Speciation and Evolution of the Pygmy Mice, Genus Baiomys Part 7

_Comparisons._--For comparisons with _B. m. brunneus_, _B. m.

infernatis_, and _B. m. pallidus_, see accounts of those subspecies.

From _B. m. nigrescens_, _B. m. musculus_ differs in: dorsum paler throughout (less of blackish brown); region of face and ears paler, more buff and fawn-colored hairs rather than blackish-brown to grayish hairs; vibrissae paler; venter paler, less dark gray and less of sooty-colored undertones, tips of hairs whitish to pale Olive-Buff rather than light gray at tips becoming darker basally; forefeet and hind feet paler, whitish to pale buff-color with flesh-colored undertones, not sooty-colored to dark brown; tail paler below; nasals flaring outward, not tapering toward midline at anteriormost point; zygoma more ma.s.sive; larger in external and cranial dimensions.

_Remarks._--Merriam (1892:170) described _Sitomys_ [= _Baiomys_]

_musculus_ on the basis of 23 specimens (from Colima City, Colima; Armeria, Colima; Plantinar, and Zapotlan, Jalisco). According to the original description, _B. musculus_ resembled a small house mouse and was smaller than any known species of _Sitomys_ except _S. taylori_ [= _Baiomys taylori_]. From _taylori_, _musculus_ differed in being larger [in size of body], and in having longer ears and tail, and larger hind feet. When Allen and Chapman (1897:203) described _Peromyscus_ [= _Baiomys_] _musculus brunneus_ from Jalapa, Veracruz, the specimens described by Merriam from Colima and Jalis...o...b..came representative of the nominal subspecies _B. m. musculus_. Osgood (1909:258) a.s.signed specimens from Colima, Guerrero, Jalisco, Michoacan, Morelos, Oaxaca, Puebla, Sinaloa, Veracruz, and Zacatecas to the subspecies _musculus_.

Subsequently, Russell (1952:21) named the subspecies _pallidus_ from the arid lowlands of Morelos; Hooper (1952:96) described the subspecies _infernatis_ from northern Oaxaca and southeastern Puebla; and Goodwin (1959:1) described a new subspecies _nebulosus_ from the Oaxaca highlands. Each of the subspecies mentioned immediately above was described from within the geographic range a.s.signed to _B. m. musculus_ by Osgood (_loc. cit._). Hall and Kelson (1959:661) mapped the range of _B. m. musculus_ so as to include Colima, parts of Jalisco, Michoacan, Guerrero, Oaxaca, and Veracruz. Lukens (1955:159), in a study of the mammals of Guerrero, has shown that the characters attributed to _B. m.

pallidus_ are not significantly different from those of pygmy mice studied from Guerrero. He (_loc. cit._) concluded that: (1) if the specimens of pygmy mice from central Guerrero were typical of the subspecies _musculus_, then _pallidus_ did not deserve subspecific recognition, or; (2) the name _B. m. musculus_ should be restricted to the larger pygmy mice inhabiting the lowlands immediately adjacent to the Pacific Coast and the area to the north. My data (see Figure 12) show pygmy mice from southwestern Nayarit, northwestern and central Jalisco, Colima, and parts of Michoacan to be significantly larger in certain cranial and external measurements than pygmy mice from Guerrero, Oaxaca, Morelos, and parts of Puebla. This finding essentially corroborates Hooper's (1952a:96) findings. It seems advisable, therefore, to restrict the range of _B. musculus musculus_ to the large mice inhabiting west-central Mexico and the coastal lowlands of Colima and Michoacan. The name _pallidus_ is applicable to the smaller mice occupying Morelos, southwestern Puebla, Guerrero, Oaxaca, and southwestern Chiapas.

_B. m. musculus_ intergrades with _B. m. pallidus_ in eastern Michoacan and central and western Guerrero. Specimens from San Jose Prura and 12 mi. S Tzitzio, Michoacan, though referable to _B. m. musculus_ because of slightly larger size of crania are intermediate in size and color between the smaller and slightly darker _pallidus_ to the south and east and the larger, slightly paler _musculus_ to the northwest.

_Specimens examined._--Total 156 all from the Republic of Mexico, and distributed as follows: NAYARIT: 3 mi. NNW Las Varas, 150 ft., 1.

