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Apatosaurus
Temporal range: Late Jurassic (Kimmeridgian), 152–151 Ma
↓
Mounted A. louisae (specimen CM 3018), Carnegie Museum of Natural History
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Dinosauria
Clade: Saurischia
Clade: †Sauropodomorpha
Clade: †Sauropoda
Superfamily: †Diplodocoidea
Family: †Diplodocidae
Subfamily: †Apatosaurinae
Genus: †Apatosaurus
Marsh, 1877
Type species
†Apatosaurus ajax
Marsh, 1877
Other species
  • †A. louisae
    Holland, 1916
Synonyms

Apatosaurus (/əˌpætəˈsɔːrəs/;[3][4] meaning "deceptive lizard") is a genus of herbivorous sauropod dinosaur that lived in North America during the Late Jurassic period. Othniel Charles Marsh described and named the first-known species, Apatosaurus ajax, in 1877, and a second species, Apatosaurus louisae, was discovered and named by William H. Holland in 1916. Apatosaurus lived about 152 to 151 million years ago (mya), during the late Kimmeridgian to early Tithonian age, and are now known from fossils in the Morrison Formation of modern-day Colorado, Oklahoma, New Mexico, Wyoming, and Utah in the United States. Apatosaurus had an average length of 21–23 m (69–75 ft), and an average mass of 16.4–22.4 t (16.1–22.0 long tons; 18.1–24.7 short tons). A few specimens indicate a maximum length of 11–30% greater than average and a mass of approximately 33 t (32 long tons; 36 short tons).

The cervical vertebrae of Apatosaurus are less elongated and more heavily constructed than those of Diplodocus, a diplodocid like Apatosaurus, and the bones of the leg are much stockier despite being longer, implying that Apatosaurus was a more robust animal. The tail was held above the ground during normal locomotion. Apatosaurus had a single claw on each forelimb and three on each hindlimb. The Apatosaurus skull, long thought to be similar to Camarasaurus, is much more similar to that of Diplodocus. Apatosaurus was a generalized browser that likely held its head elevated. To lighten its vertebrae, Apatosaurus had air sacs that made the bones internally full of holes. Like that of other diplodocids, its tail may have been used as a whip to create loud noises, or, as more recently suggested, as a sensory organ.

The skull of Apatosaurus was confused with that of Camarasaurus and Brachiosaurus until 1909, when the holotype of A. louisae was found, and a complete skull just a few meters away from the front of the neck. Henry Fairfield Osborn disagreed with this association, and went on to mount a skeleton of Apatosaurus with a Camarasaurus skull cast. Apatosaurus skeletons were mounted with speculative skull casts until 1970, when McIntosh showed that more robust skulls assigned to Diplodocus were more likely from Apatosaurus.

Apatosaurus is a genus in the family Diplodocidae. It is one of the more basal genera, with only Amphicoelias and possibly a new, unnamed genus more primitive. Although the subfamily Apatosaurinae was named in 1929, the group was not used validly until an extensive 2015 study. Only Brontosaurus is also in the subfamily, with the other genera being considered synonyms or reclassified as diplodocines. Brontosaurus has long been considered a junior synonym of Apatosaurus; its type species was reclassified as A. excelsus in 1903. A 2015 study concluded that Brontosaurus is a valid genus of sauropod distinct from Apatosaurus, but not all paleontologists agree with this division. As it existed in North America during the late Jurassic, Apatosaurus would have lived alongside dinosaurs such as Allosaurus, Camarasaurus, Diplodocus, and Stegosaurus.

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 forelimbs were slightly shorter than its hindlimbs. Most size estimates are based on specimen CM 3018, the type specimen of A. louisae, reaching 21–23 m (69–75 ft) in length and 16.4–22.4 t (16.1–22.0 long tons; 18.1–24.7 short tons) in body mass.[5][6][7][8] A 2015 study that estimated the mass of volumetric models of Dreadnoughtus, Apatosaurus, and Giraffatitan estimates CM 3018 at 21.8–38.2 t (21.5–37.6 long tons; 24.0–42.1 short tons), similar in mass to Dreadnoughtus.[9] Some specimens of A. ajax (such as OMNH 1670) represent individuals 11–30% longer, suggesting masses twice that of CM 3018 or 32.7–72.6 t (32.2–71.5 long tons; 36.0–80.0 short tons), potentially rivaling the largest titanosaurs.[10] However, the upper size estimate of OMNH 1670 is likely an exaggeration, with the size estimates revised in 2020 at 30 m (98 ft) in length and 33 t (36 short tons) in body mass based on volumetric analysis.[11]

A. ajax skull, specimen CMC VP 7180

The skull is small in relation to the size of the animal. The jaws are lined with spatulate (chisel-like) teeth suited to an herbivorous diet.[12] The snout of Apatosaurus and similar diplodocoids is squared, with only Nigersaurus having a squarer skull.[13] The braincase of Apatosaurus is well preserved in specimen BYU 17096, which also preserved much of the skeleton. A phylogenetic analysis found that the braincase had a morphology similar to those of other diplodocoids.[14] 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; instead, they display a sugary texture and little wear.[13]

Cervical vertebra of A. ajax (holotype, YPM 1860) in side and anterior view

Like those of other sauropods, the neck vertebrae are deeply bifurcated; they carried neural spines with a large trough in the middle, resulting in a wide, deep neck.[12] The vertebral formula for the holotype of A. louisae is 15 cervicals, 10 dorsals, 5 sacrals, and 82 caudals. The caudal vertebra number may vary, even within species.[15] The cervical vertebrae of Apatosaurus and Brontosaurus are stouter and more robust than those of other diplodocids and were found to be most similar to Camarasaurus by Charles Whitney Gilmore.[15][16] In addition, they support cervical ribs that extend farther towards the ground than in diplodocines, and have vertebrae and ribs that are narrower towards the top of the neck, making the neck nearly triangular in cross-section.[16] In Apatosaurus louisae, the atlas-axis complex of the first cervicals is nearly fused. The dorsal ribs are not fused or tightly attached to their vertebrae and are instead loosely articulated.[15] Apatosaurus has ten dorsal ribs on either side of the body.[17] The large neck was filled with an extensive system of weight-saving air sacs. Apatosaurus, like its close relative Supersaurus, has tall neural spines, which make up more than half the height of the individual bones of its vertebrae. The shape of the tail is unusual for a diplodocid; it is comparatively slender because of the rapidly decreasing height of the vertebral spines with increasing distance from the hips. Apatosaurus also had very long ribs compared to most other diplodocids, giving it an unusually deep chest.[18] As in other diplodocids, the tail transformed into a whip-like structure towards the end.[15]

Artistic interpretation of A. louisae

The limb bones are also very robust.[18] Within Apatosaurinae, the scapula of Apatosaurus louisae is intermediate in morphology between those of A. ajax and Brontosaurus excelsus. The arm bones are stout, so the humerus of Apatosaurus resembles that of Camarasaurus, as well as Brontosaurus. However, the humeri of Brontosaurus and A. ajax are more similar to each other than they are to A. louisae. In 1936, Charles Gilmore noted that previous reconstructions of Apatosaurus forelimbs erroneously proposed that the radius and ulna could cross; in life they would have remained parallel.[15] Apatosaurus had a single large claw on each forelimb, a feature shared by all sauropods more derived than Shunosaurus.[15][19] The first three toes had claws on each hindlimb. The phalangeal formula is 2-1-1-1-1, meaning the innermost finger (phalanx) on the forelimb has two bones and the next has one.[20] 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 Apatosaurus are very stout and represent some of the most robust femora of any member of Sauropoda. The tibia and fibula bones are different from the slender bones of Diplodocus but are nearly indistinguishable from those of Camarasaurus. The fibula is longer and slenderer than the tibia. The foot of Apatosaurus has three claws on the innermost digits; the digit formula is 3-4-5-3-2. The first metatarsal is the stoutest, a feature shared among diplodocids.[15][21]

Discovery and species

[edit]

Initial discovery

[edit]
Arthur Lakes' painting of YPM crews excavating fossils of Apatosaurus ajax at Quarry 10 in Morrison.

