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FIELD MUSEUM OF NATURAL HISTORY

FOUNDED BY MARSHALL FIELD, 1893

PUBLICATION 296
ZOOLOGICAL SERIES VOL. XVIII, No. 6

NOTES ON DINOMYS

BY

COLIN CAMPBELL SANBORN

ASSISTANT CURATOR OF MAMMALS

WILFRED H. OSGOOD

CURATOR, DEPARTMENT OF ZOOLOGY
EDITOR

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AUGUST 31, 1931

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NOTES ON DINOMYS

BY COLIN CAMPBELL SANBORN

The genus Dinomys with one species, D. branickii, was described
by Peters in 1873 from a specimen collected by Jelski in the Montana
de Vitoc, Colonia Amable Maria, in the Andes of central Peru.
Since then, about fifteen other specimens of the genus have been
recorded from Ecuador, Colombia, and the upper Rio Purus in
Brazil, but no others from Peru. This material has been the basis
for the descriptions of three new species, all characterized by skin
differences.

Field Museum has a series of twenty-four specimens secured by
Mr. Edmund Heller on the Marshall Field Peruvian Expedition of
1922-23. The majority of these are from the haciendas Buena Vista
and Vista Alegre on the Rio Chinchao, and from Pozuzo points a
short distance north of the type locality. One was bought in Manaos,
Brazil. All the specimens were purchased from natives, so very few
are perfect in every detail. The series consists of four skins with
skulls, five skins only, and fifteen skulls only.

Of the nine skins in the series but one is complete; two have
heads, feet, and part of the tail; four have heads but no tails or feet;
and two have no heads, tails, or feet. Four are sexed as males and
two as females. Six of the skins are black and three are brown, one
of the latter being the one purchased in Manaos. One of the brown
skins is sexed as a male.

The skins differ mainly in the number of white and half white
hairs. In some cases the sides are very white and the four dorsal
lines heavy and almost continuous, while in others the white hairs
are very scattered and the dorsal lines are narrow and broken.
Apparently the older the animal, the more white and the heavier
and more complete the dorsal lines. In all the specimens the two
outer lines are heavier and longer. In some the inner pair start
from three to ten inches farther down the back than the outer pair.
The only complete skin has a head and body of 730 mm. and a tail
of 190 mm. The head and body measurements on the other skins
range from 730 to 790 mm.

Of the nineteen skulls, two are so badly broken as to be of little
use. The other seventeen fall into three age groups: four males and

149

150 FIELD MUSEUM OF NATURAL HISTORY ZOOLOGY, VOL. XVIII

two females, very old, the basioccipital, basisphenoid, and pre-
sphenoid bones being fully ankylosed; two males and five females,
subadult, the basisphenoid-presphenoid suture being still open; four
in various stages of immaturity. Of these, but seven have mandibles.

The type skull illustrated by Peters is subadult, as the basi-
occipital, basisphenoid, and presphenoid sutures are still open. This
young male skull is nearly the same size as the old female measured
by Preller and the old female (type of occidentalism measured by
Lo'nnberg. It is plain then, if a young male is the same size as an
old female, that when a male is fully adult it will be much larger
than a female and it is on this basis that I have sexed the skulls in
the series before me.

The nasal bones show more individual variation than any other
part of the skull. In the two of four old males in which these bones
are present, they measure 52.2 x 31.8 and 50 x 28 mm. respectively.
In another specimen the estimated width is 27.5 mm. In the two
old females the nasals measure 49.3 x 26.8 and 42 x 22.3 mm. The
subadult specimens show about the same variation. The general
form of the nasals is the same in all the specimens; they broaden
anteriorly for about half their length and then narrow posteriorly
where the ends form a concave, parallel, or, sometimes, a convex
line. The concave formation seems to be the most common. The
broadest part of the nasals is always in the region of a pair of small
nasal foramina on the sides of the nasals, which appear in all the
eleven specimens which have these bones.

In all the females the lateral edges of the frontals are nearly
parallel. In the males the frontals are expanded anteriorly and
contracted posteriorly, the edges are roughened, and there is a short
postorbital process, much more developed in some than in others.

In the parietals the skulls again show an individual variation
which can not be attributed to age. In all, the parietals begin to
expand just back of their anterior margin and to contract just for-
ward of their posterior margin. In some this forms two converging
lines, but in others the expansion and contraction is carried so far
as to form two wide curves, the left hand side almost forming the
letter "S." The curves are more uniform in the females and reach
their greatest development in the old males. In a subadult male
they are hardly noticeable while in a very young skull they are highly
developed.

