Diplodocids, or members of the family Diplodocidae ("double beams"), are a group of
sauropod
Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their bo ...
dinosaur
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
s. The family includes some of the longest creatures ever to walk the Earth, including ''
Diplodocus
''Diplodocus'' (, , or ) was a genus of diplodocid sauropod dinosaurs, 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 διπΠ...
'' and ''
Supersaurus
''Supersaurus'' (meaning "super lizard") is a genus of diplodocid Sauropoda, sauropod dinosaur that lived in North America during the Late Jurassic period. The type species, ''S. vivianae'', was first discovered by Vivian Jones of Delta, Colorad ...
'', some of which may have reached lengths of up to .
Description
![DiplodocusDB](https://upload.wikimedia.org/wikipedia/commons/8/87/DiplodocusDB.jpg)
Diplodocids were generally large animals, even by sauropod standards. Thanks to their long necks and tails, diplodocids were among the longest sauropods, with some species such as ''
Supersaurus vivianae
''Supersaurus'' (meaning "super lizard") is a genus of diplodocid sauropod dinosaur that lived in North America during the Late Jurassic period. The type species, ''S. vivianae'', was first discovered by Vivian Jones of Delta, Colorado, in the m ...
'' and ''
Diplodocus hallorum
''Diplodocus'' (, , or ) was a genus of diplodocid sauropod dinosaurs, 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 διπΠ...
'' estimated to have reached lengths of or more.
The heaviest diplodocids, such as ''Supersaurus'' and ''
Apatosaurus
''Apatosaurus'' (; meaning "deceptive lizard") is a genus of herbivorous sauropod dinosaur that lived in North America during the Late Jurassic period. Othniel Charles Marsh described and named the first-known species, ''A. ajax'', in 1877, an ...
'', may have weighed close to 40 tonnes.
However, not all diplodocids were so large; the South American species ''
Leinkupal laticauda
''Leinkupal'' is a genus of diplodocine sauropod known from the Early Cretaceous ( Late Berriasian to Early Valanginian stage) of the Bajada Colorada Formation, southeastern Neuquén Basin in the Neuquén Province of Argentina. It contains a ...
'' was one of the smallest diplodocids, with an estimated length of only .
Their heads, like those of other sauropods, 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
).
The heads of diplodocids have been widely depicted with the nostrils on top due to the position of the nasal openings at the apex of the skull. There has been speculation over whether such a configuration meant that diplodocids may have had a trunk.
A 2006 study surmised there was no paleoneuroanatomical evidence for a trunk.
It noted that the
facial nerve
The facial nerve, also known as the seventh cranial nerve, cranial nerve VII, or simply CN VII, is a cranial nerve that emerges from the pons of the brainstem, controls the muscles of facial expression, and functions in the conveyance of tas ...
in an animal with a trunk, such as an elephant, is large as it innervates the trunk. The evidence suggests that the facial nerve is very small in diplodocids. Studies by Lawrence Witmer (2001) indicated that, while the nasal openings were high on the head, the actual, fleshy nostrils were situated much lower down on the snout.
Diplodocids had long necks, which could reach an estimated length of in the largest, longest-necked species.
The neck was typically composed of 15 vertebrae, though in ''
Barosaurus
''Barosaurus'' ( ) was a giant, long-tailed, long-necked, plant-eating sauropod dinosaur closely related to the more familiar ''Diplodocus''. Remains have been found in the Morrison Formation from the Upper Jurassic Period of Utah and South Da ...
'', the neck probably had 16 vertebrae as the result of the incorporation of an additional vertebra from the dorsal series.
The habitual
neck posture of diplodocids is controversial; studies have proposed postures ranging from nearly straight and below horizontal
to an S-curve that reaches vertical.
