Larger than Tyrannosaurus rex?
More than you ever wanted to know about a mysterious group of theropod dinosaurs!
I came across the fragmentary femur pictured above while researching Szechuanosaurus
. I never thought it'd lead me into a warren of theropod sizes and frustratingly complex taxonomy! The figure above is from Camp (1935), I added the highlights and Tyrannosaurus rex
figures (from Osborn 1906). Camp found this fragmentary femur, an ischium (?, he wasn't sure), and a "dagger-like serrate [sic] tooth" on August 30th, 1915, in Jurassic rocks of China. They were assigned the specimen number UCMP 32102 and today reside at the University of California Museum of Paleontology today. I am eager to see them, and you'll soon read why.
Camp noted the immense size of the femur, suggesting it was larger than that of Tyrannosaurus rex, at the time of this fragment's discovery T. rex was but a 9-year-old giant dinosaur, one the paleontological community had no reason to think was the heaviest to have ever lived. Yet, in 2022, after 116 years since being named the "Tyrant King Lizard", it still reigns supreme as the heaviest theropod ever discovered. However, could there be larger theropods out there?
This fragmentary femur, if truly positioned as the least width of the femur, certainly could vie for the title! Its circumference matches that of "Scotty", the 'fattest' T. rex
, and if Camp's length is true, it would be the longest theropod femur discovered, making the largest theropod ever discovered coming from the Jurassic of Asia!
It will be next to impossible to know for certain, but it certainly makes one wonder if there is an average maximum adult size to theropods, one that was reached in the Jurassic by this fragment, and again in the Cretaceous by T. rex. Perhaps there is a natural size ceiling that, regardless of time or environment, a predator simply doesn't exceed?
The Bell Curve applies to dinosaurs just as it does to animals today, suggesting ridiculously larger individuals existed. Think of humans, the average height is 5' 9", but we know 7' 11" can be reached. Similarly, elephants, snakes, crocodiles, sharks, etc., all reach much larger sizes on rare occasions with the right genetics and diet. Statistically we find only the average-sized individual in the fossil record. These supergiants existed, but the odds of those being preserved are so remote that we will never find them. Even worse? If we did, we wouldn't even know they were extremely large individuals. Why not? We don't have a grasp of the size range of large carnivores due to having found so few of each genus and their fragmentary nature. But it sure is fun to ponder something that exceeded the size of T. rex nearly 100 million years prior!
ICZN and Priority Rules
The rest of this article details the ugliness I dealt with when trying to figure out a simple question. The question? What genus is the fragmentary femur in the opening shot, and what genus (and specimen number) does this cast belong to? Both were called Szechuanosaurus
and I thought it'd be easy to learn more about a dinosaur I wasn't familiar with. Tragedy ensues...
Szechuanosaurus campi was named in 1942 by Young for 6 teeth across 4 specimen numbers, 3 of which were broken. And... that's it. That's all he used. In the same paper he named Chienkosaurus ceratosauroides from 4 isolated teeth, 3 of which consisted of only tips! Remember, this is still in the "early days" of dinosaur paleontology and our far more refined approaches to new taxa weren't universal (one could argue they still aren't ;-)). Dong et al. (1983), in their paper describing Yangchuanosaurus shangyouensis noted that 3 of the 4 Chienkosaurus teeth belong to a crocodilian and the remaining tooth differed only in position from those of Szechuanosaurus and thus they made it a junior synonym of Szechuanosaurus.
I'd like to take a moment to talk about ICZN rules and naming priority. The International Code of Zoological Nomenclature provides paleontologists with a set of rules to follow when naming animals. Things like the genus is always capitalized and an animal must have a binomial (genus + species name) in order to be valid (of which the species name is never capitalized), etc. Example: Tyrannosaurus rex is a binomial, and you should never capitalize rex. The ICZN writes a thick, comprehensive rulebook that addresses nearly every situation that can occur with what, when, and how an animal name can be created and used.
One of the most important (and frustrating I dare say) rules is that of priority
. In the case where it is determined that two separate specimen numbers that had been assigned to two separate taxa,
which name is the "official" one? We see this happen with beloved names like Eohippus
(Marsh 1876) becoming Hyracotherium
(Owen 1841) or Oreodon
(Leidy 1848), and even Brontosaurus
losing out to Apatosaurus
. In each case it was later discovered that two separately named taxa were actually the same taxon, and the one that was named first becomes the official name, the other is relegated to junior synonym status never to be used again. The rule is the animal that was named first "the oldest", as defined by date of publication, receives priority and therefore "wins". However, what happens when two animals, such as Chienkosaurus
, or Dystylosaurus
were named in the same paper (Young 1942 and Jensen 1985 respectively)? The names were published on the exact same date, so what is a researcher to do?
