Amphisbaenians are a poorly known group of squamate reptiles with over 150 extant species in 23 genera. They live almost exclusively under loose or sandy soil in tropical to temperate areas around the world, and their anatomy is modified in many ways related to this lifestyle. Most recent studies recognize four families within Amphisbaenia—Bipedidae, Amphisbaenidae, Trogonophidae, and Rhineuridae. Only the Rhineuridae are well represented in the fossil record. Two exclusively fossil families, Hyporhinidae and Crythiosauridae, have also been recognized in some studies. In this paper, a phylogenetic study of the Amphisbaenia is presented based on morphological characters investigated in living and fossil forms. Amphisbaenian monophyly is supported, but the recent identification of the late Cretaceous Sineoamphisbaena hextabularis† as a primitive amphisbaenian is not supported. The monophyly of two of the four families of extant amphisbaenians is upheld, with one family being more inclusive than previously thought. Amphisbaenidae is substantially revised, with several taxa previously included in the family being more closely related to rhineurids, and with Blanus representing a basal amphisbaenian. Rhineuridae is also revised to include the previously recognized fossil family Hyporhinidae. Trogonophidae is the sister-group to the remaining amphisbaenids, and together they form the sister-group to the expanded rhineurid clade. Bipes is the most basal amphisbaenian and Blanus is the sister-group to all remaining amphisbaenians. Crythiosauridae is removed from the Amphisbaenia because no support was found for its inclusion.

The deep nesting of rhineurids within Amphisbaenia found here contrasts with their extensive fossil record beginning in the late Paleocene. This hypothesis implies significant gaps in the fossil record of all other amphisbaenian taxa, and the reacquisition of some seemingly primitive features in some fossil rhineurids. However, the condition of the limbs in extinct rhineurids is uncertain and, if they are found to be present, the related characters could place them in a more basal position, which would then alter interpretations of character evolution. The basal positions of Bipes and Blanus imply that a round-headed cranial shape is the primitive condition for Amphisbaenia in contrast to some previous hypotheses.

In this analysis, amphisbaenians are nested within Squamata, in contrast to a hypothesized relationship as the sister-group to the remainder of squamates (alone, with snakes, or with another group of limbless burrowing lizards, Dibamidae). Weak support was found for a relationship between amphisbaenians and Dibamidae as previously suggested by some other analyses, but this is based mainly on reduction and absence features and the sister-group to Amphisbaenia is considered here to be inconclusive. Sineoamphisbaena† is found to be related to macrocephalosaurs, an extinct group previously placed with Teiidae, but placed basally among squamates by this analysis.

Morphological analyses of squamates in this study include numerous features associated with reduced or absent limbs and limb girdles, as well as other specializations presumed to be related to a burrowing lifestyle. These characters are often hypothesized to have been convergently acquired among limbless squamate clades and have been excluded or downweighted in some previous analyses. This approach is difficult to implement here because further anatomical investigations of these structures revealed useful variation for resolving relationships within amphisbaenians. Future studies will require new approaches that can address the c

We attempted to identify salamanders from the Cumberland Plateau of Tennessee that have been referred by previous investigators to Desmognathus ochrophaeus. We compared variation at 22 allozyme loci in 10 populations to allozymic variation in other desmognathines. Multidimensional scaling, cluster, and parsimony analyses indicate that populations from our southernmost localities in the plateau are referable to D. ocoee, whereas the northernmost populations are D. ochrophaeus. In contrast, animals sampled from the middle of the plateau are genetically very distinct from all members of the complex and represent a new species described herein as Desmognathus abditus. D. abditus exhibits very limited gene exchange with D. ocoee and D. ochrophaeus where it contacts those forms. A population from the Eastern Highland Rim that has previously been referred to D. ochrophaeus may represent yet another undescribed species. The southern Cumberland Plateau clearly represents an area of substantial desmognathine diversity.

Many desert organisms cope with extreme and variable conditions by retreating to sub-surface refugia, yet little is known of the patterns of refuge use by most desert inhabitants. We investigated shelter use by the Gila Monster, Heloderma suspectum, an ectotherm closely tied to sub-surface refugia in a strongly seasonal desert environment. We addressed hypotheses that ectotherms may use habitats based on availability of shelters, select shelters based on particular cues, respond to seasonal variation in refuge characteristics, and show fidelity to specific retreats. Using radiotelemetry, we monitored microhabitat use by eight to ten Gila Monsters for six years, recording timing, frequency, and duration of visitation to over 250 specific shelters. We used transects to assess shelter availability, recorded structural features of all shelters, and used dataloggers to monitor seasonal changes in microenvironments within subsets of shelters for periods up to two years. Shelters, and the habitats where they occurred, were not chosen by Gila Monsters at random. Heloderma spent more time in areas where a higher density of potential shelters was available, and selected shelters based on rockiness, slope and entrance aspect, depth, humidity, and temperature. Gila Monsters showed longer residence times and greater fidelity to shelters used during extreme periods (e.g., winter) and these patterns were paralleled by seasonal changes in the characteristics of shelters chosen. Winter shelters tended to be south-facing, rockier, deeper, and warmer than those used in other seasons, whereas dry-summer shelters were more soil-like in composition, cooler, and more humid. Gila Monsters showed strong fidelity to specific shelters, some of which were used by two or more lizards, sometimes concurrently. Seasonal variation in use of “social” shelters coincided with annual cycles of intraspecific behaviors and reproduction. Our results underscore the importance of sub-surface refugia in the ecology of a sedentary desert ectotherm. Because many other ectotherms also spend significant periods sequestered in below-ground retreats, it is surprising that ecologists have not more extensively investigated this phenomenon. An understanding of the cues used by desert ectotherms to choose refuge-sites, the spatial and temporal variability in refuge characteristics, and the fidelity shown to particular retreats, may help better explain patterns of habitat selection, behavior, distribution, and abundance.

