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Introduction: Pleistocene Vertebrate Taxa


An attempt is made here to consider all Pleistocene species-level and generic-level vertebrate taxa from Arizona, New Mexico, and Trans-Pecos Texas recorded in the literature or in the Paleobiology Collection of the UTEP Biodiversity Collections (formerly the Laboratory for Environmental Biology), Department of Biological Sciences, and Centennial Museum, University of Texas at El Paso (UTEP). Taxa are given by currently accepted scientific names, but synonyms also are given where they have been used in the literature and are apt to cause confusion. Names of higher taxa of many groups are in a state of flux. The arrangement of the higher taxa (families and above) here follows the Center for North American Herpetology's "Standard Common and Current Scientific Names" for amphibians and reptiles, the AOU Checklist for birds, and Mammalian Species of the World (Wilson and Reeder 2005) for mammals. In the case of the mammals, the on-line version is followed, where Rodentia is placed before Lagomorpha, rather than the printed version where the Rodentia is placed in volume 2 after all other taxa (presumably so that the rodents wouldn't be split between two volumes). In the case of mammals, taxonomic changes occurring after the publication date of Mammalian Species will be entered if there seems a high likelihood of general acceptance. Genera and species within families are listed alphabetically

There are different traditions regarding capitalization of common names. As examples, common names of birds usually are capitalized as proper nouns when referring to a specific kind; this is not the usual case for mammals, however. Rather than allow inconsistency in this volume, I've chosen to capitalize all proper nouns. Thus Common Raven and Chihuahua Raven, but not ravens in general.

Starting with the addition of Arizona records, some annotations have been added to taxa in the site faunal lists.

These annotations appear like this, in different sized font and inset beneath the taxon involved.

The most common annotation is the listing of the name under which the taxon was reported if the name has changed. Less commonly, some other aspect is commented upon. Annotations may be added to non-Arizona accounts as time allows.

Following the higher taxonomy of chordates noted in the Center for North American Herpetology, the turtles are recognized as a separate taxonomic class, the Chelonia as are the crocodilians (class Eusuchia).

Each taxon has its sites of occurrence mapped. No attempt has been made to be extremely accurate in placement of the dots representing the sites, the maps being designed largely to show the pattern of distribution. Site names, however, are listed in each account. Blancan-age sites are shown with a yellow-centered dot; Irvingtonian-age sites with a green-centered dot; Rancholabrean with a red-centered dot, and Pleistocene sites not specified as to North American Land Mammal Age with a dark blue-centered dot. In a few cases, records have been rejected and the site to which the taxon was assigned shown with a light-blue-centered dot. Where a reasonable approximation of the locality of a site cannot be made, a black dot is placed in the center of the dot's color field. Usually the dot will be placed near the center of the county involved (some taxa are cited only as Grand Canyon; in those cases, the dot will be placed toward the center of the canyon).

In the site and taxon accounts, citations usually are to those deemed by me to likely be most useful to the reader. In many cases, this is to one of the summaries of Pleistocene taxa (such as Harris 1993c; Morgan and Lucas 2003, 2005). Occasionally, in addition to literature cited, other pertinent references may be listed to allow the reader to delve deeper if so inclined. In some cases, I have not personally reviewed these references.

Although most people can easily visualize horses, bison, and camels, relatively few have a mental image of a Bushy-tailed Woodrat or a Merriam's Shrew. Since a large portion of the Pleistocene fauna survives today, I have tried to include images of many of the taxa; hopefully, this will help some of the dried bones come alive in the minds of the viewer.

A "?" indicates considerable doubt regarding the identification. Usually this means that the (often fragmented) specimen is consistent with the taxon, but there are other taxa also consistent with the characters available; a sort of "playing the odds". A "cf." (abbreviation of the Latin word for "compare") indicates a likely correct identification, but one that is not certain. The listing of "?" or "cf." alone indicates the uncertainty applies to the species, but not the genus unless only the generic name is given; where the uncertainty applies to genus and species, the listing is given as ? or cf. gen. et sp. "UTEP" indicates that the taxon is represented by unpublished material in the Paleobiology Collection, UTEP Biodiversity Collection, or that some change in the published data has occurred. Situations where a genus can be recognized but the species cannot be identified is given as the generic name followed by "sp." For example, Neotoma sp.

