The Armored Dinosaurs

Palaeontologia Electronica http://palaeo-electronica.org

by Peter Makovicky Kenneth Carpenter (ed.) Indiana University Press, 2001, 512 pp. 0-253-33964-2, $75.00

The Armored Dinosaurs, the newest in in subject mat- a series of paleontological offerings from ter, ranging Indiana University Press, is one of a from paleonto- recent wave of books dedicated to dino- logical history, saur paleontology. Unlike other such vol- descriptive and umes, which are either broader in their functional coverage of dinosaur-related subjects or anatomy, ich- concentrate on very popular fields such as nology, and dinosaur eggs and babies, The Armored developmental Dinosaurs is dedicated to the least stud- aspects to phy- ied of the major dinosaurian clades, logeny. One Thyreophora. Thyreophora comprises new ankylo- Stegosauria and Ankylosauria and a hand- saur and a new ful of stem taxa, but despite their public stegosaur are appeal, fossils of these animals are com- described in paratively rare. That this group is ripe for separate chapters, and several known more attention is clear: prior to the publica- taxa such as Euoplocephalus are tion of this volume, only a single cladistic reviewed. Not surprisingly, the taxonomic analysis with three ingroup taxa was avail- distribution of chapters is skewed towards able for stegosaurs, and before 1998 none the more diverse and better-known anky- was available for ankylosaurs. Recent losaurs. years have seen a revival in the study of Although not a functional anatomist, I Thyreophora, especially fueled by the enjoyed the two chapters on jaw mechan- description of a number of new ankylosau- ics in Scelidosaurus by Paul Barret and rian taxa by the book’s editor Ken Carpen- in the advanced ankylosaurid Euoplo- ter and various colleagues. cephalus by Rybczynski and Vickaryous, The book, which has its roots in the respectively. The feeding mechanics of symposium on ankylosaurs convened at ankylosaurs had received scant attention the 58th Annual Meeting of the Society of historically, and important details were Vertebrate Paleontology, goes some way probably overlooked because the teeth, toward correcting decades of neglect. The which are unusually small for such large book’s twenty-one chapters range widely animals, were considered near-vestigial

Makovicky, Peter, 2002. THE ARMORED DINOSAURS. Palaeontologia Electronica, vol. 5, issue 1, book review 2: 3pp., 109KB; http://palaeo-electronica.org. MACKOVICKY, PETER: THE ARMORED DINOSAURS structures. The two chapters also indicate categories creates a potential for doing that thyreophoran jaw mechanics were not some very exciting systematic and charac- uniform and that a detailed and compara- ter evolutionary research within the clade. tive study across Thyreophora promises to Another interesting chapter by Coria and be a fruitful field for future studies. Salgado provided conclusive evidence for The two descriptive chapters on the ankylosaurs in Argentina, strengthening primitive stegosaur Hesperosaurus and the case for an influx of Laurasian dino- the ankylosaur Cedarpelta, both written saur clades into South America late in the by Ken Carpenter in collaboration with dif- Cretaceous. For those working on ferent co-authors, offer exciting new data thyreophoran anatomy and systematics, on these groups. The description of Hes- valuable reviews are provided in chapters perosaurus is accompanied by what is such as Galton’s redescription of the brain only the second cladistic analysis of stego- of Stegosaurus and Penkalski’s review of saurs yet published. The basal Hespero- Euplocephalus specimens. saurus and far more derived The Armored Dinosaurs is largely Stegosaurus are both from the Morrison geared toward specialists and serious Formation, and the near contemporane- dinosaur enthusiasts. A couple of chap- ous age of these disparate taxa suggest ters, such as the first chapter by David we have only scratched the surface of Norman and Carpenter and Galton’s entry stegosaurian diversity. Much work remains “Othniel Marsh and the myth of the eight to be done on the systematics of this spiked Stegosaurus” make for some pretty understudied clade. The Cedarpelta dry reading if one is not a passionate stu- remains include the first disarticulated cra- dent of the history of paleontology. On the nial elements known for ankylosaurs, and other hand, one advantage of edited these show that much of the cranial orna- books is that they provide an opportunity mentation of these animals was derived to deviate from the standardized journal from the skull bones themselves, rather formats, and allow for focus on particular than deriving exclusively from osteoderms aspects of a given subject matter. Several as previously thought. This latter point is papers including ones by Ford and Kirk- further developed in a chapter by Vickary- land, Molnar, and Blows on ankylosaurian ous and colleagues. In an elegant study, armor patterns may not entice general in which ossification patterns in extant liz- readers, but they hold a wealth of informa- ards were used as the comparative basis, tion that is relevant to the taxonomy and the authors showed that highly fused and systematics of this clade. ornamented ankylosaur skulls display As with all edited volumes, chapters osteological correlates of both osteoder- vary in both scope and quality, and some mal ornamentation, and ornamentation of the entries probably would not have derived from the dermal skull bones them- made the cut in a professional journal. selves. Osteoderms account for struc- One such entry is Blow's “Possible stego- tures such as ossified eyelids and the saur dermal armor from the Lower Creta- pavement of scutes on the skull roof, but ceous of southern England” dealing with the dermal skull bones form structures isolated elements from various Wealden such as horns above the orbits and on the localities. The identity of the described cheeks. Being able to segregate these dermal elements is so tentative, that it bor- characters, many of which are important ders on the uninformative, and no useful for ankylosaurian taxonomy, into distinct

