Diplodocid

Diplodocid

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Diplodocids, or members of the family Diplodocidae ("double beams"), are a group of sauropod dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...

s. The family includes some of the longest creatures ever to walk the earth, including Diplodocus
Diplodocus
Diplodocus , or )is a genus of diplodocid sauropod dinosaur whose fossils were first discovered in 1877 by S. W. Williston. The generic name, coined by Othniel Charles Marsh in 1878, is a Neo-Latin term derived from Greek "double" and "beam", in reference to its double-beamed chevron bones...

and Supersaurus
Supersaurus
Supersaurus is a genus of diplodocid sauropod dinosaur discovered by Vivian Jones of Delta, Colorado, in the Upper Jurassic Morrison Formation of Colorado in 1972. The fossil remains came from the Brushy Basin Member of the formation, dating to about 153 million years ago...

, which may have reached lengths of up to 34 metres (111.5 ft).

Description


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
Dachshund
The dachshund is a short-legged, long-bodied dog breed belonging to the hound family. The standard size dachshund was bred to scent, chase, and flush out badgers and other burrow-dwelling animals, while the miniature dachshund was developed to hunt smaller prey such as rabbits...

" of giant dinosaurs; and their rear legs were longer than front legs, giving their back a distinctive downward slope towards the neck.
In the early 1990s, a diplodocid specimen was described with a row of keratinous (horny
Horn (anatomy)
A horn is a pointed projection of the skin on the head of various animals, consisting of a covering of horn surrounding a core of living bone. True horns are found mainly among the ruminant artiodactyls, in the families Antilocapridae and Bovidae...

, not bony) spines running down the base of the tail. Further finds have shown that rather than forming a spiny ridge down the back (as in modern reptiles like the iguana
Iguana
Iguana is a herbivorous genus of lizard native to tropical areas of Central America and the Caribbean. The genus was first described in 1768 by Austrian naturalist Josephus Nicolaus Laurenti in his book Specimen Medicum, Exhibens Synopsin Reptilium Emendatam cum Experimentis circa Venena...

), these spines were more uniformly distributed over the animal's torso. Since dermal tissue is rarely preserved in the fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

 record it is not known how widespread the feature is, but spines may have been a common feature among diplodocids.

Their necks were also extremely long, and according to recent computer simulation
Computer simulation
A computer simulation, a computer model, or a computational model is a computer program, or network of computers, that attempts to simulate an abstract model of a particular system...

s 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 marsh
Marsh
In geography, a marsh, or morass, is a type of wetland that is subject to frequent or continuous flood. Typically the water is shallow and features grasses, rushes, reeds, typhas, sedges, other herbaceous plants, and moss....

y 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 gastrolith
Gastrolith
A gastrolith, also called a stomach stone or gizzard stones, is a rock held inside a gastrointestinal tract. Gastroliths are retained in the muscular gizzard and used to grind food in animals lacking suitable grinding teeth. The grain size depends upon the size of the animal and the gastrolith's...

s (gizzard stones) to break down tough plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...

 fibers (similar to modern bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

s).

Diplodocids also had long, whip-like tail
Tail
The tail is the section at the rear end of an animal's body; in general, the term refers to a distinct, flexible appendage to the torso. It is the part of the body that corresponds roughly to the sacrum and coccyx in mammals, reptiles, and birds...

s, 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
Bullwhip
A bullwhip is a single-tailed whip, usually made of braided leather, which was originally used as a tool for working with livestock.Bullwhips are pastoral tools, traditionally used to control livestock in open country...

. This could generate a sonic boom
Sonic boom
A sonic boom is the sound associated with the shock waves created by an object traveling through the air faster than the speed of sound. Sonic booms generate enormous amounts of sound energy, sounding much like an explosion...

 in excess of 200 decibel
Decibel
The decibel is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities...

s, 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, which may be a symptom of cracking their tails.

Skin


Few skin impressions of diplodocids have been found. However, at least one significant find first reported by Stephen Czerkas in 1992 preserved portions of the skin from around the tip of the tail, or "whiplash". Czerkas noted that the skin preserved a sequence of conical spines, and that other, larger spines were found scattered around larger tail vertebrae. The spines appeared to be oriented in a single row along the mid-line of the tail, and Czerkas speculated that this midline row may have continued over the animals entire back and neck.

Classification


Diplodocidae was the third name given to what is now recognized as the single family of long-necked, whip-tailed sauropods. Edward Drinker Cope
Edward Drinker Cope
Edward Drinker Cope was an American paleontologist and comparative anatomist, as well as a noted herpetologist and ichthyologist. Born to a wealthy Quaker family, Cope distinguished himself as a child prodigy interested in science; he published his first scientific paper at the age of nineteen...

 named the family Amphicoeliidae in 1878 for his genus Amphicoelias
Amphicoelias
Amphicoelias is a genus of herbivorous sauropod dinosaur that includes what may be the largest dinosaur ever discovered, A. fragillimus. Based on surviving descriptions of a single fossil bone, A. fragillimus may have been the longest known vertebrate at in length, and may have had a mass of up...

, sometimes considered a diplodocid. However, the name Amphicoeliidae did not come into wider use and was not used in the scientific literature after 1899, making it a nomen oblitum
Nomen oblitum
A nomen oblitum is a technical term, used in zoological nomenclature, for a particular kind of disused scientific name....

("forgotten name") according to the ICZN
International Code of Zoological Nomenclature
The International Code of Zoological Nomenclature is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals...

