Speciation and Evolution of the Pygmy Mice, Genus Baiomys Part 13

_e._ _B. t. paulus_, [F] ad., 40032, KU, 18 mi. W, 2 mi. S Aguascalientes.

_f._ _B. t. subater_, [F] ad., 44543, USNM, type locality.

_g._ _B. t. taylori_, [F] ad., 57944, KU, 5 mi. E San Antonio, Texas.

_h._ Photo. of captive [M] _B. t. taylori_, 25 mi. E Austin, Texas.

1.]

[Ill.u.s.tration: PLATE 3

Photographs of skulls in ventral 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.]

[Ill.u.s.tration: PLATE 4

Photographs of skulls in ventral view of _Baiomys_. 2.

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

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

_c._ _B. t. ater_, [F] ad., 15056, UI, 1 mi. ENE Greaterville, Arizona.

_d._ _B. t. canutus_, [F] ad., 62076, KU, 1 mi. S Pericos, Sinaloa _e._ _B. t. fuliginatus_, [F] ad., 36771, KU, type locality.

_f._ _B. t. paulus_, [F] ad., 40032, KU, 18 mi. W, 2 mi. S Aguascalientes.

_g._ _B. t. subater_, [F] ad., 44543, USNM, type locality.

_h._ _B. t. taylori_, [F] ad., 57944, KU, 5 mi. E San Antonio, Texas.]

_Remarks._--This subspecies retains its chief diagnostic character, blackish mid-dorsal region, throughout nearly all parts of its range.

Specimens from the general area of Matagorda Bay and Lavaca County grade into _taylori_ in characters of color and crania. The Colorado and Brazos rivers seemingly serve as barriers reducing gene flow between _taylori_ and _subater_. These rivers may well have been important factors in the origin and the limitation of these two seemingly closely-related subspecies.

_Baiomys taylori subater_ is not differentiated in color of pelage and characters of crania from _B. t. taylori_ to the same degree that _B. t.

paulus_ is differentiated from _B. t. a.n.a.logous_, or that _B. t.

taylori_ is differentiated from several of the other subspecies of _Baiomys taylori_. _B. t. subater_ probably is a more recent occupant of the area in which it now lives than is the case with any other one of the subspecies of _taylori_. Sufficient time probably has not elapsed to allow for formation of more distinctive phenotypic patterns.

_Specimens examined._--Total 65, all from TEXAS and distributed as follows: _Brazos County_: 1/2 mi. NW College Station, 1[55]; _3 mi. W College Station_, _1 mi. W Easterwood Airport_, 1[55]; _College Station_, 1[55]. _Walker County_: Huntsville, 1[55]. _Hardin County_: Sour Lake, 1[57]. _Jefferson County_: 7 mi. S Labelle, 10. _Harris County_: 6 mi. NE Crosby, 1[56]. _Colorado County_: _10 mi. N Eagle Lake_, 1[55]; _9 mi. N Eagle Lake_, 1[55]; 2 mi. W Eagle Lake, 1; _Eagle Lake_, 1[55], 5. _Fort Bend County_: Richmond, 4[57]. _Galveston County_: _Texas City_, 6[58]; Virginia Point, 1[57]. _Brazoria County_: _Austin Bayou near Alvin_, 2[57]; 14 mi. SSE Alvin, 2[59]; type locality, 7[57] (including the type).

_Lavaca County_: 4 mi. W Hallettsville, 1[55]; _1 mi. SW Hallettsville_, 3[55]; _13.7 mi. SW Hallettsville_, 2[55]; 4 mi. NE Yoak.u.m, 11.

_Marginal records._--TEXAS: Huntsville; Sour Lake; 7 mi. S La Belle; Virginia Point; 14 mi. SSE Alvin; type locality; 4 mi. NE Yoak.u.m; 4 mi.

W Hallettsville; 1/2 mi. NW College Station.

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

[56] Carnegie Museum.

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

[58] Los Angeles County Museum.

[59] American Museum of Natural History.

=Baiomys taylori taylori= (Thomas)

_Hesperomys_ (_Vesperimus_) _taylori_ Thomas, Ann. Mag. Nat. Hist., ser. 5, 19:66, January, 1887.

