A New Tortoise, Genus Gopherus, From North-central Mexico

by John M. Legler

PLATE 7

Plate 7. Gopherus flavomarginatus new species: Top—Dorsal and ventral views of holotype (× 1/3); Middle—Lateral view of holotype (× 1/3)); Bottom—Head of paratype (USNM 61254) (× ½) and antebrachium of holotype (× 5/6). Dark outline on plastron of holotype indicates where portion of shell was removed (and then replaced) in course of preparation.

PLATE 8

Plate 8. Gopherus flavomarginatus new species: Dorsal views of paratypes (from top to bottom, IU 42953, IU 42954, and KU 39415), approximately 1/5 natural size.

Fig. 1. Gopherus flavomarginatus new species: 1a and 1b—Lateral and ventral views of skull of holotype (× 1); 1c—Cross section of paratype (USNM 60976) taken through middle of third central lamina (× 2/5).

Anomalies.—There is a high incidence of anomaly in the type series. Three of the specimens (USNM 60976, IU 42954, and KU 39415) have a supernumerary central lamina. All of the specimens from Durango are anomalous in regard to the marginal laminae. In the holotype the first marginals are small, approximately as wide as the small precentral. In the largest paratype (USNM 61254) the first and second marginals are fused to form a single large scute on each side. In the remaining Durangan paratype (USNM 60976) there are eleven normal marginals on each side but a supernumerary lamina occurs between the first and second marginal on the left and between the precentral and first marginal on the right side. The remaining three paratypes have the number of marginals that is normal for the genus.

Relationships.—Gopherus flavomarginatus differs from all other species of the genus by its larger size and by having an intergular seam that is longer than the interhumeral seam. The possession of a single, rectangular axillary scale, wider below than above, also tends to distinguish flavomarginatus from other living Gopherus; in the other species this scute (frequently paired in berlandieri) is generally triangular or at least pointed below. Femoral spurs are developed to varying degrees in the other species of Gopherus; they are usually lacking in individuals of small to medium size. In large specimens of agassizii and polyphemus that I have examined, there is but one enlarged spur, although several pointed osteodermal scales may be present on the back of the thigh.

Gopherus berlandieri, the closest relative of G. flavomarginatus in a geographic sense, has a highly arched shell and pronglike gular projections, between which there is nearly always a deep notch. Gopherus agassizii, morphologically the closest Mexican relative of flavomarginatus, differs from it in having a narrower head and in lacking the contrasting pale and dark coloration of the plastron and lateral marginal area. Gopherus polyphemus seems to be the closest relative of flavomarginatus and differs from it in having an unflared shell (anterior and posterior widths of carapace subequal or carapace narrower behind) and in the characteristics of color mentioned above. Certain proportional differences between the living species of Gopherus are summarized in table 2.