My topic — the relationships, origin and dispersal of hystricognathous rodents — is complicated by a very considerable amount of confusion among authors as to what should be included in the Suborder Hystricognathi. This confusion results, at least in part, from the fact that simplicity of arrangment of taxa has a great appeal, but that simplicity of arrangement does not necessarily reflect either what must have been the facts of the evolution of rodents, or our less than perfect knowledge of these facts.

Whatever the origins of the members of the basic Paleocene and Eocene stocks of South American mammals (Simpson, 1950, pp. 368–373; 1978, p. 321; Patterson and Pascual, 1972, pp. 260–276; McKenna, 1981, pp. 56–70; Pascual et al, Chapter 8, this volume; Cifelli, Chapter 9, this volume), no new mammal types are known from the South American Eocene that would suggest any invasion of the continent from abroad. In the Deseadan, however, two orders appear for the first time in South America, the primates and the rodents, with no known possible South American ancestors. There is essentially universal agreement that the ancestors of the earliest known South American representatives of these orders reached that continent from abroad. Both orders (but not the suborders found in South America] are well known from the Paleocene and Eocene of the northern continents.

Journal Article Functional Anatomy Get access Chordate Structure and Function, by A. J. Waterman B. E. Frye K. Johansen A. G. Kluge M. L. Moss C. R. Noback I. D. Olsen G. R. Zug. The Macmillan Co., New York; Collier-Macmillan Ltd., London, 1971, 587 p., illus., $12.95 (74-107055). Albert E. Wood Albert E. Wood Professor Emeritus Amherst College, Amherst, Mass. Search for other works by this author on: Oxford Academic Google Scholar BioScience, Volume 21, Issue 11, June 1971, Page 549, https://doi.org/10.2307/1295853 Published: 01 June 1971

The deciduous premolars of eight genera of North American Tertiary camels, together with those of Recent Lama and Camelus, are described and illustrated, and those of four other fossils are discussed on the basis of the literature. The last deciduous premolars were already fully molariform by the middle Oligocene, the earliest described. There is a progres- sive trend for the molarization to extend forward, but there is never as much molarization as there is in the related oreodonts (Family Merycoidodontidae). Although the posterior milk teeth became molariform, this was achieved in a manner different from that of the permanent molars, and there is no strict homology between parts, although the same terminology should be used for all molariform teeth. The end stage of evolution of the deciduous premolars is represented in Recent camels, where dP2 has been lost.

Four localities northwest of Deer Lodge, Montana, produce Arikareean early Miocene fossils of the Tavenner Ranch Local Fauna. A fifth, with apparently identical lithology, has produced two specimens of Oligocene aspect, one tentatively identified as Leptomeryx, which, while predominantly Oligocene, is also Arikareean. Eutypomys montanensis, new species, is more advanced than the previously known (Oligocene) members of the family and could readily be Arikareean. The relationships of the Eutypomyidae are discussed. The family is still considered to be more closely related to the beavers than to any other rodents.

Revision of the mammals from the type area of the lower Eocene Lysite is possible on the basis of three collections in the Amherst Museum. Addi- tions to the known fauna include the rodent, Leptotomus; the creodonts Thryptaco- don, Anacodon and Prolimnocyon; the uintathere, Probathyopsis; the pantodont, Coryphodon; and the artiodactyl, Diacodexis. Sufficient material is at hand to per- mit a statistical analysis of two genera, Hyopsodus and Hyracotherium, which shows that the morphologic characters heretofore used to characterize species are generally individual variants, and that not more than three species of Hyopsodus and two of Hyracotherium are present. Two new species are described: Thryptacodon loisi and Probathyopsis lysitensis.

Unworn cheek teeth of Pedetes are made up of two high-crowned lobes, apparently composed of two cusps each, except for the anterior lobe of the lower premolar, which is multicusped. After wear the lobes unite lingually in the upper teeth and buccally in the lowers. The tips of the crowns appear to have enamel-free areas. No cement is present on the crowns of teeth that have not quite come into use. The premolars seem as high-crowned as the molars, and it is not clear whether the premolars are permanent or deciduous. The only other rodents with similar tooth patterns are the North American Oligocene to Recent Geomyoidea ( Heteromyidae and Geomyidae), Griphomys from the Eocene of California and the European Miocene eomyid Bitteneria, all of which are sciuromorphous. It is suggested that the hystricomorphous pedetids may represent a highly aberrant offshoot of Asiatic early eomyids or of unknown relatives of Griphomys, paralleling the geomyoids in many respects.

