Speciation and Evolution of the Pygmy Mice, Genus Baiomys Part 12

_Peromyscus paulus_, J. A. Allen, Bull. Amer. Mus. Nat. Hist., 19:598, November 12, 1903; Elliot, Field Columb. Mus. Publ., 105(6): 136, July 1, 1905.

_Baiomys taylori paulus_, Miller, Bull. U. S. Nat. Mus., 79:137, December 31, 1912 (part); Miller, Bull. U. S. Nat. Mus., 128:317, April 29, 1924 (part); Ellerman, The Families and Genera of Living Rodents, 2:402, March 21, 1941 (part); Goldman, Smith, Miscl. Coll., 115:373, July 31, 1951 (part); Hall and Kelson, Univ. Kansas Publs., Mus. Nat. Hist., 26:367, December 15, 1952; Goodwin, Bull. Amer.

Mus. Nat. Hist., 102:318, August 31, 1953; Miller and Kellogg, Bull.

U. S. Nat. Mus., 205:511, March 3, 1955 (part); Packard, Proc. Biol.

Soc. Was.h.i.+ngton, 71:17, April 11, 1958; Packard, Jour. Mamm., 40:146, February 20, 1959; Hall and Kelson, The Mammals of North America, 2:659, March 31, 1959 (part).

[_Peromyscus_] _paulus_, Elliot, Field Columb, Mus. Publ., 95(4):136, July 15, 1904.

_Peromyscus taylori paulus_, Osgood, N. Amer. Fauna, 28:255, April 17, 1909 (part).

_Peromyscus musculus_ [_musculus_], Osgood, N. Amer. Fauna, 28:256, April 17, 1909 (part).

_Baiomys taylori_ [= _paulus_], Twente and Baker, Jour. Mamm., 32:121, February 15, 1951.

_Baiomys musculus musculus_, Goldman, Smith. Miscl. Coll., 115:336, July 31, 1951 (part).

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

_Type._--Adult male, skin and skull; No. 21165, American Museum of Natural History; Rio Sestin, Durango, Republic of Mexico; obtained on April 15, 1903, by J. H. Batty, original number 455.

_Range._--Central Chihuahua south through Durango (west to eastern edge of Sierra Madre Occidental), to Zacatecas and Aguascalientes, thence west into northern and northwestern Jalisco, see Figure 11. Zonal range: Lower Sonoran, approximately the Chihuahua Desert Biotic Province of Goldman and Moore (1945:349). Occurs from 4000 feet 2 mi. ESE Tequila, Jalisco, up to 6700 feet 2 mi. W Minaca, Chihuahua.

_Diagnosis._--Size medium to small for the species; dorsum Buffy Brown to fawn color; dorsal ground color of unworn pelage of adults varying from Buffy Brown in darkest series (especially those from higher alt.i.tudes) to Avellaneous with grayish overtones in palest series; worn pelage in mid-dorsal region of adults fawn to grayish; terminal parts of individual hairs buffy, gray basally; guard hairs on dorsum black-tipped, grayish basally; belly Light Gull Gray, distal half of hairs white, proximal half Neutral Gray; hairs in region of throat and chin white to base (some specimens with faint buffy overtones); forefeet dusky below, whitish above; hind feet whitish above, ventral surface whitish to dusky; dorsal and lateral vibrissae black, other vibrissae white. Average and extreme measurements of six adults from the type locality are as follows: total length, 109 (106-117); length of tail, 44.5 (43-48); length of body, 63 (57-69); length of hind foot, 13.1 (12.7-14.0); occipitonasal length, 17.5 (17.4-18.0); zygomatic breadth, 9.3 (9.1-9.5); postpalatal length, 6.6 (6.2-6.9); least interorbital breadth, 3.5 (3.4-3.6); length of incisive foramina, 3.8 (3.6-4.1); length of rostrum, 5.9 (5.7-6.0); breadth of braincase, 8.6 (8.5-8.8); depth of cranium, 6.6 (6.2-6.9); alveolar length of maxillary tooth-row, 3.2 (3.1-3.4); for photographs of the skull, see Plate 2_e_ and Plate 4_f_.

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

t. ater_, and _B. t. taylori_, see accounts of those subspecies. From _B. t. a.n.a.logous_, _B. t. paulus_ differs as follows: dorsal color paler having more reddish-brown than blackish-brown tones; venter whitish to buffy, instead of gray to light-gray; tail bicolored (not unicolored), usually having more hairs; hind feet white (not sooty) above. Cranially, _B. t. paulus_ differs from _B. t. a.n.a.logous_ in: skull slightly smaller in all dimensions; maxillary part of zygoma narrowing and forming oblique angle rather than a near right angle with rostrum; anterior incisive foramina constricted posteriorly; tips of nasals truncate (less rounded).

_Remarks._--J. A. Allen (1903:599) correctly pointed out that young specimens, in first pelage, were gray brown; young adults were darker and more varied with some blackish; adults and old adults were buffy to grayish. The change in color of pelage with increasing age is more p.r.o.nounced in _paulus_ than in other subspecies of _B. taylori_. Of two males collected on April 12, 1949, one, an adult, is buffy brown, and the other, an old adult with worn pelage, is grayish-brown. In mice in the earlier stages of adulthood, underfur of the dorsum is buffy at the tips and gray basally. With increased wear, the buffy tip is lost.

