BIOLOGY OF THE SAUROPOD DINOSAURS THE EVOLUTION OF GIGANTISM PDF

BIOLOGY OF THE SAUROPOD DINOSAURS THE EVOLUTION OF GIGANTISM PDF

Hence, they are of great interest in understanding the evolution of gigantism and the biophysical constraints acting upon terrestrial life (Clauss ;Sander et al. The unique gigantism of sauropod dinosaurs was made possible by a high basal . in Amniote Paleobiology: Perspectives on the Evolution of Mammals, Birds. Biology of the Sauropod Dinosaurs reports on the latest results from Sauropod Biology and the Evolution of Gigantism: What Do We Know?.

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They had very long necks, long tails, small heads relative to the rest of their bodyand four thick, pillar-like legs.

They are notable for the enormous sizes attained by some species, and the group includes the largest animals to have ever lived on land. Well-known genera include BrachiosaurusDiplodocusApatosaurus and Brontosaurus. Sauropods first appeared in the late Triassic Period[7] where they somewhat resembled the closely related and possibly ancestral group ” Prosauropoda “. By the Late Jurassic million years agosauropods had become widespread especially the diplodocids and biloogy.

By the Late Cretaceousthose groups had mainly been replaced by the titanosaurswhich dinosars a near-global distribution.

Biology of the sauropod dinosaurs: the evolution of gigantism

However, as with all other non-avian dinosaurs alive at the time, the titanosaurs died out in the Cretaceous—Paleogene extinction event. Fossilised remains of sauropods have been found on every continent, including Antarctica. The name Sauropoda was coined by O. Marsh inand is derived from Greekmeaning “lizard foot”.

Complete sauropod fossil finds are rare. Many species, especially the largest, are known only from isolated and disarticulated bones. Many near-complete specimens lack heads, tail tips and limbs.

Sauropods were herbivorous plant-eatingusually quite long-necked [13] quadrupeds four-leggedoften with spatulate spatula-shaped: They had tiny heads, massive bodies, and most had long tails. Their hind legs were thick, straight, and powerful, ending in club-like feet with five toes, though only the inner three or in some cases four bore claws. Their forelimbs were rather more slender and ended in pillar-like hands built for supporting weight; only the thumb bore a claw.

Many illustrations of sauropods in the flesh miss these facts, inaccurately depicting sauropods with hooves capping the claw-less digits of the feet, or multiple claws or hooves on the hands. The proximal caudal vertebrae are extremely diagnostic for sauropods. The sauropods’ most defining characteristic was their size. Their only real competitors in terms of size are the rorqualssuch as the blue whale. But, unlike whales, sauropods were primarily terrestrial animals.

Their body structure did not vary as much as other dinosaurs, perhaps due to size constraints, but they displayed ample variety. Some, like the diplodocidspossessed tremendously long tails, which they may have been able to crack like a whip as a signal or to deter or injure predators, [15] or to make sonic booms. However, a research published in speculated that the size estimates of A. The longest terrestrial animal alive today, the reticulated pythononly reaches lengths of 6.

Others, like the brachiosauridswere extremely tall, with high shoulders and extremely long necks. By comparison, the giraffethe tallest of all living land animals, is only 4. There was poor and now missing evidence that so-called Bruhathkayosaurusmight have weighed over metric tons but this has been questioned. Unlike other sauropods, whose necks could grow to up to four times the length of their backs, the neck of Brachytrachelopan was shorter than its backbone. On or shortly before 29 March a sauropod footprint about 5.

As massive quadrupedssauropods developed specialized graviportal weight-bearing limbs. The hind feet were broad, and retained three claws in most species. The front feet of sauropods were very dissimilar from those of modern large quadrupeds, such as elephants. Rather than splaying out to the sides to create a wide foot as in elephants, the manus bones of sauropods were arranged in fully vertical columns, with extremely reduced finger bones though it is not clear if the most primitive sauropods, such as Vulcanodon and Barapasaurushad such forefeet.

