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NARROW
Abstract Multituberculates are an extinct mammalian order that lived in Mesozoic and early Cenozoic eras. Lambdopsalis , a Paleocene multituberculate recovered in China, preserves cranial remains that allow in this study: (1) a description of its skull morphology; (2) a reconstruction of its nonfossilized structures such as the cranial nerve system and major cranial vasculature; (3) an analysis of functional adaptation of its auditory system; and (4) an interpretation of phylogenetic relationships within multituberculates themselves and among other major mammalian groups. Character analysis reveals that a number of previously used cranial features in reconstructions of mammalian phylogeny are unreliable. These include premaxillo-frontal contact, exclusion of septomaxilla from face, number of infraorbital foramina, extent of orbital exposure of palatine, presence versus absence of jugal, lacrimal, and parasphe— noid, extent of cranial process of squamosal, and reduction of alisphenoid. The bulla-like structure of Lambdopsalis is the expanded vestibular apparatus, not an enlarged tympanic bulla. The expanded vestibular apparatus, flat incudomalleal joint, and absence of a well defined fossa muscularis minor in Lambdopsalis suggest that Lambdopsalis (possibly a burrower) adapted to low-frequency perception. Lambdopsalis possesses a large alisphenoid (perforated by the trigeminal foramina) and a slender “anterior lamina of the petrosal.” The discovery supports Presley's (1981) argument of close affinity between “nontherian” and “therian” mammals, and invalidates the hypothesis of fundamental nontherian/therian dichotomy. Contrary to general con— sensus, available paleontological evidence does not indicate the existence of a uniform structural pattern of the brain— case for nontherian groups. Cranial characters coupled with dental features document monophyly for nonharamiyid multituberculates. The skull morphology of Lambdopsalis shows phylogenetic unity with taeniolabidids, and invalidity of Lambdopsalidae Chow and Qi, 1978. Assuming monophyly of Mammalia, the class is divisible into a crown group and a stem group. The crown group includes all living mammals plus the fossil therians that shared the latest common ancestor with monotremes. The stem group consists of all remaining extinct mammals. Multituberculates belong to the paraphyletic stem group, and diverged from the main lineage leading to living mammals prior to emergence of the latest common ancestor of modern mammals. More intimate relations among members of the stem group remain uncertain, but are limited to but a few reasonable alternatives.
Abstract Dr. George Gaylord Simpson, one of the most important evolutionary biologists of the Twentieth Century, was born on June 16, 1902 and died on October 6, 1984. His contributions to science include not only a modern synthesis of evolutionary thought, but original research on anthropology, mammalogy, paleontology, general biology, and statistics. His prolific writings were intended for scientific and non—scientific communities alike. He helped and encouraged many who now work in the fields of paleontology and evolutionary biology. Contributors to this book dedicate their efforts as tribute to his memory. Included authors are colleagues, former students, and friends of Dr. Simpson’s. They represent but a few of the people he would have included in these categories. The book is intended to suggest only a sampling of the diversity of George Gaylord Simpson's impact on present vertebrate paleontology, from its most senior to its very junior participants. Ms. Flanagan’s letter of invitation entreated the following from potential authors: "In the spirit of Dr. Simpson’s own writings, we encourage imaginative contributions that would be just a little different from items expected in a regular scientific journal." The title of the volume (Vertebrates, Phylogeny, and Philosophy) reflects that request. Though individual articles deal almost exclusively with fossil mammals, emphases cross the spectrum of evolutionary biology, including systematic paleontology, considerations of adaptation, ontogeny, analyses of evolutionary tem— po and mode, biogeographic procedure, and paleogeography. Philip Gingerich’s contribution stresses the crucial importance of solid empirical research to the foundations upon which theoretical/philosophical writings should be based. Mesozoic and Cenozoic taxa are considered, and two articles discuss the modern union of molecular biology, genetics, and paleontology. Most articles benefited directly from the pioneering writings of George Simpson, yet the breadth of concerns of this volume covers only a small fraction of the interests exhibited in his lifetime of evolutionary research. Kathryn Flanagan served as principal correspondent with authors and reviewers. Jason Lillegraven had principal responsibility for manuscript editing and considerations of production. We take this opportunity to thank the thirty-two authors for their contributions. Similarly, more than fifty individuals served as unpaid reviewers, and we give our most sincere thanks for their generosity of time and effort. Also, we thank Linda E. Lillegraven for creating the cover design.
