Saurophaganax

King of the Lizard Eaters

Saurophaganax maximus "King of the Lizard Eaters, Maximum", is legendary in size, yet how long and heavy was this massive Late Jurassic theropod dinosaur?  Despite its epic size, very little has been published on this giant carnivore, I believe in part because what is known was heavily damaged while being collected and none of the bones were found articulated.  

While watching a road crew at work a pair of cowboys discovered a bone graveyard in northwest Oklahoma near the town of Kenton, 2 miles from the New Mexico border and 10 miles from the Colorado border. 

 

Most of the bones taken from the site in the 1930s belonged to a number of very large Apatosaurus.  I've measured the sauropod material and one individual has to be one of, if not the, largest Apatosaurus specimen yet excavated.  That is a story for another day though :-)!

The bones were "excavated" by Works Progress Administration (WPA) workers from a place called Quarry 1 within Pit 1. I use excavate in quotations because all of the work was done by people who had zero experience in collecting or preparing fossils.  They were given jobs by the Government during the Great Depression and this crew was assigned to take the bones out of the ground.  They used gunpowder to blow 'em loose and heavy hammers and chisels to separate bone from rock.  Unfortunately for paleontologists today, the matrix is of a very similar color to the bone, meaning unskilled hands carving away the surrounding rock were often removing the exterior of the bone, removing nearly all diagnostic characters to get to the spongy bone that they could recognize as bone.  Langston (1989) does a fantastic job recounting the detailed history of this locality.  Seeing what could have makes me sad.  

 

Please be aware that this oft-cited photo of material in articulation was a complete fabrication!  It was staged in 1941 for a Natural History Magazine story, where the name Saurophagus first appeared in print.  The photo was actually taken 380 miles away from the fossil locality and was staged using the best, and largest, limb elements, which were placed into a pit dug in the side of a hill.  Yikes!

The name Saurophagus proved to have already been used, on a lizard-eating bird no less, and thus had to be changed by the laws of the International Code of Zoological Nomenclature.  In 1995 Chure chose Saurophaganax.  

The only character Stovall used to differentiate the Oklahoma material from Allosaurus was size.  Size is an awful character to use and thus later researchers often called the animal simply a giant Allosaurus.  Chure (1995) noted many of the bones were upwards of 25% larger than the largest known Allosaurus.  Paleontologists never like to use size for the following reason: how would we know if smaller bones found elsewhere were the same kind of animal as the giant version?  

Chure, an Allosaurus expert, carefully studied the material and designated the holotype to be an anterior dorsal neural arch (OMNH 1123) because it nicely preserved a character found only on Saurophaganax, a parasagittal lamina (also called paraspinal lamina). He referred numerous additional bones to Saurophaganax but noted most of them are identical to Allosaurus, simply larger.  Saurophaganax is the sister taxon to Allosaurus.

 

Chure (1995) provides 4 images (his Figure 2, E-H) of a giant right femur, specimen 01708 (labeled OMNH 1708 in Chure 2000).  He lists the total length of the femur as 1,135 mm, a tibia (OMNH 01370) as 907 mm, and MT III, the third toe bone and longest in the foot, as 470 mm.  Keep in mind these elements do not necessarily belong to the same individual as, based on the presence of 3 left metatarsal II bones, there are at least 3 large individuals from the locality.  A 4th MT II indicates the presence of a 4th Saurophaganax are in the quarry if you are keeping score :-). 

A tour of selected Saurophaganax bones

Chure (2000) referred a number of bones to Saurophaganax, I've selected a few of my favorite observations from that amazing tome.  

Skull

Two skull bones (quadrate, postorbital) and 3 teeth are known.  The skull bones are morphologically all but indistinguishable from Allosaurus.  The teeth are too damaged to make any useful comparisons other than to say they are large and sharp. 

Cervical Vertebrae 

The first cervical vertebra, dubbed the atlas (OMNH 1135) by anatomists because it holds up the head, differs from Allosaurus in 3 very technical ways that I won't list here.  Suffice to say we paleontologists love our morphology!  It is also of note that an atlas of Torvosaurus is known.   

