| Dromicosaurus | |
|---|---|
 | |
| Parts of thetype specimen: Left pubis (top), tail vertebrae (left), back vertebra (middle right), and right pubis (bottom right) | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dracohors |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | †Sauropodomorpha |
| Genus: | †Dromicosaurus van Hoepen,1920[1] |
| Species | |
Dromicosaurus is adubious genus ofsauropodomorphdinosaur from theLate Triassic orEarly Jurassic of South Africa. Its only species isD. gracilis.Dromicosaurus was named byEgbert Cornelis Nicolaas van Hoepen in 1920 from a fragmentary skeleton he had discovered in theElliot Formation inFree State. The name,lit. 'quick-walking lizard', alludes to the slender legs compared to related genera such asEucnemesaurus.Dromicosaurus has repeatedly been considered as a synonym of a species ofMassospondylus, but was considered anindeterminatesauropodomorph in the two most recent reviews.
The only known specimen was discovered by the palaeontologistEgbert Cornelis Nicolaas van Hoepen at Noupoortsnek, close to the road fromBethlehem toClarens. At the time of discovery, weathering had already freed most of the twopubes (the front bones of the pelvis) from the surrounding rock. During the excavation, the shaft of thetibia (shin bone) scattered into pieces, but van Hoepen was able to immediately fit and glue the bone back together.[1] The specimen became part of the collection of theDitsong National Museum of Natural History (at the time known as theTransvaal Museum) inPretoria, where van Hoepen was working at the time,[2] under the specimen number TM 123.[3]: 174 Van Hoepen described the specimen in 1920 as the new genus and speciesDromicosaurus gracilis. The nameDromicosaurus derives from theAncient Greekδρομικός'quickly walking' andsauros'lizard'.[1]: 118 [4] Van Hoepen selected this name because "the slender leg must have enabled the animal to go quicker than, for example,Eucnemesaurus and also implies a more slender form."[1]: 118
The specimen comes from theElliot Formation, though it is unknown if from the upper (Upper Triassic) or lower (Lower Jurassic) Elliot Formation.[3]: 174 According to van Hoepen, the specimen includes an almost complete neck vertebra (possibly the third), around eight, poorly preserved vertebrae from the front part of the tail, parts of thehumerus andradius, the well-preserved pubes, poorly preservedischia, a weatheredfemur, the well-preserved right tibia and fibula, and several foot bones including the first threemetatarsals. The length of the femur is 49.5 cm.[1]Friedrich von Huene, in 1932, stated that the neck vertebra was actually a dorsal (back) vertebra.[5]
Van Hoepen identifiedDromicosaurus as a member of theAnchisauridae, clearly different from the relatedPlateosauridae that was also recognised at that time.[1] At the time, both groups were thought to representtheropod dinosaurs, while they are classified asbasalsauropodomorphs today.[6] Von Hoepen found his newtaxon to be distinct from other taxa includingMassospondylus carinatus,Massospondylus harriesi,Aetonyx palustris,Thecodontosaurus skirtopodus,Thecodontosaurus browni,Gryponyx africanus,Teratosaurus suevicus, andPlateosaurus quenstedti. Much of the sauropodomorph material from the Lower Jurassic of southern Africa, includingDromicosaurus, would later be lumped under the speciesMassospondylus carinatus, which, at that time, was only known from fragments. Van Hoepen pointed out differences in the femur and tibia to the latter species: Thefourth trochanter (ridge on the femur where muscles attached) was located more proximally (higher on the bone) inDromicosaurus, and the proportions of the lower end of the tibia were different.[1]
Von Huene, in 1932, stated thatDromicosaurus was closely related toM. carinatus,M. harriesi, andThecodontosaurus. He argued that the high location of the fourth trochanter and the short fore limb (with the humerus measuring only half the length of the femur) suggested that the limbs were strongly bent at the knee, and that the animal must have beenbipedal.[5] In 1976,Peter Galton and Michael Albert Cluver consideredDromicosaurus gracilis as a synonym ofMassospondylus harriesi, following an opinion of John Attridge. Michael Cooper, in a 1981 monograph onMassospondylus, instead synonymisedDromicosaurus gracilis withM. carinatus.[7] The two most recent revisions, those of Galton (1990) and Galton and Upchurch (2004), instead listDromicosaurus gracilis as an indeterminate (dubious) sauropodomorph.[8][9][3]: 174