Few dinosaurs are as well studied as the Upper Cretaceous tyrannosaurid theropod Tyrannosaurus rex. It might be easy to assume that this intense focus has been driven by the fame and glory associated with working on this dinosaur. That might be partly true but, in fact, T. rex really is one of the best known dinosaurs, represented by multiple individuals that are often near-complete and well preserved. It has also – in the form of bite marks, coprolites and soft tissue traces (or alleged soft tissue traces) – left us more evidence of its behaviour than many other Mesozoic dinosaurs. T. rex might really be regarded, then, as a ‘model dinosaur’, and its familiarity and popularity might instead be argued to be coincidental, the result of its relatively early discovery (it was named in 1905) and of its status as one of the world’s largest predatory dinosaur. In celebration of 100 years of knowledge of the world’s most famous dinosaur, the Black Hills Institute of Geological Research (Hill City, South Dakota) held ‘100 Years of Tyrannosaurus rex: A Symposium’ in June 2005. Including 21 contributions from 30 authors, this book is the result.
The volume starts with Neal Larson’s review of all reported T. rex skeletons. This is an interesting catalogue, providing and illustrating a great deal of obscure and even never-before-published information. Here, we receive the first indication that not everyone involved in tyrant dinosaur research agrees on the taxonomy of the population of animals generally referred to as T. rex. Referring to the fact that ‘there is so much evidence separating Nanotyrannus from T. rex‘ (p. 2), Larson retains Nanotyrannus as a distinct taxon (as do some other contributions in the volume). He also notes the even less well known opinion of Stephan Pickering that FMNH PR2081 (aka ‘Sue’, previously BHI 2033) and a few other specimens represent a distinct species, but Larson disagrees and so does everyone else I think. Unmentioned (and clearly little known) is that yet another alleged Tyrannosaurus species, T. vannus from Big Bend National Park, was named in an unpublished thesis filed by Douglas Lawson in 1972. Several workers have noted that this specimen (the holotype is the left maxilla TMM 41436-1) falls outside the range of variation of T. rex (most recently, Brochu (2003) said that, if it is not T. rex, it represents a close relative), but we are still waiting for a definitive reassessment.
When T. rex was first described by Henry Osborn in 1905, it was described alongside a second gigantic theropod, the armour-plated Dynamosaurus imperiosus [early reconstruction shown here]. Brent Breithaupt and colleagues provide a brief review of Dynamosaurus and other tyrant dinosaur discoveries from the Rocky Mountain West. It is well known that the Dynamosaurus type specimen – sold to the British Museum (Natural History) in 1960 – was mounted in the museum’s old dinosaur gallery in a rather ‘modern’ pose: that is, with its body and tail near-horizontal and its tail well up off the ground. Those who have commented on this have usually noted that Barney Newman wanted to depict the animal in a dynamic, modern pose, and said as much in a technical paper (Newman 1970). I was therefore interested to read Alan Charig’s comment that the specimen ‘was mounted with its body in a far too horizontal position: this was done because it would otherwise have been too tall for the Gallery. Newman, who made the mount, has attempted to rationalise this (1970) by stating that the posture was much more bird-like than is suggested by earlier mounts’ (Charig 1972, p. 137) [the mount in question is shown below; an article devoted to it previously appeared here].
Mary Schweitzer and colleagues review their recent discoveries on medullary bone in T. rex and Peter Larson looks at variation within the species. While T. rex seems to include both gracile and robust individuals, Larson also discusses the idea that Nanotyrannus – argued by Carr (1999) to represent a juvenile T. rex, contra Bakker et al. (1988) – is a distinct taxon. Less familiar is the idea that what is generally known as T. rex possibly includes two species, with the ‘other one’ known provisionally as Tyrannosaurus “x”. To my knowledge, the only other outing of this idea in the literature is some very brief discussion in Horner and Lessem’s popular book The Complete T. Rex where this notion is mentioned as one of Robert Bakker’s pet hypotheses (indeed, Larson states here that the Tyrannosaurus “x” hypothesis originated with Bakker). While this is very much a minority opinion, the idea that there might have been more than one contemporaneous species in the genus is hardly crazy radical nonsense. Indeed, Maastrichtian western North America was highly unusual in apparently being home to but a single species of large theropod. Ultimately, I found the arguments put forward by Larson unconvincing however: the features suggested to distinguish the two overlap (like number of maxillary or dentary teeth), or are known to be variable in other taxa (like size of the pneumatic foramen in the lacrimal).
