Paleo

The Largest Theropod: T. rex vs Giganotosaurus?

---posted 22⁵⁸, 28/02/2025

One of the most enduring and polarizing debates in the online community of paleontology enthusiasts is the one about which species should hold the title of the largest (known) theropod, intricately linked to that of the largest terrestrial carnivore of all time. I have been involved in this debate many times over the years, and have some thoughts and opinions that I want to present here in as concise a form as possible. While legitimate arguments might be had in support of several other taxa of theropods, including Spinosaurus, Mapusaurus, Tyrannotitan, Carcharodontosaurus and even, possibly, Allosaurus sp., in recent years this debate has often boiled down to a comparison between Tyrannosaurus rex and its most traditional challenger, Giganotosaurus carolinii. It is hence the comparison between these two taxa that I want to focus on here, bearing in mind that several other giant Carcharodontosaurids might well have had similar average sizes to Giganotosaurus, but are fraught with even greater uncertainty.

T. rex is certainly the best-known, most popular and well-studied contender for the largest theropod dinosaur. Known from dozens of substantial skeletons (e.g. Mortimer 2025 [online], Paul et al. 2022, Larson [et al.] 2008]) it sports a fossil record of a quality and quantity not matched by any other theropod species that might legitimately deserve the label of "giant". Accordingly, it should not come as a surprise that the specimens that are probably the largest known individuals of any theropod are referred to T. rex. Most famously, this includes the two similar-sized and well-preserved skeletons Sue (FMNH PR 2081, femur circumference 580 mm) and Scotty (RSM P2523.8, femur circumference 590 mm), even though they both appear to be outclassed by a less well-known and less complete specimen, BHI 6248 (nicknamed Cope, femur circumference 630 mm). It is at least likely that the latter constitutes the largest theropod specimen currently described, with its femur circumference suggesting a body mass potentially 28% greater than that of Sue. Sue itself measures 12.3 to 12.4 m in total length (Paes 2016 [online], Hutchinson et al. 2011) and has variously been estimated at 8.4 t to 9.5 t (Snively et al. 2019, Hartman 2013 [online]), Bruñén 2016a, 2017 [online], Hutchinson et al. 2011) in mass, already comparable to several of the largest specimens of other theropods (e.g. Hartman 2013 [online], Folkes 2023 [online]) and significantly outclassing individuals that are reasonably complete (e.g. Snively et al. 2019, Campione et al. 2014). For BHI 6248, this suggests a plausible body mass range of 10.7-12 t. Based on this, T. rex is often simply assumed, ex- or implicitly, to have been the largest theropod, and claims to that title made by other taxa in the 90s and early 2000s have largely been ignored or dismissed on these grounds alone.

However, to focus on the size of the largest known individuals is to commit a fundamental statistical fallacy; Most other giant theropods are known from only a handful of specimens at most, and even these are often fragmentary. This makes it unlikely to recover individuals at the extremes of the size distribution for any of these taxa, and any comparison that is based on individual specimens that do not reflect the average size of the taxon is mere cherry-picking. The relevant metric for comparison between T. rex and other animals is not its maximum size (which is not even known and can only be speculated on, see Mallon and Hone 2024), but rather its average size. A caveat to this comparison lies in the inclusion of immature specimens. However, for most relevant taxa we know, or can reasonably assume, which specimens are adult (sexually mature), and can thus reasonably limit our comparisons to specimens that fulfill this criterium. A possible exception is Mapusaurus, known only from a bonebed representing multiple ontogenetic stages over an indeterminate number of total individuals. Since our present comparison is focused on Giganotosaurus, whose holotype is a mature individual (Coria and Currie 2003), we can safely limit our comparison to adults only. In doing that, we find that the average adult T. rex, based on a sample of 33 individuals with known femur length and circumference, or other material permitting their estimation, has a femur length of 1230 mm and a femur circumference of 521 mm. Contrary to common talking points, these values can be estimated fairly accurately (90% CI of femur length 1203-1249 mm, 90% CI of femur circumference 509-533 mm), demonstrating that the sample size is sufficient to estimate average size with a reasonable degree of accuracy.

Femur circumference in the two known specimens of *Giganotosaurus*
	Circumference	Comment, Source
MUCPv-Ch1	521 mm	measurement, Campione et al. 2014
MUCPv-95	533 mm 548 mm 555 mm 563 mm	2.2% larger minimum dentary depth, Coria and Currie 2006 5.2% larger centroid size (conservative) 6.6% longer alveolar margin, Folkes 2023 [online] 8% larger in unspecified measurement, Calvo and Coria 1998

Since its unveiling to the public in 1995, Giganotosaurus carolinii has been recognized as one of the largest known theropods (Coria and Salgado 1995, Calvo and Coria 1998, Mazzetta et al. 2004, Persons et al. 2019), if not the largest. Giganotosaurus is known from only two individuals, one of which is a partial dentary (MUCPv-95, Calvo and Coria 1998) measuring approximately 61 cm in length, while the smaller holotype specimen (MUCPv-Ch1, Coria and Salgado 1995) is a relatively complete skeleton (albeit not on the same level of completeness as Sue, and mostly undescribed as of now) including substantial parts of the skull, vertebral collumn and hindlimb, including a femur with a circumference of 521 mm (Campione et al. 2014), which puts it squarely within T. rex size range. The precise size difference between the two specimens has been a matter of contention: While MUCPv-95 is universally recognized as the larger specimen, estimates have variously placed it between 2% and 8% larger than the holotype specimen. This issue is caused and complicated by the lack of detail in the original descriptions of both specimens, including Calvo and Coria (1998), despite their emphasis on highlighting MUCPv-95 as 8% larger than MUCPv-Ch1, (without giving any specifics or comparative measurements). The most recent information comes from a private communication to Dan Folkes (2023 [online]), and reports that the length taken along the alveoli is 6.6% larger in MUCPv-95. This closely matches the 6.5% estimate by Hartman (2013 [online]), which can be taken as independent verification, and is also plausibly close to my own conservative estimate based on centroid size. 6.6%, despite being unpublished, thus appears as the most relevant and reliable figure to use.

