Speciation and Evolution of the Pygmy Mice, Genus Baiomys Part 11

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

[42] University of Arizona.

[43] Univ. Michigan, Museum of Zoology.

=Baiomys taylori canutus=, new subspecies

_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_, Miller, Bull. U. S. Nat. Mus., 79:137, December 31, 1912 (part); Miller, Bull. U. S. Nat. Mus., 128:317, April 29, 1924 (part); Burt, Miscl. Publ., Mus. Zool., Univ.

Michigan, 39:54, February 14, 1938; Goldman, Smith. Miscl. Coll., 115:373, July 31, 1951 (part); Miller and Kellogg, Bull. U. S. Nat.

Mus., 205:512, March 3, 1955 (part); Hooper, Occas. Papers Mus.

Zool., Univ. Michigan, 565:13, March 31, 1955; Hall and Kelson, The Mammals of North America, 2:659, March 31, 1959 (part).

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

_Type._--Adult male, skin and skull; No. 62075, University of Kansas, Museum of Natural History; 1 mi. S Pericos, Sinaloa, Republic of Mexico; obtained on June 14, 1954, by A. A. Alcorn, original number 1754.

_Range._--Central Nayarit northward through western Sinaloa, to as far north as south-central Sonora, see Figure 11. Zonal range: Lower arid tropical, closely approximating the Sinaloan Biotic Province of Goldman and Moore (1945:349). Occurs from near sea level at Escuinapa (43 feet), Sinaloa, to 3200 feet at a place 2 mi. WNW Tepic, Nayarit.

_Diagnosis._--Dorsal ground color Buffy Brown (some specimens near Olive Brown); proximal fourth of individual guard hairs of dorsum black-tipped, distal three-fourths dark grayish; dorsal underfur black-tipped having subterminal band of Buffy Brown; hair around eyes buffy to base; belly Pallid Neutral Gray with overtones of buff; individual hairs in region of chin whitish-gray to bases; vibrissae blackish to bases except ventralmost, those being white to base; tail Dark Olive above, slightly paler below. Average and extreme external measurements of 13 adults from 15 mi. N Rosario, Chele, Sinaloa, 300 ft., are as follows: Total length, 109.6 (99-120); length of tail, 43.4 (38-49); length of body, 66.2 (58-75); length of hind foot, 11.2 (10-12). Average and extreme cranial measurements of 19 adults from the same place are as follows: occipitonasal length, 18.2 (17.7-18.9); zygomatic breadth, 9.6 (9.2-10.1); postpalatal length, 6.9 (6.5-7.3); least interorbital breadth, 3.6 (3.4-3.8); length of incisive foramina, 3.9 (3.5-4.2); length of rostrum, 5.9 (5.5-6.6); breadth of braincase, 8.7 (8.3-8.9); depth of cranium, 6.5 (6.2-6.7); alveolar length of maxillary tooth-row, 3.1 (3.0-3.2); breadth of zygomatic plate, 1.8 (1.6-2.0); for photographs of skull, see Plate 2_c_, and Plate 4_d_.

_Comparisons._--From _B. t. ater_, _B. t. canutus_ differs in: dorsum slightly grayer; belly whitish to pale-gray with only faint tones of buff, rather than cinnamon-buff to buff-gray; forefeet and hind feet flesh-colored to grayish above instead of whitish to flesh-colored; tail paler above, less hairy, scales more evident; interparietal relatively larger from anteriormost to posteriormost points; incisive foramina tapering less abruptly posteriorly, not constricted towards midline; over-all size of body and cranium somewhat larger.

From _B. t. paulus_, _B. t. canutus_ differs in: dorsum grayish-brown rather than fawn-colored (not differing appreciably from extremes of darker brown specimens of _paulus_); forefeet and hind feet flesh-colored to grayish above rather than white above; tail less hairy, unicolored to faintly bicolored rather than distinctly bicolored; braincase slightly larger; alveolar length of maxillary tooth-row slightly less.

From _B. t. a.n.a.logous_, _B. t. canutus_ differs in: dorsum paler, less of dark brown hues; belly paler; forefeet and hind feet slightly paler, less sooty above; tail less hairy, paler and having scales evident; jugal of zygoma extending ventrally to a point immediately above, instead of below, level of alveolus of upper molars; nasals more nearly truncate anteriorly; infraorbital foramina less deeply notched toward midline of skull; body and skull averaging smaller throughout.

From _B. t. allex_, _B. t. canutus_ differs in: dorsal ground color grayish rather than fawn color having grayish overtones; underfur on dorsum darker gray; dorsal surface of forefeet and hind feet flesh-colored to grayish rather than flesh-colored; incisive foramina tapering to a point posteriorly rather than rounded posteriorly; interparietal relatively smaller; body and skull averaging larger throughout.

_Remarks._--Burt (1938:54) reluctantly a.s.signed specimens from Ciudad Obregon to _B. t. paulus_, probably being influenced by the resemblance in size. He suggested that, perhaps, a distinct subspecies occurs in the State of Sonora. Study of larger series of specimens than were available to Burt reveals that populations of pygmy mice inhabiting the northwest coastal plains of Mexico are indeed distinct.

