Apatosaurus
In the spring of 1877, a local miner named Arthur Lakes stood in the red earth of Morrison, Colorado. He held a fragment of bone that would change paleontology forever. Lakes sent this piece to Othniel Charles Marsh at Yale University and Edward Drinker Cope in Philadelphia. Marsh named the creature Apatosaurus ajax later that November. The name means deceptive lizard because the tail vertebrae resembled those of mosasaurs rather than other dinosaurs. This initial discovery sparked a fierce rivalry between two men who would come to define American dinosaur hunting. Lakes collected several fossils from Quarry 10 while working for Marsh. Only one specimen remains confidently assigned to Apatosaurus ajax today. The holotype skeleton YPM VP 1860 contains many vertebrae but lacks a complete skull.
Henry Fairfield Osborn mounted an Apatosaurus skeleton with a sculpted Camarasaurus head at the American Museum of Natural History. This decision stuck for decades despite evidence suggesting otherwise. Elmer Riggs published a study in 1903 claiming Brontosaurus excelsus was actually just Apatosaurus. He argued the earlier name should take priority over the newer one. Museums continued displaying these creatures as Brontosaurus anyway. William Holland defended his view in 1914 that the skull belonged to Apatosaurus. Yet no true skull appeared until Earl Douglass found CM11162 near Dinosaur National Monument in 1909. John Stanton McIntosh and David Berman finally redescribed the skulls in the 1970s. They proved Holland had been correct all along. The first museum mount received a real Apatosaurus skull on the 20th of October 1979. Even then, some scientists still debated whether the name Brontosaurus should return.
The cervical vertebrae of Apatosaurus are stouter than those of Diplodocus. Charles Whitney Gilmore noted this robustness in early comparisons. These bones carried neural spines with large troughs down the middle. The neck formed a wide deep structure unlike other diplodocids. Pneumatic fossae appear inside many vertebrae as holes filled by air sacs. Wedel stated these cavities likely connected to an avian respiratory system. The tail transformed into a whip-like structure toward its end. This tapering shape resulted from rapidly decreasing height of vertebral spines. Limb bones show similar strength patterns. The humerus resembles that of Camarasaurus more closely than Diplodocus. Femora represent some of the most robust leg bones found in any sauropod. The single manual claw on each forelimb curves slightly but ends squarely truncated. Three claws appear on each hindlimb instead. The foot displays a digit formula of three four five three two.
A 1999 microscopic study showed Apatosaurus grew rapidly during youth. Animals reached near adult sizes within about ten years. Thomas Lehman and Holly Woodward published growth data in 2008 suggesting they hit twenty-five tons in fifteen years. Peak growth rates reached one ton per year according to their calculations. Eva Griebeler examined long bone histology in 2013 for specimen SMA0014. That individual weighed eighteen thousand kilograms and died at age twenty-eight. It reached sexual maturity at twenty-one years old. Another specimen BYU 601-17328 lived thirty-one years before dying. Juvenile material shows proportionally shorter necks compared to adults. These young animals also display greater differences between front and back limbs. Multiple specimens from OMNH suggest over three individuals existed together. Some juveniles exhibit features distinguishing them clearly from relatives. The number of sacral vertebrae increased to five by maturity time. This trait was first noted in 1903 and again in 1936.
Square snouts and fine scratches on teeth indicate ground height browsing habits. Stevens and Parish speculated these sauropods fed on submerged water plants along riverbanks. Kent Stevens and Michael Parrish argued the neck could bend into a U shape laterally. Matthew Cobley disputed this finding in 2013 claiming large muscles limited movement. He suggested animals moved entire bodies to access vegetation instead. Trackways show ranges around ten kilometers per day possible. Top speeds might reach fifteen kilometers per hour according to some estimates. A juvenile trackway led some researchers to believe bipedalism occurred though others dispute it. Single claws likely grasped tree trunks when rearing up. Tail whips may have created sounds exceeding two hundred decibels. Nathan Myhrvold and Philip J. Currie modeled mechanics in 1997. Baron proposed tails functioned as tactile organs for group cohesion instead. This would allow communication while migrating without stopping frequently.
Radiometric dating places the Morrison Formation between one hundred fifty six point three million years ago and one hundred forty six point eight million years ago. Dinosaurs lived here during late Oxfordian Kimmeridgian and early Tithonian stages. Allosaurus accounted for seventy to seventy five percent of theropod specimens found there. Apatosaurus ranked second most common sauropod after Camarasaurus. Fossils appear exclusively in upper Brushy Basin Member layers dated roughly one hundred fifty two to one hundred fifty one million years ago. Additional remains from similarly aged rocks may belong to Brontosaurus instead. Other vertebrates included ray finned fishes frogs salamanders turtles lizards crocodylomorphs pterosaurs bivalves aquatic snails green algae fungi mosses horsetails cycads ginkgoes conifers fern savannas gallery forests Araucaria like trees. The environment featured distinct wet and dry seasons across shallow marine alluvial sediments. Streams carried deposits into swampy lowlands lakes river channels floodplains. Similar formations exist in Portugal Tanzania showing global connections among Late Jurassic ecosystems.
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Common questions
When was Apatosaurus first named and by whom?
Othniel Charles Marsh named Apatosaurus ajax in November 1877. The name means deceptive lizard because the tail vertebrae resembled those of mosasaurs rather than other dinosaurs.
What is the history of the Brontosaurus versus Apatosaurus debate?
Elmer Riggs published a study in 1903 claiming Brontosaurus excelsus was actually just Apatosaurus. Museums continued displaying these creatures as Brontosaurus until the first museum mount received a real Apatosaurus skull on the 20th of October 1979.
How did Apatosaurus grow and what were its physical dimensions?
A 1999 microscopic study showed Apatosaurus grew rapidly during youth with peak growth rates reaching one ton per year. Specimen SMA0014 weighed eighteen thousand kilograms and died at age twenty-eight after reaching sexual maturity at twenty-one years old.
Where and when did Apatosaurus live according to fossil evidence?
Radiometric dating places the Morrison Formation between one hundred fifty six point three million years ago and one hundred forty six point eight million years ago. Fossils appear exclusively in upper Brushy Basin Member layers dated roughly one hundred fifty two to one hundred fifty one million years ago.
What do studies say about Apatosaurus feeding habits and locomotion?
Square snouts and fine scratches on teeth indicate ground height browsing habits while trackways show ranges around ten kilometers per day possible. Top speeds might reach fifteen kilometers per hour according to some estimates and tail whips may have created sounds exceeding two hundred decibels.