Pablo Peláez-Campomanes

Long-period astronomical forcing of mammal turnover

Mammals are among the fastest-radiating groups, being characterized by a mean species lifespan of the order of 2.5 million years (Myr). The basis for this characteristic timescale of origination, extinction and turnover is not well understood. Various studies have invoked climate change to explain mammalian species turnover, but other studies have either challenged or only partly confirmed the climate–turnover hypothesis. Here we use an exceptionally long (24.5–2.5 Myr ago), dense, and well-dated terrestrial record of rodent lineages from central Spain, and show the existence of turnover cycles with periods of 2.4–2.5 and 1.0 Myr. We link these cycles to low-frequency modulations of Milankovitch oscillations, and show that pulses of turnover occur at minima of the 2.37-Myr eccentricity cycle and nodes of the 1.2-Myr obliquity cycle. Because obliquity nodes and eccentricity minima are associated with ice sheet expansion and cooling and affect regional precipitation, we infer that long-period astronomical climate forcing is a major determinant of species turnover in small mammals and probably other groups as well.

Age Structure, Residents, and Transients of Miocene Rodent Communities

The age structures of two successive rodent communities are studied on the basis of a rich record from well‐dated Miocene sections (17–10 Ma) in north‐central Spain. Community age is defined as the mean of the residence times of the community members at the time of the locality age. Community ages are negatively correlated with the numbers of community members. These members are divided into residents (with continuous membership times ≥1.54 million years) and transients (with membership times <1.54 million years). During episodes of species loss, there is a preferential disappearance of transients while residents are retained, a pattern referred to as the “seniority rule.” The residents define the studied communities. They are associated with early successional stages of vegetation, and transients are associated with later stages. Under stable conditions, early arrivals in succession are “transient” and replaced by competitive later arrivals. The reversed roles of transients and residents in the studied fossil record are explained by assuming high degrees of disturbance. We view the system within the context of nonequilibrium metapopulation theory, in which competitively superior species become transients because of their dependence on ephemeral late successional habitats.

Pedogenic carbonate stable isotope record of environmental change during the Neogene in the southern Great Plains, southwest Kansas, USA: Carbon isotopes and the evolution of C4-dominated grasslands

Fossiliferous strata in the Meade Basin (southwest Kansas) preserve numerous superposed mammalian faunas and calcareous paleosols that range in age from the Clarendonian North American Land Mammal Age (NALMA; 12.0–9.0 Ma, early late Miocene) to the early Irvingtonian NALMA (ca. 2.5–ca. 1.0 Ma, early Pleistocene). Faunas from these sections document the evolution of the small mammal community of the modern grassland ecosystem of the region, and the stable isotope composition of paleosol carbonates provides a means by which the environmental context of the evolution of the modern ecosystem may be documented. We used the stable carbon isotope composition (δ 13 C relative to Vienna Peedee belemnite [VPDB]) of 194 pedogenic carbonates from 19 measured sections to reconstruct the history of C 4 grass abundance in the Meade Basin. Paleosol carbonate δ 13 C values reflect the proportion of C 3 (trees, shrubs, cool-climate grasses) and C 4 (warm-climate grasses) plants that grew in an ancient soil and provide a means with which to reconstruct past mammalian habitats. Paleosol carbonate δ 13 C values record a three-phase increase in the abundance of C 4 biomass during the Neogene in the Meade Basin. Late Miocene sections have mean δ 13 C values of −7.6‰ ± 0.90‰ (Clarendonian) and −6.5‰ ± 0.31‰ (Hemphillian NALMA, 9.0–4.9 Ma), consistent with 17% and 26% C 4 biomass, respectively. Miocene δ 13 C values from Meade are statistically identical to published δ 13 C values for Miocene paleosol carbonates elsewhere in the southern Great Plains, supporting the widespread presence of ∼20% C 4 biomass on average in the region throughout the Miocene. The abundance of C 4 biomass increased between the end of the Hemphillian section and the beginning of the early Blancan NALMA (5.0–3.0 Ma). Early and middle Blancan (3.0–2.5 Ma) carbonates have statistically identical δ 13 C values (−4.9‰ ± 0.90‰ and −5.0‰ ± 1.10‰, respectively), suggesting a stable ecosystem during the early Pliocene, although high δ 13 C variability in densely sampled intervals suggests a high degree of landscape-scale variation in C 4 abundance. The final phase, geochronologically controlled by two well-characterized ashes (Huckleberry Ridge, 2.10 Ma; Cerro Toledo B, 1.47–1.23 Ma) and magnetostratigraphy, is a trend to higher δ 13 C values from the late Blancan to early Irvingtonian (ca. 2.5–ca 1.0 Ma) from −4‰ at the base of the section to ∼1‰ at the top, corresponding to an increase from almost 50% to 65% C 4 biomass. The abundance of C 4 biomass first reaches modern levels for the region (78% ± 10.9%) around the level of the Cerro Toledo B ash, indicating that a modern-like grassland ecosystem first appeared in the region ca. 1.3 Ma, although δ 13 C values do not remain consistently high through the rest of the section.

