L I E) RARY

OF THE

U N I VER.SITY

or ILLINOIS

REMO

GEOLOGICAL SERIES

OF

FIELD MUSEUM OF NATURAL HISTORY

Volume VI Chicago, May 15, 1935 No. 12

A NEW ARGYROHIPPUS FROM THE DESEADO
BEDS OF PATAGONIA

By Bryan Patterson
Assistant in Paleontology

Results of the First Marshall Field Paleontological Expedition
TO Argentina and Bolivia, 1922-24

The notohippid genus Argyrohippus has hitherto been known
from two species, A. jrater cuius and A. boulei, both of which occur
in the Colhu^-Huapi beds. Simpson (1932, p. 12) has recently
designated A. fraterculus as the genotype. The present communica-
tion describes a third species from the eariier Deseado beds. The
excellent specimen of A. fraterculus collected by the Scarritt Pata-
gonian Expedition has greatly facilitated the description and com-
parison of the new form. I am indebted to Mr. Elmer S. Riggs
for the privilege of describing the species. The drawings are by
Mr. Carl F. Gronemann, Staff Illustrator, Field Museum.

The premolars of the holotype were described and figured on
page 97 of this volume under the name of Argyrohippus sp.

Argyrohippus praecox sp. nov.

Holotype.— FM. No. P13834. Incomplete palate with RP^-M*
and alveolus of P^ and the root of the canine, LM^-^; horizontal
ramus of left mandible with Pi-Ms and alveoli of anterior teeth.
Collected by George F. Sternberg, 1924.

Paratypes.—FM. No. P13486. Palatal fragment with RM^-^
F.M. No. P13475. Fragment of left mandible with M i-^. Collected
by John B. Abbott, 1924. F.M. No. P14697. Fragment of left
mandible with P4-M5. Collected by George F. Sternberg, 1924.

Horizon and locality. — Deseado beds, La Flecha, province of
Santa Cruz, Argentina.

Diagnosis. — Teeth more brachyodont than those of A. frater-
culus; small upper canine present and in series with the premolars;
P^ relatively large; infraorbital foramen smaller than in A. frater-
culus and well removed (15 mm.) from anterior border of orbit.

No. 344 161

Kaiurs] Kf tt rr Survey

162 Field Museum of Natural History— Geology, Vol. VI

Discussion. — As shown by the American Museum specimen of
A. fraterculus, the most characteristic features of the genus are the
cup-Hke postero-internal cingula^ and the absence of anterior
cingula on P--*, and the thick covering of cement. The
new species possesses these characters^ and hence may be referred
with confidence to Argyrohippus. The characters given in the
diagnosis readily distinguish A. praecox from A. fraterculus.^
The teeth of the Deseado species are about one-fourth shorter than
those of the genotype. The large infraorbital foramen in A. frater-
culus is only 7 mm. from the anterior rim of the orbit. The upper
canines in the Colhu^-Huapi species, according to Ameghino (1902,
p. 82), are situated, when present, in the middle of the diastema
between I- and P-; in A. praecox the upper canine is in series with
the cheek teeth. The differences in the structure of P^ between
A. praecox and A. fraterculus have been discussed on pages 96 and 97
of this volume. They may be of specific value but in the absence of
a series of specimens I am not prepared to admit them as such.
In the holotype of A. praecox there are four mental foramina, one
in front of P2, two beneath P2 and one beneath the trigonid of
P?. In a specimen of A. fraterculus, F.M. No. P13587, there are
three, one beneath the diastema, one beneath P2 and one beneath
M 1 ; on the right side of this specimen there are two small additional
foramina one above and one below the large foramen beneath the
diastema. Mental foramina, however, tend to be variable and a
wider range of specimens is necessary before admitting these differ-
ences as specific characters. Pr may have been present in A. praecox
and the upper and lower dentitions may have been in series without
diastemata but these points cannot be determined from the available
material.

' Ameghino did not mention this character in his description of the genus
(1902, pp. 81-83). Presumably his material was too much worn to show it.

2 The cement is considerably abraded on the specimens of A. praecox but enough
remains to show its former extent. A vestige of an anterior cingulum is present
on P^ of the holotype.

^ The second Colhue-Huapl species, A. boulei, was distinguished by Ameghino
(1902, p. 83) from A. fraterculus on the basis of larger size, simpler enamel folds
in the lower cheek teeth, more procumbent symphysis and more proclivous incisors.
The difference in size between the two is about 15 per cent, not necessarily in
itself a specific character. The slight differences in the enamel folds can hardly
be considered as more than individual, possibly even age, variations. The reported
differences in the mandibular symphysis constitute the only positive claim of
A. boulei to specific distinction. Unfortunately, Ameghino has given no figures
so that it is impossible to ascertain how much variation exists in this region between
the types of the two species. The differences may well be due to pressure after
burial. A. boulei may be doubtfully retained as valid, pending further information.

650. •:>

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C<r.

A New Argyrohippus from Patagonia

r

163

164 Field Museum of Natural History — Geology, Vol. VI

A. praecox and A. fraterculus compare very closely. The former,
as shown by the differences mentioned above, is the more primitive
of the two species, a fact that is in accord with its geological horizon.
It is possible that the Deseado species was directly ancestral to the
genotype.

The paratype specimens of A. praeeox are somewhat older than
the holotype and satisfactorily show the age characters of the teeth.

