Sauropoda
Encyclopedia
Sauropoda or the sauropods (ˈ), are an infraorder
of saurischia
n ("lizard-hipped") dinosaur
s. They had long necks, long tails, small heads (in comparison to the rest of their body), and 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 Brachiosaurus
, Diplodocus
, and Apatosaurus
(which, under current classification, is a senior synonym of Brontosaurus). Sauropods first appeared in the late Triassic
Period, where they somewhat resembled the closely related (and possibly ancestral) group Prosauropoda. By the Late Jurassic
(150 million years ago), sauropods had become widespread (especially the diplodocids and brachiosaurids). By the Late Cretaceous
, those groups had mainly been replaced by the titanosaur
s, which had a near-global distribution. However, as with all other non-avian dinosaurs, the titanosaurs died out in the Cretaceous–Tertiary extinction event. Fossil
ised remains of sauropods have been found on every continent, including Antarctica.
The name Sauropoda was coined by O.C. Marsh in 1878, and is derived from Greek
, meaning "lizard foot". Sauropods are one of the most recognizable groups of dinosaurs, and have become a fixture in popular culture due to their large sizes.
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.
s (four-legged), often with spatulate (spatula-shaped: broad at the base, narrow at the neck) teeth. They had tiny heads, massive bodies, and tended to have 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, and/or multiple claws or hooves on the hands. The proximal caudal vertebrae is extremely diagnostic for sauropods.
The sauropods' most defining characteristic was their size. Even the dwarf sauropods like Europasaurus
(perhaps 5 to 6 metres, or 20 feet long) were counted among the largest animals in their ecosystem
. Their only real competitors in terms of size are the rorqual
whale
s, such as the Blue Whale
. But unlike whales, sauropods were primarily land-based animals.
Their body design did not vary as much as other dinosaurs, perhaps due to size constraints, but they still displayed ample variety. Some, like the diplodocids, possessed tremendously long tails which they may have been able to crack like a whip
to deter or even injure predators, or to make sonic boom
s. Supersaurus
, at 33 to 34 m (108.3 to 111.5 ft) long, is the longest sauropod known from reasonably complete remains, but others, like the old record holder, Diplodocus
, are still extremely long. The holotype
(and now lost) vertebra of Amphicoelias fragillimus may have come from an animal 58 metres (190.3 ft) long; its vertebral column would have been substantially longer than that of the blue whale. The longest terrestrial animal alive today, the reticulated python
, only reaches lengths of 8.7 metres (28.5 ft).
Others, like the brachiosaurids, were extremely tall, with high shoulders and extremely long necks. Sauroposeidon
is probably the tallest, reaching about 18 metres (60 ft) high, with the previous record for longest neck being held by Mamenchisaurus
. By comparison the giraffe
, the tallest of all living animals, is only 4.8 to 5.5 metres (16 to 18 ft) tall.
Some were almost incredibly massive: Argentinosaurus
is probably the heaviest at 80 to 100 metric tonnes (90 to 110 ton
s), though Paralititan
, Andesaurus
, Antarctosaurus
, and Argyrosaurus
are of comparable sizes. There is some very poor evidence of an even more massive titanosaurian, Bruhathkayosaurus
, which might have weighed between 175 to 220 tonnes (190 to 240 tons). The largest land animal alive today, the Savannah elephant
, weighs no more than 10 metric tons (11 ST).
Among the smallest sauropods were the primitive Ohmdenosaurus
(4 m, or 13 ft long), the dwarf titanosaur
Magyarosaurus
(5.3 m or 17 ft long), and the dwarf brachiosaurid Europasaurus
, which was 6.2 meters long as a fully-grown adult. Its small stature was probably the result of insular dwarfism
of a herd of sauropods stranded on an island in what is now Germany
. Also notable is the diplodocoid sauropod Brachytrachelopan
, which was the shortest member of its group thanks to its unusually short neck. 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.
). The front feet of sauropods were very dissimilar from those of modern large quadrupeds such as elephant
s. 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 Barapasaurus
, had such forefeet). The front feet were so modified in eusauropods that individual digits would not have been visible in life.
The arrangement of the forefoot bone (metacarpal) columns in eusauropods was semi-circular, so sauropod forefoot prints are horseshoe-shaped. Unlike elephants, print evidence shows that sauropods lacked any fleshy padding to back the front feet, making them concave. The only claw visible in most sauropods was the distinctive thumb claw (associated with digit I). 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
). 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 brachiosaurids), the bottom and sides of the forefoot column was likely covered in small, spiny scales, which left score marks in the prints. In titanosaurs, the ends of the metacarpal bones that contacted the ground were unusually broad and squared-off, and some specimens preserve the remains of soft tissue covering this area, suggesting that the front feet were rimmed with some kind of padding in these species.
Matthew Bonnan
has shown that sauropod dinosaur long bones grew isometrically: that is, there was little to no change in shape as juvenile sauropods became gigantic adults. 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.
n dinosaurs (such as birds and other theropods), sauropods had a system of air sacs, evidenced by indentations and hollow cavities in most of their vertebrae. 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.
. There were genera with spine
d backs, such as Agustinia
, and some had small club
s on their tails, like Shunosaurus
. Several titanosaur
s, such as Saltasaurus
and Ampelosaurus
, had small bony osteoderm
s covering portions of their bodies.
s. Most studies in the 19th and early 20th centuries concluded that sauropods were too large 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. This early notion was cast in doubt beginning in the 1950s, when a study by Kermack (1951) demonstrated that, if submerged in several metres of water, the pressure would be enough to fatally collapse the lungs and airway. However, this and other early studies of sauropod ecology were flawed in that they ignored a substantial body of evidence that the skeletons of sauropods were heavily permeated with air sacs. In 1878, paleontologist E.D. cope had even referred to these structures as "floats".
Beginning in the 1970s, 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 biomechanics, to show that sauropods were primarily terrestrial animals. In 2004, D.M. 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 which 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 macronaria
ns) floating in relatively shallow water deep enough to keep the shorter hind legs free of the bottom, and using the front limbs to punt
forward. However, due to their body proportions, floating sauropods would also have been very unstable and maladapted for extended periods in the water. This mode of aquatic locomotion, combined 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 in 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 herd
s. However, the makeup of the herds varied between species. Some bone beds, for example a site from the Middle Jurassic of Argentina
, appear 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 Alamosaurus
, Bellusaurus
, 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. Differing tooth wear suggests that juveniles had different feeding strategies than adults, 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, Myers and Fiorillo concluded that species with age-segregated herds could not have exhibited much parental care, if any. On the other hand, scientists who have studied age-mixed sauropod herds suggested that these species may have cared for their young for an extended period of time before the young reached adulthood.
