H. Thomas Goodwin

Pliocene-Pleistocene biogeographic history of prairie dogs, genus Cynomys (Sciuridae)

The genus Cynomys and both of its subgenera, Cynomys ( Cynomys ) or black-tailed prairie dogs and Cynomys ( Leucocrossuromys ) or white-tailed prairie dogs, have their earliest fossil occurrences on the Great Plains (late Blancan for the genus and early Irvingtonian for both subgenera). However, the fossil record of prairie dogs is poor prior to the late Irvingtonian. Geographic distributions of the two subgenera during the late Irvingtonian and Ranchola-brean were consistently different from Recent distributions. Cynomys ( L .) niobrarius was widely distributed across the northern and central Great Plains and commonly co-occurred with the Cynomys ( C .) new sp.- C . ( C .) ludovicianus lineage on the latter. In contrast, the Cynomys ( C .) new sp.- C . ( C .) ludovicianus lineage lived in the central and southern Great Plains, but never further north. Both subgenera, represented by C . ( L .) gunnisoni and C . ( C .) ludovicianus , lived in the southern highlands of New Mexico during Wisconsin time. The Mexican black-tailed prairie dog, C . ( C .) mexicanus , also may have lived in southern New Mexico during Wisconsin time. Biogeographic stability on the Great Plains throughout the late Irvingtonian and Rancholabrean suggests that glacial-interglacial fluctuations in climate and habitat were not sufficient to disrupt characteristic Pleistocene distribution patterns of Cynomys prior to the Holocene.

BLANCAN LAGOMORPHS AND RODENTS OF THE DEER PARK ASSEMBLAGES, MEADE COUNTY, KANSAS

Abstract A new collection of lagomorphs and rodents from the Deer Park B local fauna (l.f.) of Meade County, Kansas is described and compared with other small mammal assemblages of the Meade Basin, including the underlying Deer Park A l.f. Deer Park A was correctly assigned by Hibbard to the Blancan, bridging the gap between earlier Blancan faunas such as Fox Canyon and the late Blancan Sanders l.f. Recent fieldwork indicates that the Deer Park quarries may lie in the Rexroad Formation, rather than in the Ballard Formation as previously assumed. The geology and extinct mammalian contingent at Deer Park suggest that the lower horizon of Deer Park A was an active spring that gradually turned into a marshy environment during Deer Park B time. The rodents of Deer Park B are indicative of an open prairie ecosystem that might have been somewhat more arid than that of southwestern Kansas today.

LATE NEOGENE (LATE HEMPHILLIAN) RODENTS FROM THE PIPE CREEK SINKHOLE, GRANT COUNTY, INDIANA

Abstract Spermophilus cf. howelli, Spermophilus sp., Castor or Dipoides sp., Geomys cf. adamsi, Symmetrodontomys daamsi, sp. nov., Bensonomys hershkovitzi, sp. nov., Ogmodontomys pipecreekensis, sp. nov., and Pliophenacomys koenigswaldi n. sp. are reported from the Pipe Creek Sinkhole of Grant County, Indiana. The Geomys sample demonstrates a variable sulcus morphology of the upper incisor, suggesting it stands near the Geomys—Pappogeomys boundary. Symmetrodontomys daamsi is characterized by its short lower molars and small mandible. Bensonomys hershkovitzi has a unique m1, with an anteroconid that with little wear connects deeply with the labial cingulum, and a mesolophid. O. pipecreekensis, with relatively low dentine tracts and no enamel atoll on m1, may be related to both Ogmodontomys sawrockensis and Ogmodontomys poaphagus, although it is probably not ancestral to either of them. Ogmodontomys Hibbard is considered an endemic North American genus distinguished from Mimomys Forsyth Major on the basis of a suite of dental features, including absence of a full lamellar enamel layer on leading edges of the molar triangles. The dentition of Pliophenacomys koenigswaldi exhibits a set of features suggesting a close relationship with Pliophenacomys finneyi of the early Blancan Fox Canyon local fauna of Kansas. Together with the rhinoceros Teleoceras, the rodent assemblage collectively suggests an early Pliocene (latest Hemphillian) age for the Pipe Creek biota. This is the first report of a late Neogene rodent fauna from Indiana.