Due to incompleteness and the limited amount of descriptive data on the holotype, the overall body dimensions and mass of Giganotosaurus have likewise been variously estimated. Previous estimates of total length vary from 12.2 to 12.7 m (not counting an estimate of 13 m by Therrien and Henderson 2007, which was only based on estimated skull length and ignored all available postcranial material).

Length of the two known specimens of *Giganotosaurus*
	Total Length	Comment, Source
MUCPv-Ch1	12.2 m 12.3 m 12.4 m 12.5 m 12.7 m	Coria and Currie 2006 Bruñén 2016b [online] Hartman 2013 [online] SpinoInWonderland 2023 [online], Coria and Salgado 1995 Folkes 2023, Paul 2024
MUCPv-95	12.5–13.0 m 12.8-13.4 13.0-13.5 m 13.2-13.7	2.2% larger minimum dentary depth, Coria and Currie 2006 5.2% larger centroid size (conservative) 6.6% longer alveolar margin, Folkes 2023 [online] 8% larger in unspecified measurement, Calvo and Coria 1998

Already we can see that Giganotosaurus more than rivals T. rex, and not just in terms of total length. If we compare femur circumferences, a measurement with a strong functional linkage to body mass, even the smaller of the two known Giganotosaurus individuals already matches the average femur circumference of T. rex across 33 specimens. The second, larger specimen shows that this is unlikely to be an unusually large individual of its species, which already suggests that Giganotosaurus is likely at least as large as T. rex, if not larger, since both its known specimens squarely fall into the upper half of T. rex’ size distribution. Assuming MUCPv-95 is 6.6% larger than MUCPv-Ch1, its femur circumference is 555 mm, and the mean circumference for Giganotosaurus becomes 538 mm, which is above the 90% confidence range for the average femur circumference of T. rex. This suggests that Giganotosaurus carolinii is probably the larger species, at least in terms of average size (with comparisons of maximum size being impossible at this time).

Comparison of the distribution of femur circumferences in T. rex and Giganotosaurus carolinii, with a hypothetical normal distribution of equal variance to that observed in T. rex, but centered on the mean of Giganotosaurus "subimposed" for the Giganotosaurus sample.

We can approach this more quantitatively and estimate the significance level of the apparent size difference, and the power level (using the pwr package in R):


t.test(femur_circumference~taxon, dataset, alternative="greater")
wilcox.test(femur_circumference~taxon, dataset, alternative="greater")
require(pwr)
coh_d<-abs(diff(tapply(dataset$femur_circumference,dataset$taxon,FUN=mean)))/sd(dataset$femur_circumference)
pwr::pwr.t.test(n=2,d=coh_d,power=NULL,sig.level=0.05,alternative="greater")

R code

We observe that the p-value (probability of type I error, i.e. a false positive/false rejection of the null) from the wilcox-test is approximately 0.17 and that from the t-test 0.25, suggesting a non-significant difference in femur circumference between the two taxa. However, assuming accurate estimates of femur circumference, this still means that the probability of the obeserved differences being merely due to chance is <25%, which at least qualifies as a strong tendency by dinosaur standards. Conversely, this means that the observed difference not being due to chance is >75%, i.e. a 75% probability of Giganotosaurus being (at least slightly) larger than T. rex. While there is of course valid reasoning for dismissing a difference that does not meet agreed-upon standards for statistical significance, defaulting to p<0.05, it is worth questioning it p<0.05 is generally a realistic significance level in comparisons between dinosaurs or other poorly sampled extinct taxa. The results of a power analysis illustrate this (statistical power is the probability of type II error, i.e. a false negative/false rejection of the alternative hypothesis): For a cohen’s d of 0.417 (the difference in means divided by pooled standard deviation) as in our case, the statistical power for rejecting the null hypothesis at p<0.05 is just 0.09, i.e. there would have been only a 9% chance of achieving a statistically significant result given that the difference observed in our samples actually reflects the difference in the real populations. In order to achieve a considerably higher power, we would need to either assume a much larger actual difference (e.g. with an effect size of 2 sds, which would be equivalent to a femur circumference difference of over 8 cm, we would achieve a power of 0.38, i.e. a 38% chance of achieving a significant result), higher sample size or higher critical p-value. Since a much larger difference in size between the taxa is not parsimonious to expect (and is not suggested here), and we have to work with the sample sizes that we have, the only option is to critically reconsider our appropriate p-value. In this case, the power analysis indicates that in order to stand a >50% chance of avoiding a false negative, we would have to increase our critical p-value to 0.34, i.e. roughly a third, which I would suggest could be a reasonable rule of thumb for fossil interspecies comparisons where there is no strong mechanistic argument for favoring the null-hypothesis of no difference.

We can thus estimate that the difference in body mass based on femur circumference was likely around 10%, and further illustrate that by plotting the samples of estimated body masses (Using Campione et al.’s mathematically corrected regression equation, which tends to give plausible body mass estimates for T. rex, albeit on the low end of volumetric figures for the same specimens):

Comparison of the distribution of body mass in T. rex and Giganotosaurus carolinii as based on the results of the phylogenetically corrected cQE (Campione 2020, Campione et al. 2014), with a hypothetical normal distribution of equal variance to that observed in T. rex, but centered on the mean of Giganotosaurus "subimposed" for the Giganotosaurus sample. For the sake of simplicity, all T. rex specimens are assumed to have a femoral eccentricity of 1.2, whereas for Giganotosaurus the exact eccentricity (approx. 1.15) of MUCPv-Ch1 is used.

