Alamosaurus
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? Alamosaurus Conservation status: Fossil
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| Alamosaurus sanjuanensis Gilmore, 1922 |
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Alamosaurus is a genus of titanosaurian sauropod dinosaur from the Early Cretaceous Period of North America. It was a large quadrupedal herbivore, up to 53 feet (16 meters) in length and up to 33 tons (30 metric tonnes) in weight. Alamosaurus, like other sauropods, had a long neck and tail, which may have ended in a whiplash structure.
Etymology
Contrary to popular assertions, this dinosaur is not named after the Alamo in San Antonio, Texas, or the battle fought there. The holotype, or original specimen, was discovered in New Mexico, and at the time of its naming, no remains of Alamosaurus had been found in Texas. Instead, the name Alamosaurus comes from Ojo Alamo, the former name for the formation it was found in, which in turn was named after the nearby Ojo Alamo trading post. The term alamo itself is a Spanish word meaning "poplar" and is used for the local subspecies of cottonwood tree. The term sauros is Greek for "lizard" and is the most common suffix used in dinosaur names.
There is one named species (A. sanjuanensis). It is named after San Juan County, New Mexico, where the first remains were found.
Both genus and species were named by Smithsonian paleontologist Charles. W. Gilmore in 1922.
Location and Age
Alamosaurus remains have been discovered throughout the southwestern United States. The holotype was discovered in the Lower Kirtland Formation of New Mexico, and since then, Alamosaurus has also been found in the upper part of the Kirtland, a formation which was deposited during the Maastrichtian stage of the Late Cretaceous Period. Bones have also been recovered from other Maastrichtian formations, like the North Horn Formation of Utah, and the Black Peaks, El Picacho, and Javelina Formations of Texas. These formations start around 74 million years ago and last right up to the end of the Cretaceous, 65 million years ago. Alamosaurus may have been one of the last dinosaurs to go extinct.
Skeletal elements of Alamosaurus are among the most common Late Cretaceous dinosaur fossils found in the American Southwest and are now used to define the fauna of that time and place. Other contemporaneous dinosaurs from that part of the world include tyrannosaurs, smaller theropods, Nodocephalosaurus, Parasaurolophus, Torosaurus, and Pentaceratops, among others.
Remains
Gilmore originally descibed a scapula and ischium in 1922. In 1946, he found a more complete specimen in Utah, consisting of a complete tail, a right forelimb complete except for the tips of the toes, and both ischia. Since then, many other bits and pieces from Texas, New Mexico, and Utah have been referred to Alamosaurus without much description. Lehman & Coulson (2002) describe the most completely known specimen, a juvenile skeleton from Texas, which allowed them to make educated estimates of length and mass.
No skull material is known except for a few slender teeth, and no armor scutes have been reported, such as those found in other advanced titanosaurians like Saltasaurus.
Relationships
Alamosaurus is undoubtedly a derived member of Titanosauria, but relationships within that group are far from certain. Wilson (2002) unites Alamosaurus with Opisthocoelicaudia in a subfamily Opisthocoelicaudinae of the family Saltasauridae. The major competing analysis, performed by Upchurch et al. (2004), finds Alamosaurus as a sister taxon to Pelligrinisaurus, with both genera located just outside Saltasauridae.
Lehman & Coulson (2002) do not perform a phylogenetic analysis, but note similarities between the saltasaurid Neuquensaurus and the as-yet-unnamed Brazilian "Peiropolis titanosaur" which is used in many cladistic and morphologic analyses of titanosaurians.