The Other Saber-Tooths, Scimitar-Tooth Cats of the Western Hemisphere

The saber-tooth cats remain a paradox. That their awesome canines are a highly specialized killing device seems self-evident and yet how the saber-teeth were used is one of the enduring controversies in paleontology. Professional paleontologists and preschool children alike cannot help being mesmerized by their stunning appearance, making the saber-tooths arguably the most popular prehistoric mammals. However, a central conundrum remains captivating as ever, the sword-like canines appear to be superb weapons for cutting and slicing, yet these long and slender sabers also appear to be quite fragile and easily broken. The answers to these questions remain elusive. How was such a weapon wielded? How did the cat manage to feed on the kills when the long canines were in the way? Most important of all, how did they avoid breaking the slender canines, thereby losing their livelihood? Lacking a modern analog for the long canines, these questions will continue motivating practicing and armchair paleontologists to strive for that elusive answer. Riding on such popular interest, this book attempts to synthesize recent discoveries on the homotheriines, a less well-known (compared to the smilodontines) but no less fascinating group of cats, with a combination of relatively short canines and (often but not always) long, cursorially adapted limbs. The introduction in Chapter 1 by Larry Martin et al. lays down the overall theme of the book, including separate boxes on dating fossils, taxonomy, phylogeny, and chronologic frameworks, in an attempt to broaden the appeal to general readers. In Chapter 2, Todd Wheeler gets a chance to fully describe his now wellpublicized Robocat, a mechanical contraption mounted on a hydraulic excavator to experimentally demonstrate a saber-tooth delivering a killing bite on a dead bison. Forever in contention is the idea that saber-tooths need to deliver a bite deep enough to reach major blood vessels or other vital organs to ensure a quick kill, as a recent point-to-point bite model cleverly demonstrates (Andersson et al., 2011). Chapter 3 by Bruce Rothschild and Larry Martin briefly describes some common pathologies in saber-tooths. For professional paleontologists, Chapters 4–6 are the meaty part of the book, where osteologic descriptions are provided for Xenosmilus hodsonae (Chapter 4 by Martin et al.) and Homotherium ischyrus (Chapter 6 by Hearst et al.), and muscular reconstruction for X. hodsonae (Chapter 5 by Naples). In Chapter 8, Peter Kondrashov and Larry Martin provide osteological details on a nearly complete skull of Homotherium crenatidens, from the late Pliocene of Kuruksay, Tajikistan, in the collections of the Paleontological Institute of the Russian Academy of Sciences. Unfortunately, the chapter did little to compare this taxon with other Eurasian forms. In Chapters 7 and 9, Martin et al. attempt a taxonomic revision and try to articulate their overall framework of the North American Homotheriini both in terms of phylogenetic history and ecomorphology. In this section they lay down their arguments of migration history, climate change, and niche partitioning, as well as taxonomic philosophy (the authors strongly disagree with what they view as an overly lumping approach by recent authors, such as Turner and Antón [1997], who recognized a single European species of Homotherium latidens). As in Chapter 1, the authors attempt to advance a Nebraska-centric chronologic system, instead of the prevailing North American land mammal system, with the result that people who are not familiar with the controversies of North American land mammal age systems will likely be confused by the terminology (such as the Ogallala Chronofauna). For professional vertebrate paleontologists, the osteological descriptions and bone-by-bone comparisons, accompanied by superb illustrations (including color inserts) by Mary Tanner and Mark Hallett, are worth the price of the book by themselves. Profuse illustrations are certainly a major strength of this book. Black and white charcoal illustrations by Tanner are exhaustive and exquisite. Hallett’s art work, in about equal proportions of full-color reconstructions and black and white studies of sabertooth ecology and behavior, are mesmerizing. A spectacular reconstruction graces the back cover, depicting two individuals of Xenosmilus hodsonae in a Florida swamp with surreal skeletal reflections in the water, a playful juxtaposition also attempted by Stephanie Abramowicz in the cover of this journal (March 2010 Issue). My main quibble is related to popular terms. This book is grounded in the notion that felid saber-tooths can be categorized as dirk-toothed vs. scimitar-toothed cats, an idea whose origin was credited to Kurtén (1963) and subsequently elaborated into an ecomorphologic approach that contrasts forms with long, thin-bladed canines associated with short legs against forms with short and more rounded canines associated with long legs (Martin, 1980). However, as far as I can determine, a dirk is a short, straight thrusting dagger whereas a scimitar is a long, curved saber—these two terms seem to conjure up exactly the opposite images that they are supposed to represent in the canine morphology. It is also interesting that this paradigm of two ecomorphs breaks down in this very book, which documents a third way of being a saber-tooth—short canines with short legs in Xenosmilus. This third way is called a ‘cookie-cutter’ cat, a designation referring to the arched incisor arcade that was postulated to be able to make large, open, bleeding wounds in its prey. Once again, the cookie-cutter label, besides being also applicable to all other homotheriines, does not quite capture the true essence of Xenosmilus, i.e., the combination of short sabers with short legs. In the wooded environment in southeastern United States that Xenosmilus was apparently restricted to, its legs must have been secondarily shortened to accommodate a more ambush style of predation. The case of Xenosmilus thus leads to the question of whether or not a fourth category is yet to be discovered: long canines with long legs. The enduring mystery and charisma of the saber-tooths ensures continuing interest in books related to this genre. The editors of this book were inspired by the 1932 classic monograph by Merriam and Stock (1932), The Felidae of Rancho la Brea, in which the best known saber-tooth, Smilodon fatalis, was described in detail, including luxuriant lithographic plates as well as restorations by Charles Knight. This book succeeds in its aspirations and will become a must-have for professional and avocational paleontologists alike.