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Title: A New Subspecies of Wood Rat (Neotoma mexicana) from Colorado
Author: Finley, Robert B.
Language: English
As this book started as an ASCII text book there are no pictures available.

*** Start of this LibraryBlog Digital Book "A New Subspecies of Wood Rat (Neotoma mexicana) from Colorado" ***

A New Subspecies of Wood Rat (Neotoma mexicana) From Colorado


University of Kansas Publications
Museum of Natural History

Volume 5, No. 30, pp. 527-534, 2 figures in text
August 15, 1953

University of Kansas


Editors: E. Raymond Hall, Chairman, A. Byron Leonard,
Robert W. Wilson

Volume 5, No. 30, pp. 527-534, 2 figures in text
August 15, 1953





A New Subspecies of Wood Rat (Neotoma mexicana) from Colorado



Field and museum studies of the wood rats of Colorado have revealed the
existence of an unnamed subspecies of _Neotoma mexicana_ in eastern
Colorado south of the Arkansas River. The characters of the new
subspecies are most distinctive in the northeastern part of its range
near Two Buttes and Higbee. It differs in cranial characters from _N. m.
fallax_ and _N. m. inopinata_ and averages slightly larger, but cannot
be distinguished by coloration of the pelage.

This heretofore undescribed subspecies may be known as:

#Neotoma mexicana scopulorum# subsp. nov.

     _Type._--Mus. Nat. Hist., Univ. Kansas, No. 37137, old adult
     male, skin and skull; from 37° 47' N, 103° 28' W, three miles
     northwest of Higbee, 4300 feet, Otero County, Colorado;
     trapped 16 May 1950 by R. B. Finley, Jr., original number

     _Range._--Cañons, mesas, and foothills south of the Arkansas
     River, east to Two Buttes, Colorado, and south to Clayton, New
     Mexico. The extent of the range to the southwest in New Mexico
     has not been determined.

     _Diagnosis._--Size large for the species; interorbital
     constriction near middle of frontal rather than anteriorly;
     supraorbital ridges of frontal concave laterally; skull large,
     strongly arched at base of rostrum; rostrum wide; nasals wide
     anteriorly; upper incisors wide, light yellow; molars large,
     tooth-rows long; zygomatic arches wide and heavy;
     interparietal short, wide, and posterior margin straight or
     with a slight posterior median angle.

     _Description._--Adults in dense unworn pelage taken in
     February at Two Buttes Reservoir: size large for the species;
     tail approximately 76 per cent as long as head and body; hind
     feet of medium length. Pelage: moderately long, thick; tail
     covered with short hairs; longest vibrissae 80 mm. Color:
     sides near Raffia (11 E 6) (capitalized color names and
     designators are of Maerz and Paul, A Dictionary of Color,
     McGraw-Hill Book Co., New York, 1930) overlaid with black, the
     general effect being grayish buff (13 G 6); back darker,
     moderately to heavily overlaid with black; indistinct dark eye
     ring; underparts whitish, fur basally gray except patch of fur
     pure white to base almost always present on upper throat; dark
     line around mouth; tail bicolor, black above, whitish below;
     feet white to ankles.

     Skull: large for the species, strongly arched at base of
     rostrum; rostrum heavy; zygomatic arches widely spreading,
     heavy, squarish; braincase moderately ridged and angular;
     nasals wide anteriorly, lateral margins nearly parallel or
     converging evenly posteriorly, tapered abruptly at posterior
     ends which reach posteriorly beyond anterior plane of orbits;
     dorsal branches of premaxillae extending 0.5 to 1.2 mm.
     posterior to nasals; interorbital region moderately channeled,
     narrowly constricted near middle of frontal (instead of
     anteriorly); supraorbital ridges concave laterally, diverging
     more strongly posterior to interorbital constriction (frontal
     8.7 to 9.5 mm. wide at posterior ends of supraorbital ridges);
     temporal ridges widely flaring on parietals; occipital ridges
     prominent; interparietal broadly rectangular between temporal
     ridges, usually short in median line of skull, posterior
     margin straight or with slight median posterior angle;
     incisive foramina tapered toward both ends, sometimes narrower
     anteriorly than posteriorly; anterior palatal spine usually
     forming a blade thickened on ventral edge, and right and left
     sides usually incompletely fused; nasal septum with a
     posterior notch separating vomer from maxillary; posterior
     margin of palate usually bearing single or double point,
     sometimes straight; interpterygoid fossa moderately wide,
     lateral margins concave; sphenopalatine vacuities large;
     auditory bullae of medium size; basioccipital with low median
     ridge or crest; upper incisors wide, yellow or yellow-orange;
     molars large, M1 wider than M2; maxillary tooth-rows long,
     nearly parallel; anterointernal fold of M1 deep, cutting more
     than half way across first enamel loop.

