Alamosaurus

(AL-a-moe-SORE-us)
Name means: Reptile from the Ojo Alamo Formation

 

Species: sanjuanensis

Range: Late Cretaceous (Maastrichtian, 70-65 MYA) of New Mexico, Texas, and Utah

Size estimate: possibly 100 ft length, about 75 tons

Discovery: Charles W. Gilmore, 1922

Classification: dinosauria, saurischia, sauropoda, titanosauria, saltasauridae

 

Our image of Alamosaurus has transformed over the years. Charles Gilmore based this name on just a shoulder blade and a hip bone. Without much to go on, scientists and artists guessed the animal looked like Diplodocus. Since then we have found many more fossils from Alamosaurus and its relatives. They show that it more closely resembled Brachiosaurus, and may have grown even bigger. The sculpture you see here represents the older image of Alamosaurus, based on fossils from young individuals.

 

Alamosaurus roamed the southern end of an ancient landmass called Laramidia.  It shared its environment with the duck-billed dinosaur Gryposaurus, the horned dinosaurs Torosaurus, Ojoceratops, and Bravoceratops, and the giant pterosaur Quetzalcoatlus. In Utah it may have faced off against Tyrannosaurus rex. Though size probably protected most adults from attack, recent discoveries show that it grew bony armor plates on its rough hide.

True to Life?

 

Since no one has ever seen a living dinosaur, and the missing pieces of the fossil record withhold important clues to their appearance, no artistic representation of a dinosaur ever gets it 100% right. On top of that, new discoveries can change our ideas of extinct creatures drastically. So, how close does this sculpture come to what we know of the original animal?

Alamosaurus:

  • Like many dinosaurs, most of the fossils known for this animal come from juveniles. What you see here is based on that material, and that makes it smaller than Alamosaurus probably grew as an adult. How much bigger could it get? That’s a difficult question to answer: large skeletons tend not to preserve well, making them as rare as the skeletons of small animals. When we do find giant dinosaurs, we usually only find scattered bones, not a full skeleton, forcing us to make estimates with inadequate data. Many such attempts end up overestimating significantly. That said, a giant foot assigned to Alamosaurus could make it a contender for the largest dinosaur known. This sculpture’s head might reach as high as the shoulder of a large adult.
     

  • This sculpture takes most of its look from older depictions based on Diplodocus. 20th century artists based it on Diplodocus mainly because scientists knew more about Diplodocus at the time than almost any other sauropod, so it became a sort of archetype for all of sauropoda. Over the years, numerous discoveries have changed how we understand the evolutionary relationships between sauropods and revealed a hidden diversity of body forms. Alamosaurus belongs to the titanosaur group of dinosaurs, which in turn belongs in the macronarian group along with Brachiosaurus and Camarasaurus. Alamosaurus’ new look better resembles these latter two taxa: longer forelimbs give it a sloping back with sort of a mammoth-like profile, a neck angled away from the ground toward the trees, and a shorter tail. In life, it likely did not have the whip shown here—whip tails are characteristic of the group which includes Diplodocus, the flagellicaudatans (literally “whip-tails”).
     

  • Recent discoveries suggest that Alamosaurus may have borne the same sort of osteoderm “armor” seen in Saltasaurus and Magyarasaurus (the latter shown here at the Park). Sauropod osteoderms are extremely rare and usually found without any clue as to their arrangement on the animal—those assigned to Alamosaurus were not found in good association with other Alamosaurus bones, so their assignment is somewhat tentative as of 2022. Even so, some phylogenetic studies have found close relationships between Alamosaurus and Saltasaurus and its closest relatives, so multiple lines of evidence do support it having osteoderms. This idea has led to depictions of Alamosaurus with spiky, ankylosaur-like armor, but detailed examinations of these sauropod osteoderm’s shapes suggest they would make weak armor; Alamosaurus likely depended more on its great size for defense, at least as an adult, yet the size of the osteoderms assigned to Alamosaurus suggests that it would have retained them into adulthood. They lacked many internal bony features that strengthened ankylosaur armor. Low spikes in the center and keels along the middle of some of these osteoderms did little to strengthen them against breakage, did not get large enough to fend off attackers, and if they played a role in display, the sculpturing of the osteoderms would not have been visible from a distance. However, they may have contributed to the color patterns of the animal’s skin. One hypothesis explaining their unusual shapes and relative weakness suggests that they used them to store minerals which they would re-absorb during times of famine. If so, and considering they may have played a role in color patterns, perhaps they acted as visual indicators of the health of the animal, sort of like a lion’s mane or a gorilla’s silver back. Of course, such speculative ideas are hard to test and ought to be taken as huge maybes. At the very least, if Alamosaurus bore osteoderms, its skin texture would have looked very different from this sculpture, at least across its back and flanks.