Supernumerary Teeth in Pleistocene, Recent, and Hybrid Individuals of the Spermophilus richardsonii Complex (Sciuridae)

A supernumerary distal upper molar, always expressed bilaterally, occurred in Pleistocene (one of 204) and Recent (five of 1,667) specimens of the Spermophilus richardsonii complex. Among Recent specimens with the abnormality, three of four with known provenance came from adjacent colonies with hybrids of S. richardsonii (Richardsons ground squirrel) and S. elegans (Wyoming ground squirrel). Elsewhere, the trait was rare in S. richardsonii (one of 947) and absent in S. elegans (out of 668). Affected individuals exhibited normal P3-M2, but two aberrant teeth distal to M2. Aberrant teeth exhibited a mosaic of features typical of M2, M3, and atypical of any normal tooth. The trait was inferred to be hereditary.

Taphonomy of turtles in the Middle Eocene Bridger Formation, SW Wyoming

Abstract This study seeks to document and account for the distribution, abundance, and taphonomic condition of fossil turtles in a fossiliferous section of the Bridger Formation, Unit B (Early Middle Eocene of Wyoming). The following patterns were documented: (1) Fossils were non-randomly distributed stratigraphically and sedimentologically with most specimens concentrated in mudstones within a few meters above two of three widespread limestone beds. These concentrations were not artifacts of accumulations of eroded fossils on low angle slopes. (2) Fossil concentrations above limestones were widespread in the study area—tens of kilometers in at least one case. The well-exposed Black Mountain turtle layer shows a gradient in fossil density, highest to the south and lowest to the north. (3) Most specimens from fossil accumulations exhibited a similar taphonomic condition, with many shells mostly intact and unweathered, and with no skulls and few limb elements. Few elements bore predator tooth marks. Some bones in channel deposits were abraded, but most bones in fine-grained sediment were not. The largest concentrations of turtles were associated with specific layers of fine-grained sediment. These features suggest mass mortalities of turtles, and burial before many shells disarticulated.A model is presented to account for these data. In this model, a limestone forms in a shallow, basin-wide lacustrine environment. Then, a series of fluvial/lacustrine sedimentary units resulting from a large-scale episode of volcanism accumulated in the lake and buried the turtles. The volcanic event may have been the cause of death, from breathing ash-choked air, for large turtle populations in the lake/marsh environment, which were then buried early in the volcanic episode. Turtle populations evidently did not recover significantly until another shallow lake filled the basin.

HIBERNATION IS RECORDED IN LOWER INCISORS OF RECENT AND FOSSIL GROUND SQUIRRELS (SPERMOPHILUS)

Abstract Incremental dentin and associated enamel, features visible on the surface of lower incisors, were characterized for 3 species of ground squirrels (Spermophilus): Pleistocene and Recent S. elegans, Recent S. richardsonii, and Recent S. parryii. A hibernation mark was evident in incisor dentin and enamel, most characteristically as a sleeve of enamel terminating basally adjacent to medially depressed dentin with indistinct and often very fine increments. This mark was absent in juveniles but present in older animals of both sexes for at least 6 weeks after hibernation, eventually being lost through growth and wear of the incisor. Temporal association with hibernation was confirmed from specimens of S. richardsonii with known dates of hibernation. Parturition and onset of lactation were usually associated with reduction in thickness of dentin increments but could not be recognized unambiguously. Combining wear stage of cheek teeth with the presence and location of the hibernation mark allowed placement of many specimens into age and season categories at time of death (young of year, early-season adults, and late-season adults). Examination of lower incisors of Pleistocene S. elegans from Porcupine Cave in central Colorado showed that hibernation was recorded in fossils and confirmed the utility of event-anchored incremental dentin in elucidating taphonomic questions.

