Temporal range: Late Jurassic
|An artist's illustration of Brontosaurus excelsus|
Brontosaurus (meaning "Thunder Lizard" in Greek) is an extinct genus of apatosaurian sauropod dinosaur which lived throughout North America during the late Jurassic period, approximately 155 to 145 million years ago. It was originally considered to be a junior synonym of Apatosaurus, but is know regarded as a separate taxon after extensive scientific exploration conducted in 2015 revealed their were substantial differences between the two genera (for example, Brontosaurus can be defined as having a slimer build and slightly smaller in size).
Brontosaurus was a large, long-necked quadrupedal animal with a long, whip-like tail, and forelimbs that were slightly shorter than their hindlimbs. The largest species, B. excelsus, weighed up to 15 tonnes (15 long tons; 17 short tons) and measured up to 22 m (72 ft) long from head to tail.
The skull of Brontosaurus has not been found, but was probably similar to the skull of the closely related Apatosaurus. Like those of other sauropods, the vertebrae of the neck were deeply bifurcated; that is, they carried paired spines, resulting in a wide and deep neck. The vertebral formula was: 15 cervicals, 10 dorsals, five sacrals, and 82 caudals. The caudal vertebra number was noted to vary, even within a species. The cervical vertebrae were stouter than other diplodocids, though not as stout as in mature specimens of Apatosaurus. The dorsal ribs are not fused or tightly attached to their vertebrae, instead being loosely articulated. Ten dorsal ribs are on either side of the body. The large neck was filled with an extensive system of weight-saving air sacs. Brontosaurus, like its close relative Apatosaurus, had tall spines on its vertebrae, which make up more than half the height of the individual bones. The shape of the tail was unusual for diplodocids, being comparatively slender, due to the vertebral spines rapidly decreasing in height the farther they are from the hips. Brontosaurus also had very long ribs compared to most other diplodocids, giving them unusually deep chests. As in other diplodocids, the last portion of the tail of Brontosaurus possessed a whip-like structure.
The limb bones were also very robust. The arm bones are stout, with the humerus resembling that of Camarasaurus, and those of B. excelsus being nearly identical to those of Apatosaurus ajax. Charles Gilmore in 1936 noted that previous reconstructions erroneously proposed that the radius and ulna could cross, when in life they would have remained parallel. Brontosaurus had a single large claw on each forelimb, and the first three toes possessed claws on each foot. Even by 1936, it was recognized that no sauropod had more than one hand claw preserved, and this one claw is now accepted as the maximum number throughout the entire group. The single front claw bone is slightly curved, and squarely shortened on the front end. The hip bones included robust ilia, and the fused pubes and ischia. The tibia and fibula bones of the lower leg were different from the slender bones of Diplodocus, but nearly indistinguishable from those of Camarasaurus. The fibula is longer than the tibia, although it is also more slender.
Brontosaurus was discovered by Othniel Charles Marsh when the Bones War was happening. It was discovered after Apatosaurus.
- Brontosaurus excelsus, the type species of Brontosaurus, was first named by Marsh in 1879. Many specimens, including the holotype specimen YPM 1980, have been assigned to the species. They include FMNH P25112, the skeleton mounted at the Field Museum of Natural History, which has since been found to represent an unknown species of apatosaurine. Brontosaurus amplus, occasionally assigned to B. parvus, is a junior synonym of B. excelsus. B. excelsus therefore only includes its type specimen and the type specimen of B. amplus. The largest of these specimens is estimated to have weighed up to 15 tonnes and measured up to 22 m (72 ft) long from head to tail. Both known definitive B. excelsus fossils have been reported from Reed’s Quarry 10 of the Morrison Formation Brushy Basin member in Albany County, Wyoming, dated to the late Kimmeridgian age, about 152 million years ago.
- Brontosaurus parvus, first described as Elosaurus in 1902 by Peterson and Gilmore, was reassigned to Apatosaurus in 1994, and to Brontosaurus in 2015. Specimens assigned to this species include the holotype, CM 566 (a partial skeleton of a juvenile found in Sheep Creek Quarry 4 in Albany County, WY), BYU 1252-18531 (a nearly complete skeleton found in Utah and mounted at Brigham Young University), and the partial skeleton UW 15556 (which had once been accidentally mixed together with the holotype). It dates to the middle Kimmeridgian. Adult specimens are estimated to have weighed up to 14 tonnes and measured up to 22 m (72 ft) long from head to tail.
