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Estimating Total Length, Body Mass and Bite-Force

Posted by MBetancourt on 19 Feb 2015 at 23:19 GMT

Hi, I think I found a mistake in your publication, on page 5 of your publication you wrote: "It is an almost complete skull (DCL or “Skull length" = 1400mm)" and this measurement becomes the base of your body length, mass and bite force estimates however this measurement is not DCL (dorso cranial length) which Verdade (2000) defines as "anterior tip of snout to posterior surface of occiptal condyle". According to Bocquentin-Villanueva et al. (1989) and Aguilera et al. (2006), the 1400mm measurement for UFAC 1403 is "maximal skull length", figure 3 of Bocquentin-Villanueva et al. (1989) and your own figure 2 also agree that 1400mm is from the tip of the snout to the quadrates not DCL, the actual DCL of this skull appears to be approximately ~1220mm based on said figures.

Making this correction your estimates go down to 10.9m TTL, 5.6 metric tons of mass and 52,500 N bite-force, but the use of equations based on Caiman latirostris might be in error, while it is indeed closer phylogenetically its proportional snout length is very different at 54% of DCL according to the data in the appendix of Verdade (2003) while in P. brasiliensis this ratio is about 70% of DCL, the snout is proportionally much longer in the later thus equations based on this particular caiman are bound to overestimate the size of Purussaurus. Given those snout proportions, the American alligator seems like a much better model.

There's also something curious about your equations, why do they estimate an SVL 66% of total length? no living crocodilian has this proportions, SVL is always around 50% of TTL, Verdade (2000) original equations agree that this is too the case for the broad-snouted caiman.

Aguilera OA, Riff D, Bocquentin-Villanueva J (2006) A new giant Purussaurus (Crocodyliformes, Alligatoridae) from the Upper Miocene Urumaco Formation, Venezuela. Journal of Systematic Paleontology 4(3): 221-232
Bocquentin-Villanueva J, Buffetaut E, Negri FR (1989) Nova interpretaçao do gênero Purussaurus (Crocodylia, Alligatoridae). Anais do XI Congresso Brasileiro de Paleontologia, Curitiba, Brasil, 427– 438.
Verdade LM (2000) Regression equations between body and head measurements in the broad snouted caiman(Caiman latirostris). Revista Brasileira de Biologia 60(3):469–482.
Verdade LM (2003) Cranial sexual dimorphism in captive adult broad-snouted caiman (Caiman latirostris). Amphibia-Reptilia 24: 92-99.

No competing interests declared.