THE EARLIEST MAMMAL OF THE EUROPEAN PALEOCENE: THE MULTITUBERCULATE HAININA

Abstract A new species of multituberculate mammal, Hainina pyrenaica n. sp. is described from Fontllonga-3 (Tremp Basin, Southern Pyrenees, Spain), correlated to the later part of chron C29r just above the K/T boundary. This taxon represents the earliest European Tertiary mammal recovered so far, and is related to other Hainina species from the European Paleocene. A revision of the species of Hainina allows recognition of a new species, H. vianeyae n. sp. from the Late Paleocene of Cernay (France). The genus is included in the family Kogaionidae Rãdulescu and Samson, 1996 from the Late Cretaceous of Romania on the basis of unique dental characters. The Kogaionidae had a peculiar masticatory system with a large, blade-like lower p4, similar to that of advanced Ptilodontoidea, but occluding against two small upper premolars, interpreted as P4 and P5, instead of a large upper P4. The endemic European Kogaionidae derive from an Early Cretaceous group with five premolars, and evolved during the Late Cretaceous and Paleocene. The genus Hainina represents a European multituberculate family that survived the K/T boundary mass extinction event.

A stratigraphical framework for Miocene (MN4-MN13) continental sediments of Central Spain

New bio- and magnetostratigraphic data from the Miocene continental sediments of Central Spain are used to update the existing stratigraphical framework. Our revised record is based on the study of more than two hundred mammal faunas, ranging from the Late Ramblian (ca 18 Ma) to the Late Turolian (ca 6 Ma).

THE PLIOCENE AND PLEISTOCENE HISTORY OF COTTON RATS IN THE MEADE BASIN OF SOUTHWESTERN KANSAS

Abstract The taxonomy and dental evolution of cotton rats, genus Sigmodon, from Pliocene and Pleistocene deposits in the Meade Basin of southwestern Kansas are examined. Prosigmodon is here subsumed under Sigmodon. Morphological and multivariate statistical analyses identify 3 Sigmodon lineages and 5 immigration events in the Meade Basin. The 1st immigration event occurred during the early Blancan and the latest during the Holocene. The analyses of dental characters indicate directional trends in almost all features, representing both size and shape. A comparison of information from the cotton rat fossil record with a recent molecular phylogeny suggests the molecular phylogeny has set the origin of modern cotton rat groups too early. North American species groups probably do not predate the late Pliocene.

Pedogenic carbonate stable isotope record of environmental change during the Neogene in the southern Great Plains, southwest Kansas, USA: Oxygen isotopes and paleoclimate during the evolution of C4-dominated grasslands

