Tyrants, Despots and Peons

The origin and evolution of Tyrannosauroidea [1] is one of the interesting puzzles in theropod phylogeny (the only one more fascination (with all due apologies to Tom Holtz) [2]. Inclusion of tyrannosaurids is a no-brainer, but the origin of tyrannosaurs has found itself in strange company, including rooted close to the origin of Maniraptora (oviraptorosaurs, dromaeosaurs, birds, and troodontids, and a few other odds and ends) [3], as the sister taxa to ornithomosaurs [4], or as the most basal lineage of Coelurosauria [2], to name just a few.

In the last few years, some old and some new taxa have been described and their evolutionary placement among or around tyrannosaurs has provided a fascinating perspective on what it might mean to be a dinosaur tyrant. Only the big tyrannosaurids seem to be really “tyrant-like” at all, with their giant, robust skulls, large body size, short arms, reduced manual digits, and so on. Basal tyrannosauroids don’t seem to have any of these features, but have a few other finer details. They seem to fall into three grades of tyrannosauroid: the tyrants, described as above as large-bodied, large-headed, small-armed, and few-fingered; the other two groups seem to be grades in the explicit sense, as they do not form explicitly monophyletic groups in and of themselves.

This led me to coin the term “despot” for the first group, which includes the “psuedo”-tyrants like Guanlong wucaii. Here, “despot” would simply be a “minor” tyrant, and certainly not on the order a truly “ruling” lizard like the Tyrannosauridae. Some of them even appear to form a smaller clade within the larger Tyrannosauroidea, such as Proceratosauridae [5]

“Despots” and “peons.” Skulls are scaled to the same base length (posterior margin of the distal quadrate condyles to the anterior margin of the alveolar rim of the premaxilla), or an equivalent measure when material is lacking. All scale bars equal 5 cm.

Above is a showcase of the cranial material of various tyrannosaur-like dinosaurs, some of which are labeled despots, and some as peons.

A. Tanycolagreus topwilsoni [6]. Originally proposed as a “classic” coelurid (allied to Coelurus itself), based on TPII 2000-9-29 (holotype) and reconstructed from [6]. From the Late Jurassic of the Morrison Formation. “Despot.”
B. A specimen referred to Stokesosaurus clevelandi [7], UUVP 2999 [7]. “Despot.”
C. Ornitholestes hermanni [8]. AMNH 619 (holotype) and only known skull, modified after [9]. “Peon.”
D. Dilong paradoxus [10]. IVPP V14243 (holotype), modified after [10]. “Peon.” [n1]
E. Guanlong wucaii [11]. IVPP V14531 (holotype adult skull [see G]), modified after [11]. “Despot.”
F. Proceratosaurus bradleyi [12] (removed from Megalosaurus as Megalosaurus bradleyi in [13]). NHM R4860 (holotype) modifed after [14]. “Despot.”
G. Guanlong wucaii [11]. IVPP V14532 (paratype juvenile skull [see E]). “Despot.”
H.Eotyrannus lengi [15]. IWCMS 1990.550 (holotype), modified after [16]. “Despot.”
I. Kileskus aristotocus [5]. ZIN PH 5/117 (holotype), modified after [5]. “Despot.”

I am not the first to implicate a grouping of basal coelurosaurs, although I did so several years ago [15,16] on the basis of the foreshortened and medially deflected premaxilla, an anterior process on the postorbital projecting into the orbit, etc.; Greg Paul [18] implicated a relationship between Ornitholestes hermannii and Proceratosaurus bradleyi on several features including the apparent nasal crest (absent in Ornitholestes [9]), shape of the squamosal and the nature of its contact with the quadratojugal, and the radial arrangement of the mesial dentition of the dentary.

As time advances, some of these theropods seem less and less like “tyrants” than others, and this has suggested that some may be non-despots simply because they fall outside a basic “tyrant”-like morphology. Some of them included the long-armed, vaguely compsognathid-like Dilong imperator [10], and may have also included Sinosauropteryx prima (or rather, a specimen referred to it [19]), and even Ornitholestes hermanni [9] even though it has autapomorphically shortened its skull distinctly.

