Brachytrachelopan mesai is a short-necked sauropod dinosaur from the latest Jurassic Period (Tithonian) of Argentina. The holotype and only known specimen (Museo Paleontológico Egidio Feruglio MPEF-PV 1716) was collected from an erosional exposure of fluvial sandstone within the Cañadón Cálcero Formation on a hill approximately 25 km north-northeast of Cerro Cóndor, Chubut Province, in west-central Argentina, South America. Though very incomplete, the skeletal elements recovered were found in articulation and include eight cervical, twelve dorsal, and three sacral vertebrae, as well as proximal portions of the posterior cervical ribs and all the doral ribs, the distal end of the left femur, the proximal end of the left tibia, and the right ilium. Much of the specimen was probably lost to erosion many years before its discovery. The type species is Brachytrachelopan mesai. The specific name honours Daniel Mesa, a local shepherd who discovered the specimen while searching for lost sheep. The genus name translates as "short-necked Pan", Pan being the god of the shepherds.
Description[]
Life restoration of Brachytrachelopan mesai
File:Path/Brachytrachelopan BW2.jpg This taxon's very short neck (approximately 40% shorter than other dicraeosaurids and the shortest of any known sauropod) is evidence that this lineage specialized to fill an ecological niche not exploited by other members of this infraorder. Small for a sauropod, Brachytrachelopan measured less than 10 metres (33 ft) in length. Rauhut et al. (2005, 670) note that the high degree of fusion present between the preserved neural arches and their respective centra, as well as fusion between the sacral centra, sacral neural arches, and sacral neural spines is evidence that the holotype does not represent a juvenile animal. Hence, the small body size is not a relic of ontogeny.
Distinguishing characteristics[]
Size comparison between a human, Brachytrachelopan, and other dicraeosaurids
File:Path/Dicraeosaurids BW.png Rauhut et al. (2005, 670) diagnose Brachytrachelopan as differing from all other sauropods in the following respects: "...individual cervical vertebrae being as long as, or shorter in anteroposterior length than, high posteriorly. Further apomorphies...include a pronounced, pillar-like centropostzygapophyseal lamina in the cervical vertebrae, a pronounced anterior inclination in the mid-cervical neural spines, with the tip of the spine extending beyond the anterior end of the centrum, and anterior dorsal neural spines one to six with vertical bases and anteriorly flexed tips".
Classification[]
Following a cladistic analysis of 27 sauropod taxa and 154 anatomical characters, Rauhut et al. (2005, 671-672; Fig. 2) assigned Brachytrachelopan to the Dicraeosauridae, proposing that, within this clade, it should be considered to have a sister group relationship to the Late Jurassic African taxon Dicraeosaurus, instead of to Amargasaurus from the Lower Cretaceous of South America. Rauhut et al. (2005, 671) conclude this is indicative of a rapid evolutionary radiation and dispersal of the Dicraeosauridae following the separation of the continents of the Southern and Northern Hemispheres during the latest Middle Jurassic.
Paleoecology[]
Gallery[]
Brachytrachelopan/Gallery
Sources[]
- Rauhut O.W.M., Remes K., Fechner R., Cladera G., Puerta P. (2005). "Discovery of a short-necked sauropod dinosaur from the Late Jurassic period of Patagonia". Nature 435:670-672.