| Dystrophaeus | |
|---|---|
 | |
| Metacarpals from the holotype (USNM 2364) | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | †Sauropodomorpha |
| Clade: | †Sauropoda |
| Genus: | †Dystrophaeus Cope, 1877 |
| Species: | †D. viaemalae |
| Binomial name | |
| †Dystrophaeus viaemalae Cope, 1877 | |
Dystrophaeus is an extinctgenus ofsauropoddinosaur. Itstype and only species isDystrophaeus viaemalae, named byEdward Drinker Cope in 1877. Its fossils were found in the Tidwell Member of theMorrison Formation of Utah. Due to the fragmentary condition of its only known specimen, the affinities ofDystrophaeus are uncertain, although excavations carried out at the discovery site since 1989 have uncovered more of the original specimen and hold the potential for an improved understanding of the taxon.
Dystrophaeus viaemalae is known from a single fragmentary specimen, theholotype USNM 2364. The specimen initially consisted of a partialdorsal vertebra, a partialscapula, a nearly completeulna,[a] a partialradius, and threemetacarpals.[1] More recent excavations have discovered additional parts of the same specimen, including a phalanx,[2] teeth, and additional vertebrae from the back and tail.[3] The specimen was found in the Tidwell Member of theMorrison Formation and is approximately 158 million years old, making it the oldest species of sauropod from the Morrison Formation by several million years.[3]
Few dinosaur fossils had been collected in theAmerican West until the 1850s,[4] with expeditions by naturalists likeJoseph Leidy andFerdinand Vandeveer Hayden in South Dakota and Montana finding fragmentary fossils, mostly teeth, from dinosaurs in 1855 and 1856.[4] The next discovery came accidentally in 1859 when while Captain John N. Macomb was leading a U.S. Army Engineers survey fromSanta Fe to the confluence of theGreen andColorado Rivers, his crew camped south of what is nowMoab, Utah.[5][6] In August, a geologist from the crew namedJohn Strong Newberry, unearthed several large fossil bones in sandstone rocks elevated in a canyon wall near the camp.[5][6] Newberry successfully excavated several of the bones with several other crew members while using poor equipment, but several fossils remained in the sandstone rocks due to the team's time constraints of the expedition.[7][6] The fossils excavated consisted of only one partial skeleton, theholotypeUSNM 2364, which includes a 76.5 centimetres (30.1 in) longhumerus, a possibleulna, ascapula, a partialradius, and somemetacarpals. The specimen was from theLate JurassicMorrison Formation, and was notably from the older Tidwell Member of theOxfordian,[6] and is one of the few dinosaurs known from the member.[6] The fossils were turned over toJoseph Leidy in Philadelphia, and later toEdward Drinker Cope, who described them in theProceedings of the American Philosophical Society in 1877. Cope named the remainsDystrophaeus viaemalae, the genus name means "coarse joint" from Greekdys, "bad", andstropheus, "joint", a reference to the pitted joint surfaces serving as an attachment forcartilage.[5] Thespecific name reads asLatinviae malae, "of the bad road", a reference to the various arduous routes taken to find, reach and salvage the remains.[5]
Dystrophaeus received little attention besides its classification since before the 1970s until amateur Moab geologist Fran Barnes attempted to rediscover Newberry's originalDystrophaeus locality, eventually rediscovering the site in 1987.[6] The rediscovery was confirmed byDavid Gillette and in 2014 John Foster created theDystrophaeus Project,[8] which launched another expedition to the site the same year to recover additional material left behind by the Macomb Expedition.[8][6] Another expedition was launched in 2017, the two recent expeditions recovering various elements including teeth, vertebrae, and additional limb bones, though many remain unprepared.[6]
Not much can be surmised due to the fragmentary nature and uncertain phylogenetic position ofDystrophaeus.[6][1] As a sauropod,Dystrophaeus would have been a large, long-necked herbivore. It would have been of moderate size for a sauropod; it may have been approximately 13 metres (43 ft) long,[b] with a mass of roughly 7–12 tonnes (7.7–13.2 short tons).[c] Theulna of the only known specimen is 76.4 centimetres (30.1 in) long;[12] for comparison, the ulna of the holotype ofCamarasaurus lewisi is 77.5 centimetres (30.5 in).[13] The scapula bears a subtriangular projection on the base of the scapular blade, which Tschopp et al.'s analysis found to be anautapomorphy of the taxon, though this trait also occurs in various other sauropods.[1] The ulna is very slender, and the metacarpals are relatively short.[14]
The classification ofDystrophaeus has been rather confusing. Cope in 1877 merely concluded it was some Triassic dinosaur.[5]Henri-Émile Sauvage in 1882 understood it was a sauropod, assigning it to theAtlantosauridae.Othniel Charles Marsh however, in 1895 stated it belonged to theStegosauridae.Friedrich von Huene, the first to determine it was of Jurassic age, in 1904 created a special family for it, theDystrophaeidae, which he assumed to be herbivoroustheropods.[12] Only in 1908 von Huene realised his mistake and classified it in the sauropod familyCetiosauridae, refining this in 1927 to theCardiodontinae.Alfred Romer in 1966 put it in theBrachiosauridae, in a subfamilyCetiosaurinae.
More recently, an analysis byDavid Gillette concluded it was a member of theDiplodocidae.[2][15] Tschopp and colleagues includedD. viaemalae in a phylogenetic analysis in 2015, and found its phylogenetic position to be highly unstable. They concluded that positions in Dicraeosauridae or Camarasauridae were equally well-supported, but that it was probably not a diplodocid, and concluded that further study was required to determine its affinities.[1] However, many researchers consider the taxon to be anomen dubium.[1] Newer finds ofDystrophaeus have led paleontologistJohn Foster and colleagues to suggest it was most closely related to Macronarian or Eusauropod dinosaurs,[6] although much material has yet to be prepared.[6] According to Foster, the newly found caudal vertebrae rule out diplodocid affinities.[3]