Distinguishing anatomical features
![diploheads](https://upload.wikimedia.org/wikipedia/commons/a/ac/Diploheads.jpg)
A diagnosis is a statement of the anatomical features of an organism (or group) that collectively distinguish it from all other organisms. Some, but not all, of the features in a diagnosis are also autapomorphies - distinctive anatomical features that are unique to a given organism or group.
The clade Diplodocidae is distinguished based on the following characteristics:
*
nares: the external nares face dorsally; and the internarial bar is absent
*
jugal
The jugal is a skull bone found in most reptiles, amphibians and birds. In mammals, the jugal is often called the malar or zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species.
Anatomy ...
: the jugal forms a substantial part of the caudoventral margin of the
antorbital fenestra
An antorbital fenestra (plural: fenestrae) is an opening in the skull that is in front of the eye sockets. This skull character is largely associated with archosauriforms, first appearing during the Triassic Period. Among extant archosaurs, birds ...
*
quadratojugal The quadratojugal is a skull bone present in many vertebrates, including some living reptiles and amphibians.
Anatomy and function
In animals with a quadratojugal bone, it is typically found connected to the jugal (cheek) bone from the front and ...
processes: the angle between the rostral quadratojugal process and the dorsal quadratojugal process is approximately 130°
* paroccipital process: the distal end of the paroccipital process is rounded and tongue-like in shape
*
parasphenoid
The parasphenoid is a bone which can be found in the cranium of many vertebrates. It is an unpaired dermal bone which lies at the midline of the roof of the mouth. In many reptiles (including birds), it fuses to the endochondral (cartilage-derived) ...
: the parasphenoid rostrum is a laterally compressed, thin spike and is lacking the longitudinal dorsal groove
*
pterygoid Pterygoid, from the Greek for 'winglike', may refer to:
* Pterygoid bone, a bone of the palate of many vertebrates
* Pterygoid processes of the sphenoid bone
** Lateral pterygoid plate
** Medial pterygoid plate
* Lateral pterygoid muscle
* Medial ...
: the ectopterygoid process of the pterygoid is located below the antorbital fenestra, and is reduced, such that it is not visible below the ventral margin of the skull when examined in lateral view; also the breadth of the main body of the pterygoid at least 33% of the length of the pterygoid
*
teeth
A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...
: at least 5-6 replacement teeth occur per alveolus (as observed in ''
Nigersaurus
''Nigersaurus'' is a genus of rebbachisaurid sauropod dinosaur that lived during the middle Cretaceous period, about 115 to 105 million years ago. It was discovered in the Elrhaz Formation in an area called Gadoufaoua, in Niger. Fossils of th ...
'')
*
dorsal vertebrae
In vertebrates, thoracic vertebrae compose the middle segment of the vertebral column, between the cervical vertebrae and the lumbar vertebrae. In humans, there are twelve thoracic vertebrae and they are intermediate in size between the cervical ...
: no more than 10 dorsal vertebrae are present
*
caudal vertebrae
The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...
: 70-80 caudal vertebrae are present
*
pedal
A pedal (from the Latin '' pes'' ''pedis'', "foot") is a lever designed to be operated by foot and may refer to:
Computers and other equipment
* Footmouse, a foot-operated computer mouse
* In medical transcription, a pedal is used to control p ...
phalanges
The phalanges (singular: ''phalanx'' ) are digital bones in the hands and feet of most vertebrates. In primates, the thumbs and big toes have two phalanges while the other digits have three phalanges. The phalanges are classed as long bones.
...
: pedal phalanx I-1 has a proximoventral margin drawn out into a thin plate or heel that underlies the distal end of metatarsal I; also pedal phalanx II-2 is reduced in craniocaudal length and has an irregular shape
Skin
Few skin impressions of diplodocids have been found. However, at least one significant find was reported by Stephen Czerkas in 1992. Fossils from the Howe Quarry in
Shell, Wyoming
Shell is a census-designated place (CDP) in Big Horn County, Wyoming, United States. The population was 83 at the 2010 Census.