What does all this imply? It means we cannot be highly confident that Giganotosaurus was larger than Tyrannosaurus, but we can say that it is likely that it was – or at least decidedly more likely than for the reverse to be true. I would argue that in vertebrate paleontology, such a tendency is generally sufficient to establish a difference, because otherwise many common-sense interspecific comparisons are suddenly rendered impossible due to small sample sizes – even ones as obvious and clear-cut as that between Argentinosaurus and Epidexipteryx (which are both only known from a single specimen, thus precluding an estimation of the statistical significance of their sizen difference). In any case, it is certainly a higher significance level than any (implicit or explicit) usage of individually picked specimens can provide (it is often ignored that if even a comparison of species averages fails to achieve sufficient significance, then any comparison between single specimens is by necessity even less meaningful). There are also reasons to think that the present comparison based on femur circumference is more likely than not to underestimate the degree to which Giganotosaurus is larger. Notably, known Tyrannosaurus specimens tend to have robust femora for their (volumetrically estimated) body mass. Famously, the T. rex specimen USNM 555 has a femur circumference of 520 mm, while the Acrocanthosaurus specimen NCSM 14345 has a femur circumference of 427 mm (Campione et al. 2014). Based on this, the former specimen would be predicted to be almost twice the mass of the latter, but volumetric studies of the complete specimens suggest that the two are actually very similar in mass (Bates et al. 2009). Volumetric estimates for Giganotosaurus show a similar, albeit less extreme, trend, suggesting the larger Giganotosaurus specimen to be, volumetrically, at least on par with T. rex specimens that have femur circumferences several cm greater than its own:

Estimated body mass of the two known specimens of *Giganotosaurus*
	Body Mass	Specific Gravity, Source
MUCPv-Ch1	6.8 t 6.9 t 7.4 t 8 t 8.2 t 8.8 t	SG 0.91, Hartman 2013 [online] unspecified SG, Snively et al. 2019 SG 0.97, Bruñén 2016b [online] SG ?0.97, Paul 2024 SG 0.95, SpinoInWonderland 2022 [online] SG 0.97, Folkes 2023
MUCPv-95	7.3–9.4 t 7.9–10.2 t 8.2–10.7 t 8.6–11.1 t	2.2% larger minimum dentary depth, Coria and Currie 2006 5.2% larger centroid size (conservative) 6.6% longer alveolar margin, Folkes 2023 [online] 8% larger in unspecified measurement, Calvo and Coria 1998

Volumetric mass estimates consistently show that an upscaled MUCPv-95 (at ≥6.5% larger linearly than MUCPv-Ch1) would at least rival (e.g. Hartman 2013 [online], Bruñén 2016ab [online], Snively et al. 2019), if not exceed (SpinoInWonderland 2022 [online], Folkes 2023 [online], Paul 2024) the mass of T. rex specimens like Sue or Scotty (note the non-independent effects of the assumed density, which ranges from 0.91 to 0.97 for different estimates, the latter based on Larramendi et al. 2021).

One concern that is sometimes raised is the inclusivity of the T. rex sample used herein, specifically with the assertion that the known Giganotosaurus specimens should only be compared to those T. rex individuals that have an external fundamental system (EFS) or other clear indications of being "asymptotic" (i.e in the asymptotic growth stage sensu Erickson et al. 2004) or fully grown, and are, hence, towards the larger end of its size spectrum. However, this is based on the incorrect assumption that the "mature" state and an obliteration of most braincase sutures, noted for the Giganotosaurus holotype (Coria and Currie 2003), are evidence of a senescent growth stage. In fact, a determinate growth model may not even be the universal state for dinosaurs (Myhrvold 2013), rendering comparisons of "fully grown" individuals pointless when it is not a given that both taxa in question actually ever stopped growing. Even more importantly to this specific case, the obliteration of cranial sutures is not a reliable indicator of maturity in archosaurs: Bailleul et al. (2016) demonstrated that in Alligator, the only cranial sutures that are obliterated do so during embryonic development, while the other sutures in fact open up (rather than fuse) as the animal grows. Without detailed knowledge of the ontogenetic development of Giganotosaurus itself, the state of suture fusion on a small part of its skull is effectively useless for ascertaining its relative state of maturity, and it is not at all known if it is more appropriate to compare the available Giganotosaurus specimens to young and actively growing, or old and fully grown adults of T. rex. In the absence of such knowledge, a simultaneous comparison to both (i.e. a pooled sample of all adult T. rex individiduals) is the only option that objectively accounts for all possibilities without preferring one over the other. While it is, of course, true that the absence of information on the precise growth stage and trajectory of Giganotosaurus introduces additional uncertainty, it does not change the basic assessment of which taxon is more likely to be larger.

In conclusion, the available evidence suggests that, as a strong tendency, Giganotosaurus carolinii was probably larger than Tyrannosaurus rex. While this size difference is not statistically significant at p<0.05, it is approximately three times as probable as the reverse. Even though future study of the known material (particularly of the histology and ontogeny, but also osteology of Giganotosaurus) and the recovery of more material (particularly of Giganotosaurus) do hold the potential of changing this verdict, as of now it does meet and exceed criteria commonly applied in vertebrate paleontology in order to establish differences in size or other quantitative parameters. It also supports the statements by Persons et al. (2019) as well as earlier works (e.g. Mazzetta et al. 2004, Calvo and Coria 1998) that pointed out the probable greater size of Giganotosaurus as compared to T. rex (in spite of some methodological shortcomings or vagueness in some of these studies). As of now, it appears that at least if one wants to proclaim a largest known theropod, it should be Giganotosaurus.

