A Key to the Lizards of the United States and Canada
Total Page：16
File Type：pdf, Size：1020Kb
A Key to the Lizards of the United States and Canada. CHARLES E. BURT, Southwestern College, Winfield, Kan. PREFACE The following key is intended to give a concrete diagnosis, which may be applied in a convenient manner to each lizard that inhabits the United States or Canada. If this makes it easier for naturalists to make correct identifica- tions, or if general research on lizards is stimulated by this action, practical ends are served. The following key is based very largely on the writer's personal comparison of specimens in various collections, with special reference to those in the United States National Museum and the California Academy of Sciences. All genera have been examined critically. The herpetological literature has yielded much of value in the way of pointing out the differential characteristics of various forms, and the present writer, like any other who undertakes a similar problem in the biological field, finds himself deeply indebted to contemporary and previous workers. Cope and Van Denburgh merit special mention here. This key is purely artificial, being arranged for the convenience of its users, and not even a family sequence is maintained in the text. The ranges have been prepared (1) from published records, (2) from unpublished records held by the writer, and (3) from records verified by reliable herpetologists in recent correspondence. The known distribution of each species and subspecies is indicated, but future extensions of these limits (especially slight ones) may be expected. As Blanchard has stated in his useful "Key to the Snakes of the United States, Canada, and Lower California," a species is conceived to be a "popula- tion of similar individuals of similar habits, freely interbreeding and main- taining a high degree of constancy in most superficial as well as in all funda- mental details throughout a generally considerable area." An unusual local emphasis on minor features is common, but it is not considered of taxonomic importance in separating species and subspecies. A subspecies is of the same nature as a species, except that it actually or potentially intergrades with members of one or more adjacent populations in areas where the two or more ranges involved approach or overlap. The intermediate zone of apparent intergradation delineated for two subspecies is often narrow, especially in regions like the Great Basin and the West Coast where sharp contrasts in environments are frequently presented, but the zone of intergradation may be wider in certain instances. It is often no easy task to apply the above criteria for the recognition of species and subspecies in the actual study of specimens from diverse areas, as any systematist knows. Common names are used to accompany scientific names throughout the following key. The scientific name of an animal is the same throughout the world, but the common name often varies with the locality or language. Standardized common names have been applied by the general English- speaking public to many lizards (such as "hored toads" for the lizards of the genus Phrynosoma), while many less-known forms have been given more or less appropriate names by specialists. The present list represents an attempt (255) 256 Kansas Academy of Science to apply the most characteristic and most widely used common name to each lizard involved. In some cases obscure or inappropriately named forms have been somewhat arbitrarily named (or renamed) here in the interest of con- sistency. Various correspondents, particularly those in California and the Southwest, have offered valuable suggestions. Dr. Joseph Grinnell and others at the Museum of Vertebrate Zoology of the University of California are fol- lowed, for instance, in reserving the cognomen "swift" for higher vertebrates, and in applying other appropriate names to the lizards called "swifts" by Ditmars and his followers. The key in its present form is made possible through the cooperation of many institutions and individuals. The illustrations have been prepared with the aid of a substantial grant from the National Research Council. Construc- tive criticisms have been offered by Dr. Frank N. Blanchard, Mr. L. M. Klauber, Dr. Jean M. Linsdale, Dr. F. C. Gates, Dr. E. R. Hall and others. The following text figures were drawn by Dr. Doris M. Cochran: Nos. 2, 5-7, 17-18, 20-32, 36, 42-43, 52-53, 56-60, 62-63, and 68-71. The remaining figures were prepared through the co6peration of Mr. Albert A. Heinze, of St. Louis (Nos. 1, 3-4, 8-16, 19, 33-35, 39-41, 44-51, 54-55, 61, and 64-67). Through the courtesy of Mr. Hobart M. Smith, the drawings Nos. 37-38 of Coleonyx were copied (by Mr. Heinze) from the original sketches for his published plate (1932). The preliminary critical work on the text of this key was done at the United States National Museum during June, 1932, where facilities for the study of practically all of