(navigation image)
Home American Libraries | Canadian Libraries | Universal Library | Community Texts | Project Gutenberg | Children's Library | Biodiversity Heritage Library | Additional Collections
Search: Advanced Search
Anonymous User (login or join us)
Upload
See other formats

Full text of "A new species of the fossorial mammal Arctoryctes from the Oligocene of Colorado"

i 

s 


\ 

i 

i 






if 

J 




1 


i 

if 


■; 
ji 





UN' "RSITY OF 

ILLlK^iS LIBRARY 

AT URBANA-CHAMPAIGN 

NATURAL HIST. SURVEY 



FIELDIANA • GEOLOGY 

Published by 
CHICAGO NATURAL HISTORY MUSEUM 

Volume 10 April 24, 1956 No. 24 

A NEW SPECIES OF 

THE FOSSORIAL MAMMAL ARCTORYCTES 

FROM THE OLIGOCENE OF COLORADO 

Charles A. Reed 
College of Pharmacy, University of Illinois 

Arctoryctes terrenus Matthew (1907) has as its type a single 
left humerus from the early Miocene of South Dakota. No other 
example of this unique fossorial species has been recorded, but 
Galbreath (1953, p. 49) briefly described three humeri from the 
middle Oligocene of Logan County, Colorado, and tentatively 
assigned them to this genus. When Galbreath's paper appeared, 
there was already in press (Reed, 1954a) a description of a new but 
related genus and species, Cryptoryctes kayi, from the early Oligocene 
of Montana, based on six humeri. 

Of these two genera, Arctoryctes is not only later in time than is 
Cryptoryctes but it is also more specialized, particularly in the 
fusion of the teres tubercle and the medial epicondyle. The middle 
Oligocene humeri described by Galbreath are not only intermediate 
in time between C. kayi and A. terrenus but are also intermediate 
morphologically. It is considered, however, that they more closely 
resemble Arctoryctes terrenus than they do Cryptoryctes kayi and 
so will be described as a new species of Matthew's genus. Actually, 
these mid-Oligocene humeri differ from humeri of both Arctoryctes 
and Cryptoryctes to such a degree that they could validly be con- 
sidered to belong to a new genus, but until more is known of the 
affinities of these peculiar forms it seems better not to introduce 
more names. 

Arctoryctes galbreathi^ sp. nov. 

Holotype. — Univ. Kansas Mus. Nat. Hist. Vert. Pal. Coll. no. 
9837, a right humerus lacking the capitulum and medial epicondyle. 

1 Named in honor of Dr. Edwin C. Galbreath, who collected and first pub- 
lished a paper on the specimens here named. 

No. 793 305 



j^^"v.'^.^y<>w-.jy^.^:'«^iaMa» ^lrs:^ 



306 FIELDIANA: GEOLOGY, VOLUME 10 

Hypodigm. — The hypodigm consists of the holotype and two 
other specimens: Univ. Kansas Mus. Nat. Hist. Vert. Pal. Coll. 
no. 9838, distal two-thirds of a left humerus, lacking medial and 
lateral epicondyles; and no. 9839, a right humerus lacking the medial 
epicondyle, the tip of the pectoral process, and most of the lateral 
border. 

Horizon and locality. — Orellan horizon (middle Oligocene), 
Cedar Creek member (middle) of the White River Formation, Logan 
County, Colorado (see Galbreath, 1953, p. 49, for more exact 
locality data). 

Diagnosis. — Resembles the humerus of A. terrenus more closely 
than any other known humerus; differs from it primarily by its 
smaller size (fig. 130), and in not having the teres tubercle and the 
medial epicondyle completely fused; assigned to Arctoryctes rather 
than to Cryptorydes because of the marked similarity in structure, 
and presumably in function, of the greater tuberosity and pectoral 
process of this species and A. terrenus, as contrasted with the 
extremely high and narrow pectoral process of C. kayi. 

