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Apatosaurus

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Apatosaurus
Temporal range: Late Jurassic, 152–151Ma
Louisae.jpg
Mounted A. louisae holotype (specimen CM 3018), Carnegie Museum of Natural History
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Suborder: Sauropodomorpha
Family: Diplodocidae
Subfamily: Apatosaurinae
Genus: Apatosaurus
Marsh, 1877
Type species
Apatosaurus ajax
Marsh, 1877
Referred Species
  • Apatosaurus louisae Holland, 1916

Apatosaurus (meaning "deceptive reptile" /əˌpætɵˈsɔrəs/) is a genus of extinct sauropod dinosaurs that lived in North America during the Late Jurassic period. It was originally described in 1877 when Othniel Charles Marsh named the first known species, Apatosaurus ajax, and a second species, Apatosaurus louisae, was discovered in 1916. They range in age from 152 to 151 million years ago, during the early Tithonian ages of the Morrison Formation in Colorado, Oklahoma, and Utah. Brontosaurus has long been considered a junior synonym of Apatosaurus, its only species having been reclassified as A. excelsus in 1903. However, an extensive study published in 2015 concluded that Brontosaurus was a valid genus of sauropod distinct from Apatosaurus.[1][2] The average length of an Apatosaurus was 22.8 m (75 ft), and their average weight was at least 16.4 metric tons (18.1 short tons). A few specimens indicate a maximum length up to 30% greater than average and a weight of 33–73 t (32–72 long tons; 36–80 short tons).

The cervical vertebrae were less elongated and more heavily constructed than those of Diplodocus and the bones of the leg were much stockier despite being longer, implying that Apatosaurus was a more robust animal. The tail was held above the ground during normal locomotion. Like all sauropods, Apatosaurus had only one claw on each forelimb and three on each hindlimb. The skull of Apatosaurus, long thought to be similar to Camarasaurus, is much more similar to that of Diplodocus. Apatosaurus was a generalized browser, likely holding its head elevated, and may have grown 520 kilograms (1,150 pounds) per year until it reached 70 years of age. To lighten its bones, Apatosaurus had air sacs, which made the inside of bones sponge-like and full of holes. its tail, like that of other diplodocids, may have been used as a whip, creating loud noise.

Apatosaurus is a genus in the family Diplodocidae. It is more basal than other genera like Diplodocus and Barosaurus, and is sometimes included in its own subfamily, Apatosaurinae. Apatosaurus is one of the more common sauropods in the Morrison Formation, and is often found associated with skeletons of Allosaurus, Camarasaurus, Stegosaurus and Diplodocus. Apatosaurus is also one of the longest Morrison dinosaurs, although Supersaurus exceeds it.

Description[edit]

Comparison of A. ajax (orange) and A. louisae (red) with a human (blue) and Brontosaurus parvus (green)

Apatosaurus was a large, long-necked quadrupedal animal with a long, whip-like tail. Its fore limbs were slightly shorter than its hind limbs. Most size estimates are based on specimen CM 3018 (the type specimen of A. louisae), which reached 21–22.8 m (69–75 ft) in length[3][4] and 16.4–22.4 t (16–22 long tons; 18–25 short tons) in weight,[3][5] though past estimates have been as high as 35 t (34 long tons; 39 short tons).[3] One of the first estimates of A. louisae was found to be 21.8 m (72 ft), found by measuring the vertebral column.[6] Some specimens of A. ajax (like OMNH 1670) represent individuals 11–30% longer, suggesting weights double that of CM 3018 or 33–73 t (32–72 long tons; 36–80 short tons), potentially rivalling the largest titanosaurs.[7]

A. ajax skull, specimen CMC VP 7180

The skull was small in comparison with the size of the animal. The jaws were lined with spatulate (chisel-like) teeth that were suited to a herbivorous diet.[8] The snout of Apatosaurus and similar diplodocoids are squared, with only Nigersaurus having a squarer skull.[9] The braincase of Apatosaurus is well preserved in specimen BYU 17096. The bones are articulated, and their fusion indicates that the bones are mature. The braincase was placed in a phylogenetic analysis, and its morphology was found to be very similar to that of other diplodocoids.[10] Some skulls of Apatosaurus have been found still in articulation with their teeth. Those teeth that have the enamel surface exposed do not show any scratches on the surface, and instead display a sugary texture and little wear.[9]