You might hear, or read, that one taxon's name was chosen over another for validity because of "page priority
". This is due to a mistaken attribution that the ICZN law of priority applies to page numbers within a document. The ICZN actually added an FAQ
to address this very topic. They state, "The page, or position on a page, on which a name (or act) appears does not in itself influence its precedence relative to other names (or acts) in the same work."
They continue, "The order of precedence of simultaneously published names or acts is determined by the first reviser or by a ruling of the Commission using its plenary power. The first reviser is that author who first selects one of two (or more) simultaneously published names considered synonymous (or different original spellings of the same name) to have precedence over the other name(s)."
I personally experienced being a first reviser when I selected the diplodocid sauropod dinosaur Supersaurus to be the name that encompassed the holotypes of Ultrasauros, which was universally considered a brachiosaurid, and Dystylosaurus, which, if known at all outside of specialist circles, was considered an unknown kind of sauropod. I chose Supersaurus because it was recognized by all as a diplodocid and because all three of these taxa actually had bones belonging to the same individual specimen, I kept the diplodocid name, despite the fact it was not the first taxon named in Jensen's 1985 paper that created all three taxa.
Dong et al. (1983), by choosing to keep Szechuanosaurus over Chienkosaurus did not violate any ICZN rules. They chose the one they liked and "sunk" the other as page priority isn't an actual ICZN law.
Details, Details, and more Details...
Why go into such details (other than I tend to ramble ;-))? Stay with me on what became a nightmare ride through gorgeous specimens and not as beautiful literature...
Dong et al. (1978) name Szechuanosaurus yandonensis in a faunal list describing taxa from the Upper Shaximiao Formation Wujiaba (Zigong) dinosaur beds but provide nary a description! Just the name, and not even with a specimen number! In the same paper they note a nearly complete Yangchuanosaurus shangyouensis skeleton as from the "...dark-red sandy mudstones in the middle-upper Shaximiao Formation of the Chongqing Group)", making it older than this new mystery species.
In the Dong et al. (1983) description of Yangchuanosaurus shangyouensis they attribute the better part of a theropod skeleton (CV 00214) that lacked a skull but had numerous teeth from the Shaximiao Formation, Wujiaba, Zigong to Szechuanosaurus campi. I presume this was the same specimen as their previously noted S. yandonensis, however without a specimen number in their 1978 faunal list this is simply an assumption on my part based on the fact both come from the Shaximiao Formation and were written by the same authors.
I must note that in the 1978 paper Dong et al. spell it Y. shangyouensis, but in the 1983 paper they write, "The genus includes two species: Y. shangyuensis (sic: shangyouensis) Dong, Chang, Li and Zhow and Y. magnus sp. nov." suggesting they had a typo in the original 1978 publication, especially considering throughout (almost) the rest of the 1983 paper they use the "yue" spelling. However, the 1978 publication states, "Theropoda Yangchuanosaurus shangyouensis n. gen. and n. sp." and it has priority so it is the correct spelling. It was found near the Shangyou dam, suggesting the species name. The 1983 citation gives no indication of why they changed the name.
The Szechuanosaurus naming party is just getting started, buckle up! Dong and Tang (1985) named Gasosaurus constructus from a partial skeleton (IVPP V 7264). Why do I bring this enigmatic theropod named after a gas field into the story? Because Gao (1993) writes, "In 1984 a large amount of dinosaur specimens were recovered during the construction of the Zigong Dinosaur Museum, among which was an incomplete skeleton which was quite distinct and initially described as Gasosaurus constructus Dong and Tang 1985. An appended description is hereby conducted". He proceeds to describe ZDM 9011, a nice skeleton from the Middle Jurassic Lower Shaximiao Formation near Dashanpu, Zigong Municipality, Sichuan Province, as Szechuanosaurus zigongensis. For good measure he made as hypodigms ZDM 9012, 9013, and 9014. The trouble I have here is in the Dong and Tang (1985) paper I can find no reference to ZDM 9011 and am utterly perplexed as to why Gao (1993) references Gasosaurus. I manually translated the paper via Google translate hoping to find the specimen number ZDM 9011 but it isn't in the 1985 paper. Does anyone know why Gao wrote what he wrote? Was it simply an error? Mickey Mortimer replied in the comments (thank you!) that this was a translation error by Will Downs. Will translated a large number of Chinese dinosaur papers, allowing access to those of us who could otherwise only look at the pics and the few words typed in English.
In 1992 Yangchuanosaurus hepingensis
was named by Gao for a nearly complete skeleton with skull (ZDM 0024). However, this name lasted only two years as in 1994 Currie and Zhao moved it to Sinraptor hepingensis
, citing a number of similarities with Sinraptor.