Dorsal Vertebrae

2 dorsal vertebrae (OMNH 1906, 1450) have a large foramen that Allosaurus lacks.  One must be cautious with pneumatic characters as these large holes could be due to the great size of the individual or simply variation.

Chevrons

 

The chevrons, bones that sit underneath and in between the caudal vertebrae, are differ greatly between Allosaurus and Saurophaganax.  In Saurophaganax they look like those of Tyrannosaurus and many ornithomimids, being hatchet-shaped "meat cleavers" versus the "regular" chevrons of Allosaurus. 

The similarity of the chevrons between tyrannosaurids and Saurophaganax is a result of convergent evolution, these animals were doing something similar with their tail, quite different from what Allosaurus was doing.  I'd love to see a biomechanical study on them!

Tibia

The giant right tibia (OMNH 1370) shows some minor differences from Allosaurus.  Another right tibia ("bone no. 4666") was once suggested as a holotype (Lucas and Hunt 1985).  Yet again, other than size, it isn't distinguishable from Allosaurus tibiae.  It isn't clear if the tibia of Lucas and Hunt (1985) is the same tibia as OMNH 1370. I believe it is as Chure (2000) only lists 2 tibiae, a left (OMNH 2149, distal end only) and the aforementioned OMNH 1370.

Metatarsals

The longest metatarsal in the foot is MT III, of which 3 are known from the locality (two left, OMNH 1191 [figured in Chure (1995)], OMNH 1192) and the right (OMNH 1924), all of which have ends that have been carved horrifically.

Hand Claws  

The giant claw (left digit I, OMNH 780) is massive but otherwise looks like Allosaurus, just on massive growth hormones :-).  It certainly makes the huge Torvosaurus hand claw look small, something I didn't think was possible! 

Keep in mind these claws would have had keratinous sheaths on them, extending them possibly an additional 30% in length!

Femur

 

The famed femur is what y'all are here to read so here you go:

The large(st?) Allosaurus is AMNH 680, which Chure (2000) gives as being 1008 mm long for the right and 991 mm for the left.  These femora are straight, as is the 1090 mm Acrocanthosaurus (Harris 1998), and Tyrannosaurus which clocks in at 1,300 mm (Osborn, 1906).  Saurophaganax has a 1,135 mm long femur but, as you can see in the above illustration, it has a bow to it unlike all other large North American (and the world?) theropods.  As I write this a cast of that giant Saurophaganax femur is resting against me.  It looks so tiny when I contrast it with the Apatosaurus femur on my other side...

 

While researching this article I ended up going down a number of rabbit holes.  A series of rabbit holes is called a warren and below is some of the fun stuff I found at the bottom of the warren of giant theropod limbs.

Cast measurements 

Researchers often take measurements from casts.  I noticed Persons and Currie (2016) provided measurements of a cast of the Tyrannosaurus holotype CM 9380 (the changing from AMNH 973, which was what T. rex was originally numbered, is a fascinating story in its own right!) of 1,269 mm total length. 

Measurements from Persons and Currie (2016), Table 1

However, Osborn (1906) provided a length of 1,300 mm measured from the original bone.  Persons and Currie list a circumference of 534 mm for the same cast.  However, these measurements being made from a cast makes me suspect it is actually ~2% smaller.  Does anyone have a circumference of the actual bone instead of a cast measurement?  I have added a predicted number for what a least circumference measurement of the holotype T. rex will be (I love a good test!).

 

2% is not just for milk!

Mathew Wedel wrote an amazing post (here) about the differences he found when he compared his measurements of a cast of a Supersaurus (=Dystylosaurus) dorsal vertebra versus when he measured the actual bone.  He notes that, on average, his cast numbers were 2% smaller than the actual bone numbers.

My personal experience mirrors that as I have compared cast versus actual bone numbers and also noticed a ~2% difference, with the cast measurements being smaller.  Importantly, Wedel noted it depends on the dimension being measured, as some of his numbers were 3% smaller, while others were 1.6%.