–––References:
Bailleul, A.M., Scannella, J.B., Horner, J.R., and Evans, D.C. 2016. Fusion Patterns in the Skulls of Modern Archosaurs Reveal That Sutures Are Ambiguous Maturity Indicators for the Dinosauria. PLOS ONE, 11:e0147687. https://doi.org/10.1371/journal.pone.0147687.
Bates, K.T., Manning, P.L., Hodgetts, D., and Sellers, W.I. 2009. Estimating mass properties of dinosaurs using laser imaging and 3D computer modelling. PloS one, 4:e4532. https://doi.org/10.1371/journal.pone.0004532.
Bruñén, F. 2016a. [online]. Tyrannosaurus rex skeletal diagram (FMNH PR 2081). DeviantArt. Retrieved February 27, 2025, from https://www.deviantart.com/franoys/art/Tyrannosaurus-rex-skeletal-diagram-FMNH-PR-2081-640670460.
Bruñén, F. 2016b. [online]. Giganotosaurus carolinii skeletal diagram. DeviantArt. Retrieved February 27, 2025, from https://www.deviantart.com/franoys/art/Giganotosaurus-carolinii-skeletal-diagram-645266194.
Bruñén, F. 2017. [online]. Tyrannosaurus rex size. by Franoys on DeviantArt. DeviantArt. Retrieved February 28, 2025, from https://www.deviantart.com/franoys/journal/Tyrannosaurus-rex-size-682386614.
Calvo, J.O. and Coria, R. 1998. New specimen of Giganotosaurus carolinii (Coria & Salgado, 1995), supports it as the largest theropod ever found. Gaia, 15:117---122.
Campione, N.E. 2020. MASSTIMATE: body mass estimation equations for vertebrates. R. Retrieved from https://CRAN.R-project.org/package=MASSTIMATE.
Campione, N.E., Evans, D.C., Brown, C.M., and Carrano, M.T. 2014. Body mass estimation in non-avian bipeds using a theoretical conversion to quadruped stylopodial proportions. Methods in Ecology and Evolution, 5:913---923. https://doi.org/10.1111/2041-210X.12226.
Coria, R.A. and Currie, P.J. 2003. The braincase of Giganotosaurus carolinii (Dinosauria: Theropoda) from the upper cretaceous of Argentina. Journal of Vertebrate Paleontology, 22:802---811.
Coria, R.A. and Currie, P.J. 2006. A new carcharodontosaurid (Dinosauria, Theropoda) from the Upper Cretaceous of Argentina. Geodiversitas, 28:71---118. Coria, R.A. and Salgado, L. 1995. A new giant carnivorous dinosaur from the Cretaceous of Patagonia. Nature, 377:224. DOI: 10.1038/377224a0.
Erickson, G.M., Makovicky, P.J., Currie, P.J., Norell, M.A., Yerby, S.A., and Brochu, C.A. 2004. Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs. Nature, 430:772.
Folkes, D. 2023. [online]. The LARGEST theropod dinosaur known to science…. THECODONTIA. Retrieved February 27, 2025, from https://www.thecodontia.com/blog/the-largest-theropod-dinosaur-known-to-science.
Hartman, S.A. 2013. [online]. Mass estimates: North vs South redux. Dr. Scott Hartman’s Skeletal Drawing.com. Retrieved August 16, 2023, from https://www.skeletaldrawing.com/home/mass-estimates-north-vs-south-redux772013.
Hutchinson, J.R., Bates, K.T., Molnar, J., Allen, V., and Makovicky, P.J. 2011. A computational analysis of limb and body dimensions in Tyrannosaurus rex with implications for locomotion, ontogeny, and growth. PLoS One, 6:e26037. https://doi.org/10.1371/journal.pone.0026037.
Larramendi, A., Paul, G.S., and Hsu, S. 2021. A review and reappraisal of the specific gravities of present and past multicellular organisms, with an emphasis on tetrapods. The Anatomical Record, 304:1833---1888. https://doi.org/10.1002/ar.24574.
Larson, N.L., Larson, P.L., and Carpenter, K. 2008. One hundred years of Tyrannosaurus rex: the skeletons. Tyrannosaurus rex, the tyrant king, 1:56. Indiana University Press, Bloomington, IN.
Larson, P.L. 2008. Variation and sexual dimorphism in Tyrannosaurus rex. Tyrannosaurus rex: The Tyrant King, 103---130.
Mallon, J.C. and Hone, D.W.E. 2024. Estimation of maximum body size in fossil species: A case study using Tyrannosaurus rex. Ecology and Evolution, 14:e11658. https://doi.org/10.1002/ece3.11658.
Mortimer, M. 2025. [online]. Tyrannosauroidea. The Theropod Database. Retrieved February 28, 2025, from https://theropoddatabase.github.io/Tyrannosauroidea.html#Tyrannosaurusrex.
Mazzetta, G.V., Christiansen, P., and Fariña, R.A. 2004. Giants and bizarres: body size of some southern South American Cretaceous dinosaurs. Historical Biology, 16:71---83. https://doi.org/10.1080/08912960410001715132.
Myhrvold, N.P. 2013. Revisiting the estimation of dinosaur growth rates. PloS one, 8:e81917.
Naturalis. 2018. Tyrannosaurus rex Trix in our museum. Sketchfab. Retrieved February 21, 2025, from https://sketchfab.com/models/67e4573e2fe849f4958bb702797b938e/embed?autostart=1.
Paes, H. 2020. [online]. Tyrannosaurus rex skeletal reconstruction. DeviantArt. Retrieved February 28, 2025, from https://www.deviantart.com/randomdinos/art/Tyrannosaurus-rex-skeletal-reconstruction-831025948.
Paul, G.S., Persons, W.S., and Van Raalte, J. 2022. The Tyrant Lizard King, Queen and Emperor: Multiple Lines of Morphological and Stratigraphic Evidence Support Subtle Evolution and Probable Speciation Within the North American Genus Tyrannosaurus. Evolutionary Biology, 49:156---179. DOI: 10.1007/s11692-022-09561-5.
Paul, G.S. 2024. The Princeton Field Guide to Dinosaurs. Princeton University Press.
Persons, W.S., Currie, P.J., and Erickson, G.M. 2020. An older and exceptionally large adult specimen of Tyrannosaurus rex. The Anatomical Record, 303:656---672. https://doi.org/10.1002/ar.24118.
Snively, E., O’Brien, H., Henderson, D.M., Mallison, H., Surring, L.A., Burns, M.E., Jr, T.R.H., Russell, A.P., Witmer, L.M., Currie, P.J., Hartman, S.A., and Cotton, J.R. 2019. Lower rotational inertia and larger leg muscles indicate more rapid turns in tyrannosaurids than in other large theropods. PeerJ, 7:e6432. PeerJ Inc. https://doi.org/10.7717/peerj.6432.
Therrien, F. and Henderson, D.M. 2007. My theropod is bigger than yours… or not: estimating body size from skull length in theropods. Journal of Vertebrate Paleontology, 27:108---115. https://doi.org/10.1671/0272-4634(2007)27[108:MTIBTY]2.0.CO;2.
SpinoInWonderland. 2022. [online]. Volumetric estimate for Giganotosaurus. The Sauropodomorph’s Lair. Retrieved February 27, 2025, from https://thesauropodomorphlair.wordpress.com/2022/01/09/volumetric-estimate-for-giganotosaurus/.
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Archive

