Speciation and Evolution of the Pygmy Mice, Genus Baiomys Part 10

_Baiomys taylori taylori_, Dalquest, Louisiana State Univ. Studies (Biol. Sci. Ser.), 1:155, December 28, 1953 (part); Hall and Kelson, The Mammals of North America, 2:660, March 31, 1959 (part).

_Baiomys taylori allex_, Hall and Kelson, The Mammals of North America, 2:659, March 31, 1959 (part).

_Baiomys musculus musculus_, Hall and Kelson, The Mammals of North America, 2:661, March 31, 1959 (part).

_Type._--Adult male, skin and skull; No. 120261 U. S. Nat. Mus. (Biol.

Surv. Coll.); Zamora, Michoacan, Republic of Mexico, obtained on January 15, 1903, by E. W. Nelson, and E. A. Goldman, original number 15764.

_Range._--Central and eastern Jalisco south into Michoacan, east through Guanajuato, Queretaro, thence into Estado Mexico, and Distrito Federal, and west-central Veracruz, see Figure 11. Zonal range: approximately the Transverse Volcanic Biotic Province of Moore (1945:218) and of Goldman and Moore (1945:349). Occurs from 5000 feet, 7 mi. S Ocotlan, Jalisco, up to 8000 feet in Ixtapalapa, Distrito Federal.

_Diagnosis._--Size large for the species; dorsum dark Sepia to near blackish medially in freshly taken specimens (Sepia fading to near Fuscous in prepared specimens); belly slaty-gray, hairs Deep Neutral Gray near tips and Dusky Neutral Gray at bases; hairs on back black-tipped with subterminal band of Ochraceous-Tawny (guard hairs blackish to base); hairs of throat and chin white-tipped, gray at bases; dorsal vibrissae black, ventral and anteriormost vibrissae white; hairs on face and sides black-tipped, and Ochraceous-Tawny at base; ears spa.r.s.ely haired, individual hairs grayish, blackish, and ochraceous; tail sooty to blackish dorsally, lighter ventrally; forefeet and hind feet sooty brown on dorsal and ventral surface. Skull relatively broad interorbitally; zygoma broad and squared; cranium larger in all dimensions than in most other subspecies. Average and extreme measurements of 10 adults from 1 mi. S, 11 mi. W Zamora, 5400 ft., Michoacan, are: total length, 109.4 (102-121); length of body, 64.3 (58-72); length of tail, 44.9 (39-51); length of hind foot, 14.6 (14-15); occipitonasal length, 18.0 (17.5-18.6); zygomatic breadth, 9.4 (9.1-9.7); postpalatal length, 6.6 (6.2-7.2); least interorbital breadth, 3.5 (3.3-3.8); length of incisive foramina, 4.0 (3.8-4.2); length of rostrum, 6.2 (5.8-6.5); breadth of braincase, 8.7 (8.5-8.9); depth of cranium, 6.6 (6.3-6.9); alveolar length of maxillary tooth-row, 3.1 (3.0-3.3); for photographs of skull, see Plate 2_a_ and Plate 4_b_.

_Comparisons._--For comparisons with _B. t. allex_, _B. t. canutus_, _B.

t. paulus_, and _B. t. fuliginatus_, see accounts of those subspecies.

From _B. t. taylori_, _B. t. a.n.a.logous_ differs as follows: sides and dorsum darker, differing most in freshly prepared specimens; dorsal surface of forefeet and hind feet darker; basal part of hairs on belly darker gray; frontal bones less constricted, causing less taper anteriorly in interorbital s.p.a.ce; interparietal wider transversely; basioccipital more expanded laterally, narrowing more abruptly at suture between basioccipital and basisphenoid.

_Remarks._--The pelage of _a.n.a.logous_ becomes paler with wear as pointed out by Osgood (1909:257). A paratype, U. S. Nat. Mus. 120260, and several specimens from 1 mi. S, 11 mi. W Zamora, Michoacan, are grayish rather than brownish-black. All of these are old adults having the terminal black parts of the hairs on the dorsum nearly worn away.

Excluding such grayish individuals, _B. t. a.n.a.logous_, like _B. t.

subater_ and _B. t. fuliginatus_, is uniformly brownish-black. Both _a.n.a.logous_ and _fuliginatus_ occur in relatively high mountainous country on dark soils or pedregals, and all three of the aforementioned subspecies occur in zones of high relative humidity.