I tested this on the Saurophaganax cast versus Chure's measurements of the actual bone.  It isn't ideal as I haven't measured it myself (yet :-)) but I did find it fascinating that the cast measurements were 2% shorter and 1.6% less thick.

 Table of Measurements of bones I found interesting

Genus	Specimen #	Total Height mm	Circumference
Allosaurus	AMNH 680	1008*	381*
Acrocanthosaurus	SMU 74646 2B-1J	1090	388
Tyrannosaurus	CM 9380 (AMNH 973)	1,300	547**
Tyrannosaurus CAST	CM 9380 (AMNH 973)	1,269***	534***
Saurophaganax	OMNH 01708	1,135	440
Saurophaganax CAST	OMNH 01708	1110****	433****

*Total Height from Chure (1995). Circumference from Campione et al. (2014).  

**Osborn (1906) listed the length at 1,300 mm while other authors use 1,269 which seems to have been based on a cast measured by Parsons and Currie (2016).  I have uplifted their cast circumference by 2.04% here as Osborn did not provide a circumference on the original specimen.

***Taken from Persons et al. (2019) who's # of 1,269 for total length appears in Persons and Currie (2016) which was from a cast of CM 9380 (AMNH 973).

Saurophaganax measurements were taken from Chure (1995). Persons et al (2019) give different Saurophaganax measurements: 1,130 mm for total length and 435 mm for circumference. I do not know where these numbers came from, perhaps they measured the original specimen?

****Cast was 2.2% shorter and 1.6% thinner versus Chure (1995) measurements.

 

The Acrocanthosaurus measurements come from Harris (1998). Currie and Carpenter (2000) list NCSM 14345, as 1,277 mm total length and 425 mm circumference.  I didn't include it in the above table because, well here is the specimen as it is preserved, you make the call!

Being incomplete, I left it out of my data table but I did want to mention it as the authors say "it was at least 110 cm long" and estimated it at 128 cm.  I suspect that estimate has been used by many when modeling Acrocanthosaurus size, which is perfectly fine as long as folk are aware it isn't complete as preserved. 

 

Morrison Formation Showdown

The two (reasonably known) largest Jurassic theropods are Torvosaurus and Saurophaganax.  Comparing them directly isn't as straightforward as I would have liked as none of the material is articulated and both come from quarries with more than one individual, thus greatly hampering vertebral comparisons.

Unfortunately no femur is known for Torvosaurus and not enough cranial elements are known from Saurophaganax.  A claw comparison (scroll up to see it) is interesting but may be more a reflection of phylogeny (allosaurid versus megalosaurid) than actual length or weight.  It is awesome, though, to compare those claws side by side!

All measurements in the table below are in mm.  Torvosaurus measurements come from Britt (1991) and Saurophaganax from Chure (1995).  Measurements with an * were done by me via measuring the scale bar and then extrapolating while zoomed in at 200%+.  Not ideal I know but that is all I had to work with.

Tibia

Tibia	Torvosaurus	Saurophaganax
Length	725	907
Circumference	327	?
Winner		Saurophaganax

 

Advantage: Saurophaganax

 Metatarsal III (longest toe bone in these animals)

MT III	Torvosaurus	Saurophaganax
Length	365	470
Circumference	200	?
Winner		Saurophaganax

Advantage: Saurophaganax

 

Humerus

Humerus	Torvosaurus	Saurophaganax
Length	429	550*
Circumference	205	?
Winner		Saurophaganax

Advantage: Saurophaganax

 

Cervical Vertebrae

Atlas	Torvosaurus	Saurophaganax
Length	50	40*
Height	61	50*
Winner	Torvosaurus

Advantage: Torvosaurus

 

Dorsal vertebrae

Dorsal Vert	Torvosaurus	Saurophaganax
Length	135	100*
Winner	Torvosaurus

Advantage: Torvosaurus

Britt provides a number of Torvosaurus dorsal centra lengths, ranging from 112 to 135 mm.  Only one dorsal centrum for Saurophaganax is provided, and via scale bar it is approximately 100 mm long.  Its position in comparison to those of the Torvosaurus isn't clear and there doesn't seem to be any complete Saurophaganax centra for total width or height comparisons of the neural spine.

