Description[edit]
One of the best-known sauropods, Diplodocus was a very large, long-necked, quadrupedal animal, with a long, whip-like tail. Its fore limbs were slightly shorter than its hind limbs, resulting in a largely horizontal posture. The long-necked, long-tailed animal with four sturdy legs has been mechanically compared with a suspension bridge.[6] In fact, Diplodocus is the longest dinosaur known from a complete skeleton.[6] The partial remains of D. hallorum have increased the estimated length, though not as much as previously thought; when first described in 1991, discoverer David Gillette calculated it may have been up to 52 m (170 ft) long,[7] making it the longest known dinosaur (excluding those known from exceedingly poor remains, such as Amphicoelias). Some weight estimates ranged as high as 113 tons (125 US short tons). The estimated length was later revised downward to 33 metres (108 ft)[8] based on findings that show that Gillette had originally misplaced vertebrae 12–19 as vertebrae 20–27. The nearly complete Diplodocus skeleton at the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania, on which estimates of Seismosaurus are based, also was found to have had its 13th tail vertebra come from another dinosaur, throwing size estimates for Seismosaurusfurther off. While dinosaurs such as Supersaurus were probably longer, fossil remains of these animals are only fragmentary.[9] Modern mass estimates for Diplodocus (exclusive of D. hallorum) have tended to be in the 10- to 16-tonne (11– to 17.6-ton) range: 10 tonnes (11 tons);[10] 11.5 tonnes (12.7 tons);[11] 12.7 tonnes (14 tons);[12] and 16 tonnes (17.6 tons).[13]
Diplodocus had an extremely long tail, composed of about 80 caudal vertebrae,[14] which are almost double the number some of the earlier sauropods had in their tails (such asShunosaurus with 43), and far more than contemporaneous macronarians had (such as Camarasaurus with 53). Some speculation exists as to whether it may have had a defensive[15] or noisemaking (by cracking it like a coachwhip) function.[16] The tail may have served as a counterbalance for the neck. The middle part of the tail had 'double beams' (oddly shaped chevron bones on the underside, which gave Diplodocus its name). They may have provided support for the vertebrae, or perhaps prevented the blood vessels from being crushed if the animal's heavy tail pressed against the ground. These 'double beams' are also seen in some related dinosaurs.[17]
No skull has ever been found that can be confidently said to belong to Diplodocus, though skulls of other diplodocids closely related to Diplodocus (such as Galeamopus) are well known. The skulls of diplodocids were very small compared with the size of these animals. Diplodocus had small, 'peg'-like teeth that pointed forward and were only present in the anteriorsections of the jaws.[18] Its braincase was small. The neck was composed of at least 15 vertebrae and may have been held parallel to the ground and unable to be elevated much past horizontal.[19]
Like other sauropods, the manus (front "feet") of Diplodocus were highly modified, with the finger and hand bones arranged into a vertical column, horseshoe-shaped in cross section.Diplodocus lacked claws on all but one digit of the front limb, and this claw was unusually large relative to other sauropods, flattened from side to side, and detached from the bones of the hand. The function of this unusually specialized claw is unknown.[20]
Recent discoveries have suggested that Diplodocus and other diplodocids may have had narrow, pointed keratinous spines lining their back, much like those on an iguana.[21][22] This radically different look has been incorporated into recent reconstructions, notably Walking with Dinosaurs. How many diplodocids had this trait is unknown exactly.[23]
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