A Specialized Cretaceous Pliosaurid and the Convoluted Pathways of Plesiosaur Evolution

---posted 21⁰⁰, 03/06/2017

Thalassophonean pliosaurs are some of the most iconic and long-lasting radiations of marine reptiles. Throughout their reign, a time span that lasted from the Callovian to the Turonian, almost all members of the clade were macrophagous carnivores. Some, such as Pliosaurus and Kronosaurus, were evidently apex predators with skulls and jaws exceeding 2 m in length and could have preyed on virtually any coexisting animal (Foffa et al. 2014, McHenry 2009, Taylor & Cruickshank 1993).

The newly described thalassophonean Luskhan itilensis Fischer et al. 2017 from the Hauterivian of western Russia notably deviates from this trend. Judging from a subcomplete skeleton preserving large parts of the appendicular and axial skeleton and a complete skull with associated mandible, its functional anatomy suggests a very different ecological niche from those held by other thalassophoneans. While the specimen is large, the lower jaw measuring 159 cm and total length estimated at 6.5 m, the morphology of its skull is much more reminiscent of polycotylid plesiosauromorphs or basal, plesiomorphic pliosaurids.

Morphospace analyses based on craniodental features confirm that Luskhan (as does Peloneustes) plots much more closely with non-thalassophonean pliosaurs and polycotylids than it does with macrophagous thalassophoneans. Several telling traits mark Luskhan as a mesopredatory piscivore and/or teuthivore rather than a generalist apex predator: First and foremost, the rostrum and lower jaw are considerably more slender than in other Thalassophoneans. Secondly, the dentition is relatively small and isodont, lacking the enlarged caniniform anterior teeth of other pliosaurs, and has a more limited posterior extent. Finally, Luskhan’s mandibular symphysis makes up 34% of mandible length, greater than in any other pliosaur but within the range seen in polycotylids (a long mandibular symphysis can be linked to reduced bending and torsional strength of the jaw, Walmsley 2013).

Life reconstruction of Luskhan itilensis with a scuba diver for scale.

In all cranial ecomorphological aspects, Luskhan hence converges with polycotylids, despite being a basal member of Brachaucheninae, a clade that otherwise famously includes gigantic, macropredaceous taxa such as Kronosaurus queenslandicus. The recent discovery of another basal Brachauchenine from the Hauterivian of Russia, Makhaira rossica, which does show pronounced macrophagous adaptions (Fischer et al. 2015) furthermore indicates that brachauchenines were not secondarily macrophagous, despite having lost some of the traits found in earlier, Jurassic thalassophoneans. Luskhan thus probably represents a unique side-branch of the Pliosauridae, that independently evolved many of the features Polycotylids would sport 40 Ma later after the extinction of pliosaurs.

This is a modified translation of an entry recently published on GeoHorizon.

–––References:
Fischer, V., Arkhangelsky, M. S., Stenshin, I. M., Uspensky, G. N., Zverkov, N. G. and Benson, R. B. J. 2015. Peculiar macrophagous adaptations in a new Cretaceous pliosaurid. Royal Society Open Science 2 (12): 150552.
Fischer, V., Benson, R. B. J., Zverkov, N. G., Soul, L. C., Arkhangelsky, M. S., Lambert, O., Stenshin, I. M., Uspensky, G. N. and Druckenmiller, P. S. In press. Plasticity and Convergence in the Evolution of Short-Necked Plesiosaurs. Current Biology.
Foffa, D., Cuff, A. R., Sassoon, J., Rayfield, E. J., Mavrogordato, M. N. and Benton, M. J. 2014. Functional anatomy and feeding biomechanics of a giant Upper Jurassic pliosaur (Reptilia: Sauropterygia) from Weymouth Bay, Dorset, UK. Journal of Anatomy 225 (2): 209–219.
McHenry, C. R. 2009. ‘Devourer of Gods’: The Palaeoecology of the Cretaceous Plisaur Kronosaurus Queenslandicus. University of Newcastle. Taylor, M. A. and Cruickshank, A. R. I. 1993. Cranial anatomy and functional morphology of Pliosaurus brachyspondylus (Reptilia: Plesiosauria) from the Upper Jurassic of Westbury, Wiltshire. Philosophical Transactions of the Royal Society of London B: Biological Sciences 341 (1298): 399–418. Walmsley, C. W., Smits, P. D., Quayle, M. R., McCurry, M. R., Richards, H. S., Oldfield, C. C., Wroe, S., Clausen, P. D. and McHenry, C. R. 2013. Why the Long Face? The Mechanics of Mandibular Symphysis Proportions in Crocodiles. PLoS ONE 8 (1).

