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![[Plateosaurus engelhardti ] in Triassic morning. by Guindagear](https://images-wixmp-ed30a86b8c4ca887773594c2.wixmp.com/f/41df78b1-f116-4998-a5e0-1e2885d7fd44/d7xd2ey-ae74799c-0b70-41e9-bf7d-7fa3c438bdd2.jpg/v1/fill/w_500,h_250,q_70,strp/_plateosaurus_engelhardti___in_triassic_morning__by_guindagear_d7xd2ey-250t.jpg?token=eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJzdWIiOiJ1cm46YXBwOjdlMGQxODg5ODIyNjQzNzNhNWYwZDQxNWVhMGQyNmUwIiwiaXNzIjoidXJuOmFwcDo3ZTBkMTg4OTgyMjY0MzczYTVmMGQ0MTVlYTBkMjZlMCIsIm9iaiI6W1t7ImhlaWdodCI6Ijw9NjQwIiwicGF0aCI6IlwvZlwvNDFkZjc4YjEtZjExNi00OTk4LWE1ZTAtMWUyODg1ZDdmZDQ0XC9kN3hkMmV5LWFlNzQ3OTljLTBiNzAtNDFlOS1iZjdkLTdmYTNjNDM4YmRkMi5qcGciLCJ3aWR0aCI6Ijw9MTI4MCJ9XV0sImF1ZCI6WyJ1cm46c2VydmljZTppbWFnZS5vcGVyYXRpb25zIl19.IWHhQcx6tgc9G8WFR4hEUhRJ7RR8nBPxNSTx6b5f5xI)
Dilophosaurus wetherilli, from the Hettangian or Sinemurian Kayenta Formation of Arizona, to many seems to be a sort of quintessential early theropod.
And there are a number of good reasons for that:
Firstly, it’s been known for a long time. Welles dug up several nice, articulated skeletons as early as the 1940s. Secondly, it’s from the US…that often (though not always) helps things along. Thirdly, it’s morphology was so clearly different from other theropods known at the time, and is still so unusual compared to other well-known theropods, that it’s easily recognizable to anyone, probably leading to its inclusion, albeit in a very inaccurate form, in the original Jurassic Park movie.
And finally, it is true that Dilophosaurid-grade theropods, a number of stem-neotheropod taxa with very similar morphology (while probably not all forming a natural clade), were widespread components of upper Triassic and Lower Jurassic faunas worldwide.
Gojrasaurus quayi from the Norian of New Mexico, Zupaysaurus rougieri from the Norian of Argentina and Liliensternus liliensterni from the Norian of Germany are among the earliest theropods (note Herrerasaurids’ status as theropods is very questionable) that we could consider "large-bodied", and which filled the apex-predatory role in their ecosystems.
This type of theropod persists into the Lower Jurassic: The Elliot Fm. in South Africa (Hettangian/Sinemurian) has yielded Dracovenator regenti. The Hettangian Lufeng Fm. has Sinosaurus triassicus (formerly "Dilophosaurus sinensis"). And perhaps most famously, the Hanson Formation of Antarctica has produced Cryolophosaurus ellioti. However the latter two taxa might actually be basal Tetanurae, which would mean these forms with somewhat similar morphological features were only quite distantly related, but also imply this was a common morphology for basal members of all neotheropod lineages. And of course there is Dilophosaurus wetherilli itself, famous for its double-crests and being one of the few distinct morphotypes of theropods recognized in the early 20th century.
All of these seem to share weird head crests, more or less developed premaxillary notches and relatively slender postcranial body proportions.
As the largest predators in their various respective ecosystems, naturally we must wonder about the size of these animals.
Commonly given mass estimates tend to be extremely low for the proposed dimensional measurements. This is generally explained by the very gracile, coelophysoid-grade morphology of these taxa. Paul (³ and 2009) estimates the holotype of Dilophosaurus at 283 kg and the largest specimen at 400 kg. Smith et al. 2007 estimate Cryolophosaurus at 465 kg based on femur circumference (claiming it to be the largest Lower Jurassic theropod), even though the specimen has a femur length similar to an adult Allosaurus’ massing 1.5 t.
So were these animals really that small?
Most specimens of Dilophosaurus are, in fact, juveniles. That includes the 6 m long holotype skeleton (UCMP 37302, 53 cm skull, 56 cm femur) described in detail by Welles (1984), as well as one of the original paratypes (Welles 1970), another partial skeleton referred by Tykoski (2005) and part of the fragmentary material described by Gay (2001).
