en LIBRARY OF THE UNIVERSITY OF ILLINOIS AT URBANA-CH/^PAIGN 550.5 n V. /4-I5 GEOLOGY UNIVERSITY OF 'LLINOIS LIBRARY AT URBANA-CHAMPA/GN GEOLOGY «< ^'" 3 FIELDIANA • GEOLOGY Published by CHICAGO NATURAL HISTORY MUSEUM Volume 14 December 29, 1960 No. 3 Arctoryctes and Some Other Chadronian Vertebrate Microf ossils from Nebraska William D. Turnbull Assistant Curator of Fossil Mammals AND Charles A. Reed Collex:e of Pharmacy, University of Illinois In a report by Hough and Alf (1956) on a collection of small fos- sils from anthills in Sioux County, Nebraska, a number of species known previously only from Orellan (mid-Oligocene) and higher strata were recorded as coming from a Chadronian (early Oligocene) horizon. One such identification cautiously published as "{t)Prosca- lops" would be (if verified) the earliest record of a true mole (Mam- malia: Talpidae) in North America. At our request, the material upon which this tentative identification had been made (plus some other unidentified pieces) was kindly turned over to us by the origi- nal collector, Mr. Raymond Alf, for further study. He has since donated the specimens to Chicago Natural History Museum, and thus they bear CNHM catalogue numbers. The original report did not carry an exact locality reference for the anthill fauna. According to Alf (personal communication, 1959) the locality was designated as no. 5302 of the Raymond Alf Museum of Natural History, Webb School, Claremont, California, and is located on the Frank Arner Ranch, north of Crawford (T. 33 N., R. 53 W., Sec. 26), Sioux County, Nebraska. Among the unidentified materials turned over to us by Mr. Alf were several problematical foot bones, an C^) Arctoryctes radius (dis- cussed below), and four distal ends of humeri, two of lizards (PR403 and PR404) and two of rodents. Both lizard humeri have the dis- tinctive bulbous surfaces for articulation with radius and ulna and are about the size of the counterpart in Phrynosoma, although they Library of Congress Catalog Card Number: 60-53627 m^mi OF 1HE 41 FEB 1 1961 KiVWSITY OF llUNiilS ^^°'-°QY "-IBRARY 42 FIELDIANA: GEOLOGY, VOLUME 14 differ in detail. We doubt that a family assignment is possible. One of the rodent fragments appears to belong to a myomorph (PM3892). It compares very well with the humerus of Peromyscus in size and detail, and probably belonged to one of the several species of Eumys known to be abundantly represented in the fauna. The other rodent fragment (PM3893) is somewhat broken on its medial and lateral surfaces. In detail, it compares best with the humerus of Citellus, although it is the size of that of Eutamias. Thus it prob- ably belonged to one of the eomyids, Adjidaumo or Paradjidaumo, which Hough and Alf (1956) reported to be abundant in the fauna. Of these two genera, Adjidaumo has the smallest individuals, and so the most probable association is with this genus. ARCTGRYCTES' Humeri. — This small collection has proved to be intriguing be- cause of the association of a number of problematical foot bones and two fragmentary, fossorially specialized mammalian humeri. The latter, both distal ends of left humeri (PM3878 and PM3879), were tentatively identified as Proscalops by Hough and Alf. However, we found these specimens to be Chadronian representatives of the enigmatic Cryptoryctes-Arctoryctes group of fossorial mammals. The resemblance is closer to Arctoryctes (as presently defined) than it is to Cryptoryctes, more particularly to the Orellan A. galbreathi Reed, 1956, but the present specimens represent a somewhat less specialized form. Because of the fragmentary nature of these remains no new species is being described, although we are convinced of its validity. The two pieces of the Chadronian Arctoryctes indicate that it had a humerus of approximately the same length and configuration as that of the Orellan A. galbreathi but less specialized in the following details: (1) it was more slender; (2) there was less fusion between the teres tubercle and the medial epicondyle; (3) the medial epicondyle was less projecting; (4) the groove for the brachial artery and the median nerve was shorter; (5) the lateral epicondyle probably was less projecting. The differences are best shown by direct comparison of the drawings (fig. 24). 1 Since humeri are the only specimens known, the ordinal affinity within the Mammalia of Arctoryctes and the related Cryptoryctes remains a puzzle, which can only be solved by the finding of better-associated skeletal material than that known to date. The one definite conclusion we emphasize is that these animals were not moles (Reed, 1954). We do not agree with Saban (1958, p. 528) that these two genera are to be positively assigned to the epoicotheriid edentates. We feel that assignment within the Insectivora is equally possible, and that any assignment is at present premature. 6'as' X 0.3 Qj- S