The darkest of the material a.s.signed to _canutus_ is from Nayarit (for specific localities see specimens examined). According to Tamayo (1949:Carta de Suelos), color of soil changes from chestnut in northern Sinaloa to black in southern Sinaloa and northern Nayarit. There seems, therefore, to be a close correlation between color of pelage and color of soil in this area. In Nayarit, particularly in the central and southern parts, the mice are intermediate in color between the paler, grayer population to the north and the more brownish samples, representative of _allex_ to the south. The coastal vegetation changes from the arid tropical thorn forests of the north and central parts of Sinaloa to a savannah in Nayarit, thence to a tropical deciduous forest farther south (see Leopold, 1950:508).

In size and color, specimens from 3 mi. SE Tepic and 2 mi. SW Rosa Morada are intermediate between the larger, grayer _canutus_ and the smaller, light-brownish _allex_. In size of cranium, these specimens are more nearly like _canutus_, and are referred to that subspecies. Mice from the western coastal plain are relatively h.o.m.ogeneous as regards size of body and skull, except that those from 13.5 mi. S Acaponeta, Nayarit, average somewhat larger.

_B. t. canutus_, like _B. t. subater_, is predominantly a lowland or coastal subspecies. The pallor of the former, that lives on generally paler soils, presumably is of adaptive value.

Pygmy mice are seemingly rare in the northern part of the range of this subspecies. J. Raymond Alcorn and Albert Alcorn were successful in collecting only two specimens from the type locality after three successive nights of trapping with 100 traps set each night. Only six specimens are known from Sonora. These were obtained in the irrigated regions of Ciudad, Obregon, and Navajoa. Charles Sibley obtained one specimen 10.6 mi. SE Ciudad Obregon in a "maguey field." I obtained one specimen 1 mi. NNW Navajoa in a spa.r.s.e gra.s.sway, 20 feet wide, bordering an open sewer, which coursed northward into the Rio Mayo. Irrigated wheat fields bordered the gra.s.sway and ditch.

_Specimens examined._--Total 70 all from the Republic of Mexico and distributed as follows: SONORA: [Ciudad] Obregon, 4[44]; 10.6 mi. SE [Ciudad] Obregon, 1[45]; 1 mi. NNW Navajoa, 1. SINALOA: type locality, 2 (including the type); Culiacan, 175 ft., 2[46]; Mazatlan, 1[48]; _15 mi. N Rosario, Chele_, 300 ft., 35[47]; Rosario, 3[46]; Escuinapa, 5[48]; _Railroad Station Escuinapa_, 43 ft., 2[45]. NAYARIT: Acaponeta, 4[46]; _13.5 mi. S Acaponeta Junction_, 6[49]; 2 mi. SW Rosa Morada, 2; _2 mi.

WNW Tepic_, 3200 ft., 1; 3 mi. SE Tepic, 1.

_Marginal records._--SONORA [Ciudad] Obregon. SINALOA: type locality; Escuinapa. NAYARIT: Acaponeta; 3 mi. SE Tepic. SINALOA: Mazatlan.

[44] Coll. Univ. California, Los Angeles.

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

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

[47] Univ. Michigan, Museum of Zoology.

[48] American Museum of Natural History.

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

=Baiomys taylori fuliginatus=, new subspecies

_Baiomys taylori taylori_, Dalquest, Louisiana State Univ. Studies (Biol. Sci. Ser.) 1:155, December 28, 1953 (part).

_Baiomys taylori taylori_, Booth, Walla Walla Publs. Dept. Biol.

Sci., 20:15, July 10, 1957 (part).

_Type._--Adult male, skin and skull; No. 36765, University of Kansas, Museum of Natural History; 10 mi. E, 2 mi. N Ciudad del Maiz, 4000 ft., San Luis Potosi, Republic of Mexico; obtained on January 17, 1950, by J.

R. Alcorn, original number 10400.

_Range._--Occurs in the Sierra Madre Oriental of the northeastern third of San Luis Potosi. Zonal range: Upper Tropical (see Dalquest, 1953:10); approximates a part of the Sierra Madre Oriental Biotic Province of Goldman and Moore (1945:349, 356). Occurs from 2000 feet at El Salto up to 4000 feet at Ciudad del Maiz.

_Diagnosis._--Size large for the species; ground color of dorsum Chaetura Drab; individual guard hairs of dorsum black to base, distal fourth of hairs of underfur in posterior half of dorsum tipped with grayish-brown, proximal three-fourths Dark Neutral Gray; in anterior region of dorsum, posterior to ears, distal third of hairs grayish-brown and proximal two-thirds Dark Neutral Gray to base; sides slightly paler than dorsum; ground color of belly Neutral Gray, individual hairs of belly and throat tipped with Pallid Neutral Gray, basally Deep Neutral Gray to Dark Neutral Gray; tips of individual hairs of face Ochraceous-Tawny; lateral vibrissae whitish, dorsal and ventral vibrissae black to base; forefeet and hind feet sooty above and below, thigh bearing some white-tipped hairs; tail near Chaetura Drab above, Pale Neutral Gray below; anterior part of jugal projecting slightly ventrally and forming small protuberance at point of articulation with maxillary part of zygoma; jugal extending anteriorly nearly to lacrimal.

