THE UNIVERSITY OF ILLINOIS LIBRARY FI The person charging this material is re- sponsible for its return to the library from which it was withdrawn on or before the Latest Date stamped below. Theft, mutilation, and underlining of books are reasons for disciplinary action and may result in dismissal from the University. UNIVERSITY OF ILLINOIS LIBRARY AT URBANA-CHAMPAIGN FIELD MUSEUM OF NATURAL HISTORY FOUNDED BY MARSHALL FIELD, 1893 PUBLICATION 261 ZOOLOGICAL SERIES VOL. XVII, No. 2 BY WILFRED H. OSGOOD CURATOR, DEPARTMENT OP ZOQLOGY m 6f m CHICAGO, U. S. A. JULY 12, 1929 PRINTED IN THE UNITED STATES OF AMERICA BY FIELD MUSEUM PRESS . 5* V./7* A NEW RODENT FROM THE GALAPAGOS ISLANDS BY WILFRED H. OSGOOD The Crane Pacific Expedition of Field Museum, which is now working in the East Indies, made a brief stop in the Galapagos Islands on its outward voyage in the early part of the present year. At this time, largely through the energy of Mr. Frank Wonder, taxidermist of the expedition, an excellent series of rodents was obtained including three species, one of which proves to be quite unknown and so distinct from the others as to be of considerable interest. A discovery of this sort is somewhat surprising in view of the number of parties that have touched at the islands in recent years. It is also fortunate that it is made now, for the spread of house rats makes the extinction of such restricted types increasingly probable. In 1835, when Darwin visited the Galapagos Islands, he found a native mouse inhabiting Chatham Island and supposed it to be the only indigenous mammal of the islands. This species was described as Mus galapagoensis by Waterhouse (Zool. Voy. Beagle, Pt. II, Mammalia, p. 65, pis. xxxm-xxxiv, 1839) who adds Darwin's notation as follows: "This mouse or rat is abundant in Chatham Island. I could not find it on any other island of the group." From this it is evident that Darwin made an effort to obtain further rodents, but his narrative seems to indicate that he did not spend any time on Narborough and Indefatigable islands, the principal ones from which specimens have been taken subsequently. Since Darwin's time, no one appears to have collected any mam- mals on Chatham Island and the species discovered by him has not been taken again with certainty ; but in 1892 a closely allied or possibly identical species was described as Oryzomys bauri from Harrington Island by J. A. Allen (Bull. Am. Nat. Mus. Hist., 4, p. 48, 1892). Further specimens of this species were obtained by Heller and Snodgrass in 1898 and are now preserved in the collection of Stanford University. 21 22 FIELD MUSEUM OF NATURAL HISTORY— ZOOLOGY, VOL. XVII. In 1899, a very distinct species, Oryzomys indefessus from Indefa- tigable Island, was described by Thomas (Ann. & Mag. Nat. Hist., (7), 4, p. 280, Oct. 1899). Following this in 1904, a well-marked species allied to indefessus was described as Nesoryzomys narboroughi by Heller (Proc. Calif. Acad. Sci., (3), 3, P- 242, 1904). The genus Nesoryzomys was at this time erected by Heller to include indefessus and narboroughi. The species described below, for which the name darwini seems appropriate, brings the total for the islands to at least four and possibly five distinct forms. These divide into three groups (1) galapagoensis and bauri, which differ from each other only slightly or not at all and which belong to the typical section of the genus Oryzomys; (2) indefessus and narboroughi, which belong to an aber- rant section of the oryzomyine series and are individually well distinguished in color but sufficiently similar otherwise so that they may have been derived the one from the other in comparatively recent times; and (3) darwini, which has general relationship to indefessus and narboroughi but differs from them much more than they differ from each other. It lives side by side with indefessus on Indefatigable Island, indicating a distinction of long standing. With the addition of N. darwini to the other forms above- mentioned, the rodents of the islands take on considerably more importance than formerly and will doubtless need serious considera- tion in speculation regarding the derivation of the insular fauna. Until thorough study of mainland forms is made, however, no satis- factory conclusions are to be expected. While the oryzomyine rodents are widely distributed and greatly varied in South America, they are also highly developed in Central America, and no competent study