The first Apatosaurus fossils were discovered by Arthur Lakes, a local miner, and his friend Henry C. Beckwith in the spring of 1877 in Morrison, a town in the eastern foothills of the Rocky Mountains in Jefferson County, Colorado. Arthur Lakes wrote to Othniel Charles Marsh, Professor of Paleontology at Yale University, and Edward Drinker Cope, a paleontologist based in Philadelphia, about the discovery until eventually collecting several fossils and sending them to both paleontologists. Marsh named Atlantosaurus montanus based on some of the fossils sent and hired Lakes to collect the rest of the material at Morrison and send it to Yale, while Cope attempted to hire Lakes as well but was rejected.[22] One of the best specimens collected by Lakes in 1877 was a well preserved partial postcranial skeleton, including many vertebrae, and a partial braincase (YPM VP 1860), which was sent to Marsh and named Apatosaurus ajax in November 1877.[23][22] The composite term Apatosaurus comes from the Greek words apatē (ἀπάτη)/apatēlos (ἀπατηλός) meaning "deception"/"deceptive", and sauros (σαῦρος) meaning "lizard";[24] thus, "deceptive lizard". Marsh gave it this name based on the chevron bones, which are dissimilar to those of other dinosaurs; instead, the chevron bones of Apatosaurus showed similarities with those of mosasaurs,[25][26] most likely that of the representative species Mosasaurus. By the end of excavations at Lakes' quarry in Morrison, several partial specimens of Apatosaurus had been collected, but only the type specimen of A. ajax can be confidently referred to the species.[27][23]

During excavation and transportation, the bones of the holotype skeleton were mixed with those of another Apatosaurine individual originally described as Atlantosaurus immanis; as a consequence, some elements cannot be ascribed to either specimen with confidence.[23] Marsh distinguished the new genus Apatosaurus from Atlantosaurus on the basis of the number of sacral vertebrae, with Apatosaurus possessing three and Atlantosaurus four. Recent research shows that traits usually used to distinguish taxa at this time were actually widespread across several taxa, causing many of the taxa named to be invalid, like Atlantosaurus.[23] Two years later, Marsh announced the discovery of a larger and more complete specimen (YPM VP 1980) from Como Bluff, Wyoming, he gave this specimen the name Brontosaurus excelsus.[28] Also at Como Bluff, the Hubbell brothers working for Edward Drinker Cope collected a tibia, fibula, scapula, and several caudal vertebrae along with other fragments belonging to Apatosaurus in 1877–78 at Cope's Quarry 5 at the site.[29] Later in 1884, Othniel Marsh named Diplodocus lacustris based on a chimeric partial dentary, snout, and several teeth collected by Lakes in 1877 at Morrison.[23][30] In 2013, it was suggested that the dentary of D. lacustris and its teeth were actually from Apatosaurus ajax based on its proximity to the type braincase of A. ajax.[30] All specimens currently considered Apatosaurus were from the Morrison Formation, the location of the excavations of Marsh and Cope.[31]

A. ajax sacrum, illustrated in 1879

Second Dinosaur Rush and skull issue

[edit]

After the end of the Bone Wars, many major institutions in the eastern United States were inspired by the depictions and finds by Marsh and Cope to assemble their own dinosaur fossil collections.[32] The competition to mount the first sauropod skeleton specifically was the most intense, with the American Museum of Natural History, Carnegie Museum of Natural History, and Field Museum of Natural History all sending expeditions to the west to find the most complete sauropod specimen,[32] bring it back to the home institution, and mount it in their fossil halls.[32] The American Museum of Natural History was the first to launch an expedition,[32] finding a well preserved skeleton (AMNH 460), which is occasionally assigned to Apatosaurus, is considered nearly complete; only the head, feet, and sections of the tail are missing, and it was the first sauropod skeleton mounted.[33] The specimen was found north of Medicine Bow, Wyoming, in 1898 by Walter Granger, and took the entire summer to extract.[34] To complete the mount, sauropod feet that were discovered at the same quarry and a tail fashioned to appear as Marsh believed it should – but which had too few vertebrae – were added. In addition, a sculpted model of what the museum thought the skull of this massive creature might look like was made. This was not a delicate skull like that of Diplodocus – which was later found to be more accurate – but was based on "the biggest, thickest, strongest skull bones, lower jaws and tooth crowns from three different quarries".[15][17][33][35] 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. Osborn said in a publication that the skull was "largely conjectural and based on that of Morosaurus" (now Camarasaurus).[36]

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

In 1903, Elmer Riggs published a study that described a well-preserved skeleton of a diplodocid from the Grand River Valley near Fruita, Colorado, Field Museum of Natural History specimen P25112. Riggs thought that the deposits were similar in age to those of the Como Bluff in Wyoming from which Marsh had described Brontosaurus. Most of the skeleton was found, and after comparison with both Brontosaurus and Apatosaurus ajax, Riggs realized that the holotype of A. ajax was immature, and thus the features distinguishing the genera were not valid. Since Apatosaurus was the earlier name, Brontosaurus should be considered a junior synonym of Apatosaurus. Because of this, Riggs recombined Brontosaurus excelsus as Apatosaurus excelsus. Based on comparisons with other species proposed to belong to Apatosaurus, Riggs also determined that the Field Columbian Museum specimen was likely most similar to A. excelsus.[17]

Despite Riggs' publication, Henry Fairfield Osborn, who was a strong opponent of Marsh and his taxa, labeled the Apatosaurus mount of the American Museum of Natural History Brontosaurus.[36][37] Because of this decision the name Brontosaurus was commonly used outside of scientific literature for what Riggs considered Apatosaurus, and the museum's popularity meant that Brontosaurus became one of the best known dinosaurs, even though it was invalid throughout nearly all of the 20th and early 21st centuries.[38]

Apatosaurine mount (FMNH P25112) in the Field Museum of Natural History in the 1950s, with its original, inaccurately reconstructed skull

It was not until 1909 that an Apatosaurus skull was found during the first expedition, led by Earl Douglass, to what would become known as the Carnegie Quarry at Dinosaur National Monument. The skull was found a short distance from a skeleton (specimen CM 3018) identified as the new species Apatosaurus louisae, named after Louise Carnegie, wife of Andrew Carnegie, who funded field research to find complete dinosaur skeletons in the American West. The skull was designated CM 11162; it was very similar to the skull of Diplodocus.[37] Another smaller skeleton of A. louisae was found nearby CM 11162 and CM 3018.[39] The skull 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 Holland was waiting until an articulated skull and neck were found to confirm the association of the skull and skeleton.[36] After Holland's death in 1934, museum staff placed a cast of a Camarasaurus skull on the mount.[37]

While most other museums were using cast or sculpted Camarasaurus skulls on Apatosaurus mounts, the Yale Peabody Museum decided to sculpt a skull based on the lower jaw of a Camarasaurus, with the cranium based on Marsh's 1891 illustration of the skull. The skull also included forward-pointing nasals – something unusual for any dinosaur – and fenestrae differing from both the drawing and other skulls.[36]

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

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.[35] 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.[37] In 1998, it was suggested that the Felch Quarry skull that Marsh had included in his 1896 skeletal restoration instead belonged to Brachiosaurus.[40] This was supported in 2020 with a redescription of the brachiosaurid material found at the Felch Quarry.[41]

Recent discoveries and reassessment

[edit]

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, but shared many features of the cervical vertebrae with A. ajax.[42] Another well-preserved skull is Brigham Young University specimen 17096, a well-preserved skull and skeleton, with a preserved braincase. The specimen was found in Cactus Park Quarry in western Colorado.[14] In 2013, Matthew Mossbrucker and several other authors published an abstract that described a premaxilla and maxilla from Lakes' original quarry in Morrison and referred the material to Apatosaurus ajax.[30]

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

Almost all modern paleontologists agreed with Riggs that the two dinosaurs 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 was considered a junior synonym and was therefore long discarded from formal use.[43][44][45][46] Despite this, at least one paleontologist – Robert T. Bakker – argued in the 1990s that A. ajax and A. excelsus were in fact sufficiently distinct for the latter to merit a separate genus.[47]

In 2015, Emanuel Tschopp, Octávio Mateus, and Roger Benson released a paper on diplodocoid systematics, and proposed that genera could be diagnosed by thirteen differing characters, and species separated based on six. The minimum number for generic separation was chosen based on the fact that A. ajax and A. louisae differ in twelve characters, and Diplodocus carnegiei and D. hallorum differ in eleven characters. Thus, thirteen characters were chosen to validate the separation of genera. The six differing features for specific separation were chosen by counting the number of differing features in separate specimens generally agreed to represent one species, with only one differing character in D. carnegiei and A. louisae, but five differing features in B. excelsus. Therefore, Tschopp et al. 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 dinosaur individuals. Among the many notable differences are the wider – and presumably stronger – neck of Apatosaurus species compared to B. excelsus. Other species previously assigned to Apatosaurus, such as Elosaurus parvus and Eobrontosaurus yahnahpin were also reclassified as Brontosaurus. Some features proposed to separate Brontosaurus from Apatosaurus include: posterior dorsal vertebrae with the centrum longer than wide; the scapula rear to the acromial edge and the distal blade being excavated; the acromial edge of the distal scapular blade bearing a rounded expansion; and the ratio of the proximodistal length to transverse breadth of the astragalus 0.55 or greater.[23] Sauropod expert Michael D'Emic pointed out that the criteria chosen were to an extent arbitrary and that they would require abandoning the name Brontosaurus again if newer analyzes obtained different results.[48] Mammal paleontologist Donald Prothero criticized the mass media reaction to this study as superficial and premature, concluding that he would keep "Brontosaurus" in quotes and not treat the name as a valid genus.[49]

