The Relationships of Megaoryzomys curioi, an Extinct Cricetine 0t Rodent (Muroidea: Muridae) from the II Galapagos Islands, Ecuador DAVID W. STEADMAN and CONTRIBUTIONS TO PALEOBIOLOGY CLAYTON E. RAY SERIES PUBLICATIONS OF THE SMITHSONIAN INSTITUTION Emphasis upon publication as a means of "diffusing knowledge" was expressed by the first Secretary of the Smithsonian. In his formal plan for the Institution, Joseph Henry outlined a program that included the following statement: "It is proposed to publish a series of reports, giving an account of the new discoveries in science, and of the changes made from year to year in all branches of knowledge." This theme of basic research has been adhered to through the years by thousands of titles issued in series publications under the Smithsonian imprint, commencing with Smithsonian Contributions to Knowledge in 1848 and continuing with the following active series: Smithsonian Contributions to Anthropology Smithsonian Contributions to Astrophysics Smithsonian Contributions to Botany Smithsonian Contributions to the Earth Sciences Smithsonian Contributions to the Marine Sciences Smithsonian Contributions to Paleobiology Smithsonian Contributions to Zoology Smithsonian Studies in Air and Space Smithsonian Studies in History and Technology In these series, the Institution publishes small papers and full-scale monographs that report the research and collections of its various museums and bureaux or of professional colleagues in the world of science and scholarship. The publications are distributed by mailing lists to libraries, universities, and similar institutions throughout the world. Papers or monographs submitted for series publication are received by the Smithsonian Institution Press, subject to its own review for format and style, only through departments of the various Smithsonian museums or bureaux, where the manuscripts are given substantive review. Press requirements for manuscript and art preparation are outlined on the inside back cover. S. Dillon Ripley Secretary Smithsonian Institution SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY • NUMBER 51 The Relationships of Megaoryzomys curioi^ an Extinct Cricetine Rodent (Muroidea: Muridae) from the Galapagos Islands, Ecuador David W. Steadman and Clayton E. Ray SMITHSONIAN INSTITUTION PRESS City of Washington 1982 ABSTRACT Steadman, David W., and Clayton E. Ray. The Relationships of Megaory- zomy.s curioi, an Extinct Cricetine Rodent (Muroidea: Muridae) from the Galapagos Islands, Ecuador. Smithsonian Contributions to Paleobiology, number 51, 23 pages, 11 figures, 1 table, 1982.—Megaoryzomys curioi is a thomasomyine, not an oryzomyine as previously believed. This rodent was originally de- scribed, from three bony fragments found in a cave on Isla Santa Cruz, Galapagos, as a new species of the Antillean oryzomyine genus Megalomys. The genus Megaoryzomys was named recently for this species, based on new material from Isla Santa Cruz. Our study of additional material indicates that Megao- ryzomys curioi is not closely related to Oryzomys but is most similar to large species of Thomasomys, a genus confined to mainland South America. The Galapagos have been colonized by cricetine rodents at least three times, once by a thomasomyine and twice by oryzomyines. Of these colonists, Megaoryzomys curioi is the most divergent from mainland relatives and thus is probably derived from the earliest immigrant. Although the time of extinction of Megaoryzomys curioi has not been determined, and it has never been recorded from life, it probably survived into historic time. OKHCIAL PUBLICATION DATK is handstamped in a limited number of initial copies and is recorded in the Institution's annual report, Smithsonian Year. SERIES COVER DESICN: The trilobite Phacohs rana Green. Library of Congress Cataloging in Publication Data Steadman, David W. The relationships of Megaoryzomys curioi, an extinct Cricetine rodent (Muroidea: Muridae) from the (ialapagos Islands, Lcuador. (Smith.sonian contributions to paleobiology ; no. .')1) Bibliography: p- 1. Megaoryzomys curioi. 2. Paleontology—Recent. 3. Paleontology—Galapaeos Islands I. Ray, Clayton Edward. II. Title. III. Series. i s ■ ■ QE701.,S,')6 no. .'")1 |QL882.R()| .'iGOs |.%9'.323] 8'>-8^)7 AACR'> Contents Page Introduction 1 Acknowledgments 1 Materials and Methods 2 Abbreviations 2 Fossil Material 3 Recent Comparative Material 3 Measurements 5 Description and Comparisons 6 Systematics 15 Tribe THOMASOMYINI 15 Genus Megaoryzomys Lenglet and Coppois, 1979 15 Megaoryzomys curioi (Niethammer, 1964) 15 Discussion 16 Literature Cited 21 The Relationships of Megaoryzomys curioi^ an Extinct Cricetine Rodent (Muroidea: Muridae) from the Galapagos Islands, Ecuador David W. Steadman and Clayton E. Ray Introduction Megaoryzomys curioi (Niethammer, 1964) is the only species of vertebrate in the Galapagos Islands that is known only from fossils, having neither been seen alive nor collected from life by man. {Nesoryzomys fernandinae Hutterer and Hirsch, 1979, though not collected from life, was de- scribed from fresh owl pellets and may have been seen alive.) Megaoryzomys curioi, a muskrat-sized, cricetine rodent, was named on the basis of three bony fragments from a cave on Isla Santa Cruz. It was assigned originally to the Antillean genus Megalomys. The inadequacy of these meager frag- ments led us to question the validity of the as- signment and to try to augment the material; Ray, beginning in 1965, and Steadman, begin- ning in 1978. The abundant material that re- sulted from our efforts immediately made it clear that the species required its own, new genus (Ray and Whitmore, 1973). Early in 1978 we attempted to communicate David W. Steadman, Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560. Clayton E. Ray, Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington D.C. 20560. with Dr. Guy Coppois about our long-term proj- ect, but we received no response from him; however, during final stages of preparation of this manuscript, we received from Thomas E. Simkin a copy of Lenglet and Coppois (1979), in which the new genus Megaoryzomys was named for Megalomys curioi. We agree with Lenglet and Cop- pois (1979) that the species curioi was not correctly placed in the genus Megalomys, but we do not agree that its closest affinities are with Oryzomys. Furthermore, we feel that the work of Lenglet and Coppois is otherwise inadequate in its sys- tematic treatment of this rodent. Therefore, we review here the morphology o{Megaoryzomys based on new material and present our interpretation of its relationships. Material from Steadman's latest field work of October 1980-January 1981 will be described in his comprehensive work (in prep.) on the vertebrate paleontology of Galapa- gos, as will the material from Isla Isabela recorded herein as Megaoryzomys species. ACKNOWLEDGMENTS.—Field work in Galapagos was supported by the Smithsonian Institution from the Walcott Fund (1968-1969), from the Fluid Research Fund (1966-1967 and 1977-1978, 1980) through the kind efforts of Dr. S. Dillon 1 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY Ripley and Storrs L. Olson, and from the Grad- uate Student Program Development Fund of the University of Arizona (1980). Funds provided to Ray in 1966-1969 were used in part to defray nonpaleontological field work under the auspices of the Darwin Foundation, whereas those pro- vided to Steadman were used strictly for paleon- tological work as directed by the CDRS. Permits for this latter field research were made possible through the offices of the Direccion de Desarrollo Forestal, Ministerio de Agricultura y Ganaderia, Quito; Lcdo. Miguel Cifuentes, Intendente of Parque Nacional Galapagos; Craig MacFarland, Hendrick Hoeck, and David Duffy, past directors of the Charles Darwin Research Station; and Peter Kramer, Thomas E. Simkin, G.T. Corley Smith, and David W. Snow of the Charles Dar- win Foundation. The personnel of the Parque Nacional Galapagos and the Charles Darwin Re- search Station made Steadman's field work not only possible but extremely pleasant. Marsha S. Cox, Minard L. Hall, and Thomas E. Simkin provided valuable advice on working in Galapa- gos. We particularly thank Miguel Pozo, Edward Steadman, and James Hill for working in the field with Steadman in Galapagos. Their com- panionship, hard work, and knowledge of field techniques aided immensely in this