[Illustration: FIGS. 1-6. Skulls of _Neotoma mexicana_. All × 1.

FIGS. 1-2. _Neotoma mexicana scopulorum_, holotype.

FIGS. 3-6. _Neotoma mexicana fallax_, 1-1/2 mi. NW Golden, 6200 ft.,
Jefferson County, Colorado, 8 June 1948, [Male] No. 29182 KU.]

     Adult in worn pelage taken in May at Two Buttes peak: no molt
     in evidence; pelage thinner and rougher than in adults of same
     tooth wear taken in February in unworn pelage (described
     above); upper parts duller, less heavily overlaid with black;
     sides less richly yellowish, slightly more pinkish in hue;
     underparts with no fur white to base (as usual for the
     species). The skull of this rat has narrower nasals than other
     adults from Two Buttes and a longer interparietal with a
     posterior median angle.

     Subadult taken in April at Regnier: completing postjuvenal
     (first) molt; new pelage fairly long and thick everywhere
     except on neck and upper back, where covered by remaining
     juvenal pelage; upper parts of new pelage duller than in
     adults, sides less buffy, more grayish; juvenal pelage grayer
     than new pelage; new pelage indistinguishable from same pelage
     (second pelage of first year) of _N. m. fallax_.

     _Comparisons._--_N. m. scopulorum_ is extremely variable in
     color but averages lighter and richer in color than _N. m.
     fallax_, and about the same as _N. m. inopinata_. _N. m.
     scopulorum_ can be separated from either by the following
     cranial differences: skull larger, more strongly arched at
     base of rostrum, interorbital constriction more posterior;
     supraorbital ridges concave laterally (in contrast to
     straight, diverging); interparietal shorter in median line,
     more widely spreading and rectangular; zygomatic arches more
     widely spreading and heavier; upper incisors wider; and molars
     larger. _N. m. scopulorum_ differs from _inopinata_ also in
     paler upper incisors and less prominent basicranial ridges.

     _N. m. scopulorum_ is paler than _N. m. pinetorum_. The skulls
     of these two subspecies are of about the same size, but the
     subspecies differ in other respects as _scopulorum_ differs
     from _fallax_ and _inopinata_.

     Judging from the description and photograph of _mexicana_ in
     Goldman's revision of the genus _Neotoma_ (N. Amer. Fauna, 31:
     54-56, Pl. IV, 19 October 1910), _scopulorum_ differs from _N.
     m. mexicana_ in: larger skull; longer nasals and dorsal
     branches of premaxillae; more posterior interorbital
     constriction (supraorbital ridges more concave laterally);
     wider upper incisors; and larger molars.

     _Measurements._--Mean and extreme measurements in millimeters
     of 6 males and 5 females from 3 mi. NW Higbee and the vicinity
     of Two Buttes are, respectively, as follows: total length, 357
     (345-368), 345 (310-379); length of tail, 147 (140-158), 159
     (138-178); length of hind foot, 35 (32-38), 36.4 (35-38);
     length of ear, from notch, 25.5 (25-26), 25.7 (25-27); weight
     (in grams), 234 (213-253), 206 (161-246); basilar length, 37.9
     (36.8-38.9), 36.2 (34.5-38.6); length of nasals, 19.0
     (18.2-20.0), 17.9 (16.4-19.6); zygomatic breadth, 23.9
     (23.0-24.5), 23.3 (22.3-24.0); interorbital breadth, 5.3
     (4.9-5.6), 5.1 (5.0-5.3); breadth of rostrum, 7.2 (6.8-7.7),
     6.8 (6.7-6.9); diastema, 12.8 (12.3-13.3), 12.2 (11.1-13.7);
     alveolar length of maxillary tooth-row, 9.5 (9.2-9.8), 9.4
     (9.0-9.7); length of incisive foramina, 9.7 (9.2-10.2), 9.2
     (8.6-10.2); length of palatal bridge, 8.8 (8.4-9.2), 8.5

     _Measurements of the type._--Total length, 348; length of
     tail, 143; length of hind foot, 35; length of ear, from notch,
     25; weight (in grams), 230; basilar length, 38.1; length of
     nasals, 18.8; zygomatic breadth, 24.2; interorbital
     constriction, 5.5; breadth of rostrum, 7.2; diastema, 13.0;
     alveolar length of maxillary tooth-row, 9.2; length of
     incisive foramina, 9.7; length of palatal bridge, 8.9.