The jugal bones in all the skulls vary greatly in width, especially
anteriorly. The size of the lachrymal bone is not constant either

1931 NOTES ON DINOMYS SANBORN 151

and in one skull the top of the jugal almost touches the lower end
of the lachrymal. The width of the maxilla between the jugal and
lachrymal is also variable. In the six male skulls it ranges from
5 to 8.5 mm. This width does not seem to be governed by the size
of the jugal or lachrymal. The female skulls show the same variation
in these bones.

In other parts the skulls are fairly uniform. The skull of an old
female is slightly abnormal, due, perhaps, to a birth injury. A view
of the palatal aspect seen from above shows the palate swinging to
the right, one bulla sunken, and in other parts the skull decidedly
off center. The type skull of branickii has an abnormality shown
by the Wormian bone between the parietals and the frontals. In
a subadult female in this series, the suture between the parietals
and frontals, instead of being a straight or gently curved line, has
a very marked concavity, some 5 mm. deep in its center, which might
indicate a possible tendency toward a Wormian formation.

The first specimens of Dinomys captured since the discovery of
the type, came from the upper Rio Purus in Brazil and were sent
to Goeldi at Para. These were a live adult female and a young
male, brown in color, which Goeldi identified as branickii (Goeldi,
1904). A description of the skulls of these two specimens was pub-
lished with photographs of them a few years later (Preller, 1907).

In 1919 Ribeiro described Dinomys pacarana from Brazil, which
differed from branickii in being brown instead of black. At that
time Peters' type was the only black specimen known but since then
both colors have been found in animals from the same region.
Lonnberg had a black male and a brown female from Ecuador and
both colors are represented in the Field Museum series. The type
of pacarana, which is a subadult male, has a head and body of 630
mm. and a tail of 140 mm. The type "procedente do Amazonas"
probably came from the Rio Purus region.

Dinomys branickii occidentalis was described from near Gualea,
Ecuador, by Lonnberg in 1921. It was said to differ from branickii
in having a shorter tail, which was but 27.5 per cent of the head
and body as opposed to 37.6 per cent in branickii. The author
stated that this might be individual variation and it would appear
that it is as the tail of the complete skin in the Field Museum series
is 26 per cent of the head and body and the tail of the type of pacarana
is only 22.2 per cent. There were no skull characters given and in
size the skull is the same as branickii. The skin and skull of a
subadult topotype show no differences from the Peruvian series.

152 FIELD MUSEUM OF NATURAL HISTORY ZOOLOGY, VOL. XVIII

In the same year Anthony described D. gigas from La Candela,
Huila, Colombia, from a flat native skin without skull. This skin,
which was stated to be stretched, had a head and body of 750 mm.
and was supposed to be twice the size of either branickii or occidentalis.
The Field Museum series of branickii contains specimens of this
size and larger. The other character attributed to gigas is found
in the four dorsal stripes which are continuous and not broken as
in other known specimens. One specimen from Peru closely ap-
proaches the type of gigas as the dorsal lines have but two very
slight breaks in them due to wear. The examination of the type of
gigas shows it to be a very large, fully pelaged, and unworn specimen
which accounts for the continuous lines.

In 1923 Niceforo described a specimen from the Sierra Santa
Elena, near Medellin, Colombia, in which the spots and lines were
clear yellow instead of white. A young specimen born in the New
York Zoological Gardens has the spots and lines a brownish yellow,
and in another specimen, which is a little older, they are a dirty
white. The measurements which Niceforo gives for the skull agree
closely with those of a very young skull in the Peruvian series. The
dorsal lines in this Colombian specimen are broken and not continu-
ous as in the type of gigas.

The series of undoubted branickii thus shows variations largely
covering the characters assigned to other named forms. Brown color,
short tail, size, and unbroken dorsal lines are seen to have no value
as racial characters. The chance that more material from Colombia
will show any stronger characters for D. gigas, in view of the great
individual variation in the Peruvian series, seems to me very slight.

The status of the forms of Dinomys may be summarized as follows :

Dinomys branickii Peters.

Dinomys branickii Peters, Monatsber. Akad. Wiss. Berlin, pp. 551-552, 1873;

Festschr. Gesellsch. naturf. FT. Berlin, pp. 227-234, pis. 1-4, 1873 Colonia

Amable Maria, Montana de Vitoc, Andes of central Peru.
Dinomys pacarana Ribeiro, Archives de Escola Superior de Agricultura e

Medicina Veterinaria, 2, pp. 13-15, 1919 Amazonas, Brazil.
Dinomys branickii occidentalis Lonnberg, Arkiv. for Zoologi, 14, pp. 49-53,

1921 Gualea, Ecuador.
Dinomys gigas Anthony, Amer. Mus. Novit., No. 19, pp. 6-7, 1921 La

Candela, Huila, Colombia.
Dinomys sp., Niceforo, Bol. Soc. Colombiana Cien. Nat., pp. 317-320, 1923

Sierra Santa Elena, Colombia.