Description. — The figure shows the similarities and differences 
between the humeri of the three species under consideration much 
better than words can do. I would only point out, aside from the 
details mentioned above, that A. galbreathi has a lesser tuberosity 
much shorter than have the other two; the fusion of the teres 
tubercle and the medial epicondyle, although incomplete, is far 
advanced toward the condition found in A. terrenus, whereas there 
is no indication of such fusion in C. kayi; the head of A. galbreathi 
is slightly more rounded and directed somewhat more laterally than 
are the heads of A. terrenus and C. kayi, both of which are high 
and narrow and directed somewhat more posteriorly; and A. gal- 
breathi is quite similar to A. terrenus in the closeness, in anterior 
view, of the trochlea and the pit for the great ligament of the M. 
flexor digitorum profundus, whereas in C. kayi these structures are 
separated by a wide depression emanating from the supracondyloid 
foramen. The capitulum of A. galbreathi (not shown on figure 130, C, 
but present on no. 9838) is extremely similar to that of C. kayi, and 
thus more bulbous and not so elongate as in A. terrenus. 

Discussion. — My ideas on the major functional aspects of the 
humeri of these animals have already been presented (Reed, 1954a), 
and the humeri of A. galbreathi shed no new light upon these prob- 
lems. Only the discovery of associated skeletal remains will help 
answer the existing questions of function and ordinal relationships. 





Fig. 130. A. Cryptoryctes kayi, left humerus, anterior aspect (composite 
specimen, based mostly on CNHM-PM 1009). B. Posterior aspect of A. 

C. Arctoryctes galbreathi, right humerus, anterior aspect (KUMNH no. 9837). 

D. Posterior aspect of C. E. Arctoryctes terrenus, left humerus, anterior aspect 
(cast of AMNH no. 12864). F. Posterior aspect of E. All X 3.25. 

Abbreviations: a, greater tuberosity; b, lesser tuberosity; c, pectoral process; 
d, bicipital groove; e, deltoid process; /, teres tubercle; g, medial epicondyle; 
h, supracondyloid (entepicondylar) foramen; i, trochlea; j, fossa for origin of the 
great ligament of the M. flexor digitorum profundus; k, capitulum (missing in C); 
I, lateral epicondyle; m, head; n, olecranon fossa. 

307 



308 FIELDIANA: GEOLOGY, VOLUME 10 

With regard to more minor details, however, it appears to me that 
the similarity in the structure of the pectoral processes of the 
humeri of A. galbreathi and A. terrenus indicates a similarity in 
the use of the pectoral musculature, whereas the quite different 
shape of the pectoral process of C. kayi presupposes a somewhat 
different usage of these muscles. (It would be rash to attempt to 
judge which condition is more specialized.) At the same time, 
it would seem that the relations between the teres tubercle and the 
muscles that insert upon it (Mm. teres major and latissimus dorsi) 
would have been quite similar in A. galbreathi and A. terrenus, 
whereas this relationship would be somewhat less specialized, due to 
the more proximal position of the teres tubercle, in C. kayi. In both 
A. galbreathi and A. terrenus the presence of a groove, carrying the 
median nerve and the brachial artery, indicates a basic similarity 
caused in turn by the tendency (complete in A. terrenus) toward 
fusion of the teres tubercle and the medial epicondyle; C. kayi 
has no such groove. 

The identity of the deltoid process (even though labeled on 
C. kayi and A. terrenus) continues to puzzle me, as does the location 
of the boundary between the greater tuberosity and the pectoral 
process. We are dealing here with extremely specialized bones, and, 
as with moles (Reed, 1951), final identification of all details of 
the humerus can be accomplished only after a thorough comparison 
with more primitive forms. In this instance, however, such primitive 
forms await discovery in the Eocene. 