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.[8] 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, and found to be most similar to Camarasaurus by Charles Whitney Gilmore. The Atlas-Axis complex of the first cervicals is nearly fused in Apatosaurus louisae. The dorsal ribs are not fused or tightly attached to their vertebrae, instead being loosely articulated.[6] Ten dorsal ribs are on either side of the body.[11] The large neck was filled with an extensive system of weight-saving air sacs. Apatosaurus, like its close relative Supersaurus, has tall spines on its vertebrae, which make up more than half the height of the individual bones. The shape of the tail is unusual for a diplodocid, being comparatively slender, due to the vertebral spines rapidly decreasing in height the farther they are from the hips. Apatosaurus also had very long ribs compared to most other diplodocids, giving it an unusually deep chest.[12] As in other diplodocids, the last portion of the tail of Apatosaurus possessed a whip-like structure.[6]

The limb bones were also very robust.[12] Within the genus, the scapula of A. louisae is intermediate in morphology between those of A. ajax and A. excelsus. The arm bones are stout, with the humerus resembling that of Camarasaurus, and those of A. excelsus and A. ajax being nearly identical. 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.[6] Apatosaurus had a single large claw on each forelimb, and the first three toes possessed claws on each hindlimb. The phalangeal formula is 2-1-1-1-1, meaning that the innermost finger (phalanx) on the forelimb has two bones, the next has one, etc.[13] 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.[6][14] The single manual claw bone (ungual) is slightly curved, and squarely truncated on the anterior end. The pelvic girdle includes the robust ilia, and the fused (co-ossified) pubes and ischia. The femora of A. louisae are the stoutest of any member of Sauropoda. Roughened surface textures (rugosities) are present on both ends of the femur, and the top edge of this bone protrudes above the great trochanter. The tibia and fibula bones are 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. The foot of Apatosaurus has three claws on the innermost digits, and the digit formula is 3-4-5-3-2. In an individual of A. louisae, the astragalus was not found fused to the tibia. The stoutest metatarsal is in digit 1, and the third metatarsal is the second stoutest.[6]

Classification[edit]

Shoulder blade and coracoid of A. ajax

Apatosaurus is a member of the family Diplodocidae, a clade of gigantic sauropod dinosaurs. The family includes some of the longest creatures ever to walk the earth, including Diplodocus, Supersaurus, and Barosaurus. Apatosaurus is sometimes classified in the subfamily Apatosaurinae, which may also include Suuwassea, Supersaurus and Eobrontosaurus.[12][15][16] Othniel Charles Marsh described Apatosaurus as being allied to Atlantosaurus, within the now defunct group Atlantosauridae.[11][17] In 1878, Marsh raised his family to the rank of suborder, including Apatosaurus, Atlantosaurus, Morosaurus (=Camarasaurus) and Diplodocus. He classified this group within Sauropoda. In 1903, Elmer S. Riggs mentioned that the name Sauropoda would be a junior synonym of earlier names, and grouped Apatosaurus within Opisthocoelia.[11] Most authors still use Sauropoda as the group name.[18] John Whitlock published a study in 2011 placing Apatosaurus as the most basal diplodocid, a placement that is often supported.[19][20]

Cladogram of the Diplodocidae after Tschopp, Mateus, and Benson (2015).[1]

 Diplodocidae 

Amphicoelias altus




 Apatosaurinae 

Unnamed species





Apatosaurus ajax



Apatosaurus louisae





Brontosaurus excelsus




Brontosaurus yahnahpin



Brontosaurus parvus







 Diplodocinae 

Unnamed species




Tornieria africana





Supersaurus lourinhanensis



Supersaurus vivianae





Leinkupal laticauda




Galeamopus hayi





Diplodocus carnegii



Diplodocus hallorum





Kaatedocus siberi



Barosaurus lentus











Discovery and species[edit]

