The Tyrannosaur Chronicles The Biology of the Tyrant Dinosaurs

These chronicles break down into four parts, of which the last one is a relatively brief conclusion and outlook to the future, while the first three have more meat on the bones. Given that we are talking about much more than just T. rex, Hone starts with their evolutionary history and family tree. In the process, he provides some excellent explainers. What, for example, is the difference between similar-sounding names such as tyrannosaurines, tyrannosaurids, and tyrannosauroids? What is the logic behind cladistics? And, one that has always confused me, what species concept do palaeontologists use? The biological one obviously does not work for extinct species. Here, finally, is a popular book that addresses it: they use a morphological species concept. But how much morphological difference is enough to speak of separate species? You can see that this can be a major bone of contention, with experts disagreeing on whether certain fossils represent different species, or rather individual variation, different age groups, or different sexes of the same species.

Staying on that topic, the second part walks you through tyrannosaur anatomy, from head to tail, and from internal organs to integument, including the species for which we have evidence of filamentous feathers. Hone considers their physiology and how their bodies changed over evolutionary time, with later species growing proportionally larger and more robust heads, even when accounting for the overall increase in body size, while (famously) ending up with shorter arms and fewer fingers. Having given you an overview of the various family members and what they look like, he turns to their biology: how did these creatures reproduce and grow, who were their prey and competitors, how did they obtain their food, and what do we know about other behaviours?

The above is a brief overview of the book's accessible contents and logical structure. Rather than going into more detail, instead I want to highlight two points that stood out to me: foreshadowing and scepticism.

As I recently reviewed Hone's later books, The Future of Dinosaurs (2022) and Uncovering Dinosaur Behavior (2024), I could not help but notice how this book foreshadows certain themes that will make a return. Both books give examples of how the fossil record can be deceptive, whether through a glut or dearth of fossils. The individuals found in bonebeds did not necessarily live or even die together, while group-living organisms often lose members individually; solitary fossils do not exclude social behaviour. Here it shows up in the context of the 1997 discovery of a group of Albertosaurus fossils, which likely represented a genuine group of individuals in life. However, as clarified with examples from animals living today (think, for instance, seasonal gatherings), aggregations do not necessarily equal sociality. The Future of Dinosaurs furthermore talked about the low odds of statistical outliers being preserved in the fossil record (e.g. the largest or oldest individuals). The largest, mostly complete T. rex fossil we have is the famous "Sue", who is on display at the Field Museum in Chicago, but we have incomplete specimens with bigger bones. Similarly, both early populations of ancestral species and dwarf forms living on islands would have been few in number and thus unlikely to show up in the fossil record. Lo and behold, Hone adds, as this book was being written, scientists described the small-bodied Nanuqsaurus, a potential island species.

A second aspect I noticed is that this book is somewhat of a myth-busting exercise. The endless hyperbole in popular media and the press "overshadows a fascinating evolutionary story" (p. 24). Reconstructions showing a perfect toothy grin ignore the fact that tyrannosaurs cycled through hundreds of teeth in life, new teeth regularly forming underneath old ones. Similarly, the focus on bite power hides the fact that we have evidence of tyrannosaurs handling food items in more delicate ways. "Tyrannosaurs were much more than near-armless bone crushers [...] they were also real animals" (p. 277). The endless depictions of hunting belie the fact that, like large predators alive today, most of their time would have been spent sleeping or lounging, which then leads you to the more interesting question: how did tyrannosaurs lie down for a snooze? Hone expresses a fair amount of understandable frustration with popular depictions. To me, it highlights why books like this are so welcome and necessary.

Another side to this mythbusting is Hone's measured view on some of the more controversial and outlandish ideas that colleagues have floated over the years. I mentioned at the start how palaeontologists disagree over how much difference is enough to assign a new name to a specimen. A prime example of this is the debate around Nanotyrannus. Gregory S. Paul is one of several palaeontologists who think it is a separate species based on certain morphological characteristics, while others argue it represents a juvenile of Tyrannosaurus. For palaeontologist Phil Currie, the abovementioned aggregation of Albertosaurus fossils is evidence of advanced pack hunting behaviour, with juveniles driving prey towards the adults who would have dealt the death blow. Hone makes no bones of it (sorry): "such a specific idea about exact hunting patterns needs some strong evidence to support it, and for me it falls rather short at the moment" (p. 243). His coverage of these and other ideas foreshadows the philosophy he more explicitly expressed in Uncovering Dinosaur Behavior: to "always favor a degree of uncertainty or lack of confidence in a result, rather than embracing an interpretation confidently that may be wrong" (p. 35 therein).

A final shout-out goes to the skeletal reconstructions of whole animals and body parts by Scott Hartman. The curse of such schematic diagrams is, of course, that they look very similar to what others do. However, his note at the start of the book, explaining his methodology, shows that Paul is not the only one to bring a great deal of care and technical know-how to this craft. I actually would not have minded some more; certain morphological descriptions, such as the makeup of the shoulder girdle, would benefit from visuals drawn from a different angle.

Overall, this is a hugely enjoyable popular science book that sets the stage nicely for my next review. If Hone convinces you that there is more to tyrannosaurs than just T. rex, it is still the most famous dinosaur. But how much of this, really, is based on solid facts?