Alamosaurus

Alamosaurus was one of the last great sauropods to inhabit North America, just before the Cretaceous mass extinction. It is a key figure for understanding the ecological changes at the end of the age of dinosaurs.

🦕 Basic Info

• Scientific and common name: Alamosaurus sanjuanensis – Alamosaurus
• Meaning of the name: “Ojo Alamo Lizard” (after the Ojo Alamo geologic formation, not the Alamo fort)
• Geological epoch or period: Late Cretaceous (~70 to 66 million years ago)
• Location of discovery: Southwestern United States (Texas, New Mexico, Utah)
• Classification:
  • Kingdom: Animalia
  • Phylum: Chordata
  • Class: Reptilia
  • Order: Saurischia
  • Family: Saltasauridae
  • Genus: Alamosaurus
• Diet: Herbivore

🧪 Main Characteristics

• Size: A colossal giant, with length estimates of 28 to 30 meters and a weight of 70 to 80 tons, rivaling the largest titanosaurs of South America.
• Neck and tail: It had an extremely long neck that allowed it to reach the highest foliage, and a long tail that acted as a counterbalance.
• Armor: Like many titanosaurs, it is very likely that it had osteoderms (bony plates) embedded in its skin, which provided armor against predators.
• Body: A very robust and massive build, with columnar legs to support its immense weight.
• Posture: It had a “wide-gauge” posture, with its legs set far apart from the body, which gave it great stability.

🌍 Environment in which it lived

• Habitat: A floodplain with a system of rivers and forests.
• Climate: The climate was warm and semi-arid, with well-marked seasons.
• Ecosystem: It was the dominant herbivore of its ecosystem in southern North America. Its immense size in adulthood made it practically immune to attacks from Tyrannosaurus rex.
• Vegetation: It fed on enormous quantities of vegetation, mainly from the tops of trees like conifers.

🧬 Evolutionary Transition

• Role: It represents a successful invasion of South American titanosaurs into North America at the end of the Cretaceous.
• Relationship: It is an advanced member of the Saltasauridae family, closely related to titanosaurs from South America like Neuquensaurus and Saltasaurus.
• Biogeography: Its presence in North America is crucial proof of the existence of a land bridge (the Isthmus of Panama) that connected both continents at the end of the age of dinosaurs, allowing this migration.
• Survivor: It was one of the last sauropod genera to exist, living right up to the Cretaceous-Paleogene mass extinction event.

🦴 Fossils Found

• Material: It is known from numerous remains, although most are fragmentary. However, recent discoveries of more complete specimens have allowed for estimating its colossal size.
• Discovery: The first bones were discovered in 1921 by paleontologist Charles W. Gilmore.
• Condition: For a long time, it was thought to be a medium-sized sauropod, until the discovery of gigantic vertebrae and limb bones in the 21st century revealed its true nature as one of the largest dinosaurs.
• Relevance: It is a key fossil for understanding dinosaur migrations between the American continents and the composition of the last ecosystems of the Mesozoic.

👪 Relationship with other species

• Dinosaurs: It coexisted with the super-predator Tyrannosaurus rex and Dryptosaurus, as well as the ceratopsids Torosaurus, Triceratops, and Bravoceratops. It also shared its habitat with ankylosaurs like Nodocephalosaurus, and with ornithopods like Edmontosaurus.
• Reptiles: It shared the rivers and swamps with the giant crocodile Deinosuchus and turtles like Adocus.
• Amphibians: Aquatic environments were inhabited by amphibians such as frogs and salamanders.
• Fish: The river systems were populated by fish like the gar (Lepisosteus) and the freshwater ray (Myledaphus).
• Mammals: It lived alongside a great diversity of mammals, such as the marsupial Didelphodon and the multituberculate Mesodma.
• Birds: Primitive birds could be seen in the skies, along with the largest pterosaur (flying reptile) of all time, Quetzalcoatlus.