Valid species

[edit]
Apatosaurine specimen AMNH 460 at the AMNH as re-mounted in 1995
Apatosaurine mount (FMNH P25112) in the FMNH
Specimen NSMT-PV 20375, National Museum of Nature and Science, which may be A. ajax or a new species

Many species of Apatosaurus 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 published a study that analyzed the species and specimen relationships of Apatosaurus. They found that A. louisae was the most basal species, followed by FMNH P25112, and then a polytomy of A. ajax, A. parvus, and A. excelsus.[21] Their analysis was revised and expanded with many additional diplodocid specimens in 2015, which resolved the relationships of Apatosaurus slightly differently, and also supported separating Brontosaurus from Apatosaurus.[23]

  • Apatosaurus ajax was named by Marsh in 1877 after Ajax, a hero from Greek mythology.[50] Marsh designated the incomplete, juvenile skeleton YPM 1860 as its holotype. The species is less studied than Brontosaurus and A. louisae, especially because of the incomplete nature of the holotype. 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 date from the late Kimmeridgian to the early Tithonian ages.[21] In 2015, only the A. ajax holotype YPM 1860 assigned to the species, with AMNH 460 found either to be within Brontosaurus, or potentially its own taxon. However, YPM 1861 and NSMT-PV 20375 only differed in a few characteristics, and cannot be distinguished specifically or generically from A. ajax. YPM 1861 is the holotype of "Atlantosaurus" immanis, which means it might be a junior synonym of A. ajax.[23]
  • Apatosaurus louisae was named by Holland in 1916, being first known from a partial skeleton that was found in Utah.[51] 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 consist of a skull and a nearly complete skeleton, respectively. Apatosaurus louisae specimens all come from the late Kimmeridgian of Dinosaur National Monument.[21] In 2015, Tschopp et al. found the type specimen of Apatosaurus laticollis to nest closely with CM 3018, meaning the former is likely a junior synonym of A. louisae.[23]

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.[23]

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.[15] Marsh later mentioned it was only provisionally assigned to Apatosaurus when he reassigned it to his new genus Morosaurus in 1878.[52] Since Morosaurus has been considered a synonym of Camarasaurus, C. grandis is the oldest-named species of the latter genus.[53]
  • 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.[23]
  • 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. Many other, more mature specimens were assigned to it following the 2015 study.[23]
  • Apatosaurus minimus was originally described as a specimen of Brontosaurus sp. in 1904 by Osborn. In 1917, Henry Mook named it as its own species, A. minimus, for a pair of ilia and their sacrum.[15][54][55] In 2012, Mike P. Taylor and Matt J. Wedel published a short abstract describing the material of A. minimus, finding it 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.[55] The study of Tschopp et al. did find that a camarasaurid position for the taxon was supported, but noted that the position of the taxon was found to be highly variable and there was no clearly more likely position.[23]
  • Apatosaurus alenquerensis was named in 1957 by Albert-Félix de Lapparent and Georges Zbyweski. It was based on post cranial material from Portugal. In 1990, this material was reassigned to Camarasaurus, but in 1998 it was given its own genus, Lourinhasaurus.[21] This was further supported by the findings of Tschopp et al. in 2015, where Lourinhasaurus was found to be sister to Camarasaurus and other camarasaurids.[23]
  • Apatosaurus yahnahpin was named by James Filla and Patrick Redman in 1994. Bakker made A. yahnahpin the type species of a new genus, Eobrontosaurus in 1998,[47] and Tschopp reclassified it as Brontosaurus yahnahpin in 2015.[23]

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 Brontosaurus.[18][56][57] Othniel Charles Marsh described Apatosaurus as allied to Atlantosaurus within the now-defunct group Atlantosauridae.[17][25] In 1878, Marsh raised his family to the rank of suborder, including Apatosaurus, Atlantosaurus, Morosaurus (=Camarasaurus) and Diplodocus. He classified this group within Sauropoda, a group he erected in the same study. In 1903, Elmer S. Riggs said the name Sauropoda would be a junior synonym of earlier names; he grouped Apatosaurus within Opisthocoelia.[17] Sauropoda is still used as the group name.[21] In 2011, John Whitlock published a study that placed Apatosaurus a more basal diplodocid, sometimes less basal than Supersaurus.[58][59]

Cladogram of the Diplodocidae after Tschopp, Mateus, and Benson (2015).[23]

Diplodocidae

Paleobiology

[edit]
Tracks of a juvenile

It was believed throughout the 19th and early 20th centuries that sauropods like Apatosaurus were too massive to support their own weight on dry land. It was theorized that they lived partly submerged in water, perhaps in swamps. More recent findings do not support this; sauropods are now thought to have been fully terrestrial animals.[60] A study of diplodocid snouts showed that the square snout, large proportion of pits, and fine, subparallel scratches of the teeth of Apatosaurus suggests it was a ground-height, nonselective browser.[13] It may have eaten ferns, cycadeoids, seed ferns, horsetails, and algae.[61] Stevens and Parish (2005) speculate that these sauropods fed from riverbanks on submerged water plants.[62]

A 2015 study of the necks of Apatosaurus and Brontosaurus found many differences between them and other diplodocids, and that these variations may have shown that the necks of Apatosaurus and Brontosaurus were used for intraspecific combat.[16] Various uses for the single claw on the forelimb of sauropods have been proposed. One suggestion is that they were used for defense, but their shape and size make this unlikely. It was also possible they were for feeding, but the most probable use for the claw was grasping objects such as tree trunks when rearing.[19]

Trackways of sauropods like Apatosaurus show that they may have had a range of around 25–40 km (16–25 miles) per day, and that they could potentially have reached a top speed of 20–30 km (12–19 miles) per hour.[12] The slow locomotion of sauropods may be due to their minimal muscling, or to recoil after strides.[63] A trackway of a juvenile has led some to believe that they were capable of bipedalism, though this is disputed.[64][65]

Neck posture

[edit]
Further information: Sauropod neck posture
Skeletal diagram of A. louisae, showing the neck held high

Diplodocids like Apatosaurus are often portrayed with their necks held high up in the air, allowing them to browse on tall trees. Some studies state diplodocid necks were less flexible than previously believed, because the structure of the neck vertebrae would not have allowed the neck to bend far upward, and that sauropods like Apatosaurus were adapted to low browsing or ground feeding.[61][62][66]

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; they argue 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 pointing downward in a resting posture.[67][68] Kent Stevens and Michael Parrish (1999 and 2005) state Apatosaurus had a great feeding range; its neck could bend into a U-shape laterally.[61] The neck's range of movement would have also allowed the head to feed at the level of the feet.[62]

Matthew Cobley et al. (2013) dispute this, finding that large muscles and cartilage would have limited movement of the neck. They state 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.[69][70] The conclusions of Cobley et al. are disputed by Taylor, who analyzed 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.[67]

Physiology

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

Given the large body mass and long neck of sauropods like Apatosaurus, physiologists have encountered problems determining how these animals breathed. Beginning with the assumption that, like crocodilians, Apatosaurus 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 0.184 m3 (184 L) for a 30 t (30 long tons; 33 short tons) specimen. Paladino calculates its tidal volume (the amount of air moved in or out during a single breath) at 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.[71]

On this basis, its respiratory system would likely have been parabronchi, with multiple pulmonary air sacs as in avian lungs, and a flow-through lung. An avian respiratory system would need a lung volume of about 0.60 m3 (600 L) compared with a mammalian requirement of 2.95 m3 (2,950 L), which would exceed the space available. 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.[71] Evidence for the avian system in Apatosaurus and other sauropods is also present in the pneumaticity of the vertebrae. Though this plays a role in reducing the weight of the animal, Wedel (2003) states they are also likely connected to air sacs, as in birds.[72]

James Spotila et al. (1991) concludes that the large body size of sauropods would have made them unable to maintain high metabolic rates because they would not have been able to release enough heat.[73] They assumed sauropods had a reptilian respiratory system. Wedel says that an avian system would have allowed it to dump more heat.[72] Some scientists state that the heart would have had trouble sustaining sufficient blood pressure to oxygenate the brain.[60] Others suggest that the near-horizontal posture of the head and neck would have eliminated the problem of supplying blood to the brain because it would not have been elevated.[61]

James Farlow (1987) calculates 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, though he cautions that the regression equation being used is based on living mammals which are much smaller and physiologically different.[74] Assuming Apatosaurus had an avian respiratory system and a reptilian resting-metabolism, Frank Paladino et al. (1997) estimate the animal would have needed to consume only about 262 litres (58 imp gal; 69 US gal) of water per day.[71]

