicate that they differed in their feeding method from such theropods as allosaurs, Eustreptospondylus (“highly curved vertebrae”) and ceratosaurs (Ceratosaurus - “horned lizard”), and most likely hunted other prey.

Bird-like dinosaurs

In Late Jurassic time, other types of theropods arose, very different from such huge, weighing up to 4 tons, predators as allosaurus. These were ornithominids - long-legged, long-necked, small-headed, toothless omnivores, strikingly reminiscent of modern ostriches, which is why they got their name “bird imitators”.

The earliest ornithominid, Elaphrosaums ("light lizard"), from the Late Jurassic deposits of North America had light, hollow bones and a toothless beak, and its limbs, both hind and forelimbs, were shorter than those of later Cretaceous ornithominids, and, accordingly, it was a slower animal.

Another ecologically important group of dinosaurs that arose in the Late Jurassic are the nodosaurs, four-legged dinosaurs with massive, shell-covered bodies, short, relatively thin limbs, a narrow head with an elongated snout (but with massive jaws), small leaf-shaped teeth, and a horny beak. Their name (“knobby lizards”) is associated with the bony plates covering the skin, protruding processes of the vertebrae and growths scattered across the skin, which served as protection from attacks by predators. Nodosaurs became widespread only in the Cretaceous period, and in the Late Jurassic they, along with huge tree-eating sauropods, were only one of the elements of a community of herbivorous dinosaurs that served as prey for a number of huge predators.