John Bokma

Verifying the Weight of a Tyrannosaurus rex Skull

August 20, 2016

Today I read a post by the Tri-City Herald on Facebook regarding the arrival of a rare Tyrannosaurus rex skull at the Seattle museum. Besides the usual comments of creationists, mostly very confused about basic science, there was one person who considered the weight given a "big fish story".

To be fair, he (most likely) confused the weight of the fossil, which consists of the rock matrix and the original bone replaced with minerals that might be much heavier than the original material, with the weight of the actual skull of the Tyrannosaurus rex.

The article, Rare Tyrannosaurus rex skull arrives at Seattle museum, gave the length of the fossil as 4 foot, and the weight as 2,500 pound. Based on the photo accompanying the article I estimated the two missing dimensions on 50cm each.

Converting the dimensions to centimeters gives a volume of about 122 * 50 * 50 = 305,000 cm3. The weight, converted to grams, is about 1,133,981 g. Dividing the latter by the former and rounding it to one decimal gives 3.7 g/cm3.

Densities of Common Rocks and Minerals shows that this is not an outrageous value. For sure too high, but with two dimensions being guesses based on a photo it's not a surprise that the result is off.

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