The rapid and far-flung changes in nomenclature and taxonomy pose special difficulties when attempting to compile fossil records from publications spanning a number of decades. Straight-forward synonymy is only a minor problem; where the real difficulty lies is where taxa have been split since publication and insufficient data are available to surely assign the record to a currently recognized taxon. An example is the recent splitting of the genus Spermophilus into eight genera (Helgen et al. 2009). A literature record of "Spermophilus sp." without further information fails translation to a currently recognized genus. Likewise, the splitting of a species may leave no recourse but to assign a record to the taxon now nearest geographically to the fossil site. In many cases, the only solution is reexamination of the fossil material, not easily accomplished in a majority of cases.

A word or two regarding identifications is advisable. Dealing with fragmentary material greatly increases the probability of misidentifications. Furthermore, identifications frequently are based in part on current geographic distributions. As an example, species of cottontail rabbits now limited to eastern North America (such as the Appalachian Cottontail) are not considered when identifying Southwestern cottontails. This is suggested as potentially important especially in herptiles. Bell and Gauthier (2002) questioned the reliability of the general supposition that lizards and snakes were stable taxonomically and geographically throughout much of the Quaternary. They noted the circularity of reasoning in that the identifications of the fossils are based on the current distributions. They also pointed out that based on morphology alone, the majority of these Quaternary fossils cannot be identified to species on the currently known criteria. Driving home the difficulties in determining herpetological species identification, Bevers (2005) could find no mensural or morphological characters that as of themselves could surely discriminate any one of the 27 extant species of bufonid toads that he studied from all of the other 26 species. These uncertainties of identification, especially regarding the herpetological material, appertain to the records given in this current work.

Different ways of assigning specimens to a time span are used. The most general is "Pleistocene", meaning the time span cannot be narrowed further; subdivisions, however, sometimes are possible, such as late Pleistocene. Somewhat more limited are the North American Land Mammal Ages (NALMA): that portion of the Late Blancan falling within the Pleistocene (2.6-1.8 my), Irvingtonian (1.8-0.3 my), and Rancholabrean (0.3 mya-10 kya). In some cases, subdivisions are possible (e.g., early Irvingtonian). Most Pleistocene fossils are from the last of the glacial ages, the Wisconsin, and may be so recorded; again, sometimes with divisions possible. Age in years is possible in some cases where radiometric data are available.

Unfortunately, a number of sites have been disturbed. This is especially the case for cave sites, where pot-hunters or seekers after Spanish gold have disturbed the sediments without regard to stratigraphy. Also, many of the earlier excavated sites have less detailed stratigraphic notes than would be the case today, and it's now impossible to reconstruct the relationships. Because of such problems, some sites are recorded as, for example, "Late Wisconsin/Holocene," meaning that deposition is known to have occurred in both the late Wisconsin and the Holocene, and assignment to one or the other on stratigraphic grounds is not possible. In such cases, assignment to the Pleistocene may be made with considerable assuredness for extinct forms and for taxa that now occur nowhere near the site; however, in the absence of reliable stratigraphic data, such taxa have lost an appreciable part of their value for interpretation. It also becomes problematical as to whether extant, local animals were present in the late Wisconsin or are present in the recovered fauna because of later occurrence.

I have been somewhat more daring (or, in the judgment of some, reckless) in assigning sites to limited time spans than were Morgan and Lucas (2005), and it should be recognized that there is a degree of danger in this as well as the possibility of illuminating short-term changes. I have made decisions as to the finer divisions of age of various cave faunas on the basis of stratigraphy where available and based upon my interpretation of the chronological distribution of Pleistocene biotas. Others may interpret the chronology differently; however, it is likely that where such designations as Mid Wisconsin, Late Wisconsin, or Early/Mid Wisconsin have been made, that at least assignment to the Wisconsin is firm. I have assigned Wisconsin faunas younger than 25,000 rcy (radiocarbon years) as Late Wisconsin; faunas judged to be between about 60,000 and 25,000 as Mid Wisconsin, and older than 60,000 are Early Wisconsin.


Bell and Gauthier 2002; Bever 2005; Harris 1993c; Helgen et al. 2009; Morgan and Lucas 2003, 2005.


Last Update: 4 Dec 2013