     _Remarks._--The large size and distinctive cranial characters
     of _N. m. scopulorum_ are fairly constant in the northeastern
     part of its range, but there is a wide range of variation in
     color. The only two skins from the type locality differ
     markedly in color. Both specimens (the type and KU 37138,
     adult male) were collected on 16 May 1950 and are in
     moderately worn pelage. The upper parts of the holotype are
     much more yellowish than in KU 37138, and are even lighter
     buff than adults in unworn pelage from Two Buttes. The
     underparts of the holotype are more extensively white than in
     almost any other specimen seen of _Neotoma mexicana_. The
     basal gray coloration, where it is present along the sides of
     the venter, forms only a narrow intermediate color band
     extending not more than one third the length of the hairs. An
     extensive area of the throat, breast, axillae, median belly,
     and inguinal region is covered by hairs pure white to the
     skin. The dark line around the mouth is present, as usual for
     the species. The upper parts of KU 37138 are like those of the
     adult in worn pelage from Two Buttes peak, described above;
     the underparts have only small patches of pure white fur on
     the throat and inguinal region, being elsewhere gray at the
     base of the fur, as is usual for the species.

     The molars of the type specimen are in an advanced state of
     wear, having the pattern of the enamel folds still discernible
     but the depth of remaining enamel slight. A large alveolar
     abscess surrounds the abnormal left M1. There are two, much
     worn, peglike fragments of the tooth projecting slightly from
     an ovoid alveolar cavity 5.1 mm. long and 4.3 mm. wide. As a
     result of the reduction of wear on the opposing m1, the crown
     of m1 is much less worn than those of the other lower molars
     and projects 0.8 mm. above the occlusal level of the two
     posterior molars. A few barbed cactus glochids (bristles) are
     inbedded in the cavity around the base of the molar remnants.
     Although glochids are of rather frequent and normal occurrence
     between the teeth of _Neotoma albigula_ and _N. micropus_,
     they are not so commonly found in _N. mexicana_ and possibly
     induced the alveolar infection in this individual.

     In addition to the skins in unworn and worn pelages already
     described from Two Buttes, an extremely dark specimen is at
     hand from Two Buttes peak, taken on 9 May 1950. This specimen
     (KU 37141 [Female]) is an adult in moderately worn pelage. The
     back is dark brownish gray (Taupe, 16 A 6), the sides lighter
     (a shade lighter than Beaver, 15 A 6). The entire underparts
     are washed with reddish buff (Grain, 11 B 5) over the gray
     basal coloration, with a patch of white only in the genital
     region. The dark eye ring and dark line around the mouth are
     heavier than usual. The underside of the tail is light gray.
     The white hind feet are sharply set off from the dark gray

     Each of four skulls from Regnier (three adults and one
     subadult) differs from skulls from Two Buttes in having a
     longer interparietal with a posterior angle. The skins of five
     adults collected in December at Trinchera are less richly
     colored on the sides than skins from Two Buttes and look more
     nearly like topotypes of _N. m. fallax_. The skull of one of
     the five from Trinchera differs from skulls from Two Buttes in
     much narrower nasals anteriorly, narrower rostrum, much
     narrower upper incisors, and smaller zygomatic breadth, these
     characters being as in _fallax_.

     Four adults and one subadult from Trinidad are intergrades
     between _N. m. scopulorum_ and _N. m. fallax_, perhaps more
     nearly resembling the former. In pelage they are
     indistinguishable from specimens of _fallax_ from Gold Hill
     (the type locality), less buff than most individuals of
     _scopulorum_ from Otero, Prowers, and Baca counties. The
     skulls of the three fully mature adults are large with a wide
     zygomatic breadth, large rostrum, and large upper incisors as
     in _scopulorum_; but the upper molars are small and the bullae
     are rather small and narrow as in _fallax_. In the degree of
     arching at the base of the rostrum, the shape of the frontal,
     the shape of the interparietal, and the size of the upper
     molars, the specimens from Trinidad are intermediate. It seems
     to me best to refer them to _scopulorum_.