Growth

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

A 1999 microscopic study of Apatosaurus and Brontosaurus bones concluded the animals grew rapidly when young and reached near-adult sizes in about 10 years.[75] In 2008, a study on the growth rates of sauropods was published by Thomas Lehman and Holly Woodward. They said that by using growth lines and length-to-mass ratios, Apatosaurus would have grown to 25 t (25 long tons; 28 short tons) in 15 years, with growth peaking at 5,000 kg (11,000 lb) in a single year. An alternative method, using limb length and body mass, found Apatosaurus grew 520 kg (1,150 lb) per year, and reached its full mass before it was about 70 years old.[76] These estimates have been called unreliable because the calculation methods are not sound; old growth lines would have been obliterated by bone remodeling.[77] One of the first identified growth factors of Apatosaurus was the number of sacral vertebrae, which increased to five by the time of the creature's maturity. This was first noted in 1903 and again in 1936.[15]

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 the Apatosaurus sp. SMA 0014 weighed 20,206 kg (22.3 short tons), reached sexual maturity at 21 years, and died aged 28. The same growth model indicated Apatosaurus sp. BYU 601–17328 weighed 18,178 kg (20.0 short tons), reached sexual maturity at 19 years, and died aged 31.[77]

Juveniles

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Compared with most sauropods, a relatively large amount of juvenile material is known from Apatosaurus. 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 limb bones. OMNH juvenile material is from at least two different age groups and based on overlapping bones likely comes from more than three individuals. The specimens exhibit features that distinguish Apatosaurus from its relatives, and thus likely belong to the genus.[21][78] Juvenile sauropods tend to have proportionally shorter necks and tails, and a more pronounced forelimb-hindlimb disparity than found in adult sauropods.[79]

Tail

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Carnegie A. louisae mount (upper right), showing the long, tapering tail

The estimated tail length of Apatosaurus is approximately 54% of the total body length, with the tail sometimes hypothesized to be capable of functioning like a very long, tapering bullwhip.[80] An article published in 1997 reported research of the mechanics of Apatosaurus tails through computer simulation by Nathan Myhrvold and paleontologist Philip J. Currie. This computer modeling suggested diplodocids were capable of producing a whiplike cracking sound of over 200 decibels, comparable to the volume of a cannon being fired.[81]

A pathology has been identified on the tail of Apatosaurus, caused by 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 by the lack or inhibition of the substance that forms intervertebral disks or joints.[82] It has been proposed that the whips could have been used in combat and defense, but the tails of diplodocids were quite light and narrow compared to Shunosaurus and mamenchisaurids, and thus to injure another animal with the tail would severely injure the tail itself.[81] More recently, Baron (2020) considers the use of the tail as a bullwhip unlikely because of the potentially catastrophic muscle and skeletal damage such speeds could cause on the large and heavy tail. Instead, he proposes that the tails might have been used as a tactile organ to keep in touch with the individuals behind and on the sides in a group while migrating, which could have augmented cohesion and allowed communication among individuals while limiting more energetically demanding activities like stopping to search for dispersed individuals, turning to visually check on individuals behind, or communicating vocally.[80]

Paleoecology

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Allosaurus and A. sp., Sam Noble Oklahoma Museum of Natural History

The Morrison Formation is a sequence of shallow marine and alluvial sediments which, according to radiometric dating, dates from between 156.3 mya at its base,[83] and 146.8 mya at the top,[84] placing it in the late Oxfordian, Kimmeridgian, and early Tithonian stages of the Late Jurassic period. This formation is interpreted as originating in a locally semiarid environment with distinct wet and dry seasons. The Morrison Basin, where dinosaurs lived, stretched from New Mexico to Alberta and Saskatchewan; it 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.[85] This formation is similar in age to the Lourinhã Formation in Portugal and the Tendaguru Formation in Tanzania.[31]

Apatosaurus was the second most common sauropod in the Morrison Formation ecosystem, after Camarasaurus.[53][86] Apatosaurus may have been more solitary than other Morrison Formation dinosaurs.[87] Fossils of the genus have only been found in the upper levels of the formation. Those of Apatosaurus ajax are known exclusively from the upper Brushy Basin Member, about 152–151 mya. A. louisae fossils are rare, known only from one site in the upper Brushy Basin Member; they date to the late Kimmeridgian stage, about 151 mya. Additional Apatosaurus remains are known from similarly aged or slightly younger rocks, but they have not been identified as any particular species,[88] and thus may instead belong to Brontosaurus.[23]

Ischium of an Apatosaurus showing bite marks from a large theropod

The Morrison Formation records a time when the local environment was dominated by gigantic sauropod dinosaurs.[53] Dinosaurs known from the Morrison Formation include the theropods Allosaurus, Ceratosaurus, Ornitholestes, and Torvosaurus; the sauropods Brontosaurus, Brachiosaurus, Camarasaurus, and Diplodocus; and the ornithischians Camptosaurus, Dryosaurus, and Stegosaurus.[89] Apatosaurus is commonly found at the same sites as Allosaurus, Camarasaurus, Diplodocus, and Stegosaurus.[87] Allosaurus accounted for 70–75% of theropod specimens and was at the top trophic level of the Morrison food web.[90] Many of the dinosaurs of the Morrison Formation are of the same genera as those seen in Portuguese rocks of the Lourinhã Formation – mainly Allosaurus, Ceratosaurus, and Torvosaurus – or have a close counterpart – Brachiosaurus and Lusotitan, Camptosaurus and Draconyx, and Apatosaurus and Dinheirosaurus.[31] Other vertebrates that are known to have shared this paleo-environment include ray-finned fishes, frogs, salamanders, turtles, sphenodonts, lizards, terrestrial and aquatic crocodylomorphs, and several species of pterosaur. Shells of bivalves and aquatic snails are also common. The flora of the period has been evidenced in fossils of green algae, fungi, mosses, horsetails, cycads, ginkgoes, and several families of conifers. Vegetation varied from river-lining forests of tree ferns with fern understory (gallery forests), to fern savannas with occasional trees such as the Araucaria-like conifer Brachyphyllum.[91]

References

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Apatosaurus

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Apatosaurus (/əˌpætəˈsɔːrəs/, meaning "deceptive ") is a genus of large herbivorous sauropod belonging to the family that lived in western during the epoch, approximately 152 to 151 million years ago. Characterized by its massive size, long neck, and whip-like tail, Apatosaurus was a quadrupedal giant adapted for browsing vegetation in floodplain and woodland environments of the . The encompasses two recognized : A. ajax (the ) and A. louisae. Apatosaurus individuals typically measured 21 to 24 meters (69 to 79 feet) in length, stood about 4.5 to 5.5 meters (15 to 18 feet) tall at the shoulder, and weighed between 18 and 30 metric tons, making them among the largest land animals of their time. Their diet consisted of , with peg-like teeth suited for stripping foliage, and they likely grew to full size in about 10 years while living in herds for protection and foraging efficiency. Named in 1877 by paleontologist based on fossils from , Apatosaurus became central to the "Bone Wars" rivalry between Marsh and , leading to rapid discoveries but also taxonomic confusion. Notably, the genus was historically conflated with ("thunder lizard"), which Marsh named in 1879 for similar fossils; Brontosaurus was long regarded as a of Apatosaurus but was reinstated as a distinct genus in 2015 following a comprehensive phylogenetic analysis revealing sufficient morphological differences. Apatosaurus louisae, discovered in 1909 at what is now , represents one of the most complete specimens, weighing over 30 tons and named in honor of Louise Carnegie.

Description

Physical features

Apatosaurus exhibited a specialized morphology typical of diplodocid sauropods, featuring narrow external nares positioned far posteriorly on the skull roof and a U-shaped . The consisted of peg-like, spatulate teeth confined to the anterior portion of both jaws, lacking replacement teeth in the posterior regions and suited for cropping low-lying rather than grinding or piercing. This arrangement, with teeth forming a tight cropping when the jaws closed, facilitated efficient shearing of material. The cervical region comprised 15 elongated vertebrae, each with a high neural arch and prominent pneumatic foramina on the and neural arches, providing evidence for an extensive system of that lightened the skeletal structure and supported respiratory efficiency. These vertebrae displayed complex laminae and fossae, with bifurcated neural spines in posterior cervicals, contributing to the flexibility and length of the while maintaining structural integrity under the weight of the elongated structure. Limb bones in Apatosaurus were notably robust, reflecting adaptations for bearing immense body mass in a terrestrial environment. The femur was longer than the humerus, with both exhibiting expanded proximal and distal ends that anchored powerful musculature, enabling a columnar, pillar-like posture for the forelimbs and hindlimbs alike; this configuration minimized bending stresses during weight support. The was supported by approximately 80 caudal vertebrae, transitioning from robust, boxy anterior caudals with tall neural spines to progressively slender, elongated posterior ones that tapered to a fine point, forming a whip-like structure. Anterior chevrons were robust and box-like, enclosing the caudal neurovascular canal to form a protective sheath, while distal chevrons became slender rods, enhancing tail flexibility. Preserved skin impressions from Apatosaurus specimens reveal a covering of small, polygonal, non-overlapping scales arranged in a linear or tubercular pattern across the body, particularly on the ventral and lateral surfaces, indicative of a scaly without evidence of extensive padding or filaments.

