In Oklahoma the distribution records fit fairly well the portion of the state mapped by Braun as the Oak-Hickory Association of the Deciduous Forest, but extends a little farther west in the northeastern part of the state. A game type map published by the Oklahoma Game and Fish Department, Division of Wildlife Restoration, in 1943 shows in more detail distribution of the main vegetation types within the state. The locality records for the skink fall almost entirely within three of the fifteen vegetation types mapped, namely, the oak-pine, and oak-hickory forest of the state’s eastern edge and the post oak-blackjack oak type of the eastern and central parts. The locality records extend almost throughout the area occupied by these three types but not in attenuate westward extensions of the post oak-blackjack type that occur along several of the main stream courses. In Texas likewise the recorded localities fall mainly within the area mapped as deciduous forest, but with several slightly beyond its boundaries. In a detailed map of the “game regions” of Texas (Anonymous, 1945:1), some of these outlying localities fall into the coastal prairie area, and the remainder into the post oak and blackland prairie belts, which grade into each other and the oak-hickory forest.
The former distribution of the five-lined skink may be postulated on the basis of the fossil record of its community associates since it is a primitive and conservative type. Taylor (1936:56) explained the present discontinuous distribution of the genus on opposite sides of the world on the basis of a former northern connection of the continents. He wrote: “I regard migration from North America to Asia as having taken place via land bridges joining the Alaskan peninsula with Asia either at Bering Straits or via the Aleutian Island arc to Kamchatka, or both. One would need postulate but slight climatic changes since the present climate of this coastal region is probably no more rigorous than that of southern Canada which has three species of the genus.” However, such former northward distribution, while entirely probable, would have been possible only in a climate much milder than that which prevails at present. In Asia, tunganus on the mainland and latiscutatus on the island of Hokkaido extend north to about latitude 43°, and in North America, fasciatus extends slightly farther north. In order to have crossed between Alaska and Asia on presumed land bridges these skinks would have had to extend their ranges about 20 degrees north of their present limits, into what is now a cool climate. The winter climate of the Bering Sea is perhaps not much beyond the range of tolerance of the more cold-adapted forms of Eumeces, but the cold, cloudy, wet, and changeable summer climate is far beyond the range of tolerance of Eumeces or any other lizard.
It is highly improbable that the fossil record will yield direct evidence for the existence of a northern ancestral Eumeces of the fasciatus group. The characters by which the various forms are recognized are to be found mainly in details of pattern and scalation; the skeleton is so conservative that specific characters are ill defined or lacking even in well preserved fossil material. This hypothetical ancestor probably was a member of a deciduous forest community having components in common with the modern forests where the American and Asiatic species occur, along with types now extinct, and others which, though existing at the present time, have become separated from their original associates and occur in other regions.
Hollick (1936:11) has described a rich early Tertiary Alaskan flora strikingly different from that of the same region at the present time. Composed of genera now characteristic of warm-temperate to subtropical climates, it was remarkable in having many types of plants that are now most characteristic of the North American hardwood forests in the southeastern part of the continent. Besides such widespread genera as Fagus, Betula, Ulmus, Platanus, Castanea, Corylus, Carpinus, Crataegus, Spiraea, Myrica, Smilax, Pinus, Picea, and Abies, this flora included others now characteristic of both warm-temperate southeastern North America and Eastern Asia, as Magnolia, Nyssa, Sassafras, Persea, Benzoin, Hamamelis, Liquidambar, Celastrus, Nelumbo, and Onoclea. It included genera Carya, Taxodium and Comptonia that now are limited to SE North America, Sequoia, now limited to western North America, and also included several genera which at present are limited to southeastern Asia: Ginkgo, Glyptostrobus, Cinnamomum, Hausmannia, Artocarpus, Dillenia and Koelreuteria. This fossil flora provides strong evidence that in the early Tertiary climatic and habitat conditions as far north as Alaska were favorable for the existence of an ancestral Eumeces similar to the modern E. fasciatus, which might have given rise to both North American and Asiatic members of the fasciatus group.
There is abundant evidence for the existence of an Eocene land connection between Alaska and northeastern Siberia, permitting free interchange of faunas between the two continents, as shown by the almost simultaneous appearance of various mammalian groups in the fossil records of Asia and North America. Simpson (1947:627) has summarized the evidence that such intermigrations were occurring throughout most of the Tertiary, with occasional interruptions as in middle Eocene, and in middle and late Oligocene, and with increasing selectivity, chiefly a progressive tendency toward screening out of the groups less tolerant of cold (judged on the basis of their modern representatives). In the late Tertiary, and especially in the Pleistocene, animals known to have made migrations between North America and Asia were types now characteristic of boreal climates (e. g. pika, hare, vole, lemmings, marmot, jumping mouse, fox, wolverine, bear, moose, caribou, sheep, bison, camels, mammoth). Simpson believes that there was fairly strong climatic selectivity even in the Miocene interchanges, and he indicates several important groups that were non-migrants in the Miocene, most of them remaining so through the Pliocene and Pleistocene—the primates, Rhizomyidae, Gliridae, Viverridae, Hyaenidae, Dicerorhininae, Suidae, late Anthracotheriidae, Hippopotamidae, Tragulidae, Muntiacinae, Lagomerycidae, Giraffidae, and Bovidae. He states that there is good evidence that these are all mainly warm-climate animals which are not likely to have ranged in any force into a cold-temperate or boreal environment. In view of these conclusions it seems doubtful whether Eumeces or other reptiles could have crossed the Alaskan-Siberian land connection so late as the Miocene.
