Abstract I find a proper introduction of George Gaylord Simpson in the citation for the honorary degree of Doctor of Science which the University of Arizona awarded him in 1982. “Simpson is not only a paleonologist rare amongst his colleagues, he has made himself master of all the disciplines involved in the synthetic theory of evolution and particularly of taxonomy which makes him a great biologist. He is not only a biologist but a man of science with the widest horizon and experience.” There is not adequate space to even outline Simpson’s magnificent scientific achievements. He did within 50 years travel to every continent and every state, usually accompanied with his partner-wife, Anne Roe Simpson, who not only made significant discoveries of vertebrate fossils but read and critiqued his writing. Surely a heroic task, for Simpson authored some 800 books and articles. An event destined to have great influence on the life of Simpson occurred in 183 1. In that year the 22 year old Charles Darwin enlisted on H.M.S. Beagle to participate in a voyage that took four years to encircle the globe. Early on that voyage a stop was made in lower South America which enabled Darwin to explore parts of Patagonia and bring back a significant collection of fossils. One century and one year later the youthful Simpson followed in Darwin’s Patagonian steps and beyond them, bringing back the most important collection of vertebrate fossils yet found there. “Attending Marvels” is the delightful and informative record of that trip and remains one of his most popular books.

Abstract George Gaylord Simpson published some 21 books and monographs, 79 notes, and 271 research articles from 1925 through 1971. This primary literature totals 371 titles and 12,656 pages; 4,451 pages (35%) are devoted to mammals, and 2,363 pages (19%) are devoted to evolution. Simpson published primarily on Mesozoic and Paleocene mammals, but he also contributed significantly to the study of Eocene and Pleistocene mammals as well. Early work was concentrated on North American faunas, but interest later shifted to South America. Simpson published some 224 titles and 5,785 pages of empirical work, much of it during the first 20 years of his career. He published 109 titles and 6,675 pages of theoretical work. Research collections and museum support were important throughout Simpson’s working life. The concentration of empirical research early in Simpson’s career, with later emphasis on theoretical questions, affirms that observation and experience are important in generating ideas of lasting value.

Abstract The holotype specimen of Laopteryx prisca (YPM 1800), described by Marsh in 1881 as the cranium of a North American Jurassic bird, has been cited several times by subsequent authors as of unlikely avian identity or a possible pterosaur. Careful re-examination and illustration of the infrequently examined type specimen, and a review of the characters noted by Marsh, refute the avian identification and confirm later suspicions. A single tooth originally associated with the cranium, long thought to be lost, is also re-studied and illustrated, and is judged to be unrelated to Laopteryx .

Abstract Endocranial casts of Mesozoic mammals and of some cynodonts are reviewed. New tentative reconstructions of brains of Probainognathus and Therioherpeton are given. It is claimed that the endocast of Amblotherium is an artefact. Brains of Mesozoic mammals were lissencephalic, with no flexure, had very large olfactory bulbs, relatively extensive cerebral hemispheres diverging posteriorly, and large paraflocculi. Within this pattern two types are designated: the cryptomesencephalic type (large vermis, no dorsal midbrain exposure, and no cerebellar hemispheres) which occurs in Triconodonta and Multituberculata; and the eumesencephalic type (wide cerebellum, cerebellar hemispheres, and large dorsal midbrain exposure) which occurs in Cretaceous Tribosphenida. Overlap of the midbrain took place in individual lines of the Tribosphenida at different times during the Tertiary. If advanced cynodonts (e.g., Probainognathus and Therioherpeton) had narrow cerebellum and exposed midbrain, then both types could develop from them: the cryptomesencephalic by overlap of the midbrain by an enlarged vermis, and the eumesencephalic by acquisition of enlarged cerebellar hemispheres. If, however, the midbrain was overlapped in advanced cynodonts, then they belong to the cryptomesencephalic type. If so, the eumesencephalic type would have developed from cryptomesencephalic by secondary exposure of the midbrain and acquisition of enlarged cerebellar hemispheres. This latter is less likely, as it would involve the reduction of an already expanded vermis. The expansion of cerebral hemispheres suggests that neocortex was possibly present in all Mesozoic mammals and in some cynodonts.

Abstract The mammalian stapes is the subject of considerable investigation, but ambiguity remains with respect to the primitive condition in higher-level mammal clades and the pattern of subsequent modifications. We question the widely held belief that the strongly bicrurate, stirrup-like stapes represents the ancestral mammalian and therian state (Goodrich, 1930). The primitive stapes in the common ancestor of mammals and therapsids was probably columelliform and had a stapedial foramen for the passage of the stapedial artery. However, additional modifications are required to produce the bicrurate structure characteristic of many eutherians. Moreover, distributional evidence does not rule out the possibility that the columelliform-imperforate stapes seen in adult monotremes was ancestral for therians or a group comprising therians and monotremes.

