Diplodocids, or members of the family Diplodocidae, are sauropod dinosaurs such as the Diplodocus and the Apatosaurus. The family includes some of the longest creatures ever to walk the earth, including the Supersaurus, and the Seismosaurus, which might have reached lengths of up to 40 m (130 ft.).

While still massive, when compared to the titanosaurs and brachiosaurs, the diplodocids were relatively slender but extremely long. They had short legs, making them the "dachshund" of giant dinosaurs; and their rear legs were longer than than front legs, giving their back a distinctive downward slope towards the neck.

A diplodocid was recently found with a row of keratinous (horny, not bony) spines running down its back. Since dermal tissue is rarely preserved in the fossil record it is not known how widespread the feature is, but sails may be a common feature among diplodocids.

Their necks were also extremely long, and according to recent computer simulations they may not have been able to lift their necks like other sauropods. Instead of reaching up into trees, they may have used their necks to graze over a broad area. They may also have used their necks to reach into dense stands of conifers, or over marshy ground. Alternatively the whole of the body was raised by standing on the hind legs or by resting the front legs on some hillock.

Like other sauropods, their heads are tiny with the nostrils on the top of the head, but unlike other sauropods they have a long, sloping snout. Their teeth are only in the front of their mouth, and look like pencils or pegs. They probably used their teeth to crop off food, without chewing, and relied on gastroliths (swallowed stones) to break down tough plant fibers (similar to the way modern birds swallow gizzard stones).

Diplodocids also have a long, whip-like tail. It is thick at the base, and tapers off to be very thin at the end. Computer simulations have shown that the diplodocids could have easily snapped their tails, like a bullwhip. This could generate a sonic boom in excess of 200 decibels, and may have been used in mating displays, or to drive off predators. There is some circumstantial evidence supporting this as well: A number of diplodocids have been found with fused or damaged tail vertebrae (bones in the spine), which may be a symptom of cracking their tails.

The Amphicoelias genera, which includes the rather dubious but spectactularly long Amphicoelias fragillimus, may also be a member of this family; but is usually classified as an incertae sedis (unknown) member of the parent clade, the Diplodocidimorpha. Not enough is known about the genera to classify it more precisely.

External links

• Cracking the whip (http://www.newscientist.com/hottopics/dinosaurs/tails.jsp), from the NewScientist.
• Ivan Peterson's Whips and Dinosaur Tails (http://dml.cmnh.org/1997Dec/msg00064.html).
• The Dinosauricon's cladogram (http://dinosauricon.com/taxa/diplodocidae.html) of Diplodocidae.