Alamosaurus: The Colossal Titan from the Late Cretaceous Period

In the realm of prehistoric giants, the Alamosaurus holds a special place. This colossal dinosaur, hailing from the Late Cretaceous period, has an intriguing and fascinating history. As we delve into the world of the Alamosaurus, we invite you to join us on this journey back in time, to an era when these magnificent creatures roamed the Earth. Let’s explore the life and times of the Alamosaurus, a true titan of the dinosaur world.

Alamosaurus Key Facts

Alamosaurus pronunciationa-luh-muh-saw-ruhs
Meaning of name“Ojo Alamo lizard”
Type SpeciesAlamosaurus sanjuanensis
When it Lived70.0 to 66.0 MYA
Period & TimeLate Cretaceous
EpochMaastrichtian to Lancian
Length85.3 to 98.0 ft
Height25 ft
Weight80.0 to 88.0 tons
MobilityMoved on all four
First Discovery1921 by Charles Whitney Gilmore, John Bernard Reeside and Charles Hazelius Sternberg
Location of first findNew Mexico, USA
First Described by1922 by Charles Whitney Gilmore
HolotypeSMP VP−1625

Alamosaurus Origins: Taxonomy, Timeline, and Discovery

Alamosaurus means the “Ojo Alamo lizard”. Its name is derived from the Ojo Alamo Formation in New Mexico where its fossils were first discovered. This name pays homage to the location of its discovery, while also highlighting its reptilian nature with the Greek word “sauros“, meaning lizard.

Illustration of Alamosaurus standing on all four legs, displaying its long neck and tail, with a gray and black color pattern.
image by Alamotitan is license under CC BY-SA 4.0

In the grand tree of dinosaur taxonomy, it finds its place in the group Sauropoda, specifically the family Titanosauridae, and the species Alamosaurus sanjuanensis. This classification places it among the largest dinosaurs to have ever walked the Earth, a testament to its colossal size and stature.

It lived during the Late Cretaceous period during a time when the Earth was undergoing significant changes, with the continents drifting apart and the climate becoming more varied. Amidst this changing world, this dinosaur thrived, leaving behind a legacy that continues to captivate us to this day.

A team of Smithsonian paleontologists made the first discovery in 1921 in New Mexico, USA. This discovery marked a significant milestone in our understanding of dinosaur evolution, providing valuable insights into the diversity and adaptability of these prehistoric creatures. It was later described by Gilmore in 1922, further cementing its place in the annals of paleontology.

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Fossil Evidence

Remains have been discovered throughout the southwestern United States. Charles Whitney Gilmore, John Bernard Reeside, and Charles Hazelius Sternberg discovered the holotype specimen in June of 1921. It was found at the Barrel Springs Arroyo in the Naashoibito part of the Ojo Alamo Formation (or Kirtland Formation under a different definition) of New Mexico. This formation was deposited during the Maastrichtian age of the Late Cretaceous period.

Photograph of an Alamosaurus skeleton displayed in a museum, with its long neck extending upwards, surrounded by other dinosaur fossils and exhibits.
image by Rodney is license under CC BY 2.0

Bones have also been recovered from other Maastrichtian formations, like the North Horn Formation of Utah and the Black Peaks, El Picacho, as well as Javelina Formations of Texas. Undescribed titanosaur fossils closely associated with Alamosaurus have been found in the Evanston Formation in Wyoming.

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Physical Characteristics of the Alamosaurus

This was a gigantic quadrupedal herbivore characterized by a long neck, long tail, and relatively long limbs. Its body was covered at least partly in bony armor. It was a titan among dinosaurs, with estimates suggesting a total length of 30 meters (98 ft) or more and an approximate weight of 72.5–80 tonnes (80–88 tons) or more.

Scale chart comparing the size of three Alamosaurus specimens (BIBE 45854, USNM 15560, TMM 43621-1) to human figures, illustrating the significant size differences among the specimens, with the largest reaching up to 10 meters in height.
image by Steveoc 86 and Scott Hartman is license under CC BY-SA 3.0

Most of the complete remains come from juvenile or small adult specimens. However, three fragmentary specimens suggest that adult Alamosaurus could have grown to enormous sizes. The size is comparable to the largest known dinosaurs, like Argentinosaurus. Its estimated weight is around 80 tons.

Paleontologists have never found a skull from the Alamosaurus. However, rod-shaped teeth have been found with skeletal remains that are believed to belong to this dinosaur. The vertebrae from the middle part of its tail had elongated centra. It had vertebral lateral fossae–indentations along relatively flat areas of bone–that resembled shallow depressions.

The Alamosaurus in its Natural Habitat and Environment

As a creature of its environment, it perfectly adapted to the conditions of the Late Cretaceous period. The environment during this time was diverse, with a mix of coastal and inland regions, forests, and plains. The climate was warm, and the vegetation was lush, providing ample food for this herbivorous dinosaur.

As an herbivore, it fed on the abundant plant life of its time. It likely used its long neck to reach the tops of trees, feasting on leaves and branches that were out of reach for smaller dinosaurs. It was a quadruped, moving on all fours. This, combined with its massive size, would have made it a formidable presence in its environment. It was likely a social creature, living in herds for both protection and companionship.

Interesting Points about Alamosaurus

  • This is the only sauropod found in North America from the Late Cretaceous period.
  • Despite its massive size, it had a relatively small head.
  • It had a long, whip-like tail that it likely used for defense against predators.
  • Bony, armor-like structures known as osteoderms covered the dinosaurs’ body.
  • It likely lived in herds, moving through the landscape in search of food and water.

Contemporary Dinosaurs

In the grand theater of the Late Cretaceous period, this titan of its time shared the stage with a cast of remarkable contemporaries. Each of these Laramidian dinosaurs, distinct and unique, played their part in the symphony of existence in a changing ecosystem. 

Two such contemporary dinos were the Tyrannosaurus and Triceratops. Both of these dinosaurs really epitomize the Late Cretaceous. The Tyrannosaurus, a predator of legendary proportions, may have posed a threat to a young or injured Alamosaurus. However, the adult Alamosaurus would have been a challenge even for the mighty Tyrannosaurus due to its indomitable size and towering height. The Triceratops, on the other hand, was an herbivorous dinosaur like the Alamosaurus. Despite their shared dietary preferences, the two species occupied different ecological niches which would have reduced competition and allowed both to flourish.

The Edmontosaurus, another herbivore, also roamed the same landscapes as the Alamosaurus. This dinosaur likely occupied different feeding levels, with the Alamosaurus browsing on high tree foliage and the Edmontosaurus grazing on lower vegetation. This separation of feeding habits would have allowed these two herbivores to coexist without significant competition, each contributing to the balance of their shared ecosystem.

The Alamosaurus and its contemporaries each played their part in this ecosystem. Moreover, their coexistence paints a vivid picture of the rich biodiversity and dynamic environments of the Late Cretaceous period.

Featured Image Credit: Alamotitan, CC BY-SA 4.0, via Wikimedia Commons


Please note that the information in this article is based on various sources, drawing on scientific research, fossil evidence, and expert analysis. We aim to provide a comprehensive and accurate overview of the dinosaurs as our knowledge about them evolve.

Article last fact checked: Joey Arboleda,06-09-2023