project. The De Roy's (Andre, Jacqueline, and Gil), the De- vine's (Bud, Doris, and Steve), and the Moore's (Alan and Tui De Roy) constantly gave all sorts of advice and assistance to Steadman during field work. We also appreciate the field efforts of Srs. Camilo Calapucho, Miguel Castro, Andre De Roy, Michael Harris, and Tjitte de Vries, each of whom has collected fossils of Megaoryzomys. The late James L. Peters was instrumental in 1965 in Ray's first efforts to secure adequate material in Galapagos. Financial support for Steadman's research at the National Museum of Natural History was provided by a Summer Visiting Student fellow- ship from the Smith.sonian Institution and Na- tional Science Foundation grant DEB-7923840 to Paul S. Martin through the Department of Geo- sciences. University of Arizona. We thank the personnel of the Division of Birds, Division of Mammals, and the Department of Paleobiology, NMNH, for the many services and courtesies put forth. Steadman's travel to the BM(NH) was financed by the National Geographic Society. We thank those in charge of collections of all institu- tions from which we have been permitted to examine specimens. Most especially, we thank Miss Levitt, Andrew Currant, Anthony J. Sut- cliffe, and Cyril A. Walker of the BM(NH) for allowing us to examine specimens under their care. We thank W. Vervoort, C. Smeenk, and D.A. Hooijer, for their kindness and patience in con- nection with the loan of the indispensable skull o{Megalomys desmarestii from the Leiden Museum, and Robert T. Orr of the CAS for the loan of Galapagan oryzomyines. Discussions with Alfred L. Gardner, Michael D. Carleton, and Charles O. Handley, Jr., have enriched our knowlege of cricetine morphology and systematics. Jon A. Baskin and Michael D. Carleton provided very detailed criticisms of the manuscript. Charles O. Handley, Jr., and Paul S. Martin also read and criticized an earlier version. Naturally none of them is responsible for any remaining shortcomings. Helen F. James pro- vided an English translation of Niethammer (1964). Karena M. Schmidt and Gene Hall helped in the sorting and cleaning of fossils. The drawings of skulls and mandibles were prepared by Lawrence B. Isham, on special funds provided by Richard S. Cowan, then director of the NMNH; the drawings of enamel patterns were kindly prepared by Molly Wing, without remu- neration. The photographs are by Victor E. Krantz. This is contribution number 295 of the Charles Darwin Foundation. Materials and Methods ABBREVIATIONS.—The following are used to de- note collections from which specimens were ex- amined. AMNH American Museum of Natural History, New York BM(NH) British Museum (Natural History), London NUMBER 51 CAS California Academy of Sciences, San Francisco CDRS Charles Darwin Research Station, Isla Santa Cruz, Galapagos, Ecuador CMNH Chicago [Field] Museum of Natural History, Chicago LSU Louisiana State University, Baton Rouge UF/FSM Florida State Museum, University of Florida, Gainesville USNM former United States National Museum speci- mens deposited in the National Museum of Natural History, Smithsonian Institution The abbreviation NMNH is used in the text to denote the National Museum of Natural History, Smithsonian Institution, Washington, D.C. FOSSIL MATERIAL.—Listed below are the spec- imens of Megaoryzomys curioi and M. species ex- amined in this study with their collectors and dates collected. All localities are on Isla Santa Cruz and Isla Isabela (Figures 1 and 2). Except for Cueva de Kubler, Cueva de Iguana, and Andre's cave, we cannot vouch for the accuracy of the names or exact localities of the fossil sites in Galapagos. (MNI = minimum number of in- dividuals represented by specimens listed.) Megaoryzomys curioi, Isla Santa Cruz Cave no. 1 (= cave in Naranja Zone), different places, T. de Vries, 16 Jan 1966 USNM 284279; 5 postcranial specimens; MNI = 1 Cave no. 1, T. de Vries, 19 Nov 1966 USNM 284280-284289; 2 maxillae, 2 cranial fragments, 2 dentaries, 1 isolated tooth, 22 postcranial specimens; MNI = 3 Cave no. 1, place 2, T. de Vries, 16 Jan 1966 USNM 284295-284318; 1 nearly complete skull, 2 max- illae, 12 dentaries, 6 isolated teeth, 56 postcranial spec- imens; MNI = 9 Cave no. 3, T. de Vries, 17 Jan 1966 USNM 284290-284294; 4 dentaries, 2 isolated teeth, 19 postcranial specimens; MNI = 3 Cave no. 4 (= cave north of El Chato), T. de Vries, 21 Nov 1966 USNM 284348; 4 isolated teeth, 8 postcranial specimens; MNI = 2 Cave no. 4, T. de Vries, M. Castro, 27 Jul 1967 USNM 284319-284330; 2 maxillae, 4 cranial fragments, 2 dentaries, 18 isolated teeth, approximately 80 postcranial specimens; MNI = 2 Cave no. 5 (= cave north of Reserve in Naranja Zone), T. de Vries, 20 Nov 1966 USNM 284331-284335; 4 dentaries, 1 isolated tooth, 2 postcranial specimens; MNI = 3 Cave near Bellavista, M. Harris, Oct 1966 CDRS 4-13; 3 dentaries, 1 isolated tooth, 6 postcranial specimens; MNI = 4 Cave near Bellavista (not definitely the same cave as above), M. Castro, before Apr 1969 USNM 284336-284347; 1 maxilla, 6 dentaries, 4 isolated teeth, 7 postcranial specimens; MNI = 4 Cave in Cascajo Mountains, E. Curio, 1962/1963 BM(NH) 67.1649; 1 maxilla, 2 postcranial specimens; MNI = 1 Cueva de Kubler, D. Steadman, M. Pozo, 21, 23, 28 Jul 1979, 3 Aug 1979 USNM 284197-284270; 1 nearly complete skull, 19 max- illae, 30 cranial fragments, 16 dentaries, 116 isolated teeth, 203 postcranial specimens; MNI =12 Cueva de Iguana, various localities, D. Steadman, M. Pozo, 8-13 Jan 1978, 3-11 Jun 1978, 13-18 Jul 1978 USNM 284271-284278; 1 nearly complete skull, 3 cranial fragments, 1 maxilla, 9 isolated teeth, 18 postcranial specimens; MNI = 7 Andre's Cave, A. De Roy, Mar 1969 CDRS 1-3; 1 nearly complete skull, 1 dentary, 1 postcran- ial specimen; MNI = 1 Megaoryzomys species, Isla Isabela Cueva de Sucre (= Cueva de Hueco Sucre), 1 km north of Pueblo Santo Tomas, M. Castro, Jan 1968 USNM 284349-284357; 2 maxillae, 4 cranial fragments, 3 dentaries, 14 isolated teeth, 8 postcranial specimens; MNI = 2 RECENT COMPARATIVE MATERIAL (skulls and mandibles).— Thomasomys aureus, USNM 194818, 194821, 194827 (Peru); T. praetor, CMNH 19255, 19256 (Perd); T. pnnceps, USNM 251957 (Colom- bia); T. pyrrhonotus, CMNH 81296, 84438, USNM 304538 (Peru); T. cinereiventer, AMNH 32421, 32423, 32430 (Colombia); T. cinereus, CMNH 81309, 81312, 81326, USNM 304537 (Peru); T. hylophilus, CMNH 92558, 92560, 92561 (Colom- bia); T. ischyrus, CMNH 19795, 19799, 19801, USNM 297635 (Perii); T. kalinowskii, CMNH 23723, 23735 (Pertl); T. rhoadsi, CMNH 53210, 53211, 93146 (Ecuador); Rhipidomys leucodactylus, USNM 194495, 194496, 194499, 194501 (Perd); R. caucensis, USNM 387922, 387925 (Venezuela); R. goodfellowi, USNM 374543, 409937 (Venezu- ela); R. venezuelae, USNM 371247, 442286 (Ven- ezuela); R. venustus, USNM 137507, 371242 (Ven- ezuela); Oryzomys palustris, USNM 116531, 178297, 339957, (Mexico, Alabama, Nicaragua); Oryzomys albigulans USNM 137509, 168229, SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY 91°00' 90° 00' 100 KM J I ISLA PINTA (Abingdon I.) o 0 . ISIA RABIDA (Jervis 1.) ISIA FERNANDINA (Narborough I.) ISL^ FLOREANA (Charles I.) I I I I J I 1 L. ^ ISLA MARCHENA (Bindloe L) ISLA GENOVESA (Tower I.) ISLA SEYMOUR BALTRA (South (North Seymour) Seymour) ISLA ©, /ViSANTA-CRUZ.' PINZO'N ^dndefatigabje- \.)l (Duncan I.) ISLA SAN CRISTOBAL (Chatham I.) ISLA , SANTA FE (Barrlngton I.] ISLA ESPAt^OLA (Hood I.) 9r00' 90° 00- FIGURE 1.—The Galapagos Archipelago, showing major islands only. (See "Materials and Methods" and Figure 2 for details of localities on Isla Santa Cruz.) 172978 (Venezuela); 0. xanthaeolus, USNM 277566, 302987, 302991 (Peru); 0. bauri, USNM 392257 (Isla Sante Fe, Galapagos); Nesoryzomys indefessus, USNM 115832, 115834, 259312 (Islas Santa Cruz and Baltra, Galapagos); N. narbor- oughi, USNM 259552 (Isla Fernandina, Galapa- gos); A^. swarthi, CAS 2561 (Isla Santiago); Me- galomys "pilorides" (= desmarestii), BM(NH) 1850.11.30.6 (Martinique); M. desmarestii, BM(NH) 1855.12.24.201 (Martinique), Leiden Museum ''a" (Martinique); M. luciae, BM(NH) 1853.12.16.2 (St. Lucia); Macruroryzomys hammondi, NUMBER 51 90° 35' 90° 30' 90°25' 90°20' 90°15' 90°10' o CO h o o CO b o io CO h o O^ fi^' 0 5 10 1 1 1 1 1 1 1 1 1 1 1 t io CO b o / 1 KM / 5, Santa Rosa \ 3 O o b o ^ ' 4 • Bellavista 6,7 o • o b o 17 ^^ .8 ^ io -* b .9 10 .11 Y Puerto Ayora r>f^~v^ /v. 1 io b o c» . . .. ~' jj Academy Bay 90° 35' 90°30' 9CP25' 90°20' 90° 15' 90°10' FIGURE 2.