Apatosaurinae

Apatosaurines Temporal range: Late Jurassic, 157–146.8 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Skeleton of an apatosaurine (either Apatosaurus or Brontosaurus), American Museum of Natural History 460
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	Saurischia
Clade:	†Sauropodomorpha
Clade:	†Sauropoda
Superfamily:	†Diplodocoidea
Family:	†Diplodocidae
(unranked):	†Apatosaurinae Janensch, 1927
Genera[1]
†Amphicoelias? †Apatosaurus †Brontosaurus

Apatosaurinae (the name deriving from the type genus Apatosaurus, meaning "deceptive 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 5,000 kg (11,000 lb) 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.