Speciation and Evolution of the Pygmy Mice, Genus Baiomys

by Robert L. Packard

Study of specimens of B. musculus from Oaxaca reveals considerable variation in external and cranial measurements as well as color, corresponding to that reported by Goodwin (loc. cit.). Specimens from higher altitudes average somewhat darker and larger in external and cranial size than those at lower elevations. These differences seem to be microgeographic and not of subspecific rank. Among specimens that I have studied in Oaxaca are several from different localities (KU 63052, an adult male, from 3 mi. W Miahuatlán; KU 68964, an adult male from 3 mi. W Mitla, 6000 ft.; KU 63055, an adult female from 3 mi. S Candelario, 1200 ft.) that, according to Goodwin (in. litt.) match nebulosus in reported color, size of body and skull (except for the region of the rostrum).

Two of the three specimens (KU 63052 and 63055) are the darkest of a series in which the palest are inseparable from B. m. pallidus. Goodwin, who kindly compared the three specimens with the type of nebulosus, mentioned (in. litt.) that the skull of the type has a slenderer rostrum. Included in the series of skulls of B. m. pallidus from 3 mi. W Mitla are several adults (not seen by Goodwin) with slender rostra. B. m. nebulosus is judged to be a synonym of B. m. pallidus.

Populations of pygmy mice occurring in partially isolated areas of highland in Oaxaca seem to me to be incipient subspecies.

