The honest answer is: we do not know for sure which single dinosaur was the absolute largest, but the top contenders are a group of gigantic long‑necked sauropods, especially Argentinosaurus and Patagotitan , with some experts also highlighting Dreadnoughtus as the largest land animal we can measure with good confidence.

Quick Scoop

If you imagine “the largest dinosaur” as a single clear record‑holder, reality is messier. Fossils are often incomplete, so paleontologists must estimate length and weight from a handful of bones.

Most scientists point to titanosaurs (a group of huge, long‑necked herbivores) as the biggest land animals ever. Within that group, several species are in the running:

  • Argentinosaurus – frequently cited as the largest dinosaur ever, with length estimates of roughly 37–40 meters (about 121–131 feet) based on the size of its vertebrae and other bones.
  • Patagotitan mayorum – a titanosaur from Patagonia, reconstructed at about 37 meters (around 122 feet) long and roughly 70–77 tons in mass.
  • Dreadnoughtus schrani – about 26 meters (85 feet) long and around 59–65 tons, and crucially, it has one of the most complete skeletons among the giants, so its size is considered one of the best‑measured.
  • Other fragmentary giants like Maraapunisaurus and Bruhathkayosaurus might have been even bigger, but their fossils are very incomplete or partly lost, so they remain speculative.

So, depending on how you define “largest”:

  • Best candidate for overall largest (based on current reasonable estimates): Argentinosaurus.
  • Largest well‑measured land animal (most complete skeleton): Dreadnoughtus.
  • One of the biggest with a life‑size museum mount : Patagotitan , the titanosaur displayed at the American Museum of Natural History.

In short, the largest dinosaur we know of was almost certainly a titanosaur like Argentinosaurus or Patagotitan, but because the fossils are incomplete, scientists still debate which individual species truly holds the crown.