JALISCO: 7 mi. W Ameca, 4000 ft., 2[10]; _6 mi. W Ameca_, 4300 ft., 3[10]; _10 mi. S Ameca_, 5800 ft., 1[10]; _13 mi. S, 15 mi. W Guadalajara_, 3; _13 mi. S, 9-1/2 mi. W Guadalajara_, 1; _3 mi. ENE Santa Cruz de las Flores_, 1; 27 mi. S, 12 mi. W Guadalajara, 1; _4 mi. NE Autlan_, 3000 ft., 5[10]; _Sierra de Autlan_, 5000 ft., 2[10]; _2-1/2 mi. NNE Autlan_, 3000 ft., 8; 2 mi. SSE Autlan, 1; _5 mi. S Purificacion_, 2; Chamela Bay, 1[10]; _2 mi. N La Resolana_, 1500 ft., 6[10]; _1 mi. N San Gabriel_, 4000 ft., 32[10]; 2 mi. N Cuidad Guzman, 5000 ft., 1; 3 mi. E Navidad, 4300 ft., 10[10]. COLIMA: _type locality_, 10[11] (including the type); _3 mi. SE Colima_ (_City_), 5[10]; _4 mi. SW Colima City_, 1; Armeria, 200 ft., 8[11]; _Paso del Rio_, 20[10].

MICHOACaN: 12 mi. S Tzitzio, 6[10]; San Jose Prura, 4[12]; 1 mi. E, 6 mi.

S Tacambaro, 4000 ft., 3[13]; La Salada, 3[11]; 1/2 mi. SE Coalcoman, 15[10].

_Marginal records._--NAYARIT: 3 mi. NNW Las Varas, 150 ft. JALISCO: 3 mi. E Navidad, 4300 ft.; 27 mi. S, 12 mi. W Guadalajara. MICHOACaN: 12 mi. S Tzitzio; San Jose Prura; 1/2 mi. SE Coalcoman. COLIMA: Armeria, 200 ft. JALISCO: Chamela Bay.

[10] Univ. Michigan, Museum of Zoology.

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

[12] Chicago Natural History Museum.

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

=Baiomys musculus nigrescens= (Osgood)

_Peromyscus musculus nigrescens_ Osgood, Proc. Biol. Soc.

Washington, 17:76, March 21, 1904; Elliot, Field Columb. Mus. Publ., 105(4):136, July 1, 1905; Lyon and Osgood, Bull. U. S. Nat. Mus., 62:135, January 15, 1909; Osgood, N. Amer. Fauna, 28:259, April 17, 1909.

_Baiomys musculus nigrescens_, Miller, Bull. U. S. Nat. Mus., 79:137, March 31, 1912; Miller, Bull. U. S. Nat. Mus., 128:318, April 29, 1924; Goodwin, Bull. Amer. Mus. Nat. Hist., 68(1):40, December 12, 1934; Ellerman, The Families and Genera of Living Rodents, 2:402, March 21, 1941; Poole and Schantz, Bull. U. S. Nat.

Mus., 178:259, March 6, 1942; Hooper, Jour. Mamm., 28:50, February 15, 1947; Goldman, Smith. Miscl. Coll., 115:357, July 31, 1951; Miller and Kellogg, Bull. U. S. Nat. Mus., 205:513, March 3, 1955; Booth, Walla Walla Publs., Dept. Biol. Sci., 20:15, July 10, 1957; Hall and Kelson, The Mammals of North America, 2:661, March 31, 1959 (part).

[_Peromyscus musculus_] _nigrescens_, Elliot, Field Columb. Mus.

Publ., 95(4):176, 1904.

_B._ [_aiomys_] _m._ [_usculus_] _nigrescens_, Goodwin, Bull. Amer.

Mus. Nat. Hist., 79(2):160, May 29, 1942; Hooper, Jour. Mamm., 33:97, February 18, 1952 (part); Packard, Univ. Kansas Publs., Mus. Nat. Hist., 9:399, December 19, 1958.

_B._ [_aiomys_] _m._ [_usculus_] _musculus_, Booth, Walla Walla Publs., Dept. Biol. Sci., 20:15, July 10, 1957 (part).

_Type._--Adult female, skin and skull; No. 76827 U. S. Nat. Mus. (Biol.

Surv. Coll.); Valley of Comitan, Chiapas, Republic of Mexico, obtained on December 9, 1895, by E. W. Nelson and E. A. Goldman, original number 8719.

_Range._--Southern coastal region and eastern parts of Chiapas, southeastward into central and southern Guatemala, thence south into El Salvador (see Figure 10). Zonal range: parts of Lower Austral; also occurs in parts of the arid division of the Upper Tropical Life-zone, and in parts of the arid division of the Lower Tropical Life-zone; approximates a part of the Chiapas Highlands Biotic Province of Goldman and Moore (1945:349), and parts of the Guatemalan Subregion of Smith (1949:235).

