What Was the Biggest Dinosaur? Here Are the 4 Best Estimates

By: Sascha Bos  | 
Black and white photo of a fake T-rex towering over palm trees
Scientist's can't exactly go out and measure the heaviest or tallest dinosaur; they have to rely on estimates based around fossils and our current understanding of similar creatures. Glasshouse Images / Getty Images
Key Takeaways
  • Determining the biggest dinosaur involves estimating sizes based on incomplete fossil records and digital modeling.
  • Argentinosaurus, Patagotitan, Sauroposeidon and Dreadnoughtus are among the contenders for the largest dinosaur, with estimates varying based on available fossil evidence.
  • Dreadnoughtus, with a 70-percent-complete skeleton, is considered the largest accurately measured land animal, weighing approximately 65 tons (59 metric tonnes) and measuring 85 feet (26 meters) long.

Determining the biggest dinosaur is a tricky process. Dinosaurs are extinct, so scientists can't simply go out and measure the world's biggest dinosaurs.

Instead, they use digital modeling to make size estimates based on the fossils they discover. This poses a few problems.


Paleontologists continue to unearth new fossils, so the world's largest dinosaurs may not have been discovered yet. When scientists do find a fossil specimen, it's often incomplete, so size estimates may not be entirely accurate. Additionally, as archeologists unearth new specimens and develop better models for approximating size, these estimates can change.

Let's take a look at the species competing for the title of "largest dinosaur."



Argentinosaurus huinculensis is one of the largest dinosaurs ever discovered, and possibly the largest to have ever existed. It gets its name from the city where its fossilized bones were found: Plaza Huincul, Argentina.

Argentinosaurus was a titanosaur (not to be confused with the titanoboa), a group of giant sauropods that hold the title of the world's largest land animals and lived during the late Cretaceous period. Titanosaurs were plant-eaters and used their long necks to graze.


Size estimates place Argentinosaurus at 77 to 110 tons (70 to 100 metric tons) in weight and 121 to 131 feet (37 to 40 meters) in length. However, these estimates are based on just a few bones and may be inaccurate.

You can see Argentinosaurus' reconstructed skeleton at the Fernbank Museum of Natural History in Atlanta, Georgia.



Sauroposeidon proteles is possibly the tallest dinosaur, at an estimated 59 feet (18 meters) tall.

Discovered in Oklahoma in 1994, Sauroposeidon has the largest known neck vertebrae at 5 feet (1.5 meters) long. "It looked like a trunk of a tree," paleontologist Richard Cifelli told CBS News in 1999.


At the time of its discovery, some dinosaur enthusiasts thought Sauroposeidon, which lived in the early Cretaceous period, might be the world's largest dinosaur. Today, most scientists agree that, while Sauroposeidon is probably the world's tallest dinosaur, there are heavier and larger dinosaurs.

With only a few Sauroposeidon bones discovered, it's hard to know for sure.

You can see a reconstruction of Sauroposeidon's head and neck at the Sam Noble Museum in Oklahoma.



Named in 2017, Patagotitan mayorum, discovered in Patagonia, is the newest contender for largest dinosaur. It is estimated to have weighed 77 tons (70 metric tons), stood around 28 feet (8.5 meters) high at the head and was 122 feet (37.2 meters) long, and more of its bones have been found than Argentinosaurus and Sauroposeidon.

However, without a complete skeleton, it's hard to know the exact size of Patagotitan mayorum. You can see a complete reconstructed skeleton of Patagotitan mayorum at the American Museum of Natural History.



In 2014, Drexel University scientists discovered the 70-percent-complete skeleton of Dreadnoughtus schrani, "the largest land animal for which a body mass can be accurately calculated" at 85 feet long (26 meters) and weighing 65 tons (59 metric tons).

For comparison, the largest living land animal today is the African elephant. The largest animal to ever live is the blue whale (Balaenoptera musculus), which weighs 150 tons (136 metric tons) and is 98 feet (30 meters) long.


"Shockingly, skeletal evidence shows that when this 65-ton specimen died, it was not yet full grown," Kenneth Lacovara, PhD, the lead scientist in the discovery, said in a press release. "It is by far the best example we have of any of the most giant creatures to ever walk the planet."

Frequently Asked Questions

How do scientists estimate the size of dinosaurs?
Scientists estimate the size of dinosaurs using digital modeling based on the fossils they discover, though these estimates can be inaccurate due to incomplete specimens.
What are some challenges in determining the largest dinosaur?
Challenges include incomplete fossil records, the potential for new discoveries and the evolving methods for size estimation.