Diplodocoidea

  Diplodocoidea is composed of three families: Rebbachisauridae, Dicraeosauridae, and Diplodocidae.  Rebbachisaurids are not yet particularly well known, at the moment being an EK-LK boundary South America-Africa group (possibly into the later LK, depending on what you make of the "Antarctosaurus" jaw) with interesting feeding characteristics.  For a long while, I was hesitant to include them with the other diplodocoids.
    The other two groups of diplodocoids can be classified together (with basal Suuwassea) in a group called Flagellicaudata, which means reasonably enough "whip-tail".  Major defining characters of flagellicaudatans include bifid neural spines, most chevrons skid-like, whip-lash tail formed by rod-like caudal verts that essentially lack neural arches, peg-like teeth, and the loss of the small calcaneum (although this has recently been debated) from the ankle.  Apatosaurus takes this reduction even further, and has only wrist bone per arm plus the single ankle bone.  Some of the unusual characters of diplodocoids may be related to retention of embryonic and juvenile characteristic as adults.
    The dicraeosaurids are a peculiar offshoot of diplodocoids that are best known for their extremely tall neural spines, split down the middle in a "forking" pattern.  They are tall enough to have supported dramatic sails in life.  The necks of dicraeosaurids are also short compared to most sauropods.
    Diplodocidae provides the stereotype for what most people think of dinosaurs in general and sauropods in particular: long neck, small head, long tail, hips much higher than the shoulders, and a plump-looking body.  So far, all known diplodocids repeat this general body plan, with minor changes; for example, Apatosaurus is much more robust than average and Barosaurus has a neck much longer than the average diplodocid's.  Diplodocids probably include among their members the longest land animals to ever live, but not the heaviest, due to their lean nature.  Most of the length would have come from the neck and tail, which at the end forms a whip-lash; swinging it could have theoretically produced a sonic boom.
    Diplodocids appear to have normally held their necks from out from their bodies at a downward angle, more graceful in some than in others.  The head was usually between several inches and several feet from the ground.  A row of nonbony spines, like those of an iguana, ran down the midline of at least some diplodocoids' backs.  Diplodocids are most common from the Morrison Formation of western North America.

<--Diplodocoidea
     |--Haplocanthosaurus
     `--+--Amazonsaurus
          `--+--Amphicoelias     
               `--+--Rebbachisauridae
                    |   |--Histriasaurus
                    |   `--+--Rebbachisaurus
                    |        `--+--Limaysaurinae
                    |             |    |--Limaysaurus
                    |             |     `--Cathartesaura
                    |             `--Nigersaurinae
                    |                  |--Zapalasaurus
                    |                  `--+--Demandasaurus
                    |                       `--Nigersaurus
                    `--Flagellicaudata
                         |--Dicraeosauridae
                         |   |--Suuwassea
                         |    |--Amargasaurus
                         |    `--+--Brachytrachelopan
                         |         `--Dicraeosaurus
                         `--Diplodocidae
                              |--Apatosaurinae
                              |    `--Apatosaurus
                              `--Diplodocinae
                                   |--+--Supersaurus
                                   |    `--Dinheirosaurus 
                                   `--+--Tornieria
                                        `--+--Barosaurus
                                             `--Diplodocus
                         
Diplodocoidea: Haplocanthosaurus, like Euhelopus, is one of those things that has historically inspired disagreement.  Sauropod researchers have put it all over the place, and even make up new groups for it to belong to; some scientists have suggested a Family Haplocanthosauridae in Macronaria. Consensus appears to be gathering for a position at the base of Diplodocoidea. 