_Diagnosis._--Size medium to small for the species; dorsum Vand.y.k.e Brown mixed with blackish, individual hairs black-tipped with a subterminal band of Warm Buff, Neutral Gray at base; guard hairs of dorsum black distally, Neutral Gray basally; hairs on sides grayish-brown, facial region like dorsum; chin buffy-brown; vibrissae brown, ventrally some white; venter creamy-buff to grayish, individual hairs creamy-buff at tips, gray basally; in region of throat and chin, hairs tipped with Ochraceous-Buff; dorsal surface of forefeet and hind feet dull whitish gray to brownish-black; tail indistinctly bicolored, dusky above, grayish to brownish below; incisive foramina short, wide medially; average and extreme external and cranial measurements of 15 adults from 6 mi. NW Tonala, Chiapas, are as follows: total length, 107.5 (100-116); length of tail vertebrae, 41.1 (33-48); length of body, 66.1 (62-73); length of hind foot, 15.0 (14-16); length of ear, 10.9 (10-12); occipitonasal length, 18.9 (18.4-19.7); zygomatic breadth, 9.8 (9.4-10.2); postpalatal length, 6.9 (6.6-7.4); least interorbital breadth, 3.7 (3.5-3.8); length of incisive foramina, 4.4 (4.1-4.8); length of rostrum, 6.7 (6.1-7.1); breadth of braincase, 9.2 (9.0-9.4); depth of cranium, 6.9 (6.5-7.3); alveolar length of maxillary tooth-row, 3.1 (2.9-3.2); for photographs of skull, see Plate 1_f_, and Plate 3_f_.

_Comparisons._--For comparisons with _B. m. handleyi_, _B. m.

grisescens_, _B. m. musculus_, _B. m. pallidus_, and _B. m. pullus_, see accounts of those subspecies.

From _B. m. brunneus_, _B. m. nigrescens_ differs in: dorsum blackish-brown rather than reddish to ochraceous brown; face and ears brownish-black rather than brownish with tinges of ochraceous; vibrissae darker; forefeet and hind feet darker; venter with more grayish tones; dorsalmost part of zygomatic plate projects farther anteriorly; interparietal oval to diamond-shaped and narrower anteroposteriorly; zygomata narrower at anteriormost part; slightly smaller in most cranial and external measurements.

From _B. m. infernatis_, _B. m. nigrescens_ differs in: dorsum darker; region of face and ears darker; venter buffy to gray rather than whitish-buff; vibrissae darker; forefeet and hind feet darker; tail darker above and below; incisive foramina shorter, more constricted laterally; cranium slightly smaller in most dimensions.

_Remarks._--Hooper (1952a:93-94) reported specimens from the coastal strip of southern Chiapas as the most intensely pigmented, whereas, specimens from central and western Chiapas were distinctly paler. Crania of specimens from the coastal region of southern Chiapas were smaller than crania from the central highlands and mountains of Chiapas. My studies essentially corroborate the findings of Hooper. The gradation of color between the pale brown _pallidus_ to the north in Oaxaca, and the brownish-black _nigrescens_ to the south in Chiapas is extremely gradual. Specimens from the central and western parts of Chiapas (see Figure 10 for localities) are difficult to a.s.sign to either _pallidus_ or _nigrescens_. Equal justification exists for a.s.signment to either subspecies. I have a.s.signed the specimens to _nigrescens_ because they are geographically closer to the type locality of _nigrescens_.

Specimens from Reforma, Oaxaca (a.s.signed by Hooper, 1952a:93-94, to _nigrescens_), are nearly identical in size and color to paratypes of _pallidus_. I a.s.sign the Reforma specimens to _pallidus_.

The darkest of all the specimens examined and a.s.signed to _nigrescens_ are from 1 mi. NW San Salvador and 1 mi. S Los Planes, El Salvador. The variations in color in this subspecies closely correspond to degree of relative humidity; the palest samples are from areas of low relative humidity and the darkest are from areas of high relative humidity. In view of the present state of differentiation of specimens from the southern coastal areas of Chiapas and mountainous areas of El Salvador, it would seem that populations there might be incipient subspecies.

_Specimens examined._--Total 319. CHIAPAS: _17 mi. W Bochil_, 1[14]; _15 mi. W Bochil_, 1[14]; _14 mi. W Bochil_, 1[14]; Bochil, 6[15]; Ocuilapa, 3500 ft., 5[16]; _5 mi. NNW Tuxtla Gutierrez_, 9; _11 km. W Tuxtla Gutierrez_, 800 m., 2[15]; _10 km. W Tuxtla Gutierrez_, 800 m., 2[15]; _Tuxtla Gutierrez_, 2600 ft., 8[16], 11; _Ocozocoautla_, 10[15], 2[16]; 25 mi. E Comitan, Las Margaritas, 1250 m., 5[17], 24[15]; Cintalpa, 555 m., 1[14], 18[15], 3[17]; _Jiquilpilas_, 2000 ft., 1[16]; San Bartolome, 3[16]; _type locality_, 5700 ft., 26[16] (including the type); 15 mi. SW Las Cruces, 1; Villa Flores, 600 m., 12[15]; _23 mi. S Comitan_, 1[14]; _15 mi. S, 2 mi. E La Trinitaria_, 4; _30 mi. S Comitan_, 2[14]; 35 mi. S Comitan, 1[14]; _3 mi. E Arriga_, 1[14]; 6 mi. NW Tonala, 19; _Tonala_, 8[16]; _Los Amates_, 1[14]; Pijijiapan, 10 m., 7[15]; Mapastepec, 45 m., 25[15], 4[17].