—Localities of Megaoryzomys on Isla Santa Cruz: 1, cave no. 1 (= cave in Naranja Zone); 2, cave no. 2 (contains no remains of Megaoryzomys); 3, cave no. 3; 4, cave no. 4 (= cave north of El Chato); 5, cave no. 5 (= cave north of Reserve in Naranja Zone); 6, cave near Bellavista; 7, cave near Bellavista (not definitely the same cave as no. 6); 8, cave in Cascajo Mountains (type-locality); 9, Cueva de Kubler; 10, Cueva de Iguana; 11, Andre's Cave. (See "Materials and Methods" for further information on these sites.) BM(NH) 1913.10.24.55 (Ecuador); Nectomyssatur- atus, BM(NH) 1897.11.7.40 (Ecuador); Tylomys species, USNM 298732, 309223, 323971 (Pan- ama); T. mirae, USNM II3318 (Ecuador); Scap- teromys tumidus, USNM 392888 (Uruguay); S. cha- coensis, USNM 12170/8379 (Argentina); Kunsia tomentosus, USNM 364760 (Bolivia); Phyllotis boli- viensis, USNM 121148, 391802 (Bolivia, Chile). In addition, the following archeological material oi Megalomys was examined: M. desmarestii, USNM 293780A,B,C (dentaries; Martinique); M. luciae, LSU field No. 76ch, 76ci, 76cj (dentaries; St. Lucia); UF/FSM field No. 61a-39 (maxilla; St. Lucia). MEASUREMENTS.—Statistics (mean, range, sam- ple size) presented here are based on all adults of Megaoryzomys curioi examined in this study, exclu- sive of the holotype. Standard deviation is given for samples of 10 or more specimens. All speci- mens are from Isla Santa Cruz and are housed SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY either in the NMNH or the CDRS. Terminology for the first seven measurements follows Thomas (1905). All of the following measurements were made with dial calipers and were rounded to the nearest 0.1 mm. greatest length between uprights 55.6, 1 condylobasal length 54.45, 53.3-55.6, 2 condylobasilar length 50.50, 49.3-51.7, 2 basal length 50.25, 48.8-51.7, 2 basilar length 46.25, 45.1-47.4, 2 palatal length 30.30, 28.6-32.0, 3 patatilar length 25.33, 24.6-26.5, 3 length of diastema 16.05, 15.1-17.3,4 length of foramina incisivi 10.84, 9.6-11.7, 5 length of palate 10.35, 9.9-10.6, 4 zygomatic width 34.3-I-, 33.8+-34.8-i-, 2 minimum width of braincase just posterior to zygomatic arch 19.03, 18.7-19.2, 3 minimum interorbital width 8.22, 7.3-8.6, 4 width of zygomatic plate of maxilla 8.06, 6.9-8.7, 6 greatest width of rostrum 11.67, 11,0-12.3, 3 depth of rostrum at anterior end of foramina incisivi 11.93, 11.8-12.1, 3 least width of palate (between alveoli of M^s) 4.20, 3.5-5.1, 5 length of interparietal at midline 4.40, 4.4, 2 width of interparietal 13.60, 12.8-14.4,2 width through occipital condyles 12.00, 11.8-12.2, 2 alveolar length of upper molars 11.48±0.44, 10.9-12.3, 13 crown length of upper molars 10.86, 10.0-11.5, 5 length M' 4.92±0.28, 4.5-5.6, 20 width M' 3.56±0.17, 3.3-3.9, 20 length M^ 3.31±0.17, 3.0-3.6, 14 width M^ 3.40±0.17, 3.1-3.7, 14 length M'' 2.42, 2.3-2.5, 5 width M' 2.80, 2.7-2.9, 5 length of dentary with incisor 38.10, 36.5-40.8, 7 length of dentary without incisor 34.64, 33.4-35.5, 5 alveolar length of lower molars 12.59±0.56, 11.7-13.6, 22 crown length of lower molars 12.06, 11.5-12.7, 9 length M, 5.17±0.18, 4.8-5.5, 15 width Ml 3.28±0.12, 3.1-3.5, 14 length M2 3..54±0.15, 3.2-3.8, 16 width M2 3.29±0.14, 3.0-3.5, 15 length M3 3.35±0.23, 2.9-3.7, 11 width M.3 2.74±0.12, 2.6-2.9, 11 Description and Comparisons Megaoryzomys curioi was described from a left maxilla (lacking M'^) and fragments of a humerus and scapula that were found in 1962-1963 by Dr. E. Curio in a cave (= lava tube) of unknown name or exact locality in the Cascajo Mountain area of Isla Santa Cruz (Niethammer, 1964:596, 600). Cascajo Mountain is approximately 7-8 km north of Academy Bay, although Abs et al. (1965:52) stated that the cave was approximately 15 km northeast of Academy Bay. The three original specimens of Megaoryzomys were found with the bones of four other species of rodents: Nesoryzomys indefessus, N. darwini, and two intro- duced species, Rattus rattus and Mus musculus. Un- like the remains of Megaoryzomys, those of the other four rodents were in the form of owl pellets, probably from the Galapagos barn owl {Tyto punctatissima). The bones of Megaoryzomys, al- though not mineralized, gave Niethammer the impression of being older than those of the other rodents from the same locality. The three cotypes of Megaoryzomys curioi are deposited in the British Museum (Natural His- tory), where they are housed in the Modern Mammal Section and bear the number BM(NH) 67.1649. As Niethammer (1964:598) presented no evidence to indicate that the three specimens designated as "type" represent a single individual, the maxillary fragment should be regarded as the holotype, and the scapula and humerus as para- types. Contrary to the assertions of Lenglet and Coppois (1979:633), neither their specimens nor any others could possibly be types of their new genus, for which the species curioi, based on Niethammer's specimens, is of course the type. Our measurements of the holotype, a maxilla, of Megaoryzomys curioi (alveolar length of upper mo- lars 11.4 mm, length M^ 5.1 mm, width M^ 3.5 mm, length M^ 3.3 mm, width M^ 3.4 mm) are well within the range of variation of other speci- mens examined in this study (see "Measure- ments"). In addition, we could find no qualitative differences between our series of specimens and the holotype. Thus we are confident that our material represents the species described by Nie- thammer (1964). Niethammer (1964:598, 599) placed his species in the West Indian genus Megalomys based on the following characters: (1) the similar enamel pat- NUMBER 51 PARACONE PARACONE LINGUAL LABIAL LINGUAL A UPPER LEFT MOLARS B LOWER LEFT MOLARS FIGURE 3.—Nomenclature of enamel patterns of molars of Megaoryzomys, including only those names used in the text: A, upper left molars (USNM 284317, reversed); B, lower left molars (USNM 284290, reversed). (Terminology follows Hershkovitz (1967); AMF = anterior median fold; ASF = anterior secondary fold; IF2 = 2nd internal fold; MF = major fold; NF = minor fold; PFl = 1st primary fold; PF2 = 2nd primary fold; SFl = 1st secondary fold.) terns of its upper molars, (2) the similar pattern of the roots of the upper molars, (3) foramina incisivi that terminate anterior to the molars, (4) its large size. We will now re-analyze these char- acters, demonstrating that they do not suffice to place curioi in the oryzomyine genus Megalomys. 1. The similar enamel pattern of its upper molars. Niethammer (1964) said that the posi- tions of enamel folds 1 and 3-8 of M^"^ (as shown in figure 4 of Niethammer) in Megaoryzomys are similar to those in Megalomys desmarestii of Marti- nique, Lesser Antilles. Niethammer's enamel folds 1-8 correspond sequentially to the following terms used herein (Figure 3): M^—PF.l, SF.l, PF.2, NF, MF; M^—PF.l, PF.2, MF. The posi- tions of enamel folds in Megaoryzomys generally resemble those in Megalomys (Figure 4), but Me- gaoryzomys differs from Megalomys and resembles the Neotropical cricetine Thomasomys in lacking IF.2 on M^"^ and in the presence of AMF and ASF. Thomasomys differs from both Megaoryzomys and Megalomys in its more nearly circular para- cone on M^"^. We agree with Niethammer that the "labial grooves" (major and minor folds) are deeper in Megaoryzomys than in specimens of Megalomys at a similar stage of wear. Niethammer (1964) did not have any lower molars of Megaoryzomys. Our examination of SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY 5MM J FIGURE 4.—Comparison of enamel patterns in left upper molars: A, Thomasomys aureus, USNM 194827; B, Megaoryzomys curioi, USNM 284317 (reversed); c, Megaoryzomys curioi, USNM 284318; D, Megalomys luciae, UF/FSM field no. 61a-39. enamel patterns of the lower molars of Megaory- zomys (Figure 5) reveals more similarities to those of Thomasomys than to Megalomys. All primary, minor, and major folds in Mi_3 are deeper and wider in Megaoryzomys and Thomasomys than in Megalomys at a similar stage of wear. The MF of M2 is located more anteriorly in Megalomys than in the other two genera. Thomasomys differs from both in its prominent AMF. 2. The similar pattern of the roots of the upper molars. Because we have no specimens of Mega- lomys in which the alveoli of the upper molars are exposed, we cannot comment in detail on the status of this character, which is additionally obscured by Niethammer's (1964) failure to iden- tify the taxa represented by alveolar patterns A, B, and C in his figure 3. We have, however, found the alveolar pattern of the upper molars in Megaoryzomys (seven specimens) to be identical to those in the only specimens of Thomasomys avail- able with exposed alveoli—one specimen each of T. cinereus and T. ischyrus. 