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Titanosaurs were a diverse group of sauropod dinosaurs, which included Saltasaurus and Isisaurus. This family includes some of the heaviest creatures ever to walk the earth, such as the Argentinosaurus and the Paralititan — which might have weighed up to 100 tonnes (110 short tons), or perhaps even double that, if some poorly-described data is believed (see the Bruhathkayosaurus).

Characteristics

Titanosaurs had small heads, even when compared to other sauropods. The head was also wide, similar to the heads of the Camarasaurus and the Brachiosaurus, but more elongated. Their nostrils were large ("marcronarian"), and they all had crests formed by these nasal bones. Their teeth were either somewhat spatulate (spoon-like), or like pegs or pencils, but were always very small.

Their necks were relatively short, for sauropods, and their tail was whip-like but not as long as a diplodocid. While the pelvis (hip area) was slimmer than some sauropods, the pectoral (chest area) was much wider, giving them a uniquely "wide-gauged" stance. As a result, the fossiled trackways of titanosaurs are distinctly broader than other sauropods. Their forelimbs were also stocky, but their rear limbs were longer. Their vertebrae (back bones) were solid (not hollowed-out), which may be a throwback to more primitive saurischians. Their spinal column was more flexible, so they were probably more agile than their cousins, and better at rearing up.

From skin impressions found with the fossils, it has been determined that their skin was armored with a small mosaic of small, bead-like scales around a larger scale. One species has even been discovered with bony plates, like the Ankylosaurus.

While they were all huge, many were fairly average in size compared to the other giant dinosaurs. There were even some island-dwelling dwarf species, probably the result of allopatric speciation.

Browsing and grazing diet

Fossilized dung associated with late Cretaceous titanosaurids has revealed phytoliths, silicified plant fragments, that offer clues to a broad, unselective plant diet. Besides the plant remains that might have been expected such as cycads and conifers, discoveries published in 2005 * revealed an unexpectedly wide range of monocotyledons including palms and grasses (Poaceae), including ancestors of rice and bamboo, suggesting that herbivorous dinosaurs and grasses co-evolved.

Nesting grounds

A large titanosaurid nesting ground was recently discovered in Auca Mahuevot, in Patagonia, Argentina, and another colony has reportedly been discovered in Spain. The small eggs, about 11–12 cm (4–5 in.) in diameter, contained fossiled embryos, complete with skin impressions (though there was no indication of feathers or dermal spines). Apparently several hundred female saltosaurs dug holes, laid their eggs, and then buried them under dirt and vegetation. This gives evidence of herd behavior, which along with their armor, may have been a defense against large predators like the Abelisaurus.

Range

The titanosaurs were the last great group of sauropods before the Cretaceous-Tertiary extinction event, about 65–90 million years ago, and were the dominant herbivores of their time. The fossil evidence suggests they replaced the other sauropods, like the diplodocids and the brachiosaurids, which died out between the late Jurassic and the mid-Cretaceous.

They were widespread, especially in the southern continents that were then part of the supercontinent of Gondwana, even Australia, where sauropod remains in Queensland have recently been determined to be titanosaurid. Only Antarctica appears to have never been populated by titanosaurs.

Classification

For such a widespread and successful group (they represent roughly a third of the total sauropod diversity known to date), the fossil record of titanosaurs is poor. Only recently have skulls or relatively complete skeletons (see Rapetosaurus) of any of the roughly 50 species of titanosaur been discovered. Many are poorly known, and much of the material may be deemed invalid, or reclassified as understanding of the clade grows. The anchor taxon, the "Titanosaurus", is particularly poorly known and no longer considered a valid taxon.

The family Titanosauridae was named after the poorly known and probably invalid genus "Titanosaurus", which was coined by Lydekker in 1877 on the basis of a partial femur and two incomplete caudal vertebrae. Fourteen species have since been referred to "Titanosaurus", which distribute the genus across Argentina, Europe, Madagascar, India and Laos, and throughout 60 million years of the Cretaceous. Despite its centrality to titanosaur systematics and biogeography, a re-evaluation of all "Titanosaurus" species recognises as diagnostic only five. The type species T. indicus is invalid because it is based on 'obsolescent' characters - once diagnostic features that have gained a broader taxonomic distribution over time. Consequently, use of the genus "Titanosaurus" has largely been abandoned. The most well known "Titanosaurus" specimens have since been re-assigned to other genera, including Isisaurus. However, if Titanosaurus indicus is redescribed in the future on the basis of new remains, Titanosaurus itself becomes provisionally valid.

Some authors (like Sereno, 2005 contend that since the name "Titanosaurus" is invalid, its co-ordinated rank-taxa (e.g. Titanosaurinae, Titanosauridae, Titanosauroidea) must be abandoned [http://www.dinodata.net/Dd/Namelist/CLASSIF/Titanosauria.htm. However, while it is possible under ICZN rules to suppress family names due to dubious type species, this is not typically carried out in practice (such families as Hadrosauridae and Ceratopsidae are also based on dubious genera, Hadrosaurus and Ceratops respectively).

Normally, workers who consider all "Titanosaur-" names invalid promote Saltasaurinae and Nemegtosaurinae to family status, and leave the remaining genera outside any family.

Taxonomy

A Recent Discovery in Italy

Four well preserved skeletons of Titanosaur were found in Italy, first reported on May 2, 2006. Italian paleontologists say that this discovery will force a reassessement of current Titanosaur morphology. *

References

External links

Titanosaurs

ديناصورات مصر | Titanosauridae | Titanosauridae | Titanosauridae | Titanosauria | טיטנוזאורידים | Titanosauria

 

This article is licensed under the GNU Free Documentation License. It uses material from the "Titanosaur".

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