How big was Priconodon crassus

[Vladimír Socha]

Priconodon is a genus of ankylosaurian dinosaur known from its large teeth and some isolated bones from the Aptian-Albian age Lower Cretaceous Arundel Formation and the Potomac Group in Maryland (around 113 mya). Only rough size estimation has been done due to the scarcity of described remains, but it was probably one of the largest thyreophorans known to science (according to some internet sources, perhaps up to 13.7 meters long and almost 30 tonnes)! These estimates remain highly doubtful, however. Would ankylosaurian heavier than Apatosaurus be even viable and anatomically functional?

I suppose the largest well known thyreophoran is still Ankylosaurus magniventris (specimen CMN 8880), with the lenght of 7.6-10.0 meters and the weight of 7.95 tonnes, BTW?

References:

Benson, R. B. J.; et al. (2014). Rates of Dinosaur Body Mass Evolution Indicate 170 Million Years of Sustained Ecological Innovation on the Avian Stem Lineage. PLoS Biology. 12 (5): e1001853.

Carpenter, K. (2004). Redescription of Ankylosaurus magniventris Brown 1908 (Ankylosauridae) from the Upper Cretaceous of the Western Interior of North America. Canadian Journal of Earth Sciences. 41 (8): 961–86.

Benson, R. B. J.; et al. (2018). Cope’s rule and the adaptive landscape of dinosaur body size evolution. Palaeontology. 61 (5): 13–48.

Lipka, T. R. (1998). The Affinities of the Enigmatic Theropods of the Arundel Clay Facies (Aptian), Potomac Formation, Atlantic Coastal Plain of Maryland. In Lucas, S. G.; Kirkland, J. I.; Estep, J. W. (eds.). Lower and Middle Cretaceous Terrestrial Ecosystems. New Mexico Museum of Natural History and Science Bulletin, 14. Albuquerque: New Mexico Museum of Natural History and Science. pp. 229–234.

Marsh, O. C. (1888). Notice of a new genus of Sauropoda and other new dinosaurs from the Potomac Formation. American Journal of Science. 135: 89–94.

Clark, W. B. (1897). Outline of present knowledge of the physical features of Maryland (Report). Volume Series. Vol. 1. Maryland Geological Survey. pp. 172–188.

Coombs, Jr., W. P. (1978). The families of the ornithischian dinosaur order Ankylosauria. Palaeontology. 21 (1): 143–170.

Canale, J. I.; et al. (2022). New giant carnivorous dinosaur reveals convergent evolutionary trends in theropod arm reduction. Current Biology. 32 (14): 3195–3202.e5.

Arbour, V. M.; Mallon, J. C. (2017). Unusual cranial and postcranial anatomy in the archetypal ankylosaur Ankylosaurus magniventris. FACETS. 2 (2): 764–794.

Paul, G. S. (2019). Determining the largest known land animal: A critical comparison of differing methods for restoring the volume and mass of extinct animals. Annals of the Carnegie Museum. 85 (4): 335–358.

[Thomas Richard Holtz]

Consider this size estimate with extremely large error bars. It is true that the teeth and the vertebrae exceed the size of Peloroplites  (which at present seems to be a close relative). The sizes you see posted are based on linear extrapolations which don't really include allometry. 

So it is definitely big, but I personally don't think it is quite as big as the recent estimates suggest.

All that said, the material is so limited most of this is just speculation.

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[Nick Gardner]

Plus we have to consider the impact of how being graviportal affects size estimation. We can end up with erroneous mass estimations as a result of this. 

But Dr. Holtz raises a good point-- Error bars are often not appreciated when they need to be within the world of paleontology, especially with megafauna. We often cannot know how big something else, and often size estimations (whether mass estimation, body length, whatever) may carry particularly large error bars. And worse, sometimes very good attempts to very meticulously constrain these estimates may still carry wide error bars and then be criticized for that without consideration that prior seemingly confident estimations had much larger error bars, but this information was not presented/considered.