The study of the morphological structure of squamates (lizards and snakes) has been a popular subject among doctors, morphologists, herpetologists, and paleontologists for more than three centuries. Some of the earliest known technical studies of these organisms focused on vipers and the medical aspects associated with envenomation (e.g., Charas, 1669; Tyson, 1683). In fact, most early works on reptile biology were medically oriented and written by physicians. But today, scientists with diverse backgrounds and research interests study these organisms. Current squamate research encompasses evolutionary history, climate change, and space materials, to mention a few.
Squamate morphology is studied primarily by herpetologists and paleontologists. Yet despite the overlapping interests of these two groups and the large amount of morphological literature produced in recent years, it is uncommon to find members of these communities working side by side. Herpetologists and paleontologists tend to publish in different specialized journals and attend separate scientific meetings. Many of them are, regrettably, not even aware of the work of members of the other community! (although this varies and depends on each researcher's bibliographic “appetite”). A clear example of this lack of collaboration between herpetologists and paleontologists is the Deep Scaly project, which was the largest study on squamate evolution ever undertaken (http://archive.fieldmuseum.org/deepscaly/). This project originally included both herpetologists and paleontologists as co-funded collaborators, but the two teams diverged and published independently, and each group developed a different phylogeny based on their own independent analyses of a data set that was composed of the largest data partitions for squamate reptiles ever produced (Gauthier et al., 2012; Wiens et al., 2012).
Last year, James D. Gardner (Curator of Palaeoherpetology at the Royal Tyrrell Museum of Palaeontology in Alberta Canada) organized a symposium at the 7th World Congress of Herpetology entitled “Insights from the Fossil Record” (see, Pearson and Jones, 2013 for an overview of the meeting). One of the major achievements from the two-day symposium was bringing paleontologists and herpetologists together. The majority of presenters at the symposium were paleontologists, and they sent a clear message to the herpetologist-dominated audience: the study of paleoherpetology has not stopped producing awesome discoveries that help us to better understand the biology of today's living forms. Likewise, many paleontologists at the meeting were attending talks and posters by herpetologists to find new sources of information that could apply to their own research projects.
During that meeting I came across one poster that exemplified the interdisciplinary integration between paleontology and herpetology. The authors simulated the mechanics of mosasaur swimming using prosthetic mosasaur-like tails attached to the semiaquatic monitor Varanus salvator (Young, 2013; see also Lindgren et al,. 2011). Despite your opinion on the appropriateness of taxon selection for this study (mosasaurs are either part of the Scleroglossan stem or part of the crown Varanoidea clade), the whole idea was very creative.
James D. Gardner wanted to put together a volume in which the attendants of that meeting could present their research in more detail. That initiative was partially unsuccessful1, but I decided to borrow his idea and I took on the challenge of combining herpetology and paleontology in a single volume, in which squamate morphology is operating as the interdisciplinary lingua franca. This task was not easy but, luckily for me, as the guest editor and the person responsible for getting people involved, I received positive responses from a number of experts working on squamate morphology.
In recruiting contributions for this volume, I focused on studies by specialists working on the major clades of the squamate tree of life, and gladly, I received many interesting contributions. The volume starts with Dr. Christopher J. Bell and Jim I. Mead's appreciation of the status quo of skeletal collections in museums. They argue that the anatomical research program is still a dynamic discipline and not an expired field of study from the Victorian era that is slowly marching toward its end. Original research papers in this volume comprise the anatomy of Iguania (the chameleon's atlanto-axial complex, pedal grasping capabilities, and pectoral girdle anatomy), Gekkota (a comprehensive fossil record catalog, cranial joints), Lacertoidea (hemipeneal morphology, brille formation, cranial joints), Scincoidea (a miniaturized and putative fossil form from the Pyrenees), Amphisbaenia (ancestral morphology and niche modeling of rhineurids), Anguimorpha (a new shinisaurid record for North America, the lower jaw and tooth structure of the some anguids), and Serpentes (fossil record, jaw musculature, and gut morphology).
Returning to the question formulated in the title: what's so special about squamates? More than one hundred years has passed since the current perception of the group was formed (e.g., Cope, 1864; Boulenger, 1884). Ninety years ago, Camp (1923), in his character-based classification of lizards, produced the foundations for future research. In his monograph, he organized lizards and proposed methods to delimitate monophyletic groups long before the revolutionary works of Willi Hennig (See Moody, 1985). Following this early classification, several authors have produced improvements to the classification of squamates based on morphology (e.g., McDowell and Bogert, 1954; Underwood, 1954, 1967; Kluge, 1967, 1989; Rieppel, 1979, 1980, 1984; Borsuk-Białynicka, 1983; Presch, 1983; Evans, 1984; Gauthier, 1984; Benton, 1985; Estes et al., 1988; Frost and Etheridge, 1989; Lee, 1997; Caldwell, 1999; Conrad, 2008; Gauthier et al., 2012). These studies, along with many more not mentioned, have provided a road map that has facilitated further advances in squamate research and promoted its applications in other fields.