Exactly how segregated versus age-mixed herding varied across different groups of sauropods is unknown. Further examples of gregarious behavior will need to be discovered from more sauropod species to begin detecting possible patterns of distribution.
have speculated that sauropods could rear up on their hind legs, using the tail as the third 'leg' of a tripod. A skeletal mount depicting the diplodocid
Barosaurus lentus
rearing up on its hind legs at the American Museum of Natural History
is one illustration of this hypothesis. In a 2005 paper, Rothschild and Molnar reasoned that if sauropods had adopted a bipedal 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 2009) was 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 titanosaur
s) or would actually 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, given 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 have 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 contacted the ground. Mallison concluded that diplodocids were better adapted to rearing than elephant
s, which do so occasionally in the wild. He also argues that stress fractures in the wild do not occur from everyday behaviour, such as feeding-related activities (contra Rothschild and Molnar).
However, research on living animals has suggested that sauropod heads were held in an upright S-shaped curve. Inference from bones about "neutral head postures" which suggest a horizontal position may be unreliable, according to this research. If applied to living animals it would imply they also held their heads in this position, even though they in fact do not.
s and other fossil footprints
(known as "ichnites") are known from abundant evidence present on most continents. Ichnites have helped support other biological hypotheses about sauropods, including general fore and hind foot anatomy (see Limbs and feet above). Generally, prints from the forefeet are much smaller than the hind feet, and often crescent-shaped. Occasionally ichnites preserve traces of the claws, and help confirm which sauropod groups lost claws or even digits on their forefeet.
Generally, sauropod trackways are divided into three categories based on the distance between opposite limbs: narrow gauge, medium gauge, and wide gauge. The gauge of the trackway can help determine how wide-set the limbs of various sauropods were and how this may have impacted the way they walked. A 2004 study by Day and colleagues found that a general pattern could be found among groups of advanced sauropods, with each sauropod family being characterised by certain trackway gauges. They found that most sauropods other than titanosaur
s had narrow-gauge limbs, with strong impressions of the large thumb claw on the forefeet. Medium gauge trackways with claw impressions on the forefeet probably belong to brachiosaurids and other primitive titanosauriformes, which were evolving wider-set limbs but retained their claws. Primitive true titanosaurs also retained their forefoot claw but had evolved fully wide gauge limbs. Wide gauge limbs were retained by advanced titanosaurs, trackways from which show a wide gauge and lack of any claws or digits on the forefeet.
Period. According to Kenneth Carpenter
, whatever evolutionary pressure caused large size must have therefore been present from the early origins of the group.
Studies of mammal
ian herbivores that attained large size, such as elephant
s, have found that larger size in plant-eating animals leads to greater efficiency in digesting food. Since larger animals have longer digestive systems, food is kept in digestion for significantly longer periods of time, allowing large animals to survive on lower-quality food sources. This is especially true of animals with a large number of 'fermentation chambers' along the intestine which allow microbes to accumulate and ferment plant material, aiding digestion. Throughout their evolutionary history, sauropod dinosaurs were found primarily in semi-arid, seasonally dry environments, with a corresponding seasonal drop in the quality of food during the dry season. The environment of most gigantic Late Jurassic sauropods such as Amphicoelias
was essentially a savanna
, similar to the arid environments in which modern giant herbivores are found, supporting the idea that poor-quality food in an arid environment promotes the evolution of giant herbivores. Carpenter argued that other benefits of large size, such as relative immunity from predators, lower energy expenditure, and longer life span, were probably secondary advantages, and that sauropods attained large size primarily to help process food more efficiently.
and were originally interpreted in a variety of different ways. Their relationship to other dinosaurs was not recognized until well after their initial discovery.
The first sauropod fossil to be scientifically described was a single tooth known by the non-Linnaean
descriptor Rutellum implicatum
. This fossil was described by Edward Lhuyd
in 1699, but was not recognized as a giant prehistoric reptile at the time. Dinosaurs would not be recognized as a group until over a century later.
Richard Owen
published the first modern scientific description of sauropods in 1841, in his paper naming Cetiosaurus
and Cardiodon
. Cardiodon was known only from a two unusual, heart-shaped teeth (from which it got its name), which could not be identified beyond the fact that they came from a previously unknown large reptile
. Cetiosaurus was known from slightly better, but still scrappy remains. Owen thought at the time that Cetiosaurus was a giant marine reptile related to modern crocodile
s, hence its name, which means "whale lizard". A year later, when Owen coined the name Dinosauria, he did not include Cetiosaurus and Cardiodon in that group.
In 1850, Gideon Mantell
recognized the dinosaurian nature of several bones assigned to Cetiosaurus by Owen. Mantell noticed that the leg bones contained a medullary cavity
, a characteristic of land animals. He assigned these specimens to the new genus
Pelorosaurus
, and grouped it together with the dinosaurs. However, Mantell still did not recognize the relationship to Cetiosaurus.
The next sauropod find to be described and misidentified as something other than a dinosaur were a set of hip vertebrae described by Harry Seeley
in 1870. Seeley found that the vertebrae were very lightly constructed for their size and contained openings for air sacs (pneumatization). Such air sacs were at the time known only in bird
s and pterosaur
s, and Seeley considered the vertebrae to come from a pterosaur. He named the new genus Ornithopsis
, or "bird face" because of this.
When more complete specimens of Cetiosaurus were described by Phillips in 1871, he finally recognized the animal as a dinosaur related to Pelorosaurus. However, it was not until the description of new, nearly complete sauropod skeletons from the United States
(representing Apatosaurus
and Camarasaurus
) later that year that a complete picture of sauropods emerged. An approximate reconstruction of a complete sauropod skeleton was produced by John A. Ryder, based on the remains of Camarasaurus, though many features were still inaccurate or incomplete according to later finds and biomechanical studies. Also in 1877, Richard Lydekker
named another relative of Cetiosaurus, Titanosaurus
, based on an isolated vertebra.
In 1878, the most complete sauropod yet was found and described by Othniel Charles Marsh
, who named it Diplodocus
. With this find, Marsh also created a new group to contain Diplodocus, Cetiosaurus, and their increasing roster of relatives to differentiate them from the other major groups of dinosaurs. Marsh named this group Sauropoda, or "lizard feet".
, Haplocanthosaurus
, Jobaria
and Nemegtosauridae
. The following are two alternative recent classifications (showing supra-generic clade
s only in the second example). These are by no means an exhaustive list of recent sauropod classification schemes. In some cases, families like Vulcanodontidae, Cetiosauridae and Omeisauridae are not included because they are considered paraphyletic, or even (in the case of Camarasauridae) polyphyletic.
simplified after Wilson, 2002.
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
of saurischia
Saurischia
Saurischia meaning 'lizard' and ischion meaning 'hip joint') is one of the two orders, or basic divisions, of dinosaurs. In 1888, Harry Seeley classified dinosaurs into two orders, based on their hip structure...
n ("lizard-hipped") dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
s. They had long necks, long tails, small heads (in comparison to the rest of their body), and 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
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
include Brachiosaurus
Brachiosaurus
Brachiosaurus is a genus of sauropod dinosaur from the Jurassic Morrison Formation of North America. It was first described by Elmer S. Riggs in 1903 from fossils found in the Grand River Canyon of western Colorado, in the United States. Riggs named the dinosaur Brachiosaurus altithorax,...