On the contrary, the climate and habitat conditions with which Eumeces might have been associated, although present as far north as Alaska in the Eocene, evidently had shifted far to the south by mid-Tertiary time. Axelrod (1950:230) has described a Miocene forest of the Columbia Plateau and northern Great Basin indicative of a uniform temperate climate and an average rainfall of thirty-five to sixty inches. This forest included: (a) various genera now characteristic of the southeastern hardwood forest or confined to it—Carya, Castanea, Comptonia, Fagus, Liquidambar, Nyssa, Taxodium; (b) other genera at present more characteristic of the western United States—Sequoia, Lithocarpus, Pseudotsuga, Mahonia, Thuja, Gaultheria, Amelanchier; (c) wide-ranging genera including Alnus, Acer, Betula, Populus, Quercus, Picea, Pinus, Tsuga, Cornus, Ribes, Rosa, Hydrangea; (d) modern east Asian genera, including Ginkgo, Ailanthus, Glyptostrobus, Keteleria, Koelreuteria, Metasequoia, Pseudolarix, Pterocarya, Zelkova, which were eliminated from the North American flora in the latter part of the Tertiary. In short, this western Miocene forest was remarkably similar in many respects both to the presumably ancestral early Tertiary Alaskan forest and the modern southeastern hardwood forest. The extent of this Miocene forest is unknown but judging from the sites where it has been recorded, it had progressed about halfway, both in latitude and in actual distance, from Alaska to the area occupied by the modern southeastern deciduous forests. Several other reptilian genera have distributions similar to that of the fasciatus group, with representatives in southeastern Asia and southeastern North America that probably have parallel histories of distributional divergence from early Tertiary northern ancestors similar to contemporary species (Schmidt, 1946:148-150). Alligator, Natrix, Ancistrodon, Scincella, Elaphe, Opheodrys, and within the genus Eumeces, the obsoletus group, all provide excellent examples.
Effect of Climatic Factors
Accounts of the habits and habitat, by various authors, indicate versatility in behavior, and adaptation to a variety of habitat conditions in different climates and plant associations. Some of the differences evidently result from the skink’s tendency to maintain itself in surroundings of favorable temperature and humidity, which obviously are to be found in different types of situations at different extremes of the range. Hence even though the skink itself may remain unchanged, it tends to behave somewhat differently under diverse environmental conditions. Such environmentally enforced differences in habits would be difficult to distinguish from those having a genetic basis. Although no subspecies of Eumeces fasciatus have been recognized, local populations undoubtedly differ somewhat in size and other characters that have a genetic basis.
At the northern edge of its geographic range, fasciatus occurs in isolated colonies and seems to be restricted to open, rocky situations which receive the maximum amount of sunlight. Breckenridge (1944:96) wrote that at the two Minnesota localities representing the northwestern corner of the known range, the skinks were found at granite outcrops, and he mentions one found in western Wisconsin, at Taylor Falls, under an 18-inch slab of a basalt outcrop in sparse oak woods. Patch (1934:51) described a habitat at Arden, Ontario, among massive granite-gneiss domes, with sparse vegetation. At Point Pelee, Ontario, the species is common in the drier, more sparsely wooded situations, hiding beneath loose bark of stumps and logs.
Ruthven (1911:264) found E. fasciatus in the vicinity of sandy beaches in the Saginaw Bay region of Michigan. Elsewhere in its range it is more characteristically an inhabitant of hardwood forests, preferring the better drained and more rocky situations, according to the testimony of numerous authors. In eastern Illinois, Smith (1947:33) found it confined to the area south of the Shelbyville moraine, and not ranging into a prairie habitat. Near Elkville, Illinois, Cagle found the species abundant in higher and drier areas within sparse stands of oak in second growth woods, but it was absent from the low swampy areas adjacent to streams. Conant (1951:30, 210), describing the habitat in Ohio, stated that the species does not occur in swamps and areas that are subject to spring floods nor on dry hillsides, but is abundant in some areas where there are rotting stumps and logs remaining from former patches of swamp forest, and usually is found in low, moist situations, in wooded valleys or even at the edges of swamps and bogs. Lynn (1936:49) wrote that in Virginia, it is most often seen on steep, boulder-strewn hillsides and old sawdust piles. In the central Ozarks of Missouri, Owen (1949:49) found it abundant and saw it almost daily on rocky ledges, fallen timber, and fence rails, while E. laticeps was seen only once. Taylor (1936:59) wrote that E. fasciatus occurs where there is timber and is often found about fallen trees and rotting stumps, or about old sawmills where wood refuse has accumulated. Smith (1950:187) wrote that in Kansas the species is commonly found in wooded areas in moist situations about stones, leaves and rotten logs. Gloyd (1928:120) wrote that in Franklin County, Kansas, E. fasciatus occurred in upland situations and was the most abundant lizard where there were rocks, brush, or decaying wood. Gloyd (1932:401) also recorded it as abundant in the Pigeon Lake area, Miami County, Kansas, in wooded areas of sufficient elevation to be out of the river flood-plain.