.THE EVJlJ:iUJJONAEY'' lIISTQRY _ <->e:>--. c::s <:> �� op· "-THE ; <:::><::> º <> 4-,.. by Osvaldo A, Reig Thesis presented fer the degree of Doctor of Philosophy in the.University of London Novcmber 1972 ) UNTVF.Rf;f'l'Y oo?J COLU�OE 1,0:,; Lltllt,\ RY ------------------------------~···--·-~--..--·_...---····..,-·"·•·-- • -1 - • • • • • • ''If a man will begin with certainties, he shall end in doubts; but if he will be • • • content to begin with doubts, he shall • end in certainties. '' Francis Bacon; The Advancernent • ' of Learning, I. Y. 8 . • • • ' -2- TABLE OF CONTENTS Abs tra.ct . .................................. - .. 1 • Acknowledgemen ts ••••............•...•...•.•.•.. Z. Introduction ................................... 3. Material and methods •...•.......•.•.•••.••..••• 4. The classification of the Cricetida~ ••.•.•..••. S. The structure of the molar teeth of the Cricetidae and the nomenclature of their enamelled components .••..••.••.•......•.•.....• 6. Stra tigraphy . ................................. 7. Systematics .................•.................. 7.1. Tribe Oryzomyini, Vorontzov •••.••••.••••. 7.1.1. Genus Nectomys, Peters .••...•.•.••.•• 7.2. Tribe Akodontini, Vorontzov .•...•...•...• 7.2.1. Genus Bolomys, Thomas .........•...... 7.2~1.1. The living species of Bolomys .••• 7.2.1.2. The fossil remains of Bolomys .••• 7.2.2. Genus Dankomys, n. gen ..•.....•.••••• 7. 2. 3. Genus Akodon, Meyen ...•..•..· ....•..•• 7.2.3.1. A reassessment of the genus Akddon and its subgenera •••.•...• 7.2.3.2. The fossil representatives of . the genus Akodon .................. 7.3. Tribe Scapteromyin1, new name •.••..•••••• 7.3~1. Genus Scapteromys, Waterhouse ...••••. 7.3.2. Genus Kunsia, Hershkovitz .•.•.•.•.•.• 7.4. Tribe Wiedomy1n1, new tribe .•..•..•.•..•• 7.5. Tribe Phyllotini, Vorontzov •..••.....•.•• 7.5.1. Genu~ Phfllotis, Watrehouse ..••.••.•• 7. 5. 2. Genus· ·E11gmodon tia, Cuvier .•....•.••• 7. 6. Tri be Si"gmodontini, Vorontzov ..•.•.•.•.•. 7.6.1. Genus Reithrodon, Waterhouse ......•.• 7.7. Note on a small collection of Cricetids from the Pleistocene of Bolivia .••....•.• 8. Bios tra tigraphy. •..••.•...•.•...•..•........••••, 9. The origin and the evolutionary history of the Sigmodontinae •••••.•••.•••••••••.•••••••••• 1 O. Conclus ions .•.••.•••••••.•••••.•••....••...••.• 11 . Bi b 1 i o gr a p hy . • . • . .. 3- • .. • • ABSTRACT. , • The family Cricetidae is represented in thc prescpt • South American fauna by 44 genera and 179 species, amounting • to about 20% of thc living specics of mamrnals of this continent • • The overwhelming majority of these genera and species are South • • • Amorican endemics. The most widcly accepted hypothesis maintains that this impressive divcrsification took place in South Amcrica from a North American ernigrant stock that entered South America by thc Upper Pliocene as a part of the mass·i ve migration of Nearctic mammals following the establishment of the Panamanian land bridge. Recently, another hypothesis was proposed, which - • advocates an earlier arrival of the cricetids into South America • • -· • •• To test these alternative views, this study surveyed • the pattern of diversification of the South American cricetids; described a new and extensive fossil collection, mostly from the Plio~Pleistocene sequence of the Buenos Aires Province, Argentina, and explored the phylogenetic relationships and the major classification of the group. • lt litas found that the South American cricetids belong • mostly to a distinct subfamily, the Sigrnodontinae. The 41 • genera and 176 species of this subfamily can be grouped into • seven clearly distinguishable tribes. One of them, the Oryzo~ ' . myini, cornprises very primative cricetids, comparable to thc • Oligocene and Early Miocene cricetodontines of the Northern • Hemisphcre. Nineteen fossil taxa are describcd, among which therc are eleven new species and two new genera. Thc earliest known fossil record of the Sigmodontinae is lower Late Pliocene, ~fontcherrnosian agc. By thosc times, the living genera Bolomrs, - and phyllot,is wcre already full-fledgcd, the latter rcprescnted • -4- by an advanced species of the subgenus Auliscomys. In thc immediately overlying, late Plioceno Chapadmalalan stagc, other living genera and subgenera were found. The Early Pleistocene fossil forms belong mostly to extinct species rélated to living ones. From the Middle Pleistocene onwards, the living ~pecies predominate. One species is found in the whole sequence from the latest Pliocene to the Recent. The modern character of the Upp~r Pliocene and Lower Pleistocene South American cricetid faunas, suggests an older in situ evolution of the Sigmodontinae than the fossil record indicates. The hypothesis holding that the cricetids are rather