Taxon or Taxa: Time/Place: Comments:
Haplocanthosaurus:
Hatcher, 1903 (originally Haplocanthus Hatcher, 1903)		 H. priscus (type) (Hatcher, 1903 [originally Haplocanthus priscus]) Kimmeridgian (LJ) of Colorado and Wyoming H. priscus is one of the more derived "cetiosaurids", and has features linking it to the camarasaurids, brachiosaurids, and diplodocoids.  Haplocanthosaurus is one of the more rare Morrison sauropods, although new remains from the Morrison may belong to a relative.  A new postcranial skeleton bodes fair to confuse everyone even further.
?H. delfsi McIntosh and Williams, 1988 Kimmeridgian (LJ) of Colorado H. delfsi is much larger than the type and may not belong to this genus.  It is based on a partial skeleton that went unrecognized as a separate taxon for years.  Some researchers have suggested that this species actually belongs somewhere else.
Amazonsaurus maranhensis Carvalho, Avilla, and Salgado, 2003 Aptian-Albian (EK) of Brazil Amazonsaurus is a small sauropod based on a partial skeleton consisting of partial dorsal and caudal vertebrae, chevrons, ribs, and a partial pelvic girdle. It has had a history of phylogenetic instability, beginning as a possible dicraeosaurid, and spending time elsewhere in Diplodocoidea and even Macronaria. 
Amphicoelias: (?N.D.) Cope, 1877 A. altus (?N.D.) (type) Cope, 1877 Tithonian (LJ) of Colorado and ?Montana Based on poor remains, this animal is likely the same as another diplodocoid.  However, there has been found in Montana a partial skeleton that may belong here, which would make this a unique basal diplodocid.
A. fragillimus (N.D.) Cope, 1878 Tithonian (LJ) of Colorado A. fragillimus was based on an enormous dorsal neural arch that suggests a truly gigantic animal (scaled to Diplodocus, it may have been 58 m [190 ft] long, and may have massed upwards of 100 metric tons).  Unfortunately, it has been lost, probably destroyed (the species name isn't fragillimus for nothing; it may have simply disintegrated).

Rebbachisauridae:  The rebbachisaurids are a curious group of sauropods that in many ways resemble diplodocoids, and are usually classified with them, but lack both split neural spines and forked chevrons.  However, it is known by now that I put too much emphasis on these traits in the past.  They were tall-spined, like the dicraeosaurids, but not "exactly" like them.  They seem to have been not uncommon in their time and place.

Taxon or Taxa: Time/Place: Comments:
Histriasaurus boscarollii (?N.D.) Dalla Vecchia, 1998 late Hauterivian-early Barremian (EK) of Croatia This sauropod is the first named dinosaur from Croatia, based on a dorsal found on the Adriatic sea bottom.  It may be related to the rebbachisaurids, but it is not presently well-known.
Rebbachisaurus garasbae Lavocat, 1954 Albian (EK) of Morocco Long mixed up with brachiosaurids and camarasaurids, this taxon is poorly understood. It has very tall neural spines.
Cathartesaura anaerobica Gallina and Apesteguía, 2005 late Cenomanian (LK) of Argentina This rebbachisaurid is based on a few verts, a scapula, an ilium, and femur, as part of an associated but incomplete skeleton that took seven years to prepare and assess.
Limaysaurus tessonei Salgado, Garrido, S.E. Cocca, and J.R. Cocca, 2004 Cenomanian-early Turonian (LK) of Argentina Limaysaurus had been kicking around the ranks of nomen nudum dinosaurs for a while, but has now been promoted to respectability.  It is known from several individuals, including a specimen about 80% complete that serves as the type.
Zapalasaurus bonapartei Salgado, Carvalho, and Gorrido, 2006 Barremian-early Aptian (EK) of Argentina This sauropod is known from cervical and caudal verts (apparently at least 20 of the latter).  EK Argentina was a good place for diplodocoids, apparently, as there were also dicraeosaurids. 
Demandasaurus darwini Fernández-Baldor, Canudo, Huerta, Montero, Suberbiola, and Salgado, 2011 late Barremian-early Aptian (EK) of Spain Demandasaurus (formerly the "Spanish rebbachisaurid") is known from a partial skull and skeleton, with numerous verts and ribs, ischia, and a femur.  It may be closest to Nigersaurus, and generally is closest to African forms.
Nigersaurus taqueti Sereno, Beck, Dutheil, Larsson, Lyon, Moussa, Sadleir, Sidor, Varricchio, G. P. Wilson, and J. A. Wilson, 1999 ?late Aptian-Albian (EK) of Niger This sauropod has small, enameled teeth, arranged in a sort of dental battery, allowing it to have processed food more thoroughly than other sauropods.  It has square jaw tips on a skull tilted perpendicular to the ground (perpetual "hang-dog" appearance) and featuring interesting remodeling from typical sauropod skulls; for example, those holes and bones you expect to see posterior to the eye aren't there, the bones having shifted down.  Actually, it looks a bit like someone took a diplodocoid skull, held the eye sockets in place, then yanked the muzzle under the eyes and slid the post-eye bones down along this new "ventral margin", finishing up by comically stretching and boxing the snout and toothline.  Remains from several individuals of this small sauropod are known; the type includes a partial skull, cervicals, scapula, and fore\hindlimbs.