A. ajax sacrum, illustrated in 1879

Marsh, a Professor of Paleontology at Yale University, described and named an incomplete (and juvenile) skeleton of Apatosaurus ajax in 1877.[17] The composite term Apatosaurus comes from the Greek words apate (ἀπάτη)/apatelos (ἀπατηλός) meaning "deception"/"deceptive" and sauros (σαῦρος) meaning "lizard";[21] thus, "deceptive lizard". Marsh gave it this name based on the chevron bones, which were dissimilar to those of other dinosaurs and instead possessed similarities with mosasaur chevrons.[17][22] Two years later, Marsh announced the discovery of a larger and more complete specimen at Como Bluff Wyoming—which, because of discrepancies including the size difference, he identified as belonging to an entirely new genus and species. He named the new species Brontosaurus excelsus,[11][23] meaning "thunder lizard", from the Greek brontē/βροντη meaning "thunder" and sauros/σαυρος meaning "lizard",[21] and from the Latin excelsus, "noble" or "high".[24] All Apatosaurus specimens are from the Morrison Formation. In 1877 this formation became the center of the Bone Wars, a fossil-collecting rivalry between early paleontologists Othniel Charles Marsh and Edward Drinker Cope. It is for this reason that the publications and descriptions of taxa by Marsh and Cope were rushed at the time.[25]

Obsolete mount of an apatosaurine (possibly Apatosaurus) specimen AMNH 460 with sculpted skull, American Museum of Natural History

Elmer Riggs in the 1903 edition of Geological Series of the Field Columbian Museum argued that Brontosaurus was not different enough from Apatosaurus to warrant its own genus, and created the combination Apatosaurus excelsus. Riggs stated that "In view of these facts the two genera may be regarded as synonymous. As the term 'Apatosaurus' has priority, 'Brontosaurus' will be regarded as a synonym".[11] Nonetheless, before the mounting of the American Museum of Natural History Apatosaurus, Henry Fairfield Osborn chose to label the skeleton "Brontosaurus", even though he was a strong opponent of Marsh and his taxa.[26][27]

Unfinished A. sp. mount (FMNH P25112) in the Field Museum of Natural History, 1909

The AMNH specimen (now assigned to A. ajax) is very complete, only missing the head, feet and sections of the tail, as was the first sauropod skeleton mounted.[28] To complete the mount, sauropod feet that were discovered at the same quarry were added, as well as a tail fashioned to appear as Marsh believed it should, which had too few vertebrae. In addition, a sculpted model of what the museum felt the skull of this massive creature might look like. This was not a delicate skull like that of Diplodocus, which would later turn out to be more accurate, but was based on "the biggest, thickest, strongest skull bones, lower jaws and tooth crowns from three different quarries".[6][11][28][29] These skulls were likely those of Camarasaurus, the only other sauropod for which good skull material was known at the time. The mount construction was overseen by Adam Hermann, who failed to find Apatosaurus skulls. Hermann was forced to sculpt a stand-in skull by hand. Henry Fairfield Osborn noted in a publication that the skull was "largely conjectural and based on that of Morosaurus" (now Camarasaurus).[26]

In 1903 Riggs also described a new specimen of Apatosaurus, which was then placed in the collections of the Field Columbian Museum. Found near the Grand River Valley of Fruita, Colorado, the last cervical vertebrae were exposed from the hillside. Those cervicals were articulated with the thoracic vertebrae, which were excavated from the slope. Ten feet downhill, the distal end of a femur could be seen in the matrix. The rocks were so hard that drills and dynamite had to be used to extract the specimen. Nearly the entire rear of the skeleton was uncovered, measuring 5.5 m (18 ft). Apparently when first preserved, the entire skeleton was present, but the cervical vertebrae and forelimbs were eroded away.[11]

