A New Species of Thomasomys (Rodentia: Muridae) from Eastern Ecuador, with Remarks on Mammalian Diversity and Biogeography in the Cordillera Oriental
Author
VOSS, ROBERT S.
text
American Museum Novitates
2003
2003-12-09
3421
1
48
http://www.bioone.org/doi/abs/10.1206/0003-0082%282003%29421%3C0001%3AANSOTR%3E2.0.CO%3B2
journal article
10.1206/0003-0082(2003)421<0001:ANSOTR>2.0.CO;2
f4c2f80e-4917-4b5b-9415-0ee6377973ce
0003-0082
4734917
Thomasomys cinnameus
Anthony
Figures 11–13
SPECIMENS COLLECTED: 1.6 km (by road) W Papallacta,
10,500 ft
(UMMZ 155668– 155670); Río Papallacta valley [
3–5 km
by trail NNW Papallacta],
11,100 ft
(AMNH 155671, 155800).
OTHER MATERIAL: None.
TAXONOMY: This material of
Thomasomys cinnameus
was the first to be reported (by
Voss, 1988
: table 43) since the original description based on a single specimen collected at
8000 ft
(
2438 m
) near Hacienda San Francisco, Provincia Tunguragua,
Ecuador
(
Anthony, 1924b
). Sidebyside comparisons indicate that the Papallacta series closely resembles the
holotype
(AMNH 67401) in all qualitative and most quantitative characters. Although the
holotype
slightly exceeds the Papallacta specimens in several external and craniodental measurements (
table 5
), the differences are so small and the number of Papallacta specimens (five) is so few that these discrepancies do not seem taxonomically significant.
One of the smallest known species of the genus,
Thomasomys cinnameus
is currently regarded as a subspecies or junior synonym of
T. gracilis
Thomas (1917)
, originally described from a specimen collected at Machu Picchu in southern
Peru
(
Cabrera, 1961
;
Musser and Carleton, 1993
). However, the hypothesis that
cinnameus
and
gracilis
(with type localities separated by
1500 km
of highly dissected mountainous terrain) are conspecific is unsupported by any published analysis or discussion of character data. Rather, my examination of both
holotypes
and other representative material
6
indicates that these are unambiguously diagnosable taxa that should be recognized as distinct species.
Although similar to
Thomasomys gracilis
in size, external proportions, and pelage coloration,
T. cinnameus
consistently lacks genal vibrissae, long black tactile hairs of the upper cheek that are consistently present in
gracilis
. Among other trenchant craniodental comparisons,
cinnameus
is distinguished by (1) incisive foramina that are widest posteriorly, behind the maxillary/premaxillary suture; (2) absence of sphenopalatine vacuities; (3) smaller and less inflated auditory bullae; and (4) larger and more hypsodont molars with weakly developed cingula and stylar cusps. By contrast,
gracilis
exhibits (1) incisive foramina that are widest anteriorly, at or near the maxillary/premaxillary suture; (2) large sphenopalatine vacuities that perforate the bony roof of the mesopterygoid fossa on each side of the basisphenoid/presphenoid suture; (3) larger and more inflated auditory bullae; and (4) smaller, brachydont molars with better developed cingula and stylar cusps.
6
The comparative material of
Thomasomys gracilis
that I examined included the
holotype
(
USNM 194816
), two topotypes (
USNM 194799
,
194801
), and 12
other specimens
(
AMNH 95206
,
95207
;
USNM 194785– 194787
,
194790
,
194807
,
194808
,
194811–194813
), all of which were collected between 2774 and
4267 m
above sea level
in the
Peruvian
department of
Cusco
.
TABLE 5
Measurements (mm) and Weights (g) of
Thomasomys cinnameus
Thomasomys hudsoni
Anthony (1923)
is another small Ecuadorean taxon that has been treated without explanation as a synonym or subspecies of
T. gracilis
(see
Cabrera, 1961
;
Musser and Carleton, 1993
). However, I agree with
Anthony (1924b)
that
hudsoni
is a distinct species, differing from both
gracilis
and
cinnameus
in details of coloration and craniodental morphology. Unlike any specimens of the other small species, the
type
of
hudsoni
(AMNH 47690, from Bestión in Provincia
Azuay
) has a rostrum that is peculiarly produced beyond the incisors as a flaring bony tube with a concave (rather than convex) dorsal profile. As in
cinnameus
(and unlike
gracilis
) genal vibrissae and sphenopalatine vacuities are absent in
hudsoni
, but as in
gracilis
(and unlike
cinnameus
) the incisive foramina are widest anteriorly (near the maxillary/premaxillary suture). The auditory bullae of
hudsoni
are larger and more inflated than those of
cinnameus
but smaller and less inflated than those of
gracilis
. Unfortunately, the molars of the
type
(and only known specimen) of
hudsoni
are too worn to support confident dental comparisons.
FIELD OBSERVATIONS
: The
five specimens
of
Thomasomys cinnameus
that I collected near
Papallacta
in 1980 were trapped at elevations ranging from
3200 to 3380 m
.
Of
these, three were taken among mossy boulders in an old lava flow that impounds the
Río Tambo
to form
Laguna Papallacta
(fig. 1), and two were trapped on the ground in
Subalpine Rain Forest
in the valley of the
Río Papallacta
3–5 km
(by trail) NNW of the town
.