, Diplodocus
Diplodocus
Diplodocus , or )is a genus of diplodocid sauropod dinosaur whose fossils were first discovered in 1877 by S. W. Williston. The generic name, coined by Othniel Charles Marsh in 1878, is a Neo-Latin term derived from Greek "double" and "beam", in reference to its double-beamed chevron bones...
, and Apatosaurus
Apatosaurus
Apatosaurus , also known by the popular but scientifically deprecated synonym Brontosaurus, is a genus of sauropod dinosaur that lived from about 154 to 150 million years ago, during the Jurassic Period . It was one of the largest land animals that ever existed, with an average length of and a...
(which, under current classification, is a senior synonym of Brontosaurus). Sauropods first appeared in the late Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
Period, where they somewhat resembled the closely related (and possibly ancestral) group Prosauropoda. By the Late Jurassic
Late Jurassic
The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 161.2 ± 4.0 to 145.5 ± 4.0 million years ago , which is preserved in Upper Jurassic strata. In European lithostratigraphy, the name "Malm" indicates rocks of Late Jurassic age...
(150 million years ago), sauropods had become widespread (especially the diplodocids and brachiosaurids). By the Late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
, those groups had mainly been replaced by the titanosaur
Titanosaur
Titanosaurs were a diverse group of sauropod dinosaurs, which included Saltasaurus and Isisaurus. It includes some of the heaviest creatures ever to walk the earth, such as Argentinosaurus and Paralititan — which some believe have weighed up to 100 tonnes...
s, which had a near-global distribution. However, as with all other non-avian dinosaurs, the titanosaurs died out in the Cretaceous–Tertiary extinction event. Fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
ised remains of sauropods have been found on every continent, including Antarctica.
The name Sauropoda was coined by O.C. Marsh in 1878, and is derived from Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
, meaning "lizard foot". Sauropods are one of the most recognizable groups of dinosaurs, and have become a fixture in popular culture due to their large sizes.
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.
Description
Sauropods were herbivorous (plant-eating), usually quite long-necked quadrupedQuadruped
Quadrupedalism is a form of land animal locomotion using four limbs or legs. An animal or machine that usually moves in a quadrupedal manner is known as a quadruped, meaning "four feet"...
s (four-legged), often with spatulate (spatula-shaped: broad at the base, narrow at the neck) teeth. They had tiny heads, massive bodies, and tended to have 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, and/or multiple claws or hooves on the hands. The proximal caudal vertebrae is extremely diagnostic for sauropods.
Size
Europasaurus
Europasaurus is a basal macronarian sauropod, a form of quadrupedal herbivorous dinosaur. It lived during the Late Jurassic of northern Germany, and has been identified as an example of insular dwarfism resulting from the isolation of a sauropod population on an island within the Lower Saxony...
(perhaps 5 to 6 metres, or 20 feet long) were counted among the largest animals in their ecosystem
Ecosystem
An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....
. Their only real competitors in terms of size are the rorqual
Rorqual
Rorquals are the largest group of baleen whales, with nine species in two genera. They include the largest animal that has ever lived, the Blue Whale, which can reach , and another that easily reaches ; even the smallest of the group, the Northern Minke Whale, reaches .-Characteristics:Rorquals...
whale
Whale
Whale is the common name for various marine mammals of the order Cetacea. The term whale sometimes refers to all cetaceans, but more often it excludes dolphins and porpoises, which belong to suborder Odontoceti . This suborder also includes the sperm whale, killer whale, pilot whale, and beluga...
s, such as the Blue Whale
Blue Whale
The blue whale is a marine mammal belonging to the suborder of baleen whales . At in length and or more in weight, it is the largest known animal to have ever existed....
. But unlike whales, sauropods were primarily land-based animals.
Their body design did not vary as much as other dinosaurs, perhaps due to size constraints, but they still displayed ample variety. Some, like the diplodocids, possessed tremendously long tails which they may have been able to crack like a whip
Whip
A whip is a tool traditionally used by humans to exert control over animals or other people, through pain compliance or fear of pain, although in some activities whips can be used without use of pain, such as an additional pressure aid in dressage...
to deter or even injure predators, or to make sonic boom
Sonic boom
A sonic boom is the sound associated with the shock waves created by an object traveling through the air faster than the speed of sound. Sonic booms generate enormous amounts of sound energy, sounding much like an explosion...
s. Supersaurus
Supersaurus
Supersaurus is a genus of diplodocid sauropod dinosaur discovered by Vivian Jones of Delta, Colorado, in the Upper Jurassic Morrison Formation of Colorado in 1972. The fossil remains came from the Brushy Basin Member of the formation, dating to about 153 million years ago...
, at 33 to 34 m (108.3 to 111.5 ft) long, is the longest sauropod known from reasonably complete remains, but others, like the old record holder, Diplodocus
Diplodocus
Diplodocus , or )is a genus of diplodocid sauropod dinosaur whose fossils were first discovered in 1877 by S. W. Williston. The generic name, coined by Othniel Charles Marsh in 1878, is a Neo-Latin term derived from Greek "double" and "beam", in reference to its double-beamed chevron bones...
, are still extremely long. The holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
(and now lost) vertebra of Amphicoelias fragillimus may have come from an animal 58 metres (190.3 ft) long; its vertebral column would have been substantially longer than that of the blue whale. The longest terrestrial animal alive today, the reticulated python
Reticulated Python
Python reticulatus, also known as the reticulated python is a species of python found in Southeast Asia. Adults can grow to over 8.7 m in length but normally grow to an average of 3-6 m . They are the world's longest snakes and longest reptile, but are not the most heavily built...
, only reaches lengths of 8.7 metres (28.5 ft).
Others, like the brachiosaurids, were extremely tall, with high shoulders and extremely long necks. Sauroposeidon
Sauroposeidon
Sauroposeidon is a genus of sauropod dinosaur known from four neck vertebrae that were found in the southeastern portion of the US state of Oklahoma. The fossils were found in rocks dating to the Early Cretaceous, a period when the sauropods of North America had diminished in both size and...
is probably the tallest, reaching about 18 metres (60 ft) high, with the previous record for longest neck being held by Mamenchisaurus
Mamenchisaurus
Mamenchisaurus was a plant-eating four-legged dinosaur, known for its remarkably long neck which made up half its total length. It is known from numerous species which ranged in time from 160 to 145 million years ago, from the Oxfordian to Tithonian ages of the late Jurassic Period of...
. By comparison the giraffe
Giraffe
The giraffe is an African even-toed ungulate mammal, the tallest of all extant land-living animal species, and the largest ruminant...
, the tallest of all living animals, is only 4.8 to 5.5 metres (16 to 18 ft) tall.
