Apatosaurus louisae

Apatosaurus louisae was a massive diplodocid sauropod from the upper Morrison Formation of Utah. Compared with the more lightly built Diplodocus, it had a deeper torso, unusually robust limb bones and an extremely broad, muscular neck. Holotype CM 3018 preserves an articulated vertebral series from the atlas to near the tail tip, much of the rib cage and most of the limbs. A delicate, low skull found close to the neck helped overturn the long-standing museum image of Apatosaurus with a boxy Camarasaurus-like head. The species is one of the best-known sauropods anatomically, but the precise association of the nearby skull and the limits between Apatosaurus and Brontosaurus continue to be tested in specimen-level studies.

Its fossils occur between approximately 152 and 151 million years ago. Values shown here are approximate and reflect the current curated seed dataset.

The neck vertebrae were short, deep and heavily reinforced, producing the exceptionally thick neck characteristic of apatosaurines. Air-filled chambers lightened the vertebrae without making them mechanically flimsy. The body was carried on four stout, columnar limbs; the forefeet bore one enlarged inner claw and the hind feet had three principal claws. The small skull was long and low, with narrow pencil-like teeth concentrated at the front of the jaws. A very long series of progressively smaller tail vertebrae formed a flexible, whip-like tail, although its exact range of movement and use cannot be read directly from the bones.

• Exceptionally broad, deep and heavily reinforced neck vertebrae
• Small, low skull with pencil-like teeth at the front of the jaws
• Deep torso supported by unusually robust limb bones
• Single enlarged claw on the inner digit of each forefoot
• Three principal claws on each hind foot
• Air-filled chambers within the neck and trunk vertebrae
• Very long, tapering tail with at least seventy-three vertebrae in the holotype

On 17 August 1909, Carnegie Museum collector Earl Douglass found eight connected tail vertebrae weathering from a ridge near Jensen, Utah. Excavation exposed the remarkably complete skeleton now catalogued as CM 3018 and launched the Carnegie Quarry, later protected within Dinosaur National Monument. William J. Holland named Apatosaurus louisae in a 1915 paper, honouring Louise Carnegie. The Pittsburgh mount opened without a head, received a Camarasaurus-style skull in 1932, and finally gained a cast of the narrow associated Apatosaurus skull in 1979 after David Berman and John McIntosh's detailed 1978 study. The fragile original skull remains off public display.

Discovery credit: Earl Douglass.

Naming authors: William J. Holland.

The Carnegie Quarry formed on a Late Jurassic river floodplain near the western margin of the vast Morrison depositional basin. Seasonal streams crossed open ground carrying conifers, cycads, tree ferns, horsetails and low ferns. Floods concentrated carcasses and transported bones into sand-rich channel deposits. Apatosaurus shared this landscape with Diplodocus, Camarasaurus, Barosaurus and other sauropods, plus Stegosaurus, Camptosaurus and predators including Allosaurus and Ceratosaurus.

Apatosaurus was a terrestrial quadrupedal herbivore. Its small head and front-loaded pencil teeth were suited to cropping or stripping vegetation rather than chewing it; food would have been swallowed for processing in the gut. The broad neck and robust forequarters distinguish it mechanically from more slender diplodocids, but they do not reveal one habitual neck pose. Low-to-middle browsing is plausible, and a long neck enlarged the feeding envelope without requiring the whole body to move. Claims of herd living, combat with the neck or supersonic tail cracking remain hypotheses rather than behaviours directly preserved for A. louisae.

• The eight tail vertebrae that led Earl Douglass to CM 3018 also led to the discovery of the entire Carnegie Quarry.
• Holland named the species for Louise Carnegie, wife of museum benefactor Andrew Carnegie.
• The Pittsburgh skeleton stood headless before receiving the wrong broad skull in 1932 and the correct narrow skull cast in 1979.
• The holotype preserves sixty-four of an estimated seventy-three or more tail vertebrae.
• The real associated skull is too fragile for regular display, so museum visitors see a cast.

A research repository is not necessarily a public exhibit. Loan and display status can change, so check with the institution before visiting.

1. 01
   The Paleobiology Database

   Open source
2. 02
   A specimen-level phylogenetic analysis and taxonomic revision of Diplodocidae

   Emanuel Tschopp, Octávio Mateus, Roger B. J. Benson · PeerJ · 2015

   Open source
3. 03
   Section of Vertebrate Paleontology

   Carnegie Museum of Natural History

   Open source
4. 04
   A New Species of Apatosaurus

   William J. Holland · Annals of the Carnegie Museum · 1915

   Open source
5. 05
   Skull and relationships of the Upper Jurassic sauropod Apatosaurus (Reptilia, Saurischia)

   David S. Berman, John S. McIntosh · Bulletin of Carnegie Museum of Natural History · 1978

   Open source
6. 06
   Apatosaurus louisae

   Dinosaur National Monument, National Park Service

   Open source
7. 07
   Fossil Type Specimens in Parks

   National Park Service

   Open source
8. 08
   Historic Carnegie Quarry

   Dinosaur National Monument, National Park Service

   Open source