of the whole group has yet been undertaken. When such a study is made, it may be possible to determine something more than the general affinity of the insular and continental forms. At present, it cannot be affirmed even that the nominal genus Nesory- zomys is confined to the Galapagos, for at least in some of its charac- ters it is closely paralleled by certain forms of the mainland. How- ever, the number and diversity of the island rodents may perhaps be taken as indicating that their existence on the islands is not an accidental matter and the view is somewhat substantiated that the present land area has been reduced from former larger propor- tions. Furthermore, it seems quite certain that before the intro- duction of house rats the native rodents were more generally distri- buted throughout the different islands of the group than at present. 1929 NEW RODENT FROM GALAPAGOS ISLANDS — OSGOOD 23 Nesoryzomys darwini sp. nov. Type from Academy Bay, Indefatigable Island, Galapagos Islands. No. 30830 Field Museum of Natural History. Adult female. Collected Jan. 12, 1929 by Frank C. Wonder. Orig. No.82. Diagnosis. — Differs from N. indefessus and N. narboroughi in decidedly smaller size and in bright fulvous coloration which extends to the entire underparts; skull slender and without sharp ridges or angles. Color. — Predominating body color Cinnamon Rufous of Ridg- way; upper parts with a plentiful mixture of blackish producing a general effect of Mars Brown or darker; the blackish uniformly distributed but not producing the common oryzomyine appearance of fine lines; sides but slightly lighter than back; underparts clear Cinnamon Rufous throughout, the plumbeous basal color almost wholly concealed; ears thinly haired, brownish without, rufescent or creamy within, a tuft of clear rufescent at the upper bases; feet dull whitish tinged with rufescent proximally; tail dusky above, dull whitish below. Skull: — General form slender and elongate; zygomata compressed anteriorly; nasals very long, their posterior endings about even with lacrymals; interorbital region somewhat less constricted than in N. indefessus, but with rounded edges; braincase smoothly rounded; interparietal small; palate extended posteriorly beyond molars and with a single minute foramen between last molar and interpterygoid fossa; teeth of good size and usual oryzomyine pattern. Measurements. — Adult male and female (type), respectively: Total length 222, 204; tail vertebrae 89, 91; hind foot 27, 25. Skull of type: Greatest length 30; basilar length 22.3; zygomatic breadth 14.6; interorbital constriction 4.3; breadth of braincase 12.2; nasals 12.6; interparietal 8x2; postpalatal length 11.3; diastema 7.8; upper toothrow 4.8. Remarks. — Three specimens of this new form were collected by Mr. Wonder at Academy Bay January 12, and one more at Conway Bay January 16. On the same dates, twelve examples of N. inde- fessus were taken at Academy Bay and thirteen at Conway Bay. This and the fact that darwini has heretofore eluded capture indicate that it is much less numerous than indefessus. 24 FIELD MUSEUM OF NATURAL HISTORY— ZOOLOGY, VOL. XVII. It is readily recognizable by its small size and rufescent colora- tion. It possesses all the general characters of indefessus and nar- boroughi such as may be of generic or subgeneric significance. Ex- ternally, these characters include soft, dense pelage, relatively short tail, broad hind feet, reduced plantar tubercles, and markedly granu- lated soles. The skulls are characterized by elongate form, constricted interorbital region without marked ridges, and by a rather wide interpterygoid fossa between which and the last molars the "lateral pits" so characteristic of typical Oryzomys are reduced in size and depth producing an appearance of the back of the palate seldom seen in mainland forms. Taken collectively, these characters may be of generic importance and, at least for the present, the genus Nesoryzomys may be con- sidered as consisting only of the three species inhabiting the Gala- pagos Islands. Nevertheless, it should not be forgotten that present day generic distinctions among Neotropical rodents are on a basis which future investigation may not substantiate. In other words, it is more conservative to speak of the rodent fauna of the Galapagos as consisting of four peculiar species than as of one peculiar genus. THE LIBRARY GF IHt JUL fc&uto UNIVERSITY OF ILLINOIS UNIVERSITY OF II LINOiS URBANA