Neogene strata in the Meade Basin (southwest Kansas) preserve numerous superposed calcareous paleosols in sections that range in age from the Clarendonian North American Land Mammal Age (NALMA; 12.0–9.0 Ma, early late Miocene) to the early Irvingtonian NALMA (ca. 2.5–ca. 1 Ma, early Pleistocene). The carbon isotope compositions (δ 13 C relative to Vienna Peedee belemnite [VPDB]) of pedogenic carbonates from these sections record the protracted regional increase in the abundance of grasses using the C 4 photosynthetic pathway over this interval, with the first appearance of a modern-like grassland ecosystem having >70% C 4 biomass around 1.3 Ma. We use the stable oxygen isotope composition (δ 18 O relative to Vienna standard mean ocean water [VSMOW]) of 194 paleosol carbonates from 19 measured sections to reconstruct the climatic conditions in the Meade Basin during the rise of C 4 grasses to ecological dominance in the region. Pedogenic carbonate δ 18 O values are sensitive to soil temperature and the δ 18 O of soil water, and hence they are a paleoclimate proxy. Carbonate δ 13 C values do not exhibit consistent trends in relation to δ 18 O values, indicating no consistent relationship between short-term climatic conditions in terms of temperature or aridity and the abundance of C 4 biomass. Mean carbonate δ 18 O values within biostratigraphic intervals decrease from the Clarendonian (25.3‰ ± 0.72‰) to the early and middle Blancan (21.8‰ ± 0.87‰ and 22.1‰ ± 0.69‰, respectively), and they also exhibit a decreasing trend in the late Blancan–early Irvingtonian, from ∼25‰ to ∼21‰. The increase in δ 18 O values between the end of the middle Blancan and the beginning of the late Blancan–early Irvingtonian sections could reflect the onset of Northern Hemisphere glaciation and a change in the isotope composition of the hydrosphere due to increased ice volume. The long-term trend in δ 18 O values suggests that C 4 biomass increased coincident with some combination of decreasing temperature, increasing proportion of winter precipitation recharge of soil water, and/or increasing soil moisture. Thus, the ecological dominance of C 4 grasses in the region today does not seem to be linked to warmer temperatures or increased aridity.

LATE PLIOCENE AND EARLY PLEISTOCENE RODENTS FROM THE NORTHERN BORCHERS BADLANDS (MEADE COUNTY, KANSAS), WITH COMMENTS ON THE BLANCAN-IRVINGTONIAN BOUNDARY IN THE MEADE BASIN

Abstract New fossiliferous localities in the Borchers Badlands of southwestern Kansas add to our knowledge of rodent community change across the Plio-Pleistocene and Blancan-Irvingtonian boundaries. We report fossil rodents from ten local faunas in the Badlands that range stratigraphically from beneath the Huckleberry Ridge ash (2.10 Ma [million years ago]) to a level just beneath the Cerro Toledo B ash (1.23–1.47 Ma). The late Blancan Borchers local fauna (l.f.), includes the Meade Basin highest stratigraphic datum (HSD) for the following taxa that characterize or are found in earlier Blancan faunas: Alilepus, Geomys quinni, Sigmodon minor, and Geochelone. Borchers currently also has the HSDs for Reithrodontomys pratincola and Ondatra zibethicus /idahoensis, but the prior temporal distribution of these taxa in the Meade Basin is unknown. The stratigraphically lowest Pleistocene (Irvingtonian) l.f. in the Badlands, Nash 72, includes the lowest stratigraphic datum (LSD) for Cynomys, Reithrodontomys moorei, Microtus, and Mictomys kansasensis, all of which are found above Nash 72 and beneath the Cerro Toledo B ash. Prodipodomys is last seen at Nash 72, and Sigmodon curtisi is first encountered at Short Haul, a locality slightly younger than Nash 72. A preliminary hypothesis of age based on stratigraphic position places the Nash 72 l.f. at about 1.80 Ma, suggesting that this fauna and the genus Microtus may characterize both the Plio-Pleistocene and Blancan-Irvingtonian boundaries in the Borchers Badlands.

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.

Microdyromys remmerti, sp. nov., a new Gliridae (Rodentia, Mammalia) from the Aragonian type area (Miocene, Calatayud-Montalbán basin, Spain)

ABSTRACT A new species of Gliridae (Rodentia, Mammalia), Microdyromys remmerti, sp. nov., from the Aragonian type area in the Calatayud-Montalbán basin (Miocene, Spain) is described. This species is characterized by combining a relatively large size and a moderately complicated to very complicated and irregular dental morphology. It has a wide and continuous range of morphological variation with intermediate forms filling all the range. In the studied localities, M. remmerti, sp. nov., displays a general increase in the complexity of the dental pattern through time, showing a unique pattern of addition of extra ridges in the lower molars. Comparisons with morphologically similar species are discussed; a taxonomical and nomenclatorial issue regarding two named species of the genus is clarified. The combination of the morphometrical features that characterize M. remmerti, sp. nov., have never been found in any other glirid material outside the Calatayud-Montalbán basin, thus reinforcing the idea of the endemic character of the Gliridae faunas from the Iberian Miocene. Microdyromys koenigswaldi is proposed as most probable ancestor of M. remmerti, sp. nov. The divergent evolution of the latter species is discussed in its paleoecological context. The functional consequences of this morphological divergence could be related also with the opening of new ecological niches during the middle Aragonian (Middle Miocene).