Holmes A. Semken

Spatial Response of Mammals to Late Quaternary Environmental Fluctuations

Analyses of fossil mammal faunas from 2945 localities in the United States demonstrate that the geographic ranges of individual species shifted at different times, in different directions, and at different rates in response to late Quaternary environmental fluctuations. The geographic pattern of faunal provinces was similar for the late Pleistocene and late Holocene, but differing environmental gradients resulted in dissimilar species composition for these biogeographic regions. Modern community patterns emerged only in the last few thousand years, and many late Pleistocene communities do not have modern analogs. Faunal heterogeneity was greater in the late Pleistocene.

First accelerator mass spectrometry 14C dates documenting contemporaneity of nonanalog species in late Pleistocene mammal communities

Worldwide late Pleistocene terrestrial mammal faunas are characterized by stratigraphic associations of species that now have exclusive geographic ranges. These have been interpreted as either taphonomically mixed or representative of communities that no longer exist. Accelerator mass spectrometry {sup 14}C dates (n = 60) on single bones of stratigraphically associated fossil micromammals from two American and two Russian sites document for the first time that currently allopatric mammals occurred together between 12,000 and 22,000 yr B.P. on two continents. The existence of mammal communities without modern analogs demonstrates that Northern Hemisphere biological communities are ephemeral and that many modern biomes are younger than 12 ka. Future climate change may result in new nonanalog communities.

Paleoecological and Stratigraphic Significance of the Muskrat in Pleistocene Deposits

The muskrat (Ondatra spp.), a common element in late Kansan and post-Kansan deposits, provides a valuable Stratigraphic tool for deposits of glacial age, in terms of the chronocline proposed by Semken (1966). However, specimens of interglacial age commonly appear out of sequence in the regression. In addition, the nearly ubiquitous distribution in North America of modern muskrats has precluded paleoecological interpretations other than for the presence of permanent water. Statistical analysis of 147 fossil first-lower molars of Ondatra substantiates and refines the established chronocline. Additionally, it reveals that specimens taken from deposits regarded as interglacial in age have a significantly lower length/width ratio than have those collected from deposits regarded as glacial in age. A statistical examination of 403 Recent first-lower molars from 26 of the United States and from Manitoba, Canada, indicates the following. (1) Both O. zibethicus zibethicus and O. z. cinnamonius found in southern regions exhibit a significantly lower length/width tooth ratio than do those found in northern regions. (2) The ratios, when plotted geographically, form a predictable north-south cline, which, although progressive, has a point of inflection at 42° N. lat. (Nebraska). Specimens collected to the north give a positive residual and southern specimens a negative residual to a least-squares regression. (3) O. z. zibethicus (eastern form) and O. z. cinnamonius (plains variety) are indistinguishable on dental parameters at any given latitude. In conclusion, the data suggest that the length/width ratio is a reliable tool in distinguishing between “warm” and “cool” associated members of the population. Corresponding differences in ratios in glacial and interglacial specimens support this hypothesis. The Hay Springs local fauna, as preserved in the American Museum of Natural History, probably represents a mixed collection, taken from more than one quarry, in a section where rocks of glacial and interglacial age are preserved.

Paleoecological Significance of the Short-Tailed Shrew (Blarina), with a Systematic Discussion of Blarina ozarkensis

The parapatric distributions of Recent Blarina brevicauda brevicauda, B. b. kirtlandi , and B. b. carolinensis correspond to the subhumid microthermal, humid microthermal, and humid mesothermal climatic regions. Three late Pleistocene populations of Blarina can be equated with the extant “subspecies” B. b. brevicauda, B. b. kirtlandi , and B. b. carolinensis by means of statistical analysis of mandibular parameters. All three ecotypes are found together, distinct and sympatric, in the Pleistocene deposits of Cumberland, New Paris No. 4, and Peccary Caves, whereas Meyer Cave, Crankshaft Pit, Natural Chimneys, and Welsh Cave local faunas contain two distinct phena. Coexistence of these phena in the same deposit without apparent interbreeding suggests a specific rather than subspecific relationship. Sympatry of these phena during the Pleistocene suggests that a more equable climate existed during glacial time than at present and that sympatric phena of Blarina coexisted in partitioned niches that presently are not defined. Post-glacial continental climates subsequently divided the three phena into their existing parapatric distributions. Blarina brevicauda fossilis is synonymized with B. b, brevicauda. Blarina ozarkensis , an extinct species from the Conard Fissure, is distinguished from other species of Blarina by (1) the absence of the lingual accessory cone posterior to the protoconid on the first lower unicuspid of extant species; (2) the proportionally larger and more bulbous cingula of the third and fourth upper unicuspids, the second lower unicuspid, and the lower molars; (3) its reduced fifth upper unicuspid; (4) its reduced talonid of M3. The Conard Fissure population of B. ozarkensis is more variable than any modern population of Blarina examined.