Squamata originated in the Early Jurassic, around 193 Mya (Jones et al., 2013). Today this group accounts for the majority of living reptiles and includes more than 9,200 species. In terms of diversity, that number is nearly comparable with birds (approximately 10,000 species), and surpasses the number of mammals (5,702 species) and amphibians (7,177 species). Members of Squamata are important components of the world's ecosystems. They are distributed on all the continents except Antarctica, are found up to high latitudes in both Northern and Southern Hemispheres, and are distributed in a variety of habitats from tropical forests, to barren territories such as deserts and cold regions. Sadly, they are also disappearing fast as global temperatures change and anthropomorphic impacts on their natural territories become more severe (Sinervo et al., 2010, see also Clusella-Trullas and Chown, 2011).
In a time when the future of squamates doesn't look great, the minimum we can do is appreciate squamates for their evolutionary success and recognize their struggle for survival against the threats caused by our own civilization. I am optimistic that interdisciplinary volumes like this one will help to demolish the intellectual wall between herpetologists and paleontologists and will contribute to our understanding and conservation of these amazing organisms.
Finally, I want to mention that this special volume wouldn't be in your hands (or glowing on your computer screen) without the tremendous help from Scott Miller, Kurt Albertine, and Rosalie McFarlane. I am also grateful to the paleoartist Stephanie Abramowicz who brought back to life the extinct gecko Hoburogecko suchanovi from Höövor, Mongolia that is depicted on the cover of this issue. Although my selection of this squamate for the cover was biased by my own interests, gekkotans represent squamates well because they are consistently recovered as one of the most basal squamate groups in both molecular and morphological data sets, and they historically have been allied with virtually all other squamate clades.
I also cannot forget to thank Dr. Aaron M. Bauer and Villanova University for their support during the production of this volume. Finally, I want to acknowledge the effort of all the people that contributed to this volume by spending hours editing these manuscripts. In alphabetical order:
Aaron M. Bauer, Villanova University, USA
Faysal Bibi, American Museum of Natural History, USA
Arnau Bolet, Institut Català de Paleontologia Miquel Crusafont, Spain
Andrej Čerňanský, Senckenberg Research Institute, Germany/Geological Institute, Slovak Academy of Sciences, Slovakia
Jack L. Conrad, New York College of Osteopathic Medicine/American Museum of Natural History, USA
Ammon Corl, University of California at Santa Cruz, USA
David Cundall, Lehigh University, USA
Rui Diogo, Howard University/The George Washington University, USA
Annelise Folie, Royal Belgian Institute of Natural Sciences, Belgium
Kathleen Foster, University of California at Riverside, USA
Elyse S. Freitas, Villanova University, USA
Anthony Herrel, CNRS/Muséum national d'Histoire naturelle, France
Casey Holliday, University of Missouri, USA
Kenneth Kardong, Washington State University, USA
Jozef Klembara, Comenius University in Bratislava, Slovakia
Nicholas Longrich, Yale University, USA
Jonathan Losos, Museum of Comparative Zoology/Harvard University, USA
Carlo Meloro, Università degli Studi di Napoli Federico II, Italy/The University of Hull, UK
Ricardo (Ueso) Montero, Instituto de Herpetología/Fundación Miguel Lillo, Argentina
Scott Miller, The Anatomical Record/University of Utah, USA
Kevin Neal, Villanova University, USA
Randal Nydam, Midwestern University, USA
Samantha Payne, University of Toronto, Canada
Ana Lúcia Prudente, Museu Paraense Emílio Goeldi, Brazil
Jean-Claude Rage, CR2P, UMR 7207 CNRS/Muséum national d'Histoire naturelle, France
Beate Röll, University of Veterinary Medicine Hannover, Germany
Santiago J. Sánchez-Pacheco, University of Toronto, Canada
Kathleen K. Smith, Duke University, USA
Krister Smith, Senckenberg Research Institute Frankfurt/Main and Messel Research Station, Germany
Matthew Vickaryous, University of Guelph, Canada
Juan D. Daza*
The Anatomical Record