Rebbachisauridae i.s.: The old "Isle of Wight" diplodocid, based on a skid-shaped chevron, is probably not a diplodocid but a rebbachisaurid.

Taxon or Taxa: Time/Place: Comments:
Nopcsaspondylus alarconensis Apesteguia, 2007 Coniacian (LK) of Argentina Nopcsaspondylus is a bit of an oddity, in that it's based on a figure, from a 1902 publication, of a now-lost dorsal vertebra.  It's the most recent named diplodocoid.
Rayososaurus agrioensis Bonaparte, 1995 Aptian (EK) of Argentina Rayososaurus is a rebbachisaurid, but not the same as Limaysaurus as had been suggested.  It may be somewhat basal to other rebbachisaurids.

Dicraeosauridae: Dicraeosaurids seem to have been a Gondwanan phenomenon, a group of small, short-necked sauropods with very tall neural spines on the presacrals.  They're a bit like taking a diplodocid and messing with it in Photoshop to make it taller and shorter (fore and aft).

Taxon or Taxa: Time/Place: Comments:
Suuwassea emilieae Harris and Dodson, 2004 ?late Kimmeridgian-?early Tithonian (LJ) of Montana One of a handful of new odd Montanan Morrison sauropods, and the first to see publication, Suuwassea comes from relatively high in the formation.  It is an unusual form that seems to have both diplodocid and dicraeosaurid features; the most recent analysis put it at the base of Dicraeosauridae, which would make it the first dicraeosaurid known from the Morrison Formation, and all of Laurasia (North America+Europe+most of Asia).  The type skeleton includes bits of the upper jaw, the braincase, six cervicals, three dorsals, ribs, caudal centra, a scapula and coracoid, a humerus, and a partial lower hindlimb and foot.  This material is different from a partial skeleton first discussed a few years ago and referred to Amphicoelias, although I leapt to the opposite conclusion when I first heard about Suuwassea (described as a basal diplodocoid, verts and partial skull; the Amphicoelias stuff has a femur and pelvis, though, and comes from a different county).  Suuwassea was a smallish sauropod, something that seems to be common for the northern Morrison sauropod fauna.  
The interesting name, intended to be pronounced "SOO-oo-WAH-see-uh" comes from the Crow word "suuwassa," meaning "the first thunder heard in Spring," but the root words can be read as "ancient thunder", which can be interpreted as an homage to "Brontosaurus" and "thunder lizards". 
Amargasaurus cazaui Salgado and Bonaparte, 1991 Barremian (EK) of Argentina This sauropod is unique in the extreme tallness of its neural spines.  The forked spines could have supported one fat sail or two thin ones.  This animal is known from most of the skeleton in front of the tail.  It appears that the neck arcs downward, presenting a formidably tall profile and leaving the skull near the ground.
Brachytrachelopan mesai Rauhut, Remes, Fechner, Cladera, and Puerta, 2005   Tithonian (LJ) of Argentina A new dicraeosaurid based on most of a presacral vertebral column, ribs, an ilium, and the articular ends of the bones at the knee joint, Brachytrachelopan earned its unique name through its short neck.  Even among dicraeosaurids, it's got a short neck.  The spines of the first few dorsal verts also lean forward.  It's apparently closest to Dicraeosaurus.
Dicraeosaurus: Janensch, 1914 D. hansemanni (type) Janensch, 1914 late Kimmeridgian (LJ) of Tanzania Dicraeosaurus is a trademark animal of the Tendaguru beds in Tanzania, like Giraffatitan and Kentrosaurus.  It is on the small side for sauropods, and very stout, with a long muzzle. 
D. sattleri (Janensch, 1914 [originally Dicraeosaurus]) Tithonian (LJ) of Tanzania This sauropod is caught between Amargasaurus proper and Dicraeosaurus proper, and could be classified with either (or given its own genus).  It is slightly younger and more derived than D. hansemanni, and so may be a descendant. 