Size and mass

Adult specimens of Apatosaurus typically measured 21–23 meters in total , with estimates derived from the skeletons YPM 1861 (A. ajax) and CM 3018 (A. louisae). The shoulder height for these adults was approximately 4–5 meters, based on the proportions of the preserved limb elements in mounted reconstructions. Body mass estimates for A. louisae range from 20–25 metric tons, calculated using volumetric models of the mounted CM 3018 skeleton at the . Earlier allometric scaling methods applied to the same specimen yielded a mass of about 22.4 metric tons. Ontogenetic variation is evident in the fossil record, with juvenile Apatosaurus specimens preserving lengths under 10 meters; for example, an early juvenile diplodocid likely referable to Apatosaurus measured less than 2 meters in total body length. Among valid species, A. ajax (based on YPM 1861) was slightly smaller than A. louisae (CM 3018), with the former's vertebral column suggesting a length closer to 21 meters compared to the 21.8 meters measured for the latter's articulated .

Discovery history

Initial discovery

The initial discovery of Apatosaurus took place in the summer of 1877, when Arthur Lakes, a schoolteacher and amateur paleontologist from , unearthed a partial skeleton at Quarry 10 near . This specimen, cataloged as YPM 1860 and serving as the of A. ajax, included several vertebrae, limb elements such as a , , and , and other postcranial bones from a juvenile individual. Lakes promptly shipped the fossils to at , recognizing their significance amid the intensifying rivalry known as the . In December 1877, formally named the Apatosaurus ajax, deriving the genus from Greek words meaning "deceptive lizard" due to the unusual structure of its vertebrae, and the species in honor of the mythological hero Ajax. He interpreted the animal as a massive, herbivorous with a long neck and tail, placing it within the newly recognized group , characterized by pillar-like limbs and columnar bodies adapted for a terrestrial . A more detailed description followed in 1879, highlighting the diagnostic features of the caudal vertebrae and , which distinguished it from other giants. The fossils originated from the Brushy Basin Member of the , a (Kimmeridgian to Tithonian stages, approximately 155–145 million years ago) deposit renowned for its rich assemblage of sauropod remains across the . This discovery marked one of the earliest well-documented sauropod finds, contributing to the rapid expansion of knowledge about these enormous dinosaurs during the late .

Bone Wars and naming

The , a protracted and acrimonious rivalry between paleontologists of Yale University's Peabody Museum and of the Academy of Natural Sciences in , dominated American vertebrate from 1877 through the 1890s. This feud, fueled by personal animosity and professional ambition, accelerated the unearthing of fossils across , particularly sauropods from the , as both men raced to claim scientific priority through rapid discoveries and publications. The competition prompted large-scale, industrial-style expeditions, with teams of hired laborers using picks, shovels, and even explosives to extract specimens, transforming isolated bone outcrops into contested "bone fields." Como Bluff, , emerged as a focal point of this "Great Dinosaur Rush" after workers spotted exposed fossils in 1877, alerting both rivals. quickly dispatched field parties led by assistants like W. Williston and H. Reed, who in August 1877 uncovered the first substantial sauropod remains at the site, including vertebrae and limb bones that Marsh would later assign to Apatosaurus. Over the ensuing years, Marsh's crews excavated multiple partial skeletons from several quarries along the bluff, yielding iconic sauropod material amid constant vigilance against Cope's scouts, who occasionally poached sites or spread misinformation to disrupt operations. This frenzy resulted in the recovery of at least five partial Apatosaurus specimens by the mid-1880s, including caudal vertebrae, girdle elements, and long bones that showcased the animal's massive scale. The pressure to publish ahead of Cope contributed to the detailed description of Apatosaurus ajax in June 1879, which included the (YPM 1860) and additional material such as a large posterior cervical vertebra (YPM 1861) from the near . Just months later, in December 1879, he named a second species, excelsus, using a more complete but juvenile partial mount (YPM VP 1980) with 15 vertebrae, ribs, a , and limbs from nearby Quarry 10, though the description emphasized hurried comparisons to secure rights. These rushed namings, typical of the era's competitive publishing, often relied on fragmentary evidence and overlooked anatomical overlaps, sowing seeds for later taxonomic debates. The ' intensity scaled up collection efforts dramatically, with Marsh's annual budgets reaching thousands of dollars to sustain crews of up to 50 workers at Como Bluff, unearthing dozens of sauropod bones annually in the early . While this yielded transformative insights into sauropod diversity, the rivalry's haste compromised specimen preparation and stratigraphic recording, as bones were shipped east in plaster jackets with minimal contextual notes to beat Cope to press. By the late , exhaustion of accessible quarries and financial strains from the expeditions marked the decline of the Como Bluff boom, but the era's output established Apatosaurus as a cornerstone of sauropod .

Skull controversy and resolution

The initial discovery of Apatosaurus in 1879 by yielded a nearly complete postcranial but no associated , leaving the cranial unknown. To display the dinosaur in museum exhibits, early reconstructions relied on speculative skulls from other sauropods; for instance, the (AMNH) mounted its Apatosaurus specimen in 1905 using a sculpted Camarasaurus-like skull, assuming a short, boxy cranium suited to the animal's presumed browsing habits. Similarly, other institutions, including the (CMNH), initially left headless or used skulls, reflecting the prevailing view that Apatosaurus shared features with these relatives. By the 1910s, paleontologists began recognizing the mismatch between these mounted skulls and the slender neck vertebrae of Apatosaurus. , director of the AMNH, advocated for a Camarasaurus-style skull, arguing it better matched the robust build of the postcrania. In contrast, of the CMNH, after Earl Douglass discovered an isolated (CM 11162) near the A. louisae (CM 3018) in 1910, proposed in 1915 that this long, narrow Diplodocus-like cranium belonged to Apatosaurus, based on stratigraphic proximity and shared diplodocid traits. Osborn vehemently opposed this association, threatening professional repercussions and insisting on a deeper-ed morphology; the debate persisted in literature for decades, with Holland defending his view in publications but refraining from mounting CM 11162 on the CMNH skeleton to avoid conflict. The controversy lingered unresolved until the 1970s, when John S. McIntosh and David S. Berman reexamined CM 11162 and related material, confirming through that it represented the true Apatosaurus skull—a lightweight, elongate structure with a narrow adapted for high browsing, distinct from both and . Their 1978 analysis in the Bulletin of the established that earlier mounts were erroneous, prompting museums like the AMNH and CMNH to replace the incorrect skulls with casts of CM 11162 by the late 1970s and early 1980s. Further resolution came in the 1990s and 2000s through advanced imaging and phylogenetic studies, which affirmed the unique morphology of the Apatosaurus skull. Comparisons by Paul Upchurch and colleagues in 2004 highlighted subtle differences, such as a more robust quadrate and narrower nasal opening compared to , supporting its assignment within . In 2010, computed tomography (CT) scans of a new Apatosaurus braincase from the revealed neuroanatomical details, including an elongated endocranium consistent with diplodocid affinities but with apatosaurine-specific variations in the olfactory region, solidifying the cranial reconstruction. This prolonged debate had significant cultural repercussions, as the erroneous Camarasaurus-skulled "Brontosaurus" (a junior synonym of Apatosaurus) became the iconic "thunder lizard" in popular media and exhibits from the early 20th century onward, perpetuating a misleading image of the dinosaur until the corrections of the late 20th century.