Some were almost incredibly massive: Argentinosaurus
Argentinosaurus
Argentinosaurus is a genus of titanosaur sauropod dinosaur first discovered by Guillermo Heredia in Argentina. The generic name refers to the country in which it was discovered...
is probably the heaviest at 80 to 100 metric tonnes (90 to 110 ton
Short ton
The short ton is a unit of mass equal to . In the United States it is often called simply ton without distinguishing it from the metric ton or the long ton ; rather, the other two are specifically noted. There are, however, some U.S...
s), though Paralititan
Paralititan
Paralititan was a giant titanosaurian sauropod dinosaur genus discovered in coastal deposits in the Upper Cretaceous Bahariya Formation of Egypt. The fossil represents the first tetrapod reported from the Bahariya Formation since 1935. Its 1.69 meter long humerus is longer than that of any...
, Andesaurus
Andesaurus
Andesaurus is a genus of basal titanosaurian sauropod dinosaur which existed during the middle of the Cretaceous Period in South America. Like most sauropods, it would have had a small head on the end of a long neck and an equally long tail...
, Antarctosaurus
Antarctosaurus
Antarctosaurus is a genus of titanosaurian sauropod dinosaur from the Late Cretaceous Period of what is now South America. The type species, A. wichmannianus, was described by prolific German paleontologist Friedrich von Huene in 1929, who also described a second species in 1929. Three additional...
, and Argyrosaurus
Argyrosaurus
Argyrosaurus is a genus of herbivorous titanosaurid dinosaur that lived about 90 million years ago, during the Late Cretaceous Period of what is now South America . It was one of the largest dinosaurs, having a length of up to 20–30 metres and a weight estimated as high as eighty tonnes...
are of comparable sizes. There is some very poor evidence of an even more massive titanosaurian, Bruhathkayosaurus
Bruhathkayosaurus
Bruhathkayosaurus might have been the largest dinosaur that ever lived. The accuracy of this claim, however, has been mired in controversy and debate...
, which might have weighed between 175 to 220 tonnes (190 to 240 tons). The largest land animal alive today, the Savannah elephant
Elephant
Elephants are large land mammals in two extant genera of the family Elephantidae: Elephas and Loxodonta, with the third genus Mammuthus extinct...
, weighs no more than 10 metric tons (11 ST).
Among the smallest sauropods were the primitive Ohmdenosaurus
Ohmdenosaurus
Ohmdenosaurus is the name given to a genus of herbivorous dinosaur from the Early Jurassic. It was a very small perhaps vulcanodontid sauropod which lived in Germany...
(4 m, or 13 ft long), the dwarf titanosaur
Titanosaur
Titanosaurs were a diverse group of sauropod dinosaurs, which included Saltasaurus and Isisaurus. It includes some of the heaviest creatures ever to walk the earth, such as Argentinosaurus and Paralititan — which some believe have weighed up to 100 tonnes...
Magyarosaurus
Magyarosaurus
Magyarosaurus is a genus of dwarf sauropod dinosaur from late Cretaceous Period in what is now Romania. It is one of the smallest-known adult sauropods, measuring only six meters in length. The type species is Magyarosaurus dacus...
(5.3 m or 17 ft long), and the dwarf brachiosaurid Europasaurus
Europasaurus
Europasaurus is a basal macronarian sauropod, a form of quadrupedal herbivorous dinosaur. It lived during the Late Jurassic of northern Germany, and has been identified as an example of insular dwarfism resulting from the isolation of a sauropod population on an island within the Lower Saxony...
, which was 6.2 meters long as a fully-grown adult. Its small stature was probably the result of insular dwarfism
Insular dwarfism
Insular dwarfism, a form of phyletic dwarfism, is the process and condition of the reduction in size of large animals – typically mammals – when their population's range is limited to a small environment, primarily islands. This natural process is distinct from the intentional creation of dwarf...
of a herd of sauropods stranded on an island in what is now Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
. Also notable is the diplodocoid sauropod Brachytrachelopan
Brachytrachelopan
Brachytrachelopan is an unusual short-necked sauropod dinosaur from the latest Jurassic Period of Argentina. The holotype and only known specimen was collected from an erosional exposure of fluvial sandstone within the Cañadón Cálcero Formation on a hill approximately 25 km north-northeast...
, which was the shortest member of its group thanks to its unusually short neck. 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.
Limbs and feet
As massive quadrupeds, sauropods developed specialized graviportal (weight-bearing) limbs. The hind feet were broad, and retained three claws in most species. Particularly unusual compared with other animals were the highly modified front feet (manusManus (zoology)
The manus is the zoological term for the distal portion of the fore limb of an animal. In tetrapods, it is the part of the pentadactyl limb that includes the metacarpals and digits . During evolution, it has taken many forms and served a variety of functions...
). The front feet of sauropods were very dissimilar from those of modern large quadrupeds such as elephant
Elephant
Elephants are large land mammals in two extant genera of the family Elephantidae: Elephas and Loxodonta, with the third genus Mammuthus extinct...
s. 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
Vulcanodon
Vulcanodon was a relatively small early sauropod dinosaur genus from the Early Jurassic of southern Africa. About 6.5 metres long, Vulcanodon was herbivorous and had unusually long bones of the first toe and large claws on the inside toes. The type species, V. karibaensis, was formally...
and Barapasaurus
Barapasaurus
Barapasaurus is a genus of sauropod dinosaur from Early Jurassic rocks of India. The specific name for its only species, B. tagorei, means 'Tagore's', which honors Bengali poet, writer, painter, and musician Rabindranath Tagore.-Description:...
, had such forefeet). The front feet were so modified in eusauropods that individual digits would not have been visible in life.
The arrangement of the forefoot bone (metacarpal) columns in eusauropods was semi-circular, so sauropod forefoot prints are horseshoe-shaped. Unlike elephants, print evidence shows that sauropods lacked any fleshy padding to back the front feet, making them concave. The only claw visible in most sauropods was the distinctive thumb claw (associated with digit I). 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
Janenschia
Janenschia was a large sauropod from Late Jurassic Africa , and therefore the earliest known titanosaur. Originally thought to be a species of the diplodocid Tornieria/Barosaurus , it was later found to be a distantly related titanosaur. So far, it is only known from Tanzania...
). 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
Portugal
Portugal , officially the Portuguese Republic is a country situated in southwestern Europe on the Iberian Peninsula. Portugal is the westernmost country of Europe, and is bordered by the Atlantic Ocean to the West and South and by Spain to the North and East. The Atlantic archipelagos of the...
shows that in at least some sauropods (probably brachiosaurids), the bottom and sides of the forefoot column was likely covered in small, spiny scales, which left score marks in the prints. In titanosaurs, the ends of the metacarpal bones that contacted the ground were unusually broad and squared-off, and some specimens preserve the remains of soft tissue covering this area, suggesting that the front feet were rimmed with some kind of padding in these species.
Matthew Bonnan
Matthew Bonnan
Matthew Bonnan is an American paleobiologist and an associate professor of biological sciences at Western Illinois University. His research combines traditional descriptive and anatomical study with computer-aided morphometric analysis and modeling of vertebrate skeletons. Dr...
has shown that sauropod dinosaur long bones grew isometrically: that is, there was little to no change in shape as juvenile sauropods became gigantic adults. 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.