3. Foramina incisivi that terminate anterior to the molars. In Megaoryzomys, Thomasomys, and Rhipidomys, the posterior border of the foramina incisivi is even with, or only very slightly anterior to, the anterior border of M\ whereas in Megalo- mys the foramina incisivi terminate well anterior to the molars (Figures 6 and 9). Thus Nietham- mer's character actually supports a thomaso- myine allocation of Megaoryzomys, which differs greatly from Megalomys in this regard. 4. Its large size. Large size is of little value in assigning a cricetine rodent to genus or tribe. Among the mainland cricetines that are compa- rable in size to true Megalomys are Tylomys mirae (Peromyscini), Nectomys squamipes (Oryzomyini), Kunsia tomentosus (Scapteromyini), and Holochilus magnus (Sigmodontini), each of which is, like Megalomys, very different from Megaoryzomys. In addition, gigantism is a common occurrence in insular rodents, and thus the nearest mainland relative of any well-differentiated insular rodent NUMBER 51 FIGURE 5.—Comparison of enamel patterns of left lower molars: A, Thomasomys aureus, USNM 194827; B, Megaoryzomys curioi, USNM 284290 (reversed); c, Megaoryzomys curioi, USNM 284299 (reversed); D, Megalomys luciae, LSU field no. 76ch (reversed); E, Megalomys desmarestii, USNM 293780c. may well be smaller than its insular derivative. Gigantism in muroid rodents on islands has been abundantly documented, for example, in living species by Berry (1964, 1981) and Foster (1964), and in the Quaternary of the East Indies (Musser, 1981) and West Indies (Ray, 1962), the Canary Islands (Crusafont-Pairo and Petter, 1964), and the California Channel Islands (Gill, 1980; Walker, 1980). Certain Quaternary caviomorph rodents of the West Indies (systematically listed in Varona, 1974) also attained very large size, as did dormice in the Mediterranean (Petronio, 1970). Thus the characters used by Niethammer (1964) to refer curioi to the genus Megalomys are invalid. Except for Lenglet and Coppois (1979), no author since Niethammer (1964) has seriously questioned its original assignment to the oryzo- myine genus Megalomys. Abs et al. (1965), Orr (1966), Peterson (1966), Hooijer (1967), Hersh- kovitz (1970, 1972), Muller (1973), Hutterer and Hirsch (1979), and Patton and Hafner (in press) mention the existence of ^''Megalomys'''' in Galapa- gos without systematic comment. To evaluate its affinities further, we compared Megaoryzomys to all genera and most species of Neotropical Cri- cetinae represented in the collections of the Di- vision of Mammals, NMNH, supplemented by additional forms from the other museums. The majority of these species could be eliminated readily as near relatives of Megaoryzomys because of their relatively long palate, relatively small teeth, and differently shaped interorbital region. Table 1 includes only those species whose size or morphology are such that they deserved more serious consideration. Megaoryzomys is not closely related to Megalomys; in addition to the characters in Table \, Megalomys 10 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY Table 1.—Comparison of cranial characteristics of Megaoryzomys curioi and certain olher species of cricetine rodents Length and Size of Depression Shape of width of palate teeth relative Species along median interorbital relative to length to size of Dorsolateral Palatal suture of region of tooth row entire skull ridge of foramina frontals (Figures 7, 9) (Figures 6, 9) (Figures 6, 8, 9) braincase (Figures 6, 9) Megaoryzomys deep strongly short, narrow large well developed. large; numerous curioi constricted, with abrupt lateral expansion of squamosals but not sharp or laterally expanded Thomasomys aureus shallow to deep as in M. curioi short, narrow large as in M. curioi, but slightly less developed in parietal region small; few T praetor deep as in short, narrow large as in small lo M. curioi to intermediate in width M. curioi medium sized; few T. pnnceps intermediate as in M. curioi short, narrow large as in T. aureus small to medium sized; few T. pyrrhonotus shallow as in M. curioi short, narrow large as in T. aureus small to medium sized; few T. cinereiventer shallow wider than in M. curioi short, wide large very small small; few T cinereus shallow as in M. curioi^ but more bulbous short, wide intermediate very small extremely small; very few T hylophilus shallow as in M. curioi short, wide intermediate between T aureus and T. cmereus small; numerous T. ischyrus and shallow wider and short, wide intermediate very small small; few T. tcatinowskii more bulbous than in M. curioi T. rhoadsi shallow wider than in M. curioi short, wide intermediate very small small; few Rhipidomys shallow wider than in short, wide intermediate sharper with small; few leucodactylus M. curioi, especially in posterior half more lateral flare in interorbital region than in Thomasomys or M. curioi R. caucensis shallow wider than in M. curioi short, wide intermediate as in R. leucodactylus absent or small and few R. goodfellowi shallow wider than in M. curioi short, wide intermediate as in R. leucodactylus small; few R. venezuelae shallow as in short, wide or intermediate as in small lo M. curioi narrow M. cunoi medium sized; rather numerous R. venustus shallow wider than in M. curioi^ with more gradual posterior expansion short, wide intermediate as in R. leucodactylus absent or very small and few Oryzomys shallow wider than in long, inter- intermediate very large and sharp; at least two palustris M. curioi. mediate in oriented diagonally large foramina. with gradual width or laterally with varying lateral expansion number of of frontals smaller foraminaNUMBER 51 11 TABLE 1.—Continued Length and Size of Depression Shape of width of palate teeth relative Species along median interorbital relative to length to size of Dorsolateral Palatal suture of region of tooth row entire skull ridge of foramina frontals (Figures 7, 9) (Figures 6, 9) (Figures 6. 8, 9) braincase (Figures 6, 9) 0. atbigularis shallow or as in as in large to not well developed as in absent M. cunoi 0. palustris intermediate in size in interorbital region 0. palustris 0. xanthaeolus shallow as in as in intermediate as in as in 0. palustris 0. palustris 0. palustris 0, palustris 0. baurt shallow as in 0. palustris short, intermediate in width intermediate as in 0. palustris large; numerous Nesoryzomys shallow as in long. intermediate less distinct large; numerous indefessus and M. curioi intermediate than in M. cunoi. N. narboroughi in width especially in posterior half Megalomys absent basically as long, intermediate extremely large; large; numerous "pilorides in M. curioi. intermediate oriented mainly (= M. desmarestii) but wider in width dorsally; not sharp M. desmarestii absent wider than in M. cunoi, with more gradual posterior expansion of frontals as in Megalomys "pilorides" intermediate large; diagonally oriented; sharp large; numerous M. luciae absent as in Megalomys desmarestii as in Megalomys "pilorides" small very large; oriented mainly diagonally; sharp large; numerous Macruroryzomys shallow as in as in small medium sized. large; numerous hammondi Megalomys desmarestii Megalomys "pilorides" diagonally oriented; sharp Nectomys saturalus absent as in Megalomys desmarestii intermediate in length and width intermediate medium sized; oriented diagonally; sharp large; numerous Tylomys species very shallow wider than in short. intermediate larger and more very small; few and M. curioi intermediate distinct than T. mirae in width in M. cunoi, laterally oriented; sharp Scapteromys absent as in intermediate intermediate extremely small very small; few tumidus M. cunoi in length, narrow S. chacoensis absent as in M. curioi as in S. tumidus intermediate extremely small very small; few Kunsia tomentosus absent as in M. curioi short, narrow intermediate less distinct than in M. curioi in interorbital region only small; few Phyllotis shallow as in short, wide intermediate less distinct small to botivieruis M. cunoi overall than in M. curioi large; fewis different from Megaoryzomys in that its zygo- matic process of the squamosal joins the braincase at a more acute angle, its occipital condyles and foramen magnum are much smaller, and the masseteric crests on the dentary terminate more anteriorly (see Figure 10). Among cricetine ro- dents, Megaoryzomys differs in at least several im- portant ways (Table 1) from other large oryzo- myines {Marcruroryzomys, Nectomys), as well as Ty- lomys, Scapteromys, Kunsia, and Phyllotis. The en- demic oryzomyine rodents of Galapagos {Oryzomys galapagoensis, 0. bauri, Nesoryzomys indefessus, N nar- boroughi, N fernandinae, N darwini, and N. swarthi) also are very different from Megaoryzomys in sev- eral characters (Table 1) and may be ruled out as close relatives of the latter. 