, preventing it from displacing the name Diplodocidae as a senior synonym. More recent studies have also shown that Amphicoelias itself does not belong to this family, but is instead a more primitive diplodocoid. A similar situation occurred for the family name Atlantosauridae, named by Othniel Charles Marsh
Othniel Charles Marsh
Othniel Charles Marsh was an American paleontologist. Marsh was one of the preeminent scientists in the field; the discovery or description of dozens of news species and theories on the origins of birds are among his legacies.Born into a modest family, Marsh was able to afford higher education...

 in 1877, and which Hay argued had priority over Amphicoelidae. George Olshevsky declared Atlantosauridae a nomen oblitum in 1991, though scientists such as Steel and Nowinski had treated Atlantosauridae as a valid name as late as 1971, and the former even added a subfamily, Atlantosaurinae.

Some dinosaurs have been considered diplodocids in the past but have not been found to be members of that group in later, larger analyses of the family's relationships. Australodocus
Australodocus
Australodocus, meaning "southern beam" from the Latin australis "southern" and the Greek dokos/δοκоς "beam", is a sauropod dinosaur that lived during the Late Jurassic period, around 150 million years ago in what was then German East Africa...

, for example, was initially described as a diplodocid, but may actually have been a Macronaria
Macronaria
Macronaria is a clade of sauropod dinosaurs from the Middle Jurassic to Late Cretaceous Periods of what are now North America, South America, Europe, Asia and Africa. The name means 'large nostrils' , in reference to the large nasal openings high on the head that probably supported fleshy...

n. Amphicoelias was traditionally been considered a diplodocid due to its similar anatomy, but phylogenetic studies showed it to be a more basal member of the Diplodocoidea.

The relationships of species within diplodocidae has also been subject to frequent revision. A study by Lovelace, Hartman and Wahl in 2008 found that Suuwassea
Suuwassea
Suuwassea is a genus of diplodocoid sauropod dinosaur found in the Upper Jurassic strata of the Morrison Formation, located in southern Carbon County, Montana, USA. The fossil remains were recovered in a series of expeditions during a period spanning the years 1999 and 2000, described by J.D....

and Supersaurus were relatives of Apatosaurus, within the subfamily Apatosaurinae. However, subsequent analysis by Whitlock in 2011 showed that Supersaurus is slightly closer to Diplodocus than to Apatosaurus, and that Suuwassea is actually a primitive dicraeosaurid
Dicraeosauridae
Dicraeosauridae is a family of sauropod dinosaurs known from the Late Jurassic and Early Cretaceous of Africa and South America. Currently only three genera are recognised; the Jurassic South American genus Brachytrachelopan, the Jurassic African Dicraeosaurus and the South American Early...

.
Cladogram
Cladogram
A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...

 of the Diplodocidae after Lovelace, Hartman, and Wahl, 2008.

Cladogram
Cladogram
A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...

 of the Diplodocidae after Whitlock, 2011.


  • Family Diplodocidae
    • Dystrophaeus
      Dystrophaeus
      Dystrophaeus is the name given to an extinct genus of dinosaur from the early Kimmeridgian stage of the Late Jurassic that existed around 155.7 Ma. It was perhaps a diplodocoid sauropod. Its fossils were found in the Morrison Formation of Utah....

      ?
    • Subfamily Apatosaurinae
      • Apatosaurus
        Apatosaurus
        Apatosaurus , also known by the popular but scientifically deprecated synonym Brontosaurus, is a genus of sauropod dinosaur that lived from about 154 to 150 million years ago, during the Jurassic Period . It was one of the largest land animals that ever existed, with an average length of and a...

      • Atlantosaurus
        Atlantosaurus
        Atlantosaurus is a dubious genus of sauropod dinosaur. The type specimen, found by Arthur Lakes in the Morrison Formation of Colorado, USA, was described by Othniel Charles Marsh, a Professor of Paleontology at Yale University , in 1877 as "Titanosaurus" montanus...

      • Eobrontosaurus
        Eobrontosaurus
        Eobrontosaurus is the name given to a genus of dinosaur from the Late Jurassic of North America. It was a sauropod probably closely related to Apatosaurus. It is known from a single site from the lower Morrison Formation, dating to about 154 million years ago. It grew up to long.The type species, E...

    • Subfamily Diplodocinae
      • Barosaurus
        Barosaurus
        Barosaurus ; Greek barys/βαρυς meaning 'heavy' and saurus/σαυρος meaning 'lizard', 'heavy lizard') was a giant, long-tailed, long-necked, plant-eating dinosaur closely related to the more familiar Diplodocus...

      • Dinheirosaurus
        Dinheirosaurus
        Dinheirosaurus is a genus of diplodocid sauropod dinosaur. It has been found in the upper section of the Late Jurassic strata of the Camadas de Alcobaça Formation located in central-western Portugal at Porto Dinheiro, Lourinhã...

      • Diplodocus
        Diplodocus
        Diplodocus , or )is a genus of diplodocid sauropod dinosaur whose fossils were first discovered in 1877 by S. W. Williston. The generic name, coined by Othniel Charles Marsh in 1878, is a Neo-Latin term derived from Greek "double" and "beam", in reference to its double-beamed chevron bones...

      • Supersaurus
        Supersaurus
        Supersaurus is a genus of diplodocid sauropod dinosaur discovered by Vivian Jones of Delta, Colorado, in the Upper Jurassic Morrison Formation of Colorado in 1972. The fossil remains came from the Brushy Basin Member of the formation, dating to about 153 million years ago...

        ?
      • Tornieria
        Tornieria
        Tornieria is a genus of diplodocid sauropod dinosaur from Late Jurassic of Tanzania. It has a convoluted taxonomic history.-Discovery and naming:...


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