Old Earth Ministries Online Dinosaur Curriculum
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Lesson 44 - Brachiosaurus
Brachiosaurus is a genus of sauropod dinosaur from the Jurassic Morrison Formation of North America. It was first described by Elmer S. Riggs in 1903 from fossils found in the Grand River Canyon (now Colorado River) of western Colorado, in the United States. Riggs named the dinosaur Brachiosaurus altithorax, declaring it "the largest known dinosaur". Brachiosaurus had a proportionally long neck, small skull, and large overall size, all of which are typical for sauropods. However, the proportions of Brachiosaurus are unlike most sauropods. The forelimbs were longer than the hindlimbs, which result in a steeply inclined trunk, making the overall body shape reminiscent of a modern giraffe. Also, while the tail is a typical long dinosaur tail, it was relatively short for a sauropod.
Length: 85 feet
Weight: 48 tons (96,000 lbs)
Date Range: 154 - 153 Ma, Kimmeridgian Age, Jurassic Period
|Life Restoration of Brachiosaurus|
Brachiosaurus is the namesake genus of the family Brachiosauridae, which includes a handful of other similar sauropods. Much of what is known by laypeople about Brachiosaurus is in fact based on Giraffatitan brancai, a species of brachiosaurid dinosaur from the Tendaguru Formation of Tanzania that was originally described by German paleontologist Werner Janensch as a species of Brachiosaurus. Recent research shows that the differences between the type species of Brachiosaurus and the Tendaguru material are significant enough that the African material should be placed in a separate genus. Several other potential species of Brachiosaurus have been described from Africa and Europe, but none of them are thought to belong to Brachiosaurus at this time.
Brachiosaurus is one of the rarer sauropods of the Morrison Formation. The type specimen of B. altithorax is still the most complete specimen, and only a relative handful of other specimens are thought to belong to the genus. It is regarded as a high browser, probably cropping or nipping vegetation as high as possibly 9 metres (30 ft) off of the ground. Unlike other sauropods, and its depiction in Jurassic Park, it was unsuited for rearing on its hindlimbs. It has been used an example of a dinosaur that was most likely ectothermic due to its large size and the corresponding need for forage, but more recent research finds it to have been warm-blooded.
Like all sauropod dinosaurs, Brachiosaurus was a quadrupedal animal with a small skull, a
The placement of Brachiosaurus nostrils has been the source of much debate with Witmer (2001) describing in Science the hypothesized position of the fleshy nostrils in Brachiosaurus in as much as five possible locations.
There has also been the hypothesis of various sauropods such as Brachiosaurus possessing a trunk. Given that there are not any narrow-snouted sauropods including Brachiosaurus lies against such a hypothesis. Stronger evidence for the absence of a trunk is found in the teeth wear of Brachiosaurus, which shows the kind of wear that would result in biting and tearing off of plant matter rather than purely grinding which would be the result of having already ripped the leaves and branches off with its trunk.
Because "Brachiosaurus" brancai (Giraffatitan) is known from much more complete
Discovery and history
The genus Brachiosaurus, and type species B. altithorax, are based on a partial postcranial skeleton from Fruita, in the valley of the Colorado River of western Colorado. This specimen was collected from rocks of the Brushy Basin Member of the Morrison Formation in 1900 by Elmer S. Riggs and his crew from the Field Columbian Museum (now the Field Museum of Natural History) of Chicago. It is currently cataloged as FMNH P 25107. Riggs and company were working in the area as a result of favorable
The Fruita skeleton was not the first discovery of Brachiosaurus bones, although it was the first to be recognized as belonging to a new and distinct animal. In 1883, a sauropod skull was found near Garden Park, Colorado, at Felch Quarry 1, and was sent to Othniel Charles Marsh (of "Bone Wars" fame). Marsh incorporated the skull into his skeletal restoration of "Brontosaurus" (now Apatosaurus). It eventually became part of the collections of the National Museum of Natural History, as USNM 5730.
Additional discoveries of Brachiosaurus material in North America have been uncommon and consist of a handful of bones. Material has been described from Colorado, Oklahoma, Utah, and Wyoming, and undescribed material has been mentioned from several other sites.
Riggs derived the genus name from the Greek brachion/βραχιων meaning "arm" and sauros/σαυρος meaning "lizard", because he realized that the length of the arms was unusual for a sauropod. The species epithet "altithorax" was chosen because of the unusually deep and wide chest cavity, from Latin altus meaning "deep" and Greek thorax/θώραξ (Latin thorax), meaning "breastplate, cuirass, corslet".
Species - Brachiosaurus altithorax
FMNH P 25107, the holotype of both the genus Brachiosaurus and the species B. altithorax, consists of the right humerus (upper arm bone), the right femur (thigh bone), the right ilium (a hip bone), the right coracoid (a shoulder bone), the sacrum (fused vertebrae of the hip), the last seven thoracic (trunk) and two caudal (tail) vertebrae, and a number of ribs. Riggs described the coracoid as from the left side of the body, but restudy has shown it to be a right coracoid.
