Distribution.—The discovery of a new Gopherus from north-central Mexico increases to four the recognized forms of the genus and extends the known range of the genus onto the Mexican highlands, approximately 410 miles eastward from Alamos, Sonora (G. agassizii), approximately 100 miles westward from a point 2 mi. W of Monclova, Coahuila (G. berlandieri), and approximately 200 miles westward from Monterrey, Nuevo León (G. berlandieri).
Table 2. Bodily Proportions in the Known Species of Gopherus.
Two Specimens of G. polyphemus from Harmon, Mississippi (USNM 53166-7),
Are Considered Separately Because of Their Notably Narrower Heads.
The Size of Each Sample Is Given in Parentheses Above the Average;
Extremes Are in Parentheses Following the Averages.
|
Species and General Locality |
Greatest width of skull as a percentage of condylobasilar length |
Height of shell as a percentage of width of carapace |
Height of shell as a percentage of length of carapace |
Diameter of hind foot as a percentage of width of head |
|
G. polyphemus (Florida) |
(6) .94 (.92-.97) |
(13) .53 (.48-.58) |
(13) .39 (.36-.42) | |
|
G. polyphemus (Mississippi) |
(2) .87 (.84-.89) |
(2) .53 (.52-.54) |
(2) .43 (.40-.45) | |
|
G. berlandieri (Texas and NE Mexico) |
(21) 78 (.70-.83) |
(22) .56 (.48-.62) |
(21) .46 (.43-.51) | |
|
G. agassizii (U.S. and N. Sonora) |
(6) .77 (.70-.83) |
(8) .53 (.49-.58) |
(8) .41 (.38-.44) | |
|
G. agassizii (Alamos, Sonora) |
(4) .56 (.52-.59) |
(4 .39 (.37-.41) |
(4) .92 (.87-1.00) | |
|
G. flavomarginatus (North-central Mexico) |
(2) .83 (.82-.83) |
(3) .54 (.51-.58) |
(3) .43 (.42-.44) |
(3) .71 (.58-.78) |
Thus far, G. flavomarginatus is known only from the three localities represented in the type series and from the indefinite locality, "Bolson de Mapimí", Chihuahua, given by Duges (1888:146-7, and 1896:479). These long-doubted references of Duges to Gopherus polyphemus seem clearly to represent G. flavomarginatus, which probably occurs in several or all of the internally drained basins in northeastern Chihuahua, western Coahuila, and northern Durango. This region is within the Basin and Range physiographic province of Fenneman (1931:326-8) and the Mapimí biotic province of Smith (1949:231). Duges (supra cit.) seems to have used "Bolson de Mapimí" in a restricted sense, as it is shown on some recent maps (Nat. Geog. Soc., Map of Mexico and Central America, 1953) (American Geog. Soc., Culican Map, NG 13, 1935). Other maps show this bolson to include internally drained portions of the Mexican highlands from northeastern Chihuahua to the region near Lerdo and Torreon. Thayer (1916:73) pointed out that the Bolson de Mapimí, in its larger sense, consists of a series of basins separated by mountains of considerable elevation.
The range of G. flavomarginatus appears to be limited ultimately by the higher elevations of the Sierra Madre Occidental and the Sierra Madre Oriental to the west and east, respectively, and to the south by the Mexican plateau. The northern limits of the range are less clear; possibly the range extends as far as the portions of the United States adjacent to northeastern Chihuahua, but this is doubtful. The range seems not to overlap that of any other species of Gopherus, although the ranges of G. flavomarginatus and G. berlandieri closely approximate each other in central Coahuila.
In September, 1958, when I was collecting turtles near Cuatro Cienegas, Coahuila, I took the opportunity to query natives, as well as an American rancher, about the possible occurrence of tortoises in the area. Most persons had seen no tortoises in the area or said they had seen them only rarely. Several older men who had herded goats in the area all their lives said that tortoises (referred to as "Tortuga del Monte") were common on the other side of the Sierra de La Madera and Sierra de La Fragua ranges west of Cuatro Cienegas. These men referred probably to G. flavomarginatus. Americanos lies approximately 75 miles west-northwest of Cuatro Cienegas.
It is indeed remarkable that a population of large tortoises in northern Mexico has so long escaped the notice of naturalists. Also remarkable is the fact that the late Dr. Leonhard Stejneger, in view of his intense interest in North American chelonians and his familiarity with the genus Gopherus, did not remark on the specimens from Durango when he saw them; a thorough search of Stejneger's notes revealed no clue that he had ever studied the specimens. Perhaps his first reaction to the specimens, like mine when I first examined the two disassociated skulls, was to consider "Lerdo" a misspelling of "Laredo." However, a check of old correspondence and accession records at the National Museum confirmed, beyond doubt, the validity of the locality data for these specimens. Dr. Chaffee, the collector, frequently sent specimens of plants and animals to the Museum from Durango and Zacatecas; his home was in Lerdo.
Size.—The largest specimen of Gopherus flavomarginatus (USNM 61254) exceeds by more than 50 millimeters the length of the largest known specimens of G. agassizii, and slightly exceeds the length of the largest specimen of G. polyphemus that I have examined (USNM 51357, length of carapace 360 millimeters, a specimen formerly kept at the National Zoological Park). G. polyphemus is the largest tortoise inhabiting the United States; the maximum length of 343 millimeters given for the species by Carr (1952:334) probably more closely approaches the true maximum in free-living populations. G. agassizii rarely attains a length greater than 300 millimeters (Woodbury and Hardy, 1948:152-5). The fact that representatives of the genus do not attain a larger size in the United States may be due to the decimation of natural populations by man for food and souvenirs.
There have been several indications that a large species of tortoise existed in north-central Mexico. The Chihuahuan specimens reported by Duges (248 and 202 millimeters long, respectively) rank in size with the smaller paratypes of G. flavomarginatus; Duges stated, however, that the species was said to attain a length of one meter but that he thought such large size surely to apply to another species.
Mr. Charles M. Bogert recently related to me two stories that are here worthy of note. One of them, which Bogert learned from the late Dr. Karl P. Schmidt, concerns a collector who was sent by the Chicago Natural History Museum (then Field Museum) to Coahuila in the early part of the century to obtain materials for a desert exhibit. When the exhibit had been completed several decades later, the collector, visiting the museum, inquired as to where the large tortoises were that he had collected in Coahuila. Dr. Schmidt could find no record of such tortoises and suggested that possibly they had been confused with Galapagos tortoises (Geochelone). Dr. Robert F. Inger is unable to locate the specimens or add anything to the story. The collector stated that the large tortoises had been found in only one bolson in Coahuila.