Relationships
Eumeces is a widespread genus occurring in the New World in southern Canada and southward into Costa Rica. The greatest number of forms is in Mexico. In the Old World numerous species occur in southeastern Asia and on adjacent islands, and other species occur westward across southern Asia, and across North Africa to Morocco, with a major break in the continuity of distribution in the Himalayan region. Taylor in his revision recognized 57 forms with fifty full species, belonging to 15 major groups within the genus. Since then only relatively minor changes in classification have been proposed. Several new species and subspecies have been named, and several species have been relegated to the status of subspecies.
Within the genus there are several groups that have representatives in both the New World and the Old World. Smith and Etheridge (1953:159) point out that the most primitive line of Eumeces is best represented in the Old World, where there are two groups and nine species, while in the New World this line has only three tropical relict forms. For this reason, Smith and Etheridge concur with Taylor (1936:67) in considering the genus to be of Old World origin; but the two main lines of the genus (the four-lined and five-lined stocks) are both regarded as being of New World origin. According to this idea, the Asiatic members of these two groups migrated from the New World. In the early Tertiary, warm temperate climates extended north to the Arctic Circle, and Eumeces, or at least some of its species, may have had a distribution straddling migration routes to both North America and Asia.
Of the 15 groups within the genus, the fasciatus group, with a dozen species, has more representatives than any other. The fasciatus group is characterized by having the tail bright blue with dorsal body pattern of five light lines on a darker ground color; mid-dorsal line bifurcating on head to form lyrate markings (this striped pattern and bright color of the tail becoming dull or obsolete in the adults); medial preanal scales overlapped by those lateral to them; two pairs of nuchals; no postfemoral pocket; four supraoculars; scales on sides of body in parallel rows. The characters that separate members of the fasciatus group from each other are minor. The width and position of the light lines differ somewhat among them. The mid-dorsal light line bifurcates either on the nuchals or on the parietals. The complex of scales in the temporal region differ in shape and relative size.
The following table, compiled mostly from information set forth by Taylor (1936:186-283), indicates some of the main differences and similarities between species in the chief characters upon which the classification is based.
The close resemblance between E. fasciatus and its Asiatic relatives is remarkable considering the great distance separating them and the long time that must have elapsed since their isolation began. Some of the Asiatic forms differ from each other almost as much as they differ from fasciatus. Of the Asiatic species, elegans, tamdaoensis, oshimensis, and marginatus differ from fasciatus in markedly larger size; elegans, marginatus, oshimensis, and stimsonii differ in lacking a postnasal; all but tamdaoensis tunganus and xanthi differ in having only a single postmental; all but tunganus, E. latiscutatus okadae (and sometimes oshimensis and elegans) differ in reduced number of scale rows; all but tunganus differ in having a lateral postanal scale differentiated, and usually keeled; tunganus, xanthi and elegans differ in having a patch of enlarged scales on the posterior side of the thigh; and in all, the primary temporals and upper and lower secondary temporals differ in size and proportions. Although some of the Asiatic forms seem to be directly derived from others, fasciatus is somewhat intermediate between the more divergent forms, and fulfills most of the conditions to be looked for in an ancestral type.
Table 1. Distribution, Pattern, Size, and Lepidosis of the “Five-lined” Skinks (Fasciatus Group of the Genus Eumeces)
| fasciatus | laticeps | inexpectatus | tunganus | xanthi | elegans | tamadoensis | oshimensis | stimsonii | barbouri | marginatus | latiscutatus | |
| Distribution | E U. S., except Fla. and N New England | Most of E U. S., except N tier of states | SE U. S. | W Szechwan (in N China) | SE China | SW China, Formosa, Pesca- dores I. | Indo- China | Amami- gunto I. | Ishigaki- jima, Riu Kiu I. | Amami- shima | Okinawa | Japan, (main I.) |
| Juvenal Pattern | 5 lined | 5 or 7 lined | 5 or 7 lined | 5 lined | 5 lined | 5 lined | 5 lined | 5 lined | 7 lined | ...... | 5 lined | 5 lined |
| Max. snout-vent
length in mm. | 80 | 130 | 89 | 81 | 76 | 96 | ...... | 99 | 63 | 66 | 93 | 80 |
| Postnasal | present | present | present | present | present | absent | present | absent | absent | present | absent | present |
| Postmental | 2 | 2 | 2 | 2 | 2 | 1 | 2 | 1 | 1 | 1 | 1 | 1 |
| No. scale rows | 28-30 | 30-32 | 30-32 | 28 | 22-24 | 26-28 | ...... | 26-28 | 26 | 22 | 26 | 26 (or 24) |
| Lateral postanal scales | undiffer- entiated | undiffer- entiated | undiffer- entiated | undiffer- entiated | differ- entiated | keeled | ...... | keeled | keeled | ..... | keeled | keeled |
| Large scales on back of thigh | absent | absent | absent | present | present | present irregular | ...... | absent | enlarged; regular | absent | absent | absent |
| Median subcaudals | widened | widened | not widened | widened | widened | widened | ...... | widened | not widened | widened | widened | widened |