_B. t. a.n.a.logous_ intergrades with _B. t. paulus_ (see account of that subspecies) and _B. t. allex_ south and west of Lago de Chapala in Jalisco. Additional specimens are needed from Queretaro and San Luis Potosi in order to ascertain whether or not _B. t. a.n.a.logous_ intergrades with _B. t. fuliginatus_ or _B. t. taylori_. Specimens from western Jalisco, in the past referred to _B. t. a.n.a.logous_, are referable to _B. t. allex_ (see account of that subspecies). Specimens obtained west of, and bordering, the Rio del Naranjo in Jalisco show a mixture of characters of both _B. t. allex_ and _B. t. a.n.a.logous_. For example, specimens from 2 mi. N Ciudad Guzman resemble _a.n.a.logous_ on the dorsum, whereas, on the belly, the individual hairs are white-tipped, pale gray at the base, and in over-all appearance are whitish-gray, unlike typical _a.n.a.logous_ (being like _allex_ instead).

The dorsal surface of the forefeet are sooty to light brownish (as in _a.n.a.logous_), whereas, the hind feet are flesh-colored (as in _allex_).

Another series of specimens from 4 mi. W Leon, Guanajuato, are intergrades between _B. t. a.n.a.logous_ and _B. t. paulus_. These specimens are grayish to brownish on the dorsum, have sooty forefeet and hind feet (more nearly as in _a.n.a.logous_ than in _paulus_), are grayish-white on the venter, and have a distinctly bicolored tail (resembling that of _paulus_ more than that of _a.n.a.logous_). When the average of cranial characters is considered, both series are best referred to _a.n.a.logous_.

Hooper (1947:50) pointed out that specimens from the pedregal San Geronimo, Distrito Federal, were more nearly black than topotypes and generally showed less brownish hues typical of _a.n.a.logous_. I have examined this series and several others from this area (see Specimens examined, p. 640) and am convinced that these populations average darker. Actually, the dorsum is more nearly black and the venter is more buffy than in typical _a.n.a.logous_. The hairs of these individuals average longer than in other populations of _a.n.a.logous_. Skulls of the specimens from the pedregal are indistinguishable from those of paratypes of _a.n.a.logous_. The populations from the Distrito Federal seem to be incipient subspecies.

_Specimens examined._--Total 696, all from the Republic of Mexico, distributed as follows: SAN LUIS POTOSi: Hacienda Capulin, 5[33]; _3.3 mi. N Tamazunchale, by-road_, 2[34]; 1 mi. N Tamazunchale, 700 ft., 1[35].

VERACRUZ: Acultzingo, 4[29], 1[31]. JALISCO: 1 mi. S Jalostot.i.tlan, 5700 ft., 5; 7 mi. NW Tepat.i.tlan, 3[29]; _6 mi. N, 4 mi. E Tepat.i.tlan_, 6400 ft., 25; _2-1/2 mi. E Tepat.i.tlan_, 6200 ft., 15; _2 mi. S, 1/2 mi. W Tepat.i.tlan_, 9; _near Tepat.i.tlan_, 2; _5 mi. SW Arrandas_, 6700 ft., 6; _2 mi. E Zapotlanejo_, 23; _2-1/2 mi. E Puente Grande_ (_5-1/2 mi. SW Zapotlanejo_), 3; _8 mi. S Guadalajara_, 10[29]; _3 mi. ENE Santa Cruz de las Flores_, 9; _4 mi. NE Ocotlan_, 5050 ft., 18; _13 mi. S, 9-1/2 mi. W Guadalajara_, 1; _2 mi. WNW Ocotlan_, 5000 ft., 15; 13 mi. S, 15 mi. W Guadalajara, 2; _Ocotlan_, 5000 ft., 8[30]; _1 mi. S Ocotlan_, 5000 ft., 12; 27 mi. S, 12 mi. W Guadalajara, 9; _1-1/2 mi. N Mazatmitla_, 6[29]; _1/2 mi. NW Mazatmitla_, 4; _3 mi. WSW Mazatmitla_, 4; 2 mi. N Ciudad Guzman, 5000 ft., 18. GUANAJUATO: 4 mi. N, 5 mi. W Leon, 7000 ft., 25; 5 mi. S Salamanca, 2[29]; _5 mi. E Celaya_, 6000 ft., 6; _1 mi. E Yuriria_, 5725 ft., 3; Salvatierra, 5775 ft., 8; _NE edge Acambaro_, 6050 ft., 10; _Acambaro_, 3[30]. QUEReTARO: Toliman, 7[30]; 6 mi. E Queretaro, 6550 ft., 37. HIDALGO: Tula, 2050 m., 1[31]. MICHOACaN: _2 mi. E La Palma, SE side Lago de Chapala_, 7; type locality, 4000 ft., 10[30] (including the type); _9 mi. E Zamora_ (_Camenaro_), 2[29]; _1 mi. S, 11 mi. W Zamora_, 5400 ft., 17; S Cuitzeo, 36[29]; _Jiquilpan_, 4800 ft., 15; _11 mi. W Jiquilpan_, 6700 ft., 2; _1 mi. E Jiquilpan_, 7; _1 mi. E Zinapecuaro_, 6300 ft., 17; _4-1/2 mi. NE Tarequato_ (_Tarecuato_), 6600 ft, 1; _Tanganciguaro_ (_Tangancicuaro_), 5500 ft., 4; _2 mi. N Tarecuato_, 7200 ft., 1; _2 mi. S Maravatio_, 6650 ft, 6; _2 mi. SE Zacapu_, 6600 ft., 11; _1 mi. N Tinquindin_ (_Tinguindin_), 6300 ft., 2; _3 mi. E Morelia_, 6600 ft., 3; _11 mi. E, 2 mi. S Morelia_, 1; 2 mi. SE Hidalgo (Villa Hidalgo), 6; _1-1/2 mi. N Los Reyes_, 1; _E Los Reyes_, 18[29]; _Los Reyes_, 8[30]; _3 mi. W, 1 mi. N Patzucuaro_, 6600 ft., 2; _N Patzucuaro_, 2[29]; _Patzucuaro_ 9[31], 4[30], 4[29]; Uruapan, 1[29]; _E Uruapan_, 12; _2-1/2 mi. E Uruapan_ (_La Presca_), 2[29]; 2 mi. SW Zitacuaro, 1; 1 mi. E, 6 mi. S Tacambaro, 4000 ft., 11[37]; _La Huacana_, 1[30]. MEXICO: Templo del Sol, Pyramides de San Juan, Teotihuacan, 8000 ft., 1; _31 km. E Mexico City_, 7500 ft., 11[36]; _17 km. E Mexico City_, 7500 ft, 1[36]; _Cerro La Caldera, 11 mi. ESE Mexico_, 2350 m., 5; 4 km.