Previous workers have also included additional taxa into Tyrannosauroidea that are not shown above due to the lack of distinct cranial material, although some braincases are known. They include Iliosuchus medullaris [13], although [20] disagreed and indicate it may be more basal than Coelurosauria; Itemirus medullaris [21], although again someone [22] disagreed, this time placing it among the Dromaeosauridae; Bagaraatan ostromi [23], originally described as a generalized and indeterminate coelurosaur, before being placed into the Tyrannosauroidea by [2] and [25]; Aviatyrannis jurassica [26], which at first drew similarities to Iliosuchus incognitus and then to Stokesosaurus clevelandi, and is placed with the latter [2]; and Xiongguanlong baimoensis [27], which stresses a Guanlong-like anatomy with a vairly dervied-looking skull.

Dryptosaurus aquilunguis, originally named Laelaps aquilunguis [27], but which was preoccupied, is a somewhat shaky tyrannosauroid that may be close to the root of Tyrannosauridae [28], seems close to Appalachiosaurus montgomeriensis. It may thus be a despot, along with Appalachiosaurus, or a true tyrannosaurid if the latter is associated with albertosaurines as also suggested by [28].

[1] Osborn, H. F. 1905. Tyrannosaurus and other Cretaceous carnivorous dinosaurs. Bulletin of the American Museum of Natural History 21:259-265.
[2] Holtz, T. R., Jr. 2004. Tyrannosauroidea. p111-136 in Weishampel, Dodson & Osmólska (eds.) The Dinosauria (2nd ed.). (University of California Press, Berkeley.)
[3] Sereno, P. C. 1999. The evolution of dinosaurs. Science 284:2137-2147.
[4] Holtz, T. R., Jr. 1994. The phylogenetic position of the Tyrannosauridae: implications for theropod systematics. Journal of Paleontology 68(5):1100-1117.
[5] Averianov, A. O., Krasnolutskii, S. A. & Ivantsov, S. V. 2010. A new basal coelurosaur (Dinosauria: Theropoda) from the Middle Jurassic of Siberia. Proceedings of the Zoological Institute 314(1):42-57.
[6] Carpenter, K., Miles, C. & Cloward, K. 2005. New small theropod from the Upper Jurassic Morrison Formation of Wyoming. p23-48 in Carpenter (ed.) The Carnivorous Dinosaurs. (Indiana University Press, Bloomington.)
[7] Madsen, J. M. 1974. A new theropod dinosaur from the Upper Jurassic of Utah. Journal of Paleontology 48:27-31.
[8] Osborn, H. F. 1903. Ornitholestes hermanni, a new compsognathoid dinosaur from the Upper Jurassic. Bulletin of the American Museum of Natural History 19(12):459-464.
[9] Carpenter, K., Miles, C., Ostrom, J. H. & Cloward, K. 2005. Redescriptions of the small maniraptoran theropods Ornitholestes and Coelurus from the Upper Jurassic Morrison Formation of Wyoming. p49-71 in Carpenter (ed.) The Carnivorous Dinosaurs. (Indiana University Press, Bloomington.)
[10] Xu X., Norell, M. A., Kuang X., Wang X., Zhao Q. & Jia C. 2004. Basal tyrannosauroids from China and evidence for protofeathers in tyrannosauroids. Nature 431:680-684.
[11] Xu X., Clark, J. M., Forster, C. A., Norell, M.A., Erickson, G.M., Eberth, D.A., Jia C. & Zhao Q. 2006. A basal tyrannosauroid dinosaur from the Late Jurassic of China. Nature 439:715-718.
[12] Woodward, A. S. 1910. On a skull of Megalosaurus from the Great Oolite of Minchinhampton (Gloucestershire). Quarterly Journal of the Geological Society of London 66:111-115.
[13] von Huene, F. 1932. Die fossile Reptil-Ordnung Saurischia, ihre Entwicklung und Geschichte [The fossil reptile Order Saurischia, their development and history]. Monographien zur Geologie und Palaeontologie (Serie 1) 4:1-361.
[14] Rauhut, O. W. M., Milner, A.C. & Moore-Fay, S. 2010. Cranial osteology and phylogenetic position of the theropod dinosaur Proceratosaurus bradleyi (Woodward, 1910) from the Middle Jurassic of England. Zoological Journal of the Linnaean Society 158(1):155-195.
[15] Hutt, S., Naish, D., Martill, D. M., Barker, M. J. & Newbery, P. 2001. A preliminary account of a new tyrannosauroid theropod from the Wessex Formation (Cretaceous) of southern England. Cretaceous Research 22:227-242.
[16] Headden, J. H. 2005. Dinosaur Mailing List: Thoughts on Tanycolagreus.
[17] Headden, J. H. 2006. The Bite Stuff: On Tyrants, Despots, and Peons.
[18] Paul, G. S. 1988. Predatory Dinosaurs of the World. (Simon & Schuster, New York City.)
[19] Longrich, N. R. 2002. Systematics of Sinosauropteryx. Society of Vertebrate Paleontology, Abstracts. Journal of Vertebrate Paleontology 22(supp to 3):80A.
[20] Benson, R. B. J. 2009. An assessment of variability in theropod dinosaur remains from the Bathonian (Middle Jurassic) of Stonesfield and New Park Quarry, UK and taxonomic implications for Megalosaurus bucklandii and Iliosuchus incognitus. Palaeontology 52:857-877.
[21] Kurzanov, S. M. 1976. [Braincase structure in the carnosaur Itemirus n. gen. and some aspects of the cranial anatomy of dinosaurs]. Paleontological Journal 10:361-369.
[22] Longrich, N. R. & Currie, P. J. 2009. A microraptorine (Dinosauria–Dromaeosauridae) from the Late Cretaceous of North America. Proceedings of the National Academy of Sciences 106(13):5002-5007.
[23] Osmólska, H. 1996. An unusual theropod dinosaur from the Late Cretaceous Nemegt Formation of Mongolia. Acta Palaeontologica Polonica. 41:1-38.
[24] Carr, T. D. 2005. Phylogeny of Tyrannosauroidea (Dinosauria: Coelurosauria) with special reference to North American forms. (PhD dissertation, University of Toronto.) 1170 pp.
[25] Rauhut, O. W. M. 2003. A tyrannosauroid dinosaur from the Upper Jurassic of Portugal. Palaeontology 46:903-910.
[26] Li D.-q., Norell, M. A., Gao K.-q., Smith, N. D. & Makovicky, P. J. 2009. A longirostrine tyrannosauroid from the Early Cretaceous of China. Proceedings of the Royal Society of London, B 277:211-217.
[27] Cope, E. D. 1866. Discovery of a gigantic dinosaur in the Cretaceous of New Jersey. Proceedings of the Academy of Natural Sciences of Philadelphia 18:275-279.
[28] Carr, T. D., Williamson, T. E. & Schwimmer, D. R. 2005. A new genus and species of tyrannosauroid from the Late Cretaceous (middle Campanian) Demopolis Formation of Alabama. Journal of Vertebrate Paleontology 25(1):119–143.