Diplodocidae i.s.:

Taxon or Taxa: Time/Place: Comments:
"Diplodocus": "D." lacustris (N.D.) Marsh, 1884 late Kimmeridgian (LJ) of Colorado The eroded jaws and teeth that form the type of this taxon are too poorly preserved to prove this even belongs in Diplodocus and not, say, Apatosaurus.
"D." hayi Holland, 1924 Kimmeridgian (LJ) of Wyoming "D." hayi is based on a partial skull and skeleton from a young individual.  Some of the skull features are more like Apatosaurus, while the cervicals are more like Diplodocus, so it could represent its own genus. 
?Dyslocosaurus polyonychius McIntosh, Coombs, and Russell, 1992 ?Kimmeridgian (?LJ) of Wyoming This animal was named from a diplodocid hindlimb with at least four clawed toes, unusual because diplodocids usually have only three.  It was found from a locality that was either Kimmeridgian (LJ) or late Maastrichtian (LK) in age.  Due to the primitive nature of the foot, and the fact that no diplodocids have been found anywhere else in the LK of North America, the older age is favored here.  At times, people have suggested that it was related to the dicraeosaurids.

Apatosaurinae: An Apatosaurus-like caudal is known from the Oxfordian (LJ) of European Georgia.

Taxon or Taxa: Time/Place: Comments:
Apatosaurus:
Marsh, 1877		 A. ajax (type) Marsh, 1877 late Kimmeridgian (LJ) of Colorado Apatosaurus, one of the most robust sauropods, is much more familiar to the public as Brontosaurus.  Brontosaurus, however, was based on remains that turned out to belong to an older Apatosaurus individual, and may belong to the type species as well (although Brontosaurus partisans have claimed that a new skull shows otherwise).  
Earlier in this century, Apatosaurus was thought of as having a Camarasaurus-like head, despite the fact this particular head had no connection to the body.  A Diplodocus-like head, found associated with an Apatosaurus skeleton, had been known since the 19th century, but not considered to be the real head, due to a variety of mix-ups.  Eventually, though, the proper head was given its due.  Camarasaurus, incidentally, has long been mixed up with diplodocids; early casts of Diplodocus and Apatosaurus often used Camarasaurus (Grandpa Simpson: "...which we called Morosaurus...") parts to fill in the gaps.
Apatosaurus excelsus appears to be different from A. ajax by virtue of its significantly smaller adult size (which isn't much to go on), while A. louisae is differentiated by its much more robust skeleton.  Differences in the cranial process of the cervical ribs do not appear to be of as much significance as they once did.
A. excelsus (Marsh, 1879 [originally Brontosaurus]) Kimmeridgian (LJ) of Wyoming, Utah, and Oklahoma
A. louisae Holland, 1915 Kimmeridgian (LJ) of Utah
A. parvus (Peterson and Gilmore, 1902 [originally Elosaurus]) Kimmeridgian (LJ) of Wyoming

Apatosaurinae i.s.:

Taxon or Taxa: Time/Place: Comments:
Eobrontosaurus yahnahpin Bakker, 1998 Kimmeridgian (LJ) of Wyoming Eobrontosaurus was first described as Apatosaurus yahnahpin (Filla and Redman, 1994), then as a possible ancestor to Apatosaurus.  It was thought to be the first sauropod found preserved with "belly ribs," a common feature of theropods, but these were later shown to have been sternal ribs, which usually are not fossilized.  Recently, it was suggested to be the same as Camarasaurus, but after yet another look (this time going back to the material and not the description), it appears to be an apatosaurine again.

