Part 26 (1/2)

1951. _Neotoma angustapalata_ Baker, Univ. Kansas Publ., Mus. Nat. Hist., 5:217, December 15, type from 70 km. by highway S Ciudad Victoria, and 6 km. W Pan-American highway at El Carrizo, Tamaulipas.

_Distribution in Tamaulipas._--Southern part of state; presently known from two localities.

Baker (1951:218) reported that specimens from the type locality were taken in crevices among rocks on a small hillside that supported a spa.r.s.e cover of vegetation growing from a deep layer of humus. The specimen from eight kilometers west and 10 kilometers north of El Encino was shot about 40 yards from the entrance to a large cave, but no sign of wood rats were found there. Hooper (1953:9) reported that _N. angustapalata_ occupied caves at Rancho del Cielo, where a female with two nursing young was taken.

When Baker (_op. cit._) described _Neotoma angustapalata_ on the basis of two specimens from El Carrizo, he a.s.signed the species to the _N.

mexicana_ group because of the deep anterointernal re-entrant angle of M1. The deep angle found in _N. mexicana_ differs markedly from the typical condition in either _N. micropus_ or _N. albigula_. Study of the cranial characters and bacula of specimens of _N. micropus_ and _N.

angustapalata_ tends to corroborate the statement of Hooper (1953:10), who commented on the taxonomic relations.h.i.+ps of _N. angustapalata_ as follows: ”It should be pointed out that all characters considered ...

the specimens [_angustapalata_] appear to be large, deeply pigmented examples of the species _N. micropus_ notwithstanding the deep anterior fold in M1. The presence of that deep fold is far from an absolute character in the _mexica.n.u.s_ [_sic_] group.”

My study of 48 crania of _N. micropus_ from Tamaulipas reveals that the depth of the re-entrant angle of M1 is extremely variable, from almost absent in some individuals to deep (as in _angustapalata_) in others.

Four specimens, one (56958) from the Sierra de Tamaulipas and three (56960, 56965, 56966) from the vicinity of Altamira, have the re-entrant angle as deep as in the holotype and topotype of _angustapalata_.

Comparison of the bacula of the holotype and one topotype of _angustapalata_ with 15 bacula of _N. micropus_ reveal that on the average the baculum of _angustapalata_ differs from that of _micropus_ in being longer, and narrower at the base (greatest length, 7.1, width at base, 3.4 mm., in the topotype). One specimen of _N. micropus littoralis_ from the vicinity of Altamira, however, has a baculum of the same shape as in _angustapalata_ (this same specimen is one of the three from there in which the re-entrant angle of the M1 is deep). The shape of the baculum among specimens of _micropus_ is highly variable and bacula of specimens from different localities frequently are slightly different (see Fig. 5).

[Ill.u.s.tration: FIG. 5. Bacula of _Neotoma_. All 4.

A, _Neotoma angustipalata_ (topotype, 37062).

B, _Neotoma micropus micropus_ (4 mi. SW Nuevo Laredo, 89147).

C, _Neotoma micropus littoralis_ (Sierra de Tamaulipas, 2 mi. S, 10 mi. W Piedra, 56957).

The known distributions of _N. micropus_ and _N. angustapalata_ do not overlap (neither does the distribution of _N. albigula_ overlap with either in Tamaulipas). The four specimens of _N. micropus_ having the deep re-entrant angle in M1 are from localities near where the ranges of _angustapalata_ and _micropus_ probably meet. This could be interpreted in two ways: (1) these four specimens can be regarded as intergrades between _angustapalata_ and _micropus_, in which case the former species should be placed as a subspecies of the latter. Or the four specimens, which were collected along with other specimens that lack deep re-entrant angles in the M1, can be a.s.signed, on the basis of the deep angle, to _angustapalata_, in which case the species _micropus_ and _angustapalata_ would be in part sympatric. Until more material from critical areas is available for study, I continue to recognize _angustapalata_ as a monotypic species. I agree with Hooper that it is closely related to _N. micropus_.

_Measurements._--A female (58865) from 8 km. west and 10 km.

north of El Encino, measured as follows: 404; 198; 41; 32; greatest length of skull, 49.7; basilar length, 40.8; zygomatic breadth, 25.9; length of nasals, 18.8; length of incisive foramina, 10.8; length of maxillary tooth-row, 9.9; greatest breadth of interpterygoid s.p.a.ce, 4.0.

_Records of occurrence._--Specimens examined, 3: 8 km. W, 10 km. N El Encino, 400 ft., 1; type locality, 2.

=Neotoma micropus=

Southern Plains Wood Rat

Most of the specimens examined were trapped in brushy areas. On the Sierra de Tamaulipas, wood rats were caught in steel traps set near or between rocks. In the vicinity of La Pesca, specimens were trapped on the beach where _Spermophilus spilosoma_ and _Sigmodon hispidus_ were taken also.

Two females, obtained on May 19 and June 10 at Soto la Marina and on the Sierra de Tamaulipas, respectively, each carried 2 embryos that were 40 mm. in crown-rump length. Dice (1937:254) reported that two females collected on July 24 and August 16 on the Sierra San Carlos each carried 2 embryos that ranged from 34 to 36 mm. in crown-rump length.

_Neotoma micropus_ occurs throughout the Tamaulipan Biotic Province and is represented in Tamaulipas by two subspecies, each of which has its type locality in the state. Intergradation between the two takes place at Soto la Marina.

=Neotoma micropus littoralis= Goldman

1905. _Neotoma micropus littoralis_ Goldman, Proc. Biol.

Soc. Was.h.i.+ngton, 18:31, February 2, type from Altamira, 100 ft., Tamaulipas.

_Distribution in Tamaulipas._--From the Sierra de Tamaulipas southward.