Table 1.—Average and Extreme Measurements (in Millimeters) of Skulls of Five Age-groups
of Baiomys taylori from vic. (see [p. 595]) Altamira, Tamaulipas, Mexico.
| Age groups | Juvenile | Young | Subadult | Adult | Old adult |
| Number examined | 3 | 3 | 14 | 19 | 8 |
| Total length | 77.0 (74-79) | 92.6 (89-96) | 97.6 (91-103) | 99.9 (93-105) | 101.6 (98-107) |
| Length of tail | 27.3 (24-29) | 39.3 (37-41) | 40.4 (36-43) | 39.8 (35-45) | 40.9 (38-45) |
| Length of body | 49.6 (49-50) | 53.3 (52-55) | 57.0 (51-61) | 60.0 (56-67) | 60.7 (57-67) |
| Length of hind foot | 11.0 (11) | 13.6 (13-14) | 14.3 (13.5-15.0) | 14.5 (14-15) | 14.2 (13-15) |
| Occipitonasal length | 14.2 (13.6-15.2) | 16.3 (15.8-16.9) | 17.1 (16.7-17.6) | 17.7 (17.2-18.3) | 17.8 (17.6-18.1) |
| Zygomatic breadth | 8.1 (7.8- 8.6) | 8.7 (8.6-8.8) | 8.9 (8.6-9.3) | 9.3 (9.0-9.6) | 9.4 (9.1-9.6) |
| Interorbital breadth | 3.4 (3.3- 3.5) | 3.4 (3.3-3.6) | 3.4 (3.3-3.6) | 3.6 (3.4-3.8) | 3.5 (3.3-3.6) |
| Incisive foramina (length) | 2.9 (2.8- 2.9) | 3.5 (3.4-3.6) | 3.7 (3.6-3.9) | 3.9 (3.6-4.1) | 3.9 (3.5-4.0) |
| Depth of cranium | 5.9 (5.6- 6.2) | 6.5 (6.3-6.8) | 6.5 (6.2-6.8) | 6.7 (6.4-7.0) | 6.8 (6.5-7.1) |
| Alveolar length, upper molars | 2.7 (2.5- 2.8) | 2.9 (2.9-3.0) | 2.9 (2.8-3.1) | 3.0 (2.9-3.2) | 3.0 (3.0-3.1) |
| Postpalatal length | 4.8 (4.5- 5.3) | 5.9 (5.8-6.0) | 6.2 (5.8-6.6) | 6.5 (6.2-7.2) | 6.5 (6.3-6.7) |
| Breadth of braincase | 8.1 (7.8- 8.7) | 8.5 (8.5) | 8.4 (8.0-8.7) | 8.6 (8.3-8.9) | 8.6 (8.4-8.8) |
The method employed by Dice and Leraas (1936:2) was used to measure the secondary sexual differences, if there were any, in each of several age classes. As pointed out by Hooper (1952b:11), individual variation in small samples can obscure secondary sexual differences. The samples of B. taylori from the vicinity (see page 595) of Altamira, Tamaulipas, and the samples of B. musculus from El Salvador ([table 2]) were large enough to prevent individual variation from obscuring sexual differences. Nevertheless, no significant secondary sexual differences were found in either B. taylori or B. musculus (see [table 2]). Therefore, the sexes have been considered together for purposes of geographic studies.
Table 2.—Analysis of Secondary Sexual Variation in Adult B. taylori Vicinity of (see [p. 595])
Altamira, Tamaulipas, and Adult B. musculus from El Salvador (see [p. 595]).
(One Standard Deviation on Either Side of the Mean is Given.)
| Character | Baiomys taylori | Baiomys musculus | ||
| 21 Males | 18 Females | 17 Males | 13 Females | |
| Total length | 98.4 ± 2.95 | 100.5 ± 4.72 | 112.04 ± 5.49 | 113.12 ± 4.23 |
| Length of tail | 40.1 ± 2.31 | 40.3 ± 2.39 | 47.12 ± 2.95 | 45.70 ± 2.92 |
| Length of body | 57.83 ± 1.65 | 60.10 ± 4.13 | 66.67 ± 3.97 | 67.75 ± 2.38 |
| Length of hind foot | 14.21 ± .53 | 14.44 ± .51 | 15.60 ± .49 | 15.38 ± .64 |
| Length of ear | 10.00 ± .00 | 10.00 ± .00 | 11.80 ± .65 | 12.00 ± .41 |
| Occipitonasal length | 17.48 ± .40 | 17.47 ± .47 | 19.32 ± .35 | 19.04 ± .44 |
| Zygomatic breadth | 9.17 ± .33 | 9.15 ± .30 | 9.84 ± .21 | 9.91 ± .28 |
| Least interorbital breadth | 3.53 ± .11 | 3.48 ± .11 | 3.88 ± .08 | 3.88 ± .12 |
| Postpalatal length | 6.35 ± .19 | 6.38 ± .30 | 7.11 ± .15 | 6.95 ± .20 |
| Depth of cranium | 6.65 ± .24 | 6.61 ± .17 | 7.10 ± .18 | 7.08 ± .18 |
| Incisive foramina (length) | 3.82 ± .15 | 3.81 ± .18 | 4.43 ± .11 | 4.35 ± .14 |
| Length of rostrum | 5.87 ± .20 | 5.88 ± .21 | 6.81 ± .16 | 6.66 ± .31 |
| Breadth of braincase | 8.54 ± .23 | 8.52 ± .12 | 9.84 ± .38 | 9.52 ± .20 |
| Alveolar length, upper molars | 2.98 ± .08 | 3.01 ± .08 | 3.20 ± .09 | 3.24 ± .10 |
Length of tail varied more than any other measurement used by me in taxonomic comparisons. Clark (1941:298), Hoffmeister (1951:16), and Van Gelder (1959:239) point out that external measurements generally are more variable than measurements of the cranium, probably because different techniques of measuring are employed by different collectors. As can be noted in [table 3], females varied more than males.