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
sparse 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 assigned 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 relationships 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 _mexicanus_ [_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).
[Illustration: FIG. 5. Bacula of _Neotoma_. All x 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 assigned, 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 space, 4.0.
_Records of occurrence._--Specimens examined, 3: 8 km. W, 10
km. N El Encino, 400 ft., 1; type locality, 2.
=Neotoma micropus=