Air sacs
Along with other saurischiaSaurischia
Saurischia meaning 'lizard' and ischion meaning 'hip joint') is one of the two orders, or basic divisions, of dinosaurs. In 1888, Harry Seeley classified dinosaurs into two orders, based on their hip structure...
n dinosaurs (such as birds and other theropods), sauropods had a system of air sacs, evidenced by indentations and hollow cavities in most of their vertebrae. 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
Ornithopsis
Ornithopsis was a medium-sized Early Cretaceous sauropod dinosaur, from England. It has been considered a synonym of the wastebasket taxon Pelorosaurus, but recent research suggests that this is not as clear-cut as supposed...
) was originally misidentified as a pterosaur
Pterosaur
Pterosaurs were flying reptiles of the clade or order Pterosauria. They existed from the late Triassic to the end of the Cretaceous Period . Pterosaurs are the earliest vertebrates known to have evolved powered flight...
(a flying reptile) because of this.
Armor
Some sauropods had armorArmour (zoology)
Armour in animals is external or superficial protection against attack by predators, formed as part of the body , usually through the hardening of body tissues, outgrowths or secretions. It has therefore mostly developed in 'prey' species...
. There were genera with spine
Spine (zoology)
A spine is a hard, thorny or needle-like structure which occurs on various animals. Animals such as porcupines and sea urchins grow spines as a self-defense mechanism. Spines are often formed of keratin...
d backs, such as Agustinia
Agustinia
Agustinia is a genus of sauropod dinosaur from the Early Cretaceous Period of South America. Like all known sauropods, it was quadrupedal and herbivorous. Although some sauropods are known to have body armor, Agustinias armor was unique even among sauropods...
, and some had small club
Club (zoology)
In zoology, a club is a bony mass at the end of the tail of some dinosaurs and of some mammals, most notably the ankylosaurids and the glyptodonts...
s on their tails, like Shunosaurus
Shunosaurus
Shunosaurus, meaning "Shu Lizard", is a genus of sauropod dinosaur from Middle Jurassic beds in Sichuan Province in China, 170 million years ago...
. Several titanosaur
Titanosaur
Titanosaurs were a diverse group of sauropod dinosaurs, which included Saltasaurus and Isisaurus. It includes some of the heaviest creatures ever to walk the earth, such as Argentinosaurus and Paralititan — which some believe have weighed up to 100 tonnes...
s, such as Saltasaurus
Saltasaurus
Saltasaurus is a genus of titanosaurid sauropod dinosaur of the Late Cretaceous Period. Relatively small among sauropods, though still massive by the standards of modern creatures, Saltasaurus was characterized by a diplodocid-like head...
and Ampelosaurus
Ampelosaurus
Ampelosaurus is a titanosaurian sauropod dinosaur hailing from the Late Cretaceous Period of what is now Europe. Like most sauropods, it would have had a long neck and tail but it also carried armor in the form of osteoderms on its back. This dinosaur would have stretched about 15 meters from...
, had small bony osteoderm
Osteoderm
Osteoderms are bony deposits forming scales, plates or other structures in the dermal layers of the skin. Osteoderms are found in many groups of extant and extinct reptiles, including lizards, various groups of dinosaurs , crocodilians, phytosaurs, aetosaurs, placodonts, and hupehsuchians...
s covering portions of their bodies.
Ecology
When first discovered, the immense size of sauropods led many scientists to compare them with modern-day whaleWhale
Whale is the common name for various marine mammals of the order Cetacea. The term whale sometimes refers to all cetaceans, but more often it excludes dolphins and porpoises, which belong to suborder Odontoceti . This suborder also includes the sperm whale, killer whale, pilot whale, and beluga...
s. Most studies in the 19th and early 20th centuries concluded that sauropods were too large to have supported their weight on land, and therefore that they must have been mainly aquatic
Aquatic
Aquatic means relating to water; living in or near water or taking place in waterAquatic may also refer to:* Aquatic animal, either vertebrate or invertebrate, which lives in water for most or all of its life...
. Most life restorations of sauropods in art through the first three quarters of the 20th century depicted them fully or partially immersed in water. This early notion was cast in doubt beginning in the 1950s, when a study by Kermack (1951) demonstrated that, if submerged in several metres of water, the pressure would be enough to fatally collapse the lungs and airway. However, this and other early studies of sauropod ecology were flawed in that they ignored a substantial body of evidence that the skeletons of sauropods were heavily permeated with air sacs. In 1878, paleontologist E.D. cope had even referred to these structures as "floats".
Beginning in the 1970s, 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 biomechanics, to show that sauropods were primarily terrestrial animals. In 2004, D.M. 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 which 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 macronaria
Macronaria
Macronaria is a clade of sauropod dinosaurs from the Middle Jurassic to Late Cretaceous Periods of what are now North America, South America, Europe, Asia and Africa. The name means 'large nostrils' , in reference to the large nasal openings high on the head that probably supported fleshy...
ns) floating in relatively shallow water deep enough to keep the shorter hind legs free of the bottom, and using the front limbs to punt
Punt (boat)
A punt is a flat-bottomed boat with a square-cut bow, designed for use in small rivers or other shallow water. Punting refers to boating in a punt. The punter generally propels the punt by pushing against the river bed with a pole...
forward. However, due to their body proportions, floating sauropods would also have been very unstable and maladapted for extended periods in the water. This mode of aquatic locomotion, combined 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 in wet environments or intermingled with fossils of marine organisms.
Herding and parental care
Herd
Herd refers to a social grouping of certain animals of the same species, either wild or domestic, and also to the form of collective animal behavior associated with this or as a verb, to herd, to its control by another species such as humans or dogs.The term herd is generally applied to mammals,...
s. However, the makeup of the herds varied between species. Some bone beds, for example a site from the Middle Jurassic of Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
, appear 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 Alamosaurus
Alamosaurus
Alamosaurus is a genus of titanosaurian sauropod dinosaur from the Late Cretaceous Period of what is now North America. It was a large quadrupedal herbivore. Isolated vertebrae and limb bones indicate that it reached sizes comparable to Argentinosaurus and Puertasaurus, which would make it the...
, Bellusaurus
Bellusaurus
Bellusaurus was a small short-necked sauropod dinosaur from the Middle Jurassic which measured about long...
, 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. Differing tooth wear suggests that juveniles had different feeding strategies than adults, 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.
Exactly how segregated versus age-mixed herding varied across different groups of sauropods is unknown. Further examples of gregarious behavior will need to be discovered from more sauropod species to begin detecting possible patterns of distribution.
Rearing stance
Since early in the history of their study, scientists such as OsbornHenry Fairfield Osborn
Henry Fairfield Osborn, Sr. ForMemRS was an American geologist, paleontologist, and eugenicist.-Early life and career:...
have speculated that sauropods could rear up on their hind legs, using the tail as the third 'leg' of a tripod. A skeletal mount depicting the diplodocid
Diplodocid
Diplodocids, or members of the family Diplodocidae , are a group of sauropod dinosaurs. The family includes some of the longest creatures ever to walk the earth, including Diplodocus and Supersaurus, which may have reached lengths of up to .-Description:While still massive, when compared to the...
