David Hone - The tyrannosaur chronicles : the biology of the tyrant dinosaurs

THE TYRANNOSAUR CHRONICLES

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THE TYRANNOSAUR CHRONICLES

THE BIOLOGY OF THE TYRANT DINOSAURS

David Hone

Contents

When writing a science book of close to 90,000 words long, you can be pretty sure of two things. One: it will contain at least a couple, and probably several, pretty bad errors; and two: it will be out of date by the time it is published. The first I am largely resigned to, the second is more important to understand. The rate of discovery and scientific exploration of dinosaurs is accelerating all the time to the point that, on average, a new species is named every week or so; this is in addition to all the other new studies and assessments of behaviour, anatomy, ecology, evolution and the like that will be published in that time.

Since the tyrannosaurs were first recognised as a group of dinosaurs in 1905 with the naming of the genus Tyrannosaurus , a huge number of scientific works have been written about them. A quick search of my own, far from comprehensive digital library finds more than 1,500 papers and books that relate to the subject. One famous paper is nearly 150 pages in length and is primarily a description of a single skeleton. We do know an awful lot about tyrannosaurs, and that knowledge is expanding faster than I have been able to write this book. Already I have had to add to or rewrite sections several times to take account of new ideas, new data and even entire new species that have been described while this book was being composed.

This is not intended as a text book or reference work, so I have skimmed over citing much of the formal scientific literature that forms the basis of our knowledge of the tyrannosaurs. An exhaustive list of papers on tyrannosaurs alone might be longer than this book, so I couldnt include them all, even if I had wanted to. However, it is important to try and mention key papers, and to show the scientific basis of the ideas and hypotheses laid out over the course of this work. Where appropriate, numbered references to sources are given in the text, and the sources are listed in full at the back of the book. While the reference list is effectively far from complete, as far as possible the information here is backed by at least some scientific studies (a number, of course, are controversial, uncertain or even contradictory), except where I have made it clear that something is based primarily on my own opinions and ideas. Even so, for every paper in the reference list there are perhaps dozens more that explore the ideas expounded upon, and similarly for every fossil illustrated or mentioned, there may be dozens or hundreds more specimens that have been the subject of study or analysis to support an idea.

In this book, I have attempted to steer a middle course covering primarily what I think is the consensus opinion among dinosaur researchers. While minority ideas get a look in, the scope of the book limits the discussion of some areas. I have tried to streamline and simplify often difficult and complex issues, but without overlooking nuance or important contradictions, and to give credit as far as possible given the imposed limitations on space the intention is to provide a fair and balanced look at exactly what I think the tyrannosaurs were like.

Scientific illustration of fossils is a curious thing. The goal is to provide the most accurate possible view of extinct organisms, in this case tyrant dinosaurs and their relatives. Naturally, this cant be a literal view after all, some of the bones are usually missing, and many of those that survived were distorted by being squashed under tons of rock for tens of millions of years. To put the skeletons together in a literal fashion would render them incomplete and often oddly twisted upon themselves.

Instead, I have endeavoured to provide the most accurate possible portrayal of the skeletons as they were in the living organism. To this end, the first job was to get the proportions right. I have tried to take my own measurements of the original bones where I can, and where expense and distance have made that prohibitive, I have relied on measurements supplied by colleagues. They have all been checked against the vast and ever-growing scientific literature on dinosaurs.

Illustrating dinosaur bones in the proper shapes and proportions is all well and good, but a full skeletal reconstruction requires their arrangement in a manner consistent with the living animal. For this I have relied on detailed observation of specimens, the vast scientific literature on biomechanics and functional morphology, and dissection of extant organisms for comparative purposes.

Wherever possible, I have tried to make the creation of anatomical diagrams a data-driven process, though naturally there are limitations to our state of understanding. Missing data has been filled in from other specimens of the species or their close relatives, and logical anatomical inference was used when hard data was missing (). Future discoveries will undoubtedly require revisions of the interpretations.

Fig. 1 A panoply of Tyrannosaurus skeletons. Few dinosaur fossils are truly complete with every bone known and in good condition, but there is substantial overlap between many and so we can have great confidence in restoring the complete skeleton from these incomplete remains.

Despite any yet-undiscovered errors, every attempt has been made to provide a visual representation of these extinct beasts that matches our current understanding of them. I hope you find them as fascinating as I do.

Scott Hartman

Throughout this book there are references to various scientific names of tyrannosaurs, and indeed other dinosaurs both individual genera and species and also formal evolutionary groups (termed clades). Some of the terminology and rules for these names and their creation may seem complex and obtuse, but it is important to use them. Scientific terminology is there precisely to provide something that is specific and accurate, and not ambiguous. Theres little point in reinventing the wheel.

Few of the old taxonomic ranks of organisms (Kingdom, Phylum, Class, Order, Family, Genus and Species) are used by modern biologists and palaeontologists. While terms like the dog family and Class Aves still get bandied about, researchers are increasingly abandoning them since they dont have clear equivalents between groups. We do still think of groups within groups (so all humans are apes, all apes are primates, all primates are mammals and so on), and the technical names are still used to designate those clades ( Homo , Hominidae, Primata, Mammalia), but the ranks are not considered a part of this.

The exceptions are the genus and species names, the traditional scientific or binomial name (often called a Latin name). A few of these at least will be recognisable to many people, for example Homo sapiens , Boa constrictor and, yes, Tyrannosaurus rex . A species is the basic unit of biology, and effectively denotes a group of individuals that are more closely related to each other than to any other individuals (other species). Biologists actually have a hard time defining species due to the bewildering variety of organisms out there and the fact that in the course of evolution species and lineages are constantly changing. The individuals that make up the species Boa constrictor right now, are not those that will be around ten or a hundred years from now, or those that were around a thousand years ago. Species ultimately blur into one another, though of course thats generally hard to see on the scale of a human lifetime or in the fossil record.