Side view of A. louisae CM 3018 mounted with a cast of skull CM 11162

It was not until 1909 that an Apatosaurus skull was found, during the first expedition to what would become the Carnegie Quarry at Dinosaur National Monument, led by Earl Douglass. The skull was found a few meters away from a skeleton (specimen CM 3018) identified as the new species Apatosaurus louisae, named after Andrew Carnegie's wife Louise. The skull was designated CM 11162, and was very similar to the skull of Diplodocus. It was accepted as belonging to the Apatosaurus specimen by Douglass and Carnegie Museum director William H. Holland, although other scientists, most notably Osborn, rejected this identification. Holland defended his view in 1914 in an address to the Paleontological Society of America, yet he left the Carnegie Museum mount headless. While some thought Holland was attempting to avoid conflict with Osborn, others suspected that Holland was waiting until an articulated skull and neck were found to confirm the association of the skull and skeleton.[26] After Holland's death in 1934, a cast of a Camarasaurus skull was placed on the mount by museum staff.[27]

At the Yale Peabody Museum, a skeleton was mounted in 1931 with a skull unique from all the others. While at the time most museums were using Camarasaurus casts, the Peabody Museum sculpted a completely different skull. They based the lower jaw on a Camarasaurus mandible, with the cranium resembling Marsh's 1891 illustration. The skull also included forward-pointing nasals, something truly different to any dinosaur, and fenestrae differing from the drawing and other skulls.[26]

Skull of "Einstein" (BYU 17096) in front view

No Apatosaurus skull was mentioned in literature until the 1970s when John Stanton McIntosh and David Berman redescribed the skulls of Diplodocus and Apatosaurus. They found that though he never published his opinion, Holland was almost certainly correct, that Apatosaurus had a Diplodocus like skull. According to them, many skulls long thought to pertain to Diplodocus might instead be those of Apatosaurus. They reassigned multiple skulls to Apatosaurus based on associated and closely associated vertebrae. Even though they supported Holland, it was noted that Apatosaurus might have possessed a Camarasaurus like skull, based on a disarticulated Camarasaurus-like tooth found at the precise site where an Apatosaurus specimen was found years before.[29] On October 20, 1979, after the publications by McIntosh and Berman, the first true skull of Apatosaurus was mounted on a skeleton in a museum, that of the Carnegie.[27] In 1998, the Felch Quarry skull that Marsh included in his 1896 skeletal restoration was suggested to belong to Brachiosaurus instead.[30] In 2011, the first specimen of Apatosaurus where a skull was found articulated with its cervical vertebrae was described. This specimen, CMC VP 7180, was found to differ in both skull and neck features from A. louisae, and the specimen was found to have a majority of features related to those of A. ajax.[31]

Infographic explaining the history of Brontosaurus and Apatosaurus according to Tschopp et al. 2015

Almost all modern paleontologists have agreed with Riggs that the two species should be classified together in a single genus. According to the rules of the ICZN (which governs the scientific names of animals), the name Apatosaurus, having been published first, has priority as the official name; Brontosaurus is considered a junior synonym and has therefore been discarded from formal use.[32][33][34][35] Despite this, at least one paleontologist—Robert T. Bakker—argued in the 1990s that A. ajax and A. excelsus are in fact sufficiently distinct that the latter continues to merit a separate genus.[36] In 2015 Emanuel Tschopp, Octávio Mateus, and Roger Benson released a paper that argued that Apatosaurus excelsus, originally classified as Brontosaurus excelsus, had enough morphological differences from other species of Apatosaurus that it warranted being reclassified as a separate genus again. The conclusion was based on a comparison of 477 morphological characteristics across 81 different dinosaurs. Among the many notable differences were the wider - and presumaby stronger - neck of other Apatosaurus species compared to A. excelsus.[1]

Valid species[edit]

Apatosaurine specimen AMNH 460 at the AMNH as re-mounted in 1995

Multiple species of Apatosaurus and its synonyms have been designated from scant material. Marsh named as many species as he could, which resulted in many being based upon fragmentary and indistinguishable remains. In 2005, Paul Upchurch and colleagues authored a study published to analyze the species and specimen relationships of Apatosaurus.[18] Their analysis was revised and expanded with many additional diplodocid specimens in 2015, though this larger study found that only two species could be referred to Apatosaurus.[1]

