Sauropoda

Template:Infobox Taxonomy

Sauropoda meaning 'lizard-footed' in Greek, is a suborder or infraorder of the saurischian order of dinosaurs. They were the largest animals ever to have lived on land. The more famous members of this genus include the well known Apatosaurus, which was well-known as Brontosaurus, Brachiosaurus and Diplodocus. Sauropods first emerged as a species during the late Triassic Period, somewhat resembling the earlier Prosauropoda. However, by the late Jurassic Period, the sauropods had vast numbers, particularly in the diplodicids and brachiosaurids species. This is evident by the fact that fossilized remains of the species have been found on every continent except Antarctica. However, as complete fossil records of sauropod species 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.

General Description

Size

The Sauropods' most defining characteristic was their size. Even the smallest of the species, the dwarf sauropods, grew up to 5 to 6 metres in length, and were counted as some of the largest dinosaurs in their ecosystem. As the largest animals to have ever walked on land, the only competitor in the history of the animal kingdom are the rorqual whales, such as the blue whale.

Comparison of selected sauropods in terms of size

While many dinosaurs of different genus had individual variations from their related cousins, the sauropods had little variation between the individual species, possibly due to the forced shared evolution caused by size constraints. However, some members of the genus had individual characteristics, such as the diplodocids, who had extrememly long, whip-like tails, possibly as a defense mechanism against predators. Seismosaurus,the longest of the sauropods, would reach lengths of around 39–52 metres, most likely around 45 metres. Other sauropods, such as the brachiosaurids, were extremely tall, and had high shoulders and extremely long necks used for foraging in the high tree canopies. The Sauroposeidon was most likely the tallest of the sauropods, reaching a height of 18 metres. In terms of today's animal kingdom, the tallest living animal is the giraffe, which reaches only 4.8 to 5.5 metres in height. Due to their massive height and length, the sauropods were also the largest dinosaurs to walk on the earth. One of heaviest of the class was Argentinosaurus, which most likely weighed approximately 75 to 100 metric tonnes. Other sauropods were of comparable size to the Argentinosaurus, but there is some circumstantial evidence that an even more massive titanosaurian, the Bruhathkayosaurus, weighed a possible 175 to 220 tonnes, although a land animal this size would not have been able to support it's own weight. By comparison, the largest land animal alive today is the Savannah elephant, which weighs only 10 tonnes.

The sauropods were herbivorous creatures, and usually were quadrupeds due to their massive girth. They shared a common characteristic of small heads, with large, massive bodies and long, counter-balancing tails. At least some of the species were egg-layers, as evidence has been found that the camarasaurs and titanosaurs laid eggs. Due to their gigantic size, sauropods had thick legs to support their weight, with blunt, balanced feet that ended in five toes.

Armour

Ampelosaurus, illustrated with body armor

Typically, the sauropods main defensive mechanism against predatory dinosaurs were their intimidating size, which would discourage attacks from the much smaller carnivores, and their long tails, which in some cases could most likely be used like a whip. However, some sauropods developed further protection, in the form of body armor. The Agustinia, for example, developed spined backs, while some species, such as the Shunosaurus, had small clubs on their tails to use as a defensive weapon. Several titanosaurs, such as Saltasaurus and Ampelosaurus, had small bony protrusions covering portions of their bodies, to protect against bites and claw scratches.

Posture

There has been speculation since research into the sauropods began that the creatures could possibly rear up on their hind legs, using their tail as a balance, similar to a tripod. Speculation suggested the creatures did this in order to reach higher fauna in treetops that were inaccessible to even them. However, it has been also suggested that if these creatures could adopt a bipedal posture, there would be evidence of stress fractures in the forelimbs, from when the dinosaurs would come back down to the earth in a quadrupedal posture. There has been no evidence to support such a claim found while examining a large number of sauropod skeletons. Also, if a sauropod had stood, even briefly, in a bipedal stance, there would be massive weight placed on tail. As the sauropod grew and matured, it would grow in size, and therefore the haemal spines near the tail would have to carry an increasing amount of weight. This would likely cause some of the spines to break from the stress, and make rearing painful for the sauropod. As there has been evidence of haemal spine fractures in sauropod tail vertebrae, it has been suggested that the sauropods could possibly rear into a bipedal position during youth, or before they have fully matured, but the haemal spine may have developed into a safety measure to prevent the sauropod from rearing up once it has fully developed.

The image of a sauropod rearing on its hind legs was made famous in the film Jurassic Park, which showed a Brachiosaurus, the first dinosaur fully seen in the film, rearing on its hind legs to reach a section of a tree inaccessible to its quadrupedal height.

Classification

Taxonomy

Infraorder Sauropoda
- Ammosaurus
- Anchisaurus
- ?Isanosaurus
- Kotasaurus
- Lessemsaurus
- Family Blikanasauridae
- Family Melanorosauridae
- Family Vulcanodontidae
- Family Cetiosauridae
- Family Omeisauridae
- ?Family Tendaguridae
- Clade Turiasauria
- Division Neosauropoda
  - Haplocanthosaurus
  - ?Jobaria
  - Superfamily Diplodocoidea
    - Family Rebbachisauridae
    - Family Dicraeosauridae
    - Family Diplodocidae
  - Subdivision Macronaria
    - Family Brachiosauridae
    - Family Camarasauridae
    - Family Euhelopodidae
    - Superfamily Titanosauroidea