Taxonomy

Valid species

The genus Apatosaurus is currently recognized as comprising two valid species: A. ajax and A. louisae, based on a comprehensive specimen-level phylogenetic analysis that supports their distinction from other diplodocids, including the resurrected genus Brontosaurus. These species date to the Late Jurassic, specifically the Kimmeridgian to Tithonian stages (approximately 155–145 million years ago), and are known exclusively from the Morrison Formation in western North America. Apatosaurus ajax, the , was named and described by in 1877 based on specimen YPM 1860, a partial consisting of dorsal, sacral, and caudal vertebrae, a chevron, ribs, a , and a , collected from Quarry 10 at Garden Park in . This species is diagnosed by several autapomorphic traits, including middle caudal vertebrae with neural spines bearing prezygapophyses that project strongly anteriorly relative to the centrum, and chevrons with distal ends that are markedly expanded and V-shaped in distal view; it also exhibits a relatively robust build with taller neural spines in the mid-dorsal vertebrae compared to A. louisae, reflected in higher vertebral height-to-length ratios (approximately 1.5–2.0 in presacral vertebrae). Key referred specimens include the well-preserved partial UWGM 15556 from , which provides additional details on limb proportions, such as a humerus-to-femur length ratio of about 0.85, supporting its robust morphology. Apatosaurus louisae was named by William J. Holland in 1915 based on holotype specimen CM 3018, a nearly complete including most of the vertebral column, girdle elements, and limbs, discovered at the Iron Springs locality in , within the . This is characterized by a more gracile overall build, with a longer neck evidenced by that are proportionally longer (length-to-height ratio around 4.5–5.0) and lower neural spines in the dorsal vertebrae (height approximately 1.1–1.3 times centrum height); limb proportions differ notably, featuring a more slender (humerus-to-femur ratio near 0.90) and elongate metacarpals. Referred material, such as partial skeletons from in (e.g., CM 3378 and DNM 529), reinforces these distinctions and indicates a slightly smaller body size, with estimated lengths of 21–23 meters compared to 24–26 meters for A. ajax.

Synonymized and reassigned species

Over the course of taxonomic revisions, several species initially assigned to Apatosaurus have been synonymized with other taxa or reassigned to different genera, primarily due to overlapping morphological features in vertebrae and other skeletal elements that blurred generic boundaries. These reclassifications reflect ongoing debates in diplodocid sauropod , driven by advances in morphometric analysis and specimen-level . The Brontosaurus, erected by in 1879 with the B. excelsus based on specimens from the , was long treated as a junior of Apatosaurus. In 1903, Elmer Riggs formally synonymized the Brontosaurus with Apatosaurus, recombining B. excelsus as A. excelsus and recognizing it as distinct from A. ajax; this view was reinforced in subsequent reviews, such as Charles Gilmore's 1936 monograph and John McIntosh's 1990 revision, which emphasized insufficient separation in caudal and dorsal vertebrae to warrant generic distinction, ultimately synonymizing A. excelsus with A. ajax. However, a 2015 specimen-level phylogenetic study by Emanuel Tschopp and colleagues overturned this synonymy, reinstating Brontosaurus as valid based on quantitative analysis of 81 specimens; key distinctions included taller neural arches and more robust cervical centra in Brontosaurus compared to Apatosaurus, supporting B. excelsus as distinct from A. ajax. This reassessment highlighted how earlier synonymies overlooked subtle but consistent morphological clusters identifiable through statistical clustering and landmark-based . Similarly, Apatosaurus yahnahpin, described by McIntosh in 1990 as a new species from a partial skeleton (UW 15556) in Wyoming's Morrison Formation, was initially placed in Apatosaurus due to shared features like elongated hindlimbs and similar vertebral centrum ratios with A. louisae. The 2015 Tschopp et al. analysis reassigned it to Brontosaurus yahnahpin, citing closer matches in dorsal vertebral morphology—such as deeper pleurocoels and more pronounced laminae—to B. excelsus than to valid Apatosaurus species; this move was part of broader recognition that A. yahnahpin fell within a Brontosaurus clade in phylogenetic trees. Current consensus accepts this reassignment, though some researchers note ongoing debate over whether such differences represent true generic separation or intraspecific variation. The taxon Elosaurus parvus, named by Joseph Peterson and Charles Gilmore in 1902 for juvenile dorsal vertebrae from , was reassigned to Apatosaurus parvus by McIntosh in 1994, based on proportional similarities in neural spine height and centrum shape to adult Apatosaurus material, suggesting it represented a growth stage rather than a distinct . The 2015 study further reclassified it as Brontosaurus parvus, integrating it into the Brontosaurus hypodigm due to matching pneumatic features in the ribs and vertebrae that aligned more closely with Brontosaurus ontogenetic series than Apatosaurus. This reassignment underscores how juvenile specimens, previously dismissed as nondiagnostic, provide critical data for synonymy evaluations when analyzed phylogenetically. Atlantosaurus, established by Marsh in 1877 for fragmentary vertebrae (YPM 1859) from Colorado, was briefly considered a distinct genus but reassigned to Apatosaurus in early 20th-century reviews by Riggs and others, owing to indistinguishable morphology from A. ajax elements; later assessments, including McIntosh's 1990 work, treated it as a probable synonym due to the material's fragmentary nature and lack of unique apomorphies. By the 2010s, it was widely regarded as a nomen dubium potentially referable to Apatosaurus, though some phylogenetic placements suggest possible affinity with Brontosaurus. These synonymies and reassignments stem from challenges in distinguishing genera based on vertebral morphology, where variation in centrum , neural arch complexity, and pneumatization often overlaps across diplodocids; historical debates from the (e.g., Leonard Carpenter's 1979 morphometric comparisons supporting broad synonymy) through the (McIntosh's integrative revisions) to the (pre-Tschopp qualitative assessments) relied on qualitative comparisons, whereas the 2015 quantitative approach resolved many ambiguities by accounting for intraspecific variability.

Phylogenetic classification

Apatosaurus belongs to the Sauropoda within Dinosauria, more specifically positioned within the Diplodocimorpha, the family , and the subfamily . This placement is supported by extensive cladistic analyses that incorporate morphological characters from skeletal elements, emphasizing features such as the elongate neck and tail characteristic of diplodocoids. Within , Apatosaurus is recognized as the sister to , a distinction validated through specimen-level phylogenetic analysis involving 81 operational taxonomic units and 477 morphological characters. Key synapomorphies uniting include tall, plate-like neural spines on the posterior dorsal vertebrae, paired pneumatic foramina on the cervical centra, and a deep excavation on the posterior face of the cervical neural arches. These traits distinguish apatosaurines from other diplodocids, such as the more gracile diplodocines. The seminal cladogram from Tschopp et al. (2015) recovers a monophyletic as the sister group to Diplodocinae within , with Apatosaurus ajax and A. louisae forming a sister to the species (B. excelsus, B. yahnahpin, and B. parvus). Subsequent studies, including updates to sauropod phylogenies, have largely upheld this topology, though some analyses suggest minor adjustments in character scorings for interspecific relationships. The radiation of diplodocids, occurring during the to stages (approximately 157–145 million years ago), saw the diversification of in the floodplains of the , coinciding with the emergence of multiple giant herbivorous lineages. Debates persist regarding the of Apatosaurus following the separation of , with some researchers arguing that diagnostic differences between the genera—such as the stouter limb bones and shorter cervicals in Apatosaurus—are insufficiently robust across all specimens, potentially indicating overlap in ontogenetic variation. However, the consensus from high-impact cladistic revisions affirms the generic distinction, emphasizing the value of specimen-based approaches in resolving long-standing taxonomic uncertainties.

Paleobiology

Posture and locomotion

Apatosaurus exhibited a sub-horizontal posture in its neutral position, as inferred from the orientation of zygapophyseal facets on the and the inferred attachments of nuchal ligaments and epaxial muscles. This configuration allowed for greater lateral flexibility but limited elevation of the head much beyond the horizontal plane, contrasting with earlier upright reconstructions that overestimated vertical reach based on isolated vertebral articulations. The zygapophyseal surfaces, particularly in the posterior cervicals of A. louisae, facilitated flexion in horizontal and vertical planes while maintaining stability during low-level . The limbs of Apatosaurus supported a pillar-erect stance, with columnar femora and humeri aligned vertically beneath the body to bear immense weight efficiently. Trackway evidence from Morrison Formation sites indicates a quadrupedal gait with a relatively narrow gauge, where manus and pes impressions are positioned close to the midline, reflecting the inward rotation of the limbs characteristic of diplodocids. This posture minimized lateral sway and energy expenditure during progression over floodplain terrains. Locomotion speeds for Apatosaurus are estimated at 10-20 km/h for walking, derived from allometric scaling of limb length (hip height) and stride lengths preserved in sauropod trackways using established biomechanical models. These estimates align with observations of moderate-paced quadrupedal movement in large herbivores, where longer strides scaled positively with body size but were constrained by the pillar-like limb geometry. The elongated tail of Apatosaurus, comprising over half the total body length, primarily functioned as a to balance the anterior mass of the long neck during static postures and locomotion. It may have also served a defensive role, potentially wielded as a whip-like structure to deter predators, though direct evidence for supersonic cracking remains speculative and based on with related diplodocids. Recent analyses of dorsal ribs in Apatosaurus reveal previously undocumented pneumatic features, including camerate and camellate internal structures that reduced . These adaptations, linked to an extensive system, contributed to a lightweight thoracic framework, thereby enhancing overall mobility and reducing locomotor costs in this massive sauropod.