Consequently, mice in the later stages of adulthood are grayish.

_B. t. paulus_ intergrades with _ater_ to the north in Chihuahua (see account of that subspecies), with _a.n.a.logous_ to the south in Jalisco, and with _allex_ (see account of that subspecies) to the southwest in Nayarit and Jalisco. The zone of intergradation between _paulus_ and _a.n.a.logous_ in Jalisco approximately borders the Rio Grande de Santiago from the western part of the State to the northwest sh.o.r.e of Lago de Chapala. Nineteen specimens from 2 mi. WNW Lagos de Moreno in northwest Jalisco seem to be intermediate between _paulus_ and _a.n.a.logous_ in color, averaging slightly grayer than typical _paulus_. The series of 19 is referable to _paulus_ on the basis of cranial characters.

A series of 34 specimens from 3 mi. W La Venta, Jalisco (referable to _paulus_), is indistinguishable in color of pelage from two series of _paulus_ from 5 mi. N Durango, and from 8 mi. NE of Durango, except that the antiplantar surfaces of the hind feet are sooty as in _a.n.a.logous_.

Seemingly, features of color mentioned above as diagnostic of the two subspecies are either present or absent and there is no tendency toward intermediacy in color in the population from 3 mi. W La Venta.

The Rio Grande de Santiago may have acted in the past as a physical barrier reducing gene flow between _allex_ and _paulus_ and in separating completely the two populations for limited periods.

_Specimens examined._--Total 176, all from the Republic of Mexico and distributed as follows: CHIHUAHUA: Rancho Sanignacio, 4 mi. S, 1 mi. W Santo Tomas, 1; El Rosario, 6700 ft., 1; 2 mi. W Minaca, 6900 ft., 11; Balleza, 1[50]. DURANGO: Rosario, 1[51]; type locality, 14[51] (including the type); _San Gabriel_, 2[51]; _Rancho Santuario_, 2[51]; 1 mi. N Chorro, 6450 ft., 1; _8 mi. NE Durango_, 6200 ft., 2; 5 mi. N Durango, 6400 ft., 2. ZACATECAS: Valparaiso, 6500 ft., 10[50]. AGUASCALIENTES: _18 mi. W, 2 mi. S Aguascalientes_, 6000 ft., 1; 16 mi. S Aguascalientes, 5[52]. JALISCO: 1 mi. NE Villa Hidalgo, 6500 ft., 1; 2 mi. WNW Lagos de Moreno, 6370 ft., 19; _2 mi. ESE Tequila_, 4000 ft., 11; _3 mi. W La Venta_, 33, 1[53]; _12 mi. W Guadalajara_, 3[54]; _Atemajac_, 12[50]; 4 mi.

W Guadalajara, 5100 ft., 3; _2 mi. N, 1/2 mi. W Guadalajara_, 11; 2 mi.

NW Magdalena, 4500 ft., 7[50]; _1 mi. N Tala_, 4400 ft., 3; 3 mi. W Tala, 4300 ft., 18.

_Marginal records._--CHIHUAHUA: Rancho Sanignacio, 4 mi. S, 1 mi. W Santo Tomas; El Rosario; Balleza. DURANGO: Rosario, 6700 ft.; 1 mi. E Zarca (Blossom and Burt, 1942:1); 1 mi. N Chorro, 6450 ft. ZACATECAS: Valparaiso, 6500 ft. AGUASCALIENTES: 1 mi. N Chicalote (Blossom and Burt, 1942:4). JALISCO: 2 mi. WNW Lagos de Moreno, 6370 ft.; 4 mi. W Guadalajara, 5100 ft.; 3 mi. W Tala, 4300 ft.; 2 mi. NW Magdalena, 4500 ft. DURANGO: 5 mi. N Durango, 6400 ft.; type locality. CHIHUAHUA: 2 mi.

W Minaca, 6900 ft.

[50] United States National Museum (Biol. Surv. Collections).

[51] American Museum of Natural History.

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

[53] The Museum, Michigan State Univ.

[54] Univ. Michigan, Museum of Zoology.

=Baiomys taylori subater= (V. Bailey)

_Peromyscus taylori subater_, V. Bailey, N. Amer. Fauna, 25:102, October 24, 1905; Lyon and Osgood, Bull. U. S. Nat. Mus., 62:139, January 15, 1909; Osgood, N. Amer. Fauna, 28:255, April 17, 1909; Elliot, Check-List Mamm. N. Amer. Continent, West Indies and Neighboring Seas, Suppl., Amer. Mus. Nat. Hist, p. 44, January 8, 1917.