Proposing an ‘integral morphodynamic solution’ to tyrant dinosaur body shape and proportions, Martin Lockley and colleagues dismiss the idea that adaptation provides the explanation for the striking skull and forelimb proportions. They argue instead that ‘morphodynamic compensation’ explains how the diminutive forelimbs of these theropods were an accidental consequence of genetic investment in the proportionally gigantic skull. This is easily the strangest and most problematic contribution to the book, and even within the volume itself, other authors (Lipkin and Carpenter) note that these conclusions are untestable and speculative. Lockley and collegues have recently used similar arguments to explain the presence of short tails in pterodactyloid pterosaurs. Their arguments need to be properly evaluated by someone active in the field of evo-devo, but I find it hard to take them seriously. The dismissal of adaptation as an explanation for a given bauplan is strange given that this is one of the most fundamental concepts in evolutionary theory ['Sue', aka FMNH PR2081, shown below. From wikipedia].
Christine Lipkin and Kenneth Carpenter look anew at forelimb function in T. rex. In keeping with some previous work on the subject, the authors conclude, based on evidence from pathologies, reconstructed musculature and mathematical modelling, that the short arms of T. rex were very powerful and perhaps played a role in predation. In view of Brochu’s (2003) critique they revisit the too-avian reconstruction previously published by Carpenter and Smith (2001). However, given that these dinosaurs had banana-shaped teeth over 15 cm long and could literally bite animals in half with an astronomically high bite-force, I find it hard to accept that short didactyl arms, even very well-muscled and robust didactyl arms, were all that useful in predating upon multi-ton herbivores, but this is not to say that the arms were useless. As Lipkin and Carpenter argue, the pathologies present in T. rex forelimb and pectoral bones indicate that they were indeed subjecting their arms to extensive forces.
Digital modelling of a T. rex skeleton is used by Kent Stevens and colleagues to reconstruct possible sitting and resting poses in the animal. Relatively little technical work exists in which authors have tried to depict the resting and sitting postures of dinosaurs, and understandably there is little opportunity to test ideas on this subject. Lambe (1917) depicted a possible resting posture in Gorgosaurus and several artists have followed suit, but these reconstructions were nothing more than artistic endeavours. The beauty of the computer-generated work that Stevens and colleagues present is that it allows the digital manipulation of accurately proportioned models that incorporate data on ranges of motion, gravity and loading. So we get our first scientifically rigorous look at what a squatting and resting tyrannosaur might look like. Newman’s (1970) idea that tyrant dinosaurs might have used their strong arms to help steady themselves when rising from a recumbent posture is testable, but while it might work it appears more awkward than does the possibility that the release of the energy stored in the Achilles tendons allowed the animal to stand without resorting to this. An accompanying presentation included on the CD-ROM that comes with the book illustrates the ranges of motion permitted by the model, and excellent animations show what it is capable of [one of the stills is shown here, from Kent Stevens's website]
Phil Manning provides an overview of new ideas on footprint dynamics and how to study them and, in his second contribution in the book, Peter Larson provides an atlas of T. rex skull bones. The accompanying photos (on the CD-ROM) are excellent and useful (if you work on theropods), but are marred by the total absence of scale bars. Hans Larsson looks briefly at palatal kinesis, with the evidence for this hinting at the possibility that the kinesis so typical of birds may have originated deep within Tetanurae. Given comments made about such animals as allosauroids and coelophysoids elsewhere in the literature, there are certainly indications that cranial kinesis was present throughout the evolutionary history of the theropods [UPDATE: this was written before Holliday & Witmer (2008) was published: see discussion here] [CM 9380, T. rex holotype, shown here].