  • Apatosaurus ajax was named by Marsh in 1877 after Ajax, the hero from Greek mythology.[37] Marsh designated the fairly complete skeleton YPM 1860 as its holotype. The species remained largely unknown as it was overshadowed by A. excelsus and A. louisae. In 2005, many specimens in addition to the holotype were found assignable to A. ajax, YPM 1840, NSMT-PV 20375, YPM 1861, and AMNH 460. The specimens span from the late Kimmeridgian to the early Tithonian. A. ajax is the senior synonym of Atlantosaurus immanis and Apatosaurus laticoliis.[18]
  • Apatosaurus louisae was named by Holland in 1916 in honor of Mrs. Louise Carnegie, wife of Andrew Carnegie who funded field research to find complete dinosaur skeletons in the American West. Apatosaurus louisae was first known from one partial skeleton which was found in Utah in the United States.[38] The holotype is CM 3018, with referred specimens including CM 3378, CM 11162, and LACM 52844. The former two consist of a vertebral column, the latter two a skull and a nearly complete skeleton, respectively. A. louisae is one of the most distinct species, yet it was recovered as the most primitive species in the Upchurch phylogeny. Its specimens all come from the late Kimmeridgian of Dinosaur National Monument.[18]
Specimen NSMT-PV 20375, which may belong to a new genus

The cladogram below is the result of an analysis by Tschopp, Mateus, and Benson (2015). The authors analyzed most diplodocid type specimens separately to deduce which specimen belonged to which species and genus.[1]

 Apatosaurinae 


YPM 1840 ("Atlantosaurus" immanis type)



NSMT-PV 20375





AMNH 460



 Apatosaurus 
 Apatosaurus ajax 

YPM 1860 (Apatosaurus ajax type)


 Apatosaurus louisae 

CM 3018 (Apatosaurus louisae type)



YPM 1861 (Apatosaurus laticollis type)




 Brontosaurus 
 Brontosaurus excelsus 

YPM 1980 (Brontosaurus excelsus type)



YPM 1981 (Brontosaurus amplus type)





AMNH 5764 (Amphicoelias altus type)




FMNH P25112



 Brontosaurus yahnahpin 

Tate-001 (Eobrontosaurus yahnahpin type)


 Brontosaurus parvus 

CM 566 (Elosaurus parvus type)




UM 15556



BYU 1252-18531











Reassigned species[edit]

The most complete specimen known to date, A. sp. BYU 17096 nicknamed "Einstein"
  • Apatosaurus grandis was named in 1877 by Marsh in the article that described A. ajax. It was briefly described, figured, and diagnosed.[6] Marsh noted that it was only provisionally assigned to the genus when he reassigned it to his new genus Morosaurus in 1878.[39] It is now the oldest species of Camarasaurus, after being reassigned to that genus.[40]
  • Apatosaurus excelsus was the original type species of Brontosaurus, first named by Marsh in 1879. Elmer Riggs reclassified Brontosaurus as a synonym of Apatosaurus in 1903, transferring the species B. excelsus to A. excelsus. In 2015, Tschopp, Mateus, and Benson argued that the species was distinct enough to be placed in its own genus, so they reclassified it back into Brontosaurus.[1]
  • Apatosaurus parvus, first described from a juvenile specimen as Elosaurus in 1902 by Peterson and Gilmore, was reassigned to Apatosaurus in 1994, and then to Brontosaurus in 2015.[1]
  • Apatosaurus minimus was described originally as a specimen of Brontosaurus sp. in 1904 by Osborn. In 1917, it was named as its own species, A. minimus, by Henry Mook for a pair of ilia and their sacrum.[6][41][42] In 2012, Mike P. Taylor and Matt J. Wedel published a short abstract describing the material of "A." minimus, finding it to be hard to place among either Diplodocoidea or Macronaria. While it was placed with Saltasaurus in a phylogenetic analysis, it was thought to represent instead some form with convergent features from many groups.[42]
  • Apatosaurus alenquerensis was named in 1957 by Albert-Félix de Lapparent and Georges Zbyweski. It was based on postcrania from Portugal. In 1990 this was referred to Camarasaurus, but in 1998 it was given its own genus, Lourinhasaurus.[18]

Palaeobiology[edit]