Abstract Upper molars of two new genera and species of mammals (Falepetrus barwini and Bistius bondi) are described from rocks of Late Cretaceous age of Montana, Wyoming, and New Mexico. Although these teeth are evolutionarily advanced in being fully tribosphenic, they have combinations of characters that preclude identification of the animals that bore them as either marsupials or eutherians. A review of available dental features useful in classification of known, fully-tribosphenic mammals from the Late Cretaceous suggests the presence of four principal groups: (1) Marsupialia; (2) Eutheria; (3) “deltatheridians;” and (4) others. Groups “ 1 ” and “2” are recognized as formal taxonomic units, defined by anatomically diverse suites of derived characters. Groups “3” and “4” are recognized informally and, as a grade, dubbed “tribotheres,” mammals with tribosphenic dentitions lacking documented specializations characteristic of either marsupials or eutherians. Although group “3” may represent an evolutionary clade equivalent in taxonomic rank to marsupials or eutherians, members of group“4” (including Falepetrus and Bistius) comprise a heterogeneous conglomeration whose members have uncertain relationships to members of groups “1-3.” In addition to the evolutionary radiations of contemporary marsupials and eutherians, the tribotheres provide evidence of at least a third, if not several, broad mammalian radiations during the Cretaceous. However, available dental criteria are inadequate to allow development of a useful, phylogenetically-based classification of the tribotheres.

Abstract The genus Catopsalis Cope includes eight species (C. matthewi, C. catopsaloides, C. joyneri, C. alexanderi, C. foliatus, C. utahensis, C. fissidens, C. calgariensis) spanning Late Cretaceous through late Paleocene/early Eocene time on two continents, Asia (first two taxa) and North America (last six taxa). A cladistic analysis of dental and palatal features within the Taeniolabididae (which includes Catopsalis, Kamptobaatar, Lambdopsalis, Prionessus, Sphenopsalis , and Taeniolabis) indicates that Catopsalis is a paraphyletic taxon, composed of no fewer than five independent monophyletic groups. Taeniolabis is a monophyletic taxon, and Lambdopsalis, Prionessus , and Sphenopsalis (individually monophyletic by monotypy) together form another monophyletic group. These two clades appear to have evolved from ancestors within the paraphyletic taxon Catopsalis; accordingly, the smallest monophyletic group including all Catopsalis species also includes Taeniolabis, Lambdopsalis, Prionessus , and Sphenopsalis. C. matthewi , the most primitive member of this clade, is returned to Djadochtatherium Simpson, previously considered a junior subjective synonym of Catopsalis . The relationships demonstrated among various members of the Taeniolabididae support the hypothesis of a Late Cretaceous taeniolabidid dispersal from Asia to North America. The data additionally suggest a second dispersal event, probably in the middle to late Paleocene, in which the ancestors of the Lambdopsalis/ Prionessus/Sphenopsalis lineage dispersed from North America back to Asia.

Abstract Competitive displacement of one taxon by another in the fossil record may be indicated when: (1) an inverse correlation in diversity and, particularly, relative abundance can be demonstrated between the two groups through time; (2) aspects of their paleobiology suggest utilization of common resources; and (3) it can be shown that the two taxa evolved in allopatry prior to their sympatric association. Data from recent collections of Paleocene and Eocene mammals in the Western Interior of North America show marked inverse correlations both of generic diversity and relative abundance between multituberculates and rodents. The largest diminution in multituberculate diversity occurred in the latest Paleocene, near the Tiffanian-Clarkforkian boundary, not in the early Eocene as suggested previously. Reconstruction of diets, die1 activity patterns, locomotor habits, and body sizes of multituberculates and rodents suggests that both groups potentially utilized similar resources. The hypothesis that competitive exclusion may have played a role in the decline of multituberculates is strengthened by recent evidence that rodents evolved in Asia, immigrating to North America in latest Paleocene time. Evidence in support of alternative hypotheses employed to account for the decline and eventual extinction of multituberculates is wanting.

Abstract Although species are the basic units of many paleontological and evolutionary studies, the term “species” applied to the fossil record does not convey the same concept to all workers. Simpson’s “evolutionary species” incorporated time into the species concept, but considered each non-branching lineage as a separate species; longer lineages with more continuous fossil records may require subdivision into successional species. One’s perception of paleontological species affects, and is affected by, evolutionary philosophy and models of how new species form and evolve. For example, if species actually arise abruptly and persist for much longer periods essentially unchanged (punctuated equilibria), discrimination of paleontological species should be a relatively simple matter. Alternatively, if there is continuous change within and between successive species (gradualism), species boundaries would be nebulous, and would have to be imposed arbitrarily. We summarize our study of omomyid primates and cite other supportive evidence which suggests that, where the record is sufficiently dense, gradual evolution (requiring arbitrary boundaries) is common between species and even genera.