GUATEMALA: Chanquejelve, 1[14]; _Nenton_, 3000 ft., 1[16]; Jacaltenango, 5400 ft., 8[16]; La Primavera, 5[14]; 4 mi. S Guatemala City, 4700 ft., 3; _5 mi. S Guatemala City_, 4050 ft., 10; _6 mi. S Guatemala City_, 4680 ft., 1; _Lake Amat.i.tlan_, 4500 ft., 13[16]; El Progresso (Distrito Santa Rosa), 3[15]; _2 mi. N, 1 mi. W Cuilapa_, 2980 ft., 1[14]; _1 mi. WSW El Molino_ (_Distrito Santa Rosa_), 2; _2-1/2 mi. W, 2-1/4 mi. N San Cristobal_, 2900 ft., 1; El Zapote, 1[15].

EL SALVADOR: 1 mi. NW San Salvador, 29; 1 mi. S Los Planes, 15.

_Marginal Records._--CHIAPAS: Bochil; 25 mi. E Comitan, Las Margaritas, 1250 ft. GUATEMALA: Chanquejelve; La Primavera; Jacaltenango, 5400 ft.; 4 mi. S Guatemala City, 4700 ft.; El Progresso. _El Salvador_: 1 mi. NW San Salvador; 1 mi. S Los Planes. GUATEMALA: El Zapote. CHIAPAS: Mapastepec, 45 m.; Pijijiapan, 10 m.; 6 mi. NW Tonala; 15 mi. SW Las Cruces; Cintalpa, 555 m.; Ocuilapa, 3500 ft.

[14] American Museum of Natural History.

[15] Univ. Michigan, Museum of Zoology.

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

[17] University of Florida Collections.

=Baiomys musculus pallidus= Russell

_Baiomys musculus pallidus_ Russell, Proc. Biol. Soc. Washington, January 29, 1952; Davis and Russell, Jour. Mamm., 35:75, February 10, 1954; Miller and Kellogg, Bull. U. S. Nat. Mus., 205:512; Hall and Kelson, The Mammals of North America, 2:662, March 31, 1959.

_Peromyscus musculus brunneus_, Elliot, Field Columb. Mus. Publ., 115(8):203, 1907 (part).

_Peromyscus musculus_ [_musculus_], Osgood, N. Amer. Fauna, 28:257, April 17, 1909 (part).

_Baiomys musculus musculus_, Miller, Bull. U. S. Nat. Mus., 79:137, December 31, 1912 (part); Miller, Bull. U. S. Nat. Mus., 128:318, April 29, 1924 (part); Davis, Jour. Mamm., 25:394, December 12, 1944 (part); Hooper, Jour. Mamm., 28:50, February 15, 1947 (part); Goldman, Smith, Miscl. Coll., 115:336, July 31, 1951 (part); Miller and Kellogg, Bull. U. S. Nat. Mus., 205:512, March 3, 1955 (part); Booth, Walla Walla Publs., Dept. Biol. Sci., 20:15, July 10, 1957 (part); Hall and Kelson, The Mammals of North America, 2:661, March 31, 1959 (part); Goodwin, Amer. Mus. Novitates, 1929:1, March 5, 1959.

_B._ [_aiomys_] _m._ [_usculus_] _musculus_, Hooper, Jour. Mamm., 33:97, February 18, 1952 (part).

_B._ [_aiomys_] _m._ [_usculus_] _nigrescens_, Hooper, Jour. Mamm., 33:97, February 18, 1952 (part).

_Baiomys musculus nebulosus Goodwin_, Amer. Mus. Novitates, 1929, March 5, 1959.

_Type._--Adult female, skin and skull; No. 4501 Texas A&M Cooperative Wildlife Collection; 12 kms. NW Axochiapan, 3500 feet, Morelos, Republic of Mexico, obtained on July 28, 1950, by W. B. Davis, original number 5112.

_Range._--Guerrero thence eastward into Morelos and west central Puebla along the southern edge of the Transverse Volcanic Biotic Province (Goldman and Moore, 1945:349), south into Oaxaca, see Figure 10. Zonal range: largely Arid Lower Tropical Subzone of Goldman (1951:330). Occurs from near sea level in Oaxaca and Guerrero up to 6550 feet in Oaxaca.