modern invaders in South America, is rejected as inconsistent with modern character of the Late Pliocene and Early Pleistocene fossils, and with the pattern of tribal, generic and specific diversification of the group in the living fauna. The origin of the Sigmodontinae is considered as dubious. The tentative hypothesis is advanced that they probably differ­ entiated in South America from a cricetodontine ancestor, which entered the continent as a waif immigrant probably by Early Miocene times. This type of immigration is widely accepted for South American monkeys, caviomorph rodents and sorne procyonids. The absence'of Sigmodontinae in the known deposits of thc Miocene and Early and Middle Pliocene of South America can be explained by sampling bias. It is suggestcd that by those times thc representatives óf this subfamily evolved in areas of South America/~~{ggrto have not yielded an adequate fossil record of the history of mammals. As regards the gcographical provenance of tho early sigmodontinae stock, this is considered to be an open question. It is suggested that they might have originated eithcr in North American or in African cricetodontincs, so far not discovcred. -- -- -- -- --- ------ -s- .Fig. 1. Diagrrun of the relativa distribution or the major truca ot mamrnals ot the living South American fauna (Data after Cnbrern, 1961, modified by the author's revisions.) -6- 2.3% - 9.40/o -7- 1. ACKNOWLEDGEMENTS. This work could not have been accomplished without the assistance of several pcoplc and institutions. I am particularly indebted to Dr. Kenneth A. Kermack, whose under­ standing, advice and personal efforts madc my studies possible and to the Head of the Department far the use of the facilities of the Department of Zoology of University College London. Mrs. Frances Mussett and Miss Patricia Lees, of the same Department assisted my work in many ways, and Mrs. Doris Kermack contributed· with. her hospitality to myself, my wifc and family, to make the time I spent in London pleasant and intéresting. The John Simon Guggenheim Memorial Foundation was my main financial support for my work in London. I had the privilege to be awarded a Guggenhcim Fellowship far a second time, and the assistance of the J.S. Guggenheim Memorial Foundation is gratefully acknowlcdged. The Organisation of the American States' Programme in Genetics, and the Venezuelan CONYCIT, which also contributcd to give partial support to my work, also deserve a special mention of acknowledgement. I also wish to acknowledge my great indebtedness to the various colleagues who have loaned me the foosil specimens dcscribed in this ·paper. Galileo J. Scaglia made a special con­ tribution by concentrating his efforts as a.n outstanding collcctor to search for most of the material now available to me. Rosendo Pascual, of the Museo of La Plata; José Bonaparte, of thQ Instituto Miguel Lillo of Tucumán; and Robert Hoffstetter, of the Musée d'Histoire Naturelle de Paris, kindly made available the specimens in the collcctions in their care. I am also gratcful to the curators of the various museums who have helped me in my studies of the living cricetids. -8- Most of my work on thc living fauna of South American micc was based on the collcctions of the British.Museum of Natural History, where Dr. Gordon B. Corbet, Mr. John E. Hill and Mrs. J. Ingles gave me the neccssary facilities to study the extcnsive collections of this institution. My work at thc Unitcd States National Museum was made possible thanks to the efforts of Dr. Ch. O. Handlcy, who kindly obtained forme a Smithsonian Research Grant allowing me to spend sorne weeks working at Washington. Dr. Sydney Andcrson and Dr. R. van Helder, of the American Museum of Natural History helped on several occasions by giving me access to the rich collections under their care. Avelino Barrio, Martha Piantanida and Marino Tia responded prornptly to rny need of specimens from the collect­ ion of the Department of Biological Sciences of thc University of Buenos Aires, and so did Dr. James Patton in sending merare specimens from the collection of the Museum of Vertebrate Zoology ·at Berkeley, Dr. F. Petter doing the ,same for specimens in the Musée d'Histoire Naturelle de Pris; and Dr. J. Crespo and Dr. J. M. Gallardo, in mailing to me specirnens from the collect­ ion of mammals of the Museo Argentino de Ciencias Naturales "Bernardino Ri vadavia". Dr. Knox Jone·s and Dr. Robert Hoffmann perrnitted the study of several specirnens in the Muscum of Zoology of the University of Kansas. Moreover, much of my present expcrience with living cricetids was acquired whilst spending almost five years in charge of the collection of mammals of the Instituto of Tropical Zoology at the Central University of Venezuela, where I was