The Trackmakers of Broome

---posted 16³⁰, 10/04/2017

The Broome Sandstone in Western Australia has long been known to those people inclined towards Dinosaur ichnology, but as it turns out, only snippets of its extraordinarily rich ichnofauna had actually been described up until recently. An intriguing new paper by Salisbury et al. recently provided a full scientific description based on the results of over 400 hours of field work on the Western-Australian Dampier Peninsula, where the authors documented what may be the most diverse dinosaurian ichnofauna currently known to science, with somewhere between 11 and 21 distinct track types recognized among 150 diagnosable tracks. Among the trace fossils found at the Lower Cretaceous (Valanginian-Barremian) locality are several Sauropods, Ornithopods, Theropods and Thyreophorans.

Deposition of the Broome Sandstone primarily took place in distal river- and deltaic environments. Its age and rich fauna make it a prime locality for studying the otherwise poorly known Gondwanan Dinosaur faunas of the earlier part of the Lower Cretaceous. The faunal composition at Broome is dominated by various sauropods, but also includes several different theropods, ornithopods and thyreophorans. In this regard it bears some resemblance to Laurasian assemblages of the Upper Jurassic, such as the Morrison and Lourinha formations. This hints at a comparatively smaller degree of faunal turnover at the Jurassic-Cretaceous boundary in Gondwanan ecosystems than happened in Laurasia.

While the presence of dinosaur ichnofossils is nothing new, with theropod footprints featuring prominently in aboriginal mythology and the Dampier Peninsula being the site of the first described sauropod tracks from Australia, the full scope of its fossil biodiversity turns out to be quite staggering, even having known about previous significant discoveries at the locality.

Apart from tracks assignable to two or three previously described ichnotaxa (Megalosauropus broomensis, Wintonopus latomorum and cf. Amblydactylus kortmeyeri), Salisbury et al. described a further six novel ichnotaxa: the theropod Yangtzepus clarkei , the sauropod Oobardjidama foulkesi (Sauropoda), ornithopods Wintonopus middletonae and Walmadanyichnus hunteri and the probable stegosaurs Garbina roeorum and Luluichnus mueckei. Apart from these taxa, a insufficiently diagnosable tracks are designated as sauropod morphotypes A-E, theropod morphotypes A-C and thyreophoran morphotypes A-B. Finally, some tracks don’t warrant a taxonomic assignment below the level of Dinosauria.

Especially noteworthy is that some of the Broome tracks are perplexingly enormous. It is "Broome Sauropod Morphotype A" that is most impressive of all. Its pes prints average 106cm wide and 137cm long, but the largest specimen is 140cm wide and at least 175cm long. What’s more, the authors specifically rule out these tracks being transmitted reliefs or having been enlarged through erosion. The bottomline seems to be that these gigantic dimensions appear to be legit, and that they are probably the biggest footprints in the world for which that can be said. By comparison, the feet of the holotype of Diplodocus carnegii are a mere 59cm wide, which would result in a width of 62-71cm with realistic amounts (5-20%) of soft tissue. By the same means, the feet of the subadult holotype of Giraffatitan can be estimated at 77-88cm wide. This means that conservatively, the largest broome footprints are almost twice the size of Diplodocus or 59% larger than Giraffatitan.

Comparative length and width measurements of all identified pes prints.

Sauropods are not the only cases of gigantism in this ichnofauna. One pes print tentatively assignable to Garbina roeorum measures 80 by 70cm, which would make it enourmous for a stegosaur. Some ornithopod footprints attain or approach 80cm in length, meaning that Australia was home to giant ornithopods remains of which have yet to be unearthed. And a large manual track 29cm wide may pertain to a very large ankylosaur.

This is an abbreviated translation of a blog entry recently published in German on GeoHorizon.

–––References:
Salisbury, S. W.; Romilio, A.; Herne, M. C.; Tucker, R. T.; Nair, J. P. (2017): The Dinosaurian Ichnofauna of the Lower Cretaceous (Valanginian–Barremian) Broome Sandstone of the Walmadany Area (James Price Point), Dampier Peninsula, Western Australia. Journal of Vertebrate Paleontology 36 (sup1) pp. 1-152, DOI: 10.1080/02724634.2016.1269539

Wedel, M. 2009. How big were the biggest sauropod trackmakers? Sauropod Vertebra Picture of the Week. Url: https://svpow.com/2009/10/13/how-big-were-the-biggest-sauropod-trackmakers last accessed 10/04/2017

Are the teeth of Tyrannotitan less blade-like than those of other Carnosaurs?

---posted 19²²11/09/2015

Short answer: No
Theropod tooth data

Crown base ratios of Carnosaurs as an indicator of labiolingual compression, with Tyrannosaurus rex as an outgroup. Tooth data from Canale et al. 2015, Royo-Torres et al. 2009 and Smith et al. 2005

Frankly, I have got no idea where this myth originally came from, but being called Tyrannotitan does not imply being in any way more similar to Tyrannosaurus than its relatives were. T. rex does not have a monopoly on that part of its name, on the other hand it does seem to have one on its blunt, incrassate teeth.

–––References:
Canale, Juan I.; Novas, Fernando E.; Pol, Diego (2015): Osteology and phylogenetic relationships of Tyrannotitan chubutensis Novas, de Valais, Vickers-Rich and Rich, 2005 (Theropoda: Carcharodontosauridae) from the Lower Cretaceous of Patagonia, Argentina. Historical Biology: An International Journal of Paleobiology, 27 (1), pp. 1-32.
Royo-Torres, R.; Cobos A.; Alcalá, L. (2009): Diente de un gran dinosaurio terópodo (Allosauroidea) de la Formación Villar del Arzobispo (Titónico-Berriasiense) de Riodeva (España). Estudios Geológicos, 65 (1), pp. 91-99.
Smith, Joshua B.; Vann, David R.; Dodson, Peter (2005): Dental Morphology and Variation in Theropod Dinosaurs: Implications for the Taxonomic Identification of Isolated Teeth. The Anatomical Record, 285 (A), pp. 699-736.

