How Big Was Ankylosaurus Magniventris?


Ankylosaurus magniventris is one of the largest ankylosaurines, and likely the largest ankylosaurids in North America. It’s only rivals in size were Tarchia kielanae, and Saichania chulsanensis. Carpenter (2004) estimated its size to be 6.25 meters (20.5 feet) and around 3.2 tonnes (3.862 tons). Benson et al. (2014) estimated a weight of 4.8 tonnes for AMNH 5214. Arbour and Mallon (2017) estimated a length of 7.56 to 9.99 meters (24.8 to 32.8 feet) and 7.95 tonnes for CMN 8880, while they estimated AMNH 5214 to be 6.02 to 7.95 meters (19.8 to 26.1 feet) and 4.8 tonnes. The most likely estimates for its size are Arbour and Mallon’s for AMNH 5214, if it was an adult.



Saichania was estimated by Maryańska to be seven meters, later estimates were roughly the same length. Paul(2010) estimated S. chulsanensis to be 5.5 meters and two tonnes, which is unlikely, as an estimate of 6.25 meters and 4.08 tonnes was my result when I scaled.

Tarchia was mostly estimated on remains similar to Dyoplosaurus giganteus, with the holotype being one of the largest known ankylosaurids known as of February 5, 2018. The scaling from D. giganteus would result in eight meters and 5.75 tonnes, second only to Ankylosaurus itself. Paul(2010) estimated it to be 4.5 meters and 1.5 tonnes, a ridiculously low estimate. My scaling got 7.87 meters and 5.24 tonnes.

Image By Emily Willoughby (,; modifications by FunkMonk (Own work) [CC BY-SA 3.0], via Wikimedia Commons

So... what do you think? Please leave me a comment.


  • starman: Carpenter’s size estimate always seemed too small. Those other taxa, especially Talarurus, hardly rivaled Ankylosaurus in size. I recently blogged on the likely influence of T. rex on the evolution of A. magniventris.
  • Migatte:

    AFAIK, Saichania was the only taxon, alongside Tarchia, were the only ones to be the closest in size, I’ll edit that.

  • Vale: Can you tell us a bit more about it? Maybe how it got to be so big and a size comparison to other anyklosaurs?
  • Migatte:

    Starman has a blog about why A.  magniventris grew so large.

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