Ralph Molnar’s article complements his previous papers on cranial morphology and mechanics in T. rex (Molnar 1991, 2000). These articles are all well-written, well illustrated and pretty convincing, and the new paper included here provides a detailed discussion of the inferred cranial musculature of T. rex. One interesting area of conflict that arises from Molnar’s reconstruction concerns the soft-tissue anatomy of the antorbital fossa in T. rex, and by inference that of all theropods and perhaps of all archosaurs with large antorbital fossae. Based on the surface texture of the bone within the antorbital fossa, Molnar reconstructs T. rex with an immense pterygoideus anterior that fills the cavity and anchors to the ventral, anterior and dorsal margins of the fossa [see figure below, by Ralph Molnar]. This is the ‘conventional’ reconstruction for theropods. However, it’s flatly at odds with Witmer’s proposal that the whole of the antorbital fossa was occupied by a gigantic antorbital sinus (see Witmer 1997, fig. 6): Witmer still, of course, depicted the pterygoideus anterior musculature as anchoring in the antorbital fossa, but as being far smaller and far more ventrally restricted. Molnar is well aware of this conflict and suggests that histological examination of the fossa margins might resolve this problem. He also suggests that different archosaurs might have differed in the extent of the pterygoideus anterior. One might predict that an animal such as T. rex, specialised for power-biting and well known for possessing hypertrophied cranial musculature, might represent an extreme example at the ‘muscular’ end of the scale.
Molnar’s article will also be of use to those interested in reconstructing the life appearances of dinosaurs given that it is one of very few works that shows exactly where the tympanum belongs [see above]. Artists apparently lacking in guidance have often positioned the ear on the side of the neck, posterior to the depressor mandibulae, or even within the laterotemporal fenestra, but it should in fact be located anterior to the depressor mandibulae and just ventral to the posteroventral part of the squamosal. One unfortunate problem does afflict this paper, and that is its formatting: several of the figures are far removed from the associated text of the article and have been placed adjacent to the references.
Bruce Rothschild and Ralph Molnar look at pathologies, of which a great many are known from tyrant dinosaurs. This is a useful survey, but questions might be raised as to whether the aetiologies they propose are the most likely ones. They suggest, for example, that healing fractures observed in gastralia present evidence that tyrants could survive and recover from accidental falls. Well, maybe, but falling flat on your belly is not the only way in which you might receive broken gastralia (interactions with prey and conspecifics are just as likely).
Greg Paul’s paper on ‘the totally extreme lifestyles and amazing habits of the gigantic mega-awesome tyrannosaurid superhyperpredators of the Late Cretaceous of North America and Asia’ (or something like that) essentially consists of a series of informed speculations that, while appearing reasonable based on what we know, will be annoying to some given his habit of making unsupported assertions. He provides an extended critique on tyrant dinosaur hindlimb anatomy, limb posture and running speed, and he continues to disagree strongly with those who argue that T. rex was limited to elephant-like speeds. New work indicates that tyrannosaurs grew quickly and died young (as did, as a generalisation, all dinosaurs it seems), a discovery that leads Paul to imagine that tyrant dinosaurs were ‘chronically living closer to the edge of danger and death’. In other words, that they lived reckless, dangerous lives where caution was thrown to the wind: more like salmon than elephants, notes Paul. The comparative work presented here on the skulls of the different tyrants is useful.
John Happ describes an exciting Triceratops specimen that many will already be familiar with because of its appearance on television documentaries: it would appear that a large predator with a very powerful bite grabbed hold of one of the animal’s brow horns and bit it off, and also damaged the side of the frill with a bite. The Triceratops survived, but appears to have suffered from osteomyelitis following the attack. By reconstructing the angle of attack employed by the predator, Happ shows how the Triceratops and its attacker (T. rex is the only candidate) engaged in face-to-face conflict. The unknown factor is how common interactions of this sort were. Paul notes in his paper that this was quite likely an attack gone wrong, as attacking an elephant-sized horned herbivore from the front and biting its horns is probably not a good idea.
In a long-awaited contribution, Thomas Holtz provides a formal, critical answer to John Horner’s proposal that T. rex was an obligate scavenger, unable to kill live prey and destined for a life of wandering the Cretaceous landscape ever in the quest of decomposing carcasses. It’s difficult to be sure whether Horner really believes his own hypothesis: one gets the impression that he likes promoting it because it earns him lectures and TV appearances, and surely he knows that it’s not really a defensible point of view. Horner’s claim that T. rex had ‘beady little eyes’ (and hence poor eyesight) is shown to be incorrect, and Holtz also tackles claims that hindlimb proportions and tooth morphology support a scavenging lifestyle when the data shows that they don’t. Holtz reviews the evidence for predatory behaviour in giant tyrant dinosaurs, concluding (like Paul) that they were most likely canid- or hyaenid-like ‘jaw-based’ predators, able to resist significant twisting and skull loading when grabbing prey, and also able to withstand occasional contact with bone.