Range. Andes Mountains from central Colombia through Ecuador to
central Peru, and east to the Rio Purus region of Brazil.

1931 NOTES ON DINOMYS SANBORN 153

I wish to thank Mr. H. E. Anthony for the loan of the American
Museum material, including the type of gigas and a topotype of
occidentalis, and also for the description of Niceforo's specimen
which Mr. Anthony copied for me.

Mr. Heller kindly sent me the history of the specimens which
he collected and some notes on the habits of the animal, which are
as follows:

"The natives in the Huallaga River headwaters such as the coca
haciendas of Buena Vista and Vista Alegre have the unusual habit
of saving the skulls of all their larger game animals. The skulls I
obtained from the cabins or huts where the hunters lived. The
skulls are kept together in long strings tied to the ceiling over a
smoky fire to keep the blow-flies away. The skulls often are as
black as if they came from the La Brea tar pits of California. The
hunters from whom I secured the skulls were in some cases Indians
who worked on the haciendas and in other cases they were Mestizos
from the highlands who had worked in the coca fields of the montana.
They all believed that it was good luck to keep the skulls of their
game as this custom was sure to cast a favorable spell over them
and make it much easier to secure more game of the same sort in
their future hunting trips.

"Dinomys (Terrible Mouse) is not a fighter but merely fights as
a last resort to save its life. It is slow in motion and can not turn
about quickly, therefore it has no rear protection from alert foes
like ocelots, tayras, coatis, etc. It therefore lives in rocky cliffs,
or holes in the ground by preference, where it can back up and
secure rear protection. With its large teeth it can fight any ordinary
enemy. Dogs are used to trail Dinomys I believe. Although I
spent several months in Dinomys territory and was taken by local
guides to cliffs where Dinomys had been secured, I never met one
of these rare rodents nor did I ever find a burrow or little cave
where they had recently lived.

"My pet Dinomys followed me closely everywhere I went and
at night slept under my bed. She had a firm belief that her safety
lay in keeping at my heels. She had no home feeling for any cabin
we occupied. When alone she was always worried and full of fear
apparently."

This pet was brought home by Mr. Heller and placed in a Chicago
zoo, but on its death was not preserved.

154 FIELD MUSEUM OF NATURAL HISTORY ZOOLOGY, VOL. XVIII

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REFERENCES

ANTHONY, H. E.

1921. New Mammals from British Guiana and Colombia. Am. Mus. Novit.,
No. 19, pp. 6-7.

GOELDI, EMIL A.

1904. On the Rare Rodent, Dinomys branickii, Peters. P. Z. S. Lond., Pt. 2,
pp. 158-162, pi. 10.

LONNBERG, ElNAR

1921. A Second Contribution to the Mammalogy of Ecuador, with Some
Remarks on Caenolestes. Arkiv. for Zoologi, Band 14, No. 4, pp. 49-53,
fig. 2.

NICEFORO, M., HERMANO

1923. Guagua Caballuna, Dinomys Sp. (?). Bol. Soc. Colombiana Cien. Nat.,
pp. 317-320.

PETERS, WILH. C. H.

1873. Monatsber. Akad. Wiss. Berlin, pp. 551-552.

1873. Ueber Dinomys, eine merkwiirdige neue Gattung von Nagethieren aus
Peru. Festschr. Gesellsch. naturf. Fr. Berlin, pp. 227-234, pis. 1-4.

POCOCK, R. I.

1926. The External Characters of a Young Female Dinomys branickii Exhibited
in the Society's Gardens. P. Z. S. Lond., Pt. 1, pp. 211-230, figs. 8-12.

PRELLER, WILHELM

1907. Zur Kenntnis der Morphologic und post-embryonalen Schadelmetamor-
phose von Hydrochoerus Capybara im Vergleich mit den Schadeln der ubrigen
Caviiden und Beschreibung und Vergleichung zweier Schadel von Dinomys
branickii. Archiv fur Naturgeschichte, Band 1, pp. 409-421, taf. 12-14.

RIBEIRO, ALIPIO DE MIRANDA

1919. Dinomys pacarana? Archives da Escola Superior de Agricultura e
Medicina Veterinaria, 2, Nos. 1 and 2, pp. 13-15, 3 pis., Nictheroy (E. do Rio),
Brazil.

THE LIBRARY OF THE

OCT 8 - 1931

UNIVERSITY OF ILLINOIS.

155

UNIVERSITY OF ILLINOIS-URBANA