12 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY CM FIGURE 6.—Skulls in ventral aspect: A, Thomasomys aureus, female, USNM 194827; B, Nesoryzomys swarthi, male, CAS 2561, Isla Santiago; c, Megalomys desmarestii, Leiden Museum "a," Marti- nique; D, Megaoryzomys curioi, USNM 284318 (certain details of the palate are from USNM 284199); D', Megaoryzomys curioi, USNM 284318 (missing parts indicated by stippling, scale 1/2 that of Figures A-D). NUMBER 51 13 FIGURE 7.—Skulls in dorsal aspect: A, Thomasomys aureus, female, USNM 194827; B, Nesoryzomys swarthi, male, CAS 2561, Isla Santiago; c, Megalomys desmarestii, Leiden Museum "a," Marti- nique; D, Megaoryzomys curioi, USNM 284318; D', Megaoryzomys cunoi, USNM 284318 (missing parts indicated by stippling, scale 1/2 that of Figures A-D). o L CM FIGURE 8.—Skulls in lateral aspect: A, Thomasomys aureus, female, USNM 194827; B, Nesoryzomys swarthi, male, CAS 2561, Isla Santiago; c, Megalomys desmarestii, Leiden Museum "a," Martinique; D, Megaoryzomys curioi, USNM 284318; D', Megaoryzomys cunoi, USNM 284318 (missing parts indicated by stippling, scale 1/2 that of Figures A-D). NUMBER 5\ 15 Certain species of Thomasomys, however, are very similar to Megaoryzomys. The three largest species of Thomasomys that we examined {aureus, praetor, and princeps) show a particularly strong resemblance to Megaoryzomys. (The skull of T. aureus is not aberrant within Thomasomys, although Hooper and Musser (1964) regarded the phallic characters of T. aureus to be unlike those of other Thomasomys.) In Table \, Megaoryzomys consistently differs from these three species of Thomasomys only in the size and number of palatal foramina. The strongly constricted interorbital region, the short and narrow palate, and the large teeth are partic- ularly diagnostic characters of large species of Thomasomys that are also shared with Megaoryzo- mys, leaving little doubt that Megaoryzomys is a member of the tribe Thomasomyini. Reig (1980:263) has advocated merging the thomaso- myine and oryzomyine groups, but we follow the more widely accepted arrangement at least for the present, because of the closer relationship of Thomasomys and Rhipidomys (the only other genus of living thomasomyine) to each other than to any oryzomyine. The skull of Megaoryzomys resembles that of the larger species of Thomasomys and differs from that of Rhipidomys in its deeper depression along the sagittal suture of the frontals, its strongly con- stricted interorbital region (except in R. venezu- elae) , its narrow palate (except in R. venezuelae), its larger teeth, and its more rounded, less laterally expanded dorsolateral ridge of the braincase (ex- cept in R. venezuelae). Meanwhile, we can find only two characters in which Megaoryzomys resem- bles Rhipidomys more than Thomasomys, namely their shorter, deeper rostrum and their more an- gular (less-domed) braincase. The truncated, deep rostrum of Megaoryzomys and Rhipidomys is closely approached, however, by an adult and an immature specimen of Thomasomys praetor (CMNH 19255, 19256). It is unfortunate that we do not as yet have a baculum of Megaoryzomys, as its morphology in neotropical cricetines appears to have taxonomic value at both the tribal and generic levels (Hooper and Musser, 1964). We feel that Megaoryzomys is different enough from other thomasomyines to maintain its status as a separate genus, although the name Megaoryzomys is an infelicitous choice for a member of the Thomasomyini. Systematics Order RODENTIA Superfamily MUROIDEA Family MURIDAE Subfamily CRICETINAE Tribe THOMASOMYINI OsTEOLOGiCAL DIAGNOSIS.—Small to large cri- cetine rodents that differ from other tribes of Cricetinae in having the following unique com- bination of characters: (1) short palate, (2) molars pentalophodont (fide Hershkovitz, 1962, 1967), (3) molars medium-sized to large relative to size of skull. Genus Megaoryzomys Lenglet and Coppois, 1979 Megaoryzomys Lenglet and Coppois, 1979. TYPE-SPECIES.—Megalomys curioi Niethammer, 1964. AMENDED DIAGNOSIS.—Large thomasomyine rodents that differ from Thomasomys and Rhipido- mys in possessing the following unique combina- tion of characters: (1) very large size (condylo- basal length of skull more than 50 mm, zygomatic width more than 30 mm, crown length of upper molars more than 9 mm, length of dentary with- out incisor more than 30 mm, crown length of lower molars more than 10 mm), (2) deep de- pression along median suture of frontals (shared with certain species of Thomasomys), (3) palatal foramina large and numerous, (4) zygomatic plate of maxilla very wide, (5) zygomatic process of squamosal joining braincase at more obtuse angle, (6) braincase more rectangular (parietals flatter, less domed) in posterior aspect, (7) poste- rior margin of interparietal straight, (8) molars planar. Megaoryzomys curioi (Niethammer, 1964) FIGURES 3-11 Megalomys curioi Niethammer, 1964:596 [original descrip- tion]. Megalomys spec. nov.—Abs et al., 1965:53. Megaoryzomys curioi.—Lenglet and Coppois, 1979:635 [generic re-assignment]. 16 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY FIGURE 9.—Skulls of Megaoryzomys curioi from Isla Santa Cruz in dorsal and ventral aspects: A, USNM 284199; B, USNM 284318. HOLOTYPE.—Left maxilla with M'~", BM(NH) 67.1649 (Modern Mammal Section). PARATYPES.—A partial humerus and a partial scapula, collected with the holotype and bearing the same catalog number. DISTRIBUTION.—Isla Santa Cruz, Galapagos, Ecuador. See Figure 2 for a map of localities. AGE.—Quaternary. Probably both Pleistocene and Holocene, but absolute age determinations are not available for sites containing Megaoryzomys. DIAGNOSIS.—As for the genus. Discussion Zoogeography: Our removal of Megaoryzomys from the tribe Oryzomyini and its placement in the Thomasomyini necessitates a reassessment of its zoogeographic implications. By showing that Megaoryzomys is not closely related to Megalomys, a genus actually confined to the West Indies, Me- gaoryzomys can no longer be used as evidence for the supposed high degree of faunal resemblance between the terrestrial vertebrates of Galapagos and the West Indies, an idea championed by Niethammer (1964) and many other authors, nor can one refer any longer to "the present relict Caribbean and Pacific distribution of the [giant oryzomyine] group" (Hershkovitz, 1970:794). Thus the following statements of Miiller (1973:114) are untenable because of reliance on erroneous systematic conclusions. The genus Megalomys was previously known only ... in the Antilles. . . . The range is therefore a relict range indi- cating a wider distribution in former times. The fact that the Galapagos form differs very little from those of the Antilles indicates that the Galapagos populations probably reached those islands during the Pleistocene. Steadman (in press) has shown that proposed West Indian affinity for terrestrial organisms in Galapagos is illogical in light of the approxi- mately synchronous emergence of the Galapagos and the Panamanian land bridge. Whereas the supposed occurrence of Megalomys in Galapagos is not supported on either a morphological or a zoogeographical basis, the relationship of Megao- ryzomys to Thomasomys in fact fits perfectly into the biogeographical conclusions of Porter (1976), who refuted any supposed relationships between the floras of Galapagos and the West Indies and stated (p. 745): "The geographical evidence is overwhelming that the indigenous Galapagos flora has been derived almost totally from South America, most probably from the Andean re- gion." NUMBER 51 17 CM FIGURE 10.