Szechuanosaurus gets its first new name
Chure (2000) points out Szechuanosaurus campi, the species that establishes the validity of the genus name Szechuanosaurus, is based off of non-diagnostic teeth and should be considered a nomen dubium, "dubious name", and shouldn't be used for anything but the teeth originally assigned to it. Thus Szechuanosaurus as a name goes away, leaving some great specimens nameless. He makes CV 00214 the holotype of a new name, Szechuanoraptor dongi, and suggests both ZDM 9011 and CV 00214 are within the range of variation to belong to the same species. Though ZDM 9011 is from older beds than CV 00214 this doesn't automatically mean they are different taxa, we need to have characters that we can use to separate them and, to Chure, there were none. Much of taxonomy, shockingly to many, is subjective in nature, based on the opinion of an expert who has studied much material and gets a feel for what is different. However, as Chure's work was published within a dissertation it isn't considered valid by the ICZN, as that group requires names to be published in peer-reviewed, readily accessible scientific journals. With the advent of online publishing, I think the ICZN has some more rules to finetune, but that is a discussion for another day.
Carrano et al (2012) also point out that Szechuanosaurus
as a name must be restricted to only the original teeth. However, one of their trees results in assigning ZDM 9011, the old S. zigongensis
, to a new genus! Yep, it is now known as Yangchuanosaurus zigongensis.
Their study also lumps CV 00214, S. shangyouensis
with CV 00215 (the holotype of Yangchuanosaurus
, see below) to Yangchuanosaurus shangyouensis.
For the sake of completeness, I'll note here they move a different species of Yangchuanosaurus, Y. magnus
(CV 00216, also below) to Y. shangyouensis
as well and yet another species, Y. hepingensis
, to Sinraptor
(agreeing with Currie and Zhao 1994).
Yangchuanosaurus shangyouensis was named in 1978 by Dong et al. based on a nearly complete skeleton including skull (CV 00215) from the Upper Shaximiao Formation "350 m from the base of the dam at Shangyou Reservoir, Yongchuan". Dong et al. (1983) better described it and, in doing so, created another species, Y. magnus, based off of another reasonably complete skeleton and skull (CV 00216), this time from the Upper Shaximiao Formation from the Hongjiang Machine Factory in Yongchuan, ~700 miles away. The distance isn't that big of a deal as in the western United States we routinely refer animals found far away from one another to the same species. Think about elephants and lions today, they are found all over Africa, yet we call them the same species.
Dong et al. (1983) create Yangchuanosaurus magnus
(CV 00216) based on the following 4 differences from Y. shangyouensis
(CV 00215): massive size difference, the absence of a small mandibular foramen, "...one of the maxillary depressions perforating the maxilla", and "...ilia and sacrum are readily distinguishable" on Y. magnus
by virtue of "Four of the five sacral spines are fused with the anterior sacral centrum more robust than the other centra."
All of these characters are known to be variable in dinosaurs. Size is intuitive, a younger animal is smaller than an older one. In dinosaurs, the degree of sacral vertebral fusion is related to the age of the individual. The skull features listed are, at least in other theropods, known to be variable between individuals of the same size. If all four characters are variable then they can't be used to make them separate species, so they have to be the same species, and since Y. shangyouensis
was named first (1978 vs 1983) it takes priority and becomes the name for both of them.
The did note that Y. magnus
was the largest known Late Jurassic theropod from China at the time of their writing and, to my knowledge remains so, unless the fragmentary femur Camp found is larger, which I suspect it is. Still, Yangchuanosaurus
is of large Allosaurus
in size and nothing to be trifled with!
Let's recap with name, specimen number, and author
1935: Unnamed theropod UCMP 32102 (Camp)
1942: Szechuanosaurus campi* V235-239 (Young)
1978: Szechuanosaurus yandonensis CV 00214? (Dong et al.)
1978: Yangchuanosaurus shangyouensis* CV 00215 (Dong et al.)
1983: Szechuanosaurus campi CV 00214 (Dong et al.)
1983: Yangchuanosaurus magnus CV 00216* (Dong et al.)
1985: Gasosaurus constructus ZDM 9011 (Dong and Tang)
1992: Yangchuanosaurus hepingensis ZDM 0024* (Gao)
1993: Szechuanosaurus zigongensis ZDM 9011* (Gao)
1994: Sinraptor hepingensis ZDM 0024 (Currie and Zhao)
2000: Szechuanoraptor dongi CV 00214*, referred ZDM 9011 (Chure)
2012: Yangchuanosaurus shangyouensis CV 00214 (Carrano et al.)
2012: Yangchuanosaurus shangyouensis CV 00216 hypodigm (Carrano et al.)
2012: Yangchuanosaurus zigongensis ZDM 9011 (Carrano et al.)