The community is named for the abundance of fossil shells located in the area. Nearby exposed formations such as the ...
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 animal's entire back and neck.
Skin fossils have been discovered at the Mother’s Day Quarry that have been assigned to ''Diplodocus'' sp. These skin fossils exhibit a vast amount of scale diversity, the scales of which vary in shape, size, orientation, and 3-dimensional relief depending on their location on the integument. Some of the scale orientations may indicate where the skin originated on the body. For instance, a scale orientation consisting of arching rows of square scales is noted to look similar to scale orientations seen around crocodilian limbs, so it is hypothesized that this area may have come from around a limb in life. Due to the high diversity of scales seen on a relatively small area of skin, the small size of the scales, and the presence of small and juvenile individuals at the Mother’s Day Quarry, it is hypothesized that the skin originated from a small or juvenile individual.
Paleobiology
Diet and feeding
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
A gastrolith, also called a stomach stone or gizzard stone, is a rock held inside a gastrointestinal tract. Gastroliths in some species are retained in the muscular gizzard and used to grind food in animals lacking suitable grinding teeth. In othe ...
s (gizzard stones) to break down tough
plant
Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclud ...
fibers (similar to modern
bird
Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...
s).
Diplodocines have highly unusual teeth compared to other sauropods. The crowns are long and slender, and elliptical in cross-section, while the apex forms a blunt, triangular point.
The most prominent wear facet is on the apex, though unlike all other wear patterns observed within sauropods, diplodocine wear patterns are on the labial (cheek) side of both the upper and lower teeth.
![Seismosaurus skull](https://upload.wikimedia.org/wikipedia/commons/9/95/Seismosaurus_skull.jpg)
This implies that the feeding mechanism of ''Diplodocus'' and other diplodocids was radically different from that of other sauropods. Unilateral branch stripping is the most likely feeding behavior of ''Diplodocus'',
as it explains the unusual wear patterns of the teeth (coming from tooth–food contact). In unilateral branch stripping, one tooth row would have been used to strip foliage from the stem, while the other would act as a guide and stabilizer. With the elongated preorbital (in front of the eyes) region of the skull, longer portions of stems could be stripped in a single action.
Also, the palinal (backwards) motion of the lower jaws could have contributed two significant roles to feeding behaviour: 1) an increased gape, and 2) allowed fine adjustments of the relative positions of the tooth rows, creating a smooth stripping action.
Young ''et al.'' (2012) used biomechanical modelling to examine the performance of the diplodocine skull. It was concluded that the proposal that its dentition was used for bark-stripping was not supported by the data, which showed that under that scenario, the skull and teeth would undergo extreme stresses. The hypotheses of branch-stripping and/or precision biting were both shown to be biomechanically plausible feeding behaviors.
Diplodocine teeth were also continually replaced throughout their lives, usually in less than 35 days, as was discovered by Michael D'Emic ''et al.'' Within each tooth socket, as many as five replacement teeth were developing to replace the next one. Studies of the teeth also reveal that it preferred different vegetation from the other sauropods of the Morrison, such as ''Camarasaurus''. This may have better allowed the various species of sauropods to exist without competition.
Growth
Long-bone histology enables researchers to estimate the age that a specific individual reached. A study by Griebeler et al. (2013) examined long bone histological data and concluded that the diplodocid MfN.R.2625 weighed , reached sexual maturity at 23 years and died at age 24. The same growth model indicated that the diplodocid MfN.R.NW4 weighed , and died at age 23, before reaching sexual maturity.
Paleopathology
An unnamed diplodocid specimen from the
Morrison Formation
The Morrison Formation is a distinctive sequence of Late Jurassic, Upper Jurassic sedimentary rock found in the western United States which has been the most fertile source of dinosaur fossils in North America. It is composed of mudstone, sandsto ...
nicknamed "Dolly" shows evidence of a throat infection that created cauliflowered bone in the vertebral air sacs. The infection is theorized to have been similar to
aspergillosis
Aspergillosis is a fungal infection of usually the lungs, caused by the genus ''Aspergillus'', a common mould that is breathed in frequently from the air around, but does not usually affect most people. It generally occurs in people with lung dise ...