EvolutionVolume 19, Issue 1 p. 115-130 ArticleFree Access GRADES AND CLADES AMONG RODENTS Albert E. Wood, Albert E. Wood Biology Department, Amherst College, Amherst, MassachusettsSearch for more papers by this author Albert E. Wood, Albert E. Wood Biology Department, Amherst College, Amherst, MassachusettsSearch for more papers by this author First published: March 1965 https://doi.org/10.1111/j.1558-5646.1965.tb01696.xCitations: 62AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume19, Issue1March 1965Pages 115-130 ReferencesRelatedInformation

Upper milk molars of oreodonts, hitherto not adequately known, are described for the genera Merycoidodon, Promerycochoerus, Merychyus, Cyclopidius, and Hypsiops. General and sometimes specific differences show up clearly in these teeth. The milk teeth do not support the transfer of Merycoidodon gracilis to Miniochoerus. The patterns of the milk teeth are in accord with the phylogenetic tree given by Thorpe. The milk molars apparently are all replaced at or near the same time, and after all the permanent molars have erupted. There is progressive molarization of the deciduous molars.

Unworn teeth are figured and described for Anomalurus, Petromus and Thryonomys, and partly worn teeth for Pedetes. Anomalurus has five-crested teeth, although the teeth of the related Anomalurops have only four. It is impossible to determine which is the primitive number, and hence the ancestry of the family is uncertain. Petromus has four-crested teeth. The upper teeth of Thryonomys are four-crested; the lower molars have only three crests. Both of these families seem to have had a four-crested ancestry, and probably are related at the superfamily level. The ctenodactylids also have a four-crested pattern, but otherwise do not seem close to the Thryonomyoidea. The tooth pattern of Pedetes is based on two transverse rows of two cusps each, unlike that of any other rodents. The pedetids are completely isolated.

EvolutionVolume 13, Issue 3 p. 354-361 ArticleFree Access EOCENE RADIATION AND PHYLOGENY OF THE RODENTS Albert E. Wood, Albert E. Wood Biology Department, Amherst College, Amherst, Mass.This study was assisted by grants from the National Science Foundation and from the Marsh Fund of the National Academy of Sciences.Search for more papers by this author Albert E. Wood, Albert E. Wood Biology Department, Amherst College, Amherst, Mass.This study was assisted by grants from the National Science Foundation and from the Marsh Fund of the National Academy of Sciences.Search for more papers by this author First published: September 1959 https://doi.org/10.1111/j.1558-5646.1959.tb03022.xCitations: 24 AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume13, Issue3September 1959Pages 354-361 ReferencesRelatedInformation

Journal Article Are There Rodent Suborders? Get access Albert E. Wood Albert E. Wood Search for other works by this author on: Oxford Academic PubMed Google Scholar Systematic Biology, Volume 7, Issue 4, December 1958, Pages 169–173, https://doi.org/10.2307/2411716 Published: 01 December 1958

Journal Article WHAT, IF ANYTHING, IS A RABBIT? Get access Albert E. Wood Albert E. Wood Biology Department Amherst College Amherst Mass Search for other works by this author on: Oxford Academic Google Scholar Evolution, Volume 11, Issue 4, 1 December 1957, Pages 417–425, https://doi.org/10.1111/j.1558-5646.1957.tb02913.x Published: 01 December 1957 Article history Received: 09 March 1957 Published: 01 December 1957

Journal Article A Revised Classification of the Rodents Get access Albert E. Wood Albert E. Wood Biology Department, Amherst College, Amherst, Massachusetts Search for other works by this author on: Oxford Academic Google Scholar Journal of Mammalogy, Volume 36, Issue 2, May 1955, Pages 165–187, https://doi.org/10.2307/1375874 Published: 01 May 1955 Article history Received: 24 July 1954 Published: 01 May 1955