Apatosaurinae (from Ancient Greek words ἀπάτη (apátē), meaning "deception", and σαῦρος (saûros), meaning "lizard") is a subfamily of diplodocid sauropods, an extinct group of large, quadrupedal dinosaurs, the other subfamily in Diplodocidae being Diplodocinae. Apatosaurines are distinguished by their more robust, stocky builds and shorter necks proportionally to the rest of their bodies. Several fairly complete specimens are known, giving a comprehensive view of apatosaurine anatomy.
The subfamily includes only two genera for certain, Apatosaurus and Brontosaurus, according to a 2015 study, though Amphicoelias and a species of Atlantosaurus may also belong to this group. All members are known from the Late Jurassic-aged Morrison Formation of the American West, dating to between 157 and 146.8 million years ago. Fossils were first unearthed in 1877 by crews working for American paleontologist Othniel Charles Marsh in the midst of the Bone Wars, a fossil-hunting rivalry with naturalist Edward Drinker Cope. Marsh went on to name both genera of apatosaurine; Apatosaurus in 1877 and Brontosaurus in 1879. For many years, Brontosaurus was considered a taxonomic synonym of Apatosaurus after a 1903 study by paleontologist Elmer Riggs considered them synonyms. This was the prevalent notion until a 2015 paper led by Emmanuel Tschopp argued that the two were separate genera, however some authors still consider the two synonyms. According to Tschopp and colleagues, there are six valid species of apatosaurine; three in Brontosaurus and two in Apatosaurus.
Apatosaurines were nonselective low-browsers, utilizing their peg-like teeth to feed on plants like ferns, cycadoids, and horsetails. They also had rapid growth rates, with studies finding that apatosaurines reached adult sizes in just ten years, possibly peaking in gained in a single year. As in their relatives the diplodocines, both Apatosaurus and Brontosaurus bore long, whip-like tails which potentially were used for defense or as a tactile organ, for touch. Of note is the robustly built and boxy cervical (neck) vertebrae of apatosaurines, with a study hypothesizing that their necks were used for intraspecific fighting between individuals. Being from the Morrison Formation, apatosaurines coexisted with a menagerie of other taxa such as the sauropods Diplodocus, Barosaurus, and Brachiosaurus; herbivorous ornithischians Stegosaurus, Dryosaurus, and Nanosaurus; as well as the carnivorous theropods Allosaurus, Marshosaurus and Ceratosaurus. This formation was a hotspot of sauropod biodiversity, with over 16 recognized genera, which resulted in niche partitioning between different sauropods.
Discovery and history Initial discoveries and naming
The first apatosaurine 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. 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. By this time, the Morrison Formation had become the center of the Bone Wars, a fossil-collecting rivalry between Marsh and Cope. Because of this, the publications and descriptions of taxa by the two were rushed at the time. Marsh named Atlantosaurus montanus based on some of the fossils sent and hired Lakes, while Cope attempted to hire Lakes as well but was rejected.Kohl, M. F., & McIntosh, J. S. 1997, Discovering Dinosaurs in the Old West: The field journals of Arthur Lakes. One of the best specimens collected by Lakes in 1877 was a well preserved partial postcranial skeleton and a partial braincase (YPM VP 1860), which was sent to Marsh and named Apatosaurus ajax in November 1877. The composite term Apatosaurus comes from the Greek words ()/ () meaning "deception"/"deceptive", and () meaning "lizard"; thus, "deceptive lizard", the same meaning as Apatosaurinae's name. 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, most likely that of the representative species Mosasaurus. Marsh believed that both genera were part of a clade he named Atlantosauridae in 1877. Based on remains from the same quarry, Atlantosaurus immanis was described by Marsh in an 1878 article based on an incomplete postcranial skeleton, though it became mixed with the holotype of A. ajax. A 1906 paper described gastroliths from the A. immanis holotype, but gastrolith use in sauropods has since been disproven. Later studies of the A. immanis holotype have determined that they are from an apatosaurine, potentially Apatosaurus itself according several studies, though Tschopp and colleagues stated it was a dubious apatosaurine.