2012: Sinraptor hepingensis ZDM 00214 (Carrano et al.)
2012: nomen dubium Szechuanosaurus campi V235-239 Carrano et al.)
What kind of theropod is a Yangchuanosaurus? It is a metriacanthosaurid, which means "moderately-spined lizard". What does that even mean, "moderately spined"? Let's take a brief sojourn into theropod neural spines.
In 1923, theropod dinosaur backbones excavated from the Early Cretaceous of England were named Altispinax
"with high spines" because, you guessed it, they had tall neural spines. Acrocanthosaurus
"high spined lizard" was named in 1950 for its tall spines (yes, dorsals vs cervical but you try finding Acro dorsal illustrations :-)). The neural spines are 3x the height of the centra.
Contrast those with Allosaurus
where the neural spine is 1.5x or so the height of the centra.
dorsals sit in an in-between spot, coming it at 2.5:1 ratio of centrum height to neural spine height. Thus the moniker "moderately high-spined" theropod.
These Asian theropods lived around 160 million years ago, 10 million years before Allosaurus
, and their closest cousins are found in Europe. Yangchuanosaurus
, and even Metriacanthosaurus
are all part of the Allosauroidea, a group of dinosaurs that are more derived than the "primitive" megalosauroids which show up around 170 million years ago.
If you've stayed with me this far, thank you! I've flitted about from various topics with precious little yarn connecting them. I'll conclude with (and keep in mind I'm a simple sauropod lad!) the fact I'm not convinced
all of these taxa belong with Yangchuanosaurus
. The caudal vertebrae of CV 00215 are, to me, markedly different in proportions than CV 00214 and CV 00216. Unless I publish something in a peer-reviewed journal that remains simply my opinion. Yet going through all of these papers it hit home that so much of paleontology is one (or a small team's) opinion. The cladistic analysis in the 2012 researched result in 91 most parsimonious trees (TNT) and over 400,000 using PAUP. From there all kinds of mathematical tricks of the trade were deployed to the strict consensus tree published in their Figure 7A. Change one character, add one taxon, remove one taxon and the results subtly shift. For a large-scale paper that isn't an issue, for the position on the tree of a single specimen number that can be a very large change. Yet I'm not lashing out at cladistics, at least they provide a matrix of characters that can be debated, qualitative folk like myself use a suite of characters, plus my experience and "gut", which is just as squirrely as 400,000 trees. One advantage to the "quals" is they often provide descriptions and illustrations that are far more useful than a 0 or 1. Cladograms rarely hold up over time at the specimen level while great descriptive work and illustrations are timeless.
My prediction is at some point in the next 100 years CV 00214, 00215, 00216 and ZDM 9011 will be better described, illustrated, heck even put in 3D scans, and our knowledge of them will change such that they will appear to be different species and, I'd wager, different genera. I'll leave you with this, what makes something a genus versus a species? The 2022 bird taxonomy update resulted in 82 new bird species being named: 5 brand new, 118 new via splits, and 41 lost via lumping. These changes from animals that we can see, hear, and DNA test! Dinosaur taxonomy is, at best, directionally correct, and at worse nowhere close to what really happened. But it is the quest that keeps us all going! :-)
Camp, C.L., 1935. "Dinosaur remains from the Province of Szechuan", Bulletin of the Department of Geology of the University of California 23: 467-471
Carrano, M. T.; Benson, R. B. J.; Sampson, S. D. 2012. "The phylogeny of Tetanurae (Dinosauria: Theropoda)". Journal of Systematic Palaeontology. 10 (2): 211–300
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
Currie, Phillip J.; Zhao, Xi-Jin 1993. "A new carnosaur (Dinosauria, Theropoda) from the Jurassic of Xinjiang, People's Republic of China". Canadian Journal of Earth Sciences. 30 (10): 2037–2081
Dong and Tang, 1985. "A new Mid-Jurassic theropod (Gasosaurus constructus gen et sp. nov.) from Dashanpu, Zigong, Sichuan Province, China". Vertebrata Pal Asiatica. 23(1), 77-82.
Dong, Z., Chang, Li & Zhou, 1978. "A new carnosaur from Yongchuan County, Sichuan Province", Ke Xue Tong Bao 5: 302-304
Dong, Z-M., Zhou, S., Zhang, Y. 1983. "The dinosaurian remains of Sichuan Basin, China", Palaeontologica Sinica (new series C), 23: 1–145
Gao, Y., 1993. "A new species of Szechuanosaurus from the Middle Jurassic of Dashanpu, Zigong, Sichuan", Vertebrata Pal Asiatica 31(4): 308-314
Young, C.C., 1942. "Fossil vertebrates from Kuangyuan, N. Szechuan, China", Bulletin of the Geological Society of China, 22: 293-309