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THE LIBRARY OF THE

SEP 20 1944

UNIVERSITY OF ILLINOIS

GEOLOGICAL SERIES

OF
FIELD MUSEUM OF NATURAL HISTORY

Volume 8 Chicago, August 14, 1944 No. 12

AN OSTEOBORUS FROM HONDURAS

By Paul O. McGrew

Assistant Curator, Paleontology

Certain mammals have been described previously from the
Pliocene deposits of Gracias, Honduras (Olson and McGrew, 1941).
A Field Museum expedition to that region in 1941-42 discovered
additional members of the Gracias fauna, among which is the dog
described below. The particular interest of the specimen is that it
extends the reported range of a well-known North American genus
and species deep into the Central American isthmus. It also suggests
that the Gracias fauna might be Hemphillian in age rather than
Clarendonian as previously supposed.

To the various government officials of the Republic of Honduras
and the Department of Gracias, who gave us priceless assistance and
co-operation, I am extremely grateful.

Osteoborus cynoides (Martin)

Hyaenognathus cynoides Martin, Journ. Mamm., 9, pp. 235-236, pi. 21, 1928.
Osteoborus cynoides (Martin) Stirton and Vanderhoof, Univ. Calif. Publ.,
Bull. Dept. Geol. Sci., 23, pp. 175-182, figs. 1-3, 1933.

Referred specimen. — F.M. No. P26972, right maxillary with
P^-M^, left maxillary with PA-M^.

Osteoborus was first recognized as a distinct genus by Stirton and
Vanderhoof (1933). Within the genus they included certain species
that had previously been referred to Hyaenognathus, Borophagus,
Aelurodon, and Porthocyon. The vertical range of the genus is from
Barstovian (Crocker Springs) through the Hemphillian (Hemphill).
Among the species of the genus a rather definite progressive trend

No. 562 75

HIST.

76 Field Museum of Natural History— Geology, Vol. 8

may be observed. The earlier species are distinguished from
Aelurodon with difficulty while the species from the Hemphillian
have greatly reduced P£l$ and a very high P4.

In the Honduras specimen P^ is reduced to the same extent as
in Osteoborus cynoides of the Hemphillian. It has only one cusp

Fig. 25. Osteoborus cynoides.
withP^-Ma. F.M. No. P26972.

Lateral and ventral views of right maxillary
X 1.

proper, which is low and median in position. P- is like that of all
advanced species of the genus. The parastyle appears to be some-
what more reduced than in other specimens but considering the
extreme variation in this character it probably is not significant.
The apparent identity of the Honduras specimen with Osteoborus
cynoides suggests a Hemphillian age for the Gracias fauna. This is
at variance with the conclusions drawn from a study of the Gracias
horses (Olson and McGrew, 1941). Clarendonian horses, particu-
larly those described by Johnson (1937) are extremely close to the
Honduras species, but until more adequate studies are made of the

SSo.S'

An Osteoborus from Honduras 77

diminutive horses of both the Clarendonian and Hemphillian faunas
the real significance of this similarity cannot be established. On
the other hand, we can not be sure of the structural range of Osteo-
borus in the Clarendonian. It seems unlikely, however, that this
provincial age would have species as advanced as 0. cynoides. It
is probably best to reserve positive judgment on the age of the
Gracias fauna until further facts are available.

REFERENCES

Johnson, C. S.

1937. Calippus regulus from the Clarendon Beds of Donley County, Texas.
Amer. Mid. Nat., 18, pp. 905-907, 1 fig.

Olson, E. C, and McGrew, P. O.

1941. Mammalian Fauna from the Pliocene of Honduras. Bull. Geol. Soc.
Amer., 52, pp. 1219-1244, figs. 1-5, pis. 1-4.

Stirton, R. A., and Vanderhoof, V. L.

1933. Osteoborus, a New Genus of Dogs, and Its Relations to Borophagus Cope.
Univ. Calif. Publ., Bull. Dept. Geol. Sci., 23, pp. 175-182, figs. 1-3.