ENE Tlalma.n.a.lco, 2290 m., 9; _Hacienda Cordoba_ (_Cordova_), 6. MEXICO, D. F.: _Cerro de la Estrella, Ixtapalapa_, 2450 m., 1; _3/4 mi. S, 1 mi.

E Churubusco_, 2400 m., 2; _5 km. S Mexico City, South of Cd.

Universitaria_, l[32]; _Pedregal San Angel_, _2.6 mi. S Monumento a Obregon, 2_; _El Pedregal, 1 km. S San Angel_, 2260 m., 1; _Falda SW Cerro Zacatepec, 3.9 mi. SW Monumento a Obregon_, 1; _2 mi. N Tlalpan, Zacayuca_, 2380 m., 5; _Tlalpan_ (_Pedregal_), 2400 m., 21[31]; _San Geronimo_, 37[29], 6[38]; _Santa Rosa_, 2700 m., 1[32]; _Tlalpan_, 8; _3/4 mi. SW Las Fuentes, Tlalpan_, 2450 m., 25[30]; _Tepepan_, 6[29]; _Rancho La Noria, 1 mi. W Xochimilco_, 2270 m., 4; _500 meters N Xochitepec_, 2250 m., 7; 200 m. N San Mateo Xalpa (Jalpa), 2390 m., 2.

_Marginal records._--SAN LUIS POTOSi: Hacienda Capulin; 1 mi. N Tamazunchale. HIDALGO: Tula, 2050 m. MEXICO: Templo del Sol, Pyramides de San Juan, Teotihuacan. VERACRUZ: Acultzingo. MEXICO: 4 km. ENE Tlalma.n.a.lco. MEXICO, D. F.: 200 m. N San Mateo Xalpa (Jalpa), 2390 m.

MICHOACaN: 2 mi. SW Zitacuaro; 1 mi. E, 6 mi. S Tacambaro; Uruapan.

JALISCO: 2 mi. N Ciudad Guzman; 27 mi. S, 12 mi. W Guadalajara; 13 mi.

S, 15 mi. W Guadalajara; 7 mi. NW Tepat.i.tlan; 1 mi. S Jalostot.i.tlan, 5700 ft. GUANAJUATO: 4 mi. N, 5 mi. W Leon. QUEReTARO: 6 mi. E Queretaro, 6550 ft.; Toliman.

[29] Univ. Michigan, Museum of Zoology.

[30] U. S. Nat. Museum (Biol. Surv. Coll.).

