The Diplodocidae are a family of sauropods which were named by O. C. Marsh in 1884 and mostly lived in the middle and upper Jurassic periods.. They are some of the largest animals that have ever existed at up to 60 metric tons, with long skulls, a light mandible, slender teeth, and peg-like legs. Plant eaters, these animals are best known for their size and whip-like tails which were used to balance out their necks. With such long necks, they could reach up higher on trees where there was less competition for greenery it is thought by some. Others say that they couldn't support their necks that well and just ate ground vegetation.

With the use of computers, biophysicists have found that these animals may have been able to crack their tails like whips. There have been a number of contradicting studies over the years about the necks of these animals and whether or not they could be lifted very high. The studies are still inconclusive.

Clades: Animalia: Vertebrata: Tetrapoda: Sauropsida: Archosauromorpha: Ornithodira: Dinosauria: Sauropodomorpha: Sauropoda: Diplodocimorpha

Diplodocidae

• unnamed form -- Early Cretaceous -- England
• Dinheirosaurus
• Dyslocosaurus
• Dystrophaeus
• Apatosaurinae
  • Apatosaurus
  • Eobrontosaurus
• Diplodocinae
  • indeterminate material -- Georgian Republic
  • Barosaurus
  • Diplodocus
    • Dystylosaurus
    • Seismosaurus
    • Supersaurus

Sources:
http://dinosauricon.com/taxa/diplodocidae.html
http://www.dinodata.net/Dd/Namelist/CLASSIF/Diplodocidae.htm
http://flood.nhm.ac.uk/cgi-bin/dino/body.dsml?bodytype=1&sort=Genus