The size of Tyrannosaurus Rex

Alright, figured i would get this one done as i have more to work with as opposed to other creatures i've highlighted.

We have a larger list of specimens to work with for the species, some of the more complete ones that i'm going to base some of my math on are:

CM 9380

AMNH 5027

"Black Beauty"( RTMP 81.6.1)

"Wankel's Rex"(MOR 555)

"Stan"(BHI 3033)

Peck's Rex( MOR 980)

"Sue"(FMNH PR 2081)

"Bucky"

I will be excluding "Jane" as i believe She represents a subadult Nanotyrannus.

Note that we have many more tyrannosaurus specimens in decent condition, so guessing at its size is much easier then the other large carnivores i've covered. We have young adults(Bucky and Black Beauty) as well as a couple large individual Tyrannosaurus(Sue and Stan)

I will not be touching the 'Sexual dimophism in Tyrannosaurus' subject either, because only B-rex has had its gender determined, and it's a female.

Not to any ones suprise, but right now we start with sue. Sue isn't really way bigger than tyrannosaurus specimens. It is still the largest (and the heaviest) relatively complete Tyrannosaurus though. Sue is slightly taller than holotype due longer femur. Some specimens like MOR 980 are nearly as long as sue. It isn't impossible that there might larger tyrannosaurus than sue. Although intial estimates put her at 12.8 meters, a more realistic estimate wasplaced in somewhat recent years(12.3 meters). 

Saying sue is the largest tyrannosaur because she is the 'largest' our of some thirty individuals is, in my opinion, ridiculous.  Sue is not incredibly bigger than other specimens. Also, Sue might be the only known T. rex that has reached asymptotic size, all other specimens are over 5 years younger or so, how can we be so sure that Sue's size is not average for a specimen of its age? it's like if we found a 40 year old bull elephant and call it a freak because of its size when all the other elephants we've found were around 25-30 years old (thus just finishing their rapid growth phase). 

For example, let's look at UCMP 137538, a pedal phalanx that supposedly rivals the size of sue.

Oh, really?

UCMP 137538's phalanx IV-2 13 cm
FMNH PR2081's phalanx IV-2 11,1 cm
UCMP's bone is over 17 % bigger than the same bone in Sue.
Sue length: 12.3 m
UCMP 137538 estimated length: ~14.4 m 
wait...

That one actually took me by suprise good deal. Assuming that pedal phalanx isn't infected, and actually belongs to a tyrannosaurus, it is indeed larger then Sue.

The chances of this individual a fossilized freak are ridiculously low.

Don't forget that tyrannosaurs specimens show osteogenetic changes.
The owner of this bone wasn't necessary 15 m, though still possibly bigger than Sue.

Also, for the claims of this thing belonging to another large predator, There's no evidence so far suggesting there is another large predator in hell creek formation, aside from Tyrannosaurus "X", and Nano. Most scientists do not separate T. X, and nano is not big enough. T. rex is the most logical conclusion. While you state alternatives of slim possibilities, none has been proven to be more probable. 

UCMP 137538 isn't the only T. rex specimen that might be larger than Sue. MOR 1126 a.k.a C. rex (Celeste), UCMP 118742 (however based on Sue, it would be slightly smaller than FMNH, but based on holotype CM 9380 or AMNH 5027, it would be ~13.6 m in length or more) and MOR 008, which skull is around 10 cm bigger than in Sue. 

Now, going into the implications of the supposed maxilla/ size ratio, we can get some sort of idea of how large the specimens mentioned at the beginning of this post are.

Maxilla size/body ratio provided by Frank Fang.

1- AMNH 5027- 22 years old, 12.5 meters, skull length 1.36 meters. Based on AMNH 5027, UCMP 118742 would be around 14.19 meters.

2 - Mor 008- 22 years old (maxillary 720mm). Base on that, UCMP 118742 would be 15.4 meters long.

3 - MOR1125(B-rex) 18 years old, 10.54 meters (maxillary 680mm). Based on that UCMP 118742 would be 12.5 meters.

4 - Stan (BHI 3033) 18 years old, 11.9 meters (maxillary 775mm). Based on that, UCMP 118742 would be 12.56 meters.

5 - Holotype (CM 9380) 12.04 meters, 22 years old (maxilla 695mm). Based on that number, UCMP 118742 would be 14.45 meters.

6 - Peck's T.rex/Rigby's T.rex (MOR 980) 21 years old, 12.8 meters (maxilla 770mm). Based on that, UCMP 118742 would be 13.46 meters.

7 - MOR 555 22 years old 12.4 meters (maxilla 798mm). Based on that, UCMP 118742 would be 12.59 meters.

Fang's measurements account for cartilage that was supposedly on and around the tail when these creatures when they were alive, which is quite baseless imo. Half a meter should be deducted off of the total lengths of each i believe....so i did the math on it :D

1.)AMNH 5027- 22 years old, 12.0 meters, skull length 1.36 meters. Based on AMNH 5027, UCMP 118742 would be around 13.8 meters.

2.)Mor 008- 22 years old, 12.4 meters(maxillary 720mm). Base on that, UCMP 118742 would be 15.4 meters long.(!)

3.)MOR1125-  18 years old, 10.54 meters (maxillary 680mm). Based on that UCMP 118742 would be 12.5 meters.

4.) BHI 3033-18 years old, 11.9 meters (maxillary 775mm). Based on that, UCMP 118742 would be 12.56 meters.( this one is actually quite close)

5.) CM 9380-  12.04 meters, 22 years old (maxilla 695mm). Based on that number, UCMP 118742 would be 14.06 meters.

6.) MOR 980 - 21 years old, 12.3 meters (maxilla 770mm). Based on that, UCMP 118742 would be 12.8 meters.

7.) MOR 555 22 years old 11.8 meters (maxilla 798mm). Based on that, UCMP 118742 would be 12.05 meters.

The 15 meter result one doesn't hold as much water, for me anyways. A 15m T. rex is not impossible, you could even argue it is probable, but there is no evidence for it at now, and these speculations on potential maximum size apply to other species even more so.

Basing off of the numbers, and the sizes of the individuals aforementioned in the post, my calculations put the average tyrannosaurus at 11.56 meters and 7 tons in weight.

The fact that Tyrannosaurus did not stop growing, does not mean animals as large as 15 m are plausible, a maximum size around 12-13 m seems more plausible, but a 15 m long one would need a different bone structure to allow the massive animal to support its own weight, and Tyrannosaurus certainly was not built to reach that size.

Here's a size chart with multiple tyrannosaurus specimens, photo credit goes to Scott Hartman.

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