Dystrophaeus
From Greek 'dys' meaning 'bad' and 'stropheus' meaning 'joint', giving 'coarse joint'; refers to the pitted joint surfaces that served as attachments for cartilage.
Dystrophaeus is an extinct genus of sauropod dinosaur. Its type and only species is Dystrophaeus viaemalae, named by Edward Drinker Cope in 1877. Its fossils were found in the Tidwell Member of the Morrison Formation of Utah. Due to the fragmentary condition of its only known specimen, the affinities of Dystrophaeus 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.
Under dispute
Dystrophaeus is a poorly known taxon whose long-standing diplodocoid identification has been rejected. Tschopp and colleagues (2015) consistently recovered it within Dicraeosauridae under implied weighting but found it too unstable to place under equal weighting, with constrained searches supporting dicraeosaurid and camarasaurid positions nearly equally; Foster and colleagues (2016) rule out a diplodocoid identity but leave a macronarian versus outside-Neosauropoda position unresolved. Its candidate positions span non-neosauropod Eusauropoda to several neosauropod clades.
Diagnosis
- Humerus distally the most contracted known among Dinosauria; distal extremity truncate with oval outline resembling a tibia, surface roughened with coarse pits
- Proximal humerus with T-shaped cross-section a short distance below the head; greater tuberosity a huge crest as prominent as the head, separated from it by a marked concavity forming a neck
- Articular surfaces of limb bones rugose and pitted, indicating reduced mutual movement and probable cartilaginous cap rather than ossified epiphyses
- Probable sternum with digitate borders bearing five digitiform processes, including a slender compressed process projecting at right angles near the middle of one side
- Metatarsal shafts solid, filled with coarse cancelli; proximal ends truncate with trapezoidal or triangular outlines; articular surfaces pitted and roughened
Species
Dystrophaeus viaemalae Cope, 1877
Type species
From Latin 'viae malae' meaning 'of the bad road', a reference to the various arduous routes taken to find, reach, and salvage the fossil remains.
- Holotype
- USNM 2364 , National Museum of Natural History, Smithsonian Institution
- Material
- Humerus, three metatarsals, distal end of probable ulna, probable sternum, probable scapula, and additional unidentified fragments found in close proximity.
- Horizon
- lower Tidwell Member, Morrison Formation, Oxfordian, Late Jurassic , 161.5–154.8 million years ago
- Locality
- East Canyon Quarry, Utah, United States
References
- Cope, E. D. (1877). On a dinosaurian from the Trias of Utah. Proceedings of the American Philosophical Society 16: 579-584. cope1877a
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Tschopp, E.; Mateus, O.; Benson, R. B. J. (2015). A specimen-level phylogenetic analysis and taxonomic revision of Diplodocidae (Dinosauria, Sauropoda). PeerJ 3: e857. PeerJ. doi:10.7717/peerj.857
Within Dicraeosauridae under implied weighting, too unstable to place under equal weighting; constrained searches support dicraeosaurid and camarasaurid positions about equally.
tschopp2015a -
Foster, J. R.; Irmis, R. B.; Trujillo, K. C.; McMullen, S. K.; Gillette, D. D. (2016). Dystrophaeus viaemalae Cope from the basal Morrison Formation of Utah: Implications for the origin of eusauropods in North America. Journal of Vertebrate Paleontology, Program and Abstracts 138.
Poster abstract on new referred material; rules out a diplodocoid identity but leaves a macronarian versus outside-Neosauropoda position unresolved. Runs no phylogenetic analysis.
foster2016a -
Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Sauropods. Princeton University Press.
Favors basal Macronaria or a position outside Neosauropoda.
jones2026b