 

 Caudal Vertebrae

Caudal Vert	Torvosaurus	Saurophaganax
Length	127	130*
Width	90	130*
Height	280	320*
Winner		Saurophaganax

Advantage: Saurophaganax

Keep in mind there is no way to know if we are exact positions so take these comparisons with a packet of salt.

 

Winner

???

 

Conclusions

What should we take away from the measurement comparison?  In one sense, not much.  We are working with disarticulated elements w/o direct comparisons, with measurements made by different researchers (meaning we can't know for certain they picked the same spots) and I used numbers estimated via scale bars (yikes!). 

Where we can make direct comparisons, limb-to-limb, preserved Saurophaganax elements indicate it had longer limbs.  What I don't have is a circumference comparison which would allow us to compare robustness, an indicator of weight. 

I look to the vertebrae as a weight proxy and the neck and back bones of Torvosaurus in this comparison are larger, suggesting a heavier neck and back.  However, my favorite part of these animals, their tails, is where Saurophaganax shines.  *HOWEVER*, other than the atlas, we are in no way confidently comparing position to position, which in vertebrae means nearly everything.  

I'll defer to engineering-minded skeletal specialists and artists to continue the fray.  I went into this warren thinking Torvosaurus was an unassailable giant and conclude (for now) that not all is as bright lined as I thought going in, and that Saurophaganax truly is a giant that does not get the love, or press, that it should.  Prehistoric Planet 2 needs to include these big beasts!

I'll leave you with this thought, these two animals may have actually faced off.  I say this based solely on geography, their ranges may very well have overlapped!  Imagine that, two titans vying for supremacy over a prolific hunting ground somewhere in southeastern Colorado 150 million years ago...

 

Bibliography

Britt, B.B. 1991. Theropods of the Dry Mesa Quarry (Morrison Formation, Late
Jurassic), Colorado, with emphasis on the osteology of Torvosaurus tanneri. Brigham Young University Geology Studies 37: 1-72.

Chure, D.J. 1995. A reassessment of the gigantic theropod Saurophagus maximus from the Morrison Formation (Upper Jurassic) of Oklahoma. USA. in: Sun, A.L. and Wang, Y.Q. (eds.) Sixth Symposium on Mesozoic Terrestrial Ecosystems and Biotas, Short Papers. China Ocean Press, Beijing: 103-106.

Chure, D.J. 2000. A new species of Allosaurus from the Morrison Formation of Dinosaur National Monument (UT-CO) and a revision of the theropod family Allosauridae. Unpublished Ph.D. dissertation. Columbia University, New York, 964

Currie P. J. & Carpenter K. 2000. - A new specimen of Acrocanthosaurus atokensis (Theropoda, Dinosauria) from the Lower Cretaceous Antlers Formation (Lower Cretaceous, Aptian) of Oklahoma, USA. Geodiversitas 22 (2) : 207-246.

Harris, J.D. 1998. A reanalysis of Acrocanthosaurus atokensis, its phylogenetic status, and paleobiogeographic implications, based on a new specimen from Texas. New Mexico Museum of Natural History and Science, Bulletin 13: 75 pp.

Lucas, S.G. and Hunt, A.P. 1985. Dinosaurs from the Upper Jurassic Morrison Formation in New Mexico. New Mexico Journal of Science 25(1): 1-12.

Osborn, H.F. 1906. Tyrannosaurus, Upper Cretaceous Carnivorous dinosaur (second communication). Bulletin of the American Museum of Natural History XXII: 281-296 + plate XXXIX.

Persons WS, Currie PJ. 2016. An approach to scoring cursorial limb proportions in carnivorous dinosaurs and an attempt to account for allometry. Sci Rep 6:19828.

Persons, S. W.; Currie, P. J.; Erickson, G. M. (2020). "An Older and Exceptionally Large Adult Specimen of Tyrannosaurus rex". The Anatomical Record. 303 (4): 656–672.

Ray, E.G. 1941. Big for his day. Natural History 48(1):36-39.