Late Pliocene and Pleistocene History of the Donnelly Ranch Vertebrate Site, Southeastern Colorado
Abstract Two superposed faunas were discovered in southeastern Colorado at the Donnelly Ranch vertebrate site. Sediments containing a late Blancan assemblage are unconformably overlain by sediments containing a Rancho La Brean assemblage. The pre-Nebraskan Donnelly Ranch fauna is slightly older than the Sand Draw, Broadwater, and Blanco faunas. It is younger than the Curtis Ranch fauna. Faunal and paleomagnetic correlation indicate it is about 2.5 m.y. old. Tapirus, Geoche/one , and Sigmodon indicate the climate was mild and precipitation was much more effective than at present. Savanna, plains, and marsh communities are represented by the fauna. The Sangamon Mesa De Maya fauna correlates best with the early Sangamon Cragin Quarry fauna. Mammals, molluscs, and pollen indicate that temperatures were more equable than present and precipitation may have been slightly more effective during cooler summers. The fauna consists primarily of grassland inhabitants but a marsh com— munity is represented in artesian spring sediments. The gross topographic and stratigraphic relations, sediment size analysis, fossil orientation, and sedimentary structures indicate stream, viscuous intermediate, and mudflow deposition on a low alluvial fan at the foot of Mesa De Maya. The sediment source was local consisting of basalt from Mesa De Maya, igneous, reworked metamorphic, and sedimentary rock from the Ogallala Formation, and sedimentary rock containing marine fossils from Cretaceous sediments. An artesian spring deposit consisting of predominantly silt size quartz particles was found overlying a gley soil. During the Sangamon, massive caliche formed in channel sands and nodular caliche formed in the mudflow deposits of the alluvial fan. Potassium argon dates, paleomagnetism, and topographic position and correlation indicate that Mesa De Maya is older than Fowlis Mesa and the average age for both of these basalt flows is about 3.3 million years. The Mesa De Maya flows issued from local vents and flowed nearly to the present extent of the mesa. Scarp recession has been minor since the lavas erupted. Flow direction interpreted from air photographs indicate the flows were largely con— trolled by topography and did not form an extensive sheet of lava from Mesa De Maya to Fowlis Mesa. Erosion has carved deep canyons between the lobes of the flows and has caused a reversal of topography where hills of Ogallala once stood. More than 400 feet of Ogallala and Cretaceous sediments were removed prior to deposi— tion of Pleistocene sediments. Erosion and deposition in the Donnelly Ranch area has been relatively minor since the Sangamon.
Taphonomy and Population Dynamics of an Early Pliocene Vertebrate Fauna, Knox County, Nebraska
Abstract The principal purpose of this study is to determine from geological and biological evidence how a concentration of fossil bones originated. The Verdigre quarry of earliest Pli— ocene age in the Valentine Formation, northeastern Nebraska forms the basis for the investi— gation. Some 40 genera of mammals, 7 of reptiles, 2 of amphibians, and 6 of fishes are rep— resented in a collection of over 20,000 identifiable specimens recovered from a small exca— vation in a 4-5 foot-thick lens of extremely poorly sorted, gravelly, silty, clayey sand. The open framework and textural inversion of the fossiliferous stratum indicate very rapid deposition, probably in a single flood. Preferred orientation of long bones shows that the depositional current flowed from the NNW. The site of deposition was an off-channel de— pression on a broad floodplain which was subaerially exposed (mudcracked)prior to the flood. The great majority of the fossil remains do not represent animals killed by the flood as they are completely disarticulated and often somewhat abraded, except for 7 articulated skele— tons. Stream table experiments suggest that current sorting is probably responsible for the scarcity of elements such as ribs, vertebrae, sacra, and phalanges compared with rami, meta— podia, tibiae, etc. Discrete age groups, distinguished on the basis of tooth eruption and wear.(Kurten, 1953), are present in Verdigre mammals represented by large samples. Four hundred seventy-five Mery— aodus (antilocaprid)individuals fall into 7 year-classes: one juvenile (.8 year)and 6 adult (1.8- 6.8 years). Burrs on the horns of Meryaodus males are annual but cannot be used in population dynamics studies of collections of transported remains because they are easily re— moved by abrasion. Fifty-seven Protohippus (3-toed horse)individuals fall into 3 juvenile (-.2, .8, and 1.8 years)and at least 7 adult age classes.The lack of individuals of inter— mediate ages and the large proportion of animals of reproductive age in the samples indicate that non-selective catastrophic death accounts for most, and possibly nearly all, of the dis— articulated mammal remains in the quarry. Merycodus and Protohippus at least, died in the winter –– about 2-3 months before the season of giving birth. Growth ring study of catfish vertebrae and gar scales indicates that these aquatic forms were also winterkilled. Shotwell's (1955)method of determining the proximity of various habitats to vertebrate quarry sites is not applicable to the Verdigre assemblage, and probably not to other collections, because it fails to consider e.g.: sedimentary evidence, such as indications of size-sorting the possibility different effects of catastrophic and attritional mortality on the composition of quarry faunas the great mobility of grazing mammals. There is evidence that size sorting is responsible for differences in ‘completeness’ of various mammals in Shotwell's published samples as well as in the Verdigre quarry. Sites of deposition of late Tertiary quarry faunas were in stream valleys; the interstream grassland habitat was probably rarely if ever directly sampled by depositional processes. Mass occurrences of grazing animals such as in the Verdigre bonebed are interpreted as resulting from mortalities which occurred down on floodplains at times of environmental stress. Early Pliocene vegetation in the Verdigre area resembled that of parts of the Gulf Coast of southern Texas and northern Mexico; forests occupied the broad floodplains and savannas the interfluves (MacGinitie, 1962). Crocodiles and giant land tortoises in the fauna indicate a normally frost-free climate. The presence of sharks and batoids suggests marine influence; stream gradients may have been significantly lower and the shoreline of the Gulf may have been closer to Nebraska in the early Pliocene than at present.