The volume ends with a look at the role of T. rex in popular culture, by Don Glut. From the art of Charles Knight to the Zallinger mural and its role in sci-fi stories and movies, T. rex has been a constant presence, and one invariably portrayed quite inaccurately. This continued until recently (the BBC’s T. rex in Walking With Dinosaurs is one of the least accurate modern renditions of this animal: it’s shown here), but has finally begun to change. Brief contributions by other authors are also included elsewhere in the book and look at such topics as the age of T. rex-bearing beds, and at the discovery and taphonomy of specific individuals.
Tyrannosaurus rex: the Tyrant King contains some very interesting contributions, and everyone involved in tyrant dinosaur, or Cretaceous theropod, research will want at least some of the papers that are included; Molnar’s and Holtz’s chapters in particular are sound contributions to the literature, and it is good to see the studies by Happ and Stevens et al. in print. But the book also incorporates some unusual and problematic articles that, one cannot help but assume, might have appeared here because they could not be published elsewhere. A phylogenetic perspective on the book’s subject is notably absent, and – given the controversial and very interesting claims about the validity of Nanotyrannus and additional Tyrannosaurus species – it’s unfortunate that nobody submitted a paper that provided a rigorous, empirical analysis of T. rex systematics. This is partly because another special meeting on tyrannosaurs was held at the Burpee Museum of Natural History just a few months after the Hill City meeting, and for whatever reason this is the one where the phylogenetic papers were presented. I also found the lack of abstracts from the contributions unhelpful (particularly in writing this review, when access to brief summaries would have been very helpful!) and, as is unfortunately par for the course for IUP volumes, the editing is not too hot and typos are easy to find.
Peter Larson and Kenneth Carpenter (2008). Indiana University Press, Bloomington and Indianapolis, 435pp. ISBN 978-0-253-35087-9, $49.95 (hardback, includes CD-ROM).
This book review originally appeared in the Palaeontological Association Newsletter 69: available (for free download) here and is reproduced with permission.
Refs – –
Bakker, R. T., Williams, M. & Currie, P. 1988. Nanotyrannus, a new genus of pygmy tyrannosaur, from the latest Cretaceous of Montana. Hunteria 1 (5), 1-30.
Brochu, C. A. 2003. Osteology of Tyrannosaurus rex: insights from a nearly complete skeleton and high-resolution computed tomographic analysis of the skull. Journal of Vertebrate Paleontology 22, Supplement to Number 4, pp. 1-138.
Carpenter, K. & Smith, M. 2001. Forelimb osteology and biomechanics of Tyrannosaurus rex. In Tanke, D. H. & Carpenter, K. (eds) Mesozoic Vertebrate Life. Indiana University Press (Bloomington & Indianapolis), pp. 90-116.
Carr, T. D. 1999. Craniofacial ontogeny in Tyrannosauridae (Dinosauria, Coelurosauria). Journal of Vertebrate Paleontology 19, 497-520.
Charig, A. J. 1972. The evolution of the archosaur pelvis and hind-limb: an explanation in functional terms. In Joysey, K. A. & Kemp, T. S. (eds) Studies in Vertebrate Evolution. Oliver & Boyd (Edinburgh), pp. 121-155.
Holliday, C. M. & Witmer, L. M. 2008. Cranial kinesis in dinosaurs: intracranial joints, protractor muscles, and their significance for cranial evolution and function in diapsids. Journal of Vertebrate Paleontology 28, 1073-1088.
Lambe, L. M. 1917. The Cretaceous theropodous dinosaur Gorgosaurus. Memoirs of the Geological Society of Canada 100, 1-84.
Molnar, R. E. 1991. The cranial morphology of Tyrannosaurus rex. Palaeontographica Abteilung A 217, 137-176.
– . 2000. Mechanical factors in the design of the skull of Tyrannosaurus rex (Osborn, 1905). Gaia 15, 193-218.
Newman, B. H. 1970. Stance and gait in the flesh-eating dinosaur Tyrannosaurus. Biological Journal of the Linnean Society 2, 119-123.
Witmer, L. M. 1997. The evolution of the antorbital cavity of archosaurs: a study in soft-tissue reconstruction in the fossil record with an analysis of the function of pneumaticity. Journal of Vertebrate Paleontology 17 (Supplement to No.1), pp. 73.