Abstract The fossil record of lorisiforms in Asia is currently restricted to specimens recovered from a half-dozen localities of Miocene age (13 Ma to 7 Ma) in the Siwalik Group of northern Pakistan and in related deposits of India. More than one lorisid taxon is represented in the Pakistan material, but Nycticeboides simpsoni Jacobs, 1981 is currently the only named species. A partial skeleton of Nycticeboides , although poorly preserved, possesses diagnostic lorisid synapomorphies of the auditory region and the vertebral column. The fact that Nycticeboides was a small animal is important for understanding its ecology. A primate frugivore with the M 1 dimensions of Nycticeboides should have a body weight of only about 500 g according to commonly-used regression statistics. However, if Nycticeboides was mostly insectivorous, and its molar teeth scaled to body size in the manner characteristic of highly insectivorous primates and non-zalambdodont insectivores, then it may have weighed much less than this estimate.

Abstract Work of the past fifty years, or so, has shed much additional light on the phylogeny and history of the Order Rodentia. Classical views have been challenged, and new concepts invoked, or older views rediscovered. Of these new concepts, hystricomorphy, rather than protrogomorphy, as a primitive state for rodents seems difficult to accept, and is not really new. Hystricognathy versus sciurognathy as the fundamental division of the Rodentia seems perilous if pardlelism is as important a phenomenon as is frequently suggested. The argument for multiserial incisor enamel, rather than pauciserial, as the primitive incisor kind is very persuasive, but perhaps more work is needed on Eocene rodent enamel. Punctuated equilibrium, if really a new idea, seems promising in explaining the obscure origin of most rodent groups, but gradualism is evident in many specific lines of descent in rodents. Virtually excluding temporal consideration from phylogenetic studies seems extreme, as does cladistic analysis when it excludes parallelisms and paraphyletic groups. In spite of recent work, the gap between Eocene groups such as the Paramyidae and Ctenodactyloidea, and the Oligocene and later families remains considerable, and largely unexplained. Extraterrestrial collision events in this case can hardly be regarded as pertinent for rodents.

Abstract A new species of machaeroidine creodont, Machaeroides simpsoni , is described from the Lostcabinian and Gardnerbuttean of the Wind River Formation, Natrona County, Wyoming. The sabertooth adaptation is fully developed in this species, which has a combination both of more primitive characters and a more derived sabertooth condition than in the Bridgerian species, M. eothen . Some morphological features of Machaeroides indicate that the machaeroidines are more closely allied with the oxyaenids than with the limnocyonids.

Abstract Three species of artiodactyls (Diacodexis sp. cf. D. secans, Simpsonodus chacensis [new genus and species], and Wasatchia grangeri) are reported from the San Jose Formation, New Mexico; these three and an additional four taxa (Simpsonodus sp., W. pattersoni, Bunophorus sinclairi , and Hexacodus pelodes) occur in the Debeque Formation, Colorado. The new diacodexeid genus, Simpsonodus , includes D. chacensis and W. lysitensis. Wasatchia pattersoni , new species, the most derived known species of Wasatchia , is morphologically suitable as an ancestor to Bunophorus , with which it overlaps stratigraphically. Diacodexis sp. cf. D. secans is morphologically and apparently phylogenetically intermediate between D. secans , on the one hand, and Hexacodus and Antiacodon on the other. The early Eocene record of diacodexeids is robust enough to indicate: (1) the gradual and continuous divergence of D. secans and Diacodexis sp. cf. D. secans in the mosaic distribution of derived character states; and (2) from these taxa, respectively, the gradational origin of other diacodexeids/leptochoerids and antiacodontids/homacodontids. In these instances, microevolutionary processes appear to account for the macroevolutionary pattern.

Abstract A rodent fauna was collected from three localities in the Almagre facies of the San Jose Formation, San Juan Basin, New Mexico. The fauna contains approximately 350 isolated rodent teeth, predominantly from the Sciuravidae. The taxa include Knightomys depressus, Pauromys sp., Lophiparamys debequensis, Paramys copei, Paramys excavatus, Mattimys kalicola , and two new species (Apatosciuravus jacobsi and Knightomys cf. K. minor). Microparamys reginensis has been placed in the genus Knightomys based on discovery of the upper dentition and additional specimens of lower dentition. This is the first record of Mattimys kalicola, Lophiparamys debequensis , and Pauromys in the San Jose Formation. This rodent fauna is early Eocene (Wasatchian Land Mammal Age), and correlates closely to the Lysitean “subage” based on presence of Lophiparamys debequensis and Knightomys cf. K. minor .