—Left dentaries in lateral aspect: A, Thomasomys aureus, female, USNM 194827; B, Nesoryzomys swarthi, male, CAS 2561, Isla Santiago; c, Megalomys desmarestii, Leiden Museum ''a," Martinique; D, Megaoryzomys curioi, USNM 284290 (reversed). Thomasomyine rodents are characterized by Hershkovitz (1972:386) as being closely related to, but less diverse than, the oryzomyines. Some of its species are the most primitive of living my- omorphs. The forms of Thomasomys are mainly terrestrial- scansorial. Others, especially those of the thomasomyine genus Rhipidomys, are specialized for arboreal life. Within the Thomasomyini, Megaoryzomys has its closest living relatives in the larger species of Thomasomys, a genus of approximately 27 species confined to South America between 8°N and 35°S latitude (Patterson and Pascual, 1972), where they inhabit forests from approximately 1200 to 4000 m elevation. None of the living species of Thomasomys inhabits coastal areas; how- ever, in proposing that a species of Thomasomys was the ancestor of Megaoryzomys, we must at- tempt to explain how such a species reached the Pacific coast of South America. No matter which of the competing scenarios for the biogeographic and geological history of northwestern South America proves to approach reality more closely (McKenna, 1981:63, 64), it would seem that a primitive thomasomyine must have been avail- able at low elevation in the right place for early, possibly even pre-Pleistocene, colonization of Galapagos. It seems very unlikely that this was accomplished through rafting for long distances down a river from the highlands and then out to sea, such as would necessarily be the case if a species of Thomasomys were to colonize Galapagos today. Instead it seems more reasonable to sup- pose that a species of Thomasomys, very likely now extinct, did indeed live in the coastal lowlands of northwestern South America in the past and drifted out to Galapagos on a floating mat of vegetation. Orr (1966:280, fig. 4) figured and briefly discussed floating mats of vegetation in the Guayas River of southwestern Ecuador, and King (1962) recorded an abundance of similar rafts in the Rio Tortuguero, a sluggish stream of low gradient in Costa Rica. Mats such as these could easily support a small population of rodents for many days. Evolution: Neither Thomasomys or Rhipidomys has a fossil record in mainland South America, so we do not know the range of morphological vari- ation in Pleistocene thomasomyines, the probable ancestral group for Megaoryzomys. 18 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY FIGURE 11.—Left dentaries of Megaoryzomys curioi in medial aspect: A, USNM 284207, Cueva de Kubler; B, USNM 284306, cave no. 1, place 2; c, USNM 284333, cave no. 5; D, USNM 284245, Cueva de Kubler. Hooijer (1959, 1966) and Husson (1960) pro- vided evidence that Thomasomys once occurred in the coastal lowlands of northern South America, where Thomasomys species is recorded in a Qua- ternary fossil site on the southern Caribbean is- land of Bonaire, near Venezuela. These specimens were more conservatively treated by Hooijer (1967:400) as "very similar to Thomasomys, to which genus it may or may not belong." The combined effects of Plio-Pleistocene uplift of the Andes and the probable altitudinal lowering of vegetational zones during glaciation (see Simpson 1975, 1979) give additional credibility to the suggestion that Thomasomys occurred at much lower elevations in the past than it does today. It may be noted in passing that the derivation of Megaoryzomys from Thomasomys, now restricted to higher elevations on the mainland, is analogous to the derivation o{Megalomys from its close main- land relative, Macruroryzomys, now restricted to the Ecuadorean Andes (Ray, 1962; followed by Hershkovitz, 1970). The large fossil vertebrate faunas of La Caro- lina, Ecuador, and Talara, Peru (Campbell, 1976, 1979, and references therein), provide evidence for the late Pleistocene existence of a more for- ested habitat than exists today at low elevations on the west coast of tropical South America. Certain birds at Talara are strong indicators of "at least a heavy scrub or riparian forest" (Camp- bell 1979:140), in an area that is extremely barren today with only widely scattered small shrubs (see figure 2 of Campbell, 1979). The wetter, more forested conditions that ex- isted during glacial times in coastal Peru and Ecuador are contrasted with apparent glacial aridity in Galapagos (Colinvaux 1972; Colinvaux and Schofield 1976a,b). The possible effects of these past arid conditions on the evolution and past altitudinal distribution of Megaoryzomys are difficult to state in our present lack of chronolog- ical control on its fossil sites. We do know that Megaoryzomys probably was widespread on Islas Santa Cruz and Isabela. Its known occurrences on Santa Cruz (Figure 2) range in elevation from near sea level to approximately 200 m, and the single record of Megaoryzomys from Isabela (Figure 1) is at approximately 300 m elevation. This rodent therefore lived in a variety of habitats ranging from arid coastal scrub to moist highland forest. Because of the very poor preservation of bones in caves on Santa Cruz and southern Isa- bela that are above 300 m elevation (Steadman, pers. observ.), we may never know the highest NUMBER 51 19 altitudes inhabited by Megaoryzomys. The species of Thomasomys are strictly forest-dwellers, and so it may be that Megaoryzomys did not occur in the open areas of the highest regions of Santa Cruz and Isabela, where the vegetation is variously dominated by the shrub Miconia and a variety of ferns, grasses, and sedges (Wiggins and Porter, 1971). Gigantism frequently occurs in rodents on is- lands, and most of the differences between Megaoryzomys and Thomasomys may be due to al- lometric changes associated with an increase in size. This possibility is in harmony with the closer resemblance of Megaoryzomys to the larger species of Thomasomys than to the smaller species. Insular gigantism in rodents is generally attributed to the following causes (Sondaar, 1977; Wassersug et al., 1979, and references therein): (1) predator avoidance, (2) drift toward larger size in the absence of predators because of no need to avoid them, (3) interspecific competition with other rodents, (4) selection for larger size in the absence of larger herbivores, regardless of the presence or absence of other rodents. Some combination of any of these reasons may have been involved in the attainment of large size in Megaoryzomys. It is now apparent that Galapagos has been colonized successfully by cricetine rodents at least three different times, once by a thomaso- myine and twice by oryzomyines. The coloniza- tions that produced the endemic genera Megaory- zomys and Nesoryzomys presumably occurred much earlier than that of Oryzomys (Patton and Hafner, in press). We agree with Patton and Hafner that Nesoryzomys is best maintained as a distinct genus, at least until its relationships to mainland crice- tines are resolved. Certainly Nesoryzomys is not part of the same colonization that produced Ory- zomys bauri and 0. galapagoensis. Cabrera (1961) and Orr (1966) regarded Nesoryzomys as a subgenus of Oryzomys, although Orr (1966) cor- rectly noted that these taxa are very different in the shape of their interorbital regions and in their development of supraorbital ridges (see plate xxiii of Heller, 1904). In addition, the karyotypic data of Gardner and Patton (1976:20) showed Nesory- zomys to be "so aberrant chromosomally as to demand recognition as a full genus," whereas Oryzomys bauri was indistinguishable from 0. xan- thaeolus of coastal Peru. Gyldenstolpe (1932) and Patton and Hafner (in press) also noted that 0. bauri and 0. galapagoensis are allied to 0. xanthaeo- lus. The marked similarity of 0. bauri to 0. gala- pagoensis led Cabrera (1961) and Patton and Haf- ner (in press) to recommend their synonymy. Paleoecology: Niethammer (1964) indicated that both the Galapagos barn owl (Tyto punctatis- sima) and the short-eared owl {Asio flammeus gala- pagoensis) were responsible for the owl pellets as- sociated with the three cotypes of Megaoryzomys. These pellets contained two species of bats and four species of small rodents, but Niethammer justifiably doubted that the remains of Megaory- zomys were also the remnants of owl pellets, be- cause they represented an animal too large to be a prey item for either Tyto or Asio. Each of these owls preys heavily on rodents when available, although