A possible genus of apatosaurine, Amphicoelias, was discovered in 1877 in Morrison Formation outcrops near Cañon City, Colorado by Aaron Ripley who was working for Cope. Ripley sent the remains, consisting of dorsal vertebrae, a femur, and a pubis, to Cope's home Philadelphia on October 21, 1877. In December 1877, Cope named Amphicoelias, the genus name from the Greek terms amphi meaning "both" and kolios "concave" in reference to the anatomy of the dorsal vertebrae. Three species were referred: A. altus, A. fragillimus, and A. latus. Of these, only A. altus is still considered part of the genus whereas A. fragillimus is now Maraapunisaurus and A. latus is a synonym of Camarasaurus supremus or C. grandis.Carpenter, K. (1998). Vertebrate biostratigraphy of the Morrison Formation near Cañon City, Colorado. Modern Geology, 23, 407.
The discovery of another large and fairly complete sauropod skeleton was announced in 1879 by Marsh. The specimen was collected from Morrison Formation rocks at Como Bluff, Wyoming by William Harlow Reed. Marsh identified it as belonging to an entirely new genus and species, which he named Brontosaurus excelsus, meaning "thunder lizard", from the Greek / meaning "thunder" and / meaning "lizard", and from the Latin excelsus, "noble" or "high". Brontosaurus excelsus type specimen (YPM 1980) was one of the most complete sauropod skeletons known at the time, preserving many of the characteristic but fragile cervical vertebrae. A year later in 1880, another partial postcranial Brontosaurus skeleton was collected near Como Bluff by Reed, including well-preserved limb elements. Marsh named this second skeleton Brontosaurus amplus in 1881, but it was considered a synonym of B. excelsus in 2015.
Second Dinosaur Rush and skull issue 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. 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, bring it back to the home institution, and mount it in their fossil halls. The American Museum of Natural History was the first to launch an expedition, 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. The specimen was found north of Medicine Bow, Wyoming, in 1898 by Walter Granger, and took the entire summer to extract. To complete the mount, sauropod feet that were discovered at the same quarry and a tail fashioned to appear as Marsh believed it shouldbut which had too few vertebraewere added. In addition, a sculpted model of what the museum thought the skull of this massive creature might look like was made.Riggs, E.S. (1903). "Structure and Relationships of Opisthocoelian Dinosaurs. Part I, Apatosaurus Marsh" (PDF). Publications of the Field Columbian Museum Geographical Series. 2 (4): 165–196. OCLC 494478078. Archived (PDF) from the original on October 9, 2022. These skulls were likely those of Camarasaurus, the only other sauropod for which good skull material was known at the time, causing workers 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).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. 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. 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.Parsons, K.M. (1997). "The Wrongheaded Dinosaur". Carnegie Magazine. Archived from the original on April 14, 2010. 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.
In August 1883, Marshall P. Felch collected a disarticulated partial skull (USNM V 5730) of a sauropod further south in the Felch Quarry at Garden Park, Colorado and sent the specimen to Yale. Marsh referred the skull to B. excelsus, later featuring it in a skeletal reconstruction of the B. excelsus type specimen in 1891 and the illustration was featured again in Marsh's landmark publication, The Dinosaurs of North America, in 1896. At the Yale Peabody Museum, the skeleton of Brontosaurus excelsus was mounted in 1931 with a skull based on the Marsh reconstruction of the Felch Quarry skull. While at the time most museums were using Camarasaurus casts for skulls, the Peabody Museum sculpted a completely different skull based on Marsh's recon. The mandible was based on that of a Camarasaurus. In 1998, the Felch Quarry skull that Marsh included in his 1896 skeletal restoration was suggested to belong to Brachiosaurus instead and this was supported in 2020 with a redescription of the brachiosaurid material found at the Felch Quarry.
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 CM3018) identified as the new species Apatosaurus louisae. The skull was designated CM11162; it was very similar to the skull of Diplodocus. The skull was accepted as belonging to the Apatosaurus specimen by Douglass and Carnegie Museum director William J. Holland, although other scientistsmost notably Osbornrejected this identification. Holland defended his view in 1914 in an address, 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. After Holland's death in 1934, museum staff placed a cast of a Camarasaurus skull on the mount.