- Brontosaurus yahnahpin is the oldest species, known from a single site from the lower Morrison Formation, Bertha Quarry, in Albany County, Wyoming, dating to about 155 million years ago. It grew up to 21 metres (69 ft) long. The type species, E. yahnahpin, was described by James Filla and Patrick Redman in 1994 as a species of Apatosaurus (A. yahnahpin). The specific name is derived from Lakota mah-koo yah-nah-pin, "breast necklace", a reference to the pairs of sternal ribs that resemble the hair pipes traditionally worn by the tribe. The holotype specimen is TATE-001, a relatively complete postcranial skeleton found in Wyoming, in the lower Morrison Formation. More fragmentary remains have also been referred to the species. A re-evaluation by Robert T. Bakker in 1998 found it to be more primitive, so Bakker coined the new generic name Eobrontosaurus, derived from Greek eos, "dawn", and Brontosaurus.
Posture and locomotion
Historically, sauropods like Brontosaurus were believed to be too massive to support their own weight on dry land, so theoretically they must have lived partly submerged in water, perhaps in swamps. Recent findings do not support this, and sauropods are thought to have been fully terrestrial animals.
Diplodocids like Brontosaurus are often portrayed with their necks held high up in the air, allowing them to browse on tall trees. Though some studies have suggested that diplodocid necks were less flexible than previously believed, other studies have found that all tetrapods appear to hold their necks at the maximum possible vertical extension when in a normal, alert posture, and argue that the same would hold true for sauropods barring any unknown, unique characteristics that set the soft tissue anatomy of their necks apart from that of other animals.
Trackways of sauropods like Brontosaurus show that the average range for them was around 20–40 km (12–25 mi) per day, and they could potentially reach a top speed of 20–30 km (12–19 mi) per hour. The slow locomotion of sauropods may be due to the minimal muscling or recoil after strides.
Various uses have been proposed for the single claw on the forelimb of sauropods. They were suggested to have been for defence, but the shape and size of them makes this unlikely. Other predictions were that it could be for feeding, but the most probable is that the claw was for grasping objects like tree trunks when rearing.
James Spotila et al. (1991) suggest that the large body size of Brontosaurus and other sauropods would have made them unable to maintain high metabolic rates, as they would not be able to release enough heat. However, temperatures in the Jurassic were 3 degrees Celsius higher than present. They assumed that the animals had a reptilian respiratory system. Wedel found that an avian system would have allowed them to dump more heat. Some scientists have argued that the heart would have had trouble sustaining sufficient blood pressure to oxygenate the brain.
Juvenile Brontosaurus material is known based on the type specimen of B. parvus. The material of this specimen, CM 566, includes vertebrae from various regions, one pelvic bone, and some bones of the hind limb.
An article that appeared in the November 1997 issue of Discover Magazine reported research into the mechanics of diplodocid tails by Nathan Myhrvold, a computer scientist from Microsoft. Myhrvold carried out a computer simulation of the tail, which in diplodocids like Brontosaurus was a very long, tapering structure resembling a bullwhip. This computer modeling suggested that sauropods were capable of producing a whip-like cracking sound of over 200 decibels, comparable to the volume of a cannon.
James Spotila et al. (1991) suggest that the large body size of Brontosaurus and other sauropods would have made them unable to maintain high metabolic rates, as they would not be able to release enough heat. However, temperatures in the Jurassic were 3 degrees Celsius higher than present. They assumed that the animals had a reptilian respiratory system. Wedel found that an avian system would have allowed them to dump more heat. Some scientists have argued that the heart would have had trouble sustaining sufficient blood pressure to oxygenate the brain.Juveniles
In popular culture
- Brontosaurus appears in the video game ARK: Survival Evolved.
- It will appear in the video game, The Isle, where it is shown with speculative neck spikes.
- Brontosauruses appears at Epcot's Universe of Energy.
- Brontosaurus appeared in the documentary series PBS The Dinosaurs.
- Brontosaurus appeared in Zoboomafoo.
- Brontosaurus appeared in the video game Jurassic Park Builder.