Tyrannosaurus rex

[DinoFan83]

I'd like to post some food for thought on the sizes of UCMP's 2 most famous Tyrannosaurus specimens (UCMP 137538 and UCMP 118742), as well as the 'giant' skull MOR 008, for those who do not know.

UCMP 137538:
These writeups by SpinoInWonderland should be plenty sufficient to show why it is nowhere near as large as often thought. Not to mention this supports these.
http://sauropodomorphlair.blogspot.com/2...eally.html
https://www.deviantart.com/spinoinwonder...-370912332
https://www.deviantart.com/spinoinwonder...-373140864

UCMP 118742:
This maxilla's giant size was based on a combination of an incorrectly extrapolated growth trajectory and a misconception about its age. According to the Theropod Database, the maxilla is 81 cm long, which is over 6% smaller than Sue's 86.1 cm maxilla. And based on the mean estimate of 7900 kg for Sue I have calculated in this thread, UCMP 118742 would have been around 6600 kg. In fact, its maxilla is barely any larger than that of MOR 555 (80 cm), and judging by the fact that both were estimated at age 16 in Erickson et al. 2004, I would consider MOR 555 to be the best base.
Going off of the estimation for MOR of 6000 kg in Bates et al. (2009), UCMP 118742 ends up at 6200 kg - substantially smaller than Sue. And given that it's already an adult judging by the age estimation, there is no need to apply any growth rate for it. This is also worth a read.

MOR 008:
This is commonly famed as being the largest known Tyrannosaurus skull and larger than that of Sue. However, this is almost certainly not the case, for the following reasons:
-The skull's giant size appears to be based on poorly restoring the missing pieces; Scott Hartman agrees with this.
-Following the Theropod Database, the maxilla and dentary (72 and 88 cm) are substantially smaller than those of Sue (86.1 and 101 cm) as well as MOR 555 (80 and 99 cm), and aren't even much larger than those of the 6600-6900 kg AMNH 5027 (71 and 85 cm) or the 600-700 kg CM 9380 (69.5 and 85 cm). Going by this, even if MOR 008 was a smaller headed specimen I find it difficult to envision it exceeding 7000 kg, and it could well have been larger headed meaning possibly >5000 kg for it.

Hopefully this helps to clear up any misconceptions on these 3 specimens' sizes. Reply