_Baiomys taylori_ [_taylori_], Mearns, Bull. U. S. Nat. Mus., 56:381, April 13, 1907; Stickel and Stickel, Jour. Mamm., 30:141, May 23, 1949.

Baiomys taylori taylori, 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. 327, 1928; Ellerman, The Families and Genera of Living Rodents, 2:402, March 21, 1941; Taylor and Davis, Texas Game, Fish and Oyster Comm. Bull., 27:56, August, 1947 (part); Blair, Texas Jour. Sci., 2:104, March 31, 1950; Goldman, Smith. Miscl. Coll., 115:373, 426, July 31, 1951; Baker, Univ. Kansas Publs., Mus. Nat. Hist., 5:212, December 15, 1951; Blair, Texas Jour. Sci., 4:242, June 30, 1952; Hooper, Occas. Papers, Univ. Michigan, Mus. Zool., 544:7, March 25, 1953; Dalquest, Louisiana State Univ. Studies (Biol. Sci. Ser.), 1:155, December 28, 1953 (part); Blair, Adv. in Genetics, 5:10, January 27, 1954; Miller and Kellogg, Bull. U. S. Nat. Mus., 205:511, March 3, 1955; Baker, Univ. Kansas Publs., Mus. Nat. Hist., 9:273, June 15, 1956; Packard, Proc. Biol. Soc. Washington, 71:17, April 11, 1958; Hall and Kelson, The Mammals of North America, 2:659, March 31, 1959 (part).

_Cricetus_ (_Vesperimus_) _taylori_, Thomas, Proc. Zool. Soc.

London, 68:446, November 20, 1888.

_Sitomys taylori_, Merriam, Proc. Biol. Soc. Washington, 7:170, September 29, 1892.

_Sitomys_ (_Baiomys_) _taylori_, True, Proc. U. S. Nat. Mus., 16(972):758, February 7, 1894; J. A. Allen, Bull. Amer. Mus. Nat.

Hist., 6:181, May 31, 1894.

_S._ [_itomys_] _taylori_, Rhoads, Proc. Acad. Nat. Sci.

Philadelphia, 46:256, October, 1894.

_Peromyscus_ (_Baiomys_) _taylori_, J. A. Allen, Bull. Amer. Mus.

Nat. Hist., 8:65, April 22, 1896.

[_Peromyscus_] _taylori_, Trouessart, Cat. Mamm., 1:517, 1898.

_Peromyscus taylori_ [_taylori_], Elliot, Field Columb. Mus. Publ., 105(4):135, July 1, 1905; V. Bailey, N. Amer. Fauna, 25:101, October 24, 1905; Elliot, Field Columb. Mus. Publ., 115(8):203, 1907; Osgood, N. Amer. Fauna, 28:253, April 17, 1909.

_Type._--Adult male, skin and skull; No. 87.11.24.1, British Museum, Natural History; San Diego, Duval County, Texas; obtained by William Taylor.

_Range._--North-central to southeastern Texas, excluding the coastal plain north of the region of Matagorda Bay, thence south into the southern part of Tamaulipas and west into Coahuila and Nuevo Leon, see Figure 11. Occurs from near sea level in Texas up to 1500 feet in Coahuila. Zonal range: mostly Lower Austral (in Mexico and southeastern half of Texas, the Tamaulipas Biotic Province of Goldman and Moore, 1945:349, and Blair, 1952:230).

_Diagnosis._--Size medium for the species; dorsum grayish in freshly taken specimens to Hair Brown in preserved specimens; individual guard hairs of dorsum black-tipped, grayish basally, underfur black-tipped with a subterminal band of olive-buff; sides of body pale-grayish near venter, individual hairs buffy proximally, grayish basally; belly pale grayish, individual hairs white-tipped, Pale Neutral Gray basally; throat and chin colored as is belly; forefeet and hind feet sooty-gray dorsally, spa.r.s.ely-haired ventrally, thus appearing flesh-colored; tail unicolored gray to sooty-gray. Average and extreme cranial measurements of 22 adults from 6 mi. SW San Geronimo, Coahuila, are as follows: occipitonasal length, 18.0 (17.4-19.0); zygomatic breadth, 9.6 (9.2-10.2); postpalatal length, 6.5 (5.9-7.1); least interorbital breadth, 3.6 (3.3-3.8); length of incisive foramina, 4.0 (3.6-4.3); length of rostrum, 6.1 (5.7-6.7); breadth of brain case, 8.8 (8.5-9.1); depth of cranium, 6.5 (6.0-7.0); alveolar length of maxillary tooth-row, 3.1 (3.0-3.3). Average and extreme external measurements of 19 adults from 6 mi. SW San Geronimo are as follows: total length, 102.2 (95-115); length of tail vertebrae, 39.4 (21-46); length of body, 62.8 (53-76); length of hind foot, 14.0 (12-15); length of ear from notch, 10.7 (10-12); for photographs of skull, see Plate 2_g_, and Plate 4_h_.