LOWER INCISORS OF PRAIRIE DOGS (CYNOMYS) AS BIORECORDERS OF HIBERNATION AND SEASON OF DEATH

Abstract Incremental dentin and associated enamel, features visible at the surface of lower incisors of rodents, may chronicle important life-history information. This study investigated surface features of lower incisors representing 4 taxa of prairie dogs (Cynomys) in relation to hibernation and season of year. A set of abnormalities in dentin and enamel, observed on 20 of 138 incisors, always chronicled an event ending in late winter or early spring and was interpreted as a hibernation mark. Hibernation was recorded in the incisors of obligate hibernators, C. leucurus and C. gunnisoni, as well as in 20% of specimens of the facultative heterotherm, C. ludovicianus, with relevant winter growth record. Inspection of prairie dog incisors from museum collections elucidated patterns in the timing of spring emergence across species, sexes, and elevations. Growth rates of prairie dog incisors (estimated from thicknesses of circadian dentin increments) showed general seasonal patterns when pooled by sex and species, but daily growth rates recorded along individual incisors often fluctuated idiosyncratically through time. However, incisors that chronicled a significant temporal trend in daily growth rate registered either early-season (increased growth rate through time) or late-season growth (decreased growth rate through time). None of 11 late-Pleistocene fossil C. niobrarius churcherii exhibited a hibernation mark, but 4 of these exhibited significant decrease in growth rate along their incisors, probably indicating animals that died late in the active season.

Hibernation and Overwinter Body Temperatures in Free-Ranging Thirteen-Lined Ground Squirrels, Ictidomys tridecemlineatus

Abstract Free-ranging, juvenile thirteen-lined ground squirrels (Ictidomys tridecemlineatus) in southwestern Michigan were fitted in late summer or fall with external skin-temperature loggers. Data were obtained the following spring for five males and three females. During the heterothermal period, all squirrels exhibited 11–22 prolonged (  =  9.4 d) torpor bouts punctuated by typically brief (  =  14.3 h) arousal bouts, with mean monthly torpor bouts becoming longer and deeper until Feb. and reversing thereafter. Torpor-bout duration increased as minimum skin and soil temperatures decreased. On average, males initiated the first torpor bout later in fall, terminated the last torpor bout significantly earlier in spring and thus spent less time in the heterothermal period than did females. Three males displayed relatively short torpor bouts and long arousal bouts as they approached the end of hibernation. Squirrels gained weight variably in fall and spring, and one female lost 39% of body mass during hibernation.

Morphologically derived ground squirrels from the Borchers local fauna, Meade County, Kansas, with a redescription of ?Spermophilus cragini

ABSTRACT We provide a description of the complete adult and upper deciduous cheek dentition of ?Spermophilus cragini, previously known only from M1–M3, from the transitional Blancan–Irvingtonian Borchers locality, Meade County, Kansas. We also present evidence for two additional morphologically derived ground squirrels in the fauna. All three forms are united with the clade including Cynomys and Spermophilus, indicating early diversity in this clade on the Great Plains, but placement within the clade is less certain. ?Spermophilus cragini, the best represented of the three, is more derived in several features than known species of the subgenus Spermophilus but lacks some derived features expected in Cynomys. This fossil species resembled Cynomys in size and, likely, in biology. The other derived morphs from Borchers may belong to undescribed taxa but are too poorly represented to allow formal recognition; one (morph B) exhibits a derived structure of m3. None of the adequately known morphs from Borchers a...

Odontometric Patterns in the Radiation of Extant Ground-dwelling Squirrels within Marmotini (Sciuridae: Xerini)

Abstract I document odontometric variation across ground-dwelling squirrels of the Holarctic tribe Marmotini. Dental size, which correlates well with published average body mass values across species, accounts for most odontometric variation across the clade. Dental shape variation primarily reflects relative size of P3 (upper cheek teeth) and relative width of p4–m1 + length of m3 (lower cheek teeth). Shape variables and relative tooth crown height covary significantly across species, suggesting a common functional complex or shared genetic control. When dental morphology is mapped on published DNA-based phylogenies, Sciurotamias (Chinese rock squirrels), Ammospermophilus (antelope squirrels), and basal subgenera within Spermophilus (ground squirrels [Callospermophilus and Otospermophilus]) are shown to retain inferred primitive dental morphology—small to moderate dental size, relatively small P3, relatively narrow p4–m1 + shortened m3, and relatively low tooth-crown height. Other clades depart from this morphotype in size (very small in Tamias [chipmunks] and very large in Marmota [marmots]), tooth shape (especially 2 clades representing Eurasian and North American subgenus Spermophilus), or in both attributes (notably Cynomys [prairie dogs]), with frequent homoplasy. A plot of odontometric distance against published estimates of divergence time between sister clades suggests a roughly “clocklike” accumulation of odontometric change through time but highlights episodes of rapid odontometric evolution during the origins of Marmota, Cynomys, and Spermophilus parryii (arctic ground squirrel).