, though research is ongoing. Whether or not the infection contributed to the dinosaur's death remains unknown.
Tail function
Diplodocids also had long, whip-like
tail
The tail is the section at the rear end of certain kinds of animals’ bodies; 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, r ...
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
A bullwhip is a single-tailed whip, usually made of braided leather or nylon, designed as a tool for working with livestock or competition.
Bullwhips are pastoral tools, traditionally used to control livestock in open country. A bullwhip's leng ...
. This could generate a
sonic boom
A sonic boom is a sound associated with shock waves created when an object travels through the air faster than the speed of sound. Sonic booms generate enormous amounts of sound energy, sounding similar to an explosion or a thunderclap to t ...
in excess of 200
decibel
The decibel (symbol: dB) is a relative unit of measurement equal to one tenth of a bel (B). It expresses the ratio of two values of a power or root-power quantity on a logarithmic scale. Two signals whose levels differ by one decibel have a po ...
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
vertebra
The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...
e, which may be a symptom of cracking their tails: these are particularly common between the 18th and the 25th caudal vertebra, a region the authors consider a transitional zone between the stiff muscular base and the flexible whiplike section.
However, Rega (2012) notes that ''
Camarasaurus
''Camarasaurus'' ( ) was a genus of quadrupedal, herbivorous dinosaurs and is the most common North American sauropod fossil. Its fossil remains have been found in the Morrison Formation, dating to the Late Jurassic epoch (Kimmeridgian to Titho ...
'', while lacking a tailwhip, displays a similar level of caudal co-ossification, and that ''
Mamenchisaurus
''Mamenchisaurus'' (or spelling pronunciation ) is a genus of sauropod dinosaur known for their remarkably long necks which made up nearly half the total body length. Numerous species have been assigned to the genus; however, many of these might ...
'', while having the same pattern of vertebral metrics, lacks a tailwhip and doesn't display fusion in any "transitional region". Also, the crush fractures which would be expected if the tail was used as a whip have never been found in diplodocids.
More recently, Baron (2020) considers the use of the tail as a bullwhip unlikely because of the potentially catastrophic muscle and skeletal damage such speeds could cause on the large and heavy tail. Instead, he proposes that the tails might have been used as a tactile organ to keep in touch with the individuals behind and on the sides in a group while migrating, which could have augmented cohesion and allowed communication among individuals while limiting more energetically demanding activities like stopping to search for dispersed individuals, turning to visually check on individuals behind, or communicating vocally.
Classification
![Dinosaurs in Their Time- Jurassic Era Room (2705542612)](https://upload.wikimedia.org/wikipedia/commons/8/86/Dinosaurs_in_Their_Time-_Jurassic_Era_Room_%282705542612%29.jpg)
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 (July 28, 1840 – April 12, 1897) was an American zoologist, paleontologist, comparative anatomist, herpetologist, and ichthyologist. Born to a wealthy Quaker family, Cope distinguished himself as a child prodigy interested ...
named the family Amphicoeliidae in 1878 for his genus ''
Amphicoelias
''Amphicoelias'' (, meaning "biconcave", from the Greek ἀμφί, ''amphi'': "on both sides", and κοῖλος, ''koilos'': "hollow, concave") is a genus of herbivorous sauropod dinosaur that lived approximately 150 million years ago during t ...
'', 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
In zoological nomenclature, a ''nomen oblitum'' (plural: ''nomina oblita''; Latin for "forgotten name") is a disused scientific name which has been declared to be obsolete (figuratively 'forgotten') in favour of another 'protected' name.
In its p ...