The arrangement of the forefoot bone metacarpal columns in eusauropods was semi-circular, so sauropod forefoot prints are horseshoe-shaped.

Sauropoda – Wikipedia

Unlike elephants, print evidence shows that sauropods lacked any fleshy padding to back the front feet, making them concave. Almost all sauropods had such a claw, though what purpose it served is unknown. The claw was largest as well as tall and laterally flattened in diplodocids, and very small in brachiosaurids, some of which seem to have lost the claw entirely based on trackway evidence. Titanosaurs may have lost the thumb claw completely with the exception of early forms, such as Janenschia.

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Titanosaurs were most unusual among sauropods, as in addition to the external claw, they completely lost the digits of the front foot. Advanced titanosaurs had no digits or digit bones, and walked only on horseshoe-shaped “stumps” made up of the columnar metacarpal bones. Print evidence from Portugal shows that, in at least some sauropods probably brachiosauridsthe bottom and sides of the forefoot column was likely covered in small, spiny scales, which left score marks in the prints.

Matthew Bonnan [36] [37] has shown that sauropod dinosaur long bones grew isometrically: Bonnan suggested that this odd scaling pattern most vertebrates show significant shape changes in long bones associated with increasing weight support might be related to a stilt-walker principle suggested by amateur scientist Jim Schmidt in which the long legs of adult sauropods allowed them to easily cover great distances without changing their overall mechanics.

Along with other saurischian dinosaurs such as birds and other theropodssauropods had a system of air sacs, evidenced by indentations and hollow cavities in most of their vertebrae that had been invaded by them.

Biology of the Sauropod Dinosaurs

Pneumatic, hollow bones are a characteristic feature of all sauropods. The bird-like hollowing of sauropod bones was recognized early in the study of these animals, and, in fact, at least one sauropod specimen found in the 19th century Ornithopsis was originally misidentified as a pterosaur a flying reptile because of this. Some sauropods had armor. There were genera with small clubs on their tails, like Shunosaurusand several titanosaurssuch as Saltasaurus and Ampelosaurushad small bony osteoderms covering portions of their bodies.

The study suggested that Nigersaurusfor example, replaced each tooth every 14 days, Camarasaurus replaced each tooth every 62 days, and Diplodocus replaced each tooth once every 35 days. Camarasaurus ‘s teeth took longer to grow than those for Diplodocus because they were larger. It was also noted by D’Emic and his team that the differences between the teeth of the sauropods also indicated a difference in diet.

Diplodocus ate plants low to the ground and Camarasaurus browsed leaves from top and middle branches. According to the scientists, the specializing of their diets helped the different herbivorous dinosaurs to coexist. By reducing their heads to simple harvesting tools that got the plants into the body, the sauropods needed less power to lift their heads, and thus were able to develop necks with less dense muscle and connective tissue. This drastically reduced the overall mass of the neck, enabling further elongation.

Sauropods also had a great number of adaptations in their skeletal structure.

Some sauropods had as many as 19 cervical vertebrae, whereas almost all mammals are limited to only seven. Additionally, each vertebra was extremely long and had a number of empty spaces in them which would have been filled only with air. An air-sac system connected to the spaces not only lightened the long necks, but effectively increased the airflow through the trachea, helping the creatures to breathe in enough air. Considering that the metabolism would have been doing an immense amount of work, it would certainly have generated a large amount of heat as well, and elimination of this excess heat would have been essential for survival.

When sauropods were first discovered, their immense size led many scientists to compare them with modern-day whales. Most studies in the 19th and early 20th centuries concluded that sauropods were too dinlsaurs to have supported their weight on land, and therefore that they must have been mainly aquatic. Most life restorations of sauropods in art through the first three quarters of the 20th century depicted them fully or partially immersed in water.

Inpaleontologist E. Cope had even referred to these structures as “floats”. Beginning in the s, the effects of sauropod air sacs on their supposed aquatic lifestyle began to be explored. Paleontologists such as Coombs and Bakker used this, as well as evidence from sedimentology and biomechanicsto show that sauropods were primarily terrestrial animals.