[31] Chicago Natural History Museum.

[32] American Museum of Natural History.

[33] Museum of Natural History, Louisiana State University.

[34] Univ. Illinois, Mus. Nat. History.

[35] The Museum, Michigan State Univ.

[36] Texas A & M, Cooperative Wildlife Research Collection.

[37] Univ. California, Mus. Vert. Zoology.

[38] University of Florida Collections.

=Baiomys taylori ater= (Blossom and Burt)

_Baiomys taylori ater_ Blossom and Burt, Occas. Papers Mus. Zool., Univ. Michigan, 465:2, October 8, 1942; Blair and Blossom, Contrib.

Lab. Vert. Biol., Univ. Michigan, 40:1, March, 1948; Hoffmeister and Goodpaster, Ill. Biol. Monogr., 24(1):115, December 31, 1954; Miller and Kellogg, Bull. U. S. Nat. Mus., 205:511, March 3, 1955; Hoffmeister, Amer. Midland Nat., 55:281, April, 1956; Packard, Jour.

Mamm., 40:146, February 20, 1959; Hall and Kelson, The Mammals of North America, 2:659, March 31, 1959 (part).

_Peromyscus taylori paulus_, Osgood, N. Amer. Fauna, 28:256, April 17, 1909 (part).

_Baiomys taylori_ [_ater_], Justice, Jour. Mamm., 38:520, November 20, 1957.

_Type._--Adult male, skin and skull; No. 85425, University of Michigan, Museum of Zoology; 7 mi. W Hereford, Cochise County, Arizona, obtained on March 25, 1941, by Philip M. Blossom, original number 2195.

_Range._--Southeastern Arizona, north to Graham County, thence east to the Animas Valley, Hidalgo County, New Mexico; south to northern Chihuahua and northwest to the southern border of Cochise County, Arizona, see Figure 11. Zonal range: largely lower Sonoran (Apachian Biotic Province of Dice, 1943:56). Occurs from 4300 feet in Chihuahua up to 6200 feet in New Mexico.

_Diagnosis._--Size medium for the species; dorsum between Mummy Brown and Prouts Brown; individual tips of hairs intermixture of black and Ochraceous-Tawny, bases of all hairs slate-gray; sides of body and face, Buffy Brown to Cinnamon Brown; belly Cinnamon Buff, proximal half of individual hairs Deep Neutral Gray, distal half white; in region of throat, proximal fourth of individual hairs gray, distal three-fourths white; dorsal vibrissae black to base, ventral vibrissae white to base; tail brownish above, gray below; dorsal and ventral surface of forefeet and hind feet buffy to gray; interparietal somewhat compressed anteroposteriorly. Average and extreme cranial measurements of 15 adults from 9-1/2 mi. W New Mexico State Line, 5-1/2 mi. N Mexican border, Cochise County, Arizona, are as follows: occipitonasal length, 18.0 (17.5-18.6); zygomatic breadth, 9.5 (9.2-9.9); postpalatal length, 6.6 (6.0-7.1); least interorbital breadth, 3.6 (3.4-3.8); length of incisive foramina, 4.0 (3.8-4.2); length of rostrum, 6.1 (5.7-6.4); breadth of braincase, 8.6 (8.4-9.1); depth of cranium, 6.5 (6.3-6.9); alveolar length of maxillary tooth-row, 3.2 (3.1-3.4). Average and extreme external measurements for six adults from 9 mi. W Hereford, Cochise County, are as follows: total length, 106.3 (98-115); length of tail vertebrae, 42.3 (39-46); length of body, 64 (59-69); length of hind foot, 13.6 (13-14.2); length of ear from notch, 11.1 (10.5-11.5); for photographs of skull, see Plate 2_b_, and Plate 4_c_.

_Comparisons._--For comparisons with _B. t. canutus_, see account of that subspecies. From _B. t. paulus_, the subspecies to the southeast, _B. t. ater_ differs in: dorsum darker brown; tail less strikingly bicolored; belly buffy rather than whitish to white-gray; forefeet and hind feet darker dorsally and ventrally; posterior margin of basioccipital bowed anteriorly in a broad U-shape with a secondary small median anteriorly directed U-shaped curve, rather than bowed anteriorly in a simple U-shape; interparietal more compressed anteroposteriorly; coronoid process of mandible so acutely recurved that tip of coronoid points posteroventrally and appears sickle-shaped.