'' ("forgotten name") according to the
ICZN
The International Code of Zoological Nomenclature (ICZN) is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals. It is also informally known as the ICZN Code, for its publisher, the I ...
, 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 (October 29, 1831 – March 18, 1899) was an American professor of Paleontology in Yale College and President of the National Academy of Sciences. He was one of the preeminent scientists in the field of paleontology. Among h ...
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'', for example, was initially described as a diplodocid, but may actually have been a
Macronaria
Macronaria is a clade of sauropod dinosaurs. Macronarians are named after the large diameter of the nasal opening of their skull, known as the external naris, which exceeded the size of the orbit, the skull opening where the eye is located (hence ...
n.
''Amphicoelias'' was traditionally 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'' is a genus of Dicraeosauridae, dicraeosaurid sauropod dinosaur found in the Upper Jurassic strata of the Morrison Formation, located in southern Carbon County, Montana, Carbon County, Montana, United States. The fossil remains were ...
'' and ''Supersaurus'' were relatives of ''Apatosaurus'', within the subfamily Apatosaurinae. However, a 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 is a family of diplodocoid sauropods who are the sister group to Diplodocidae. Dicraeosaurids are a part of the Flagellicaudata, along with Diplodocidae. Dicraeosauridae includes genera such as ''Amargasaurus'', ''Suuwassea'', ''D ...
.
![Apatosaurus Clean](https://upload.wikimedia.org/wikipedia/commons/5/59/Apatosaurus_Clean.png)
The subfamily Diplodocinae, was erected to include ''Diplodocus'' and its closest relatives, including ''
Barosaurus
''Barosaurus'' ( ) was a giant, long-tailed, long-necked, plant-eating sauropod dinosaur closely related to the more familiar ''Diplodocus''. Remains have been found in the Morrison Formation from the Upper Jurassic Period of Utah and South Da ...
''.
The Portuguese ''
Dinheirosaurus
''Dinheirosaurus'' is a genus of diplodocid sauropod dinosaur that is known from fossils uncovered in modern-day Portugal. It may represent a species of ''Supersaurus''. The only species is ''Dinheirosaurus lourinhanensis'', first described by J ...
'' and the African ''
Tornieria
''Tornieria'' ("for Tornier") is a genus of diplodocid sauropod dinosaur from the Late Jurassic in Lindi Region of Tanzania. It has a convoluted taxonomic history.
Discovery and naming
In 1907, German paleontologist Eberhard Fraas who wa ...
'' have also been identified as close relatives of ''Diplodocus'' by some authors.
Cladogram
A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to d ...
of the Diplodocidae after Tschopp, Mateus, and Benson (2015).
Evolution and biogeography
Diplodocids probably evolved in North America, where most diplodocid fossils are found.
However, diplodocids have been found on most continents, including South America, Europe, and Africa. Diplodocids and their close relatives, dicraeosaurids, must have diverged from each other by the time the earliest known dicraeosaurid, ''
Lingwulong
''Lingwulong'' is a genus of dicraeosaurid sauropod dinosaur from the Middle Jurassic of what is now Lingwu, Yinchuan, Ningxia, China. The type and only species is ''L. shenqi'', known from several partial skeletons. It is the earliest-aged neo ...
'', appears in the fossil record.
''Lingwulong'' was originally thought to be possibly as old as Early Jurassic, but is now considered to date to the late Middle Jurassic.
References
External links
*
Cracking the whip', from the NewScientist.
''Sauropod dinosaur may have whipped its tail like Indiana Jones'' (says Nathan Myhrvold) from the NewScientist.
* Ivan Peterson's
'.
of several diplodocids, from Scott Hartman's Skeletal Drawing website.
{{Portal bar, Dinosaurs, Cretaceous, Paleontology
Flagellicaudata
Bajocian first appearances
Early Cretaceous extinctions
Taxa named by Othniel Charles Marsh
Prehistoric dinosaur families