Radio tracking of 40 free-ranging eastern brownsnakes (Pseudonaja textilis) in an agricultural landscape in southeastern Australia clarified the spatial ecology of these highly venomous animals. Most snakes over-wintered in burrows within a small area on the bank of an irrigation canal, dispersing into agricultural land during the warmer months. The snakes sheltered overnight in burrows or soil cracks, reusing the same retreat on successive nights and moving about to forage during the day. Successive shelter-sites averaged 152 m apart, and the snakes moved between them on average every six days. Home ranges of adult snakes were small (average MCP = 5.8 ha), and did not differ significantly between years with varying prey abundance. Movement patterns depended upon the snakes' sex, reproductive condition and body size. Adult males moved earlier in spring than did the (smaller) adult females, moved further and more often, and had larger home ranges. Home range size increased with body size in males, but not in females. Shelter-site selection was influenced by the location of potential prey (House Mice, Mus domesticus) and the location of other snakes. When radio-tracked snakes moved, they generally traveled from areas of lower to higher prey abundance (as determined by mammal-trapping). Throughout most of the year, adult male snakes were avoided by females and by other males. Adult males rarely cohabited with other snakes, and their arrival at an occupied burrow generally induced the resident snake to depart. Our study thus provides the first strong evidence that agonistic interactions can influence the spatial ecology of snakes.

Squamate reptiles generally have been ignored in the search for a unified theory for the evolution of sociality due to the perception that they exhibit little social behavior beyond territoriality and dominance hierarchies and display polygynous mating systems. However a growing body of research has revealed unsuspected levels of social complexity and diversity in mating systems within the squamate lineage, particularly among the members of the Australian Scincid genus Egernia. Several species of Egernia are amongst the most highly social of all squamate reptiles, exhibiting stable social aggregations and high levels of long-term social and genetic monogamy. Social complexity is widespread within the Egernia genus, with reports of social aggregations in 23 of the 30 described species. The purpose of this review was to examine the potential for the Egernia genus as a model system for study of the evolution of sociality and monogamy within squamate reptiles.

Current evidence indicates there is substantial variability in social complexity both within and between species, with social organization covering the spectrum from solitary to highly social. Four highly social Egernia species are known to live in stable social aggregations consisting of closely related individuals (adults, subadults, juveniles; i.e., ‘family’ groups) that appear to utilize chemical cues to recognize group members (kin recognition). Enhanced vigilance against predators is one presumed benefit of group membership. Additionally, juveniles within social groupings appear to receive low levels of indirect parental care. Several Egernia species create scat piles that mark group territories. Three Egernia species exhibit long-term social and genetic monogamy and several inbreeding avoidance strategies have been documented. However, it is currently unknown whether monogamy is widespread within Egernia.

Egernia species occupy a broad range of habitats, although most are terrestrial, saxicolous or semi-arboreal. Several species display an attachment to a permanent home site, generally a rock crevice, burrow or tree hollow. Egernia species take 2–5 years to mature, live for 5–25 years, and are viviparous with litter size positively correlated with body size. Several Egernia species are herbivorous, with the degree of herbivory increasing with body size and during ontogeny in larger species. Most smaller species are either insectivorous or omnivorous. Species of Egernia have a wide range of reptilian, avian, and mammalian predators. Several larger species possess several behavioral and morphological features to prevent their extraction from rock crevices, including highly modified keeled scales and numerous defensive behaviors. Color pattern polymorphism is present in five Egernia species.

Potential ecological correlates of sociality and monogamy are discussed. The life-history hypothesis predicts long-lived, late-maturing species should evolve complex sociality. The habitat availability hypothesis relies on the assumption that refugia may be limited in some ecological settings, and group formation is a consequence of co-habitation of available refugia. These hypotheses are not mutually exclusive, and testable predictions are formulated and discussed. Specific future research directions are outlined to take advantage of Egernia as a model system for comparative research on a lineage that represents an indep