Barosaurus lentus
Barosaurus
Barosaurus ; Greek barys/βαρυς meaning 'heavy' and saurus/σαυρος meaning 'lizard', 'heavy lizard') was a giant, long-tailed, long-necked, plant-eating dinosaur closely related to the more familiar Diplodocus...
rearing up on its hind legs at the American Museum of Natural History
American Museum of Natural History
The American Museum of Natural History , located on the Upper West Side of Manhattan in New York City, United States, is one of the largest and most celebrated museums in the world...
is one illustration of this hypothesis. In a 2005 paper, Rothschild and Molnar reasoned that if sauropods had adopted a bipedal 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.
Titanosaur
Titanosaurs were a diverse group of sauropod dinosaurs, which included Saltasaurus and Isisaurus. It includes some of the heaviest creatures ever to walk the earth, such as Argentinosaurus and Paralititan — which some believe have weighed up to 100 tonnes...
s) or would actually 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, given 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 have 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 contacted the ground. Mallison concluded that diplodocids were better adapted to rearing than elephant
Elephant
Elephants are large land mammals in two extant genera of the family Elephantidae: Elephas and Loxodonta, with the third genus Mammuthus extinct...
s, which do so occasionally in the wild. He also argues that stress fractures in the wild do not occur from everyday behaviour, such as feeding-related activities (contra Rothschild and Molnar).
Head and neck posture
There is controversy over whether sauropods held their heads near vertically or horizontally. The claim that the long necks of sauropods were used for browsing high trees has been questioned on the basis of calculations of the energy needed to create the arterial blood pressure for the head if it was held upright. These calculations suggest this would have taken up roughly half of its energy intake. Further, to supply blood to the head vertically held high would have required blood pressure of around 700 mmHg at the heart. This would have required that their hearts were 15 times the size of whales of similar size. This suggests it was more likely the long neck was usually held horizontally to enable them to feed on plants over a very wide area without needing to move their bodies—a potentially large saving in energy for 30 to 40 ton animals. In support of this, reconstructions of the necks of Diplodocus and Apatosaurus show that they are basically straight with a gentle decline orientating their heads in a "neutral, undeflected posture" when close to ground.However, research on living animals has suggested that sauropod heads were held in an upright S-shaped curve. Inference from bones about "neutral head postures" which suggest a horizontal position may be unreliable, according to this research. If applied to living animals it would imply they also held their heads in this position, even though they in fact do not.
Trackways and locomotion
Sauropod trackwayTrackway
A trackway is an ancient route of travel for people or animals. In biology, a trackway can be a set of impressions in the soft earth, usually a set of footprints, left by an animal. A fossil trackway is the fossilized imprint of a trackway. Trackways have been found all over the world...
s and other fossil footprints
Ichnite
An ichnite is a fossilised footprint. This is a type of trace fossil. Over the years, many ichnites have been found, around the world, giving important clues about the behaviour of the animals that made them...
(known as "ichnites") are known from abundant evidence present on most continents. Ichnites have helped support other biological hypotheses about sauropods, including general fore and hind foot anatomy (see Limbs and feet above). Generally, prints from the forefeet are much smaller than the hind feet, and often crescent-shaped. Occasionally ichnites preserve traces of the claws, and help confirm which sauropod groups lost claws or even digits on their forefeet.
Generally, sauropod trackways are divided into three categories based on the distance between opposite limbs: narrow gauge, medium gauge, and wide gauge. The gauge of the trackway can help determine how wide-set the limbs of various sauropods were and how this may have impacted the way they walked. A 2004 study by Day and colleagues found that a general pattern could be found among groups of advanced sauropods, with each sauropod family being characterised by certain trackway gauges. They found that most sauropods other than titanosaur
Titanosaur
Titanosaurs were a diverse group of sauropod dinosaurs, which included Saltasaurus and Isisaurus. It includes some of the heaviest creatures ever to walk the earth, such as Argentinosaurus and Paralititan — which some believe have weighed up to 100 tonnes...
s had narrow-gauge limbs, with strong impressions of the large thumb claw on the forefeet. Medium gauge trackways with claw impressions on the forefeet probably belong to brachiosaurids and other primitive titanosauriformes, which were evolving wider-set limbs but retained their claws. Primitive true titanosaurs also retained their forefoot claw but had evolved fully wide gauge limbs. Wide gauge limbs were retained by advanced titanosaurs, trackways from which show a wide gauge and lack of any claws or digits on the forefeet.
Size evolution
Several scientists have attempted to address the question of why sauropods attained such huge sizes. Gigantic sizes were reached early in sauropod evolution, going back to the first true sauropods in the late TriassicTriassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
Period. According to Kenneth Carpenter
Kenneth Carpenter
Kenneth Carpenter is a paleontologist. He is the museum director of the USU Eastern Prehistoric Museum and author or co-author of a number of books on dinosaurs and Mesozoic life...
, whatever evolutionary pressure caused large size must have therefore been present from the early origins of the group.
Studies of mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
ian herbivores that attained large size, such as elephant
Elephant
Elephants are large land mammals in two extant genera of the family Elephantidae: Elephas and Loxodonta, with the third genus Mammuthus extinct...
s, have found that larger size in plant-eating animals leads to greater efficiency in digesting food. Since larger animals have longer digestive systems, food is kept in digestion for significantly longer periods of time, allowing large animals to survive on lower-quality food sources. This is especially true of animals with a large number of 'fermentation chambers' along the intestine which allow microbes to accumulate and ferment plant material, aiding digestion. Throughout their evolutionary history, sauropod dinosaurs were found primarily in semi-arid, seasonally dry environments, with a corresponding seasonal drop in the quality of food during the dry season. The environment of most gigantic Late Jurassic sauropods such as Amphicoelias
Amphicoelias
Amphicoelias is a genus of herbivorous sauropod dinosaur that includes what may be the largest dinosaur ever discovered, A. fragillimus. Based on surviving descriptions of a single fossil bone, A. fragillimus may have been the longest known vertebrate at in length, and may have had a mass of up...
was essentially a savanna
Savanna
A savanna, or savannah, is a grassland ecosystem characterized by the trees being sufficiently small or widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach the ground to support an unbroken herbaceous layer consisting primarily of C4 grasses.Some...
, similar to the arid environments in which modern giant herbivores are found, supporting the idea that poor-quality food in an arid environment promotes the evolution of giant herbivores. Carpenter argued that other benefits of large size, such as relative immunity from predators, lower energy expenditure, and longer life span, were probably secondary advantages, and that sauropods attained large size primarily to help process food more efficiently.
History of discovery
The first scrappy fossil remains now recognized as sauropods all came from EnglandEngland
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
and were originally interpreted in a variety of different ways. Their relationship to other dinosaurs was not recognized until well after their initial discovery.