Abstract The fauna of the Skyline channels, West Texas, of early Duchesnean age, contains the following taxa: Simidectes magnus, Harpagolestes sp., Hyaenodon cf. H. vetus, Mahgarita stevensi, ?Leptotomus coelumensis (new species), Duchesneodus cf. uintensis , ? Hyracodon sp. indet., Amynodontopsis bodei, Protoreodon pumilus, Agriochoerus sp. indet., Leptoreodon sp., and Hendryomeryx sp. Simidectes is the most common form; this apparently is its last appearance, along with Harpagolestes and Leptoreodon . It is the first appearance of Hyaenodon, ?Duchesneodus , and Hyracodon .

Abstract The seven species of Pseudhipparion are, from oldest to youngest, as follows: unnamed species; P. retrusum; P. curtivallum , new combination; P. hessei , new species; P. gratum; P. skinneri , new species; and P. simpsoni , new species. They range from late Barstovian through latest Hemphillian in the Great Plains and the Gulf Coastal Plain. Both the phylogenetic relationships among these species and the phylogenetic position of this genus among other hipparionine horses are discussed. A notable feature of Pseudhipparion evolution is its prevailing tendency toward dwarfing. All crown dimensions except unworn height decrease through time, although analysis is complicated by the fact that sample means are larger in the Great Plains than in contemporaneous Gulf Coast samples, in keeping with Bergmann’s Rule. Rates of change in several dental measurements between various Pseudhipparion species pairs, calculated over intervals of about one million years, have a mean value of 0.11 darwins, which is equal to or greater than in other hipparionine species pairs. In P. simpsoni , the final late Hemphillian species, root formation was delayed ontogenetically, producing extremely high-crowned (incipiently hypsodont) cheek teeth and incisors. Potential crown heights are 85 mm in upper premolars and 110 mm in upper molars; and the enamel patterns are greatly simplified. Such extreme hypsodonty was attained during no more than 1.5 million years within the late Hemphillian at a rate of at least 0.58 darwins, roughly six times the normal rate of crown height increase in hipparionine horses.

Abstract New data from the middle and late Miocene Siwalik deposits of Pakistan provide accurate estimates of real temporal durations of extinct species of rhizomyid rodents. Most early rhizomyid species survive on the order of millions of years, with at least two spanning about five million years, and display apparent stasis in most characters. Average species duration for all Rhizomyidae of the Potwar Plateau is about 1.2 million years, a figure in line with other estimates for all Mammalia. Three closely related species show sharp differences in hypsodonty, while other traits remain static in each species or change slowly within the clade, on a scale above the species level. Evolution of this lineage shows at least one step in a staircase pattern, with descendants replacing ancestors, and entails an abrupt morphological change that provides a nonarbitrary definition for species boundaries. One ancestral morphotype appears to survive for a short time with its daughter species. Whereas early nonburrowing Rhizomyidae display longterm stasis, later species, some with burrowing adaptations, are shorter lived and at least one rhizomyine shows rapid, perhaps continuous phyletic change. “The time at which an evolving population became different enough from its ancestry to be called a different species cannot, even in theory, be a precise, naturally defined date unless the new, descendant species arose in a single, abrupt step.” G. G. Simpson, 1953, p. 35

Abstract Abelmoschomys simpsoni , n. gen. et sp., from the latest Clarendonian of Florida, is the earliest known species of Neotropical sigmodontine rodent. Neotropical sigmodontines initially evolved and diversified in North America in the late Miocene. This group is derived from the North American genus Copemys , and forms the sister group of the peromyscines. The Neotropical sigmodontines entered South America in the Pliocene at about the time of formation of the Panamanian land bridge. This hypothesis is supported by evidence from physiology, karyology, molecular systematics, comparative anatomy, and paleontology, and is not contradicted by parasite data. The present day diversity of sigmodontines in South America is that expected for its continental area. Taxonomic frequency rates necessary to produce the more than 200 species of South American sigmodontines as determined by the geometric growth equation range between 0.68 and 0.82 per million years. Although these rates are higher than those previously reported for Cenozoic mammals, they are comparable to rates for other muroid radiations. These high rates may account for discrepancies between divergence times calculated by the molecular clock versus the fossil record. “Is it of any interest to anyone but a mouse fancier? (The answer is yes.)” George Gaylord Simpson (1980, p. 196)

Abstract Two species of very hypsodont bovids are recorded from the middle Miocene (Astaracian/Vallesian) Beglia Formation of west-central Tunisia. They are presumed to be members of the Rupicaprini, a tribe that may have had Mediterranean origin. The Tunisian species show very early development of hypsodonty and loss of the basal pillars. The Rupicaprini are shown to have an important center of evolution in the Mediterranean region throughout the later Tertiary.