A figure (Figure 1) of the Aspidoscelis bilobatus holotype (KUMVP5084). A, Median view of the left dentary, enlarged. B, Lateral view of the left dentary. C, Single tooth from near the middle of the series and diagrammatic cross section. From the original description (Taylor 1941)
A figure (Figure 2) of Aspidoscelis bilobatus referred material from the original description (Taylor, 1941). A, Fragment from near the anterior tip of the left dentary (KUMVP 5091), enlarged. B, Fragment of the anterior part of right maxilla (KUMVP 5081), median view, enlarged. C, Same, lateral view.
REPTILIA (Reptiles) SQUAMATA (PART) (Other Lizards) TEIIDAE (Whiptails, Racerunners, and Ameivas)

Rexroad Racerunner
Aspidoscelis bilobatus (Taylor 1941)

Conservation Status:


The outer face of the type specimen shows no part of the coronoid but the scar of attachment is indicated by a slightly depressed area, extending forward to the middle of the fourth tooth (from last). Below the diastema between the eighth and ninth teeth (from last) is a forward-directed foramen, which is situated above the level of the middle of the dentary. The region toward the ventral surface, lying below the fifth to eighth teeth, is smooth, lacking any distinct striation or rugosity. On the inner face of the dentary the Meckelian groove, which is lateral (but becoming ventral anteriorly), and the Meckelian cavity are completely exposed, owing to the absence of the thin splenial, which covers the groove.
The teeth are pleurodont and unequally bilobed, the small lobe being anterior. The second, fourth, and fifth teeth (from last) show a very faint trace of a still smaller posterior notch or lobe, which is a counterpart of the third lobe, present in certain living species of Aspidoscelis; The teeth are wider in proportion to length when compared with modern representatives of Aspidoscelis living in this southwestern region, and the crowns seem more blunt, but the latter difference may be due to age and wear. The relative size of the teeth and their characters are shown in figure 1 (of Taylor, 1941).
The jaw of this extinct species has been compared with the jaws of the living Aspidoscelis sexlineata (Linne), A. perplexa Baird and Girard, A. gularis Baird and Girard, and A. melanostetha Cope. Actually, the only one of these species known in this territory today is A. sexlineatus. This form agrees in the normal absence of distinctly trilobed teeth, but differs in having more slender and somewhat more tapering, laterally compressed teeth. The bases are proportionally closer together and the upper parts are somewhat more widely separated. In A. gularis, living in Texas, the four or five posterior teeth are generally trilobed, the posterior lobe being nearly as distinct as the anterior. The posterior teeth of A. melanostetha are more like those of A. sexlineata, and the outer posterior face of the dentary is very definitely sculptured and somewhat rugose. A. perplexa has teeth that are heavier on the basal portions, and the posterior part of the dentary is smooth. Also, the anterior extension of the coronoid is shorter, reaching forward only to the level of the third tooth, and it is more pointed. The teeth taper more towards their tips and their bases are closer together than in the described new species.
Measurements of the type specimen in millimeters, are as follows: extreme length of fragment figured, 7; elevation of dentary at posterior lateral foramen, 1.8.

Rexroad formation Upper Pliocene, Loe. 2, about 16 miles southwest of Meade, Meade County, Kansas.
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  • Occurrence Summary:  
  • 3
  • 3
    Museum Vouchers 
  • 0
    Other Observations 
Some county occurrences indicated below may be too imprecise to map above.
County Breakdown: County Name (# occurrences):
Meade (3);

Fossil History:
Known only from the type locality.

Natural History:

The estimated total length of the lower jaw of this species is 25 mm, based on proportional measurements in living species. This jaw size suggests a species somewhat larger than any of the four mentioned forms.

1941 Taylor, Edward H. Extinct lizards from Upper Pliocene deposits of Kansas. State Geological Survey of Kansas, Bulletin 38(5):165-176
Original descriptions of Aspidoscelis bilobatus, Plestiodon striatulatus, Eumecoides hibbardi, and Eumecoides mylocoelus.
1992 Trauth, Stanley E. A new subspecies of Six-lined Racerunner, Cnemidophorus sexlineatus (Sauria: Teiidae), from southern Texas. Texas Journal of Science 44(4):437-443
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Travis W. Taggart © 1999-2024 — w/ Sternberg Museum of Natural History, Fort Hays State University