Linnaean taxonomy
Linnaean taxonomy can mean either of two related concepts:# the particular form of biological classification set up by Carl Linnaeus, as set forth in his Systema Naturæ and subsequent works...
descriptor Rutellum implicatum
Rutellum
Rutellum is the pre-Linnaean name given to a dinosaur specimen from the Middle Jurassic. It was a sauropod, possibly a cetiosaurid, which lived in what is now England. The specimen, called Rutellum implicatum, was described in 1699 by Edward Lhuyd, and is notable as the earliest named entity that...
. This fossil was described by Edward Lhuyd
Edward Lhuyd
Edward Lhuyd was a Welsh naturalist, botanist, linguist, geographer and antiquary. He is also known by the Latinized form of his name, Eduardus Luidius....
in 1699, but was not recognized as a giant prehistoric reptile at the time. Dinosaurs would not be recognized as a group until over a century later.
Richard Owen
Richard Owen
Sir Richard Owen, FRS KCB was an English biologist, comparative anatomist and palaeontologist.Owen is probably best remembered today for coining the word Dinosauria and for his outspoken opposition to Charles Darwin's theory of evolution by natural selection...
published the first modern scientific description of sauropods in 1841, in his paper naming Cetiosaurus
Cetiosaurus
Cetiosaurus meaning 'whale lizard', from the Greek cetus/κητος meaning 'sea monster' and saurus/σαυρος meaning 'lizard', was a sauropod dinosaur from the Mid to Late Jurassic Period in what are now Europe and Africa. It is estimated to have been about long and to have weighed roughly...
and Cardiodon
Cardiodon
Cardiodon was a genus of sauropod dinosaur, based on a tooth from the late Bathonian-age Middle Jurassic Forest Marble Formation of Wiltshire, England...
. Cardiodon was known only from a two unusual, heart-shaped teeth (from which it got its name), which could not be identified beyond the fact that they came from a previously unknown large reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
. Cetiosaurus was known from slightly better, but still scrappy remains. Owen thought at the time that Cetiosaurus was a giant marine reptile related to modern crocodile
Crocodile
A crocodile is any species belonging to the family Crocodylidae . The term can also be used more loosely to include all extant members of the order Crocodilia: i.e...
s, hence its name, which means "whale lizard". A year later, when Owen coined the name Dinosauria, he did not include Cetiosaurus and Cardiodon in that group.
In 1850, Gideon Mantell
Gideon Mantell
Gideon Algernon Mantell MRCS FRS was an English obstetrician, geologist and palaeontologist...
recognized the dinosaurian nature of several bones assigned to Cetiosaurus by Owen. Mantell noticed that the leg bones contained a medullary cavity
Medullary cavity
The medullary cavity is the central cavity of bone shafts where red bone marrow and/or yellow bone marrow is stored; hence, the medullary cavity is also known as the marrow cavity...
, a characteristic of land animals. He assigned these specimens to the new genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Pelorosaurus
Pelorosaurus
Pelorosaurus was a huge plant-eating dinosaur. Pelorosaurus was one of the first sauropod dinosaurs ever discovered. Pelorosaurus lived during the Early Cretaceous period, about 138-112 million years ago. Fossils referred to Pelorosaurus have been found in England and Portugal...
, and grouped it together with the dinosaurs. However, Mantell still did not recognize the relationship to Cetiosaurus.
The next sauropod find to be described and misidentified as something other than a dinosaur were a set of hip vertebrae described by Harry Seeley
Harry Seeley
Harry Govier Seeley was a British paleontologist.-Career:Seeley was born in London, the son of Richard Hovill Seeley, goldsmith, and his second wife Mary Govier. He attended classes at the Royal School of Mines, Kensington before becoming an assistant to Adam Sedgwick at the Woodwardian Museum,...
in 1870. Seeley found that the vertebrae were very lightly constructed for their size and contained openings for air sacs (pneumatization). Such air sacs were at the time known only in bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s and pterosaur
Pterosaur
Pterosaurs were flying reptiles of the clade or order Pterosauria. They existed from the late Triassic to the end of the Cretaceous Period . Pterosaurs are the earliest vertebrates known to have evolved powered flight...
s, and Seeley considered the vertebrae to come from a pterosaur. He named the new genus Ornithopsis
Ornithopsis
Ornithopsis was a medium-sized Early Cretaceous sauropod dinosaur, from England. It has been considered a synonym of the wastebasket taxon Pelorosaurus, but recent research suggests that this is not as clear-cut as supposed...
, or "bird face" because of this.
When more complete specimens of Cetiosaurus were described by Phillips in 1871, he finally recognized the animal as a dinosaur related to Pelorosaurus. However, it was not until the description of new, nearly complete sauropod skeletons from the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
(representing Apatosaurus
Apatosaurus
Apatosaurus , also known by the popular but scientifically deprecated synonym Brontosaurus, is a genus of sauropod dinosaur that lived from about 154 to 150 million years ago, during the Jurassic Period . It was one of the largest land animals that ever existed, with an average length of and a...
and Camarasaurus
Camarasaurus
Camarasaurus meaning 'chambered lizard', referring to the hollow chambers in its vertebrae was a genus of quadrupedal, herbivorous dinosaurs. It was the most common of the giant sauropods to be found in North America...
) later that year that a complete picture of sauropods emerged. An approximate reconstruction of a complete sauropod skeleton was produced by John A. Ryder, based on the remains of Camarasaurus, though many features were still inaccurate or incomplete according to later finds and biomechanical studies. Also in 1877, Richard Lydekker
Richard Lydekker
Richard Lydekker was an English naturalist, geologist and writer of numerous books on natural history.-Biography:...
named another relative of Cetiosaurus, Titanosaurus
Titanosaurus
Titanosaurus is a genus of sauropod dinosaur, first described by Lydekker in 1877. It is known from the Maastrichtian Lameta Formation of India...
, based on an isolated vertebra.
In 1878, the most complete sauropod yet was found and described by Othniel Charles Marsh
Othniel Charles Marsh
Othniel Charles Marsh was an American paleontologist. Marsh was one of the preeminent scientists in the field; the discovery or description of dozens of news species and theories on the origins of birds are among his legacies.Born into a modest family, Marsh was able to afford higher education...
, who named it Diplodocus
Diplodocus
Diplodocus , or )is a genus of diplodocid sauropod dinosaur whose fossils were first discovered in 1877 by S. W. Williston. The generic name, coined by Othniel Charles Marsh in 1878, is a Neo-Latin term derived from Greek "double" and "beam", in reference to its double-beamed chevron bones...
. With this find, Marsh also created a new group to contain Diplodocus, Cetiosaurus, and their increasing roster of relatives to differentiate them from the other major groups of dinosaurs. Marsh named this group Sauropoda, or "lizard feet".
Classification
Classification of the sauropods has largely stabilised in recent years, though there are still some uncertainties, such as the placement of EuhelopusEuhelopus
Euhelopus is a genus of sauropod dinosaur that lived during the Early Cretaceous, between 130 and 112 million years ago . It lived in what is now Shandong Province in China. A large herbivore, it weighed approximately 15-20 tons and attained an adult length of 15m...
