The Morrison Titan - Part 2: Not a Diplodocus clone

In my previous post, I mentioned that Amphicoelias' known bone proportions are different from those of Diplodocus. But sadly, most reconstructions don't seem to recognize it.

Um, Carpenter, that's a big Diplodocus clone.

They don't seem to portray the actual Amphicoelias at all. They're just Diplodocus copies. They ignore the actual proportions of the animal, flying in the face of what the known fossils suggest. Let's see what's known from the Amphicoelias holotype again:

How do these compare to Diplodocus? Turns out, they're not really clones of one another.

Well, we'll start with the vertebrae.

Amphicoelias seems to have a proportionally larger neural arch compared to it's centrum than Diplodocus does. Amphicoelias also has a proportionally narrower centrum than Diplodocus. The proportional lengths of their centra are similar, though. Their neural arches, by themselves, are also similar in overall proportions.

Next, the pubis.

It's massive in proportion. Amphicoelias' pubis just blows Diplodocus' one out of the water. The 10th dorsal of Diplodocus carnegii CM 84 measures about ~26.7 centimeters long, while that of Amphicoelias altus measures about ~24 centimeters long, a little shorter than the D. carnegii centrum, however, this is due to the differing shape of the centra as preserved. Overall, the centra are essentially the same size aside from width. However, the pubis of A. altus measures about ~1.17 meters long, while that of D. carnegii is about ~1 meter long. Despite having similarly-sized posterior dorsal centra, A. altus has a significantly larger pubis. This is indication of a massive hip, and subsequently, a deep torso.

Then we get to the femora.

The femura of A. altus are notably long, with the complete right femur measuring at ~1.77 meters in length. By comparison, D. carnegii CM 84 has a femur about ~1.54 meters long. Keep in mind that D. carnegii's 10th dorsal centra is similar in size to that of A. altus. This is a clear indication of longer limbs than Diplodocus proportionally, and in the case of D. carnegii, also in absolute terms.

Another way to look at it would be to scale a Diplodocus reconstruction to the provided measurements of the individual bones, treating them as separate individuals, then comparing the results to see how much they differ.

The skeleton of Diplodocus carnegii CM 84 is estimated to be approximately ~26 meters long. Since the anterior dorsal centra of CM 84 and A. altus are about the same size, scaling CM 84 to the A. altus dorsal would give an animal practically identical in size. However, scaling CM 84 to the A. altus pubis then gives a size about 17% larger in linear dimensions, or about ~30.4 meters or so. Scaling CM 84 to the A. altus femur gives an animal about ~29.9 meters long, or about ~15% larger in linear dimensions. This is another pretty good indicator that the two diplodocoids differed quite a bit in their bodily proportions.

All in all, this animal isn't really proportioned that similar to Diplodocus. It's clearly something else.

Overall, the resulting animal would be a deep-chested, long-limbed one. It would be proportionally narrower since their proportional width across the diapophyses (the "wings" of the neural arch) are similar, while the hips and the body suggested by it are deeper and the legs longer. Tall, but not rotund. At least, for Amphicoelias altus.

What about the giant Amphicoelias fragillimus? Would it have had similar proportions? Where would it differ? As of now, we lack the data needed to give a truly concrete answer. It would depend on the affinities of A. fragillimus in the sauropod family tree, and how close it would be to A. altus. That would be the subject of the next post.

The Morrison Titan - Part 1

Argentinosaurus is commonly considered to be the largest dinosaur.

If not it, some giant Cretaceous gigapod such as Puertasaurus is given the crown. Nowadays, it seems that whether the question of what is the largest known dinosaur is brought up, most people would answer with something within Titanosauria and from the Cretaceous period. In 2014, the bones of an unnamed gigantic titanosaur, with a femur requiring three forklift pallets to hold, has been unearthed and a skeletal mount of it, restored with speculative portions, has been placed on display.

 But do the Cretaceous titanosaurs really hold the crown?

Likely not so.

A few brachiosaurs such as Breviparopus and Ultrasauripus possibly rival or exceed the sizes of supergiant titanosaurs like Argentinosaurus or Puertasaurus.

Even the good old Brachiosaurus altithorax could probably reach Argentinosaurus-esque sizes, as a large specimen (~2.42-meter humerus) in the BYU collections (Paul, 1988) suggests. This B. altithorax specimen probably massed over 70 tonnes, vindicating Walking With Dinosaurs' Brachiosaurus mass figure.