Fig. 35. Argyrohippus praeeox sp. nov. x \. a, Holotype, F.M. No. P13334. RC-M*. 6, Para-
type, P.M. No. P13486. RMi^-». c, Paratype, F.M. No. P14697. LPj-M,. d, Paratype, F.M.
No. P13475. LMt-3.

As in many notoungulates, the grinding surfaces of the molars
increase in transverse diameter and the details of the crown pattern
become obscured by wear. There is a fold in the posterior face of
the enamel of the protolophs of M^-^ of F.M. No. P13486. As shown
by a photograph supplied by Professor W. B. Scott, a similar fold is
present on one of Ameghino's specimens of A. fraterculus. It is
impossible to state at present whether this feature is an age character
or an individual variation.

Ameghino considered that Argyrohippus was descended from
Morphippus and ancestral to Notohippus. The latter suggestion
may eventually be proved correct but Notohippus is too little known
at present for any definite statement to be made. The former
suggestion was unlikely on morphological grounds and the discovery

A New Argyrohippus from Patagonia 165

of A. praecox as a contemporary of Morphippus in the Deseado
greatly increases its improbability.

Measurements. — The antero-posterior measurements have been
taken from the mid-points of the anterior and posterior faces of the
teeth. The transverse measurements of the lower cheek teeth have
been taken across the entoconids, except for P?, which lacks this
cusp. Transverse measurements of the upper cheek teeth are not
given for the sufficient reason that this diameter in most notoun-
gulates with high-crowned teeth varies so much with age as to be
useless.

Field Mus. Field Mus. Field Mus. Field Mus.
No. P13334 No. P13486 No. P13475 No. P14697

Canine,* antero-posterior diameter 4

Canine, transverse diameter. . ." 3.25

Length, F^-M^ 90

Length, Pi-* 45

F^,^ a.p 5.25

P^, a.p 9.5

P^, a.p 12

P*, a.p 12

Length, M^-^ 46 48.5

MJ-, a.p 16 15

M2,a.p 17.5 17

M^, a.p 17 17.5

Length, P^-M^ 90.5

Length, P^-* 34.5

P5,a.p 10

Pj, tr.. 5.75

P3, a.p 12

P3, tr 7.25

P^, a.p 12.75 13.25

Pi, tr 7.75 7.75

Length, Mj-^ 54.5

Ml, a.p 15.5 15.25

Mi, tr 9.25 9 9

Mt, a.p 17.5 17 17.5

M J, tr 9 10.25 9.25

M5, a.p 21.75 23.5

M3, tr 7.75 9

Depth of ramus beneath alveolus be-
tween P:f and M 1 , external 36

' Measured from the root.
- Measured from the alveolus.

THE AGE OF THE LA FLECHA DEPOSIT

When the collection from this locality was prepared it was
believed that the beds were a redeposit containing both Deseado
and Colhu^-Huapi fossils, and on page 15 of this volume a specimen
was stated to have come from the latter horizon. The belief that
specimens of Colhu^-Huapi age were included was based on the
specimen described above, which was at that time referred to A.

166 Field Museum of Natural History — Geology, Vol. VI

fraterculus, and on a series of leontiniids with a dental formula of
l>o4>l> which were tentatively assigned to Colpodon. Direct com-
parison of the Argyrohippus with the American Museum specimen
of A. fraterculus has now revealed that the La Flecha form
represents a distinct, more primitive species. The identification of
the leontiniids was made on the authority of Loomis, who gave
(1914, pp. 108-109) the dental formula of Colpodon as l,or4,f
and of the Deseado Ancylocoelus as f >o>l>l. In his first account of
Ancylocoelus, Ameghino (1895, p. 650) held that Pi was lacking.
In his second report (1897, p. 475), however, he stated that the
tooth which was lacking above and below and formerly believed by
him to be the Pi might be the canine. The number of teeth of
Ancylocoelus, according to Ameghino, is therefore the same as in
Colpodon. During the summer of 1934 I was able to study some
casts of Ameghino's specimens of Ancylocoelus in the British Museum
(Natural History) . The casts are identical with the leontiniids from
La Flecha in Field Museum. These specimens show that the tooth
that is lacking is the canine, thereby making the dental formula
of Ancylocoelus identical with that of Colpodon. The entire fauna
from La Flecha is therefore of Deseado age. The specimen described
and figured by me on pages 15 to 17 of this volume under the name
of Colpodon sp. is in reality Ancylocoelus frequens Ameghino.

REFERENCES

Ameghino, F.

1895. Premiere contribution a la connaissance de la faune mammalogique des
couches a Pyrotherium. Bol. Inst. Geog. Arg., 15, pp. 603-660.

1897. Mammiferes cr6taces de I'Argentine (Deuxieme contribution a la con-
naissance de la faune mammalogique des couches a Pyrotherium). Ibid., 18,
pp. 406-521.

1902. Premiere contribution a la connaissance de la faune mammalogique des
couches a Colpodon. Bol. Acad. Nac. Cienc. Cordoba, 17, pp. 71-132.

Loomis, F. B.

1914. The Deseado Formation of Patagonia. Amherst, 1914, pp. 1-232

Simpson, G. G.

1932. New or Little-known Ungulates from the Pyrotherium and Colpodo
Beds of Patagonia. Amer. Mus. Nov., 576, pp. 1-13,

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