The Myth and Truth of UCMP 118742

---posted 17²⁰, 20/08/2015

The Berkeley Tyrannosaurus rex specimen UCMP 118742. Anyone who has made experiences with T. rex fanatics has probably read of this specimen at some point, as evident from a quick google search most likely in the context of someone asserting some extreme body size for it. Why is it so famous? Because it is large, of course. How large exactly? That part of the equation always seems to get misrepresented.

There is only an isolated maxilla, which makes my job both easier and more difficult at the same time. More difficult, because as always when scaling up from a single bone there is quite a bit of uncertainty involved in the final estimate.
Easier because Larson (2008) luckily gave some measurements, and those represent pretty much everything relevant that you can measure in the specimen. So there is virtually nothing left that could suggest a size estimate other than what is indicated by these measurements.
So how do UCMP 118742’s measurements stack up against the size record holder and most complete known tyrannosaur, FMNH PR 2081?

Measurements of the Berkeley maxilla and Sue compared.
	UCMP 118742	FMNH PR 2081	ratio
depth	390	400	0.975
length	810	855	0.947
diagonal length	690	720	0.958
tooth row length	625	645	0.969

The obvious implication is that UCMP 118742 is on average just 96.2% the size of Sue, and no more than 97.5% based on the largest measurement. The geometric mean of its maxillary measurements is 607.5, compared to 631.3 for FMNH PR 2081, implying a total length of 11.84m, which is large, but not exceptional. To anyone with an elementary school level of math education this should suggest that Sue, at 12.3m, is the bigger specimen, shouldn’t it?

Messing with growth rates
Well, sadly, this is only the beginning of the argument. Granted, they somehow manage to make it look as if the specimen itself was already larger than sue, which is plain wrong, looking at the fact that every single one of its measurements is actually smaller. But there is an additional bit of information about the individual from which this maxilla came in Table S2 of the Supplement of Erickson et al. 2006: It is apparently 16 years of age. Now, as we know T. rex’ growth slowed down as it matured, until older adults (such as Sue) only experienced negligible growth, and a 16 year old would still be in a phase of fast growth (albeit not a juvenile, as fanboys like to claim), right?
This is Erickson et al.’s growth model for T. rex: Growth curve for Tyrannosaurus rex following Erickson et al. 2004
The weight figures are the typical underestimation based on obsolete femur-circumference regressions, but we can use them to compare between each other and estimate total lengths:

Growth curve for Tyrannosaurus rex, modified from Erickson et al. 2004 so that the dependent variable is a length estimate scaled isometrically from FMNH PR 2081 instead of a weight estimate.

The first vertical line demarks the age of 16 years, the second that of 28 years, the age of the oldest known Tyrannosaurus.
This is technically what the fanboy claims are based on; the assumption that they can extrapolate the theoretical "fully grown", size of UCMP 118742 based on its actual size and age. That they did so using incorrect and biased premises is hopefully self-evident, but hypothetically, is this a sound method?
The model predicts total lengths of 9.62m and 12.22m at ages of 16 and 28 years respectively. So during this part of its life, the average T. rex is expected to grow 27%, or 2.6m. Applying these to UCMP 118742 results in hypothetical "adult" sizes of 15.05m and 14.45m respectively.

Before jumping to conclusions: This is not to say that this T. rex would ever have grown that big, and far less even to say that this means T. rex was 14-15m long (it is not, more on that in a future post).
There are several problems with this method. Perhaps the most obvious is sample size. The growth model bases on just a handful of specimens, so the uncertainty involved is very high, and so is the potential impact of adding even a single additional specimen.

Sample of Tyrannosaurus rex length estimates based on femur lengths in Larson (2008) added to data and growth model from Erickson et al. 2004 to demonstrate variability of T. rex sizes with respect to the crowth curve.

Attentive readers might have noticed that UCMP 118742 was not part of the original dataset (not surprising considering the data set bases on femur measurements), and adding it could have a rather significant impact, meaning these estimates are already biased because they exaggerate the difference between the average 16-year old and a fully grown T. rex.

Also, the method assumes that its growth would have continued just as fast as that of any other T. rex (14.45m estimate), or even at an accellerated rate (15.05m estimate). But this was probably not the case, after all, had it grown just like any other T. rex, it would not have been an estimated 11.8m long at the age of 16 in the first place
Many people become oblivious of individual variation as soon as it comes to the tyrant king, but not all specimens of a species grow the same way, and being larger than expected for one’s age during adolescence does not automatically mean being larger later in life (think back to your time at school!). One T. rex might already have been close to full-sized at a given age, while others weren’t.
And indeed, that is what seems to be the case with T. rex specimens that apparently stopped growing at a much earlier age than predicted by this model, around the age of UCMP 118742 to be exact. Horner & Padian (2004) document this in MOR 1125, which they state to have "effectively stopped growing at 16±2 years". This could plausibly apply here too; since the animal had already achieved a large size it could also have grown more slowly from then on. The tyrannosaurine analogue of a human teenager who is very tall at 15, but doesn’t get any larger from then on.
Considering it had already reached a size consistent with those of large adults (e.g. CM 9380), is there any reason to assume this individual would have grown much bigger? Probably not.
And finally, a note to all those people who were eager to see T. rex as the unchallenged biggest theropod due to just this specimen: In all probability, similar cases existed among other giant theropods, their ontogeny just hasn’t been studied yet and/or too few specimens have been found so far. This is a single individual, even if it were the abnormal giant of your wildest dreams, it would not have a profound impact on the size of T. rex as a species.

In a nutshell, it is pointless to estimate a hypothetical adult size for such a specimen, and it is dishonest to refer to it as if it were an actual size recorded for the species. We will never know how big it would have grown, but it is most likely that it is just a precocious teenager, big for its age, but not necessarily extraordinarily large had it grown into senescence. and in the end, keep in mind that it didn’t. It is better to stick to real specimens.