The only substantially complete adult individual is one of the paratypes, UCMP 77270 (Welles 1970). This individual has dorsal and sacral vertebrae on average 18% longer than the holotype, although its precaudals in general are 14% longer, owing to the negatively allometric neck length. It also has an appreciably larger skull, at 62 cm, and a slightly longer femur, at 59 cm (all measurements for this specimen from the theropod database², holotype from Welles 1984).
Dilophosaurus tends to get portrayed as downright ridiculously skinny, likely mostly inspired by Greg Paul’s shrinkwrapped skeletal.
To test this, I made a volumetric 3D model based on ScottHartman’s composite Dilophosaurus skeletal (which is considerably more robust-looking than Paul’s), scaled to 6 m total axial length (that measurement by Welles is probably reliable, as the skeleton was found in articulation and is very complete). For the body width, I adapted the dorsal view skeletal of Syntarsus rhodesiensis from Paul (2016), which is probably quite conservative.
For the holotype, I’m getting a volume of 366 l, which translates to a mass of 330 kg (assuming a density of 0.9). So very light for its length, but a bit heavier than the 283 kg Paul and Mortimer list it at.
Dilophosaurus tends to get portrayed as downright ridiculously skinny, likely mostly inspired by Greg Paul’s shrinkwrapped skeletal.
To test this, I made a volumetric 3D model based on ScottHartman’s composite Dilophosaurus skeletal (which is considerably more robust-looking than Paul’s), scaled to 6 m total axial length (that measurement by Welles is probably reliable, as the skeleton was found in articulation and is very complete). For the body width, I adapted the dorsal view skeletal of Syntarsus rhodesiensis from Paul (2016), which is probably quite conservative.
For the holotype, I’m getting a volume of 366 l, which translates to a mass of 330 kg (assuming a density of 0.9). So very light for its length, but a bit heavier than the 283 kg Paul and Mortimer list it at.
We can estimate total length of the adult UCMP 77270, using the length ratios of all overlapping vertebrae, as ~6.9 m. I’d suggest scaling body mass from only the dorsal and sacral vertebrae, because the largest part of the mass is located in the torso, which gives a mass estimate of ~544 kg.
A couple of other speculative size estimates for more or less related species:
>Liliensternus liliensterni (larger individual, subadult, von Huene 1934):
>Gojirasaurus quayi (UCM 47221, subadult, Carpenter 1997):
Femur length: 42 cm
Total length (based on all precaudal vertebrae, scaling from UCMP 37302): 5.1 m
Body mass (based on dorsal and sacral vertebrae): 178 kg>Gojirasaurus quayi (UCM 47221, subadult, Carpenter 1997):
Tibia length: 47 cm
Pubis length: 50 cm
Total length (based on 3 mid-posterior dorsal vertebrae, scaling from UCMP 37302): 5.0 m
Total length (based on 3 mid-posterior dorsal vertebrae, scaling from UCMP 37302): 5.0 m
Total length (based on tibia): 5.1 m
Body mass (based on dorsal vertebrae and tibia): 187-199 kg
(long pubis might imply deeper body shape)
>Zupaysaurus rougieri (PULR-076, ?adult, Arcucci & Coria 2003):
Skull length e. 42 cm (measured in Fig. 2E)
Total length (based on skull and axis length, scaling from UCMP 37302): 5.3 m
Body mass (same method): ?221 kg
(very long axis might just be due to proportionately long neck)
>Dracovenator regenti (BP/1/5243, ?adult, Yates 2005):
Skull length e. 56 cm
Total length (based on skull length): 6.3 m
Body mass (based on skull length): 389 kg
>Cryolophosaurus ellioti (FMNH PR1821, late subadult/young adult, Smith et al. 2007):
Femur length: 77 cm
Total length (based on all precaudal vertebrae, scaling from UCMP 37302): 7.9 m
Body mass (based on the dorsal and sacral vertebrae): 794 kg
Body mass (based on reverse-calculated femur-circumference of 233mm from Smith et al. 2007, using Anderson et al. 2009 and cQE-phylocor from Campione et al. 2014): 687 kg
Discussion and Conclusions (for now):
Dilophosaurus, and probably most other coelophysoids, were probably a little heavier than commonly cited, and quite a lot when taking into account that many are immature. Adult Dilophosaurus seem to have approached or exceeded 500 kg, not the 400kg from Paul or 330 from Mortimer. However this estimate is very sensitive to placement of the vertebrae in question, and there is some serious confusion because Welles confusingly labels dorsals 1 through 5 as pectorals, while Mortimer confusingly labels what I think is probably dorsal/pectoral 1 as cervical 10. So take the size of the larger individual with a grain of salt. Welles (1970) claims the specimen was one third larger; if he was referring to linear dimensions, then this estimate is quite conservative, although if he meant volumetrics it is too high.
