North American Jumping Mice (Genus Zapus).

by Philip H. Krutzsch.

INTRODUCTION

The jumping mice (Genus _Zapus_) are widely distributed over northern North America, occurring as far north as the Arctic Circle and as far south as Georgia, Missouri, Oklahoma, New Mexico, Arizona, and central California. In some years these small rodents are locally common in moist places that are either gra.s.sy or weedy; the jumping mice are notable for the much enlarged hind legs and the exceptionally long tail.

Members of the Genus as a whole have received no serious comprehensive taxonomic attention in the 54 years since Preble's (1899) revisionary work. In this time 15 new names have been proposed, mostly for subspecies, and only a few attempts have been made at grouping related named kinds.

In the present account it is aimed to record what is known concerning geographic distribution, taxonomically significant characters, and interrelationships of the known kinds as well as to provide means for recognizing the species and subspecies in the genus. In addition, attention is given to the probable center of origin of the subfamily Zapodinae and to the relationships and taxonomic positions of the genera _Zapus_, _Napaeozapus_, and _Eozapus_.

MATERIALS, METHODS, AND ACKNOWLEDGMENTS

The present report is based on a study of approximately 3,600 specimens that were a.s.sembled at the Museum of Natural History of the University of Kansas or that were examined at other inst.i.tutions. Most of these specimens are stuffed skins with skulls separate. Skulls without skins, skins without skulls, entire skeletons, and separately preserved bacula are included as a part of the total. Almost every specimen is accompanied by an attached label, which bears place and date of capture, name of collector, external measurements, and s.e.x.

Specimens used in the study of geographic variation were arranged by season of capture and according to geographic location; then they were segregated as to s.e.x, and, under each s.e.x, by age. Next, individual variation was measured in comparable samples of like age, s.e.x, season, and geographic origin. Finally, comparable materials were arranged geographically in order to determine variations of systematic significance.

The only external measurements used were total length, length of tail, and length of hind foot; these measurements were recorded by the collectors on the labels attached to the skins. Height of the ear was not used since it was not recorded by many of the collectors.

In order to determine which cranial structures showed the least individual variation but at the same time showed substantial geographic variation, a statistical a.n.a.lysis was made of the 30 measurements, of cranial structures, heretofore used in taxonomic work on _Zapus_. The following measurements of the skull showed the least individual variation but showed some geographic variation and therefore, were used in this study. See figs. 1-3 which show points between which measurements were taken:

_Occipitonasal length._--From anteriormost projection of nasal bones to posteriormost projection of supraoccipital bone.

_a_ to _a'_

_Condylobasal length._--Least distance from a line connecting posteriormost parts of exoccipital condyles to a line connecting anteriormost projections of premaxillary bones. _b_ to _n_

_Palatal length._--From anterior border of upper incisors to anteriormost point of postpalatal notch. _b_ to _b'_

_Incisive foramina, length._--From anteriormost point to posteriormost point of incisive foramina. _c_ to _c'_

_Incisive foramina, breadth._--Greatest distance across incisive foramina perpendicular to long axis of skull. _f_ to _f'_

_Zygomatic length._--From anteriormost point of zygomatic process of maxillary to posteriormost point of zygomatic process of squamosal. _d_ to _d'_

_Zygomatic breadth._--Greatest distance across zygomatic arches of cranium at right angles to long axis of skull. _j_ to _j'_

_Breadth of inferior ramus of zygomatic process of maxillary._--Greatest distance across inferior ramus of zygomatic process of maxillary taken parallel to long axis of skull.

_d_ to _e_

_Palatal breadth at M3._--Greatest distance from inside margin of alveolus of right M3 to its opposite. _g_ to _g'_

_Palatal breadth at P4._--Same as above except taken at P4.

_g_ to _g'_

_Mastoid breadth._--Greatest distance across mastoid bones perpendicular to long axis of skull. _h_ to _h'_

_Breadth of braincase._--Greatest distance across braincase taken perpendicular to long axis of skull. _i_ to _i'_

_Interorbital breadth._--Least distance across top of skull between orbits. _k_ to _k'_

_Length of maxillary tooth-row._--From anterior border of P4 to posterior border of M3. _l_ to _l'_

_Breadth of base zygomatic process of squamosal._--Greatest distance across base of zygomatic process of squamosal taken parallel to long axis of skull. _m_ to _m'_

[Ill.u.s.tration: FIGS. 1-3. Three views of the skull to show points between which measurements of the skull were taken. Based on _Z. t. monta.n.u.s_, adult, female, No. 22165 KU, Cascade Divide, 6400 ft., Crater Lake Nat'l Park, Klamath County, Oregon. 4.]

The baculum has a characteristic size and shape according to the species, and the following significant measurements of the structure were taken:

_Greatest length._--From posteriormost border of base to anteriormost point on tip.

_Greatest breadth at base._--Greatest distance across base taken parallel to long axis of bone.

_Greatest breadth at tip._--Greatest distance across tip taken parallel to long axis of bone.

In the descriptions of color the capitalized color terms refer to those in Ridgway (1912). Any color term that does not have the initial letter capitalized does not refer to any one standard.

In the description of the subspecies the two s.e.xes are treated as one because no significant secondary s.e.xual variation was found. Only fully adult specimens of age groups 3 to 5, as defined on pages 377 and 388, have been considered.

Unless otherwise indicated, specimens are in the University of Kansas Museum of Natural History. Those in other collections are identified by the following abbreviations:

AMNH. American Museum of Natural History.

CAS. California Academy of Science.

CM. Carnegie Museum.

Chic. AS. Chicago Academy of Science.

Clev. MNH. Cleveland Museum of Natural History.

LMH. Collection of Lawrence M. Huey.

JKJ. Collection of J. Knox Jones, Jr.

CMNH. Colorado Museum of Natural History.

FM. Chicago Museum of Natural History.

HM. Hastings Museum, Hastings, Nebraska.

ISC. Iowa State College.

MCZ. Museum of Comparative Zoology.

MO. University of Missouri Museum of Zoology.

MVZ. Museum of Vertebrate Zoology, Berkeley, Calif.

NMC. National Museum of Canada.

NGFP. Nebraska Game, Forestation, and Parks Commission.

NCS. North Carolina State College.

OHIO. Ohio Wildlife Research Unit, Ohio State University.

OKLA. Oklahoma Agricultural and Mechanical College.

PM. Provincial Museum of British Columbia.

ROM. Royal Ontario Museum of Zoology.

SDM. San Diego Natural History Museum.