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The Subspecific Status of Two Central American Sloths

BY

E. RAYMOND HALL and KEITH R. KELSON


University of Kansas Publications Museum of Natural History

Volume 5, No. 24, pp. 313-317 November 21, 1952


University of Kansas LAWRENCE 1952


University of Kansas Publications, Museum of Natural History

Editors: E. Raymond Hall, Chairman, A. Byron Leonard, Edward H. Taylor,
Robert W. Wilson

Volume 5, No. 24, pp. 313-317 November 21, 1952


University of Kansas Lawrence, Kansas


PRINTED BY FERD VOILAND, JR., STATE PRINTER TOPEKA, KANSAS 1952

25-4545

[Transcriber's Note: Words surrounded by tildes, like ~this~ signifies
words in bold. Words surrounded by underscores, like _this_, signifies
words in italics.]




The Subspecific Status of Two Central American Sloths

BY

E. RAYMOND HALL and KEITH R. KELSON


New name combinations for two kinds of Central American sloths that
heretofore have stood in the literature as nominal species are given
below, along with the evidence supporting their relegation to
subspecific rank. Research assistance has been provided from a contract
(NR 161-791) between the Office of Naval Research, Department of the
Navy, and the University of Kansas.


~Bradypus griseus ignavus~ Goldman

Goldman (Smiths. Misc. Coll., 60(22):1, February 28, 1913) named the
three-toed sloth from extreme eastern Panamá (Marraganti: 1 specimen,
the type) and northwestern Colombia (Atrato River: 2 specimens) as
_Bradypus ignavus_. He characterized the newly-named species as
differing from _Bradypus griseus_ (type locality Cordillera de Chucu,
Veragua, Panamá) and _Bradypus castaneiceps_ (type locality, Chontales,
Nicaragua) in "nasals shorter, with anterior border concave or
emarginate, the emargination deepest at median suture; squamosal arm of
zygoma broader, more rounded, less acutely pointed anteriorly; palate
less deeply grooved posteriorly; symphysis of mandible less produced
anteriorly beyond plane of first molars." Later, Goldman (Smiths. Misc.
Coll., 69(5):57-58, April 24, 1920) arranged _Bradypus castaneiceps_ as
a subspecies of _B. griseus_, reaffirmed the full specific identity of
_Bradypus ignavus_, and identified specimens from Tapalisa, Cituro, and
Real de Santa Maria, all in eastern Panamá, as belonging to _B.
ignavus_.

In order to satisfy ourselves about the taxonomic relationship of _B.
ignavus_ to _B. griseus_, we have examined the following materials in
the American Museum of Natural History: _ignavus_: Panamá: Cituro (No.
38191), Tapalisa (No. 38102), Real de Santa Maria (Nos. 37619-37621);
_griseus_: Panamá: La Chorrera (No. 31427); Costa Rica: Juan Viñas (No.
2824), Palmar (No. 139313), Vijagual, San Carlos (No. 139833);
_castaneiceps_: Nicaragua: Chontales (Nos. 28477 and 28478).

The specimens from Real de Santa Maria, Tapalisa, and Cituro, average
darker than all others, but this darkness is approached in certain
specimens of _griseus_ (for example, No. 139833, from Vijagual, San
Carlos). The broader, more rounded and less acutely pointed squamosal
arm of the zygoma supposedly characteristic of _ignavus_ is matched in
certain specimens of _griseus_ (for example, in No. 2824 from Juan
Viñas, Costa Rica) and the character is variable among specimens
referred to _ignavus_; the shape of the squamosal arm is of doubtful
taxonomic worth in the present connection. The depth of the grooving on
the palate seems to vary with age and is of questionable value
taxonomically. The emarginate nasals of _ignavus_ are matched in
_griseus_ (No. 139833) from Vijagual, San Carlos, Costa Rica. The
extension of the anterior symphyseal region of the mandible is short in
_ignavus_; the specimen with the longest extension (No. 37621 from El
Real), however, has the extension only barely shorter than does No.
139933 of _griseus_ from Vijagual, San Carlos, Costa Rica. In brief,
while we see the characters of _ignavus_ as set forth by Goldman (_op.
cit._), we find them to be of only an average sort and not pronounced.
Further, a specimen (No. 139833) from Vijagual, San Carlos, Costa Rica,
provides a morphological intergrade between _griseus_ and _ignavus_.
Accordingly, we arrange _ignavus_ as a subspecies of _griseus_; the name
of the animal from extreme eastern Panamá should stand as _Bradypus
griseus ignavus_ Goldman, 1913.


~Cyclopes didactylus mexicanus~ Hollister

Hollister (Proc. Biol. Soc. Washington, 127:210, October 31, 1914) named
_Cyclopes mexicanus_, on the basis of light-golden upper parts and
large, especially broad, auditory bullae, as specifically distinct from
_Cyclopes dorsalis_ Gray (= _Cyclopes tridactylus dorsalis_ Gray). Our
comparisons and examination of the specimens used by Hollister and a few
other specimens acquired since 1914 convince us that _C. mexicanus_ is
taxonomically valid and that Hollister, in general, correctly indicated
its diagnostic characters. Nevertheless, there is considerable evidence
that _C. mexicanus_ is only subspecifically distinct from _C. dorsalis_.
In the first place, an adult _C. dorsalis_, not seen by Hollister, from
El Banco, Chiriquí, Panamá (No. 248343 USBS), has more inflated,
although narrower, auditory bullae than do specimens of _C. mexicanus_.
In the second place, the two specimens mentioned by Hollister (_loc.
cit._) as from "Tabasco and southern Vera Cruz" actually are both from
Tabasco (No. 100040 USBS from Teapa, and No. 100174 USBS from
Montecristo). Each, as Hollister indicated, is darker on the upper parts
than his other referred specimens (two others from Montecristo in
Tabasco and another from El Salto in Chiapas). To us this suggests
intergradation with _C. dorsalis_. Incidentally, the specimen that
Hollister mentioned from Veracruz (No. 78111 USBS, from Minatitlan), and
that he indicated as having dark upper parts, really has light upper
parts. Third, a skin from Petén, Libertad, Guatemala (Harry Malleis
field No. 504, immature female), that the late Major E. A. Goldman
and one of us (Hall) once examined, has considerable dark brown on the
chin, throat and midventral line, as well as a dark mid-dorsal stripe.
The specimen is intermediate in color, as well as geographically,
between _C. t. dorsalis_ and _C. mexicanus_, although referable to the
latter. Taken together, the above evidence indicates subspecific status
for the northern, Mexican, animal and we conclude that it should stand
as _Cyclopes tridactylus mexicanus_ Hollister.

_Transmitted July 1, 1952._