Artistic interpretation of an individual of A. louisae arching its neck down to drink

It was historically believed that sauropods like Apatosaurus were too massive to support their own weight on dry land, so it was theorized that 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.[43]

Feeding[edit]

A study of diplodocid snouts showed that the square snout, large proportion of pits, and fine subparallel scratches in Apatosaurus suggests it was a ground-height nonselective browser.[9] It may have eaten ferns, cycadeoids, seed ferns, horsetails, and algae. Kent Stevens and Michael Parrish (1999 and 2005) suggest that Apatosaurus had a great feeding range as its neck could bend into a U-shape laterally.[44] The neck's range of movement would have also allowed the head to graze below the level of the body, leading some scientists to speculate that these sauropods grazed from riverbanks on submerged water plants.[45]

Matthew Cobley et al. (2013) disputed this, finding that large muscles and cartilage would have limited movement of the neck. They state that the feeding ranges for sauropods like Diplodocus were smaller than previously believed and the animals may have had to move their whole bodies around to better access areas where they could browse vegetation. As such, they might have spent more time foraging to meet their minimum energy needs.[46][47] The conclusions of Cobley et al. were disputed by Mike Taylor, who analysed the amount and positioning of intervertebral cartilage to determine the flexibility of the neck of Apatosaurus and Diplodocus. He found that the neck of Apatosaurus was very flexible.[48]

In 1987, James Farlow calculated that an Apatosaurus-sized dinosaur about 35 t (34 long tons; 39 short tons) would have possessed 5.7 t (5.6 long tons; 6.3 short tons) of fermentation contents.[49] Assuming Apatosaurus had an avian respiratory system and a reptilian resting-metabolism, Frank Paladino et al. (1997) estimate that the animal would need to consume only about 262 liters (69 gallons) of water per day.[50]

Posture and locomotion[edit]

Further information: Sauropod neck posture
Tracks of a juvenile, indicating bipedal posture

Diplodocids like Apatosaurus are often portrayed with their necks held high up in the air, allowing them to browse on tall trees. Some studies suggest that diplodocid necks were less flexible than previously believed, because the structure of the neck vertebrae would not have permitted the neck to bend far upwards, and that sauropods like Apatosaurus were adapted to low browsing or ground feeding.[44][45][51] Other studies by Taylor find 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. Apatosaurus, like Diplodocus, would have held its neck angled upward with the head pointed downwards in a resting posture.[48][52]

In 2008, footprints of a juvenile Apatosaurus were reported from Quarry Five in Morrison, Colorado. Discovered in 2006 by Matthew Mossbrucker, these footprints show that juveniles could run on their hind legs in a manner similar to that of the modern basilisk lizard.[53] Trackways of sauropods like Apatosaurus 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.[8] The slow locomotion of sauropods may be due to the minimal muscling or recoil after strides.[54]

Various uses have been proposed for the single claw on the forelimb of sauropods. It has been suggested that they were 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.[14]

Physiology[edit]

Further information: Physiology of dinosaurs
Tail vertebrae of specimen FMNH P25112, showing pneumatic fossae (holes)

Given the large body mass of Apatosaurus, combined with its long neck, physiologists have encountered problems determining how these animals managed to breathe. Beginning with the assumption that Apatosaurus, like crocodilians, did not have a diaphragm, the dead-space volume (the amount of unused air remaining in the mouth, trachea and air tubes after each breath) has been estimated at about 0.184 m3 (184 l) for a 30 t (30 long tons; 33 short tons) specimen. Its tidal volume (the amount of air moved in or out during a single breath) has been calculated by Paladino to be 0.904 m3 (904 l) with an avian respiratory system, 0.225 m3 (225 l) if mammalian and 0.019 m3 (19 l) if reptilian.[50]