The giant Oklahoma Apatosaurus ajax specimens, which probably massed between ~50-60 tonnes or so, aren't even fully grown, they lack cervical rib fusion, which corresponds to roughly ~80% of fully-grown adult dimensions in Diplodocus and Giraffatitan. It's probable that Apatosaurus ajax adults reached the 100-tonne mark, surpassing Argentinosaurus and possibly rivaling Puertasaurus in size.

But how about something larger than even them? It turns out that such creatures probably existed. Three are known, but one is known only from a footprint (~1.5-meter wide footprint in Plagne, France). That'll be a story for another time. Another is known from an incomplete sacrum ("Brachiosaurus" nougaredi from North Africa), which will also be a story for another time.

One day, in 1878, during the Bone Wars, Edward Drinker Cope discovered the bones of a sauropod dinosaur in the Morrison Formation. He named the animal Amphicoelias, meaning "double hollow", "amphi" meaning "both sides" and "coelias" from "koilos", meaning "hollow". The binomial name was Amphicoelias altus, meaning "high double hollow", "altus" meaning "high" or "elevated".

It was far from complete. Here's what Cope found of it, along with additional elements assigned later on such as a shoulder girdle and an ulna:

More recently, analysis of the scapula material revealed a camarasaurian nature, while the ulna, being referred to A. altus largely based on disagreement with Camarasaurus and the other sauropods in Cope's collection, is probably a candidate for exclusion.

From Tschopp and Mateus, 2015:

"The holotype of Amphicoelias altus originally included a tooth, two dorsal vertebrae, a pubis, and a femur (Cope, 1877a). A scapula, coracoid, and an ulna were later provisionally referred to the specimen (Osborn & Mook, 1921). However, the strongly expanded distal end of the scapula, and the relatively deep notch anterior to the glenoid on the coracoid actually resemble more Camarasaurus than any diplodocid (McIntosh, 1990b; E Tschopp, pers. obs., 2011). The same accounts for the single tooth stored at AMNH (Osborn & Mook, 1921). The tooth has already been excluded from scores of A. altus in recent phylogenetic analyses (Whitlock, 2011a; Mannion et al., 2012), which is followed here. Mannion et al. (2012) furthermore excluded the referred forelimb elements. Given that personal observations confirmed the rather camarasaurid than diplodocid morphology of the scapula and coracoid, but not particularly the ulna, two different preliminary phylogenetic analyses were performed with a reduced (excluding the tooth, the scapula and the coracoid, but including the ulna) and the extended holotype Amphicoelias altus OTU (including all referred elements other than the tooth). Because both analyses yielded the same position for the specimens, the reduced holotype was preferred in the final analysis. The risk of adding dubious information from potentially wrongly referred material was thus circumvented. More detailed analysis is needed in order to refine these assignments."

 Removing the referred shoulder girdle and ulna, this is what's left from the holotype, the original specimen that Cope found of it:

Not that much. But it's enough to give us a bit of an idea about the animal's size and proportions.

Now, this doesn't seem like an animal anywhere near Argentinosaurus size, let alone larger. But here's the thing - it's not alone. It had a cousin that was much, much larger.

Later in 1878, Cope, back in the Morrison, found a huge bone. A fragmentary neural arch from a posterior dorsal, around 1.5 meters tall. A single bone fragment, from a bone that isn't really very big by itself compared to the rest of the body, as tall as a person. Whatever animal bore this bone must have been truly immense in life.

This gigantic bone was assigned by Cope to a new species, Amphicoelias fragillimus, meaning "fragile double hollow".

Had this fossil survived to the present, Giraffatitan would have never taken fame as the "largest known dinosaur" for decades, and Tyrannosaurus would have never been called "the king of the dinosaurs". Argentinosaurus would not have had the fame for it's size that it has now, and the Chubut monster titanosaur wouldn't have looked so impressive. But this was not to be.

The bone was in very bad condition and was crumbling. It's condition deteriorated to the point that it was soon discarded, possibly by Cope himself. The fragility that gave it it's name, was the cause of it's destruction.

The legendary giant of the Jurassic, was lost, and then forgotten by almost all but a few. Ok, this animal has gained a little popularity recently, but is still very obscure. The big reason for this recent gain in popularity is Carpenter's 2006 paper, which attempts to estimate size based on the smaller A. altus dorsal and Diplodocus.