, Haplocanthosaurus
Haplocanthosaurus
Haplocanthosaurus is a genus of sauropod dinosaur. Two species, H. delfsi and H. priscus, are known from incomplete fossil skeletons. It lived during the late Jurassic period , 155 to 152 million years ago. The type species is H. priscus, and the referred species H...
, Jobaria
Jobaria
Jobaria was a sauropod dinosaur discovered in the Sahara Desert in 1997. It was named after "Jobar", a creature of local legends, and is thought to have been about 18 metres long. It was found in the Tiourarén Formation, originally thought to represent the Hauterivian to Barremian stages of the...
and Nemegtosauridae
Nemegtosauridae
Nemegtosauridae is a family of probably titanosaurian sauropod dinosaurs based originally on two late Cretaceous Mongolian species known only from their diplodocid-like skulls: Nemegtosaurus and Quaesitosaurus. Authorities disagree as to the relationship of these two genera with other sauropods,...
. The following are two alternative recent classifications (showing supra-generic clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
s only in the second example). These are by no means an exhaustive list of recent sauropod classification schemes. In some cases, families like Vulcanodontidae, Cetiosauridae and Omeisauridae are not included because they are considered paraphyletic, or even (in the case of Camarasauridae) polyphyletic.
Taxonomy
This taxonomy follows Wilson & Sereno 1998, Yates 2003 and 2010, Galton 2001,http://dml.cmnh.org/2003Jul/msg00103.html and Wilson 2002, with ranks after Benton, 2004.- Infraorder Sauropoda
- IsanosaurusIsanosaurusIsanosaurus was one of the first true sauropod dinosaurs, with all four legs always on the ground. It lived 210 million years ago in Thailand. The type species is Isanosaurus attavipachi...
- KotasaurusKotasaurusKotasaurus is the name given to a genus of dinosaur from the Early Jurassic period, about 208 million to 188 million years ago. It was an early sauropod, sharing some similarities with prosauropods...
- LessemsaurusLessemsaurusLessemsaurus is an extinct genus of sauropodomorph dinosaur named for the writer of popular science books Don Lessem. The type species, L. sauropoides, was formally described by José Fernando Bonaparte in 1999...
- Family BlikanasauridaeBlikanasaurusBlikanasaurus was a genus of sauropodomorph dinosaur found in Lower Elliot Formation rocks from the Late Triassic in what is now South Africa's Cape Province. Known from a left lower limb only, it has been variously classified as a prosauropod or basal sauropod...
- Family MelanorosauridaeMelanorosauridaeThe Melanorosauridae were a family of sauropodomorph dinosaurs which lived during the Late Triassic and Early Jurassic. The name Melanorosauridae was first coined by Friedrich von Huene in 1929. Huene assigned several families of dinosaurs to the infraorder Prosauropoda: the Anchisauridae, the...
- Family VulcanodontidaeVulcanodontidaeThe Early Jurassic sauropod dinosaurs Zizhongosaurus, Barapasaurus, Tazoudasaurus, and Vulcanodon may form a natural group of basal sauropods called the Vulcanodontidae. Basal vulcanodonts include some of the earliest known examples of sauropods. The family-level name Vulcanodontidae was erected by...
- Family Cetiosauridae
- Family OmeisauridaeOmeisauridaeOmeisauridae is a family of sauropods. Wilson, when naming the family in 2002, included Omeisaurus and Mamenchisaurus, but if Mamenchisaurus is included, Mamenchisauridae has priority, as it was named in 1972...
- ?Family TendaguridaeTendaguriaTendaguria is a genus of sauropod dinosaur from the Late Jurassic of Tanzania.It was a large sauropod from the Tendaguru fossil locality in Tanzania; based on two anterior dorsal vertebrae from Nambango, 15 kilometers southeast of Tendaguru Hill, Tanzania, probably in the Upper...
- Clade TuriasauriaTuriasauriaTuriasauria is an unranked clade of sauropod dinosaurs, named for the genus Turiasaurus, a gigantic eusauropod from southwestern Europe. The clade also includes two other known members, Galveosaurus and Losillasaurus. All three taxa thus far referred to Turiasauria have come from the Villar del...
- Division NeosauropodaNeosauropodaNeosauropoda is a division-level clade of sauropods within Dinosauria, and consists of the group leading to Diplodocoidea and Macronaria. Haplocanthosaurus was a typical basal neosauropod from around 150 million years ago, in the Late Jurassic...
- HaplocanthosaurusHaplocanthosaurusHaplocanthosaurus is a genus of sauropod dinosaur. Two species, H. delfsi and H. priscus, are known from incomplete fossil skeletons. It lived during the late Jurassic period , 155 to 152 million years ago. The type species is H. priscus, and the referred species H...
- ?JobariaJobariaJobaria was a sauropod dinosaur discovered in the Sahara Desert in 1997. It was named after "Jobar", a creature of local legends, and is thought to have been about 18 metres long. It was found in the Tiourarén Formation, originally thought to represent the Hauterivian to Barremian stages of the...
- Superfamily DiplodocoideaDiplodocoideaDiplodocoidea was a superfamily of sauropod dinosaurs, which included some of the longest animals of all time, including slender giants like Supersaurus, Diplodocus, Apatosaurus, and Amphicoelias...
- Family RebbachisauridaeRebbachisauridaeRebbachisauridae is a family of sauropod dinosaurs known from fragmentary fossil remains from the Cretaceous of South America, Africa, and Europe.-Taxonomy:...
- Family DicraeosauridaeDicraeosauridaeDicraeosauridae is a family of sauropod dinosaurs known from the Late Jurassic and Early Cretaceous of Africa and South America. Currently only three genera are recognised; the Jurassic South American genus Brachytrachelopan, the Jurassic African Dicraeosaurus and the South American Early...
- Family Diplodocidae
- Family Rebbachisauridae
- Subdivision MacronariaMacronariaMacronaria is a clade of sauropod dinosaurs from the Middle Jurassic to Late Cretaceous Periods of what are now North America, South America, Europe, Asia and Africa. The name means 'large nostrils' , in reference to the large nasal openings high on the head that probably supported fleshy...
- Family BrachiosauridaeBrachiosauridaeBrachiosauridae are a family of dinosaurs, whose members are known as brachiosaurids. They were herbivorous quadrupeds with longer forelegs than hind legs - the name derives from the Greek for arm lizard - and long necks...
- Family Camarasauridae
- Family EuhelopodidaeEuhelopusEuhelopus is a genus of sauropod dinosaur that lived during the Early Cretaceous, between 130 and 112 million years ago . It lived in what is now Shandong Province in China. A large herbivore, it weighed approximately 15-20 tons and attained an adult length of 15m...
- Superfamily Titanosauroidea
- Family Brachiosauridae
- Haplocanthosaurus
- Isanosaurus
Phylogeny
CladogramCladogram
A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...
simplified after Wilson, 2002.