_Baiomys taylori subater_, Miller, Bull. U. S. Nat. Mus., 79:136, December 31, 1912; Miller, Bull. U. S. Nat. Mus., 128:317, April 29, 1924; Anthony, Field Book of North American Mammals, p. 348, 1928; Baker, Jour. Mamm., 21:223, May 14, 1940; Ellerman, The Families and Genera of Living Rodents, 2:402, March 21, 1941; Blair, Jour. Mamm., 22:378, November 14, 1941; Poole and Schantz, Bull. U. S. Nat. Mus., 178:259, March 6, 1942; Blair, Jour. Mamm., 23:196, May 14, 1942; Blair and Blossom, Contrib. Lab. Vert. Biol., Univ. Michigan, 40:1, March, 1948; Miller and Kellogg, Bull. U. S. Nat. Mus., 205:511, March 3, 1955; Hall and Kelson, The Mammals of North America, 2:659, March 31, 1959.

_Baiomys taylori_ [= _subater_], Taylor and Davis, Texas Game, Fish and Oyster Comm. Bull., 27:56, August, 1947 (part).

_Type._--Subadult female, skin and skull; No. 32616/44539 U. S. Nat.

Mus. (Biol. Surv. Coll.); Bernard Creek, near Columbia, Brazoria County, Texas; obtained on February 25, 1892, by W. Lloyd, original number 1122.

_Range._--Southeastern Texas, north of Matagorda Bay west to Lavaca County, north to Brazos and Walker counties thence east to Jefferson County, see Figure 11. Occurs from near sea level in Brazoria and Galveston counties, up to 500 feet in western part of range. Zonal range: Humid division of lower Austral (the western part of the Austroriparian Biotic Province of Dice, 1943:18-21).

_Diagnosis._--Size medium to large for the species; mid-dorsal region Clove Brown (sooty in freshly captured specimens); some parts of mid-dorsal region all blackish; individual guard hairs of dorsum black-tipped, Deep Neutral Gray basally; underfur black-tipped with subterminal band of light buff, Neutral Gray at base; belly grayish-white, laterally Isabella Color; distal three-fourths of hairs in region of throat and chin white, proximal fourth light gray; in median region of belly distal half of individual hairs white, proximal half dark gray; vibrissae in most specimens black to base. Average and extreme cranial measurements of six adults from 7 mi. S La Belle are as follows: occipitonasal length, 18.9 (17.5-19.4); zygomatic breadth, 9.6 (9.1-9.9); postpalatal length, 6.8 (6.2-7.2); least interorbital breadth, 3.7 (3.4-3.9); length of incisive foramina, 4.0 (3.6-4.2); length of rostrum, 6.5 (6.1-6.8); breadth of braincase, 8.7 (8.3-8.9); depth of cranium, 6.7 (6.6-6.8); alveolar length of maxillary tooth-row, 3.1 (2.9-3.2). Average and extreme external measurements of four adults from Richmond are as follows: total length, 111.5 (108-118); length of tail vertebrae, 43.5 (41-47); length of body, 68 (67-71); length of hind foot, 14 (13-15); for photographs of the skull, see Plate 2_f_, and Plate 4_g_.

_Comparisons._--Because _B. t. subater_ intergrades only with _B. t.

taylori_ to the south and west, _subater_ is compared only with _taylori_. Young adults of both subspecies in unworn pelage show best the colors that differentiate the two subspecies. Old adults of _subater_ in worn pelage appear grayish, resembling _taylori_, and at that age, only certain cranial characters are of taxonomic use.

Cranially, _subater_ differs from _taylori_ in: presphenoid not shaped like an hour-gla.s.s; parapterygoid processes thicker medially; interparietal diamond-shaped instead of elongated and compressed. Skull slightly larger in most measurements.

[Ill.u.s.tration: PLATE 1

Photographs of skulls in dorsal view of _Baiomys_. 2.

_a._ _B. m. brunneus_, [F] ad., 10834, AMNH, Jalapa, Veracruz.

_b._ _B. m. grisescens_, [F] ad., 257080, USNM, Comayabuela, Honduras.

_c._ _B. m. handleyi_, [F] ad., 275597, USNM, Sacapulas, Guatemala.

_d._ _B. m. infernatis_, [F] ad., 91499, MZUM, Teot.i.tlan, Oaxaca.

_e._ _B. m. musculus_, [F] ad., 45462, USNM, Colima, Colima.

_f._ _B. m. nigrescens_, [M] ad., 76834, USNM, Comitan, Chiapas.

_g._ _B. m. pallidus_, [F] ad., 4802, Texas A & M, Axochiapan, Morelos.

_h._ _B. m. pullus_, [F] ad., 71608, KU, 8 mi. S Condega, Nicaragua.

_i._ _B. t. allex_, [F] ad., 45453, USNM, Colima, Colima.]

[Ill.u.s.tration: PLATE 2

Photographs of skulls (_a-g_) in dorsal view of _Baiomys_. 2.

_a._ _B. t. a.n.a.logous_, [F] ad., 120265, USNM, Zamora, Michoacan.

_b._ _B. t. ater_, [F] ad., 15056, UI, 1-1/2 mi. ENE Greaterville, Arizona.

_c._ _B. t. canutus_, [F] ad., 62076, KU, 1 mi. S Pericos, Sinaloa.

_d._ _B. t. fuliginatus_, [F] ad., 36771, KU, type locality.