Tyrannosaurus rex

[DinoFan83]

There is a great deal of contention over the average size of known adult T. rex specimens, so I took a moment to calculate what I could from known data. 

Here are all the adult T. rex specimens I could find data on (adult meaning 15 years or older, as this is when T. rex virtually stops growing) to get an idea of average size of known specimens. 
The proxy on which this is based will be femur length, with all bone measurements for both preserved and estimated femur length taken either from Tyrannosaurus Rex, the Tyrant King or the Theropod Database (unless stated otherwise of course).  

Tyrannosaurus Rex, the Tyrant King has a very helpful table of T. rex bone measurements, including femoral dimensions (link). With the exception of BHI 4100, all the listed measurements are from adult specimens, as per the Theropod Database.
 
Note, however, that some of the specimen measurements differ from what is given elsewhere and more recently for them. Specifically, the femoral lengths of CM 9380 and BHI 3033 are 128 and 127 cm as per Scott Hartman, MOR 1125's femur is 107 cm as per Schweitzer et al. (2016), and Sue's femur is 132.5 cm as per the Theropod Database, so I will be using those respective figures for them.

I will also be including femur length figures for some specimens either not listed in the table or listed in the table and preserving femora but not having the femora listed. Namely, those are Scotty (133 cm), Bucky (116 cm), MOR 009 (114.3 cm) and DMNH 2827 (111 cm).

Finally, there are very complete specimens like Tristan, Victoria and Trix that preserve femora but are awaiting description. They will be included in the sample when that happens.

The average of specimens known from femora:  

Adding all the measurements up results in a total femur length average of about 119.9 cm (129.5+120+99+121+120+116+118+119+111+118+128+132.5+123.2+127.5+107+126+127+114.3+133+111+116 equals 2517, divided by 21).
However, there are some specimens that have to have their femoral lengths estimated one way or the other (for example, specimens that don't preserve femora or don't have complete femora), and I will calculate a potential femur length for them so they can be included in the sample.

Estimates of femur length for less complete specimens:

The specimens whose femoral length I will be estimating based on other specimens are MOR 008, LACM 23844, AMNH 5027, BHI 4182, UCMP 118742, BHI 6231, BMNH R7994, and NHM R8001. Sue will be used as a base for all due to its completeness and resultant overlap with every specimen here.
 
-MOR 008 has a maxilla and dentary 72 and 88 cm respectively, compared to the 86.1 and 101 cm maxilla and dentary in Sue, the mean of which results in a 113.3 cm femur.
 
-LACM 23844 has a 92 cm dentary compared to 101 cm in Sue, which results in a 120.7 cm femur.
 
-AMNH 5027 has a dentary and ilium 85 and 151.5 cm respectively, compared to the 101 and 146 cm dentary and ilium in Sue, the mean of which results in a 126.9 cm femur.
 
-BHI 4182 has a 91 cm dentary compared to 101 cm in Sue, which results in a 119.4 cm femur.  

-UCMP 118742 has an 81 cm maxilla compared to 86.1 cm in Sue, which results in a 124.7 cm femur.    

-BHI 6231 has a 36 cm humerus compared to 39 cm in Sue, which results in a 122.3 cm femur.

-BMNH R7994 has a femur 49 cm in circumference compared to Sue's 58 cm (only circumference listed but no length, probably meaning an incomplete femur that needs a length estimate), which results in a 111.9 cm femur.

-NHM R8001 has a femur with the same situation as that of BMNH R7994, which results in another 111.9 cm femur.  
 
Adding these estimates up results in an average of about 118.9 cm (113.3+120.7+126.9+119.4+124.7+122.3+111.9+111.9 equals 951.1, divided by 8).  

Overall Average:  

Adding up all known and extrapolated femur lengths and then dividing them by the sample size (2517 plus 951.1 equals 3468.1, divided by 29) results in a mean femur length of about 119.6 cm. This is approximately 6000 kg based on Sue, which is 8200 kg (my mean estimation on page 13) with a 132.5 cm femur.
  
Therefore, based on this, the average adult T. rex going by known specimens is about 6000 kg. Not exactly as large as some people may have thought, but it most certainly isn't small - assuming this is correct, T. rex would average the size of an African bush elephant bull. Reply