He arrives at a total last dorsal height of ~2.7 meters, a total length of ~58 meters and a mass of ~122.4 tonnes, approximately ~30 or so tonnes more massive than the average blue whale, or probably 50-70 tonnes more than Argentinosaurus.

However, his reconstruction depicts the animal as an upscaled clone of Diplodocus. Amphicoelias' actual known proportions are significantly different from those of Diplodocus. I will compare their proportions bone-by-bone in the next post.

"The Morrison Titan" - coming soon

Will be back when I make the skeletal reconstructions.

For now, let's just say that it's huge. Possibly one of the largest dinosaurs that ever walked the Earth, and almost certainly beyond the leagues of that awesomebro giant called Argentinosaurus.

Coming soon

Samson's height pt2

In my previous post, I dealt with the myth of the mounted skeleton of the "Samson" Tyrannosaurus specimen being ~4.6 meters tall at the hips. The skeletal mount itself turned out to be only around ~3.7 meters tall at the top of the hips. But even then, it's ilium is reconstructed somewhat too deep, in contrast to what actual Tyrannosaurus ilia suggest.

While Samson does have a preserved fibula and fragments of it's tibia, their measurements weren't listed.

I tried my hand at reconstructing Samson's hindlimbs. Parts in light gray are preserved but not measured.

Unmeasured and missing limb portions were scaled using FMNH PR2081 as a guide. The ilium is based on that of AMNH 5027, and FMNH PR2081 was used as a guide to cross-scale it.

Here's the measurements:
Ilium length = ~144.33 centimeters
Femur length = ~129.5 centimeters
Tibia length =  ~112.9 centimeters
Fibula length =  ~102.3 centimeters
Total hip height = ~341.4 centimeters

It actually ends up at a normal Tyrannosaurus rex hip height. Not surprising, given that it's known bone measurements are really no larger than that of a normal large Tyrannosaurus rex specimen (and smaller than those of FMNH PR2081).

Here's how it compares to the mythical ~4.6-meter Samson:

Notice how the real Samson's bones obviously don't fit in a ~4.6-meter hip?

references/sources
Scott Hartman's Tyrannosaurus skeletals
Theropod Database
AMNH 5027 illustration

Samson's height

Tyrannosaurus is 4 meters tall, blah blah blah. That's what most random online sources tall you.

But that figure is total nonsense, a fantasy with no basis in reality. In reality, T. rex's hip height levels out at around ~3.5 meters, give or take, whether the T. rex be Stan to CM 9380 to Sue.

Tyrannosaurus rex skeletal reconstructions by Scott Hartman. I do not own anything from this.

But is Sue the tallest Tyrannosaurus? Some, well, sources (including Wikipedia) states that Samson is the tallest known T. rex at an alleged ~4.6 meters in hip height. This is a mounted skeleton of Samson, with a woman standing next to the skeleton for scale:

Samson's mounted skeleton, mostly speculative though

And here's Samson's known bones and measurements, from the Theropod Database:

"skull (1.4 m), mandibles (dentary 870 mm), twenty-two teeth, nine cervical vertebrae, two cervical ribs, seven dorsal vertebrae, ten dorsal ribs, seventeen caudal vertebrae, four chevrons, femora (1.295 m), tibial fragments, fibula, metatarsal II (610 mm), metatarsal III, metatarsal IV (635 mm), ten pedal phalanges"

Samson's mounted skeleton measured

 If Samson were to be ~4.6 meters tall at the hips, then the woman standing next to it would have to be around ~1.99 meters tall. Although not impossible, women, or for that matter, humans, of that height are rare, and they tend to have more elongated builds. Assuming that this woman is almost 2 meters tall isn't the most parsimonius option. Also, this would make Samson's femur around ~1.61 meters long, which is a whopping ~24.32% longer than the measurement from the Theropod Database.

Assuming an average height of ~1.65 meters for the woman, Samson would be around ~3.8 meters tall at the hips. It's much lower than the exaggerated ~4.6 meter figure, but it's still a bit too high, as this would make Samson's femur around ~1.33 meters long, longer than the actual femur measurement.

Taking the femur length of ~1.295 meters, this yields a total hip height of ~3.7 meters for Samson (while the woman would be around ~1.6 meters tall). This is quite tall for a Tyrannosaurus, but not so tall as to be implausible.