With the removal of the East African Giraffatitan, Brachiosaurus is known only from the Morrison Formation of western North America. The Morrison Formation is interpreted as a semiarid environment with distinct wet and dry seasons, and flat floodplains. Vegetation varied from gallery forests (river–lining forests in otherwise treeless settings) of conifers, tree ferns, and ferns, to fern savannas with rare Araucaria-like trees. Several other sauropod genera were present in the Morrison Formation, with differing body proportions and feeding adaptations. Among these were Apatosaurus, Barosaurus, Camarasaurus, Diplodocus, Haplocanthosaurus, and Supersaurus. Brachiosaurus was one of the less abundant Morrison Formation sauropods. In a survey of over 200 fossil localities, John Foster reported 12 specimens of the genus, comparable to Barosaurus (13) and Haplocanthosaurus (12), but far fewer than Apatosaurus (112), Camarasaurus (179), and Diplodocus (98). Brachiosaurus fossils are found only in the lower-middle part of the expansive Morrison Formation (stratigraphic zones 2-4), dated to about 154-153 million years ago, unlike many other types of sauropod which have been found throughout the formation.
In contrast to most other sauropods, brachiosaurids had an inclined back, due to their long forelimbs. Therefore, if the neck exited the body in a straight line, it already pointed upwards. The exact angle is influenced by how the pectoral girdle is reconstructed, that is how the shoulder blades are placed on the ribcage. The mobility of the neck was reconstructed as quite low by Stevens and Parrish, while other researchers like Paul and Christian and Dzemski argued for more flexible necks.
Brachiosaurus is thought to have been a high browser, feeding on foliage well above the ground. Even if it did not hold its neck near vertical, and instead had a straighter neck, its head height may still have been over 9 metres (30 ft) above the ground. It probably fed mostly on foliage above 5 metres (16 ft). This does not preclude the possibility that it also fed lower at times, between 3 to 5 metres (9.8 to 16 ft) up. Its diet likely consisted of ginkgoes, conifers, tree ferns, and large cycads, with intake estimated at 200 to 400 kilograms (440 to 880 lb) of plant matter daily. However, more recent studies estimate that ~240 kilograms (530 lb) of plant matter would have been sufficient to feed a 70 metric tons (77 short tons) sauropod, so Brachiosaurus may have required only about 120 kilograms (260 lb) of fodder a day. Brachiosaur feeding involved simple up–and–down jaw motion. The teeth were arranged to shear material as they closed, and were probably used to crop and/or nip vegetation.
It has repeatedly been suggested, e.g. in the movie Jurassic Park, that Brachiosaurus could rear into a bipedal or tripodal (with tail support) pose to feed. However, a detailed physical modelling-based analysis of sauropod rearing capabilities by Heinrich Mallison showed that while many sauropods could rear, the unusual brachiosaurid body shape and limb length ratio made them exceptionally ill suited for rearing. The forward position of the center of mass would have led to problems with stability, and required unreasonably large forces in the hips to obtain an upright posture. Brachiosaurus would also have gained relatively little from rearing (only 33% more feeding height), compared to other sauropods, for which a bipedal pose may have tripled the feeding height.
Like all sauropods, Brachiosaurus was homeothermic (maintaining a stable internal temperature) and endothermic (controlling body temperature through internal means), meaning that it was able to actively control its body temperature, producing the necessary heat through a high basic metabolic rate of its cells. In the past, Brachiosaurus has been used an example of a dinosaur for which endothermy is unlikely, because of the combination of great size (leading to overheating) and great caloric needs to fuel endothermy. However, these calculations were based on incorrect assumptions about the available cooling surfaces (the large air sacs were not known), and a grossly inflated body mass. These inaccuracies resulted in overestimation of heat production and underestimation of heat loss. The large nasal arch has been postulated as an adaptation for cooling the brain, as a surface for evaporative cooling of the blood. Again, when this was proposed, cooling via the air sacs was not known, and thus not taken into account. Furthermore, other similar sized sauropods had no comparable structure. Additionally, in proportion to the entire animal, the nasal arch is very small, and would thus have made only an insignificant contribution to heat loss.
The original Brachiosaurus specimens collected by Elmer Riggs for the Field Museum of Natural History (Chicago) were not put on display in the museum until 1994, when a skeletal mount (made up of resin casts rather than actual fossil bones) was constructed inside the museum's main Stanley Field Hall. The mount stood until 1999, when it was moved to the B Concourse of United Airlines' Terminal One in O'Hare International Airport. At the same time, a second cast (in bronze) of the Field Museum's B. altithorax was constructed outside the museum.
Brachiosaurus is one of the best-known dinosaurs amongst both paleontologists and the general public. A main belt asteroid, 1991 GX7, has been named 9954 Brachiosaurus in honor of the genus. The genus has been featured in many films and television programs, most notably the Jurassic Park and Walking with Dinosaurs series. The digital model of Brachiosaurus used in Jurassic Park went on to become the starting point for the ronto models in the 1997 special edition of the science fiction film Star Wars Episode IV: A New Hope.
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