the forms (including many types) were provided through the kindness of Dr. Leonhard Stejneger and Dr. Doris M. Cochran. Moreover, an extensive series of North American lizards was loaned by the United States National Museum for use in checking the key during periods of revision extending from the academic year 1932-1933 until the present time (1935). The writer is likewise grateful to Mr. Joseph R. Slevin, of the Cali- fornia Academy of Sciences, and to Dr. Joseph Grinnell, of the Museum of Vertebrate Zoblogy of the University of California, for courtesies rendered in connection with the examination of certain western lizards in California during August, 1932. GLOSSARY (See Figure 1 for illustration of terms (lealing with the scales of the head) Acuminate. Drawn to a point. Appressed limbs. Arms and legs extended toward each other at the sides. Bands. Usually applied to wide strips of color of considerable length, with especial reference to dark layers. Base of tail. Region opposite posterior margin of thigh. Body length. Tip of snout to anus. Canthus rostralis. Real or imaginary line connecting superciliary ridge at outer edge of supraocular area with tip of snout. Denticulations. Tooth-like projections. Femoral pores. Glandular, rounded openings, which are arranged in single longitudinal series on the lower surfaces of the thighs of certain lizards. Frontal. A median plate or series of scales between the eyes of various reptiles. The frontal scales of lizards are roughly opposite the frontal bones of the skull. Fronto-parietal. One or two median scales which appear on top of the head between the parietal and frontal scutes of certain lizards. Ground color. Predominant or basic color in the color pattern. Burt: Lizards of United States and Canada 257 Gular. Throat region. Head width. Measurement of head at widest point, usually at angle of jaws behind eyes. Imbricate. Overlapping like the shingles on a roof. Interparietal. Median parietal scale. Keeled. With a median longitudinal or diagonal ridge. Labial. Pertaining to the lips; the upper and lower labial scales border the mouth opening laterally. Lines. Usually applied to narrow dark longitudinal markings of considerable length. Mental. Scale at tip of chin. Nasal. Scale in which the nostril lies. If the nasal plate is divided by a vertical suture, the anterior half is called the "anterior nasal" and the posterior half is the "posterior nasal," or "postnasal." Occipital. Pertaining to the dorsal base of the skull, as (1) occipital spines of "horned toads," or (2) occipital scales of most lizards. Occipital scales, when present, are usually larger than the scales of the back but smaller than the forelying parietal scales. Occiput. Back of head, see occipital. Parietal. Dorsal area in front of occiput and back of the level of the eyes. The parietal scales are roughly opposite the parietal bones of the skull. Plate. Large flat scale. Posthumeral. Pertaining to the arm pit; axillary. Postanal plates. Subcaudal scales just back of anus. A few of these scales are decidedly enlarged in the adult males of certain lizard species. Postmental. Chin-scale or scales just behind mental plate. Postnasal. See nasal. Reticulation. Network. Rostral. Scale at tip of snout. Scales from occiput to base of tail. Transverse series of scales, counted along middorsal line from region opposite hinder margin of the thighs forward to the hindermost of the large scales on top of the head. Scale rows. Longitudinal series of scales, counted best in a circle around the middle of the body. Scute. Large flat scale. Spinose. With sharp, projecting points, spiny. Streak. Dull or diffused stripe, line or band. Stripes. Usually applied to narrow light markings of considerable length, especially to longitudinal ones. Subcaudal scales. Scales on the under surface of the tail. Superciliary ridge. Outer border of supraocular area. Supraoculars. Scales above eye on top of head, usually enlarged and plate-like, often forming a convex area; see supraorbital. Supraocular granules. Small scales separating enlarged supraocular scales from the large median head plates in various lizards. Supraorbital. Pertaining to the space above the eye, see supraoculars. Suture. Point of union between two scales. Tail length. Anus to tip of tail. Since many lizard tails are lost and regen- erated later, to a greater or lesser degree, it is obvious that maximum tail measurements may be obtained in perfect specimens only. Tympanum. Ear drum membrane, at the ear opening. Vertebral. Pertaining to the vertebral column; middorsal. 17-1602 A KEY TO THE LIZARDS OF THE UNITED STATES AND CANADA The arrangement adopted in this key was selected after considerable hesitation. It is the standard spread dichotomous form made so familiar to American biologists by its adoption in the various editions of Asa Gray's classic "Manual of Botany" and like- wise to the herpetologists of the world through its employment by John Edward Gray and G.