Access

You are not currently logged in.

Access your personal account or get JSTOR access through your library or other institution:

login

Log in to your personal account or through your institution.

If You Use a Screen Reader

This content is available through Read Online (Free) program, which relies on page scans. Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.

Semiaquatic Snakes of the Genus Thamnophis from the Isolated Drainage System of the Río Nazas and Adjacent Areas in Mexico

Roger Conant
Copeia
Vol. 1963, No. 3 (Sep. 25, 1963), pp. 473-499
DOI: 10.2307/1441468
Stable URL: http://www.jstor.org/stable/1441468
Page Count: 27
  • Read Online (Free)
  • Download ($12.00)
  • Subscribe ($19.50)
  • Cite this Item
Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Semiaquatic Snakes of the Genus Thamnophis from the Isolated Drainage System of the Río Nazas and Adjacent Areas in Mexico
Preview not available

Abstract

Several streams traversing portions of the Chihuahuan Desert in northern Mexico were once part of a master river system, the Pleistocene or post-Pleistocene Río Nazas, which emptied into the Rio Grande during one or more pluvial periods of the past. Several species of fishes, the turtle, Pseudemys scripta, and the water snake, Natrix erythrogaster, which occur in one or more of the now isolated drainage systems, are identical with or only subspecifically distinct from their counterparts in the Rio Grande. It is assumed that these aquatic and semiaquatic vertebrates achieved their present relict distributions in the desert by working headward from the Rio Grande. Three species of garter snakes, Thamnophis eques, T. melanogaster, and T. rufipunctatus, are also closely associated with the now disrupted streams. A detailed study of scutellation and pattern variations among the Thamnophis populations from the several rivers and adjacent areas suggests that migration along the streams contributed to present-day distribution patterns, but that a more important factor was probably overland movement during the pluvials. All three species of Thamnophis are widespread upon the Mexican plateau, and none is known to occur in the Rio Grande system downstream from the Río Conchos in Chihuahua. A new race of Thamnophis eques from high elevations in the Sierra Madre Occidental of Durango and Chihuahua is described.

Page Thumbnails

  • Thumbnail: Page 
473
    473
  • Thumbnail: Page 
474
    474
  • Thumbnail: Page 
475
    475
  • Thumbnail: Page 
476
    476
  • Thumbnail: Page 
477
    477
  • Thumbnail: Page 
478
    478
  • Thumbnail: Page 
479
    479
  • Thumbnail: Page 
480
    480
  • Thumbnail: Page 
481
    481
  • Thumbnail: Page 
482
    482
  • Thumbnail: Page 
483
    483
  • Thumbnail: Page 
484
    484
  • Thumbnail: Page 
485
    485
  • Thumbnail: Page 
486
    486
  • Thumbnail: Page 
487
    487
  • Thumbnail: Page 
488
    488
  • Thumbnail: Page 
489
    489
  • Thumbnail: Page 
490
    490
  • Thumbnail: Page 
491
    491
  • Thumbnail: Page 
492
    492
  • Thumbnail: Page 
493
    493
  • Thumbnail: Page 
494
    494
  • Thumbnail: Page 
495
    495
  • Thumbnail: Page 
496
    496
  • Thumbnail: Page 
497
    497
  • Thumbnail: Page 
498
    498
  • Thumbnail: Page 
499
    499