Mid-Wisconsinan stratigraphy and paleoenvironments at the St. Charles site in south-central Iowa

A sequence of loess-mantled sediments exposed along Clanton Creek provides the first evidence of fluvial, pedologic, and biotic environments before the last glacial maximum in south-central Iowa. Two fining-upward fluvial sequences, one inset into the other, are exposed. Radiocarbon ages indicate that the alluvial fills are about 34,000 yr old. Basal gravel in the oldest fill contains well-preserved mammoth ( Mammuthus ) bones. Sparse seeds from this horizon suggest weedy flood-plain conditions. The younger alluvial fill contains well-preserved pollen, plant macrofossils, and insects. The pollen is dominated by nonarboreal taxa and Pinus , suggesting a prairie border or savanna environment. Vascular-plant and bryophyte macofossils indicate a variety of aquatic and marsh environments on the flood plain. Insects are mostly sympatric in mixed conifer and hardwood forest that extends along latitude 47° to 49° between eastern North Dakota and New England, but forest beetles are rare, and the fauna is dominated by openground forms. The site is interpreted as an open flood plain dotted with marshes and oxbow lakes; it was surrounded by open woodland or savanna similar to that in north-eastern North Dakota at present. July temperatures at the St. Charles site were probably 3 to 5 C° cooler than those at present. The pre-loess stratigraphy of the site differs markedly from that of upland sites and demonstrates that correlation between upland and lowland sequences cannot be done without adequate dating.

Ancient DNA supports southern survival of Richardson's collared lemming (Dicrostonyx richardsoni) during the last glacial maximum

Collared lemmings (genus Dicrostonyx) are circumpolar Arctic arvicoline rodents associated with tundra. However, during the last glacial maximum (LGM), Dicrostonyx lived along the southern ice margin of the Laurentide ice sheet in communities comprising both temperate and boreal species. To better understand these communities and the fate of these southern individuals, we compare mitochondrial cytochrome b sequence data from three LGM‐age Dicrostonyx fossils from south of the Laurentide ice sheet to sequences from modern Dicrostonyx sampled from across their present‐day range. We test whether the Dicrostonyx populations from LGM‐age continental USA became extinct at the Pleistocene–Holocene transition ~11000 years ago or, alternatively, if they belong to an extant species whose habitat preferences can be used to infer the palaeoclimate along the glacial margin. Our results indicate that LGM‐age Dicrostonyx from Iowa and South Dakota belong to Dicrostonyx richardsoni, which currently lives in a temperate tundra environment west of Hudson Bay, Canada. This suggests a palaeoclimate south of the Laurentide ice sheet that contains elements similar to the more temperate shrub tundra characteristic of extant D. richardsoni habitat, rather than the very cold, dry tundra of the Northern Arctic. While more data are required to determine whether or not the LGM southern population is ancestral to extant D. richardsoni, it seems most probable that the species survived the LGM in a southern refugium.

Fossils of Uncertain Affinity from the Upper Devonian of Iowa

Thousands of specimens of the enigmatic fossil Gluteus minimus (new genus, newt species) occur in a 5-centimeter-thick interval within the Maple Mill Shale and in equivalent deposits of the Devonian of eastern Iowa. They are roughly lenticular. bilobed fossils up to 11 millimeters in diamiter and 8 milllimeters thic. These objects consistently asymmetrical in the same direction. defy placement in any known higher taxon when their morphology. histology, and apatitic composition considered.

Overprinting of taphonomic and paleoecological signals across the forest–prairie environmental gradient, mid-continent of North America

Abstract. Taphonomic factors may significantly alter faunal assemblages at varying scales. An exceptional record of late Holocene (<4000 yr old) mammal faunas establishes a firm baseline to investigate the effects of scale on taphonomy. Our sample contains 73 sites within four contiguous states (North Dakota, South Dakota, Iowa, and Illinois, USA) that transect a strong modern and late Holocene environmental gradient, the prairie-forest ecotone. We performed detrended correspondence (DCA) and non-metric multidimensional scaling (NMDS) analyses. Both DCA and NMDS analyses of the data sets produced virtually the same results, and both failed to reveal the known ecological gradient within each state. However, both DCA and NMDS analyses of the unfiltered multistate data set across the entire gradient clearly reflect an environmental, rather than taphonomic, signal. DCA tended to provide better separation of some clusters than did NMDS in most of the analyses. We conclude that a robust mammal data set collected across a strong environmental gradient will document species turnover without the removal of taphonomic factors. In other words, taphonomy exhibits varying scale-dependent effects.

In Quest of Great Lakes Ice Age Vertebrates

J. Alan Holman. 2001. In Quest of Great Lakes Ice Age Vertebrates. Michigan State University Press, East Lansing, 230 p. The intended audience for In Quest of Great Lakes Ice Age Vertebrates includes the general public, students, and teachers, as well as professional biologists and geologists. Despite this incredibly broad range of potential readers, Holman succeeds. The book is directed toward the student end of the above spectrum but there is something special for everyone, even those living beyond the Great Lakes region. Use of “Great Lakes” in the title, however, is somewhat misleading because the book reviews the Pleistocene of states and provinces contiguous to the western Great Lakes. Those states south of Lakes Erie and Ontario, Pennsylvania and New York, are not included The ten chapters described below are accompanied by extensive list of references, both technical and general. These arranged by individual or multiple chapters. Some are further subdivided by geography, which can complicate an author search. Two indices, one general and the other taxonomic, are well presented and there is a complete faunal list, organized by region, of fossils recovered from the area. The first six chapters are primarily for newcomers, the last four will be appreciated by all. Chapter 1, “Introduction,” is a primer for geological (e.g., uniformitarianism), biological (what is a vertebrate), and paleontological (fossil preservation) terminology. Each topic is covered concisely, frequently within a paragraph, and will assist students with interpretative aspects of the book. Chapter 2, “The Pleistocene Ice Age,” reviews the academic history of the Great Ice Age, compares chronological terms used in both North America and Europe, and illustrates the positions of the Wisconsinan ice sheet between 9.9 and 21 k. Most importantly it describes continental-scale habitat destruction inflicted by advancing ice and then the subsequent wasteland open for recolonization …