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Diplodocids Fossil range: Late Jurassic
Apatosaurus, an example of a diplodocid.
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Sauropsida Superorder: Dinosauria Order: Saurischia Suborder: Sauropodomorpha Superfamily: Diplodocoidea Family: Diplodocidae Marsh, 1884
Genera
?Amphicoelias Australodocus Dinheirosaurus Cetiosauriscus Subfamily Apatosaurinae Supersaurus Apatosaurus Eobrontosaurus Subfamily Diplodocinae Barosaurus Diplodocus Seismosaurus

Diplodocids, or members of the family Diplodocidae ("double beams"), were sauropod dinosaurs such as Diplodocus and Apatosaurus. The family includes some of the longest creatures ever to walk the earth, including Supersaurus and Seismosaurus, which might have reached lengths of up to 35 m (116 ft.).

While still massive, when compared to the titanosaurids 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 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.

Like other sauropods, their heads were tiny with the nasal openings on the top of the head (though in life the nostrils themselves would have been close to the tip of the snout). Their teeth were only present in the front of the mouth, and looked like pencils or pegs. They probably used their teeth to crop off food, without chewing, and relied on gastroliths (gizzard stones) to break down tough plant fibers (similar to modern birds).

Diplodocids also had long, whip-like tails, which were thick at the base and tapered 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 rather dubious but spectactularly long Amphicoelias may also be a member of this family; but is usually classified as an incertae sedis (unknown) member of the parent clade, the Diplodocoidea. Not enough is known about the genus to classify it more precisely.

• Cracking the whip, from the NewScientist.
• Ivan Peterson's Whips and Dinosaur Tails.
• Skeletal restorations of several diplodocids, from Scott Hartman's Skeletal Drawing website.

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