Diplodocinae:

Taxon or Taxa: Time/Place: Comments:
Supersaurus vivianae Jensen, 1985 (including Dystylosaurus edwini and Ultrasauros macintoshi Jensen, 1985) Kimmeridgian (LJ) of Colorado and Wyoming At first thought to be a brachiosaurid-like animal, this is instead a very large diplodocid.  Remains of it and Brachiosaurus were once given the name Ultrasauros.  The holotype (the remains on which the species was based) was a dorsal that actually belonged to the holotype individual of Supersaurus, while the referred scapula actually belonged to an old, large Brachiosaurus.
In addition, Dystylosaurus edwini Jensen 1985, based on a dorsal, which may have been bifurcated, and originally thought of as a large brachiosaurid, is probably part of the holotype individual of Supersaurus.  All of these remains leave Supersaurus with a partial skeleton instead of a few large bits and pieces.
After being removed from Brachiosauridae, it was thought to be closest to Barosaurus, possibly even an old individual, differing mostly in the extent of presacral neural spine bifurcation (it is reduced in comparison to the latter). New remains from Wyoming show it was distinct and possibly closer to Apatosaurus.
Dinheirosaurus lourinhanensis Bonaparte and Mateus, 1999 late Kimmeridgian-early Tithonian (LJ) of Portugal This sauropod is part of a newly-discovered LJ Portuguese dinosaur fauna that has just recently been described in depth.  It is based mostly on vertebrae, including 2 cervicals and 9 dorsals, along with 7 partial centra.  It may be a derived diplodocid.  A second specimen initially thought to belong to it is instead from a more Apatosaurus-like sauropod.
Tornieria africana Sternfield, 1911 (originally Gigantosaurus africana [Fraas, 1908]) Tithonian (LJ) of Tanzania This Tendaguru sauropod species has usually been referred to Barosaurus in the past, but no one ever really said why.  It's clearly a diplodocid, but doesn't actually belong in Barosaurus.  It hasn't historically attracted much attention.  The hind legs were robust with short shins.
Possible second species T. gracilis (Janensch, 1961 [originally Barosaurus]) was actually a case of Janensch finding some gracile specimens and suggesting that they were a variant, which later authors enlarged into a species.
Barosaurus lentus
Marsh, 1890		 Kimmeridgian (LJ) of Utah and South Dakota This diplodocine is very close to Diplodocus, and if not for its neck specializations, could be considered a probable synonym.  Like Brachiosaurus and Haplocanthosaurus, this animal has been considered to be in the second tier of Morrison sauropods as far as frequency of finding is concerned; however, restudy suggests that it was fairly common, just not as recognized as other sauropods.  It is very long, especially in the neck, compared to other diplodocids (which aren't slouches themselves!)
Diplodocus:
Marsh, 1878		 D. longus (type) Marsh, 1878 (including D. hallorum [Gillett, 1991 {originally Seismosaurus}]) Kimmeridgian (LJ) of Colorado, New Mexico, and Utah This diplodocine is the longest well-known sauropod.  Several skeletons and a handful of skulls are known, including a juvenile skull that shows a narrower snout and less crowding of the teeth to the front.  D. carnegii is tentatively retained as a separate species, but there's a good chance it's the same as the type.  At one time in the past some workers wanted to have this sauropod walking with sprawled, lizard-like limbs, but this would have dislocated the joints and forced the animal to walk in trenches because of its deep rib cage.
A partial skull and three cervicals named Morosaurus agilis Marsh, 1889, has occasionally been assigned to or at least suspected of belonging to Haplocanthosaurus priscus, one of several sauropods from the same location, but restudy suggests that it actually belonged to a juvenile D. longus.
D. hallorum, also known as Seismosaurus, has been nick-named a "dachshund" due to its long, low build.  It was probably just a large specimen of D. longus.  Most of the rear end of one individual is known.  Although quite long, early estimates of 150 feet plus are overstated.  Possible gastroliths referred to this species may actually be rocks that just happened to be present.
D. carnegii Hatcher, 1901 (?D. longus) Kimmeridgian (LJ) of Utah and Wyoming

 

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