Titanosaur

Titanosaurs (members of the group Titanosauria) were a diverse group of sauropod dinosaurs which included Saltasaurus and Isisaurus of Africa, Asia, South America, Europe and Australia. The titanosaurs were the last surviving group of long-necked sauropods, with taxa still thriving at the time of the extinction event at the end of the Cretaceous. The group includes the largest land animals known to have existed, such as Patagotitan—estimated at 37 m (121 ft) long with a weight of 69 tonnes (76 tons)—and the comparably sized Argentinosaurus and Puertasaurus from the same region. The group's name alludes to the mythological Titans of Ancient Greece, via the type genus (now considered a nomen dubium) Titanosaurus. Together with the brachiosaurids and relatives, titanosaurs make up the larger clade Titanosauriformes. Titanosaurs had small heads, even when compared with other sauropods. The head was also wide, similar to the heads of Camarasaurus and Brachiosaurus but more elongated. Their nostrils were large ('macronarian') 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 of average length, for sauropods, and their tails were whip-like, but not as long as in the diplodocids. 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 fossilised trackways of titanosaurs are distinctly broader than other sauropods. Their forelimbs were also stocky, and often longer than their hind limbs. Their vertebrae (back bones) were solid (not hollowed-out), which may be a throwback to more basal saurischians. Their spinal column was more flexible, so they were probably more agile than their cousins and better at rearing up. Unlike other sauropods, some titanosaurs had no digits or digit bones, and walked only on horseshoe-shaped 'stumps' made up of the columnar metacarpal bones. From skin impressions found with the fossils, it has been determined that the skin of many titanosaur species was armored with a small mosaic of small, bead-like scales around a larger scale. One species, Saltasaurus, has even been discovered with bony plates, like the ankylosaurs. Studies published in 2011 also indicate that titanosaurs such as Rapetosaurus (on which the examinations were performed), may have used the osteoderms common in the various genera for storing minerals during harsh changes in climate, such as drought. While they were all huge, many were fairly average in size compared with the other giant dinosaurs. There were even some island-dwelling dwarf species such as Magyarosaurus, probably the result of allopatric speciation and insular dwarfism. The family Titanosauridae was once used for derived titanosaurs, but Wilson and Upchurch (2003) found the type genus Titanosaurus dubious based on the figures and original description. Weishampel et al., in the second edition of The Dinosauria, also did not use the family Titanosauridae, and instead used several smaller titanosaur families such as Saltasauridae and Nemegtosauridae, coining Lithostrotia for derived titanosaurs. A handful of Argentine sauropod workers, however, continue to use Titanosauridae for titanosaurs now placed in Lithostrotia. In the second edition of The Dinosauria, the clade Titanosauria was defined as all sauropods closer to Saltasaurus than to Brachiosaurus. Subsequent cladistic analyses have defined Titanosauria as including Saltasaurus but not Euhelopus or Brachiosaurus. Relationships within the Titanosauria have historically been extremely variable from study to study, complicated by the fact that clade and rank names have been applied inconsistently by various scientists. One possible cladogram is presented here, and follows a 2007 analysis by Calvo and colleagues. The authors notably used the family Titanosauridae in a broader fashion than other recent studies, and coined the new clade name Lognkosauria.