| Brachiosauridae Fossil range: Jurassic - Cretaceous | |
|---|---|
 Mounted skeleton of Brachiosaurus in Berlin. | |
| Scientific classification
| |
|
Brachiosauridae | |
| |
Brachiosauridae are a family of dinosaurs, whose members are known as brachiosaurids. They were herbivorous quadrupeds with longer forelegs than hind legs - the name derives from the Greek for arm lizard - and long, 45-degree angle necks. Despite their apparently distinctive features, there is some dispute as to whether Brachiosauridae is really a distinct family or a collection of basal Titanosauriformes. As a result, there is also some dispute about which animals belong within this family.
Their masses would have ranged from 20 to 90 tons, and their unusually long and upright necks gave them access to the leaves of treetops that would have been inaccessible to other sauropods. Their long and spatulate (spoon-shaped) teeth were capable of processing tougher plant material than some other sauropods (such as Diplodocus). Some palaeontologists had speculated that if they could have reared upon their hind-limbs even higher branches could be reached. However, their short tail and hind-limbs would have placed the creatures center of gravity quite far forward, and made such an action difficult.
Brachiosaurids existed until at least the late Campanian era (71-83 Ma), as caudal vertebrae from that era have been found in Mexico.[1] Brachiosaurid fossils were first found in Africa in the early 20th century, and are now known to have existed in Europe and North America. The first evidence of brachiosaurids in Asia was recovered in 2001,[2] although the find consisted only of a few teeth[3]
The largest mounted skeleton in the world is a brachiosaurid; the Brachiosaurus at the Humboldt Museum in Berlin, Germany.
Description[]
The Brachiosauridae are composed of quadrupedal dinosaurs that are generally very large, with the exception of the possible insular dwarf Europasaurus. The brachiosaurids can be distinguished from other macronarian taxa by their broad, thick and spoon-shaped teeth. Their maxillaryteeth were twisted apically, at the top, and the shape of these teeth was optimal for biting off resistant vegetation. While brachiosaurids, like other sauropods, did not perform significant food processing in their mouths, their teeth enabled them to slice through food instead of having to pull it from tree branches. Evidence for this precision shearing consists of apical wear facets on the teeth and distinctive bone structure that suggests orthal, vertical, jaw action.
In addition, the characteristic long necks of brachiosaurids are distinct from those of other long-necked dinosaur taxa. They possessed a narrow neck composed of twelve to thirteen extremely long cervical vertebrae that was laterally inflexible and dorsoventrally, vertically, flexible. This meant that brachiosaurids could angle their necks up and lift their heads, enabling them to graze from treetops up to a height of about fourteen meters. It has been argued that other sauropods lacked this dorsoventral flexibility and that their necks stretched outwards in front of them instead of upwards. Brachiosaurids have more often been found in the conifer-rich sites, like the Tendaguru, than in the Morrisondeposits, suggesting that their fitness was increased by the presence of taller conifer food sources.
However, the giant size and long necks of brachiosaurids meant that they required tremendous pressure to bring oxygenated blood to their brains. It has been proposed that sauropods possessed a four-chambered double pump heart, with one pump for oxygenated and one pump for deoxygenated blood.
As in all Macronaria, the forelimbs of brachiosaurids are long relative to the hindlimbs, but this trait is more pronounced in brachiosaurids. The forelimbs were very slender for a sauropod and the metacarpal bones of the forelimb were elongated.These adaptations overall increased the stride length of the forelimbs, arguably resulting in an uneven gait. However, it was previously argued that they were hindlimb dominant like other sauropods, and thus had the ability to rear up on their hindlimbs.Based on the structure of their legs, making it impossible for them to run, it is likely that they moved about in a low walking speed (20–40 km/day), but were capable of moving faster when necessary, up to 20–30 km/hour, depending on leg length.
Brachiosaurids shared synapomorphies, new traits typical for the group. They possessed middle and rear back vertebrae with long, 'rod-like' transverse processes. In the pelvis, the ischium had a shortened pubic peduncle, the contact surface with the pubic bone.Their humeri, upper arm bones, had a large deltopectoral crest. Their skull roofs showed wide supratemporal fenestrae, openings for the muscles. They had neural archesplaced more on front of the vertebrae, shoulder blades that were expanded at the top end, irregularly shaped coracoids in the shoulder girdle, and triangular projections on the underside of the front branch of their quadratojugal bones at the lower rear corner of the skull.
References[]
- ^ Kirkland, J. I.; Agullion-Martinez, M. C.; Hernandez-Rivera, R.; Tidwell, R. 2000. "A late Campanian brachiosaurid proximal caudal vertebra from Coahuila, Mexico: evidence against a Cretaceous North American sauropod hiatus". Journal of Vertebrate Paleontology 20 (supplement to Number 3), Abstracts of Papers, Sixtieth Annual Meeting, pp. 51A–52A.
- ^ Lim, J.-D.; Martin, L.D.; Baek, K.-S. (March 2001). "The first discovery of a brachiosaurid from the Asian continent". Naturwissenschaften (Springer Berlin) 88 (2): 82–84. doi:.
- ^ http://web.archive.org/web/20060518013655/http://www.abc.net.au/news/newsitems/200605/s1635673.htm