–––References:
Larson, Peter (2008): Variation and Sexual Dimorphism in Tyrannosaurus rex. In: Larson, Peter; Carpenter, Kenneth: Tyrannosaurus rex the Tyrant King. Bloomington, pp. 103-128.
Erickson, Gregory M.; Currie, Philip J.; Inouye, Brian D.; Winn, Alice A. (2006): Tyrannosaur Life Tables: An Example of Nonavian Dinosaur Population Biology. Science, 313 (5784), pp. 213-217.
Erickson, Gregory M.; Makovicky, Peter J.; Currie, Philip J.; Norell, Mark A.; Yerby, Scott A.; Brochu, Christopher A. (2004): Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs. Nature, 430 (7001), pp. 772-775.
Horner, John R.; Padian, Kevin (2004): Age and growth dynamics of Tyrannosaurus rex. Proceedings of the Royal Society B, Vol. 271 (1551), pp. 1875-1880.

Carcharocles subauriculatus–bigger yet smaller than we think?

---posted 19¹¹, 22/07/2015

Well first of all, C. subauriculatus is actually the older, and hence the valid name, not the inexplicably more popular C. chubutensis (PalaeoDB ONLINE).

This shark species is not nearly as well known, or indeed as common (at least based on ocurrence in museum displays) as its bigger relative, C. megalodon, but it, too, is among the largest chondrichthyans in earth’s history.

The size figure one sees cited commonly is a little over 12m, based on the regression between tooth height and total length in Gottfried et al. (1996) and the largest teeth, which reportedly approach 13cm in diagonal, or slant length. However, this is fallacious on more than one level, because the method was not supposed to be used with the diagonally measured length, but with vertical tooth height, and because it assumes the same proportions within the dentition as in Great White Sharks, which do not actually appear to be present in C. subauriculatus.

So, how large was this taxon really?
Purdy et al. 2001 figured, described and listed measurements for two sets of associated teeth, each representing the partial dentition of a single animal.
Better still, the fact that the lateral cusplets (a paedomorphic feature) are absent or very weakly developed is a strong indication that the specimens were adults at the time of death.
The smaller of the two, USNM 411881, has one upper quadrant almost completely preserved. Based on the relative widths of the overlapping teeth, the second one, USNM 299832, is 15.8% bigger.
Completing the dentition by extrapolating the missing anteriormost tooth from the larger specimen (and the diminuitive posteriormost tooth, which is not preserved in either specimen, from C. megalodon), the result is an estimated summed tooth width of ~600m, resulting in a total of ~1200mm in both sides of the upper jaw. Adding 15% of interdental spacing (admittedly a little liberal), this results in the overall length of the upper toothrow being ~1380mm, that of the larger individual is thus an estimated 1598mm long.

How does this help us? Much it turns out, since estimating the size of a shark from a complete or nearly complete dentition is much more reliable than using a single tooth. Lowry et al. 2009 examined the relationship between the length of the tooth row (or bite circumference) and the total length of the shark, and found a strong correlation. Since the best overall analogue in terms of size, ecology and morphology is probably the Great White, the formula relevant here is that for C. carcharias, which we can transform and solve for total length:

LOG(tooth row length)=1.007*LOG(total length)-0.8
LOG(tooth row length)=LOG(10^-0.8*total length^1.007)
tooth row length=10^-0.8*total length^1.007
(tooth row length/10^-0.8)^(1/1.007)=total length

Length estimates based on Lowry et al. 2009

So these specimens were ~8.2 and ~9.5m long, and based on published length-weight-regressions (Casey & Pratt 1985, Kohler et al. 1995) for C. carcharias they probably massed ~5.0-6.0 and ~7.8-9.4t respectively.
But that is not the end of the story. Purdy et al. mention a first lower lateral tooth that is 9.5cm tall, which is 79% and 56% bigger than the equivalent teeth in the aforementioned dentitions, suggesting a tooth-row length of ~2474-2489mm and a total length of 14.5-14.7m.
To put this into perspective, that is well within the territory of C. megalodon, and actually above its average size (which, for adults, is about 14m based on data from Pimiento & Balk 2015).
Obviously every estimate that just bases on a single tooth is prone to huge margins of error, so this should be taken with a grain of salt. All this shows is that what is popularized about this species’ size is not founded on facts all that firmly.

–––References:
  Casey, John G.; Pratt, Harold L. (1985) Distribution of the White Shark, Carcharodon carcharias, in the Western North Atlantic. Memoirs of the Southern California Academy of Sciences, 9 (Biology of the White Shark, a Symposium.) pp. 2-14
  Kohler, Nancy E.; Casey, John G.; Turner, Patricia A. (1995): Length-Length and Length-Weight Relationships for 13 Shark Species from the Western North Atlantic. Fishery Bulletin, 93 pp. 412-418
  Lowry, Dayv; Castro, Andrey L. F. de; Mara, Kyle; Whitenack, Lisa B.; Delius, Bryan; Burgess, George H.; Motta, Philip: (2009): Determining shark size from forensic analysis of bite damage. Marine Biology, 156 pp. 2483-2492
  Pimiento, Catalina; Balk, Meghan A. (2015): Body-size trends of the extinct giant shark Carcharocles megalodon: a deep-time perspective on marine apex predators. Paleobiology, 41 (3) pp. 479-490
  Purdy, Robert W.; Schneider, Vincent P.; Applegate, Shelton P.; McLellan, Jack H.; Meyer, Robert L.; Slaughter, Bob H. (2001): The Neogene Sharks, Rays, and Bony Fishes from Lee Creek Mine, Aurora, North Carolina. In: Ray, Clayton E.; Bohaska, David J.: Geology and Paleontology, of the Lee Creek Mine, North Carolina, III. Smithsonian Contributions to Paleobiology, 90 pp. 71-202
  PaleoDB: Fossilworks: Carcharodon subauriculatus. http://fossilworks.org/bridge.pl?a=taxonInfo&taxon_no=83172 (accessed 21 July 2015)

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