_Comparisons._--For comparisons with _B. t. subater_, _B. t. a.n.a.logous_, and _B. t. fuliginatus_, see accounts of those subspecies. From _B. t.

paulus_, found to the southwest, _B. t. taylori_ differs as follows: dorsum grayish rather than fawn-colored; hairs on dorsal parts of forefeet and hind feet sooty-gray (not white to white-brown); venter gray to Light Drab-Gray, rather than whitish with gray overtones; tail unicolored instead of bicolored; skull averaging slightly larger over-all; maxillary part of zygoma forms right angle with rostrum rather than obtuse angle; incisive foramina extending posteriorly to anterior plane of first upper molars instead of to a transverse plane at middle of right and left first upper molars; bullae less inflated; interorbital region broader relative to length of skull; rostrum sloping gently from frontonasal suture to anterior tip of nasals rather than declining abruptly from frontonasal suture to anterior tip of nasals.

_Remarks._--The geographic range of _taylori_ is relatively large, and the subspecies is locally variable. Nevertheless, none of the external and cranial measurements of specimens a.s.signed to this subspecies differs significantly from the corresponding measurements of material from the type locality and adjacent areas in southeastern Texas. In southeastern Texas, south of the Guadalupe River, south to the coastal plain of Tamaulipas, this subspecies differs in color (being paler) from _B. t. subater_ with which _taylori_ might be confused. The foothills of the Sierra Madre Oriental in western Tamaulipas, north through Nuevo Leon and Coahuila, seem to mark the southwestern limit of the range a.s.signable to _taylori_.

On December 27, 1958, a specimen, KU 81552, was obtained 3 mi. N Bowie, Montague County, Texas. This record station extends the known range of _B. taylori_ 65 miles northward from the previous northernmost locality, listed by Hunsaker, Raun, and Swindells (1959:447). Two specimens, KU 81553 and 81554, were collected by the author 2 mi. NE Cedar Hill, Dallas County, Texas, on October 31, 1958. These two specimens, plus the single specimen from Bowie County are all paler with more buffy bellies than either _B. t. taylori_ or _B. t. subater_. They may represent an incipient subspecies. I tentatively a.s.sign them to _B. t. taylori_ because of the pale rather than dark (like _B. t. subater_) pelage.

Additional specimens are needed from these areas and from the hiatus between the ranges of _B. t. taylori_ and _B. t. subater_ the better to understand the manner in which these two subspecies intergrade.

Among named subspecies of _Baiomys taylori_, _B. t. taylori_ most closely resembles _B. t. subater_ to the north in Texas. Nine specimens examined from Yoak.u.m are intergrades between _taylori_ and _subater_.

These specimens have the sooty dorsal color of _subater_, but ventrally are inseparable from topotypes of _taylori_. In length of body and tail, specimens from Yoak.u.m are like _subater_, but in length of hind foot, they are intermediate between the two subspecies. Cranially, they are like _subater_. When all characters are considered, the specimens are best referred to _subater_. Bailey (1905:103) suggested that specimens from the southern part of the range, which he ascribed to _subater_, tended to a more grayish color than topotypes of _subater_, therefore, grading into _taylori_. The zone of intergradation runs from Matagorda Bay northwest through Lavaca County, thence north to the Colorado River, and closely follows the boundary between the Lower Austral and Humid Division of Lower Austral Life-zone as plotted by Bailey (_loc. cit._). Findley (1955:44) pointed out that where two life-zones meet, the resulting populations of shrews are mostly intergrades. Such is the case between these two subspecies of _Baiomys taylori_ in an area where life-zones might seem less important than in the mountainous west.