Both Galbreath (1953) and myself (Reed, 1954a) have expressed 
a firm disbelief in the conclusion of Schlaikjer (1933) that the 
humerus of A. terrenus (the only specimen known to Schlaikjer) 
could be that of a mole. But the idea cannot be discarded that 
perhaps there existed, in Cryptoryctes and Arctoryctes, a functional 
humero-clavicular joint, for the greater tuberosity of A. galbreathi 
has an extremely smooth surface, very much like the articular 
surface of the humeral head. The condition in A. terrenus is similar, 
for Dr. G. G. Simpson of the American Museum of Natural History, 
who was asked to examine the original type, has written as follows 
(personal communication) : "The Arctoryctes terrenus type humerus 
has, all over the bone, a matte surface much like unglazed porcelain. 
The greater tuberosity is smooth, without any roughening for 
muscle attachment. It is as smooth as the apparent articulation for 
the scapula, but no smoother than some non-articulating surfaces 
on the bone. It is not polished. I think that it could well be an 
articular surface, but do not consider this certain." 



REED: A NEW SPECIES OF ARCTORYCTES 309 

The greater tuberosity of Cryptorydes kayi is not as smooth as 
in Arctorydes and is thus less similar to an articular surface. It is 
interesting in correlation with these observations that in the primi- 
tive talpid Galemys, the desman of the Pyrenees, the whole of the 
greater tuberosity appears smooth, as if it were a synovial surface, 
but actually the clavicle articulates with only a small part of this 
greater tuberosity. A smooth surface does not, therefore, prove 
an articulation. 

No matter what the final decision may be as to the presence or 
absence of a humero-clavicular joint in Cryptorydes and Ardorydes, 
it will be difficult to consider them as talpids unless a direct phylo- 
genetic relationship can be shown in the fossil record. For I have 
previously expressed my belief (Reed, 1954b), based upon anatomical 
studies within the Talpidae, that a change in the relationship 
between the pectoral process and the tendon of the long head of the 
M. biceps brachii was the primary (pre-adaptive?) change in mor- 
phology in this family that led to fossorial specialization, and that 
the humero-clavicular joint was a secondary specialization. Even 
if Cryptorydes and Ardorydes are shown eventually to have had 
a humero-clavicular joint, they definitely lack the peculiar relation- 
ship between the pectoral process and the biceps tendon found in all 
talpids (see Reed, 1951, 1954a, for functional details) — a relation- 
ship, furthermore, which is always specialized in exact correspon- 
dence with the degree of fossorial behavior. It is difficult to believe 
that even an aberrant line of talpids would have become increasingly 
fossorial, as Cryptorydes and Ardoryctes did become, if they had 
previously lost the primary talpid specialization. 

In addition, as pointed out by Galbreath (1953, p. 49), the 
discovery of a typical humerus of a true talpid in the middle Oli- 
gocene of Colorado weakens Schlaikjer's argument for an association 
between the humerus of Ardorydes and the skull of the late Oligocene 
and early Miocene mole, Proscalops. 

As to the possible relationships of the three species within 
the Cryptorydes-Arctoryctes group, it is my opinion (and not a par- 
ticularly defensible one) that a common Eocene ancestor gave 
rise to two known phylogenetic lines, one leading to Cryptorydes, 
and the other, probably through A. galbreathi, to A. terrenus. 
Although I had previously stated (Reed, 1954a) that Cryptorydes 
could have been ancestral to Ardoryctes, the finding and study of 
the humeri of A. galbreathi make this statement seem less probable 
than when those words were written. 



810 FIELDIANA: GEOLOGY, VOLUME 10 

ACKNOWLEDGMENTS 

I am particularly grateful to Dr. Edwin C. Galbreath, of the 
University of Kansas, who courteously relinquished all rights to 
the specimens which form the basis of this paper — specimens he 
collected and first discussed. I am also indebted to the Museum 
of Natural History of the University of Kansas for its kindness 
in lending me the three humeri forming the hypodigm of Arctoryctes 
galbreathi. For the examination of the type specimen of A. terrenus, 
I wish to thank Dr. George G. Simpson of the American Museum 
of Natural History. 

ADDENDA 

In the two years since this paper was written, several fossils have 
been found and several papers published that should be discussed, 
and I wish to thank the press of Chicago Natural History Museum 
for allowing me to insert these remarks. 