Henderson noted that, due to their extensive system of air sacs, sauropods would have been buoyant and would not have been able to submerge their torsos completely below the surface of the water; in other words, they would float, and would not have been in danger of lung collapse due to water pressure when swimming. Evidence for swimming in sauropods comes from fossil trackways that have occasionally been found to preserve only the forefeet manus impressions. Henderson showed that such trackways can be explained by sauropods with long forelimbs such as macronarians floating in relatively shallow water evolutino enough to keep the shorter hind legs free of the bottom, and using the front limbs to punt forward.

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This mode of aquatic locomotioncombined with its instability, led Henderson to refer to sauropods in water as “tipsy punters”. While sauropods could therefore not have been aquatic as historically depicted, there is evidence that they preferred wet and coastal habitats. Sauropod footprints are commonly found following coastlines or crossing floodplains, and sauropod fossils are often found yhe wet environments or intermingled with fossils of marine organisms.

Many lines of fossil evidence, from both bone beds and trackways, indicate that sauropods were gregarious animals that formed herds. However, the makeup of the herds varied between species. Some bone beds, for example a site from the Middle Jurassic of Argentinaappear to show herds made up of individuals of various age groups, mixing juveniles and adults.

However, a number of other fossil sites and trackways indicate that many sauropod species travelled in herds segregated by age, with juveniles forming herds separate from adults.

Such segregated herding strategies have been found in species such as AlamosaurusBellusaurus and some diplodocids. In a review of the evidence for various herd types, Myers and Fiorillo attempted to explain why sauropods appear to have often formed segregated herds.

Studies of microscopic tooth wear show that juvenile sauropods had diets that differed from their adult counterparts, so herding together would not have been as productive as herding separately, where individual herd members could forage in a coordinated way. The vast size difference between juveniles and adults may also have played a part in the different feeding and herding strategies. Since the segregation of juveniles and adults must have taken place soon after hatching, and combined with the fact that sauropod hatchlings were most likely precocialMyers and Fiorillo concluded that species with age-segregated herds would not have exhibited much parental care.

Further examples of gregarious behavior will need to be discovered from more sauropod species to begin detecting possible patterns of distribution. Since early in the history of their study, scientists, such as Osbornhave speculated that sauropods could rear up on their hind legs, using the tail as the third ‘leg’ of a tripod.

In a paper, Rothschild and Molnar reasoned that if sauropods had adopted a thd posture at times, there would be evidence of stress fractures in the forelimb ‘hands’. However, none were found after they examined a large number of sauropod skeletons. Heinrich Mallison in dinosauds the first to study the physical potential for various sauropods to rear into a tripodal stance.

Mallison found that some characters previously linked to rearing adaptations were actually unrelated such as the wide-set hip bones of titanosaurs or would have hindered rearing. For example, titanosaurs had an unusually flexible backbone, which would have decreased stability in a tripodal posture and would have put more strain on the muscles.

Likewise, it is unlikely that brachiosaurids could rear up onto the hind legs, as their center of gravity was much farther forward than other sauropods, which would cause such a stance to be unstable. Diplodocids, on the other hand, appear to biloogy been well adapted for rearing up into a tripodal stance.

Diplodocids had a center of mass directly over the hips, giving them greater balance on two legs. Diplodocids also had the most mobile necks of sauropods, a well-muscled pelvic girdle, and tail vertebrae with a specialised shape that would allow the tail to bear weight at the point it touched the ground. Mallison concluded that diplodocids were better adapted to rearing than elephantswhich do so occasionally in the wild. He also argues that stress fractures in the wild do not occur from everyday behaviour, [55] such as feeding-related activities contra Rothschild and Molnar.

There is controversy over how sauropods held their heads and necks, and the postures they could achieve in life. Various research looking at the problem from aspects, such as the neutral articulation of the neck vertebra and estimating the range of motion, the metabolic and energy requirements of having incredibly long necks, and comparison to living animals, have come to different conclusions.