Feeding mechanisms

Apatosaurus possessed peg-like, spatulate teeth confined to the front of its jaws, adapted for cropping vegetation such as ferns and cycads rather than grinding or . These teeth exhibited weak occlusion, with minimal contact between upper and lower dentitions during jaw closure, indicating that oral processing was limited and food was primarily ingested whole. Gastroliths, polished stones occasionally associated with sauropod skeletons including those attributed to Apatosaurus, have been interpreted as aiding intra-abdominal grinding to break down tough plant material, compensating for the inefficiencies of the dental apparatus. The neck of Apatosaurus, with its flexible vertebral column, enabled a range of heights, from low ground-level to elevated reaches estimated at 5-7 meters vertically, allowing access to a variety of foliage in its . Jaw featured a simple up-and-down motion driven by modest adductor muscles, resulting in a low bite force of approximately 1-2 kN, sufficient only for nipping branches and leaves without significant mastication. Dental wear patterns on Apatosaurus teeth, characterized by fine scratches and pits, suggest a diet dominated by tough, abrasive vegetation from the flora, including and horsetails alongside ferns and cycads. Recent analyses of using calcium isotopes indicate niche partitioning among Morrison sauropods, with Apatosaurus consuming a more varied array of tougher plants compared to relatives like . Stable carbon isotope studies from 2025 further confirm a dominance of C3 plants in the diet, consistent with the isotopic signatures of low-browsing gymnosperms and ferns prevalent in the environment.

Growth and ontogeny

Histological examination of long bones from multiple Apatosaurus specimens demonstrates a pattern of rapid early growth followed by deceleration in later ontogenetic stages. Juvenile bones exhibit plexiform and woven-fibered tissues with high vascularization, indicative of fast deposition rates, while subadult and adult bones show parallel-fibered and lamellar-zonal tissues interrupted by lines of arrested growth (LAGs), signaling seasonal pauses and overall slower appositional growth. This transition reflects determinate growth typical of large sauropods, where juveniles prioritized rapid size increase to reduce predation risk before shifting to sustained, lower-rate expansion. Growth rates derived from these histological data and modeling suggest Apatosaurus achieved substantial mass accumulation early in life, with initial juvenile phases estimated at 30-50 kg per year, accelerating to peak rates of approximately 520-1000 kg per year during mid-ontogeny before tapering off. For instance, modeling based on Curry's growth series indicates that Apatosaurus excelsus reached near-adult body mass (around 25 metric tons) in 20-30 years, with LAG counts in mature femora and humeri revealing 20-25 annual increments to skeletal maturity. These patterns align with broader sauropod , emphasizing accelerated juvenile phases to attain efficiently. Ontogenetic changes in Apatosaurus morphology are evident in preserved juvenile material, such as specimen CM 566, a small A. louisae individual represented by partial vertebrae and limb elements measuring under 2 meters in total length. Juveniles displayed proportionally shorter necks relative to body size compared to s, potentially aiding maneuverability in dense vegetation, alongside tails that were more flexible due to less ossified chevrons and zygapophyses, allowing greater lateral motion for balance or evasion. This precocial is inferred from the rapid histological growth and lack of associated nesting traces, suggesting hatchlings—likely 10-20 kg—could autonomously shortly after emerging from eggs. Lifespan estimates, derived from extensive LAG counts in bones, place maturity at 20-30 years, with total potentially reaching 70-100 years, comparable to modern large herbivores. Hypotheses of in Apatosaurus stem from observed size variations among mature specimens, with some suggesting males were larger for display or combat, but these remain unconfirmed due to insufficient diagnostic skeletal traits and potential ontogenetic or intraspecific overlap. No clear bimodal distributions in metric data support sex-based differences, and soft-tissue indicators like ornaments are absent in the fossil record.

Physiology and metabolism

Apatosaurus exhibited an advanced respiratory system characterized by extensive postcranial skeletal pneumaticity, which supported a complex air sac system analogous to that in birds. This system included pneumatic foramina and fossae in the vertebrae and a previously unreported form of pneumaticity in the dorsal ribs, where superficial fossae occur along the rib canal sulcus, indicating invasion by diverticula from cervical and abdominal air sacs. These features facilitated efficient unidirectional airflow through the lungs, enhancing oxygen uptake in a large-bodied animal. Bone histology reveals that Apatosaurus maintained a mesothermic metabolic rate, intermediate between ectothermy and endothermy, with growth patterns and vascularization in long bones suggesting elevated but not fully mammalian-like metabolism. This metabolic strategy allowed for rapid juvenile growth while conserving energy in adulthood, consistent with histological evidence of cyclical growth lines and fibrolamellar bone tissue. The cardiovascular system of Apatosaurus was adapted to support its massive body size, likely featuring a fully divided four-chambered heart capable of generating high systemic blood pressure to perfuse distant tissues, including the elevated neck and head. Thoracic volume estimates indicate space for a heart of approximately 500 liters, enabling separation of pulmonary and systemic circulations to prevent pulmonary hypertension despite the animal's girth. In the warm, seasonal, of the , Apatosaurus would have required robust water balance mechanisms, with likely achieved through efficient renal function and behavioral strategies to minimize evaporative losses in a landscape dominated by floodplains and ephemeral water sources. Studies of the Apatosaurus braincase demonstrate an emphasis on olfaction, with relatively large olfactory tracts and bulbs in the indicating a well-developed for detecting food or conspecifics, while the optic lobes suggest vision was less dominant compared to chemosensory capabilities.

Paleoecology

Geological context

Apatosaurus fossils are primarily known from the Brushy Basin Member of the Upper Jurassic , which represents the upper portion of this extensive sedimentary sequence. This member consists predominantly of mudstones, siltstones, and sandstones interbedded with layers (bentonites), deposited in a fluvial-lacustrine environment during the late to stages, approximately 155 to 145 million years ago. The geographic distribution of Apatosaurus specimens is confined to the , with key localities in , , , and . Notable sites include the Mygatt-Moore Quarry in western and Reed's Quarry 9 in southeastern , both within the Brushy Basin Member, as well as exposures in the where the formation thins to about 60 meters. Taphonomic processes in the Brushy Basin Member favored the preservation of large sauropod bones like those of Apatosaurus due to the riverine depositional setting, characterized by meandering streams and environments. Rapid in channel sandstones and overbank muds protected robust skeletal elements from prolonged exposure and , resulting in a bias toward the recovery of complete or partially articulated large bones rather than disarticulated small elements or juveniles. Radiometric dating using U-Pb zircon has precisely constrained the age of Apatosaurus-bearing strata in the Brushy Basin Member, with dates such as 152.51 ± 0.47 Ma from Reed's Quarry 9 confirming a latest placement. These ages align the with global stages, correlating the Brushy Basin to the upper Formation in and the Argiles de l'Aveyron in , while regionally it overlies the Sundance Formation and underlies the Lower Dakota Group.

Contemporaneous fauna

Apatosaurus lived during the period, approximately 155 to 145 million years ago, in what is now the , primarily within the . This formation represents one of the most productive sources of dinosaur fossils, revealing a diverse assemblage of vertebrates that coexisted with Apatosaurus. The included a mix of large herbivores, apex predators, and smaller opportunistic species, forming a complex dominated by sauropod dinosaurs. Among the herbivores, other long-necked sauropods such as Diplodocus, Camarasaurus, and Brachiosaurus were common contemporaries, sharing similar riparian and floodplain habitats while likely partitioning food resources by height or plant type. Ornithischian dinosaurs, including the plated Stegosaurus and the iguanodontian Camptosaurus, also inhabited these environments, with Stegosaurus scavenging or browsing low vegetation and Camptosaurus grazing on ferns and cycads. These herbivores contributed to the high biomass of plant-eaters in the Morrison, with Apatosaurus serving as one of the dominant megaherbivores, its massive size allowing it to access mid-level foliage that smaller species could not. Predatory theropod dinosaurs posed significant threats to juvenile or weakened Apatosaurus individuals. Allosaurus, the most abundant large theropod in the Morrison, was a versatile hunter capable of tackling sauropods through pack behavior or opportunistic scavenging, as evidenced by its remains in multiple quarry sites. Smaller theropods like , with its distinctive nasal horn, and the massive also roamed these landscapes, preying on a range of vertebrates from small dinosaurs to larger herbivores. Smaller fauna rounded out the ecosystem, including crocodylomorphs such as , which lurked in rivers and wetlands as ambush predators on fish and small terrestrial animals. Pterosaurs, represented by species like indeterminate rhamphorhynchoids similar to and pterodactyloids such as , filled aerial niches, likely feeding on insects or fish near water bodies. Early mammals, such as the tiny and multituberculates like Glirodon, were rare but present as nocturnal insectivores or omnivores in the . Direct evidence of interactions between Apatosaurus and its contemporaries includes theropod bite marks on sauropod bones from the , such as punctures and grooves attributed to teeth, indicating scavenging or failed predation attempts on carcasses or live animals. The 's hotspots, particularly in areas like the Howe Quarry and Bone Cabin Quarry, highlight this rich assemblage, with Apatosaurus fossils often found in association with these taxa, underscoring its role as a key component of the megaherbivore guild.