Saban (1954) has left open the possibility that Arctoryctes and 
Cryptoryctes might be included in the Chrysochloridae, contrary 
to my opinion (Reed, 1954a) that the chrysochlorids belong to 
a totally different fossorial type. It is true that Matthew originally 
thought that Arctoryctes was a chrysochlorid, and this designation 
was copied in many subsequent papers, but I can see no possibility 
of such relationship. 

White (1954, p. 403) discussed three humeri which he assigned 
to the Talpidae, genus and species undetermined. These specimens 
are from the Canyon Ferry Reservoir area, Montana, and are 
Chadron (early Oligocene) in age. When I tried to borrow this 
material, two of the three specimens had been misplaced, but the 
one available (USNM no. 18915) definitely belongs to Cryptoryctes 
kayi. Presumably the other two specimens do, too, for if White 
had had in hand a mixture of humeri from moles and from Crypto- 
ryctes, he would have noted the differences immediately. The 
removal of these humeri from the Talpidae to Cryptoryctes leaves 
as the oldest known North American moles the material from the 
mid-Oligocene of Colorado and Wyoming mentioned by Galbreath 
(1953, p. 49), unless the Proscalops? listed by Hough and Alf (1956) 
from the early Oligocene of Nebraska is definitely determined to 
be talpid. 

It is very possible that the humeri of Cryptoryctes kayi and the 
partial skull named Kentrogomphios strophensis by White (1954, 



REED: A NEW SPECIES OF ARCTORYCTES 311 

p. 404) will some day be found to belong together, but until associ- 
ated remains are discovered this idea is purely conjectural. 

One recently found and hitherto undescribed humerus deserves 
mention, as extending the range of Arctoryctes galbreathi into Mon- 
tana. USNM no. 21310 is a left humerus from the Toston Forma- 
tion, Orellan horizon (mid-Oligocene), and definitely belongs to 
A. galbreathi. This humerus lacks the lateral epicondyle, the 
capitulum, and part of the trochlea, and the edge of the head and 
greater tuberosity are eroded, but it has preserved the medial 
epicondyle, missing on all specimens of the hypodigm. This fortu- 
nate preservation has allowed me to publish a more accurate re- 
construction (fig. 130, C, D) of the missing medial epicondyle of 
the type specimen than I could otherwise have done. 



REFERENCES 

Galb^eath, E. C. 

1953. A contribution to the Tertiary geology and paleontology of northeastern 
Colorado. Univ. Kansas Pal. Contr., Vertebrata, 4, pp. 1-120, figs. 1-26, 
pis. 1, 2. 

Hough, J., and Alf, R. 

1956. A Chadron mammalian fauna from Nebraska. Jour. Pal., 30, pp. 132- 
140, 4 figs. 

Matthew, W. D. 

1907. A lower Miocene fauna from South Dakota. Bull. Amer. Mus. Nat. 
Hist., 23, pp. 169-219, figs. 1-26. 

Reed, C. A. 

1951. Locomotion and appendicular anatomy in three soricoid insectivores. 

Amer. Mid. Nat., 45, pp. 513-671, figs. 1-34. 
1954a. Some fossorial mammals from the Tertiary of western North America. 

Jour. Pal.. 28, pp. 102-111, figs. 1-8. 
1954b. The origin of a familial character: A study in the evolutionary anatomy 

of moles. Anat. Rec, 118, p. 343. 

Saban, R. 

1954. Phylog^nie des Insectivores. Bull. Mus. Nat. d'Hist. Nat., ser. 2, 26, 
pp. 419-432. 

SCHLAIKJER, E. M. 

1933. Contributions to the stratigraphy and paleontology of the Goshen Hole 
area, Wyoming. I. A detailed study of the structure and relationships of 
a new zalambdodont insectivore from the middle Oligocene. Bull. Mus. 
Comp. Zool., 76, pp. 1-27, figs. 1-7, pi. 1. 

White, T. E. 

1954. Preliminary analysis of the fossil vertebrates of the Canyon Ferry 
Reservoir area. Proc. U. S. Nat. Mus., 103, pp. 395-438, figs. 40-51.