Specimens examined.—Total 824 all from the Republic of México and distributed as follows: Puebla: 2 mi. S Atlixco, 5800 ft., 1; 1 mi. SSW Tilapa, 5800 ft., 2; 6 mi. SW Izucár de Matemores, 7; Piaxtla, 3900 ft., 4[18]; Acatlán, 4100 ft., 1. Morelos: 5 mi. W Tepoztlán, 6000 ft., 7[19]; 1 mi. W Tepoztlán, 6000 ft., 9[19]; 2 mi. SW Tepoztlán, 7000 ft., 1[20]; Cuernvaca, 9[19]; 6 mi. W Yautepec, 4500 ft., 1[20]; Yautepec, 12[19]; 3 mi. N Alpuyeca, 4000 ft., 2[20]; Puente de Ixtla, 2[19]; Tetecala, 4[21]; 2 km. S Jonacatepec, 4500 ft., 6[20]; type locality, 6 (including the type). Guerrero: Yerbabuena, 1800 m., 1; Cueva de tia Juana [= 1.5 km. SSW Yerbabuena], 1; Laguna Honda, 1840 m. [= 1.5 km. S Yerbabuena], 3; 9 mi. SE Taxco, 3800 ft., 1[22]; 17 km. S Taxco, 4000 ft., 2[20]; Iguala, 5[19]; 3.2 km. SSE Iguala, 970 m., 1; 1 km. SSE Texcaizintla, 1600 m., 2; Teloloapán, 20[19], 5[24]; 1 km. N Chapa, 1470 m., 6; Chapa, 1470 m., 5; El Limón, 3[18]; 2¹/₂ mi. W Mexcala, 2100 ft., 1[20]; Río Balsas, 1[18]; Ayusinaha [= Ayotzinapa], 1[18]; Tlapa, [Pg 628] 3900 ft, 1[18]; 2.5 mi. S Almolonga, 5600 ft., 13[20]; 1 km. N Zihuatanejo, 1; Zihuatanejo Bay, 4[19]; Las Gatas [= 2 km. S. Zihuatanejo], 2; 2 km. SSE Zihuatanejo, 9; 4 mi. W Chilpancingo, 5800 ft., 3[20]; Chilpancingo, 4800 ft., 14[18], 21[19], 45[21]; 2 mi. N Tixtla, 4400 ft., 3[20]; 3.2 km. S Chilpancingo, 4; Cd. Chamilpa [= 12 km. ESE Chilpancingo], 5; Tlalixtaquilla, 4200 ft., 2[18]; 15 km. S. Chilpancingo, 4300 ft., 10[20]; 1 mi. SW Colotlipa, 2700 ft., 16[20]; 2 mi. SW Colotlipa, 2700 ft., 1[20]; Achuitzotla, 2800 ft., 7[20]; 8 mi. SW Colotlipa, 1[20]; 5 mi. S Rincón, 2600 ft., 2[20]; 8 mi. SW Tierra Colorado, 600 ft., 1[20]; Río Aguacatillo, 30 km. N Acapulco, 1000 ft., 3[20]; 5 mi. ESE Tecpán, 50 ft., 9; Ejido Viejo, 12 km. NNW Acapulco, 1; 2 mi. NNW Acapulco, 7; Acapulco, 3[18], 3[21]; Omentepec, 200 ft., 7[18]. Oaxaca: 4 mi. E Huajuapám, 5000 ft., 1; 2 mi. NW Tamazulapán, 6550 ft., 1; Yalalag, 3000 ft., 5[18]; 11 mi. NW Oaxaca [City], 1; Yaganiza, 3900 ft., 1[18]; Oaxaca [City], 5000 ft., 15, 7[21], 7[19], 5[24]; 3 mi. ESE Oaxaca [City], 30; 4 mi. ESE Oaxaca [City], 5050 ft., 1; 10 mi. SE Oaxaca [City], 1[22]; Cerro Ocotepec, 1[23]; Tepantepec, 9[23]; 1 mi. E Tlacolula, 5500 ft., 53[19]; 3 mi. W Mitla, 11; Jalapa, El Campanario, 1[23]; 2 mi. SE Matalán, 5950 ft., 14; Lachiguiri, 2[23]; Tres Cruces, 10[23]; Agua Blanca, 11[23]; San José, 1[23]; Reforma, 30[19], 7[21], 10[23], 6[24] Totolapa, 1[18]; Nejapa, 85 km. WNW Tehuantepec, 500 m., 12[19], 6[24]; Chicapa, 2[18]; Gueladu [= Jalapa], 6[23]; Juchitán, Laguna Superior; Manteca, 8[23], 1[23]; San Bartolo, 3000 ft., 1[18]; Ejutla, 1400 m., 21[19]; El Bambita, Tequisitlán 4[23]; Mixtequilla, 2[23]; Guiencola, 5[23]; Tehuantepec, 200 ft., 26[18], 11[19]; Sola de la Vega, 26[19], 3[24]; Huilotepec, 13[18], 3[23]; Santa Lucia, 24[23]; Cerro de Paste, Tenango, 7[23]; Sta. C. Quieri, 3[23]; Santa Marie Ecatepec, Zarzamora, 13[23]; Rincón Bamba, 11[23]; 3 mi. W Miahuatlán, 5300 ft., 1; Miahuatlán, 12[19], 1[23], 6[24]; San Juan Acaltepec, 5[23]; Zapotitlán, 1[23]; Llano Grande, 3[18]; Pinotepa, 700 ft., 2[18]; Juquila, 8[18]; Arroyo, San Juan, north of Cerro Otate, 1[23]; Cerro Otate, 3[23]; 3 mi. S Candelaria, 1.

Marginal records.—Morelos: 5 mi, W Tepoztlán, 6000 ft. Puebla: 2 mi. S Atlixco, 5800 ft.; Acatlán, 4100 ft. Oaxaca: 2 mi. NW Tamazulapán, 6550 ft; Tepantepec; Oaxaca [City], 5000 ft; Yalalag, 3000 ft; Jalapa, El Campanario; Reforma; Huilotepec; 3 mi. S Candelaria; Cerro Otate; Pinotepa, 700 ft. Guerrero: Acapulco; Zihuatanejo Bay; El Limón; 9 mi. SE Taxco, 3800 ft.

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

[19] Univ. Michigan, Museum of Zoology.

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

[21] Chicago Natural History Museum.