[n1] Yes, Dilong imperator seems to be a particularly basal form, with enough “compsognathid”-like features as to preumse it wasn’t very “despotic” at all. I’ll likely get into this later.

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8 Responses to Tyrants, Despots and Peons

  1. Good overview, curious to see what you think about Dilong specifically, it looks very “coelurid” to me.

    * Dilong paradoxus, btw, not d. imperator ;)

  2. Christopher says:

    When and where was D. imperator named?

  3. Eric says:

    Huh so are Ornitholestes, Coelurus, and Tanycolagreus actually tyrannosaurs or are they just basal coelurosaurs? I’ve heard talk of both and I would like an answer if you don’t mind.

    • Tanycolagreus has features in common with tyrannosauroids, at least, while the others have slightly less features, or have features in common with tyrannosauroids that are plesiomorphic for them (which doesn’t necessarily disqualify them). Carr and Williamson are currently working on a broader tyrannosauroid-based analysis, in which I am certain many of these taxa’s relationship, Sinosauropteryx and comsognathids (also implied to be close) can be resolved to some degree.

  4. Fabrizio says:

    Hello, Mr Headden!

    Very nice post! Non-tyrannosaurid tyrannosauroids are a very fascinating but poorly understood group. Hope they will find new COMPLETE remains as soon as possible! What bout Embasaurus, AMNH 2906 and the undescribed tyrannosauroid from Bissekty Formation?

    • You’d have to ask some other people on these taxa. They seem, like Alectrosaurus, Appalachiosaurus and Dryptosaurus, to be close to tyrannosaurids and beyond the point I’d call anything a “despot.”

      See my other reply to comments in this post: a new analysis is in prep which will help clarify tyrannosauroid relationships.

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