The Alamosaurus was an enormous dinosaur that roamed the earth about 72 to 66 million years ago. This lies right towards the end of the Cretaceous Period, in the Maastrichtian age. All of the dinosaurs became extinct about 65 million years ago, due to the Cretaceous Paleogene extinction event. Thus, it could possibly have been one of the last non avian dinosaurs to exist on the earth. Its fossils were discovered all throughout the southwestern region of the United States.
The size of the Alamosaurus was gigantic. Its length is estimated to be about 16 meters from snout to tail and its weight was expected to be between 45 and 60 tons. This would make one of the largest known North American dinosaurs. Some of the biggest known dinosaurs originate from South America, like the Argentinosaurus. Hence, some scientists believe that the Alamosaurus could have evolved in South America and then migrated to North America whilst the two continents were connected.
The Alamosaurus was a sauropod, and thus plant eating. Its young ones were likely predated upon by the larger Cretaceous theropods, but apart from that it remained unchallenged.
The Alamosaurus was named after the Ojo Alamo Formation, where its holotype was discovered. Many texts and reports claim that it was named after the Alamo Fort in Texas, or after the town of Alamo Mission in San Antonio. But this is untrue. The suffix 'saurus' is derived from the Greek word 'sauros' which translates to lizard in English. Thus, the name denotes 'the lizard from Alamo'.
The species name A. sanjuanensis is derived from the San Juan County of New Mexico, where the fossils of the dinosaur were first discovered.
The nomenclature of the remains was performed by scientist Charles Gilmore in the year 1922.
Discovery and nature of fossils
- The holotype of the Alamosaurus was excavated in the Oja Alamo Formation (or Kirtland Formation, depending upon the definition used) in the year 1922. At that time, a single scapula and both halves of the pelvic girdle were discovered. The bones were found in the Naashoibito member of the rock formation.
- In the year 1946, Gilmore found some more bone fragments in the North Horn Formation of Utah, which were attributed to the Alamosaurus. They consisted of all the coccygeal vertebrae of the tail, an undisturbed right forelimb which lacked digits and both the ischia of the hip.
The middle coccygeal vertebrae had elongated centra and lateral fossae that resembled those of the Saltasaurus and the Malawisaurus. But even these bones were not enough to accurately describe the size of the Alamosaurus.
- A juvenile specimen was discovered in the later 2000s in the Black Peaks Formation of Texas, which is attributed to the Alamosaurus, and it is the most complete sample acquired yet. Based on the dimensions of the limb bones of this juvenile specimen, the size of the dinosaur was estimated by scientists. They found that it was possibly as large as the South American titanosaurians.
- No skull bone has yet been attributed to this dinosaur; but a few loose teeth have been.
The Alamosaurus is classified under suborder Sauropodomorpha, clade Titanosauria and family Saltasauridae. Titanosaurians were large sauropods that existed on the earth from the late Jurassic period to the end of the Cretaceous. It is also included in the subfamily Opisthocoelicaudiinae, which includes titanosaurians that lacked wrist bones and digits. This explained the conspicuous absence of phalanges in the skeletal remains of the Alamosaurus.
Charles Whitney Gilmore was a vertebrate paleontologist who worked for the Smithsonian for over 40 years. He has classified and named the remains of many dinosaurs, which include the Apatosaurus, Diplodocus, Alamosaurus and Brachyceratops among many other.
Gilmores' first assignment was to sort out the bones collected by O. C. Marsh during the famous competition with E. D. Cope. He later undertook numerous excavation expeditions during his tenure at the Smithsonian and raised many notable exhibits there such as the famous Diplodocus longus display. He has published almost 200 scientific papers in his career.
The turtle Gilmoermys was named in his honor.
- As mentioned before, the Alamosaurus was one of the largest known dinosaurs. Its length, to the tip of its tail was about 52 feet. Some scientist speculate that it could grow as long as 79 feet. Its height, when the neck was raised, was a staggering 29 feet, again, which could have been as much as 41 feet.
Its weight is projected to be around 50,000 to 60,000 kilos.
- The neck of the Alamosaurus was very long, about 1/3rd the length of its entire body.
- It had a small head, just like the other titanosaurians.
- Its legs were thick and muscular.
- It had long tail that was stout at the base and tapering towards the end.
- Although dismissed initially, scientists today believe that the Alamosaurus was armored. This conclusion was drawn from the fact that it is closely related to the Saltasaurus, which was armored. Furthermore, the juvenile specimen that was discovered recently displayed evidence of such armoring. This protective layer is basically bony deposits underneath the skin in the form scales or plates, similar to those shown by modern crocodiles.
Due to the armor being embedded in soft tissue, it is very difficult to judge its presence or absence based on the scarce fossil evidence that the Alamosaurus has.
Habits and habitat
The Alamosaurus was herbivorous dinosaur. It used its long neck to forage leaves and vegetation from atop tall tree. Due to its sheer size and weight, it had a slow gait and could not run very well. While the nesting grounds and eggs of other titanosaurians have been found, no such data exists for the Alamosaurus.
The habitat of this dinosaur consisted of semi-arid plains with water available intermittently in the form of lakes and swamps.
Related and coexisting species
The Alamosaurus is related to the Saltasaurus, Gondwanatitan and Malawisaurus.
It likely coexisted with the Tyrannosaurus, Kritosaurus, and Torosaurus. Its fossils have, on many occasions, been found with those of Quetzalcoatlus.
The concluding notes
The recently discovered specimen of the Alamosaurus has shown that was biggest known North American dinosaur. It is possible that this dinosaur was present on the right till the Cretaceous Paleogene Extinction Event. This indicates that dinosaurs could have continued their dominance on the earth but for the extinction event.
Its discovery was key in understanding North American titanosaurians.