2 MACKOVICKY, PETER: THE ARMORED DINOSAURS information on taxonomic diversity can be straining the monophyly of clades he extracted from this chapter. views as stable and for which he chooses The aspect I found most disappointing a set of diagnostic characters prior to anal- about the book, was its lack of rigorous ysis. In a time where systematists are systematics-based approaches to charac- increasingly working toward creating ter evaluation and phylogenetic conclu- super-trees, Carpenter instead decides to sions. In a chapter revising the small restrict his analyses to “mini-trees”. Obvi- nodosaur Struthiosaurus austriacus, ously, the notion of testing phylogenetic Pereda-Suberbiola and Galton conclude hypotheses through the addition of taxa that this animal is a small, primitive nodo- and characters is completely ignored, and saur that shows a pedomorphic reduction the reference list reveals a surprising in body size relative to its larger, more absence of systematic literature: only a derived, but mostly older cousins. Hetero- single paper in Systematic Biology is chrony is essentially a phylogenetic con- cited. In his various analyses of these cept, so one would expect that characters constrained and small data sets, Carpen- indicative of heterochronic change should ter proceeds to make some inexplicable show transformations to states that are errors such as including a taxon with all seen in juveniles of outgroup taxa. No question marks, and using bootstrap anal- such analysis is presented by the authors, yses or the distance-based neighbor-join- and indeed the conclusions that S. austri- ing algorithm rather than parsimony acus is both primitive and pedomorphic anlysis, although he remains under the relative to its larger cousins seem some- impression that he is conducting the latter. what incongruous. Fortunately, for those interested in ankylo- Most distressing was the final chapter saur systematics, a global parsimony anal- on ankylosaurian systematics by the editor ysis was recently published by Matt Ken Carpenter. The systematic nature of Vickaryous and colleagues. (Canadian the title prompted me to read this chapter Journal of Earth Sciences 38: 1767-1780). first, but my initial interest quickly turned to My misgivings aside, The Armored dismay. Discouraged by his efforts to Dinosaurs is the best volume around on achieve well resolved trees using global thyreophorans, and a must-have for any parsimony analyses, and unconcerned as serious student of dinosaurs. It provides a to whether this problem is due to missing lot of detailed, new information on various data or homoplasy, Carpenter appeals to aspects of thyreophoran anatomy and Geraat Vermeij’s controversial paper biology. It, furthermore, presents some (Paleobiology 25: 431-433) to argue for a novel approaches and much-needed reap- “compartmentalized” approach to ankylo- praisals, and even its shortcomings serve saur systematics. This compartmentalized their purpose: namely to define future approach amounts to little more than con- research efforts within Thyreophora.