     Two first-year adults from Fisher Peak and Long Cañon are
     indistinguishable from topotypes of _fallax_ of similar age
     and also resemble a young adult and a subadult from Trinidad,
     but all are insufficiently mature to show subspecific
     characters distinctly. Until adequate series are available
     from southwestern Las Animas County it seems best to regard
     all specimens from the three localities as representatives of
     a single uniform population which is intermediate between
     _fallax_ and _scopulorum_ but more nearly like the latter.
     Unfortunately no other specimens are available from the
     foothill zone south of the Arkansas River where morphological
     intergradation and ecological transition between _fallax_ and
     _scopulorum_ might reasonably be expected to occur.

     Three specimens from the north side of the Arkansas River,
     about 26 miles below Canon City, Pueblo County, are like
     _fallax_ in size, dorsal profile of the skull, and shape of
     the interorbital constriction; but they approach _scopulorum_
     in shape of the interparietal, size of the rostrum, and size
     of the molars. They are intergrades referrable to _fallax_.

     _Neotoma mexicana_ was first reported from Oklahoma by W.
     Frank Blair in 1939 (Amer. Midl. Nat., 22:126) who referred a
     specimen from Tesequite Canyon, Cimarron County, to _N. m.
     fallax_. I have seen one specimen (MZ 80469) from Tesequite
     Canyon and refer it to _scopulorum_.

     Of _scopulorum_, each of eight skulls, of the 28 skulls
     examined, has an anteroexternal enamel fold on the m3 and one
     (BSC 35222/47487 [Male]) has an anterointernal fold on the m3.
     Of the other 19 mandibles, a few are too old to show such a
     fold, which tends to be obliterated with wear in later age,
     and the others lack the fold.

     Two other wood rats (_N. albigula warreni_ and _N. micropus
     canescens_) occur at many of the same localities as _N. m.
     scopulorum_. The dens of _scopulorum_ almost always are
     situated among rocks, but the dens of _warreni_ and
     _canescens_ are in a variety of other situations as well as
     among rocks. Houses of sticks or cactus joints piled up around
     the base of a juniper (_Juniperus monosperma_), thicket of
     skunkbush (_Rhus trilobata_), clump of soapweed (_Yucca
     glauca_) or tree cactus (_Opuntia arborescens_) have been
     found to shelter only _N. a. warreni_ or _N. micropus
     canescens_. When these wood rats are associated with
     _scopulorum_ among the rocks, their dens can be recognized by
     the compact midden of innumerable cactus spines. The dens of
     _scopulorum_ have only a few loosely scattered spine areoles
     or none at all.

     I am grateful to the officials of the following institutions
     for permission to examine specimens from the collections under
     their care: Denver Museum of Natural History; Biological
     Survey Collection, U. S. Fish and Wildlife Service; American
     Museum of Natural History; Museum of Vertebrate Zoology,
     University of California; Museum of Zoology, University of
     Michigan. The drawings of the skulls were made by Victor Hogg.

     _Specimens examined._--Total 66, distributed as follows:

     #Colorado.# _Baca County_: "Furnace Canyon" [= Furnish Canyon],
     1 (DMNH); Regnier, 4500 ± ft., 4 (2 DMNH, 2 KU); Two Buttes
     Reservoir, 4200 ± ft., 5 (3 DMNH, 2 KU). _Las Animas County_:
     Fisher Peak, "about 8000 ft." [6 mi. SE Trinidad], 1 (BSC);
     Long Cañon (near Martinsen), 1 (BSC); Mesa de Maya, 1 (MZ); 9
     mi. W jct. Purgatory [= Purgatoire] & Chaquaqua [= Chacuaco]
     rivers ("Red Rock Canyon," collector's field notes), 1 (MVZ);
     Trinchera, 6 (5 DMNH, 1 AMNH); Trinidad, 5 (BSC); 20 mi. E
     Walsenburg, "Huerfano Co." [probably Las Animas County], 1
     (DMNH). _Otero County_: 3 mi. NW Higbee, 4300 ft., 4 (KU).
     _Prowers County_: Two Buttes peak, 4600 & 4650 ft., 2 (KU).

     #New Mexico.# _Union County_: Clayton, 9 (BSC); 9 mi. NE Des
     Moines on the "Carramba River" [= Cimarron River], 1 (DMNH);
     Folsom, 6 (BSC); Raton Range (Oak Cañon), 8 (BSC); Sierra
     Grande, 9 (BSC).

     #Oklahoma.# _Cimarron County_: Tesequite Canyon, 1 (MZ).

_Museum of Natural History, University of Kansas, Lawrence. Transmitted
April 20, 1953._


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