Tyto is much more prone to roost in caves than is Asio. Remains of Megaoryzomys also occur in caves that are not ancient roosting sites of Tyto but instead are either natural traps or simply places where Megaoryzomys died (Stead- man, pers. observ.). Thus it may be that some of the fossils of Megaoryzomys in Cueva de Kubler were not prey items of Tyto. We believe that adults of Megaoryzomys could have been prey items of Tyto punctatissima only if they were killed and eaten within the roosting cave, whereas small, young individuals of Megaoryzomys apparently were preyed upon more frequently than adults and were not necessarily taken within a cave. Extinction: The chronology of extinction of Megaoryzomys is very speculative. There are no absolute age determinations available as yet for any mammal-bearing fossil deposit in Galapagos, although this situation may be remedied soon by several radiocarbon samples (carbonized wood) from Cueva de Kubler that have been submitted for age determination. Both Nesoryzomys indefessus and N. darwini survived until 1935-1945 on Isla Santa Cruz (Eckhardt, 1972), although they are now presumed to be extinct through predation by introduced mammals or competition from the introduced black rat, Rattus rattus (Brosset, 1963; 20 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY Niethammer, 1964; Clark, 1981), which did not reach Santa Cruz until the 1930's or 1940's (Eck- hardt, 1972; Patton et al., 1975). URattus or other introduced mammals had also recently caused the extinction of Megaoryzomys, it seems inexpli- cable that such a large rodent would have escaped the notice of sailors, explorers, residents, and sci- entific collectors who have combed Santa Cruz for the past 100 years. Thus it seems likely that Megaoryzomys became extinct before the other na- tive rodents died out on Santa Cruz, even though we cannot yet assign an age to this event. We have no evidence of contemporaneity of Megaoryzomys and Rattus. Niethammer (1964) noted that the bones of Megaoryzomys from the type-locality were not in the form of owl pellets as were those of Rattus and Nesoryzomys. In addi- tion, these remains of Megaoryzomys gave Nietham- mer the impression of being older than those of the other rodents, as he stated (1964:605): "Presumably, the remains [of Megaoryzomys] were of a more remote origin than the recent pellets with which they might have been mixed by pure chance [our translation]." Megaoryzomys occurs in excavations IIB and IIC of Cueva de Kubler, where the sediments also contain bones of intro- duced Rattus and mice {Mus musculus), with much more numerous fossils of a large and small species of Nesoryzomys (probably N indefessus and N dar- wini, respectively). Although all five species of rodents may occur at the same stratigraphic levels in the unlaminated, loose cave sediments of Cueva de Kubler, the bones of Rattus and Mus are less mineralized, much lighter in color, and there- fore apparently significantly younger than those oi Nesoryzomys or Megaoryzomys (Steadman, 1981). Bones of Megaoryzomys occur commonly on the surfaces of floors of lava tubes, small rock shelters, and ledges on the walls of fissures, suggesting to us that Megaoryzomys became extinct probably within the past several centuries. The possibility of the involvement of feral dogs, cats, and pigs in the extinction of Megaoryzomys, as stated by Niethammer (1964), is also suggestive of a recent extinction. Slevin (1959:7) listed dogs, cats, pigs, and burros as the introduced mammals of Santa Cruz, exclusive of rodents. Eckhardt (1972) added goats and cattle to this list. Steadman has seen dogs, cats, rats, mice, goats, pigs, cattle, and burros on Santa Cruz from 1978 to 1981, with the first four species very common at least locally. Nearly all of these animals became established only after the initial period of human settlement on Santa Cruz, placed at early in the 20th century by Slevin (1959:108). It is not difficult to imagine how people and feral dogs, cats, rats, and pigs could devastate the population of a large rodent that evolved in the absence of mammalian pre- dators and that, like the other vertebrates of Galapagos, would not have been wary when ap- proached by an alien mammal. Rattus has lived on Isla Isabela for a longer time than on Santa Cruz; the first definite record of any rodent on Isabela is that of a specimen of Rattus taken in 1891 by G. Baur (Allen, 1892). Charles Darwin did not mention the presence of Rattus or any other rodent on Isabela during his brief visit there in 1835 (Patton et al., 1975), although he noted Oryzomys galapagoensis on San Cristobal and Rattus on Santiago. According to Slevin (1959:107) the first permanent human set- tlement of Isabela occurred in 1893 with the establishment of the villages of Villamil on the southern coast and Santo Tomas in the southern highlands. Thus 1893 is the last probable date for the establishment on Isabela of many of its feral mammals, which include dogs, cats, cattle, and burros (Slevin, 1959:7). It seems reasonable to suggest that Megaoryzomys species became extinct on Isabela within the past two centuries, unno- ticed by man. As noted by Heller (1904), the fact that no species of Nesoryzomys has been recorded living on Isabela (members of this genus occur on Santa Cruz, Baltra, Santiago, and Fernandina) strongly suggests an early colonization of Isabela by Rattus and resultant extinction of Nesoryzomys prior to any thorough scientific surveys. This suggestion has recently been confirmed by Stead- man's field work on Isabela in 1980, which pro- duced remains of a small species of Nesoryzomys as well as additional material of Megaoryzomys. This material will be treated in detail in another paper. Literature Cited Abs, M., E. Curio, P. Kramer, and J. Niethammer 1965. Zur Ernahrungsweise der Eulen auf Galapagos: Ergebnisse der Deutschen Galapagos-Expedition 1962/63, ly.. Journal fur Ornithologie, 106(1) :49-57, 2 tables. Allen, J.A. 1892. On a Small Collection of Mammals from the Galapagos Islands, Collected by Dr. G. Baur. Bul- letin of the American Museum of Natural History, 4:47- 50. Berry, R.J. 1964. The Evolution of an Island Population of the House Mouse. Evolution, 18(3):468-483, 3 figures, 7 tables. 1981. Town Mouse, Country Mouse: Adaptation and Adaptability in Mus domesticus (M. musculus domes- ticus). Mammal Review, 11(3):91-136, 10 figures, 17 tables. Brosset, A. 1963. Statut Actuel des Mammiferes des lies Galapagos. Mammalia, 27(3):323-338, plate 12. Cabrera, A. 1961. Catalogo de los Mamiferos de America del Sur, II (Sirenia-Perissodactyla-Artiodactyla-Lagomorpha- Rodentia-Cetacea). Revista del Museo Argentino de Ciencias Naturales "Bernardino Rivadavia'' e Instituto Nacional de Investigacio'n de las Ciencias Naturales, Ciencias Zoologicas, 4(2): xxn + pages 309-732, frontispiece. Campbell, K.E., Jr. 1976. The Late Pleistocene Avifauna of La Carolina, Southwestern Ecuador. In S.L. Olson, editor. Col- lected Papers in Avian Paleontology Honoring the 90th Birthday of Alexander Wetmore. Smithsonian Contributions to Paleobiology, 27:155-168, 3 figures, 2 tables. 1979. The Non-Passerine Pleistocene Avifauna of the Talara Tar Seeps, Northwestern Peru. Life Sciences Contributions, Royal Ontario Museum, 118: 203 pages, 31 figures, 12 tables. Clark, D.A. 1981. Foraging Patterns of Black Rats across a Desert- Montane Forest Gradient in the Galapagos Is- lands. Biotropica, 13(3): 182-194, 4 figures, 3 tables. Colinvaux, P.A. 1972. Climate and the Galapagos Islands. Nature, 240(5375): 17-20, 3 figures. Colinvaux, P.A., and E.K. Schofield 1976a. Historical Ecology in the Galapagos Islands, I: A Holocene Pollen Record from El Junco Lake, Isla San Cristobal. yowrW of Ecology, 64(3):989-l012, 6 figures, 5 tables. 