Taller than Sue? Maybe, if that ilium, which isn't actually known from Samson, was actually reconstructed accurately. Why is the front part of that ilium so much higher than the rear portion, with a steep transition closer to the rear portion? That's not the case with Tyrannosaurus ilia.

Tyrannosaurus rex specimen AMNH 5027. Notice the ilium shape.

Sue and Stan skeletal reconstructions by Scott Hartman. Notice their ilium shape.

We'll see more about Samson in the next post.

Xinghesaurus size

Well, in my last post, based on the only existing photographs of the Xinghesaurus mount, it appears to be a sauropod roughly ~2.6-2.7 meters at the hips. But what about the total size?

Total size is a bit trickier, since the only side-view image of the Xinghesaurus mount has much of it obscured by other objects. But I did the best I could, using parts from the other photographs, and taking some parts of other nemegtosaurs, to fill in the obscured and blurry areas. Cross-scaling was at the best I could do, utilizing the landmarks I could actually make out.

I also reposed the mount's spinal column to something more titanosaurian, rather than diplodocoidean.

Looks more like a titanosaur now. Not a diplodocoid wannabe!

Torso length, defined as dorsal+ilium length here, is around ~3.3-3.4 meters.

Axial length ends up at ~14.86-15.38 meters.

Xinghesaurus ends up at Camarasaurus tier in length, but is much less bulky, with more of it's length being composed of it's long neck and tail.

But how about mass? Well, that's a bit more difficult. But this should give you an idea:

A bit larger than a male African forest elephant in terms of torso size, but much larger in total dimensions.

If I have to guess, probably around ~3-3.5 tonnes.

The forgotten Xinghesaurus

Some dinosaurs, like Tyrannosaurus, get far too much attention. Many others get much less, but still get attention. And there's the obscure.

Xinghesaurus is one of the most obscure dinosaurs ever named. It's not even formally described! So far, the palaeocommunity has ignored the very existence of this mysterious sauropod. There is no single raw measurement or even a single mention in a survey.

A Xinghesaurus mount was displayed in a Tokyo museum exhibit, one which also contains a mounted skeleton of the enormous Mamenchisaurus sinocanadorum(supposedly claimed to have a mass upwards of 70 tonnes, but is likely closer to 50 tonnes).

A closer look, perhaps?

Much better. Seems to be a nemegtosaurid with similarities to Huabeisaurus.

Here's one from the rear:

This is what we have of it so far. A mounted skeleton without a description paper or a single bone measurement. We don't even know how much of it is reconstructed.

But maybe we can estimate it's size based on these pictures?

Well, we can, but we have to take the results with a grain of salt. For starters, the bones can be compared with something close in proximity to it as to minimize the impact of perspective, such as the people surrounding the mounted skeleton.

Using that man bending down just beside the Xinghesaurus' hindlimb as a guide, the femur is around 2/3 of the man's height. Assuming that the man is at the average human height of ~165 centimeters, the Xinghesaurus femur would be about ~110 centimeters long. If we use the average height for Japanese males instead, which is about ~170.7 centimeters, the Xinghesaurus femur ends up at ~113.8 centimeters long.

Using the picture of the Xinghesaurus' rear, the resulting femur length could be used to estimate the hip height and possibly body width.

 

The hip height, which is approximately ~2.379 times the femur length, would be about ~2.617 meters based on the ~110-centimeter femur, or ~2.708 meters based on the ~113.8-centimeter femur.

The width at the hips(~75% of femur length) would be about ~82.5 centimeters based on the ~110-centimeter femur and ~85.35 centimeters based on the ~113.8 centimeter femur.

Based on the very limited information we have to date, Xinghesaurus seems to be a small sauropod, although you still don't want it to step on your toes.

But how large is it overall, at least based on the mount? We'll see in the next post.

Possibly the largest biped ever...and it's from the Triassic

Many people think of the Triassic as the time when dinosaurs were relatively minor players in the scene, being runts in a world full of non-dinosaur giants.

This isn't true. There are already large dinosaurs in the Triassic, especially the basal sauropodomorphs, also known as "prosauropods", some of which can grow up to multiple tonnes in mass.

But there is one.

One basal sauropodomorph to rule them all.

One so large, it would completely change your entire concept of Triassic animal life.

One so large, that it takes the throne of the largest known biped.

Unfortunately, it doesn't have a name yet.