On this basis, its respiratory system would likely have been parabronchi, with multiple pulmonary air sacs like in avian lungs and a flow-through lung. Furthermore, an avian system would need a lung volume of only about 0.60 m3 (600 l) compared to a mammalian requirement of 2.95 m3 (2,950 l), which would exceed the available space. The overall thoracic volume of Apatosaurus has been estimated at 1.7 m3 (1,700 l) allowing for a 0.50 m3 (500 l), four-chambered heart and a 0.90 m3 (900 l) lung capacity. That would allow about 0.30 m3 (300 l) for the necessary tissue.[50] Evidence for the avian system in Apatosaurus and other sauropods is also in the pneumaticity of the vertebrae. Though this plays a role in reducing the weight of the animal, Wedel (2003) states that they also likely connected to air sacs as in birds.[55]

James Spotila et al. (1991) suggest that the large body size of Apatosaurus and other sauropods would have made them unable to maintain high metabolic rates as they would not be able to release enough heat.[56] They assumed that the animals had a reptilian respiratory system. Wedel found that an avian system would have allowed then to dump more heat.[55] Some scientists have argued that the heart would have had trouble sustaining sufficient blood pressure to oxygenate the brain.[43] Others argue that the near horizontal posture of the head and neck would have eliminated the problem of supplying blood to the brain, as it would not be elevated.[44]

Growth[edit]

Juvenile A. sp. mount, Sam Noble Oklahoma Museum of Natural History

A 1999 microscopic study of Apatosaurus bones concluded that the animals grew rapidly when young and reached near-adult sizes in about 10 years.[57] In 2008, a study on the growth rates for sauropods was published, authored by Thomas Lehman and Holly Woodward. They found that by using growth lines and length to mass, Apatosaurus would have attained a mass of 25 t (25 long tons; 28 short tons) in 15 years. This would imply sauropods had a growth rate of 5,000 kg (11,000 lb) per year. An alternative method, using limb length and body mass, found Apatosaurus to grow 520 kg (1,150 lb) per year until individuals reached an age of around 70.[58] These estimates have been suggested to be unreliable as the methods producing them are not sound as old growth lines would have been obliterated due to bone remodelling.[59] One of the first identified growth factors of Apatosaurus was the number of sacral vertebrae, which increased to five by maturity. This was first noted in 1903, and then again in 1936.[6]

Long-bone histology enables researchers to estimate the age that a specific individual reached. A study by Eva Griebeler et al. (2013) examined long bone histological data and concluded that the Apatosaurus sp. SMA 0014 weighed 20,206 kg (22.3 short tons), reached sexual maturity at 21 years and died at age 28. The same growth model indicated that Apatosaurus sp. BYU 601–17328 weighed 18,178 kg (20.0 short tons), reached sexual maturity at 19 years and died at age 31.[59]

Juveniles[edit]

A relatively large amount of juvenile material is known from Apatosaurus compared to most sauropods. Multiple specimens in the OMNH are from juveniles of an undetermined species of Apatosaurus; this material includes partial shoulder and pelvic girdles, some vertebrae, and bones of the limbs. The juvenile material is from at least two different age groups, and likely more than three individuals. The specimens exhibit distinguishing features of Apatosaurus, justifying their referral. The bones are proportionately slightly different from all adult sauropod specimens.[18][60]

Tail[edit]

An article that appeared in the November 1997 issue of Discover Magazine reported research into the mechanics of Apatosaurus tails by Nathan Myhrvold, a computer scientist from Microsoft. Myhrvold carried out a computer simulation of the tail, which in diplodocids like Apatosaurus 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.[61]

A pathology has also been identified on the tail of Apatosaurus, due to a growth defect. Two caudal vertebrae are seamlessly fused along the entire articulating surface of the bone, including the arches of the neural spines. This defect might have been caused due to the lack or inhibition of the substance that forms intervertebral disks or joints.[62]

Paleoecology[edit]

Map of the fossils of Dinosaur National Monument

The Morrison Formation is a sequence of shallow marine and alluvial sediments which, according to radiometric dating, ranges between 156.3 million years old (Ma) at its base,[63] to 146.8 million years old at the top,[64] which places it in the late Oxfordian, Kimmeridgian, and early Tithonian stages of the Late Jurassic period. This formation is interpreted as a semiarid environment with distinct wet and dry seasons. The Morrison Basin, where dinosaurs lived, stretched from New Mexico to Alberta and Saskatchewan, and was formed when the precursors to the Front Range of the Rocky Mountains started pushing up to the west. The deposits from their east-facing drainage basins were carried by streams and rivers and deposited in swampy lowlands, lakes, river channels and floodplains.[65] This formation is similar in age to the Lourinha Formation in Portugal and the Tendaguru Formation in Tanzania.[66]

