Alamosaurus
Interestingly, Alamosaurus is the only sauropod known from this region after the sauropod hiatus - a period of around 30 million years during which no sauropods have been found in this region. This has led some paleontologists to propose that Alamosaurus may have migrated north from South America. At the time, the area it lived in was the southern end of the island continent Laramidia. The environment there consisted of mostly semi-arid plains - areas with little rain, but not completely dry like a desert - with some lakes and swamps. Alamosaurus was one of the last surviving dinosaurs, going extinct at the end of the Cretaceous period.
The only known species, Alamosaurus sanjuanensis, was discovered in 1922 by paleontologist Charles Whitney Gilmore in New Mexico. It was named after both the Ojo Alamo Formation and San Juan County, where the fossils were unearthed.
How Big Was Alamosaurus?
Size estimates for Alamosaurus vary due to the fragmentary nature of the fossils, but it is clear that it was gigantic. Most of the more complete remains are of juveniles or small adults, but other fragmentary specimens suggest much larger maximum sizes. Current estimates are a length from head to tail of around 26 - 30 m - with the neck alone being close to a third of this length - and a shoulder height of around 5 m. Weight estimates vary even more but are also massive, at around 30 - 80 tonnes or more, making them around 10 times heavier than an African elephant!
An Armored Plant-Eater
Alamosaurus had some armor on parts of its body in the form of osteoderms - hard, bony plates that develop in the skin - similar to the armor on modern crocodiles. This is unsurprising, as Alamosaurus is related to other sauropods such as Saltasaurus which are known to have been armored.
Unfortunately no Alamosaurus skull has yet been found, but like other sauropods it likely had a small head for its size. Peg-like teeth have been found alongside Alamosaurus skeletons, similar to the teeth of other sauropods, which they would have used for stripping vegetation. Sauropods generally did not chew their food, but instead relied on their gut to process it. This helped to reduce the weight of the head, allowing their necks to get longer. Alamosaurus likely fed on a variety of plants present at the time such as ferns, conifers, and cycads. While there is some evidence of other sauropods, particularly from the Jurassic period, using gastroliths (gizzard stones) similar to modern birds and crocodiles, it is not yet clear whether Alamosaurus had them.
Behavior and Ecology of Alamosaurus
Alamosaurus lived alongside some of the most iconic dinosaurs of the Late Cretaceous, including Tyrannosaurus rex, the ceratopsian Torosaurus, and dromaeosaurs - relatives of Velociraptor. It also lived alongside the massive pterosaur Quetzalcoatlus, which soared through the skies above. Thanks to its sheer size, an adult Alamosaurus was probably safe from predators, though the young, sick, or elderly might have fallen prey to carnivores like T. rex. Little is known about the social behavior of Alamosaurus. While often shown traveling in herds in pop culture, there’s currently no solid fossil evidence to support this. No nests or eggs have been found either, but based on other sauropods, it likely laid round eggs about the size of grapefruits. Most researchers believe sauropods did not raise their young, instead laying many eggs in the hope that a few would survive to adulthood.References & Attributions
Image: Size scale comparing 3 different Alamosaurus specimens to a human - Steveoc 86 and Scott Hartman, CC BY-SA 3.0, via Wikimedia Commons
Image: Hypothetical Restoration of Alamosaurus - Alamotitan, CC BY-SA 4.0, via Wikimedia Commons