This paper: A Diplodocus-sized basal sauropodomorph from the Late Triassic of South Africa

This piece of scientific literature speaks of a dinosaur in the legendary size class by pre-Jurassic standards. Estimated at up to ~15 tonnes, it competes in size with midsize Jurassic sauropods such as Diplodocus, and throws Spinosaurus right off the throne of largest known biped.

It also shows that you don't need to be a Jurassic or a Cretaceous dinosaur to be a legendary giant.

This dinosaur is closely related to Aardonyx. It's bones are, on average, ~190% of the dimensions of Aardonyx bones. It's femur alone is ~1.5 meters long, longer than any known theropod femur.

This image below should give you an idea of size. The king of the tyrant dinosaurs only just about matches the enormous Triassic legend in height only, and consider that basal sauropodomorphs are pretty low-slung for their size. This comparison doesn't even address the increase in bulkiness and robusticity that the large size would have required due to natural scaling laws.

Maybe we should reconsider about how we picture the Triassic period. Maybe it wasn't too different from the two later periods.
Tyrannosaurus based on Scott Hartman's skeletal.

A rather large sauropod claw...

 Article here: http://www.sudouest.fr/2014/07/26/angeac-charente-16-une-rarissime-griffe-de-dinosaure-decouverte-juste-avant-l-orage-1626256-726.php

A ~34-centimeter long sauropod claw was found in Early Cretaceous(~130 Ma) rocks at the site of Angeac-Charente in France. It was unearthed on July 27, 2014 before a storm arrived.

It was heavily eroded, missing the tip. It's length could likely be be closing it at around ~40 centimeters in life, give or take.

That claw would have been long enough to impale a human right through.

According to the article, the sauropod could have measured ~40 meters long in life, which would make it one of the largest known dinosaurs. But, as I've stated several times in the past, estimating total size based on toe bones is unwise.

 

Another image just to give you a further idea of it's size.

I translated the article as much as I can. There may be errors as I am not a French speaker.

Translated article:

The phenomenal discoveries continue on the paleontological site Angeac-Charente, one of the largest in Europe. The first three weeks of excavation have already collected 800 determinable bones and several thousand fragments. With a stegosaurus vertebra and a fossil turtle, a 34-centimeter sauropod claw was unearthed on Saturday. The large herbivore that lived there 130 million years ago could measure 40 meters in length.

This is actually the terminal phalanx of the finger of a large sauropod leg. It measures 0.34 meters long and it's impressive size is related with the rest of the animal, one of the largest known species in the world. It was covered with a horny sheath.

"The terminal phalanges of the four fingers were short and covered with a nail or shoe resembling those of the elephant" says Jean-François Tournepiche, the curator of the Museum of Angoulême, who oversees the excavations with Ronan Allain, a paleontologist at the Natural History Museum of Paris.
 
"To support a weight of several tens of tonnes, the leg bones of the animal are structured as elements of a column and feet rest on the ends of phalanges" he explains.
 
Researchers have had little time to savor this rare find. Afterwards, a violent storm made ​​landfall on the site. The excavation site was almost completely flooded. Scientists tell the story of the day which played with their nerves on their blog, called "The wrath of the great sauropod".

Are conservative reconstructions that much better than liberal ones?

Are they?

Most who look into the palaeozoology field thinks so, and even I thought so. We assume that fragmentary taxa look just like their relatives.

But after Deinocheirus, which with it's unique, unexpected features, does this line of thought still hold true? We have long assumed Deinocheirus to look just like a plain ornithomimosaur, but much larger.

To me, at least, it placed doubt on my idea of conservative > liberal in palaeo-restorations.

Conservative reconstructions may still be better than liberal ones, but the difference between their validity may likely never be as significant as it once was, to me at least.

Spinosaurus has no sail

There are popular mainstream beliefs that are just plain wrong.

One of them, is the issue I shall address: Sailbacked Spinosaurs.


Spinosaurus has traditionally been depicted with a sail. Jurassic Park 3 is also to blame for this as well.

But just because it's depicted as such, doesn't mean it's true. In fact, it's in this case, it's pretty wrong.

The comparisons used to give Spinosaurus a sail are Dimetrodon and Edaphosaurus, they even literally put a Dimetrodon sail on a spinosaurid's body in some reconstructions, like the one shown below:

Spinosaurus does NOT look like this!

Whoever made that depiction, obviously did not look at, or completely ignored, the fossils.

Spinosaurus holotype IPHG 1912. Note the broadness of the spines, and the fact that they look nothing like that of Dimetrodon.