Apatosaurus was the second most common sauropod in the Morrison Formation ecosystem, after Camarasaurus.[40] It may have been a more solitary animal than other Morrison Formation dinosaurs.[67] Supersaurus has a greater total length and thus is the greatest of all sauropods from the Morrison.[12] Apatosaurus fossils have been found only in the upper levels of the Morrison. Fossils of Apatosaurus ajax are known exclusively from the upper portion of the formation (upper Brushy Basin Member), about 152–151 million years ago. A. louisae fossils are rare, known only from one site in the upper Brushy Basin Member, dated to the late Kimmeridgian stage (about 151 million years ago). Additional Apatosaurus remains are known from even younger rocks, but they have not been identified as any particular species.[68]

Ischium of an Apatosaurus showing bite marks from a large theropod

The Morrison Formation records an environment and time dominated by gigantic sauropod dinosaurs.[40] Dinosaurs known from the Morrison include the theropods Ceratosaurus, Ornitholestes, and Torvosaurus, the sauropods Brontosaurus, Brachiosaurus, Camarasaurus, and Diplodocus, and the ornithischians Camptosaurus, Dryosaurus, and Stegosaurus.[69] Apatosaurus is commonly found at the same sites as Allosaurus, Camarasaurus, Diplodocus, and Stegosaurus.[67] Allosaurus accounted for 70 to 75% of theropod specimens and was at the top trophic level of the Morrison food web.[70] Many of the dinosaurs of the Morrison Formation are the same genera as those seen in Portuguese rocks of the Lourinha Formation (mainly Allosaurus, Ceratosaurus, and Torvosaurus), or have a close counterpart (Brachiosaurus and Lusotitan, Camptosaurus and Draconyx, Apatosaurus and Dinheirosaurus).[66] Other vertebrates that shared this paleoenvironment included ray-finned fishes, frogs, salamanders, turtles, sphenodonts, lizards, terrestrial and aquatic crocodylomorphans, and several species of pterosaur. Shells of bivalves and aquatic snails are also common. The flora of the period has been revealed by fossils of green algae, fungi, mosses, horsetails, cycads, ginkgoes, and several families of conifers. Vegetation varied from river-lining forests of tree ferns, and ferns (gallery forests), to fern savannas with occasional trees such as the Araucaria-like conifer Brachyphyllum.[71]

In popular culture[edit]

Outdated 1897 restoration by Charles R. Knight of A. excelsus submerged in water, and Diplodocus dragging its tail

The length of time taken for Rigg's 1903 reclassification of Brontosaurus as Apatosaurus to be brought to public notice, as well as Osborn's insistence that the Brontosaurus name be retained despite Rigg's paper, meant that the entangled Brontosaurus/Apatosaurus became one of the most famous dinosaurs. Apatosaurus have often been depicted in cinema, beginning with Winsor McCay's 1914 classic Gertie the Dinosaur, one of the first animated films.[72] McCay based his unidentified dinosaur on the apatosaurine skeleton in the American Museum of Natural History.[73]

As late as 1989, the U.S. Postal Service caused controversy when it issued four "dinosaur" stamps: Tyrannosaurus, Stegosaurus, Pteranodon and Brontosaurus. The use of the term Brontosaurus in place of Apatosaurus, as well as the fact that Pteranodon were technically pterosaurs and not dinosaurs, led to complaints of "fostering scientific illiteracy."[74] The Postal Service defended itself (in Postal Bulletin 21744) by saying, "Although now recognized by the scientific community as Apatosaurus, the name 'Brontosaurus' was used for the stamp because it is more familiar to the general population." Palaeontologist Stephen Jay Gould also supported this position in his essay "Bully for Brontosaurus", though he echoed Riggs's original argument that Brontosaurus is a synonym for Apatosaurus.[75]

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External links[edit]