In most cranial measurements averaging as large as _B. t. a.n.a.logous_.

Average and extreme measurements of the type and three additional paratypes, all adults, are: total length, 105.5 (101-109); length of tail, 39.8 (35-42); length of body, 65.8 (63-68); length of hind foot, 14.3 (14-15); length of ear from notch, 11 (11); occipitonasal length, 18.1 (18.1-18.8); zygomatic breadth, 9.6 (9.3-9.8); postpalatal length, 6.5 (6.0-6.7); least interorbital breadth, 3.4 (3.3-3.6); length of incisive foramina, 4.0 (3.8-4.2); length of rostrum, 6.3 (6.1-6.4); breadth of braincase, 8.8 (8.6-8.9); depth of cranium, 6.7 (6.5-6.8); alveolar length of maxillary tooth-row, 3.2 (3.1-3.3); for photograph of skull, see Plate 2_d_, and Plate 4_e_.

_Comparisons._--From _B. t. taylori_, _B. t. fuliginatus_ differs in: dorsum slightly darker than in darkest _taylori_; tail densely haired, bicolored rather than unicolored; belly sooty to grayish rather than grayish to whitish; forefeet and hind feet sooty to grayish rather than flesh-colored; incisive foramina less bowed laterally, more nearly straight; interparietal compressed anteroposteriorly, less diamond-shaped.

From _B. t. paulus_, _B. t. fuliginatus_ differs in: dorsum dusky to blackish rather than fawn color; belly sooty to grayish rather than buffy to whitish-gray; forefeet and hind feet sooty to grayish rather than whitish; zygoma more nearly forming a right angle with rostrum or skull, less tapered anteriorly; anterior part of jugal possessing ventral projection; jugal extending nearly to lacrimal on posterior surface of maxillary part of zygoma.

From _B. t. a.n.a.logous_, _B. t. fuliginatus_ differs in: mid-dorsal region blacker, less brownish; tail distinctly bicolored rather than unicolored to faintly bicolored; incisive foramina not constricted medially; presphenoid broader (at narrowest point); jugal differs much the same as it does from _paulus_; nasals anteriorly truncate instead of rounded.

_Remarks._--Dalquest (1953:155-157) and Booth (1957:15) a.s.signed all of the pygmy mice that they examined from the state of San Luis Potosi to _B. t. taylori_. Examination of all of the material that was available to Dalquest, plus additional specimens at the University of Kansas Museum of Natural History, reveals that there are three subspecies in San Luis Potosi. _B. t. taylori_ occurs in the eastern part of the State at lower alt.i.tudes; _B. t. a.n.a.logous_ occurs to the southeast at higher alt.i.tudes; _B. t. fuliginatus_ occurs in the northeastern part of the State in the Sierra Madre Oriental.

Specimens obtained from Ebano, Pujal, and Tamuin, representative of _B.

t. taylori_, are much paler on the belly and on the ventral surface of the forefeet and hind feet than are specimens from Ciudad del Maiz, representative of _B. t. fuliginatus_. The tail in _B. t. taylori_ is nearly unicolored and less hairy than in the paratypical series of _fuliginatus_. Specimens from 4 km. NE Ciudad Valles are nearly intermediate in color of the belly, dorsum, forefeet and hind feet, and tail, between the palest mice from the coastal plain and the darker mice in the mountains of the northeastern part of the State (specimens from El Salto average paler, however, than the type and paratypes). These specimens seem to be intergrades between _B. t. taylori_ to the east on the coastal plain and _fuliginatus_ to the northwest in the mountains.

It seems best to refer the mice from 4 km. N Ciudad Valles to _B. t.

taylori_ on the basis of the average of external and cranial characters.

Specimens from 6 mi. SW San Geronimo, Coahuila, also referred to _B. t.

taylori_, resemble in color the mice from 4 km. N Ciudad Valles. When more specimens are obtained from the front range of the Sierra Madre Oriental, at lower alt.i.tudes, the manner in which these two subspecies intergrade with one another will be better understood. At present, populations from higher alt.i.tudes in the mountains seem to represent a dark subspecies; populations from the coastal plain represent a pale subspecies, and those from the lower slopes and high valleys seemingly are intergrades. _B. t. fuliginatus_ occurs in a somewhat limited strip of chernozem soil (or suelos negros of Tamayo, 1949: Carta de Suelos).

The populations occurring at lower alt.i.tudes on the coastal plain are on generally paler soils.

_Specimens examined._--Total 39, all from the Republic of Mexico, as follows: SAN LUIS POTOSi: El Salto, 24 Mus. Nat. Hist., Louisiana State Univ., 7 Amer. Mus. Nat. Hist.; type locality, 8 (including the type).

_Marginal records._--See specimens examined.

=Baiomys taylori paulus= (J. A. Allen)