By looking at the fossils, it's pretty obvious that Spinosaurus' neural spines looked nothing like a sailback's. In fact, Spinosaurus spines actually resemble bison and chameleon spines more(not perfect matches though) than those pathetic thin rods.

Spinosaurus skeletal reconstruction by Scott Hartman. Note the broadness and the spacing of the spines. There's little space between each neural spine. Image only used for illustration. I obviously have no claims towards this image.

Bison skeleton. The tall elongated spines support a heavy hump. The spines are close together, and are broad, like Spinosaurus. However, the bison's neural spines are thicker in frontal view, and that's where the chameleon comes in.

Chamaeleo melleri, a ridgebacked chameleon. it's spines also compare to Spinosaurus', but isn't as elongated, and the chameleon's spines are spaced farther from each other than that of bison and Spinosaurus.

Chamaleo melleri, in the flesh. There is no clear distinction between ridge and back.

The dorsal structure of Spinosaurus seems to possess attributes of both bison and chameleon spines. It is therefore likely that Spinosaurus had a ridge. It would have looked like a vertically-elongated triangle with a somewhat thin and rounded top in cross-section.

The neural spines of sailbacks only have to support itself and a vascular network. They can, and do get thinner distally, from all directions. This is not the case with Spinosaurus.

No suitable comparison can give Spinosaurus a skin sail.

Oh, and here's the Dimetrodon and Edaphosaurus stuff:

Dimetrodon skeleton. Note the thin rod-like spines, which look absolutely NOTHING like the ones found in Spinosaurus.

Edaphosaurus skeleton. Again, a total lack of resemblance to the spines of Spinosaurus.

Those sailbacks have spines which, aside from being long and elongated, have nothing in common with that of Spinosaurus!

In the top image, I have photoshopped a Spinosaurus restoration, to incorporate the more likely dorsal structures. The same has been done with the Ouranosaurus carcass. Here is the original, and very wrong, image.

Whether that structure is muscle or fat remains is still debatable.

With this, we can say, that a Dimetrodon-backed Spinosaurus is silliness.

If it had a sail, why would it evolve broad spines, when thin rods could have done the job?

Simple answer: It did NOT evolve a sail. Animals do not waste energy developing useless structures.

How large is UCMP 137538, really?

Many of you who are interested in dinosaurs, may have seen people in forums and youtube who fuzz over the legend of the "14-15 meter Tyrannosaurus", and refer to the specimen "UCMP 137538".

UCMP 137538 is known from a single 13-centimeter long pedal phalanx, which has been assumed to be a left pedal phalanx from comparisons with FMNH PR2081. That is a weak assumption, as the bone looks quite different from that of FMNH PR2081.

For starters, it may not even be a tyrannosaurid. It could have been a gigantic therizinosaur, since a herbivorous lifestyle isn't limited by the constraints of a carnivorous one, such as the need to run down prey. If you read the paper about UCMP 137538, you will see that the only real diagnosis done is the one assigning it as a theropod.

It's assignment to Tyrannosaurus is based on nothing but size and location, both of which are weak arguments for assigning isolated fossils to specific genera/species. It's also partly based on the assumption that Tyrannosaurus is the only large theropod living at North America at the Maastrichtian age, which is quite an almost-baseless assumption, considering that the vast majority of the dinosaurs are very likely undiscovered.

It's placement within the foot is also uncertain, the paper bases it's placement on nothing but superficial appearance.


Then how large would it be?




Answer: Completely unknown.


The problem is, it's just an isolated toe bone. Even the enigmatic Amphicoelias fragillimus is known from better remains(A D9/D10 vertebra).

The giant sizes come from scaling it up from FMNH PR2081, and the naive fanboys seemingly only scale from that specimen. FMNH PR2081 isn't the only tyrannosaur specimen however. And Tyrannosaurus isn't the only tyrannosaur. For all we know, UCMP 137538 may actually be a non-Tyrannosaurus tyrannosauroid.

Even IF it was a Tyrannosaurus or a very similar genus, you should still stay away from those 14+ meter calculations. Tyrannosaurus specimens can show quite a lot of variation.

BHI 3033(~10.9 meters, probably around 6 tonnes?), has toe bones that come close in size to that of FMNH PR2081. Not to mention that with pathogeny, digit bones can vary greatly even within individuals.

It is entirely possible that UCMP 137538 may actually be smaller than FMNH PR2081(~12.3 meters, ~8 tonnes).