_Remarks._--Blossom and Burt (1942:1) described _B. t. ater_ as the darkest of the known subspecies. It is dark, but specimens from some parts of the ranges of _B. t. a.n.a.logous_, _B. t. fuliginatus_, and _B.

t. subater_ exceed in melanins the darkest individuals of _ater_. Blair and Blossom (1948:5) also concluded by the use of an Ives tint photometer that _B. t. subater_ was significantly darker than _B. t.

ater_.

When paratypes of _ater_ and specimens of _B. t. paulus_ are compared, the darkest individuals of _ater_ exceed but slightly the darkest of _paulus_. The darkest specimens of _paulus_ occur in southern Zacatecas, and northern Jalisco, and the palest of the series are in northern Durango and southern Chihuahua. When paratypes of _ater_ and _paulus_ are compared, the difference in color is readily distinguishable.

Specimens from 1-1/2 mi. N San Francisco, in northern Chihuahua, appear to be intermediate in color between _ater_ and _paulus_ except for a faint tinge of buff ventrally. In characters of the crania, these specimens resemble _ater_ and are referred to that subspecies. A slightly different pattern of color is present in pygmy mice from the Peloncillo Mountains and the Animas Valley of New Mexico; the upper parts resemble those of paratypes of _ater_, but the venter has only the faintest suggestion of the buffy wash. Crania of these specimens from New Mexico are inseparable from those of paratypes of _ater_, and the specimens are, therefore, referred to _ater_.

When specimens are arranged by localities from Arizona east into southern New Mexico, thence south into Chihuahua and Durango, gradual intergradation in color is evident from dark in the north to pale browns in the south, whereas, size and shape of interparietal and size and shape of coronoid process of the lower jaw divide quite distinctly into two morphological types in central Chihuahua.

Cranial variation in size and proportion among adults is slight throughout the range of _ater_ compared to variation detected in other subspecies of _Baiomys taylori_. Perhaps such a relatively stable pattern of characters of the crania reflects the h.o.m.ogeneity of the gene pool, with respect to these characters, of the populations sampled. The fact that the color of the pelage of this subspecies varies considerable throughout its known range and that the crania do not is perhaps a clue to the mode of inheritance of characters in these mice. Seemingly, color of pelage is inherited independently of characters of the cranium. The relative lack of variability in the crania of _ater_ may result from uniform environmental conditions, which have served to select for uniform characters in the populations. All of the other wide-ranging subspecies of _B. taylori_ occupy more diverse habitats than _ater_.

Secondly, the rather abrupt change in the cline of measured characters of the crania between _ater_ and _paulus_ in central Chihuahua suggests a secondary zone of intergradation. The probable cessation of gene flow in the past between these two subspecies, allowing _ater_ to be isolated for a time, may also, in part, account for the relative lack of variability in the crania of _ater_.

_Specimens examined._--Total 58, distributed as follows: ARIZONA: _Graham County_: 1-1/2 mi. SW Ft. Grant, Graham Mts., 1[39]; _Pima County_: 1-1/2 mi. ENE Greaterville, Thurber Ranch, 2[39]; _Santa Cruz County_: Patagonia, 3[39]; _Cochise County_: _9 mi. W Hereford_, 10[43]; type locality, 2[43] (including the type); _5 mi. W Hereford_, 5[43]; 9-1/2 mi. W New Mexico State Line, 5-1/2 mi. N Mexican border, 20[42]; _3 mi. E, 1 mi. N Chiricahua_, 1[42]. NEW MEXICO: _Hidalgo County_: 18 mi.

S, 2 mi. W Animas, 2; _22 mi. S, 2 mi. W Rodeo_, 6000 ft., 1[40]; _22 mi.

S, 2 mi. E Rodeo_, 6000 ft., 3[40]; 25-1/2 mi. S Animas, 6200 ft. (in Big Bill Canyon), 1[40]. CHIHUAHUA: _5-1/2 mi. N, 2 mi. W San Francisco_, 5100 ft., 1; _2-1/2 mi. N, 3 mi. W San Francisco_, 5200 ft., 1; 1-1/2 mi. N San Francisco, 5100 ft., 4; Casas Grandes, 4300 ft., 1[41].

_Marginal records_--ARIZONA: 1-1/2 mi. SW Ft. Grant, Graham Mts. NEW MEXICO: 18 mi. S, 2 mi. W Animas; 25-1/2 mi. S Animas (in Big Bill Canyon). CHIHUAHUA: 1-1/2 mi. N San Francisco; Casas Grandes. ARIZONA: Patagonia; 1-1/2 mi. ENE Greaterville, Thurber Ranch.

[39] University of Illinois, Museum of Natural History.

[40] University of New Mexico.