1976b. Historical Ecology in the Galapagos Islands, II: A Holocene Spore Record from El Junco Lake, Isla San Cristobal./ouraa/ of Ecology, 64(3): 1013-1026, 3 figures, 2 plates, 1 table. Crusafont-Pairo, M., and F. Pelter 1964. Un Murine geanl fo.ssile des lies Canaries, Cana- riomys bravoi Cien. Nov., Sp. Nov. (Rongeurs, Mur- ides). Mammalia, 28(4):607-612, 1 figure. Eckhardt, R.C. 1972. Introduced Plants and Animals in the Galapagos Islands. BioScience, 22(10) :585-590, 3 figures, 1 table. Foster, J.B. 1964. Evolution of Mammals on Islands. Nature, 202(4929):234, 235, 1 table. Gardner, A.L., and J.L. Patton 1976. Karyotypic Variation in Oryzomyine Rodents (Cricetinae) with Comments on Chromosomal Ev- olution in the Neotropical Cricetine Complex. Occasional Papers of the Museum of Zoology, Louisiana State University, 49: 48 pages, 10 figures, 2 tables. Gill, A.E. 1980. Evolutionary Genetics of California Islands Pero- myscus. In D.M. Power, editor, The California Islands: Proceedings of a MultidiscipUnary Symposium, pages 719-743, 1 figure, 10 tables. Santa Barbara, Cal- ifornia: Santa Barbara Museum of Natural His- tory. Gyldenstolpe, N. 1932. A Manual of Neotropical Sigmodont Rodents. Kungliga Svenska Vetenskapsakademiens Handlingar, third series, 11(3): 164 pages, 18 plates, tables. Heller, E. 1904. Mammals of the Galapagos Archipelago, Exclu- sive of the Cetacea. In Papers from the Hopkins Stanford Galapagos Expedition, 1898-1899. Pro- ceedings of the California Academy of Sciences, third series (Zoology), 3(7):233-249, plate 23, tables. Hershkovitz, P. 1962. Evolution of Neotropical Cricetine Rodents (Mur- idae) with Special Reference to the Phyllotine 21 22 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY Group. Fieldiana, Zoology, 46: 524 pages, 123 fig- ures, 66 tables. 1967. Dynamics of Rodent Molar Evolution: A Study Based on New World Cricetinae, Family Muridae. Journal of Dental Research, 46(5) (part 1, supple- ment) :829-842, 8 figures. 1970. Supplementary Notes on Neotropical Oryzomys dimidiatus and Oryzomys hammondi (Cricetinae).yowr- nal of Mammalogy, 51 (4): 789-794, 2 figures, 2 tables. 1972. The Recent Mammals of the Neotropical Region: A Zoogeographic and Ecological Review. In A. Keast, E.G. Erk, and B. Glass, editors. Evolution, Mammals, and Southern Continents, pages 311-431, 16 figures, 6 tables. Albany: State University of New York Press. Hooijer, D.A. 1959. Fossil Rodents from Curasao and Bonaire. Studies on the Fauna of Curaqao and Other Caribbean Islands, 9(35): 27 pages, 1 unnumbered figure, 3 plates, 10 tables. 1966. Fossil Mammals of the Netherlands Antilles. Ar- chives Neerlandaises de Zoologie, 16(4):531, 532. 1967. Pleistocene Vertebrates of the Netherlands An- tilles. In P.S. Martin and H.E. Wright, Jr., editors. Pleistocene Extinctions: The Search for a Cause, pages 399-406, 1 figure. New Haven: Yale University Press. Hooper, E.T., and G.G. Musser 1964. The Glans Penis in Neotropical Cricetines (Family Muridae) with Comments on Classification of Muroid Rodents. Miscellaneous Publications, Museum of Zoology, University of Michigan, 123: 57 pages, 9 figures, 2 tables. Husson, A.M. 1960. De Zoogdieren van de Nederlandse Antillen. [Mammals of the Netherlands Antilles.] Uitgaven van de Natuurwetenschappelijke Werkgroep Nederlandse Antillen, Curasao, 12: 170 pages, 27 figures, 42 plates, tables. [In Dutch; English summary on pages 143-170.] Hutterer, R., and U. Hirsch 1979. Ein neuer Nesoryzomys von der Insel Fernandina, Galapagos (Mammalia, Rodentia). Bonner Zoolo- gische Beitrdge, 30(3-4):276-283, 3 figures, 1 table. King, W. 1962. The Occurrence of Rafts for Dispersal of Land Animals into the West Indies. Quarterly Journal of the Florida Academy of Sciences, 25(l):45-52, 1 table. Lenglet, G., and G. Coppois 1979. Description du crane et de quelques ossements d'un genre nouveau eteint de Cricetidae (Mam- malia-Rodentia) geant des Galapagos: Megaoryzo- mys (gen. nov.). Bulletin de I'Academic Royale de Belgique (Classe des Sciences), fifth series, 65 (ll):632-648, 7 figures, 2 plates, 5 tables. McKenna, M.C. 1981. Early History and Biogeography of South Amer- ica's Extinct Land Mammals. In R.L. Ciochon and A.B. Chiarelli, editors, Evolutionary Biology of the New World Monkeys and Continental Drift, pages 43-77. New York and London: Plenum Press. Muller, P. 1973. The Dispersal Centres of Terrestrial Vertebrates in the Neotropical Realm. Biogeographica, 2: 244 pages. The Hague: W. Junk. Musser, Guy G. 1981. The Giant Rat of Flores and Its Relatives East of Borneo and Bali. Bulletin of the American Museum of Natural History, 169(2) :67-176, figures 1-40, tables 1-16. Niethammer, J. 19(54. Contribution a la connaissance des mammiferes terreslres de I'lle Indefatigable (= Santa Cruz), Galapagos. Mammalia, 28(4):593-606, 4 figures, 4 tables. Orr, R.T. 1966. Evolutionary Aspects of the Mammalian Fauna of the Galapagos. In R.I. Bowman, editor. The Galapagos: Proceedings of the Symposia of the Galapagos International Scientific Project, pages 276-281, figures 1-4. Berkeley: University of California Press. Brus- sels: Palais des Academies. Patterson, B., and R. Pascual 1972. The Fossil Mammal Fauna of South America. In A. Keast, F.C. Erk, and B. Glass, editors. Evolution, Mammals, and Southern Continents, pages 247-309, 13 figures, 12 tables. Albany: State University of New York Press. Patton, J.L., and M.S. Hafiier In press. Biosystemalics of the Native Rodents of the Galapagos Archipelago, Ecuador. In R.I. Bowman and A.E. Levilon, editors. Patterns of Evolution in Galapagos Organisms. San Franci.sco: American As- .sociation for the Advancement of Science, Pacific Division. Patton, J.L., S.Y. Yang, and P. Myers 1975. Genetic and Morphologic Divergence among In- troduced Rat Populations {Rattus rattus) of the Galapagos Archipelago, Ecuador. Systematic Zool- ogy, 24(3):296-310, 2 figures, 7 tables. Peterson, R.L. 1966. Recent Mammal Records from the Galapagos Islands. Mammalia, 30(3):441-445, plate 25, 2 tables. Petronio, C. 1970. I Roditori Pleistocenici della Grotta di Spinagallo NUMBER 51 23 (Siracusa). Geologica Romana, 9:149-194, 28 figures, 6 plates, tables. Porter, D.M. 1976. Geography and Dispersal of Galapagos Islands Vascular Plants. Nature, 264(5588): 745, 746, 2 tables. Ray, C.E. 1962. Oryzomyine Rodents of the Antillean Subregion. 356 pages, 30 figures, 41 tables. Doctoral disser- tation, Harvard University, Cambridge, Massa- chusetts. Ray, C.E., and F.C. Whitmore, Jr. 1973. Paleontology. In T. Simkin, W.G. Reeder, and C. MacFarland, editors, Galapagos Science: 1972 Status and Needs, pages 67, 68. Washington, D.C. [Printed for the Smithsonian Institution; sponsored by the National Science Foundation and the University of Wisconsin.] Reig, O.A. 1980. A New Fossil Genus of South American Cricetid Rodents Allied to Wiedomys, with an Assessment of the Sigmodontinae. Journal of Zoology, London, 192 (2): 25 7-281, 4 figures, 2 tables. Simpson, B.B. 1975. Pleistocene Changes in the Flora of the High Tropical Andes. Paleobiology, 1(3): 273-294, 20 fig- ures, 5 tables. 1979. Quaternary Biogeography of the High Montane Regions of South America. In W.E. Duellman, editor. The South American Herpetofauna: Its Origin, Evolution, and Dispersal. Monograph of the Museum of Natural History, University of Kansas, 7:157-188, 8 figures. Slevin, J.R. 1959. The Galapagos Islands: A History of Their Explo- ration. Occasional Papers of the California Academy of Sciences, 25: x -I- 150 pages, 31 figures. Sondaar, P.Y. , 1977. Insularity and Its Effect on Mammal Evolution. In M.K. Hecht, P.C. Goody, and B.M. Hecht, editors, Major Patterns in Vertebrate Evolution, pages 671-707, 10 figures, 1 table. New York: Plenum Press. [NATO Advanced Study Institutes series, volume 14.] Steadman, D.W. 1981. Vertebrate Fossils in Lava Tubes in the Galapagos Islands. In B.F. Beck, editor, Proceedings of the Eighth International Congress of Speleology, Volume II, pages 549, 550. Americus: Georgia Southwestern Col- lege. In press. The Origin of Darwin's Finches. Transactions of the San Diego Society of Natural History, 19. Thomas, O. 1905. Suggestions for the Nomenclature of the Cranial Length Measurements and of the Cheek-Teeth of Mammals. Proceedings of the Biological Society of Washington, 18 (34): 191-196, I figure. Varona, L.S. 1974. Catalogo de los Mamiferos Vivientesy Extinguidos de las Antillas. 139 pages, map. Havana: Academia de Ciencias de Cuba. Walker, P.L. 1980. Archaeological Evidence for the Recent Extinction of Three Terrestrial Mammals on San Miguel Island. In D.M. Power, editor. The California Is- lands: Proceedings of a Multidisciplinary Symposium, pages 703-717, 4 figures, 5 tables. Santa Barbara, California: Santa Barbara Museum of Natural History. Wassersug, R.J., H. Yang, J.J. Sepkoski, Jr., and D.M. Raup 1979. The Evolution of Body Size on Islands: A Com- puter Simulation. The American Naturalist, 114(2):287-295, 4 figures. Wiggins, I.L., and D.M. Porter, editors 1971. 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