Habitat and paleoenvironment

Apatosaurus inhabited the floodplains and riverine environments of the in western , characterized by semi-arid conditions with meandering rivers and seasonal flooding. Sedimentary deposits, including sandstones and mudstones, indicate a of low-relief plains periodically inundated by rivers, supporting a mosaic of wetlands and drier uplands. The vegetation was predominantly ferns and horsetails in open floodplains, interspersed with , cycads, and ginkgoes along watercourses, forming dense riparian galleries that provided ample for large herbivores. The paleoclimate was warm and subtropical, influenced by monsoonal patterns with wet summers and prolonged dry winters, as evidenced by calcrete paleosols and traces in the sediments. Annual estimates range from 600 to 900 mm, sufficient to sustain river systems but leading to episodic droughts that concentrated animal populations near water sources. Oxygen ratios (δ¹⁸O) from teeth and sediments further confirm fluctuating water availability, with higher values during dry phases indicating reliance on evaporative sources. Ecologically, Apatosaurus filled the niche of a high-level browser, accessing mid- to upper-canopy in forests, which minimized with ground-level feeders among sympatric sauropods. Carbon isotope data (δ¹³C) from enamel suggest a diet enriched in ¹³C relative to other diplodocoids, consistent with consumption of sun-exposed, higher-elevation in open habitats rather than shaded ferns. Bone beds, such as those at Como Bluff, imply seasonal migrations to follow riverine vegetation flushes, while theropod bite marks on sauropod remains highlight predation risks in these congregated settings. This positioning in the underscores Apatosaurus's role in a dynamic shaped by climatic variability and resource distribution.

References

  1. https://www.nhm.ac.uk/discover/dino-directory/apatosaurus.html
  2. https://geology.utah.gov/popular/dinosaurs-fossils/age-of-dinosaurs/
  3. https://www.nps.gov/dino/learn/nature/apatosaurus-louisae.htm
  4. https://www.nps.gov/places/apatosaurus-louisae.htm
  5. https://palaeo-electronica.org/content/2022/3653-apatosaurine-feeding-mechanism
  6. https://www.researchgate.net/publication/362318913_A_novel_feeding_mechanism_of_diplodocid_sauropods_revealed_in_an_Apatosaurine_skull_from_the_Upper_Jurassic_Nail_Quarry_Morrison_Formation_at_Como_Bluff_Wyoming_USA
  7. https://peerj.com/articles/857/
  8. https://www.nature.com/articles/s41598-021-97856-6
  9. https://doc.rero.ch/record/14932/files/PAL_E2077.pdf
  10. https://pmc.ncbi.nlm.nih.gov/articles/PMC7891087/
  11. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0078213
  12. https://pmc.ncbi.nlm.nih.gov/articles/PMC3045712/
  13. https://www.tandfonline.com/doi/abs/10.1080/08912960601118651
  14. https://pubs.geoscienceworld.org/paleosoc/paleobiol/article/34/2/264/86480/Modeling-growth-rates-for-sauropod-dinosaurs
  15. https://www.researchgate.net/publication/272152509_A_new_specimen_of_Apatosaurus_ajax_Sauropoda_Diplodocidae_from_the_Morrison_Formation_Upper_Jurassic_of_Wyoming_USA
  16. https://ucmp.berkeley.edu/history/marsh.html
  17. https://www.wyohistory.org/encyclopedia/como-bluff
  18. https://main.wsgs.wyo.gov/outreach/cultural-geology/guide-como-bluff
  19. https://www.amnh.org/explore/news-blogs/brontosaurus-apatosaurus
  20. https://carnegiemuseums.org/archive_article/the-wrongheaded-dinosaur-nov-dec-1997/
  21. https://www.jstor.org/stable/1303324
  22. https://www.carnegiemuseums.org/archive_article/the-wrongheaded-dinosaur-nov-dec-1997/
  23. https://www.biodiversitylibrary.org/part/228587
  24. https://bioone.org/journals/american-museum-novitates/volume-2010/issue-3677/591.1/The-Braincase-of-Apatosaurus-Dinosauria--Sauropoda-Based-on-Computed/10.1206/591.1.full
  25. https://www.smithsonianmag.com/science-nature/why-brontosaurus-still-matters-63478606/
  26. https://palaeo-electronica.org/content/pdfs/1518.pdf
  27. https://palaeo-electronica.org/content/2024/5327-new-diplodocine-sauropod
  28. https://www.nature.com/articles/nature.2015.17257
  29. https://pmc.ncbi.nlm.nih.gov/articles/PMC3812995/
  30. https://bioone.org/journals/journal-of-vertebrate-paleontology/volume-26/issue-4/0272-4634_2006_26_907_BGCOMS_2.0.CO_2/BURLY-GAITS--CENTERS-OF-MASS-STABILITY-AND-THE-TRACKWAYS/10.1671/0272-4634%282006%2926%5B907:BGCOMS%5D2.0.CO%3B2.full
  31. https://www.sciencedirect.com/science/article/abs/pii/0031018282900050
  32. https://www.amnh.org/exhibitions/dinosaurs-ancient-fossils/sauropod-biomechanics/a-strange-tale
  33. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0143800
  34. https://www.tandfonline.com/doi/abs/10.1080/02724634.2024.2316665
  35. https://pmc.ncbi.nlm.nih.gov/articles/PMC2197205/
  36. https://pmc.ncbi.nlm.nih.gov/articles/PMC1634776/
  37. https://www.tandfonline.com/doi/abs/10.1080/08912969809386568
  38. https://www.jsg.utexas.edu/news/2025/07/clues-for-dinosaurs-diets-found-in-the-chemistry-of-their-fossil-teeth/
  39. https://www.tandfonline.com/doi/abs/10.1080/02724634.1999.10011179
  40. https://www.cambridge.org/core/journals/paleobiology/article/ontogenetic-stages-in-the-long-bone-histology-of-sauropod-dinosaurs/1356BF5D49026E7EB70F9182574729E7
  41. https://www.researchgate.net/publication/40664458_Modeling_growth_rates_for_sauropod_dinosaurs
  42. https://www.researchgate.net/publication/236883873_Sexual_dimorphism_in_dinosaurs
  43. https://svpow.com/2011/05/16/why-the-long-necks-probably-not-sexually-selection/
  44. https://www.researchgate.net/publication/379483871_A_previously_unreported_form_of_dorsal_rib_pneumaticity_in_Apatosaurus_Dinosauria_Sauropoda_and_implications_for_pneumatic_variation_among_diplodocid_dorsal_ribs
  45. https://pubs.usgs.gov/publication/70027238
  46. https://www.nps.gov/dino/learn/nature/morrison-formation.htm
  47. https://pubs.geoscienceworld.org/sepm/jsedres/article/89/10/1017/574611/A-chronostratigraphic-framework-for-the-Upper
  48. https://www.researchgate.net/publication/316660460_A_U-Pb_zircon_age_for_Reed%27s_Quarry_9_Upper_Jurassic_Morrison_Formation_Albany_County_WY
  49. https://www.journals.uchicago.edu/doi/10.1086/712368
  50. https://palaeo-electronica.org/content/2014/811-taphonomy-of-the-morrison-fm
  51. https://pubs.usgs.gov/pp/0183/report.pdf
  52. https://palaeo-electronica.org/content/2003/1804/appendix-a-morrison-pterosaurs.htm
  53. https://www.cambridge.org/core/journals/paleobiology/article/taphonomy-and-paleoecology-of-the-dinosaur-beds-of-the-jurassic-morrison-formation/B92D6DE5FF6A469557F98BF580691FCF
  54. https://terra.rice.edu/department/faculty/morganj/ESCI536/Readings/TurnerPeterson-SedGeol2004.pdf
  55. https://www.researchgate.net/publication/338787932_What_factors_influence_our_reconstructions_of_Morrison_Formation_sauropod_diversity
  56. https://etd.ohiolink.edu/acprod/odb_etd/ws/send_file/send?accession=ucin1090853934&disposition=inline
  57. https://www.academia.edu/14551511/The_implications_of_a_dry_climate_for_the_paleoecology_of_the_fauna_of_the_Upper_Jurassic_Morrison_Formation
  58. https://www.geol.umd.edu/undergraduate/paper/breeden.pdf
  59. https://pmc.ncbi.nlm.nih.gov/articles/PMC10655710/
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