The commonly cited length estimate for Liliensternus are pretty much spot-on when scaling from vertebral lengths of Dilophosaurus. The mass estimates however, such as Paul’s (2009 and ³ 130kg) appear too low based on the relative length of the dorsal and sacral vertebrae. Furthermore, the known specimens are both subadults (Tykoski 2005), which implies larger sizes for adult individuals.
Gojirasaurus is possibly slightly larger than Liliensternus, based on the vertebral and tibial lengths, although the lack of available cervicals results in a slightly lower total length estimate based on the dorsals alone. Its pubis is even slightly longer than that of the Dilophosaurus holotype, which could imply a slightly deeper-bodied morphology. Carpenter’s estimate of 5.5 m could be roughly accurate.
Zupaysaurus has a relatively small skull based on the restoration in the description paper, but a very long axis (11 cm). The mass estimate presented here might be too high due to this. There are more vertebrae preserved, which sadly don’t have any reported measurements, so I currently can’t make a better estimate.
Zupaysaurus has a relatively small skull based on the restoration in the description paper, but a very long axis (11 cm). The mass estimate presented here might be too high due to this. There are more vertebrae preserved, which sadly don’t have any reported measurements, so I currently can’t make a better estimate.
I agree with Smith et al. 2007’s claim that Cryolophosaurus is the largest Lower Jurassic theropod, but I think their mass figure and most other size figures for this taxon are underestimates. The holotype may well have approached 8m and 800 kg (which is also much more consistent with the reported lengths of its vertebrae and the femur). Finally, considering its poorly fused sacrum (Smith et al.), it may well be a young individual that was still well below average adult size.
References:
References:
Anderson, J. F., A. Hall‐Martin, and D. A. Russell. 1985: Long‐bone circumference and weight in mammals, birds and dinosaurs. Journal of Zoology 207:53–61.
Arcucci, A. B., and R. A. Coria. 2003: A new Triassic carnivorous dinosaur from Argentina. Ameghiniana 40:217–228.
Campione, N. E., D. C. Evans, C. M. Brown, and M. T. Carrano. 2014: Body mass estimation in non-avian bipeds using a theoretical conversion to quadruped stylopodial proportions. Methods in Ecology and Evolution 5:913–923.
Carpenter, K. 1997: A Giant Coelophysoid (Ceratosauria) Theropod from the Upper Triassic of New Mexico.(With 8 figures and 3 tables in the text). Neues Jahrbuch fur Geologie und Palaontologie-Abhandlungen 205:189–208.
Gay, R. 2001: New specimens of Dilophosaurus wetherilli (Dinosauria: Theropoda) from the early Jurassic Kayenta Formation of northern Arizona. Mesa Southwest Museum Bulletin 8:19–23.
von Huene, F. F. 1934: Ein neuer Coelurosaurier in der thüringischen Trias. Palaeontologische Zeitschrift 16:145–170.
Paul, G. S. 2009, 2016: The Princeton field guide to dinosaurs. Princeton University Press, Princeton.
Smith, N. D., P. J. Makovicky, W. R. Hammer, and P. J. Currie. 2007: Osteology of Cryolophosaurus ellioti (Dinosauria: Theropoda) from the Early Jurassic of Antarctica and implications for early theropod evolution. Zoological Journal of the Linnean Society 151:377–421.
Tykoski, R. S. 2005: Anatomy, ontogeny, and phylogeny of coelophysoid theropods.PhD Thesis, University of Texas at Austin.
Welles, S. P. 1970: Dilophosaurus (Reptilia, Saurischia), a new name for a dinosaur. Journal of Paleontology 44:989.
Welles, S. P. 1984: Dilophosaurus wetherilli (Dinosauria, Theropoda). Osteology and comparisons. Palaeontographica Abteilung A:85–180.
Yates, A. M. 2005: A new theropod dinosaur from the Early Jurassic of South Africa and its implications for the early evolution of theropods.
¹Hartman, Scott. 2015: New-look Dilophosaurus. DeviantArt. Downloaded from www.deviantart.com/scotthartma… on 9 September 2018.
²Mortimer. : Coelophysoidea. Downloaded from theropoddatabase.com/Coelophys… on 11 September 2018.
³Paul, Gregory S. 2010: Data - Gregory S. Paul’s Dinosaur Mass Table. Downloaded from gspauldino.com/data.html on 11 September 2018.
