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Introduction: Pleistocene Vertebrate Taxa

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An attempt is made here to consider all Pleistocene species-level and generic-level vertebrate taxa from Arizona, southern California, Chihuahua, extreme southern Nevada, New Mexico, Sonora, 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

Bucking the generally accepted taxonomy recognizing the Chelonia (or Testudinata) as an order within the class Reptilia, turtles are recognized as a separate taxonomic class as are the crocodilians (class Eusuchia).

Nomenclature

Nomenclature has to do with the naming of things, with the legalistics, so to speak. This section is primarily for the non-biologist, for most organismal biologists are familiar with the material covered here. The zoologist is bound by the "International Code of Zoological Nomenclature." (Plants, bacteria, and viruses likewise have codes of nomenclature that apply to those taxa; although somewhat similar, they differ in detail.)

Historically, it was found necessary to introduce a standard common to all workers in a field so as to promote stability and communication. One of the problems is obvious—common names are useless on other than a regional basis. The fledermaus of German is the ratón volador of Spanish and the "bat" of English. This was incentive to go to the common language of science during the 18th Century, which was Latin. A Latin (or Latinized) name applied to a taxon could be understood everywhere as belonging to a specific group—or so it was thought.

New problems of communication arose, however. Not infrequently, the same taxon was named by workers in different places (and, of course, with different names), usually due to ignorance of earlier names. Once used in a particular region, there was local reluctance to abandon a name for another. Thus it became necessary to erect a set of rules governing which name would serve. The rule of priority states that the first name applied according to the rules of nomenclature is the legitimate name (there are provisions for suppressing obscure "long-lost" names in favor of widely used ones, however). Names that were applied according to the rules but that are invalid for any of several reasons are synonyms.

Another problem was the nature of the name itself. Before treated by Linnaeus, the "name" of a species was a descriptive phrase in Latin. Linnaeus, in the 1758 10th edition of Systema Naturae, stabilized the name of a species as consisting of two words (the binomial system of nomenclature), a noun followed by adjective (in Latin, of course). The first word is also the name of the genus that the species belongs to.

Thus the real name of humankind is Homo sapiens, and the genus to which we belong is Homo. Note that the generic part of the species name is always capitalized and that the specific portion is, in animals, never capitalized. The species to which we belong is not sapiens (this is akin to trying to call a red barn a "red")—both parts of the name are necessary (when no confusion can occur, it is legitimate to abbreviate, usually by the first letter, the generic portion; e.g., H. sapiens).

The rules also call for setting apart generic names, subgeneric names, species names, and subspecies names in different type from that used in the main text; by tradition, this is done by use of italics (or, in manuscript, by underlining, which is the printer's symbol for italics). You may have noticed, for example, that in the italicized figure captions in these web pages, the species names are not italicized, thus separating them from the rest of the caption.

The novice may wonder why there may be a name and date after the scientific name. This primarily is to aid the practicing taxonomist and can be ignored by others. The name is the author(s) (the person or persons who named the taxon) and the date is the year of publication. If the description of a species was published under a different generic name, the name is placed in parentheses. For example, Neotoma cinerea (Ord 1815) was described by Ord in 1815 as Mus cinereus (Mus currently is the genus of the house mouse and close relatives, but in the earlier days included animals that today we consider quite different). It became Neotoma cinerea in 1858 when Baird shifted it to the genus Neotoma.

The plural of genus is genera, and both the singular and plural of species is species: thus one genus, two genera; one species, two species.

Another problem treated by the rules relates to tying the name and the taxon together. Many of the early descriptions (or specimens on which the descriptions were based) were so poor that the animal being described was later unrecognizable. In other cases, a name was based on a series of specimens that eventually was found to include several different species (or even higher taxa). Today, there is a set of rules governing the requirements for a legitimate species (or generic or subspecific) description. Among other things, including the requirements concerning publication, a single specimen, the holotype, must be named so as to tie the name to a particular taxon. Originally, the "type" referred to the ideal essence (a metaphysical concept) of a species; variation in a species was considered essentially a series of imperfections, of deviations from the essence (reportedly, in the early days, if a specimen thought to better reflect the essence was found, a new holotype was substituted for the old). As taxonomy matured and it was realized that variation is a property of a species, it was accepted that no single specimen can adequately represent it. Thus, this concept was dropped (though it still lingers on subconsciously in many cases). Today, the type (holotype) is merely a name bearer. Whatever taxon is actually represented by the holotypic specimen is the taxon that the name is associated with forever.

There are seven ranks of the taxonomic hierarchy which are considered minimal to classify a taxon—this is the obligate taxonomic hierarchy:

Kingdom
   Phylum
      Class
         Order
            Family
               Genus
                  Species

To minimally classify an animal, it must be placed within each of these seven ranks—that is, assigned to a kingdom, a phylum, etc. In addition to these obligate levels, however, is a large number of finer divisions, such as subkingdom, superphylum, infraclass, etc. (there are more than 30 in fairly common use—this site occasionally will use a few of these that are self evident). The principle in each case is the same—if we haven't made errors, all entities within a given taxon are more closely related to one another than any is to an entity in a different taxon; e.g., members of a subgenus are more closely related to each other than to any member of a different subgenus of the same genus.

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.

Annotations

Starting with the addition of Arizona records (and picking up earlier as time allow), 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 earlier site accounts as time allows.

Site Presentation

map dotsEach taxon has its sites of occurrence mapped. Be warned that 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. Rancholabrean sites are shown with a red-centered dot, Irvingtonian-age sites with a green-centered dot, Blancan-age sites with a yellow-centered dot, and Pleistocene sites not specified as to a lower chronological level with a dark blue-centered dot. Sites where two land mammal ages are found or where it is uncertain to which of two ages applies are shown with a split 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, Jefferson 1991a and 1991b). 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 is no diagnostic feature present to separate it from some other taxa; 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 were given in the publication (or may have been unavailable) 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 related taxon now nearest geographically to the fossil site. In many cases, the only real 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 in herptiles, for example. 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 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 (ca. 1.80-0.25 my), and Rancholabrean (ca. 0.250 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; by their nature, cave often have features susceptible to stratigraphic mixing (e.g., interstices between loosely fitting rock fall; strong water currents entering during storms) or support animals, such as woodrats and snakes, that burrow within the cave fill. A further(and often worse) factor is human disturbance because of pot hunting or the seeking of Spanish gold.

A handicap when working with earlier excavated sites is that often relatively little care was taken in terms of stratigraphy and perhaps less in recording stratigraphic notes. Because of this, in many cases it now is 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 I have done so in at least some cases) 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.

Literature.

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

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Last Update: 9 Jun 2014